Existing methods for collecting and studying algae are diverse. This is determined both by the ecological and morphological originality of representatives of various departments and ecological groups, and by the diversity of goals and approaches to their study. It is not possible here to give a complete comprehensive picture of all methods of studying algae, especially those aimed at achieving special goals. Therefore, in this section we will limit ourselves to considering only methods for collecting and studying algae from continental water bodies for the purposes of floristicosystematic and hydrobiological studies.
Due to the fact that most algae are microscopic in size, detecting them with the naked eye in natural habitats, as a rule, is only possible under the condition of mass development, causing a change in the color of the habitat: water, soil or other substrate (“blooming” of water, “blooming”). "soil, etc.). Usually the amount of algae is not so significant; however, collection of material should be carried out even in cases where the most careful examination of the substrate does not allow them to be seen with the naked eye.
Phytoplankton sampling methods
The choice of phytoplankton sampling method depends on the type of reservoir, the degree of development of algae, research objectives, available instruments, equipment, etc. In order to study the species composition of phytoplankton with intensive development of the latter, it is enough to scoop up water from the reservoir and then examine it under a microscope . However, in most cases, various methods of preliminary concentration of microorganisms are used. One of these methods is filtering water through plankton networks of various designs (Fig. 7.1).
Rice. 7.1. Planktonic networks: 1-3 - Apstein networks; 4 - Burge network; 5 - a glass for it; 6 - cylindrical network "zeppelin"
The plankton net consists of a brass ring and a conical bag sewn to it made of mill silk or nylon sieve No. 77, having 5929 cells per 1 cm 2. A diagram of the pattern of a net cone for a plankton net is shown in Fig. 7.2. The narrow outlet of the cone-shaped bag is tightly attached to a cup having an outlet tube closed with a stopcock or Mohr clamp. When collecting plankton from the surface layers of water, the plankton net is lowered into the water so that the upper hole of the net is located at a distance of 5-10 cm above its surface. Using a liter mug, they scoop up water from the surface layer (up to 15-20 cm deep) and pour it into the net, thus filtering 50-100 liters of water. In large bodies of water, plankton samples are taken from a boat. It is recommended to pull the plankton net on a thin rope behind a moving boat for 5-10 minutes.
For vertical collections of plankton, specially designed nets are used. In small bodies of water, plankton samples can be collected from the shore by gradually wading into the water, carefully scooping up the water with a mug in front of you and filtering it through a net, or by casting a net on a thin rope into the water and carefully pulling it out. Having finished collecting plankton, the plankton net is rinsed by lowering it several times into water up to the upper ring to wash off algae that have lingered on the inner surface of the net. The plankton sample concentrated in this way, located in the cup of the plankton net, is poured through the outlet tube into a previously prepared clean jar or bottle. Before starting and after completing sample collection, the net must be rinsed well, and when finished, dried and placed in a special case. Net samples of plankton can be studied in a living and fixed state.
To quantitatively record phytoplankton, samples of a certain volume are taken. Network fees can also be used for these purposes, subject to mandatory accounting of the amount of water filtered through the network and the volume of the collected sample. However, usually sampling for quantitative recording of phytoplankton is carried out with special devices - bathometers of various designs (Fig. 7.3). The bathometer of the Rutner system has been widely used in practice (see Fig. 7.3, 1). Its main part is a cylinder made of metal or plexiglass, with a capacity of 1-5 liters. The device is equipped with top and bottom covers that tightly cover the cylinder. The bathometer is lowered under water with the lids open. When the required depth is reached, as a result of strong shaking of the rope, the lids close the holes of the cylinder, which, closed, is removed to the surface. The water contained in the cylinder is drained through a side pipe equipped with a tap into the prepared vessel.
When studying phytoplankton in surface layers of water, samples are taken by scooping water into a vessel of a certain volume. In reservoirs with poor phytoplankton, it is advisable to take samples of at least 1 liter in volume in parallel with net collections, which make it possible to capture small, relatively large objects. In reservoirs with rich phytoplankton, the volume of a quantitative sample can be reduced to 0.5 l and even to 0.25 l (for example, when the water “blooms”).
Condensation of quantitative phytoplankton samples can be carried out by two methods that give approximately the same results - sedimentary and filtration. Condensation of samples using the sedimentary method is carried out after their preliminary fixation and settling in a dark place for 15-20 days by sucking out the middle layer of water using a glass tube, one end of which is tightened with a mill sieve No. 77 in several layers, and the second is connected to a rubber hose. Suction is carried out very slowly and carefully to prevent disturbance of the sediment and suction of the surface layer of the sample. The sample condensed in this way is shaken and, after measuring its volume, transferred to a smaller vessel.
When condensing samples by the filtration method, “preliminary” and, if necessary (if the size of planktonic organisms are very small) bacterial filters are used. In this case, water samples are not pre-fixed, and phytoplankton is studied in a living state. For long-term storage, the filter with sediment is fixed in a certain volume of liquid.
Phytobenthos sampling methods
Existing methods for sampling phytobenthos involve collecting algae living on the surface of bottom soils and sediments, in their thickness (up to 1 cm deep) and in a specific bottom layer of water 2-3 cm thick. To study the species composition of phytobenthos, it is enough to extract a certain amount of bottom water to the surface soil with sediments. In shallow water (up to 0.5-1.0 m depth) this is achieved using a test tube or siphon lowered to the bottom - a rubber hose with glass tubes at the ends, into which the fluff is sucked in (Fig. 7.4, 1). At great depths, high-quality samples are taken using a bucket or glass attached to a stick, as well as various rakes, “cats”, dredges, bottom grabs, sludge suckers, of which the Perfilyeva sludge sucker is the easiest to manufacture and easy to use (Fig. 7.4, 2) . The main part of this device is a U-shaped tube with unequal ends. A thin metal tube is connected to the short end of the tube, to which is attached a long rubber hose with a clamp at the free end. At the same end of the U-shaped tube, a wide-necked bottle is secured with a rubber stopper. A weight is attached to the long open end of the tube. The device is lowered using a rope to the bottom of the reservoir, where, under the influence of a load, the long end of the U-shaped tube cuts into the thickness of the bottom sediments; after this, the end of the rubber hose remaining on the surface is released from the clamp, allowing air to escape, and the sludge is forcefully sucked into the jar through the long end of the tube. Then the device is removed to the surface, and the contents of the jar are transferred to the container prepared for the sample. To take quantitative samples of phytobenthos, Vladimirova’s microbenthometer is used. Its main part is a brass tube 25-30 cm long with an internal diameter of 4-5 cm, on the basis of which the internal cross-sectional area of the tube is calculated. At the upper end of this tube there is a sleeve with a cone-shaped funnel, into which a ground-in cap-valve hermetically fits on a lever (Fig. 7.5). A tube with an open lid on a collapsible wooden rod is lowered to the bottom and the sharpened lower end is cut into the thickness of the bottom soil a few centimeters. By pulling the rope attached to the free end of the lever, close the upper sleeve of the tube with a lid, after which the device is carefully removed to the surface. When the tube comes out of the water, close the bottom hole of the tube with your palm to prevent soil from falling out. After opening the lid, carefully pour the top layers of water into a glass container until turbidity appears. This first portion of water, containing planktonic organisms, is poured overboard. The remaining water or soil in the tube is easily shaken and transferred to the container prepared for the sample, having previously measured its volume. Vladimirova’s microbenthometer is convenient to use at depths of 2.0-2.5 m.
Rice. 7.4. Devices for collecting phytobenthos samples: 1 - siphon; 2 - Perfilyev suction pump; 3 - glass for sludge; 4 - sludge bucket; 5 - rakes; 6 - "cat"
A more advanced microbenthometer model, which allows taking samples from any depth, was proposed by V. S. Travyanko and L. V. Evdokimova (Fig. 7.5). Travyanko and Evdokimova's microbenmeter consists of a tube 30-35 cm long with an internal diameter of 5-6 cm, equipped in the upper part with an automatically operating stabilizer valve. On a measuring rope, a tube with an open valve in a vertical position is lowered over the side of the boat. Under the influence of a weight attached to the device, the tube cuts into the thickness of the bottom, while the valve hermetically seals the upper hole. Using a rope, the device is removed to the surface; When it comes out of the water, the lower hole of the tube is closed with the palm of your hand. Then the top layer of water is drained overboard through the side pipe, and the tube containing the soil monolith and the rest of the water is unscrewed from the stabilizer with the valve box, shaken, and after measuring the volume, the sample is transferred to the container prepared for it.
Methods for collecting periphyton samples
To study the species composition of periphyton, plaque on the surface of various underwater objects (pebbles, crushed stone, stones, stems and leaves of higher aquatic plants, mollusk shells, wooden and concrete parts of hydraulic structures, etc.) is removed using a regular knife or special scrapers and spoons (Fig. 7.6). However, this causes the death of many interesting organisms. Some of them are carried away by water currents, the organs (organelles) that attach algae to the substrate are destroyed, and the pattern of mutual placement of the components of the biocenosis is disrupted. Therefore, it is better to collect algae together with the substrate, which is completely or partially carefully removed to the surface of the water so that the current does not wash away the algae from it. The extracted substrate (or its fragment), together with algae, is placed in a vessel prepared for the sample and filled with either a small amount of water from the same reservoir for the purpose of further studying the collected material in a living state, or with a 4% formaldehyde solution.
To quantitatively record periphyton, algae are thoroughly washed off the surface of the extracted substrate using water and a brush over a wide vessel (cuvette, basin), and, having measured the volume of the wash, transfer it to the container prepared for the sample. In addition to the volume of washout, to quantitatively account for periphyton, it is also necessary to know the area of the substrate from which algae are washed away. To do this, cover the specified surface with a damp cloth and outline its contours with an ink pencil. The area is calculated using the weighted average area method: the resulting contour of the substrate surface is transferred to tracing paper and cut out; A square with a side of 1 cm (area 1 cm2) is cut out of the same paper and weighed. Knowing the mass of a paper square and the mass of a contour cut from the same paper, calculate the required area.
When studying epiphytic algae washed from the stems of leaves of higher aquatic plants, quantitative accounting is carried out not only per unit area, but also per unit mass (wet and air-dry) of the substrate plant. To do this, a section of the plant from the surface of which epiphytes have been washed off is weighed, then dried to an air-dry state and weighed again.
Methods for collecting terrestrial and soil algae
Terrestrial algae that form variously colored plaques and films on trees, rocks, stones, damp soil, roofs and walls of houses, etc., are collected, if possible, together with the substrate in sterile paper bags or in glass containers with a 4% formaldehyde solution . Methods for collecting and studying soil algae are described in specialized literature.
Labeling and recording samples, keeping a field diary
All collected material is divided into two parts for the purpose of further studying algae in a living and fixed state. Living material is placed in sterile glass vessels, test tubes, flasks, jars, closed with cotton plugs, without filling them to the top, or in sterile paper bags. To keep algae alive under expeditionary conditions, aquatic samples are packaged in damp wrapping paper and placed in boxes. Periodically, samples are unpacked and exposed to diffuse daylight to maintain photosynthetic processes and oxygen enrichment. Despite all precautions, not all of the collected material can be preserved, so short excursion trips are more favorable for working with living material than long expeditions.
The material to be fixed is placed in cleanly washed and dried non-sterile glass containers (test tubes, bottles, jars), tightly closed with rubber or cork stoppers. Aqueous samples are fixed with 40% formaldehyde, which is added to the sample in a ratio of 1:10. Algae located on a solid substrate (on paper filters, pebbles, empty shellfish shells, etc.) are poured with a 4% formaldehyde solution. Good preservation of algae and their color is also ensured by a solution of formaldehyde and chrome alum (5 ml of 4% formaldehyde and 10 g of K 2 SO 4 ⋅ Cr 2 (SO 4) 3 ⋅ 24H 2 O in 500 ml of water). In the field, you can also use a solution of iodine with potassium iodide (10 g of KI is dissolved in 100 ml of water, add 3 g of crystalline iodine and another 100 ml of water, shake until the crystals are completely dissolved, store in a dark bottle for several months), which is added to the sample in a ratio of 1:5. Hermetically sealed fixed samples can be stored in a dark place for a long time.
All collected samples are carefully labeled. The labels, filled in with a simple pencil or indelible paste, indicate the sample number, time and place of collection and the name of the collector. The same data is simultaneously recorded in a field diary, in which, in addition, the results of measurements of pH, water and air temperature, a schematic drawing and a detailed description of the studied reservoir, the higher aquatic vegetation developing in it, and other observations are recorded.
Methods for qualitative study of material
The collected material is preliminarily examined under a microscope in a living state on the day of collection in order to note the qualitative state of the algae before the onset of changes caused by storage of living material or fixation of samples (formation of reproductive cells, transition to the palmelle state, destruction of cells, colonies, loss of flagella and motility, etc. .d.). In the future, the collected material continues to be studied in parallel in a living and fixed state. Working with living material is a necessary condition for the successful study of algae that, when fixed, change their body shape, shape and color of chloroplasts, lose flagella, motility, or even completely collapse as a result of exposure to fixatives. To keep the collected material alive, you should protect it in every possible way from overheating and contamination with fixatives, and begin studying it as soon as possible.
Algae in a living state, depending on their size and other features, are studied using a binocular stereoscopic magnifying glass (MBS-1) or more often using light microscopes of various brands using different systems of eyepieces and lenses, in transmitted light or by the phase contrast method, in compliance with the usual rules of microscopy.
For microscopic study of algae, preparations are prepared: a drop of the liquid being studied is placed on a glass slide and covered with a cover glass. If algae live outside of water, they are placed in a drop of tap water or hydrated glycerin. When studying the drug for a long time, the liquid under the cover glass gradually dries out and should be added. To reduce evaporation, a thin layer of paraffin is applied along the edges of the coverslip.
If long-term observations of the same object are necessary, the hanging drop method gives a good result. A small drop of the test liquid is applied to a clean cover glass, after which the cover glass, the edges of which are coated with paraffin, paraffin oil or petroleum jelly, is placed drop down on a special glass slide with a hole in the middle so that the drop does not touch the bottom of the well (Fig. 7.7). Such a preparation can be studied for several months, keeping it in a humid chamber during breaks between work.
When studying algae with a monad structure, their mobility is a serious obstacle. However, as the drug dries, the movement gradually slows down and stops. Slowing down the movement can also be achieved by gently heating the preparation or adding cherry glue. It is recommended to fix mobile algae with osmium (IV) oxide vapor (the flagella are well preserved), crystalline iodine (fixation with iodine vapor allows not only to preserve the flagella, but also to color the starch, if any, blue, which has diagnostic value), 40 % formaldehyde, a weak solution of chloral hydrate or chloroform. The duration of exposure to pairs of fixatives is established experimentally, depending on the specifics of the object. The most convenient for study are weakly fixed preparations, in which some of the algae have lost their mobility, while others continue to move slowly. Preparations should be studied immediately after fixation, since algae (especially those without cell membranes) become deformed within a short period of time.
In many cases, in addition to comparative morphological analysis of signs, they resort to cytological methods of studying the material. When studying intracellular structures, especially in small flagellates, intravital staining is used with weak (0.005-0.0001%) solutions of neutral red, methylene blue, neutral blue, trypan red, brilliant cresyl blue, Congo red, Janus green, allowing more clearly identify the cell membrane, papillae, mucus, vacuoles, mitochondria, Golgi apparatus and other organelles.
Many dyes give good results only after using special fixation methods (when studying samples fixed with formaldehyde, successful use of dyes is possible only after thoroughly washing the material under study with distilled water). The best fixative for the cytological study of algae, including the study of their ultrastructure, is a 1-2% solution of osmium (IV) oxide (the solution cannot be stored for long periods of time). Algae that do not have cell walls are easily and quickly fixed with methanol. Lugol's solution (1 g of potassium iodide and 1 g of crystalline iodine in 100 ml of water) not only fixes algae well, but also turns starch blue.
Staining of nuclei. To study nuclei, Clark's alcohol-acetic fixative (3 parts of 96% ethyl alcohol and 1 part of glacial acetic acid) or Carnoy's liquid (6 parts of 96% ethyl alcohol, 3 parts of chloroform and 1 part of glacial acetic acid) are successfully used. The algae are kept in a freshly prepared fixative solution for 1-3 hours, then washed with 96% ethyl alcohol (2 min) and water (10 min). It should be emphasized that in the cytological study of algae, in most cases, depending on the specifics of the objects, the most effective fixatives, dyes and exposure time are selected experimentally.
