According to most authors studying the origin of life on Earth, the evolutionary primary environment of life was precisely the aquatic environment. We find a lot of indirect confirmation of this position. First of all, most organisms are not capable of active life without water entering the body, or at least without maintaining a certain fluid content inside the body. The internal environment of the organism, in which the main physiological processes take place, obviously still retains the features of the environment in which the evolution of the first organisms took place. Thus, the content of salts in human blood (maintained at a relatively constant level) is close to that in ocean water. The properties of the aquatic oceanic environment have largely determined the chemical and physical evolution of all forms of life. Perhaps the main distinguishing feature of the aquatic environment is its relative conservatism. For example, the amplitude of seasonal or daily temperature fluctuations in the aquatic environment is much less than in the ground-air one. The bottom topography, the difference in conditions at different depths, the presence of coral reefs, etc. create a variety of conditions in the aquatic environment. Features of the aquatic environment result from the physicochemical properties of water. Thus, the high density and viscosity of water are of great ecological importance. The specific gravity of water is comparable to that of the body of living organisms. The density of water is about 1000 times that of air. Therefore, aquatic organisms (especially those actively moving) are faced with a large force of hydrodynamic resistance. For this reason, the evolution of many groups of aquatic animals was in the direction of the formation of body shape and types of movement that reduce drag, which leads to a decrease in energy consumption for swimming. Thus, a streamlined body shape is found in representatives of various groups of organisms living in water - dolphins (mammals), bony and cartilaginous fish. The high density of water is also the reason that mechanical vibrations (vibrations) propagate well in the aquatic environment. It had great importance in the evolution of the senses, orientation in space and communication between aquatic inhabitants. Four times faster than in air, the speed of sound in water determines the higher frequency of echolocation signals. Due to the high density of the aquatic environment, its inhabitants are deprived of the obligatory connection with the substrate, which is characteristic of terrestrial forms and is associated with the forces of gravity. Therefore, there is a whole group of aquatic organisms (both plants and animals) that exist without an obligatory connection with the bottom or other substrate, "soaring" in the water column. Electrical conductivity opened up the possibility of evolutionary formation of electrical senses, defense and attack.
Question 7. Ground-air environment of life. The ground-air environment is characterized by a huge variety of living conditions, ecological niches and organisms inhabiting them. It should be noted that organisms play a primary role in the formation of the conditions of the ground-air environment of life, and above all, the gas composition of the atmosphere. Almost all oxygen in the earth's atmosphere is of biogenic origin. The main features of the ground-air environment are a large amplitude of changes in environmental factors, inhomogeneity of the environment, the action of gravitational forces, and low air density. The complex of physical-geographical and climatic factors inherent in a particular natural zone leads to the evolutionary formation of morphophysiological adaptations of organisms to life in these conditions, a variety of life forms. The high oxygen content in the atmosphere (about 21%) determines the possibility of the formation of a high (energy) level metabolism... The atmospheric air is characterized by low and variable humidity. This circumstance largely limited (limited) the possibilities of mastering the ground-air environment, and also directed the evolution of water-salt metabolism and the structure of the respiratory organs.
Question 8. Soil as a living environment . Soil is the result of the activity of living organisms. The organisms inhabiting the ground-air environment led to the emergence of soil as a unique habitat. Soil is a complex system that includes a solid phase (mineral particles), a liquid phase (soil moisture) and a gaseous phase. The ratio of these three phases determines the characteristics of the soil as a living environment. An important feature of the soil is also the presence of a certain amount of organic matter. It is formed as a result of the dying off of organisms and is part of their excretions (secretions). The conditions of the soil habitat determine such properties of the soil as its aeration (that is, saturation with air), humidity (presence of moisture), heat capacity and thermal regime (daily, seasonal, annual temperature variation). The thermal regime, in comparison with the ground-air environment, is more conservative, especially at great depths. In general, the soil is characterized by fairly stable living conditions. Vertical differences are typical for other soil properties, for example, light penetration naturally depends on depth. Many authors note the intermediate position of the soil environment of life between the aquatic and ground-air environments. In the soil, organisms with both water and air types of respiration are possible. The vertical gradient of light penetration in soil is even more pronounced than in water. Microorganisms are found throughout the entire soil layer, and plants (primarily root systems) are associated with the outer horizons. Soil organisms are characterized by specific organs and types of movement (burrowing limbs in mammals; the ability to change body thickness; the presence of specialized head capsules in some species); body shape (round, volkovate, worm-like); strong and flexible covers; reduction of eyes and disappearance of pigments. Among the soil inhabitants, saprophagia is widely developed - eating the corpses of other animals, rotting remains, etc.
Minsk Educational Institution "Gymnasium No. 14"
Abstract in biology on the topic:
“ WATER - THE ENVIRONMENT ”
Prepared by a student of grade 11 "B"
Maslovskaya Evgeniya
Teacher:
Bulva Ivan Vasilievich
1. Aquatic habitat - the hydrosphere.
2. Water is a unique environment.
3. Ecological groups of aquatic organisms.
4. Modes.
5. Specific adaptations of aquatic organisms.
6. Filtration as a type of food.
7. Adaptation to life in drying up water bodies.
8. Conclusion.
1. Aquatic environment - hydrosphere
In the process of historical development, living organisms have mastered four habitats. The first is water. Life in water originated and developed for many millions of years. Water covers 71% of the earth's area and makes up 1/800 of the land volume or 1370 m3. The bulk of the water is concentrated in the seas and oceans - 94-98%, polar ice contains about 1.2% of water and a very small share - less than 0.5%, in the fresh waters of rivers, lakes and swamps. These ratios are constant, although in nature, without ceasing, there is a circle of water (Fig. 1).
The aquatic environment is home to about 150,000 species of animals and 10,000 plants, which is, respectively, only 7 and 8% of the total species of the Earth. Based on this, it was concluded that evolution on land was much more intense than in water.
In the seas-oceans, as in the mountains, vertical zoning is expressed. The ecology of the pelagial, the entire water column, and the benthal, the bottom, are especially different in ecology.
The water column - the pelagial, is vertically divided into several zones: epipeligial, bathypeligial, abyssopeligial, and ultra-abyssopeligial (Fig. 2).
Depending on the steepness of the descent and the depth at the bottom, several zones are also distinguished, which correspond to the indicated zones of the pelagic:
Littoral - the edge of the coast, flooded during high tides.
Supralittoral - the part of the coast above the upper tidal line, where the spray of the surf reaches.
Sublittoral - a gradual descent of land up to 200m.
Bathyalnaya - a steep descent of land (continental slope),
Abyssal - a smooth lowering of the bottom of the ocean floor; the depth of both zones together reaches 3-6 km.
Ultraabyssal - deep-water depressions from 6 to 10 km.
2. Water is a unique environment.
Water is a completely unique environment in many ways The water molecule, made up of two hydrogen atoms and one oxygen atom, is remarkably stable. Water is a one-of-a-kind compound that simultaneously exists in a gaseous, liquid and solid state.
Water is not only a life-giving source for all animals and plants on Earth, but is also a habitat for many of them. These include, for example, numerous species of fish, including crucian carp that inhabit