When staining nuclei with acetocarmine, only algae with thick cell walls are subjected to pre-fixation with an alcohol-acetic fixative. To prepare the dye, 2 g of carmine is boiled in 400 ml of 45% glacial acetic acid for 4 hours using reflux. If the latter is not available, you can use a regular glass funnel. The resulting dark red solution is cooled, filtered and stored indefinitely in a dark glass vessel. Add a little dye to a drop of water with algae on a glass slide, cover it with a cover glass and observe the coloring under a microscope. Sometimes, for better staining, the preparation is carefully heated over the flame of a gas burner, preventing the liquid from boiling under the cover glass. In addition to the nuclei, the basal bodies of flagella, vacuoles and pyrenoids are stained.
For the study of mitosis and cytochemical detection of DNA, the Feulgen reaction, which causes red staining of nuclear chromatin, is indispensable; while the rest of the cytoplasm remains colorless. To carry out the Feulgen reaction, three solutions are prepared. Solution A: 82.5 ml of concentrated hydrochloric acid is mixed with 1000 ml of distilled water. Solution B (Schiff's reagent): 1 g of basic fuchsin is dissolved in 200 ml of boiling water, cooled to 50 ° C, filtered, 20 ml of solution A are added and after cooling to 25 ° C, 1 g of anhydrous Na 2 SO 4 is dissolved, and then added 300 mg activated carbon; After 24 hours, this solution should completely discolor; if it remains yellow, a new solution should be prepared. Solution B: 200 ml of water is mixed with 10 ml of 10% Na 2 SO 4 and 10 ml of solution A.
After treatment with an alcohol-acetic fixative, the material is immersed for 6-8 minutes (exposure time is selected experimentally) in solution A, heated to 60°C, then for a moment in cold solution A, rinsed with water and immersed for 1 hour in solution B; then, after washing three times with solution B, rinse with water and prepare a permanent preparation. It should be noted that in some algae, for example species of the genera Spirogyra Link, Oscillatoria Vauch., DNA in the presence of the Schiff reagent gives a very weak Feulgen reaction.
Quite often, hematoxylin is used to stain algae nuclei. Freshly prepared hematoxylin solutions do not have coloring ability. It manifests itself some time after the “ripening” of the solution, during which oxidation of hematoxylin occurs. The most commonly used for algae are Heidenhain's hematoxylin and Delafield's hematoxylin. The first dye matures quite quickly, the preparation of the second takes several months. For staining with Heidenhain hematoxylin, two solutions are prepared. Solution A contains 2.5 g of ferroammonium alum in 100 ml of water, solution B - 10 ml of a 10% alcohol solution of hematoxylin (in absolute ethyl alcohol) in 90 ml of water. Solution B should have an intense wine-red color. The material, washed after fixation, is etched for 6-12 hours (depending on the specifics of the object) in solution A, and then quickly rinsed with distilled water and stained in solution B for 12-24 hours (also depending on the object). The color field of the material is differentiated with constant monitoring in solution A, then again quickly rinsed with distilled water and washed in water for 10-30 minutes. The chromatin structures of the nuclei, basal bodies of flagella and mitochondria are painted black (Fig. 7.8, 1).
The Giemsa method allows for differential staining of nuclei and other cellular organelles. Algae lacking a cell membrane are fixed with methanol or osmium (IV) oxide; the rest are colored after hydrolysis with hydrogen chloride oxide. Before staining, it is recommended to expose the material to 1 N for several minutes. HCl at 60°C. Then the acid is thoroughly washed with distilled water. For coloring, use a diluted dye: 1-2 drops of the main dye in 1 ml of water; staining time 20-60 min. The colored preparations are quickly rinsed with distilled water, passed through anhydrous acetone, a mixture of acetone and xylene in a ratio of 2:1, acetone and xylene in a ratio of 1:2, xylene and enclosed in cedar oil. Nuclear chromatin and chromosomes are stained red - red-violet, nucleoli - blue, chloroplasts - light blue (pyrenoids remain colorless), and flagella and their basal bodies - light red.
Cell membrane staining. To study the chemical nature of the cell membrane, use a 0.01% solution of rutin red (a reagent for pectin substances) and chlorine-zinc-iodine (20 g of zinc chloride, 6.5 g of potassium iodide, 1.3 g of crystalline iodine in 10. 5 ml of water), turning cellulose blue. To identify the structure of the surface of the cell membrane and papillae, a 0.1% aqueous solution of gentian violet is used, which also stains mucus well. To detect mucus, in addition, mascara is used, which, without penetrating into the mucus, makes it clearly visible. Details of the surface structure of cell covers are clearly visible in a 5% aqueous solution of nigrosin. To study the structure of the cell walls of filamentous algae, they are treated with a KOH solution and then stained with Congo red.
Coloring of flagella. Flagella are examined under a light microscope using Lefler staining. To do this, the material is fixed with osmium (IV) oxide, briefly immersed in absolute alcohol and left to dry. Then add a few drops of dye (a mixture of 100 ml of a 20% aqueous solution of tannin, 50 ml of a saturated aqueous solution of FeSO 4 and 10 ml of a saturated alcohol solution of basic fuchsin) and heat over a burner flame, without boiling, until steam appears. After rinsing with distilled water, the preparation is stained with carbolfuchsin for 10 minutes (100 ml of a 5% aqueous solution of freshly distilled phenol and 10 ml of a saturated alcohol solution of basic fuchsin; the mixture is left for 48 hours, filtered and stored for a long time), then rinsed again distilled water, allow to dry and place in Canada balsam. This method can be used to determine the presence or absence of hairs on the flagella (Fig. 7.8, 2, 3). Observations on the length of flagella, the nature of their movement, and the place of attachment are carried out on living material using the phase contrast method.
Study of chloroplasts, stigma; pyrenoid coloration. Chloroplasts should be studied on living material, since they are deformed when fixed. It is also difficult to maintain the stigma. The protein body of the pyrenoid after preliminary fixation is well stained by Altman. The dye consists of 1 part of a saturated solution of picric acid in absolute ethyl alcohol, 7 parts of 50% ethyl alcohol and 1 part of a saturated aqueous solution of fuchsin. Staining lasts at least 2 hours. Staining of the protein bodies of pyrenoids can be carried out without preliminary fixation of the material using acetic azocarmine C. To 4 ml of glacial acetic acid add 55 ml of water and 5 g of azocarmine C. The resulting mixture is boiled for about an hour using a reflux refrigerator, cool, filter and store in a dark glass vessel. The dye solution is added to a drop of water with algae on a glass slide, covered with a coverslip and observed under a microscope. The protein body of the pyrenoid is painted intense red, the rest of the cell is light pink (Fig. 7.8, 4).
Identification of assimilates. Starch turns blue when exposed to any reagents containing iodine. The most sensitive of them - iodine chloral (small crystals of iodine in a solution of chloral hydrate) - allows you to detect the smallest grains of starch and distinguish the starch around the pyrenoid from the stromal starch (Fig. 7.8, 5, 6). The presence of paramylon can be detected by dissolving it with 4% KOH. The presence of chrysolaminarin is detected only through very complex microchemical reactions. Oil and fats are colored red by Sudan III (0.1 g of Sudan III in 20 ml of absolute ethyl alcohol) or black by osmium (IV) oxide (Fig. 7.8, 7).
Study of vacuoles. Vacuoles with cell sap become more visible due to intravital staining with a weak solution of neutral red. Pulsating vacuoles can be observed on living material in a light microscope due to their periodic filling and emptying. The use of a phase contrast device, the addition of a 1% aqueous solution of tannin, and fixation of the material with osmium (IV) oxide facilitates the identification of these organelles.
Mitochondria staining. Mitochondria are well stained with free access to oxygen with a 0.1% solution of Janus green (Fig. 7.8, 8). Therefore, a drop of water with algae on a glass slide is covered with a cover glass only some time after adding the dye.
Golgi apparatus staining. The Golgi apparatus darkens when the material is fixed with osmium(IV) oxide. It can also be stained with a 0.5% aqueous solution of trypan blue; A 0.01% aqueous solution of methylene blue stains the cell contents blue, while the Golgi apparatus remains colorless.
Methods for making permanent preparations
For the manufacture of permanent preparations, glycerin-gelatin is used. One part by weight of gelatin is infused in 6 parts by weight of distilled water for several hours, then 7 parts by weight of pure glycerin and a crystal of an antiseptic, for example, thymol or carbolic acid, are added. The mixture is heated in a water bath, stirring with a glass rod, until the gelatin is completely dissolved. To precipitate the turbidity, add raw egg white and filter through a paper filter, using a hot filter funnel and frequently changing the paper. The cooled glycerin-gelatin should be transparent. When used, it is melted by heating in a water bath. This medium mixes well with water, so when using it there is no need for prolonged drying of the material.
The preparations are prepared as follows: algae is transferred from water to a drop of glycerin and left to dry for a while; then a drop of molten glycerin-gelatin is applied to a heated glass slide, the algae is transferred into it and covered with a coverslip; After the glycerin-gelatin has completely hardened, the edges of the cover glass are coated with varnish. Such drugs can be stored horizontally for several years.
Preparations enclosed in Canada balsam or in synthetic resins on a methyl methacrylate basis are preserved even longer. The latter harden quickly, are transparent, chemically neutral and have a suitable refractive index. Before being encased in Canada balsam or synthetic resins, the material must be completely dehydrated by passing through alcohols of increasing strength to absolute and clove oil or xylene, which contribute to its clarification. Material dyed using the Giemsa method is placed in cedar oil, which hardens over time, in which the paints are preserved indefinitely.
Special methods for preparing preparations are used in the study of Bacillariophyta, Dinophyta and Desmidiales, the taxonomy of which is based on the structure of the cell covers (see). Preparing diatoms for microscopy involves destroying all organic substances that obscure the structure of the shell. This is achieved either by calcining the material or treating it with concentrated mineral acids, in particular sulfuric acid. When using the first method, a drop of the suspension, freed from impurities and containing diatom cells, is applied to a clean, fat-free cover glass, dried and, placed on a mica plate, calcined over a burner flame or on an electric stove until all organic substances are completely burned (for half an hour or more). ). When studying benthic diatoms with powerful shells, calcination is carried out in an electric furnace at a temperature of 450°C. If cover slips melt during prolonged heating, the material is calcined on mica plates and then transferred to cover slips. The calcination method makes it possible to preserve the smallest and most delicate shells of planktonic species, does not disturb the natural arrangement of cells in the colony, and requires a small amount of test material. However, samples contaminated with large amounts of organic matter are better treated chemically.
During cold treatment with acids, samples are pre-cleaned from coarse organic and mineral impurities on watch glasses, washed from formaldehyde and salts with distilled water by settling or centrifugation. The resulting precipitate is poured with concentrated sulfuric acid for several days, then several crystals of potassium dichromate or potassium nitrate are added and washed several times with distilled water, followed by centrifugation until the acid is completely washed away.
Along with the cold method, hot treatment with acids is used. In this case, the algae is pre-boiled for 10-15 s in diluted hydrochloric acid, and then washed from it. The resulting precipitate with a minimum amount of water is transferred to a flask, four to five times the volume of concentrated sulfuric or nitric acid is added, filling the flask no more than halfway, and boiled in a water or sand bath under a hood for 15 minutes - 1 hour. The browned mass is clarified by adding KNO 3 crystals. After cooling, the precipitate is pipetted into a test tube with water, carefully adding the acid with diatoms to the water to avoid boiling and splashing of the acid, and the precipitate is washed until neutral.
The material obtained after calcination or treatment with acids is preserved with 2-3% formaldehyde for subsequent storage or directly used for the manufacture of permanent preparations. For this purpose, a suspension with diatom cells is applied to thin, clean, fat-free coverslips and dried. A small amount of synthetic resin (pleurax, hyrax, etc.) with a refractive index above 1.6 is placed on a glass slide, melted over a burner flame and covered with a cover glass with the material under study, gently pressing on it and leveling the medium with a thin, uniform layer. Excess medium is removed using xylene.
Diatoms, which have very thin and delicate shells, are studied on dry preparations in an air environment. To make them, a suspension with diatom cells is applied to a cover glass, dried, placed on a glass slide and sealed around the edges with varnish.
When studying Desmidiales and armored Dinophyta, the material is treated with Javel water, which helps to clarify it. To prepare javel water, grind 20 parts of bleach in 100 parts of water, add 100 parts of a 15% solution of potassium carbonate and leave for several hours, after which the mixture is shaken several times. Potassium carbonate solution is gradually added to the filtrate until the appearance of precipitate stops. After repeated filtration, the liquid is poured into a tightly closed dark glass container and stored in the dark. The material under study is precipitated by centrifugation, the sediment is filled with Javel water for 1-2 days, tightly closing the vessel with a stopper. The material treated in this way is washed 2-3 times with distilled water. To reveal their structure, it is recommended to tint the shells of dinophytes with trypan blue or an alcohol solution of iodine after clearing with Javel water.
To decalcify algae encrusted with lime (for example, Charophyceae), or living in calcareous rocks (boring algae), lactic acid is used, which also helps clarify the preparation, and in its absence, hydrochloric acid is used.
Methods for measuring algae size
When studying the species composition of algae, their size is measured, which is an important diagnostic feature. To measure microscopic objects, an eyepiece micrometer with a measuring ruler is used (Fig. 7.9). The price of divisions of an eyepiece micrometer is determined using an object micrometer (a glass slide with a ruler printed on it, the value of each division of which is 10 μm; Fig. 7.9), individually for each microscope and lens (for more details, see). When studying the linear dimensions of algae, it is advisable to measure as many specimens as possible (10-100) with subsequent statistical processing of the data obtained.
All studied objects should be carefully sketched using drawing devices (RA-4, RA-5) and simultaneously photographed using a microphoto attachment (MFN-1, MFN-2).
When identifying algae, accuracy should be achieved. When studying the original material, it is necessary to note any, even minor, deviations from the diagnosis in size, shape and other morphological features, and record them in your descriptions, drawings, and microphotographs.
When processing samples qualitatively, it is desirable to determine the frequency of occurrence of individual species, using symbols for this. There are various scales for assessing the frequency of algae occurrence. As an example, the Starmach scale is given below: + - very rare (the species is not present in every preparation); 1 - single (1-6 copies in the preparation); 2 - few (7-16 copies in the preparation); 3 - quite a lot (17-30 copies in the preparation); 4 - many (31-50 copies in the preparation); 5 - very many, absolute predominance (more than 50 copies in the preparation).
Transmission and scanning electron microscopy are increasingly used in the practice of algological research. Methods for preparing preparations and studying them using transmission and scanning electron microscopes are described in specialized literature.
Methods for quantitative counting of algae
Only quantitative samples of phytoplankton, phytobenthos and periphyton can be counted. Data on the number of algae are the starting point for determining their biomass and recalculating other quantitative indicators (content of pigments, proteins, fats, carbohydrates, vitamins, nucleic acids, ash elements, respiration rate, photosynthesis, etc.) per cell or per unit of biomass . The number of algae can be expressed in the number of cells, coenobia, colonies, pieces of threads of a certain length, etc.
Counting the number of algae is carried out on special counting glasses (graphed into stripes and squares), onto the surface of which a drop of water from a thoroughly mixed test sample is applied with a stamp pipette (Fig. 7.10, 1) of a certain volume (mostly 0.1 cm 3). In the absence of a counting glass, you can use a regular glass slide provided that it is moved on the microscope stage using a slide. If you don't have a stamp pipette, use a regular graduated pipette, cutting off the lower extended part to make the inlet hole wider. To count the number of algae, counting chambers of Nageotte with a volume of 0.01 cm 3 (Fig. 7.10, 2), “Uchinskaya” (0.02 cm 3), etc. can also be used. You can also use chambers used for counting blood cells - Goryaev, volume 0.9 mm 3 (Fig. 7.10, 3, 4), Fuchs-Rosenthal, etc. When using Goryaev and Fuchs-Rosenthal chambers, the cover glass is carefully ground to the side surfaces of the counting glass until Newton's rings appear, and then the chamber is filled with a drop the test sample using a pipette. Depending on the number of organisms in the test sample, either all or part of the tracks (squares) on the surface of the counting glass can be counted. It is necessary to carry out repeated counts of several (at least three) drops from the same sample, each time using a pipette to select a sample for counting after thoroughly shaking the sample.
Phytoplankton abundance calculation. When studying quantitative samples of phytoplakton (or a cultural suspension of algae), the number of organisms per 1 liter of water is recalculated using the formula
where N is the number of organisms in 1 liter of water in the studied reservoir (culture fluid); k is a coefficient showing how many times the volume of the counting chamber is less than 1 cm 3; n is the number of organisms found on the viewed tracks (squares); A is the number of tracks (squares) on the counting plate (in the chamber); a is the number of tracks (squares) on which algae were counted; V is the initial volume of the sample taken (cm 3); υ is the volume of the condensed sample (cm 3).
Calculation of benthos and periphyton abundance. When studying quantitative samples of phytobenthos and periphyton, in which relatively large organisms usually predominate, a stamp pipette with a volume of 0.1 cm 3 is used primarily. Calculation of the number of algae in benthos and periphyton samples is carried out on 10 cm 2 of the substrate surface according to the formula
where N is the number of organisms per 10 cm 2 of the substrate surface; n is the number of organisms in a calculated drop of water with a volume of 0.1 cm 3; υ - sample volume (cm 3); 5 - cross-sectional area of the tube in the microbenthometer (for benthic samples) or the surface area of the substrate from which algae are washed away (for fouling samples) (cm 2).
Calculation of the number of epiphytic algae. When studying epiphytic algae, their numbers are also calculated per 1 g of wet (or air-dry) mass of the substrate plant using the following formula:
where N is the number of organisms per 1 g of wet (air-dry) mass of the substrate plant; n is the number of organisms in a calculated drop of water with a volume of 0.1 cm 3; υ - sample volume (cm 3); P is the wet or air-dry mass (g) of that area of the plant substrate from which the epiphytes were washed away.
The quantitative content of algae in samples is most fully reflected by the indicators of their biomass, which are determined using counting, weight, volume, and various chemical (radiocarbon, chlorophyll, etc.) methods.
Determination of biomass. To determine the biomass of algae using the counting-volume method, it is necessary to have data on their numbers in each specific sample for each species separately and their average volumes (for each species from each specific sample). There are different methods for determining the body volume of algae. The stereometric method is considered the most accurate, using which the body of the algae is equated to some geometric body or combination of such bodies, after which their volumes are calculated using formulas known in geometry based on the linear dimensions of specific organisms. Sometimes they use ready-made, previously calculated average body volumes for different types of algae, which are given in the works of many authors (see bibliographic references in the work on p. 318). The relative water density of freshwater algae is usually taken to be 1.0-1.05, for hyperhalobic algae - 1.1-1.2. Biomass is calculated for each species separately and then summed. The counting-volume method for determining biomass is widely used in the practice of hydrobiological research when studying the quantitative relationships of various components of biocenoses, patterns of distribution of algae in different biotopes of the same reservoir or in different reservoirs, seasonal and long-term dynamics of algae development, etc.
With intensive development of algae, you can use the weight method. In this case, the test sample is filtered through a pre-dried and weighed paper filter (in parallel, distilled water is filtered through control filters). Then the filters are weighed and dried in an oven at 100°C to constant weight. Based on the data obtained, the dry and wet weight of the sediment is calculated. Subsequently, by burning the filters in a muffle furnace, the content of organic substances in the sediment can be determined.
The disadvantages of this method are that it gives an idea only of the total mass of all organic and inorganic substances, living organisms and inanimate impurities, animal and plant origin, suspended in the sample. The contribution of representatives of individual taxa to this total mass can only be approximately expressed in mass fractions after calculating their ratio under a microscope in several fields of view.
The most complete picture of algal biomass can be obtained by combining several different research methods.
The algal flora of rivers consists of three main components: algae of autotrophic origin (green, blue-green, diatoms, euglena, etc.), periphyton (fouling algae) and benthic algae growing on the bottom and caught in the plankton.
The development of algae is determined by the presence of nitrogen and phosphorus, light, water movement, its temperature and turbidity. Blue-green and green algae develop at temperatures from 4 to 23°C (maximum development - from 19 to 23°C), most euglenoids - from 2 to 28°C (their maximum development is observed in summer and early autumn). At the same time, diatoms develop well at low water temperatures. Two peaks of their development were noted - spring and autumn.
The role of phytoplankton and phytomicrobenthos in shaping water quality is twofold. On the one hand, they are active agents of biological self-purification, since they release oxygen and absorb nutrients that directly enter the reservoir or are formed during the decomposition of organic substances. On the other hand, newly formed organic matter during photosynthesis, when it dies, enters the water and represents a source of secondary (biological) pollution. As a rule, phytoplankton biomass in the range of 1 – 4 mg/l does not cause a deterioration in water quality; at a concentration of algae of 5–10 mg/l it significantly deteriorates, and at a concentration of 10–50 mg/l or more there is a threat of biological pollution and the appearance of toxicants.
Phytomicrobenthos, as a rule, plays a positive role in shaping water quality, since bottom algae produce insignificant biomass, which cannot cause significant secondary biological pollution.
Current speed as a factor limiting the vegetation of algae and ensuring satisfactory water quality appears for phytoplankton at a flow speed of 1 m/s, for phytomicrobenthos – above 1 m/s.
Algae live primarily in aquatic environments, but they are also found in soil, on rocks, on tree trunks, inside limestone substrates, in the air, in hot springs, and in the ice of the North Pole and Antarctica. We know the very first information about algae from the books of the ancient Roman scientist Pliny the Elder. He gave the name to these plants - Algae, which means “herbaceous sea shoots”. In Russia, in the twenties of the 19th century, the naturalist I. A. Dvigubsky proposed the name “water plants” for plants growing in water, but in 1927 the scientist M. A. Maksimovich changed it to “algae”. Since then we have used this name both colloquially and as a scientific term.
The definition of algae used in textbooks on botany and popular science literature is as follows: “Algae are lower, i.e., layered (lacking division into stems and leaves), spore plants containing chlorophyll in their cells and living mainly in water."
Algae play a huge role in nature and human life. In reservoirs, as creators of organic matter, they are the first link in food chains. In terms of the content of proteins, fats and carbohydrates, algae are not inferior to hay and are high-calorie food for numerous aquatic animals - rhizomes, worms, small crustaceans, caddis flies and mollusks. Some freshwater algae are edible for humans; they are eaten in China, Japan, Canada, USA, France, Australia, and Korea. Algae are widely used in livestock farming as feed and feed additives, since proteins, vitamins and physiologically active substances increase the resistance of animals to various diseases and accelerate their growth and reproduction.
Algae produce and release various chemical compounds and biologically active substances into the environment and thus affect the formation of the quality of natural waters and their organoleptic properties (taste, color and smell). For example, Anabaena and Microcystis give the water a marshy smell, and Asterionella and Synedra give it a fishy smell. The “blooming” of water is accompanied by a deterioration in its physicochemical parameters, an increase in color, a decrease in transparency, an increase in oxidability, and chlorine absorption.
Blue-green algae produce toxins that have a wide range of biological effects. Based on the nature of their effect on warm-blooded animals, they are divided into two large groups: neurotoxins and hepatotoxins. Consumption of water in which blue-green algae develop en masse can lead to gastroenteritis and other gastrointestinal diseases, severe muscle pain, cramps, and paresis of the limbs. There are known cases of people getting conjunctivitis after swimming in “blooming” water, allergic damage to the skin and mucous membranes, and liver damage from hepatotoxins of algal origin present in the water.
Phytoplankton that develops en masse causes the death of fry and adult fish. Algae take an active part in the shallowing of water bodies, which occurs due to the sedimentation of phytoplankton. In addition, the massive development of algae also has a purely mechanical harmful effect - it clogs the filtering devices of water supply stations and condensers of hydroelectric power plants.
Since most freshwater algae are microscopic in size, it is possible to see them with the naked eye in nature only if they develop massively - by changing the color of their habitat: water, soil or other substrate.
In stagnant bodies of water, with the massive development of blue-green algae, the water acquires a bluish-green tint, and bluish or turquoise-colored foamy accumulations appear on its surface. If continuous cotton wool-like accumulations of green threads (“mud”) float on the surface of stagnant bodies of water, these are most likely accumulations of filamentous green algae. Slimy green films on the soil in moist areas or at the water's edge also indicate the presence of algae. Sometimes higher aquatic plants become overgrown with algae, and in this case they can be seen in the form of thin threads or a slippery coating on the leaves of plants on the underside of the leaf, immersed in water. Shapeless brown loose clusters, green mucous balls or even small green branched bushes consisting of thin threads on the surface of a branch that has lain in water for a long time are also algae. Maybe there is no formalized fouling, only some kind of brown loose dirt at the water's edge of a standing reservoir - these are also accumulations of microscopic algae.
Blue-green. Any organisms living on Earth occupy a specific and unique place in the composition of biocenoses, are irreplaceable and deserve careful study. However, the role of some groups in the evolution and existence of the biosphere seems especially significant. Such a group, according to modern science, is undoubtedly cyanobacteria.
Back in the 19th century, scientists drew attention to the undoubted similarity between blue-green algae and bacteria.
Blue-green algae, by the nature of their cellular organization, are quite consistent with gram-negative bacteria and represent an independent branch of their evolution; cyanobacteria are characterized by high morphological complexity and the ability to carry out photosynthesis with the release of molecular oxygen. Thus, the term “cyanobacteria” is quite justified. Although cyanobacteria, from the point of view of formal systematics, cannot be considered a high-ranking taxon, they played a special role in the evolution of life on Earth, and they are of great importance in the functioning of the modern biosphere. More than 1,500 species of blue-green algae have been described, among them there are unicellular forms that reproduce by division, budding or fragmentation of the cell into a number of daughter cells, colonial forms and filamentous forms. The threads can be simple or branching. Cell sizes vary significantly: their diameter in some species can be fractions of a micrometer, while in others it can be tens of micrometers. Colonies of cyanobacteria or tufts formed by filamentous forms can be macroscopic in size. Individual cells or filaments of some cyanobacteria are capable of crawling along a dense substrate.
Different types of cyanobacteria have a variety of adaptation mechanisms that determine their successful development in certain environmental conditions. Some forms of Scytonema, for example, form a pigment that concentrates on the surface of the cell and effectively protects it from ultraviolet rays, which determines the ability of this cyanobacteria to develop in direct sunlight.
Diatoms. G a group of protozoa, traditionally considered as part of algae, characterized by the presence of a kind of “shell” in the cells. The shell consists of two halves - epithecus And hypotheques, and the epitheca is larger, and its edges overlap the edges of the hypotheca. As a result of cell division, daughter cells receive one half of the shell and add a smaller one to it. Obviously, because of this, the population gradually becomes smaller and after several divisions the cells form auxospores without a shell. Auxospores grow in volume and subsequently give rise to a new large generation.
The shell consists of amorphous silica. Massive accumulations of diatom skeletons form the rock diatomite.
Typical of spring and autumn phytoplankton, they are the main group in many reservoirs during this period. Sometimes flowering may occur.
Green algae. Green algae (lat. Chlorophyta) – a group of lower plants. In modern taxonomy, this group has the rank of department, including unicellular and colonial planktonic algae, unicellular and multicellular forms of benthic algae. All morphological types of thallus are found here, except for rhizopodial unicellular and large multicellular forms with a complex structure. Many filamentous green algae attach to the substrate only in the early stages of development, then they become free-living, forming mats or balls.
The most extensive department of algae at this time. According to rough estimates, this includes from 13,000 to 20,000 species. All of them are distinguished primarily by the pure green color of their thalli, similar to the color of higher plants and caused by the predominance of chlorophyll over other pigments.
Genera of filamentous green algae can be identified by their chromatophore (analogous to chloroplasts in plant cells). Most often, these algae develop in the form of large accumulations of green threads in small standing reservoirs and river backwaters. Spirogyra is the most common.
This is what people call “tina”. Spirogyra species are most often indicators of slightly polluted waters. This genus does not have a saprobity index. Mougeotia and Zygnema species are indicators of clean waters.
Golden algae. Golden algae (lat. Chrysophyta) - a division of lower plants, which includes mainly microscopic algae of various shades of yellow. Golden algae are unicellular, colonial and multicellular. About 800 species are known.
Dinoflagellates. This is a type of protist from the alveolate group. Most representatives are bilaterally symmetrical or asymmetrical flagellates with a developed intracellular shell. A significant part of dinoflagellates are characterized by the ability to photosynthesize, and therefore the group is also called dinophyte algae. Some representatives (for example, night lights) are capable of luminescence. In total, 5–6 thousand species have been described.
Representatives whose mass outbreaks lead to the emergence of “ red tides».
Euglena algae. Order of protozoa. Unites about 1000 species, among them there are many colorless forms. Euglenids have one or more flagella, with the exception of a small group of flagellaless forms, as well as attached organisms.
Euglena also has an ocellus that reacts to light.
Cells lack cellulose membranes. Under the plasmalemma there is a dense, elastic, protein layer of protoplast called pellicle. The constancy of cell shape depends on its density. Each chloroplast has a three-layer membrane. According to the theory of endosymbiosis, the third membrane of the chloroplast is the plasmalemma of the green alga absorbed by the ancestral zooflagellate, or the endocytic membrane of the host.
Red algae. Red algae (lat. Rhodophyta) – department of plants. These are inhabitants primarily of marine reservoirs; few freshwater representatives are known. Usually these are quite large plants, but microscopic ones are also found. Among red algae there are unicellular (extremely rare), filamentous and pseudoparenchyma forms, but there are no truly parenchyma forms. Fossil remains indicate that this is a very ancient group of plants.
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On the issue of the diet of silver carp in ponds of Moldova
Recently, herbivorous fish - silver carp and grass carp - have been successfully introduced into the reservoirs of Moldova. This is extremely important for obtaining additional fish products by using the plant part of the natural food supply of reservoirs. However, to successfully complete this task, a detailed study of the compliance of environmental conditions with the development needs of these fish in our reservoirs, as well as the state of the food supply for them, is necessary. It is also necessary to know to what extent the available food supply is consumed by the new settlers.
This report presents the results of a study of the contents of the intestinal tracts of a significant number of silver carp specimens introduced by larvae in 1961 into the ponds of the Falesti fish farm. The collection of material began in 1962 in the second year of life of these fish and continued until September 1965 inclusive.
Our data show that in the conditions of ponds in Moldova, silver carp are extremely poor at using animal hydrobionts for food. Representatives of zooplankton were found in the intestinal tracts of only 24% of the fish studied. In most cases, the number of zooplankters in the intestines was 1-2 species, and only as an exception, 8 species were found in one of the intestines. In total, 18 species of zooplankter were identified in the intestines we studied, and the occurrence of each of them is very low. Only copepodite stages of copepods were found in seven, while the remaining species were found in no more than 2-3 intestines. Zooplankters were found in food mainly in spring and autumn, that is, when the amount of phytoplankton in ponds is lowest. This is clearly seen from the above table 1, where it is shown that the maximum content of zooplankton in the intestines corresponds to the lowest content of phytoplankton over the entire period of research. All this suggests that silver carp are forced to switch to feeding on zooplankton only during periods when phytoplankton in ponds is extremely poor. In other periods, single occurrences of zooplankters in the food of silver carp are purely accidental, as rightly pointed out by P. N. Saxena. Note that the zooplankton of the ponds where the studied silver carp are reared is quite diverse and abundant [Zelenin and Naberezhny, 1962], but it is almost not used by the silver carp.
The main source of food for silver carp in the reservoirs of Moldova is planktonic algae. The occurrence of phytoplankton in the intestines we studied was 100%. In the food spectrum of the 45 specimens of silver carp we examined, 102 species and varieties of planktonic algae were found, of which Cyanophyta - 8, Bacillariophyta - 14, Chrysophyta - 1, Pyrrophyta - 1, Euglenophyta - 27, Volvociphyceae - 3, Protococcophyceae -45 and Desmidiales -3. The same ratio of diversity of the main groups of planktonic algae is typical for our ponds, including the ponds of the Falesti fish farm, where the fish under study are grown. The predominant groups of algae in the diet of silver carp in terms of diversity were protococcal and euglena algae. These groups also predominate in the phytoplankton of most of our ponds.
In terms of biomass, the dominant groups of algae in the food spectrum of silver carp turned out to be euglena and blue-green, which often cause intense “blooming” of water in our ponds. Only at the beginning of September 1962 did the diatom predominate in the food spectrum of silver carp - Cyclotella meneghiniana, the average weight of which in the intestines exceeded 8 g ( table 1). In the intestines of individual fish, the weight of diatoms by this period was about 16 g or 91% of the weight of the food bolus.
Table 1
Changes in the composition of food in silver carp over the years
| Components food coma |
1962 | 1963 | ||||||
| VI | VIII | IX | V | VI | VIII | IX | XII | |
| average weight fish, g |
58 | 182 | 381,5 | 455 | 350 | 597 | 523 | 359 |
| food weight lump, g |
3,5 | 9,5 | 19,2 | 17 | 8 | 25 | 29 | 3,2 |
| avg. index filling % |
563 | 524 | 428 | 376 | 221 | 421 | 556 | 89 |
| ratio weight algae to food weight lump, % |
7,3 | 2 | 46 | 14 | 7 | 1,4 | 1,6 | 0,3 |
| Seaweed | ||||||||
| Cyanophyta | 0,04 | 0,03 | 0,03 | 0,02 | 0,03 | 0,07 | 0,07 | 0,0003 |
| Bacillariophyta | 0,001 | 0,02 | 8,02 | — | 0,06 | 0,03 | 0,02 | 0,0005 |
| Euglenophyta | 0,26 | 0,10 | 2,54 | 1,82 | 0,28 | 0,16 | 0,03 | 0,0002 |
| Protococco- phyceae |
0,005 | 0,01 | 0,05 | 0,40 | 0,07 | 0,04 | 0,03 | — |
| Total algae, g |
0,30 | 0,19 | 9,58 | 2,37 | 0,53 | 0,32 | 0,35 | 0,01 |
| Zooplankton, g | 0,06 | 0,007 | — | — | — | — | — | — |
continuation
| Components food coma |
1964 | 1965 | |||||
| V | VII | VIII | X | IV | VI | IX | |
| average weight fish, g |
1450 | 1083 | 1680 | 2500 | 1377 | 3000 | 2866 |
| food weight lump, g |
46 | 33 | 21 | 6 | — | — | 26 |
| avg. index filling % |
316 | 321 | 255 | 24 | 4,1 | — | 90,3 |
| ratio weight algae to food weight lump, % |
46,2 | 29 | 8,7 | 0,08 | — | — | 4,4 |
| Seaweed | |||||||
| Cyanophyta | 22,2 | 9,60 | 1,60 | — | 0,03 | 0,001 | 2,34 |
| Bacillariophyta | 0,05 | 0,01 | 0,03 | 0,002 | 0,01 | 0,004 | 0,015 |
| Euglenophyta | 0,60 | 0,37 | 0,06 | — | 0,03 | 0,01 | 2,81 |
| Protococco- phyceae |
0,05 | 0,05 | 0,01 | 0,003 | 0,003 | 0,02 | 0,02 |
| Total algae, g* |
23,5 | 10,1 | 1,62 | 0,005 | 0,04 | 0,04 | 5,91 |
| Zooplankton, g | 0,015 | — | — | 0,4 | 0,47 | — | — |
(* the rest of the food bolus consisted of digested algae and mineral particles)
Note that in the food spectrum of silver carp caught at the end of September, diatoms were noticeably inferior in weight to the same euglena and blue-green algae.
In the intestinal tracts of fish caught in April, the species composition of phytoplankton was very poor, and the average weight of algae in a food coma on average did not exceed 0.038 g, with fluctuations in individual specimens from 0.011 to 0.064 g, with an average fish weight of 1317 g. It should be noted that the weight of zooplankton in a food coma during this period reached its maximum - 0.047 g. The dominant algae in the nutritional spectrum of silver carp in the spring were euglenophytes. In May, the number of algae species in the food spectrum of silver carp increases noticeably, and species such as Scenedesmus quadricauda, S. bijugatus, S. arcuatus var. platydiscus, Crucigenia quadrata from protococcal ones become its integral part and dominate in the number of individuals. In terms of biomass in May 1963, euglena algae clearly dominated with an average of 1.824 g, mainly due to species such as Euglena acus, E. texta, E. oxyuris, Stromobmonas acuminata var. verrucosa, Trachelomonas intermedia, Phacus orbicularis etc. The total weight of algae in May 1963 in the intestines of fish averaged 2.371 g or 14% of the total weight of the food bolus with an average fish weight of 455 g. In May 1964 the average weight of algae in the food bolus was 23.475 g or 46.2% of its total weight. Note that in the intestines of individual specimens the amount of algae reached 46.388 g or 91% of the weight of the food coma. The weight of the fish in this case did not exceed 1500 g. The predominant group of algae in the food of silver carp in May 1964 were blue-green, mainly Oscillatoria sp.., whose weight averaged 22.237 g with fluctuations from 0.122 to 44.352 g in the food bolus with an intestinal filling index according to Zenkevich 24-321‰. It is appropriate to note that the same type of blue-green algae predominated in the food of silver carp in July of the same year. Their maximum weight in this case was 27 g, with a total weight of algae in the intestines of 28 g and a fish weight of 1800 g.
In June, the amount of algae in the food spectrum of silver carp is insignificant. This is explained by the fact that during this period, as we have established [Shalar, 1963], there is a noticeable decline in the development of phytoplankton in water bodies of Moldova, associated with the deterioration of meteorological and hydrological conditions. The main part of the food coma during this period consisted of sludge particles and cake. The predominant place among algae in the intestines of silver carp caught in June was Scenedesmus quadricauda, S. acuminatus, Coelastrum sphaericum, Cyclotella sp., Synedra ulna, Euglena spp., Phacus, Trachelomonas, and of the blue-greens most often encountered during this period Oscillatoria sp. and Merismopedia tenuissima. All these species by this time are dominant in the phytoplankton of ponds. In July, August and especially in September, blue-green algae begins to develop en masse in the phytoplankton - Aphanizomenon flos-aquae and, as a consequence of this, it also becomes dominant in the food bolus of silver carp. For example, in September 1965, the weight of this algae together with Microcystis aeruginosa, as can be seen from table I, averaged 2.338 g, and in individual intestines their weight reached 4.672 g with an average weight of 3000 g. All this suggests that, contrary to the statements of R. A. Savina, at least in the reservoirs we studied, silver carp indiscriminately ate all types of algae found in plankton. Mass species of phytoplankt are always dominant in the food spectrum of the fish we studied. It was not possible to detect any selectivity of silver carp to certain types of algae, and it is unlikely that it exists.
In winter, according to observations made in December 1963, the weight of algae in the intestines of fish did not exceed 10 mg. The diversity of algae in the food spectrum of silver carp in winter was only four species: Lobomonas denticulata, Cyclotella sp., Trachelomonas sp. and Oscillatoris sp.. Let us note that the phytoplankton in these ponds was extremely poor in winter, and the species indicated here are characteristic of them during this period.
Thus, changes in the feeding spectrum of silver carp over the seasons are completely dependent on seasonal changes in phytoplankton in ponds. This position is also confirmed by changes in the filling index, which during the period of mass development of phytoplankton reaches maximum values ( table 1). And the fact that silver carp uses for food all types of algae found in plankton opens up wide possibilities for the further introduction of these valuable fish species into the water bodies of Moldova, the phytoplankton of which is exceptionally rich both in qualitative and quantitative terms.
List of organisms found in the intestines of silver carp and their percentage of occurrence
| names of organisms | met tea- bridge % |
names of organisms | met tea- bridge % |
|
Cyanophyta |
Protococcophyceae |
||
| Daclylococcopsis irregularis G. M. Smith |
2 | Schroederia setigera (Schroed) Lemm. |
51 |
| Merismopedia tenuissima Lenim |
37 | Sch. spiralis (Printz) Korschik. |
2 |
|
Micricystis aeruginosa Kütz. |
22 | Lambertia ocellata Korschik. | 2 |
|
M. pulverea (Wood) Forti |
7 |
Pediastrum boryanum |
7 |
| Gomphosphaeria lacustris Chod |
14 | P. duplex Meyen | 4 |
|
Aphanizomenon flos-aquae |
40 |
Tetraedron caudatum |
4 |
| Oscillatoria sp. | 100 | T. minutissimum Korchik | 4 |
|
Romeria leopoliensis (Racib.) |
2 | T. incus (Teiling) G. M. Smith. |
2 |
|
Bacillariophyta |
Oocystis borgei Snow | 4 | |
| Melosira granulata (Ehr.) Ralfs |
2 | Oocystis sp | 24 |
| Melosira sp. | 2 |
Ankistrodesmus |
20 |
| Cyclotella meneghiniana Kütz |
90 | A. acicularis (A. Br.) Korschik. |
40 |
| Synedra actinastroides Lemn |
2 | A. arcuatus Korschik. | 33 |
| S. ulna (Nitzsch) Ehr. | 9 | A. angustus Born. | 61 |
| Rhoicosphenia curvata (Kütz.) Grun. |
2 | A. falcatus (Corda) Ralfs | 4 |
| Navicula sp. | 20 | Hyaloraphidium rectum Korschik. |
15 |
| Pinnularia sp. | 2 | H. contorlum Pasch. et Korschik. |
4 |
|
Caloneis amphisbaena |
2 |
H. contortum var. |
4 |
| Gyrosigma sp. | 2 |
Kirchneriella obesa (West) |
20 |
| Nitzschia acicularis W. Sm. | 4 | K. lunaris (Kirchn.) Moeb. | 9 |
| N. reversa W. Sm. | 3 | Dispora crucigenioides Printz. |
2 |
| Nitzschia sp. | 50 |
Dictyosphaerium |
11 |
|
Surirella ovata Kütz. |
14 | Coelastrum sphaericum Naeg. |
13 |
|
Chrysophyta |
C. microporum Naeg. | 16 | |
|
Goniochloris fallax Fott |
7 | Crucigenia apiculala Schmidle |
15 |
|
Pyrrophyta |
C. fenestrata Schmidle | 15 | |
| Glenodinium sp. | 4 | C. tetrapedia (Kirch.) W. et W. |
37 |
|
Euglenophyta |
C. quadrata Morren | 4 | |
|
Trachelomonas volvocina |
2 |
Tetrastrum |
4 |
|
T. intermedia Dang. |
31 | T. glabrum (Roll) Ahlstr. ef Tiff. |
13 |
|
T. abrupta Swir. |
19 | Actinastrum hantzschii var. fluviatile Schroed. |
9 |
|
T. planctonica Swir. |
29 | A. hantzschii var. gracile Roll |
33 |
|
T. asymmetrica Roll. |
15 | Scenedesmus obliquus (Turp) Kütz. |
7 |
|
T. bernandinensis |
4 | S. acuminatus (Lagerh.) Chod. | 64 |
|
Trachelomonas sp. |
80 |
S. acuminatus var. biseriatus Reinh |
23 |
|
Strombomonas acuminata var. verrucosa Teod. |
15 | S. acuminatus var. elongatus Smith | 7 |
| S. deflandrei (Roll) Defl. | 2 | S. bijugatus (Turp.) Kütz. | 33 |
| S. fluviatilis (Lemm.) Defl. | 11 | S. arcuatus var. platydiscus Smith. | 7 |
| S. treubii (Wolosz.) Defl. | 2 | S. apiculatus (W. et W.) Chod | 2 |
| Euglena polymorpha Dang. | 2 | S. brasiliensis Bohl | 2 |
| E. spathirhyncha Skuja | 4 | S. quadricauda (Turp) Breb | 73 |
| E. texta (Duj.) Hübner | 24 |
S. quadricauda var. eualternans Proschk. |
2 |
| E. vermicularis Prosch.- Lavr. |
2 | S. opoliensis Richt | 9 |
| E. acus Ehr. | 73 | S. opoliensis var. alatus Deduss. | 2 |
| E. oxyuris Schmarda | 25 | S. protuberans Fritsch. | 17 |
| Euglena sp. | 40 |
Desmidiales |
|
| Lepocinclis ovum (Ehr.) Mink. |
2 | Closterium acicularis | 2 |
| Lepocinclis sp. | 7 | Closterium sp. | 26 |
|
Phacus curvicauda Swir. |
22 | Cosmarium sp. | 2 |
| Ph. arnoldii Swir. | 29 |
Rotatoria |
|
| Phacus pleuronectes (Ehr.) Duj. |
4 | Brachionus angularis | 4 |
| Ph. orbicularis Hübner | 29 | B. bennini | 2 |
| Ph. longicauda (Ehr.) Duj. | 4 | Keratella cochlearis | 2 |
| Ph. longicauda var. tortus Lemm. | 9 | Lecane sp. | 2 |
| Phacus sp. | 33 | Colurella adriatica | 7 |
|
Volvociphyceae |
Asplanchna sieboldi | 2 | |
| Lobomonas denticulata Korsch. |
4 |
Cyclopidae |
|
| Phacotus coccifer Korsch. | 11 | Nauplii cyclops | 9 |
|
Pandorina morum (Müll.) Bory |
4 | Copepodite stage of Cyclops | 15 |
|
Cladocera |
Acanthocyclops vernalis | 11 | |
| Juvenile Daphnia | 2 | Cyclops vicinus | 11 |
| Moina Dubia | 2 | Paradiptomus alluaudi | 4 |
| Leydigia leidigii | 2 | ||
| Alona sp. | 2 | ||
| Chydorus sphaericus | 2 |
LITERATURE
Zelenin A. M., Naberezhny A. I. On the issue of growing grass carp (Ctenopharyngodon idella Vab) and silver carp (Hypophtalmichthys molitrix Vab.) in Moldova. Biological resources of reservoirs of Moldova, 1962.
Savina R. A. Nutrition of silver carp. In: Fishery development of herbivorous fish. M., 1966.
Saxena R. A. Algoflora of the fish farm ponds “Kalgan-Chirchik” and nutrition of the common silver carp. Author. Ph.D. dissertation, 1965.
Shalar V. M. Features of phytoplankton development in the Dubossary reservoir. Abstract of Ph.D. dissertation, 1963.
© 1970. Copyright for the article belongs to V.M. Shalar, A.M. Zelenin, A.I. Naberezhny, N.I. Yalovitskaya (Institute of Zoology of the Academy of Sciences of the Moldavian SSR).
Use and copying of the article is permitted with the indication of the author and a link to the source, |
Term plankton(Greek “plankton” - wandering) was first introduced into science by Gezen in 1887 and, according to the original concept, meant a collection of organisms floating in water. Somewhat later, in the composition of plankton they began to distinguish phytoplankton(plant plankton) and zooplankton(animal plankton). Consequently, phytoplankton is a collection of free-floating (in the water column) small, mainly microscopic, plants, the bulk of which are algae. Accordingly, each individual organism from the phytoplankton composition is called phytoplankter.
Ecologists believe that phytoplankton in the life of large bodies of water plays the same role as plants on land, i.e., it produces primary organic matter, due to which directly or indirectly (through the food chain) the rest of the living world exists on land and in water . This is true. However, it should be remembered that phytoplankton, as well as terrestrial plant communities, includes fungi and bacteria, which, with rare exceptions, are not capable of creating organic matter themselves. They belong to the same ecological group of heterotrophic organisms that feed on ready-made organic matter, to which the entire animal world belongs. Fungi and bacteria participate in the destruction of dead organic matter, thereby fulfilling, although a very important role in the cycle of substances, a fundamentally different role than green plants. Despite this, the main function of phytoplankton in general should still be recognized as the creation of organic matter by algae. Therefore, further we will talk here only about microscopic algae that are part of phytoplankton. This is all the more justified since the composition of fungi in the phytoplankton community is still very poorly studied, and planktonic bacteria (bacterioplankton) in the ecology of water bodies are usually considered separately.
The existence of planktonic organisms in suspension in water is ensured by some special adaptations. In some species, various kinds of outgrowths and appendages of the body are formed - spines, bristles, horn-like processes, membranes, etc. (Fig. 27); in other species, substances with a specific gravity of less than one accumulate in the body, for example, droplets of fat, gas vacuoles (in some blue-green algae, Fig. 28), etc. The mass of the cell is also lightened by reducing its size: cell sizes in planktonic species, as a rule, are noticeably smaller than those of closely related bottom algae. The smallest organisms, several micrometers in size, forming the so-called nannoplankton.
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The composition and ecology of individual representatives of algal phytoplankton in different water bodies are extremely diverse. Phytoplankton exists in bodies of water of various natures and sizes - from the ocean to a small puddle. It is absent only in reservoirs with a sharply anomalous regime, including thermal waters (at water temperatures above +70, +80 °C), dead waters (contaminated with hydrogen sulfide), and clean periglacial waters that do not contain mineral nutrients. There is also no living phytoplankton in cave lakes and at great depths of reservoirs, where there is insufficient solar energy for photosynthesis. The total number of phytoplankton species in all marine and inland waters reaches 3000.
In different bodies of water, and even in the same body of water, but in different seasons of the year, the number and ratio of species of individual taxonomic groups are very different. Let us consider its main complexes according to the main ecological categories of water bodies.
Marine phytoplankton consists mainly of diatoms and peridinium algae. The use of centrifugation and sedimentation methods helped to discover in plankton a significant number of small-sized species that were previously unknown. Of the diatoms in marine phytoplankton, representatives of the class of centric diatoms (Centrophyceae) are especially numerous, in particular the genera Chaetoceros, Khizosolenia, Thalassiosira, Corethron, Planktoniella and some others (Fig. 29 , 1-6), completely absent from freshwater plankton or represented in it by only a small number of species.
The composition of flagellated forms of pyrophytic algae in marine phytoplankton is very diverse, especially from the class of peridinians (Fig. 29, 7-10). This group is quite diverse in freshwater phytoplankton, but still has fewer species than in marine phytoplankton, and some genera are represented only in the seas: Dinophysis, Goniaulax and some others. Also very numerous in marine phytoplankton are calcareous flagellates - coccolithophores, represented in fresh waters by only a few species, and silicoflagellates, or silicoflagellates, found exclusively in marine plankton (Table 9).
The most characteristic morphological feature of representatives of marine phytoplankton is the formation of various kinds of outgrowths: bristles and sharp spines in diatoms, collars, lobes and parachutes in deridine. Similar formations are also found in freshwater species, but there they are much less pronounced. For example, in marine species of Ceratium, the horn-like processes are not only much longer than in freshwater ones, but in many species they are also curved. It is assumed that such outgrowths contribute to the soaring of the corresponding organisms. According to other ideas, outgrowths such as spines and horn-like formations were formed as a protective device against phytoplankter being eaten by crustaceans and other representatives of zooplankton.
Although the marine environment is relatively homogeneous over large areas, a monotonous distribution of phytoplankton is not observed. Heterogeneity of species composition and differences in abundance are often pronounced even in relatively small areas of sea water, but they are especially pronounced in large-scale geographic distribution. Here the ecological effect of the main environmental factors is manifested: water salinity, temperature, lighting conditions and nutrient content.
Marine tropical phytoplankton are characterized by the greatest species diversity, generally the lowest productivity (with the exception of upwelling areas, which will be discussed below) and the most pronounced morphological features of marine phytoplankton (the various types of outgrowths mentioned above). Peridineans are extremely diverse here, among which there are not only individual species, but also entire genera, distributed exclusively or predominantly in tropical waters. The tropical zone is the optimal biotope (place of existence) and for calcareous flagellates - coccolithophores. Here they are most diverse and in some places develop in such a mass that their calcareous skeletons form special bottom sediments. Tropical waters, compared to the cold waters of the northern and arctic seas, are much poorer in diatoms. Blue-greens, as in other marine areas, are represented by a very small number of species, and only one of them, belonging to the genus Oscillatoria erythraea, develops in such numbers in some areas of the tropics that it causes “blooming” of the water.
Unlike the tropics, in polar and subpolar sea waters, phytoplankton is dominated by diatoms. It is they who create that huge mass of lervic plant products, on the basis of which powerful accumulations of zooplankton are formed, which in turn serves as food for the largest herds of whales in the Antarctic, herring and whales in the polar waters of the Arctic.
Peridinea in Arctic waters are much less represented than in the seas of temperate latitudes and, especially, tropical ones. Coccolithophores are also rare here, but silicoflagellates are diverse and in places numerous. Marine blue-green algae are absent, while some types of green algae develop in significant quantities.
No less significant are the differences in the composition and productivity of algae in two other large biotopes of the seas, delimited in the latitudinal direction - the oceanic and neritic regions, especially if all inland seas are included in the latter. The special features of oceanic plankton are listed above. Although they are different in tropical and subpolar waters, they generally reflect the characteristic features of marine phytoplankton. Oceanic plankton, and only it, consists exclusively of species that complete their entire life cycle in the water column - in the pelagic zone of the reservoir, without connection with the ground. In neritic plankton there are already significantly fewer such species, and in the plankton of continental waters they can only be found as an exception.
The neritic or shelf zone is an area of the sea extending from the coast to the end of the continental shelf, which usually corresponds to a depth of about 200 m. In some places it is narrow, in others it extends for many hundreds and even thousands of kilometers. The main ecological features of this zone are determined by a more pronounced connection with the shore and bottom. Here there are significant deviations from oceanic conditions in water salinity (usually downward); reduced transparency due to mineral and organic suspended matter (often due to higher plankton productivity); deviations in temperature conditions; more pronounced turbulent mixing of waters and, which is especially important for plant plankton, increased concentration of nutrients.
These features determine the following characteristic features in the composition and productivity of phytoplankton in the neritic zone:
1) many oceanic species drop out of this community, others are represented in varying degrees by modified forms (varieties);
2) many specific marine species appear that are not found in oceanic plankton;
3) a complex of brackish-water species is formed that are completely absent in oceanic plankton, and in the highly desalinated waters of some inland seas, with a water salinity below 10-12°/00 (°/00, ppm - a thousandth of a number, a tenth of a percent) , freshwater species reach significant diversity, which become predominant when water is desalinated to 2-3°/00;
4) the proximity of the bottom and shores contributes to the enrichment of neritic phytoplankton with temporary planktonic (meroplanktonic) species.
Due to the diversity of biotopes, neritic phytoplankton in general is much richer in species composition than oceanic phytoplankton. The phytoplankton of the neritic zone of temperate latitudes is dominated by diatoms and peridinians, but among them there are many brackish-water species, which mostly develop in the desalinated waters of the inland seas (Baltic, Black, Azov, etc.). In the life cycle of many species of neritic plankton, the bottom phase (resting stage) is well defined, which in temperate latitudes determines a clearer seasonal change (succession) of phytoplankton. In general, neritic phytoplankton is several times more productive than oceanic phytoplankton.
The phytoplankton of desalinated inland seas differs significantly in composition and productivity not only from oceanic plankton, but also from typical neritic plankton. An example is the phytoplankton of the Baltic Sea. The salinity of water in the upper layer of the central part of the Baltic is 7-8°/00, which is approximately 4.5-5 times less than the salinity of the ocean, but 20-40 times more than the salinity of fresh waters. In the gulfs of Riga, Finland and Bothnia, salinity drops to 5-6°/00, off the coast - to 3-4°/00, and at river mouths and in some estuary bays (Neva Bay, Curonian Lagoon, etc.) the water is completely fresh.
Although the phytoplankton of the Central Baltic and even in the open part of the Gulf of Riga, Finland and Bothnia is dominated by a marine complex of species, in the strict sense it can only be called marine by its origin. Typical oceanic species are completely absent here. Even marine neritic plankton is extremely depleted here and is represented only by euryhaline species - capable of tolerating wide fluctuations in salinity, although preferring low salinity values. This Baltic phytoplankton complex, marine in origin but brackish in ecology, is dominated by diatom species: Chaetoceros thalassiosira, Sceletonema, Actinocyclus. Peridineans that are regularly found but do not reach large numbers include Goniaulax, Dinophysis baltica, and several species of silicoflagellates.
In the phytoplankton of the Central Baltic and especially its bays, an important role is played by a complex of species of freshwater origin, mainly blue-green: Anabaena, Aphanizomenon, Nodularia, Microcystis, which in summer in stable sunny weather develop in such a mass that even in the central part of the sea they form a “bloom” of water (mainly due to the development of Aphanizomenon and Nodularia, and in the southern part of the sea also Microcystis).
IN freshwater complex Green algae are also common: Oocystis (all over the sea), species of Scenedesmus and Pediastrum, more numerous in the bays.
Freshwater phytoplankton differs from typical marine phytoplankton in a huge variety of green and blue-green algae. Particularly numerous among the green ones are unicellular and colonial volvox and protococcal species: species of Chlamydomonas, Gonium, Volvox, Pediastrum, Scenedesmus, Oocystis, Sphaerocystis, etc. (Fig. 30). Among the blue-greens there are numerous species of anabena, microcystis, aphanizomenon, Gloeotrichia, etc.
The species diversity of diatoms here is less than in the seas (if we do not take into account the large diversity of temporary planktonic species) (Fig. 31); In terms of productivity per unit of water surface, the role of diatoms in fresh and sea waters is on average comparable.
The most characteristic genus of marine phytoplankton, Chaetoceros, is completely absent in lakes and ponds, and Rhizosolenia, which is abundant in the seas, is represented in fresh waters by only a few species.
In the freshwater phytoplaktope, the peridinea are represented in a much poorer quality and quantity. Common among them are the species of Ceratium and Peridinium, Fig. 64. In fresh waters, there are no siliceous flagellates and very rare coccolithophores, but some other flagellates are represented here in a variety of ways and often in large numbers. These are mainly chrysomonads - species of Dinobryon, Mallomonas, Uroglena, etc. (Fig. 68, 69), as well as euglena - Euglena, Trachelomonas and Phacus ( Fig. 195, 201, 202); the former mainly in cold waters, and the latter in warm waters.
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One of the significant features of freshwater phytoplankton is the abundance of temporary planktonic algae. A number of species, which are considered to be typically planktonic, in ponds and lakes have a bottom or periphytonic (attachment to any object) phase in their life cycle. Thus, the diversity of environmental conditions in inland water bodies also determines a significantly greater diversity of ecological complexes and species composition of freshwater plankton compared to the seas.
In large deep lakes, the differences between freshwater phytoplankton and sea phytoplankton are less pronounced. In such giant lakes as Baikal, the Great Lakes, Ladoga, Onega, diatoms predominate in the phytoplankton almost all year round. Here, as in the seas, they create the main products. The species composition of diatom lake plankton is different from marine plankton, but their ecology has a lot in common. For example, Melosira islandica, a widespread species of phytoplankton in Lakes Ladoga and Onega, as well as Melosira baicalensis from Lake Baikal, during the resting phase after the spring outbreak, do not sink to the bottom (or only partially sink), as is observed in other freshwater species in smaller reservoirs, but are retained in the water column, forming characteristic interseasonal accumulations at a certain depth. In large lakes, as in the seas, there are great differences in the productivity of phytoplankton: in the central part of the reservoir, productivity is very low, and off the coast, especially in shallow bays and against river mouths, it increases sharply.
The phytoplankton of the world's two largest salt water lakes - the Caspian Sea and the Aral Sea - is even more similar to the sea. Although the water salinity in them is significantly lower than sea water (in the Caspian Sea 12-13°/00, in the Aral Sea 11-120/00), the phytoplankton composition here is dominated by algae of marine origin, especially among diatoms: species of Chaetoceros, Rhizosolenia etc. Among the flagellates, typical brackish-water species are Exuviella and others. In the desalinated zones of these lakes, freshwater species predominate, however, at a water salinity of even 3-5°/00, brackish-water phytoplankton of marine origin is still very diverse.
In its most typical form, freshwater phytoplankton, both in composition and ecology, and in production properties, is represented in medium-sized lakes of the temperate zone, for example, in lakes of the Baltic basin. Here, depending on the type of lake and the season of the year, the phytoplankton is dominated by diatoms, blue-green or green algae. Typical diatoms are Melosira, Asterionella, Tabellaria, Fragilaria, Cyclotella, etc.; among the blue-green ones are species of Microcystis, Anabaena, Aphanizomenon, and Gloeotrichia. The main representatives of green algae in lake plankton are the protococcal ones listed above, and in waters with very soft water, under the influence of swamps, desmidids are numerous: species of Cosmarium, Staurastrum, Closterium, Euastrum, etc. In shallow lakes and ponds, green algae are often dominated by Volvox: Volvox, Chlamydomonas, Pandorina, Eudorina. In the phytoplankton of lakes of the tundra and northern taiga, chrysomonads are very diverse: species of Dinobryon, Synura, Uroglenopsis, Mallomonas. The group of peridinea, the most characteristic of marine phytoplankton, is represented in fresh waters everywhere (in all water bodies), but by a relatively small number of species, which everywhere, with rare exceptions, reach low numbers. In the smallest bodies of water - in small lakes and ponds - euglenae are very diverse and often numerous, especially species of Trachelomonas, and in warm reservoirs of the tropics and subtropics there are also euglena, lepocynclis, Phacus, etc.
In each individual reservoir, depending on the physical and chemical characteristics of the regime and the season of the year, one or another of the listed groups of algae predominates, and during periods of very intensive development, often only one species dominates.
In small temporary reservoirs - puddles, dug holes - small volvox species of the genus Chlamydomonas are quite common, the mass development of which often turns the water green.
In the literature, river phytoplankton is often classified as a special category of freshwater plankton. In large rivers with very slow flows, of course, algae have time to multiply within a limited area of the river under relatively uniform conditions. Consequently, a composition of phytoplankton that is somewhat unique to these conditions may be formed here. However, even in this case, the initial “material” for a given river community is organisms carried by the current from an upstream section of the river or from lateral tributaries. Most often, the composition of phytoplankton in a river is formed as a mixture of phytoplankton of tributaries, transformed to one degree or another under the influence of river conditions.
The transformative role of river conditions in the formation of its phytoplankton is clearly demonstrated when a large lowland river flows through a city or past a large plant that pollutes the water with domestic and industrial wastewater. In this case, the composition of phytoplankton in the river above the city characterizes clean water, but within the city and immediately beyond its outskirts, under the influence of organic pollution, phytoplankton is greatly depleted and so-called saprobic species predominate - indicators of saprobic, i.e., polluted, waters. However, below, partly due to the sedimentation of suspended organic matter, partly due to their disintegration as a result of microbiological processes, the water becomes clear again, and the phytoplankton takes on approximately the same appearance as above the city.
The composition and distribution of phytoplankton in individual reservoirs and its changes within one reservoir are influenced by a large complex of factors. Of primary importance among physical factors are the light regime, water temperature, and for deep reservoirs - the vertical stability of water masses. Of the chemical factors, the main importance is the salinity of the water and the content of nutrients in it, primarily salts of phosphorus, nitrogen, and for some species also iron and silicon. Let's look at some of these factors.
The influence of illumination as an environmental factor is clearly manifested in the vertical and seasonal distribution of phytoplankton. In seas and lakes, phytoplankton exists only in the upper layer of water. Its lower limit in sea, more transparent waters is at a depth of 40-70 m and only in a few places reaches 100-120 m (Mediterranean Sea, tropical waters of the World Ocean). In lake waters, which are much less transparent, phytoplankton usually exists in the upper layers, at a depth of 10-15 m, and in waters with very low transparency it is found at a depth of 2-3 m. Only in high-mountain and some large lakes (for example, Baikal) with In clear water, phytoplankton are distributed to a depth of 20-30 m. In this case, water transparency affects algae not directly, but indirectly, since it determines the intensity of penetration of solar radiation into the water column, without which photosynthesis is impossible. This well confirms the seasonal course of phytoplankton development in water bodies of temperate and high latitudes, which freeze in winter. In winter, when the reservoir is covered with ice, often with a layer of snow, despite the highest water transparency of the year, phytoplankton is almost absent - only very rare physiologically inactive cells of some species are found, and in some algae - spores or cells in the dormant stage.
Given the overall high dependence of phytoplankton on illumination, the optimal values of the latter for individual species vary over a fairly wide range. Green algae and most species of blue-green algae, which develop in significant numbers in the summer season, are especially demanding of this factor. Some species of blue-greens develop en masse only at the very surface of the water: Oscillatoria - in tropical seas, many species of Microcystis, Anabaena, etc. - in shallow inland waters.
Diatoms are less demanding on lighting conditions. Most of them avoid the brightly lit surface layer of water and develop more intensively only at a depth of 2-3 m in the low-transparent waters of lakes and at a depth of 10-15 m in the clear waters of the seas.
Water temperature is the most important factor in the general geographic distribution of phytoplankton and its seasonal cycles, but in many cases this factor acts not directly, but indirectly. Many algae are able to tolerate a wide range of temperature fluctuations (eurythermal species) and are found in plankton of different geographical latitudes and in different seasons of the year. However, the temperature optimum zone, within which the greatest productivity is observed, for each species is usually limited by small temperature deviations. For example, the diatom Melosira islandica, widespread in lake plankton of the temperate zone and subarctic, is usually present in plankton (for example, in Lakes Onega and Ladoga, in the Neva) at temperatures from +1 to + 13 ° C, and its maximum reproduction is observed at temperatures from +6 to +8 °C.
The temperature optimum for different species does not coincide, which determines the change in species composition over the seasons, the so-called seasonal succession of species. The general scheme of the annual cycle of phytoplankton in lakes of temperate latitudes is as follows. In winter, under the ice (especially when the ice is covered with snow), phytoplankton is almost absent due to the lack of solar radiation. The vegetation cycle of phytoplankton as a community begins in March - April, when solar radiation is sufficient for photosynthesis of algae even under ice. At this time, small flagellates - Cryptomonas, Chromulina, Chrysococcus - are quite numerous - and the number of cold-water diatom species - Melosira, Diatoma, etc. - begins to increase.
In the second phase of spring - from the moment the ice breaks up on the lake until temperature stratification is established, which usually happens when the upper layer of water warms up to +10, +12 °C, a rapid development of the cold-water diatom complex is observed. In the first phase of the summer season, at water temperatures from +10 to + 15 °C, the cold-water complex of diatoms stops growing. At this time, diatoms are still numerous in the plankton, but other species are moderately warm-water: Asterionella, Tabellaria . At the same time, the productivity of green and blue-green algae, as well as chrysomonads, increases, some species of which reach significant development already in the second phase of spring. In the second phase of summer, at water temperatures above + 15 °C, maximum productivity of blue-green and green algae is observed. Depending on the trophic and limnological type of the reservoir, at this time there may be a “blooming” of water caused by species of blue-green (Anabaena, Aphanizomenon, Microcystis, Gloeotrichia, Oscillatoria) and green algae (Scenedesmus, Pediastrum, Oocystis).
In summer, diatoms, as a rule, occupy a subordinate position and are represented by warm-water species: Fragilaria and Melosira granulata. In autumn, with a drop in water temperature to +10, +12 °C and below, an increase in the productivity of cold-water diatom species is again observed. However, unlike the spring season, blue-green algae play a noticeably larger role at this time.
In sea waters of temperate latitudes, the spring phase in phytoplankton is also marked by an outbreak of diatoms; summer - an increase in species diversity and abundance of peridinea with a depression in phytoplankton productivity in general.
Among the chemical factors influencing the distribution of phytoplankton, the salt composition of water should be put in first place. At the same time, the total concentration of salts is an important factor in the qualitative (species) distribution among types of reservoirs, and the concentration of nutrient salts, primarily nitrogen and phosphorus salts, is a quantitative distribution, i.e., productivity.
The total concentration of salts of normal (in an ecological sense) natural waters varies over a very wide range: from approximately 5-10 to 36,000-38,000 mg/l (from 0.005-0.01 to 36-38°/0O). In this salinity range, two main classes of water bodies are distinguished: marine with a salinity of 36-38°/00, i.e. 36,000-38,000 mg/l, and fresh with a salinity from 5-10 to 400-500 and even up to 1000 mg /l. Brackish waters occupy an intermediate position in terms of salt concentration. These classes of waters, as shown above, also correspond to the main groups of phytoplankton in terms of species composition.
The ecological significance of the concentration of nutrients is manifested in the quantitative distribution of phytoplankton as a whole and its constituent species.
The productivity, or “yield,” of microscopic phytoplankton algae, like the yield of large vegetation, under other normal conditions, depends to a very large extent on the concentration of nutrients in the environment. Of the mineral nutrients for algae, as for terrestrial vegetation, nitrogen and phosphorus salts are primarily needed. The average concentration of these substances in most natural bodies of water is very small, and therefore high productivity of phytoplankton, as a stable phenomenon, is possible only if mineral substances constantly enter the upper layer of water - the zone of photosynthesis.
True, some blue-green algae are still able to absorb elemental nitrogen from air dissolved in water, but there are few such species and their role in nitrogen enrichment is significant only for very small bodies of water, in particular in rice fields.
Inland reservoirs are fertilized with nitrogen and phosphorus from the shore, due to the supply of nutrients by river water from the drainage area of the entire river system. Therefore, there is a clear dependence of the productivity of lakes and shallow inland seas on soil fertility and some other factors operating within the drainage area of their basins (river systems). The least productive phytoplankton is in periglacial lakes, as well as in reservoirs located on crystalline rocks and in areas with a large number of swamps within the drainage area. Examples of the latter are the lakes of North Karelia, the Kola Peninsula, Northern Finland, Sweden and Norway. On the contrary, reservoirs located within highly fertile soils are characterized by a high level of productivity of phytoplanktops and other communities (the Sea of Azov, the Lower Volga reservoirs, the Tsimlyansk reservoir).
The productivity of phytoplankton also depends on water dynamics and the dynamic regime of water. The influence can be direct and indirect, which, however, is not always easy to distinguish. Turbulent mixing, if it is not too intense, under other favorable conditions, directly contributes to increasing the productivity of diatoms, since many species of this division, having a relatively heavy shell of silicon, sink to the bottom in calm water. Therefore, a number of abundant freshwater species, in particular from the genus Melosira, intensively develop in the plankton of lakes of temperate latitudes only in spring and autumn, during periods of active vertical mixing of water. When such mixing ceases, which occurs when the upper layer warms up to +10, +12 °C and the formation of temperature stratification of the water column in many lakes, these species drop out of the plankton.
Other algae, primarily blue-green algae, on the contrary, cannot tolerate even relatively weak turbulent mixing of water. In contrast to diatoms, many blue-green species develop most intensively in extremely calm water. The reasons for their high sensitivity to water dynamics are not fully established.
However, in cases where vertical mixing of waters extends to great depths, it suppresses the development of even relatively shade-tolerant diatoms. This is due to the fact that during deep mixing, algae are periodically carried by water currents outside the illuminated zone - the photosynthesis zone.
The indirect influence of the dynamic factor on the productivity of phytoplankton is that with vertical mixing of water, nutrients rise from the bottom layers of water, where they cannot be used by algae due to lack of light. Here, the interaction of several environmental factors is manifested - light and dynamic regimes and the supply of nutrients. This relationship is typical for natural processes.
Already at the beginning of this century, hydrobiologists discovered the special importance of phytoplankton in the life of water bodies as the main, and in the vast oceanic expanses, the only producer of primary organic matter, on the basis of which the rest of the diversity of aquatic life is created. This has determined increased interest in studying not only the qualitative composition of phytoplankton, but also its quantitative distribution, as well as the factors regulating this distribution.
An elementary method for quantifying phytoplankton, which has been the main method for several decades, and has not yet been completely abandoned, is the method of straining it from water using plankton grids. In a sample concentrated in this way, the number of cells and colonies by species is calculated and their total number per unit surface of the reservoir is determined. This simple and accessible method, however, has a significant drawback - it does not fully take into account even relatively large algae, and the smallest ones (nannoplankton), which significantly predominate in many reservoirs, are not captured by plankton nets.
Currently, phytoplankton samples are taken mainly with a bathometer or planktobatometer, which makes it possible to “cut out” a monolith of water from a given depth. The sample is concentrated by sedimentation in cylinders or by filtration through microfilters: both ensure that algae of all sizes are taken into account.
When huge differences in the sizes of algae that make up phytoplankton were determined (from several to 1000 microns or more), it became clear that abundance values cannot be used for a comparative assessment of phytoplankton productivity in water bodies. A more realistic indicator for this purpose is the total biomass of phytoplankton per unit area of the reservoir. However, later this method was rejected for two main reasons: firstly, calculations of the biomass of cells that have different configurations in different species are very labor-intensive; secondly, the contribution of small, but rapidly reproducing algae to the total production of the community per unit of time can be significantly greater than that of large, but slowly reproducing algae.
The true indicator of phytoplankton productivity is the rate of formation of matter per unit of time. To determine this value, a physiological method is used. During the process of photosynthesis, which occurs only in light, carbon dioxide is absorbed and oxygen is released. Along with photosynthesis, algal respiration also occurs. The latter process, associated with the absorption of oxygen and the release of carbon dioxide, prevails in the dark, when photosynthesis stops. The method for assessing phytoplankton productivity is based on a quantitative comparison of the results of photosynthesis (production process) and respiration (destruction process) of the community based on the oxygen balance in the reservoir. For this purpose, water samples are used in light and dark bottles, exposed in a reservoir, usually for a day at different depths.
To increase the sensitivity of the oxygen method, which is unsuitable for unproductive waters, they began to use an isotope (radiocarbon) version of it. However, subsequently the shortcomings of the oxygen method as a whole were revealed, and at present the chlorophyll method, based on the determination of the chlorophyll content in a quantitative sample of phytoplankton, is widely used.
Currently, the level of phytoplankton productivity in many inland water bodies is determined not so much by natural conditions as by socio-economic conditions, i.e., population density and the nature of economic activity within the reservoir's catchment area. This category of factors, called anthropogenic in ecology, i.e., originating from human activity, leads to the depletion of phytoplankton in some water bodies, and in others, on the contrary, to a significant increase in its productivity. The first occurs as a result of the discharge of toxic substances contained in industrial wastewater into a reservoir, and the second occurs when the reservoir is enriched with nutrients (especially phosphorus compounds) in mineral or organic form, contained in high concentrations in waters flowing from agricultural areas and cities and small villages (domestic wastewater). Nutrients are also found in wastewater from many industrial processes.
The second type of anthropogenic influence - the enrichment of a reservoir with nutrients - increases the productivity of not only phytoplankton, but also other aquatic communities, including fish, and should be considered as a process favorable from an economic point of view. However, in many cases, spontaneous anthropogenic enrichment of water bodies with primary nutrients occurs on such a scale that the water body as an ecological system becomes overloaded with nutrients. The consequence of this is the excessively rapid development of phytoplankton (“blooming” of water), the decomposition of which releases hydrogen sulfide or other toxic substances. This leads to the death of the animal population of the reservoir and makes the water unfit for drinking.
There are also frequent cases of intravital release of toxic substances by algae. In freshwater bodies of water, this is most often observed with the massive development of blue-green algae, in particular species of the genus Microcystis. In sea waters, water poisoning is often caused by the massive development of small flagellates. In such cases, the water sometimes turns red, hence the name of this phenomenon - “red tide”.
A decrease in water quality as a result of anthropogenic overload of a reservoir with nutrients, causing excessive development of phytoplankton, is usually called the phenomenon of anthropogenic eutrophication of a reservoir. This is one of the sad manifestations of human pollution of the environment. The scale of this process can be judged by the fact that pollution is intensively developing in such huge fresh water bodies as Lake Erie, and even in some seas.
The natural fertility of sea surface waters is determined by various factors. The replenishment of nutrients in shallow inland seas, for example the Baltic and Azov, occurs mainly due to their supply by river waters.
Surface waters of the oceans are enriched with nutrients in areas where deep waters reach the surface. This phenomenon is included in the literature under the name of upwelling. Upwelling is very intense off the Peruvian coast. Based on the high production of phytoplankton, the production of invertebrates is extremely high here, and due to this the number of fish increases. A small country, Peru in the 60s took first place in the world in terms of fish catches.
The powerful productivity of phytoplankton in the cold waters of the Arctic seas and especially in the waters of the Antarctic is also determined by the rise of deep waters enriched with nutrients. A similar phenomenon is observed in some other areas of the ocean. The opposite phenomenon, i.e., depletion of surface waters in nutrients, which inhibits the development of phytoplankton, is observed in areas with stable isolation of surface waters from deep waters.
These are the main features of typical phytoplankton.
Among the communities of small plants and animals inhabiting the water column, there is a complex of organisms that live only at the very surface of the water - in the zone of the surface film. In 1917, Nauman gave this community, not so significant in terms of species composition, but a very unique community, a special name - Neuston(Greek “nein” - to swim), although, obviously, it is only an integral part of plankton.
The life of neuston organisms is associated with the surface film of water, and some of them are located above the film (epineuston), others - below the film (hyponeuston). In addition to microscopic algae and bacteria, small animals also live here - invertebrates and even the larvae of some fish.
Large concentrations of neuston organisms were initially found in small bodies of water - in ponds, dug holes, in small bays of lakes - in calm weather with a calm water surface. Later, a variety of neuston organisms, mostly small animals, were found in large bodies of water, including the seas.
The composition of freshwater neuston algae includes species of different systematic groups. A number of representatives of golden algae were found here - Chromulina, Kremastochrysis; from euglena - euglena (Euglena), trachelomonas (Tgachelomonas), as well as some green ones - chlamydomonas (Chlamydomonas), kremastochloris (Kremastochloris) - and small protococcal, certain species of yellow-green and diatoms.
Some species of neuston algae have characteristic adaptations to exist at the surface of the water. For example, species of Nautococcus have mucus parachutes that hold them to the surface film. In Cremastochrysis (Fig. 32, 1), a scaly parachute is used for this; in one species of green algae, such a microscopic parachute protrudes above the surface tension film in the form of a cone-shaped cap (Fig. 32, 2).
The advantages of the existence of neuston organisms at the boundary of the water and air environments are unclear, however, in some cases they develop in such numbers that they cover the water with a continuous film. Often, planktonic algae (especially blue-green algae) during the period of mass development float to the very surface of the water, forming huge accumulations. Sharply increased concentrations of aquatic bacteria were also found. In the neuston community, microscopic animals are also quite diverse, which, even in the seas, under conditions of an almost constantly turbulent surface, at times form significant accumulations at the lower edge of the water surface.
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The concept of “algae” is scientifically vague. The word “algae” literally means only that these are plants that live in water, but not all plants in water bodies can be scientifically called algae, such plants as reeds, reeds, cattails, water lilies, egg capsules, small green plates of duckweed and etc., are seed (or flowering) plants. The scientific term “algae” does not apply to these plants; they are called aquatic plants
The concept of “algae” is not systematic, but biological. Seaweed ( Algae) is a collective group of organisms, the main part of which, according to modern ideas, is included in the kingdom of Plants ( Plantae), in which it makes up two sub-kingdoms: purple algae, or red algae - Rhodobionta and real algae - Phycobionta(the third subkingdom of the plant kingdom includes higher (embryonic or leafy) plants - Embryobionta). The remaining organisms classified as algae are now no longer considered plants: blue-green and prochlorophyte algae are often considered an independent group or classified as bacteria, and euglena algae are sometimes classified as a subkingdom of animals - protozoa. Different groups of algae arose at different times and, apparently, from different ancestors, but as a result of evolution in similar living conditions they acquired many similar features.
Organisms classified as algae have a number of common characteristics. In morphological terms, the most significant feature for algae is the absence of multicellular organs - roots, leaves, stems, typical of higher plants. Such a body of algae that is not divided into organs is called a thallus, or thallus. .
Algae have a simpler (compared to higher plants) anatomical structure - there is no conductive (vascular) system, therefore algae classified as plants are avascular plants. Algae never form flowers or seeds, but reproduce vegetatively or by spores.
Algae cells contain chlorophyll, thanks to which they are able to assimilate carbon dioxide in the light (i.e., feed through photosynthesis); they are primarily inhabitants of the aquatic environment, but many have adapted to life in the soil and on its surface, on rocks, on tree trunks and in other biotopes.
Organisms classified as algae are extremely diverse. Algae belong to both prokaryotes (prenuclear organisms) and eukaryotes (truly nuclear organisms). The body of algae can be of all four degrees of complexity generally known for organisms: unicellular, colonial, multicellular and noncellular, their sizes vary within very wide limits: the smallest are comparable to bacterial cells (do not exceed 1 micron in diameter), and the largest marine brown algae reach 30–45 m in length.
Algae are divided into a large number of divisions and classes and their division into systematic groups (taxa) is made according to biochemical characteristics (set of pigments, composition of the cell membrane, type of reserve substances), as well as submicroscopic structure. However, modern systematics of algae is characterized by many different systems. Even at the highest taxonomic levels (superkingdoms, subkingdoms, divisions and classes), taxonomists cannot come to a consensus.
According to one of the modern systems, algae are divided into 12 divisions: blue-green, prochlorophyte, red, golden, diatom, cryptophyte, dinophyte, brown, yellow-green, euglenophyte, green, charophyte. In total, about 30 thousand species of algae are known.
The science of algae is called algology or phycology, it is considered as an independent branch of botany. Algae are objects for solving issues related to other sciences (biochemistry, biophysics, genetics, etc.). Algology data is taken into account when developing general biological problems and economic problems. The development of applied algology proceeds in three main directions: 1) the use of algae in medicine and in various areas of the economy; 2) to resolve environmental issues; 3) accumulation of data on algae to solve problems in other industries.
The structure of algae.
The main structural unit of the body of algae, represented by unicellular and multicellular forms, is the cell. There are different types of algae cells, they are divided by shape (spherical, cylindrical, etc.), functions (sexual, vegetative, capable and not capable of photosynthesis, etc.), location, etc. But the most important classification these days is considered cells according to the features of their fine structure, detected using an electron microscope. From this point of view, a distinction is made between cells containing typical nuclei (i.e., nuclei surrounded by nuclear membranes, membranes) and cells that do not have typical nuclei. The first case is the eukaryotic structure of the cell, the second is the prokaryotic structure . Blue-green and prochlorophyte algae have a prokaryotic cell structure, while representatives of all other divisions of algae have a eukaryotic cell structure.
The vegetative body of algae (thallus) is characterized by morphological diversity; algae can be unicellular, colonial, multicellular and noncellular. Their sizes within each of these forms vary widely - from microscopic to very large.
The peculiarity of unicellular forms of algae is determined by the fact that their body consists of one cell, therefore its structure and physiology combine cellular and organismal features. This is an autonomous system capable of growing and self-reproducing; a small, unicellular algae invisible to the naked eye is a kind of factory that extracts raw materials (absorbing solutions of mineral salts and carbon dioxide from the environment), processes and produces such valuable compounds as proteins, carbohydrates and fats. In addition, the important products of its vital activity are oxygen and carbon dioxide and, thus, it actively participates in the cycle of substances in nature. Single-celled algae sometimes form temporary or permanent aggregations (colonies).
Multicellular forms arose after the cell went through a long and complex path of development as an independent organism. The transition from a unicellular to a multicellular state was accompanied by a loss of individuality and associated changes in the structure and functions of the cell. Within the thalli of multicellular algae, qualitatively different relationships develop than between the cells of unicellular algae. With the emergence of multicellularity, differentiation and specialization of cells in the thallus appeared. From an evolutionary point of view, this should be considered as the first step towards the formation of tissues and organs.
Siphon algae constitute a unique group: their thalli are not divided into cells, however, they also have unicellular stages in their development cycle.
The color of algae is diverse (green, pink, red, orange, almost black, purple, blue, etc.), due to the fact that some algae contain only chlorophyll, while others contain a number of pigments that color them in different colors.
Algae (more precisely, blue-green algae, or cyanobacteria) were the first organisms on Earth that, through the process of evolution, acquired the ability to photosynthesize, the process of producing organic substances under the influence of light. Photosynthesis uses carbon dioxide (CO2) as a source of carbon, water (H2O) as a source of hydrogen, and as a result free oxygen is released.
Power type with the help of photosynthesis, in which the body, using the energy of photosynthesis, synthesizes all the necessary organic substances from inorganic ones, has become one of the main ways of feeding algae and other green plants. However, many algae can, under certain conditions, quite easily switch from the photosynthetic method of nutrition to the assimilation of various organic compounds, while the body uses ready-made organic substances for nutrition, or combines this method of nutrition with photosynthesis.
In addition to using organic compounds as a carbon source, algae can switch from assimilating inorganic nitrate nitrogen to assimilating nitrogen from organic compounds; some blue-green algae can do without bound forms of nitrogen altogether and fix free nitrogen from the atmosphere as nitrogen-fixing organisms.
The variety of feeding methods of algae allows them to have wide habitats and occupy a variety of ecological niches.
Reproduction of their own kind in algae occurs through vegetative, asexual and sexual reproduction.
Origin of algae.
The question of the origin and evolution of algae is very complex due to the diversity of these plants, especially their submicroscopic structure and biochemical characteristics; in addition, most algae have not been preserved in the fossil state and there are no connecting links between modern plant divisions in the form of organisms of intermediate structure.
The easiest way to solve the question is about the origin of prokaryotic (prenuclear) algae - blue-green algae, which have many common characteristics with photosynthetic bacteria. Most likely, blue-green algae originated from organisms close to purple bacteria and containing chlorophyll ().
There is currently no consensus on the origin of eukaryotic (nuclear) algae. There are two groups of theories, emanating from either a symbiotic or a non-symbiotic origin, however, each of these theories has its own objections.
According to the theory of symbiogenesis, chloroplasts and mitochondria of cells of eukaryotic organisms were once independent organisms: chloroplasts were prokaryotic algae, mitochondria were aerobic bacteria (). As a result of the capture of aerobic bacteria and prokaryotic algae by amoeboid eukaryotic organisms, the ancestors of modern groups of eukaryotic algae arose. Some researchers also attribute a symbiotic origin to chromosomes and flagella.
According to the theory of non-symbiotic origin, eukaryotic algae arose from an ancestor common with blue-green algae, which had chlorophyll and photosynthesis with the release of oxygen; in this case, modern photosynthetic prokaryotes (blue-green algae) are a side, dead-end branch of plant evolution.
The main factors influencing the development of algae.
The main factors influencing the development of algae are light, temperature, the presence of water, carbon sources, minerals and organic substances. Algae are widespread throughout the globe and can be found in water, in and on soil, on tree bark, on the walls of wooden and stone buildings, and even in inhospitable places such as deserts and glaciers.
Factors influencing the development of algae are divided into abiotic, not related to the activity of living organisms, and biotic, caused by this activity. Many factors, especially abiotic ones, are limiting, i.e. they are able to limit the development of algae. The life of all organisms, including algae, depends on the content of necessary substances in the habitat, the importance of physical factors, as well as the range of resistance of the organisms themselves to changes in environmental conditions. The level at which a specific factor can act as a limiting factor is different for different types of algae. In aquatic ecosystems, limiting factors include temperature, transparency, the presence of a current, the concentration of oxygen, carbon dioxide, salts and nutrients. In terrestrial habitats, the main limiting factors are climatic: temperature, humidity, light, etc., as well as the composition and structure of the substrate. These two groups of factors, together with population interactions, determine the nature of terrestrial communities and ecosystems.
For most algae, water is a permanent habitat, but many of their species can live outside of water. Among plants that live on land, based on their resistance to desiccation, they are divided into poikilohydric, which are unable to maintain a constant water content in tissues, and homohydric, which are capable of maintaining constant hydration of tissues. In poikilohydric algae (blue-green and some green algae), when cells dry out, they shrink without irreversible changes in ultrastructure and, therefore, do not lose viability; when moistened, their normal metabolism is restored. The minimum humidity at which normal activity of such plants is possible varies. Cells of homohydric algae die when they dry out, so such plants, as a rule, live in conditions of constant excess moisture. Homoyhydric algae include, for example, some types of green and yellow-green algae.
Salinity and mineral composition of water are the most important limiting factors affecting the distribution of algae.
Algae live in water bodies of varying salinity: from fresh water bodies, the mineralization of which usually does not exceed 0.5 g/l, to extremely saline (hyperhaline) water bodies, the salt concentration of which ranges from 40 to 347 g/l. Despite the fact that in general algae are characterized by such a wide range of salt tolerance, specific species for the most part stenohaline, i.e. are able to live only at a certain salinity level. Euryhaline There are relatively few species of algae that can exist at different salinities.
Water acidity is also a limiting factor. The tolerance of different algae taxa to changes in acidity (pH) varies as much as it does to changes in salinity. Some types of algae live only in alkaline waters, with a high pH value, while others live in acidic waters, with a low pH value.
The presence in the environment of macro- and microelements, which are necessary components of the algae body, is crucial for the intensity of their development.
Elements and their compounds, related to macroelements, are required by organisms in relatively large quantities. The most important are nitrogen and phosphorus; potassium, calcium, sulfur and magnesium are almost as necessary.
Microelements are needed by plants in extremely small quantities, but they are of great importance for their life, since they are part of many vital enzymes. Microelements often act as limiting factors. These include 10 elements: iron, manganese, zinc, copper, boron, silicon, molybdenum, chlorine, vanadium and cobalt.
Algae of different departments have unequal needs for macro- and microelements. For example, for the normal development of diatoms, a fairly significant amount of silicon is required, which is used to build their shell. With a lack of silicon, the shells of diatoms become thinner.
In almost all freshwater and marine ecosystems, the limiting factor is the concentration of nitrates and phosphates in water. In fresh water bodies with a low carbonate content, the concentrations of calcium salts and some others can be considered limiting factors.
Algae need light as a source of energy for photochemical reactions and as a regulator of development. Its excess, as well as its deficiency, can cause serious disturbances in the development of algae. Therefore, light is also a limiting factor when there is too much or too little illumination.
The distribution of algae in the water column is largely determined by the availability of light necessary for normal photosynthesis. The layer of water above the habitat of photoautotrophic organisms is called euphotic zone. In the sea, the boundary of the euphotic zone is usually located at a depth of 60 m, occasionally dropping to a depth of 120 m, and in clear ocean waters - to approximately 140 m. In lake, much less transparent waters, the boundary of this zone usually runs at a depth of 10–15 m, and in the most transparent glacial and karst lakes - at a depth of 20–30 m.
Optimal light levels for different types of algae vary widely. In relation to light, heliophilic and heliophobic algae are distinguished. Heliophilus(light-loving) algae require a significant amount of light for normal functioning. These include the majority of blue-green algae and a significant amount of green algae, which grow abundantly in the surface layers of water in the summer. Heliophobic(bright light avoidant) algae are adapted to low light conditions. For example, most diatoms avoid the brightly lit surface layer of water and in low-transparent lake waters they develop intensively at a depth of 2–3 m, and in clear sea waters – at a depth of 10–15 m.
In algae of different divisions, depending on the composition of special light-sensitive pigments, maximum photosynthetic activity is observed at different light wavelengths. Under terrestrial conditions, the frequency characteristics of light are quite constant, so the intensity of photosynthesis is also constant. When passing through water, light from the red and blue regions of the spectrum is absorbed, and greenish light, weakly perceived by chlorophyll, penetrates into the depths. Therefore, mainly red and brown algae survive there, having additional photosynthetic pigments that can use the energy of green light. This makes clear the enormous influence of light on the vertical distribution of algae in the seas and oceans: in the near-surface layers, as a rule, green algae predominate, deeper - brown, and in the deepest areas - red. However, this pattern is not absolute. Many algae are able to exist in conditions of extremely low illumination, which is not typical for them, and sometimes in complete darkness. At the same time, they may experience certain changes in the pigment composition or in the way they feed. Thus, representatives of many divisions of algae are capable, in the absence of light and an excess of organic substances, to switch to feeding on organic compounds of dead bodies or animal excrement.
For algae living in aquatic biotopes, water movement plays a huge role. The movement of water masses ensures the influx of nutrients and the removal of waste products from algae. In any continental and marine reservoirs there is a relative movement of water masses, therefore almost all algae in reservoirs are inhabitants of flowing waters. The only exceptions are algae that develop in particularly extreme conditions (in the voids of rocks, thick ice, etc.).
Algae have very wide temperature tolerance ranges. Some of their species are able to exist both in hot springs, the temperature of which is close to the boiling point of water, and on the surface of ice and snow, where temperatures fluctuate around 0 ° C.
In relation to temperature, algae are distinguished: eurythermal species, existing in a wide temperature range (for example, green algae from the order Oedogoniales, sterile threads of which can be found in shallow bodies of water from early spring to late autumn), and stenothermic, adapted to very narrow, sometimes extreme temperature zones. Stenothermals include, for example, cryophilic(cold-loving) algae that grow only at temperatures close to 0 ° C and thermophilic(heat-loving) algae that cannot exist at temperatures below 30° C.
Temperature determines the geographic distribution of algae developing in the aquatic environment. In general, with the exception of widespread eurythermal species, the distribution of algae exhibits geographic zoning: specific taxa of marine planktonic and benthic algae are confined to certain geographic zones. Thus, large brown algae (Macrocystis) dominate the northern seas. As we move south, red algae begin to play an increasingly prominent role, and brown algae fade into the background. The phytoplankton of tropical waters is extremely rich in dinophyte and golden algae. In the northern seas, phytoplankton is dominated by diatoms. Temperature also affects the vertical distribution of planktonic and benthic algae. Here it acts mainly indirectly, accelerating or slowing down the growth rate of individual species, which leads to their displacement by other species that grow more intensively in a given temperature regime.
Algae, being part of ecosystems, are connected with their other components by multiple connections. The direct and indirect impacts that algae undergo due to the vital activity of other organisms are classified as biotic factors.
In most cases, algae act as producers of organic matter in an ecosystem. Therefore, the most important factor limiting the development of algae in a particular ecosystem is the presence of animals that subsist by eating algae.
Different types of algae are able to influence each other by releasing chemicals into the external environment (this interaction between plants is called allelopathy). Sometimes this is an obstacle to their coexistence.
Some species of algae may develop competitive relationships with each other for habitats.
Humans have a significant impact on natural ecosystems, which makes the anthropogenic factor very significant for the development of algae. By laying canals and constructing reservoirs, people create new habitats for aquatic organisms, often fundamentally different from the reservoirs of a given region in hydrological and thermal conditions. Wastewater discharges often lead to depletion of the species composition and death of algae or to the massive development of certain species. The first occurs when toxic waters are discharged, the second occurs when the reservoir is enriched with nutrients (especially nitrogen and phosphorus compounds). The consequence of excessive discharge of nutrients into a reservoir can be its eutrophication, which leads to the rapid development of algae (“water blooms”), oxygen deficiency, and the death of fish and other aquatic animals. Algae, especially aerophytic and soil ones, can also be affected by atmospheric emissions of toxic industrial waste. Very often, the consequences of human intervention in the life of ecosystems are irreversible.
Ecological groups of algae.
Algae are distributed throughout the globe and are found in various aquatic, terrestrial and soil biotopes. There are various known environmental groups these organisms: 1) planktonic algae; 2) neuston algae; 3) benthic algae; 4) terrestrial algae; 5) soil algae; 6) algae from hot springs; 7) algae of snow and ice; 8) algae of salt water bodies; 9) algae existing in a calcareous substrate.
Algae of aquatic habitats.
Planktonic algae.
Plankton is a collection of organisms that inhabit the water column of continental and marine reservoirs and are not able to resist transport by currents (i.e., as if floating in the water). Plankton includes phyto-, bacterio- and zooplankton.
Phytoplankton is a collection of small, mostly microscopic plants free-floating in the water column, the bulk of which are algae. Phytoplankton inhabit only the euphotic zone of water bodies (the surface layer of water with sufficient illumination for photosynthesis).
Planktonic algae live in a wide variety of bodies of water - from a small puddle to the ocean. They are absent only in reservoirs with a sharply anomalous regime, including thermal (at a water temperature above +80 ° C and dead (contaminated with hydrogen sulfide) reservoirs, in clean periglacial waters that do not contain mineral nutrients, as well as in cave lakes. Total The biomass of phytoplankton is small compared to the biomass of zooplankton (1.5 and more than 20 billion tons, respectively), but due to the rapid reproduction of its production in the World Ocean is about 550 billion tons per year, which is almost 10 times more than the total production of all animal population of the ocean.
Phytoplankton is the main producer of organic matter in water bodies, due to which aquatic heterotrophic animals and some bacteria exist. Phytoplankton is the initial link in most food chains in a body of water: small planktonic animals feed on them, which feed on larger ones. Therefore, in areas of greatest phytoplankton development, zooplankton and nekton are abundant.
The composition and ecology of individual representatives of algal phytoplankton in different water bodies are extremely diverse. The total number of phytoplankton species in all marine and inland waters reaches 3000.
The abundance and species composition of phytoplankton depends on a complex of factors discussed above. In this regard, the species composition of planktonic algae in different reservoirs (and even in the same reservoir, but at different times of the year) is not the same. It depends on the physical and chemical regime in the reservoir. In each season of the year, one of the groups of algae (diatoms, blue-greens, golden, euglenaceae, green and some others) develops predominantly, and often only one species of one or another group dominates. This is especially pronounced in freshwater bodies of water.
In inland water bodies there is a much greater diversity of ecological conditions compared to sea water bodies, which determines a significantly greater diversity of species composition and ecological complexes of freshwater phytoplankton compared to sea water. One of the significant features of freshwater phytoplankton is the abundance of temporary planktonic algae in it. A number of species, which are considered to be typically planktonic, in ponds and lakes have a bottom or periphytonic (attachment to any object) phase in their development.
Marine phytoplankton consists mainly of diatoms and dinophytes. Although the marine environment is relatively homogeneous over large areas, there is no uniformity in the distribution of marine phytoplankton. Differences in species composition and abundance are often pronounced even in relatively small areas of sea water, but they are especially clearly reflected in the large-scale geographic zonality of distribution. Here the effect of the main environmental factors is manifested: water salinity, temperature, light and nutrient content.
Planktonic algae usually have special adaptations for living suspended in the water column. In some species these are various kinds of outgrowths and appendages of the body - spines, bristles, horny processes, membranes, parachutes; others form hollow or flat colonies and secrete mucus profusely; still others accumulate in their bodies substances whose specific gravity is less than the specific gravity of water (fat droplets in diatoms and some green algae, gas vacuoles in blue-green algae). These formations are much more developed in marine phytoplankters than in freshwater ones. Another such adaptation is the small body size of planktonic algae.
Neuston algae.
The collection of marine and freshwater organisms that live near the surface film of water, attach to it, or move along it is called neuston. Neuston organisms live both in small bodies of water (ponds, water-filled pits, small bays of lakes) and in large ones, including the seas. In some cases, they develop in such quantities that they cover the water with a continuous film.
The composition of neuston includes unicellular algae that are part of different systematic groups (golden, euglenophytes, green, certain species of yellow-green and diatoms). Some neuston algae have characteristic adaptations for existing at the surface of the water (for example, slimy or scaly parachutes that hold them on the surface film).
Benthic algae.
Benthic (bottom) algae include algae adapted to exist in an attached or unattached state on the bottom of reservoirs and on a variety of objects, living and dead organisms in the water.
The predominant benthic algae of continental water bodies are diatoms, green, blue-green and yellow-green multicellular (filamentous) algae, attached or not attached to the substrate.
The main benthic algae of the seas and oceans are brown and red, sometimes green, macroscopic attached thallous forms. All of them can be overgrown with small diatoms, blue-green and other algae.
Sometimes algae growing on objects introduced into water by humans (ships, rafts, buoys) are classified as periphyton. The identification of this group is justified by the fact that its constituent organisms (algae and animals) live on objects moving or flowing around water. In addition, these organisms are removed from the bottom and, therefore, are exposed to different light and temperature conditions, as well as other conditions for the supply of nutrients.
The possibility of benthic algae growing in specific habitats is determined by both abiotic and biotic factors. Among the latter, competition with other algae and the presence of animals that feed on algae (sea urchins, gastropods, crustaceans, fish) play a significant role. The influence of biotic factors leads to the fact that certain types of algae do not grow at all depths and not in all bodies of water with suitable light and hydrochemical conditions.
Abiotic factors include light, temperature, as well as the content of biogenic and biologically active substances, oxygen and inorganic carbon sources in water. The rate at which these substances enter the thallus is very important, which depends on the concentration of the substances and the speed of water movement.
Benthic algae that grow in moving waters have advantages over algae that grow in slow-moving waters. The same level of photosynthesis can be achieved in them with less light, which promotes the growth of larger thalli; the movement of water prevents the settling of silt particles on rocks and stones, which interfere with the fixation of algae buds, and also washes away algae-eating animals from the soil surface. In addition, despite the fact that during strong currents or strong surf the algae thalli are damaged or torn from the ground, the movement of water still does not prevent the settlement of microscopic algae and microscopic stages of large algae. Therefore, places with intense water movement (in the seas these are straits with currents, coastal areas of the surf, in rivers - stones on riffles) are characterized by the lush development of benthic algae.
The influence of water movement on the development of benthic algae is especially noticeable in rivers, streams, and mountain streams. In these reservoirs there is a group of benthic organisms that prefer places with a constant flow. In lakes where there are no strong currents, wave motion becomes of primary importance. In the seas, waves also have a significant impact on the life of benthic algae, in particular on their vertical distribution.
In the northern seas, the distribution and abundance of benthic algae is influenced by ice. Algae thickets can be destroyed (erased) by the movement of glaciers. Therefore, for example, in the Arctic, perennial algae are most easily found near the shore among boulders and rock ledges that impede the movement of ice.
The intensive development of benthic algae is also facilitated by the moderate content of nutrients in the water. In fresh waters, such conditions are created in shallow ponds, in the coastal zone of lakes, in river backwaters, in the seas - in small bays. If in such places there is sufficient lighting, hard soils and weak water movement, then optimal conditions for the life of phytobenthos are created. In the absence of water movement and its insufficient enrichment with nutrients, benthic algae grow poorly.
Hot spring algae.
Algae that can withstand high temperatures are called thermophilic. In nature, they settle in hot springs, geysers and volcanic lakes. They often live in waters that, in addition to high temperatures, are characterized by a high content of salts or organic substances (heavily polluted hot wastewater from factories, factories, power plants or nuclear plants).
The maximum temperatures at which it was possible to find thermophilic algae, judging by different sources, range from 52 to 84 ° C. In total, about 200 species of thermophilic algae were discovered, but there are relatively few species that live only at high temperatures. Most of them can withstand high temperatures, but develop more abundantly at normal temperatures. Typical inhabitants of hot waters are blue-green algae, and to a lesser extent, diatoms and some green algae.
Algae of snow and ice.
Snow and ice algae make up the vast majority of organisms that settle on frozen substrates (cryobiotopes). The total number of algae species found in cryobiotopes reaches 350, but true cryophiles, capable of vegetating only at temperatures close to 0° C, are much smaller: slightly more than 100 species. These are microscopic algae, the vast majority of which are green algae (about 100 species); Several species include blue-green, yellow-green, golden, pyrophytic and diatom algae. All these species live in the surface layers of snow or ice. They are united by the ability to withstand freezing without damaging fine cellular structures and then, upon thawing, quickly resume vegetation using a minimum amount of heat. Only a few of them have a resting stage; most lack any special adaptations to withstand low temperatures.
Developing in large quantities, algae are capable of causing green, yellow, blue, red, brown, brown or black “blooming” of snow and ice.
Algae from salt water bodies.
These algae grow at high concentrations of salts in water, reaching 285 g/l in lakes with a predominance of table salt and 347 g/l in Glauber (soda) lakes. As salinity increases, the number of algae species decreases; only a few can tolerate very high salinity. In extremely saline (hyperhaline) water bodies, single-celled mobile green algae predominate. They often cause red or green “blooms” in salt water bodies. The bottom of hyperhaline reservoirs is sometimes completely covered with blue-green algae. they play a big role in the life of salt water bodies. The combination of organic mass formed by algae and a large amount of salts dissolved in water causes a number of unique biochemical processes characteristic of these reservoirs. For example, Chlorogloea sarcinoides (Chlorogloea sarcinoides) from the blue-greens, which develops in huge quantities in some salt lakes, as well as a number of other massively growing algae, are involved in the formation of medicinal mud.
Algae of non-aquatic habitats.
Aerophilic algae.
Aerophilic algae are in direct contact with the air around them. The typical habitat of such algae is the surface of various extra-soil solid substrates that do not have a clearly expressed physical and chemical effect on the settlers (rocks, stones, tree bark, etc.). Depending on the degree of moisture, they are divided into two groups: aerial algae, living in conditions of only atmospheric moisture and, therefore, experiencing a constant change of wetting and drying; And aquatic algae, subject to constant irrigation with water (spray from a waterfall, surf, etc.).
The conditions for the existence of algae in these communities are very unique and are characterized, first of all, by frequent and sharp changes in temperature and humidity. During the day, aerophilic algae become very warm, cool at night, and freeze in winter. Aerial algae are particularly susceptible to changing moisture conditions, as they are often forced to transition from a state of excess moisture (for example, after a rainstorm) to a state of minimal moisture (during dry periods), when they dry out enough to be ground into powder. Aquatic algae live in conditions of relatively constant moisture, however, they also experience significant fluctuations in this factor. For example, algae living on rocks irrigated by the spray of waterfalls experience a moisture deficit in the summer, when the flow decreases significantly.
Relatively few species (about 300) have adapted to such unfavorable living conditions. Aerophilic algae are represented by microscopic algae from the departments of blue-green, green and, to a much lesser extent, diatoms and red algae.
When aerophilic algae develop in large quantities, they usually take the form of powdery or slimy deposits, felt-like masses, soft or hard films or crusts. Algae growths are especially abundant on the surface of wet rocks. They form films and growths of various colors. As a rule, species equipped with thick mucous membranes live here. Depending on the light intensity, the mucus can be colored more or less intensely, which determines the color of the growths. They can be bright green, golden, brown, ocher, purple, brown or almost black, depending on the species that form them.
Thus, aerophilic algal communities are very diverse and arise both under quite favorable and extreme conditions. Their external and internal adaptations to this lifestyle are varied and similar to those found in soil algae, especially those developing on the soil surface.
Edaphilic algae.
The main living environment of edaphophilic algae is soil. Their typical habitats are the surface and thickness of the soil layer, which has a certain physical and chemical effect on the algae. Depending on the location of algae and their lifestyle, three groups of communities are distinguished within this type. This terrestrial algae, massively developing on the soil surface under atmospheric moisture conditions; water-terrestrial seaweed, growing massively on the surface of the soil, constantly saturated with water (this group also includes algae of caves) and soil seaweed, inhabiting the soil layer. Typical conditions are life among soil particles under the influence of an environment that is very complex in terms of a complex of factors.
Soil as a biotope is similar to aquatic and aerial habitats: it contains air, and it is saturated with water vapor, which ensures breathing with atmospheric air without the threat of drying out. However, the soil is fundamentally different from the above-mentioned biotopes in its opacity. This factor has a decisive influence on the development of algae. Intensive development of algae as phototrophic organisms is possible only where light penetrates. In virgin soils this is a surface layer of soil up to 1 cm thick, but in such soils algae are found at a much greater depth (up to 2 m). This is explained by the ability of some algae to switch to heterotrophic nutrition in the dark. Many algae remain dormant in the soil.
To survive, soil algae must be able to tolerate unstable humidity, sudden temperature fluctuations and strong insolation. These properties are ensured by a number of morphological and physiological features (smaller sizes compared to aquatic forms of the same species, abundant mucus formation). The amazing viability of these algae is evidenced by the following observation: when soil algae, stored for decades in an air-dry state in soil samples, were placed in a nutrient medium, they began to develop. Soil algae (mostly blue-green) are resistant to ultraviolet and radioactive radiation.
A characteristic feature of soil algae is the ability to quickly move from a dormant state to active life and vice versa. They are also able to tolerate varying variations in soil temperature. The survival range of a number of species lies from –20° to +84° C. It is known that terrestrial algae make up a significant part of the vegetation of Antarctica. They are almost black in color, so their body temperature is higher than the ambient temperature. Soil algae are also important components of biocenoses in the arid zone, where the soil heats up to 60–80° C in summer.
The listed properties of soil algae allow them to live in the most unfavorable habitats. This explains their wide distribution and rapid growth even with the short-term appearance of the necessary conditions.
The vast majority of soil algae are microscopic, but they can often be seen on the soil surface with the naked eye. The massive development of microscopic forms causes greening of the slopes of ravines and the sides of forest roads, and the “blooming” of arable soils.
The number of all types of soil algae is close to 2000. They are represented by blue-green, green, diatoms and yellow-green algae.
Lithophilic algae.
The main living environment of lithophilic algae is the opaque dense calcareous substrate surrounding them. As a rule, they live deep in solid rocks of a certain chemical composition, surrounded by air (i.e., out of water) or submerged in water. There are two groups of lithophilic communities: boring algae and tuff-forming algae.
Boring algae are organisms that penetrate into the calcareous substrate. These algae are not numerous in number of species, but they are extremely widespread: from the cold waters of the north to the constantly warm waters of the tropics. They live in both continental and marine reservoirs, near the surface of the water and at a depth of more than 20 m. Boring algae settle on calcareous rocks, stones, calcareous animal shells, corals, large algae soaked in lime, etc. All boring algae are microscopic organisms. Having settled on the surface of the limestone substrate, they gradually penetrate into it due to the release of organic acids that dissolve the lime underneath them. Algae grow inside the substrate, forming numerous channels through which they maintain contact with the external environment.
Tuff-forming algae – organisms that deposit lime around their body and live in the peripheral layers of the environment they deposit, within the limits accessible to the diffusion of light and water. The amount of lime produced by algae varies. Some species secrete it in very small quantities; in the form of small crystals it is located between individuals or forms cases around cells and filaments. Other species secrete lime so abundantly that they gradually become completely immersed in the sediment, which ultimately leads to their death.
Tuff-forming algae are found in water and in terrestrial habitats, in seas and fresh water bodies, in cold and hot waters.
Cohabitation of algae with other organisms
Of particular interest are cases of algae cohabiting with other organisms. Most often, algae use living organisms as a substrate, along with stones, concrete and wooden structures, etc. Based on the nature of the substrate on which fouling algae settle, they include: epiphytes, settling on plants, and epizoites living on animals.
Algae can also live in the tissues of other organisms: both extracellularly (in mucus, intercellular spaces of algae, in the membranes of dead cells) and intracellularly. Such algae are called endophytes. They are characterized by the presence of more or less permanent and strong ties between partners. A wide variety of algae can be endophytes, but the most numerous are endosymbioses of unicellular green and yellow-green algae with unicellular animals.
Among the symbioses formed by algae, the most interesting is their symbiosis with fungi, known as lichen symbiosis, as a result of which a peculiar group of plant organisms emerged, called “lichens”. This symbiosis shows a unique biological unity that led to the emergence of a fundamentally new organism. At the same time, each partner of the lichen symbiosis retains the features of the group of organisms to which it belongs. Lichens represent the only proven case of the emergence of a new organism as a result of the symbiosis of two.
Algae play a huge role in nature. They are the main producers of organic food and oxygen in the Earth's aquatic ecosystems, and, in addition, play a large role in the overall balance of oxygen on the planet. In terrestrial habitats, soil algae, along with other microorganisms, play the role of pioneers of vegetation. Algae are involved in the processes of formation of primitive soils on substrates devoid of soil cover, as well as in the processes of restoration of soils disturbed by severe pollution. Algae take part in the construction of coral reefs - the most ambitious geological formations created by living organisms. The geochemical role of algae is primarily associated with the cycle of calcium and silicon in nature.
The historical role of algae is great. The emergence of an oxygen-containing atmosphere, the emergence of living creatures on land and the development of aerobic forms of life that now dominate our planet are all the results of the activity of the most ancient photosynthetic organisms - blue-green algae. The massive development of algae in past geological eras led to the formation of thick rock strata. From algae came the plants that colonized the land.
It is difficult to overestimate the importance of algae for human life. Algae play an important role in solving a number of global problems that concern all of humanity, including food, energy, environmental protection, development of the Earth's subsoil and the riches of the World Ocean, finding new sources of industrial raw materials, building materials, pharmaceuticals, biologically active substances and new biotechnology objects.
Natalya Novoselova
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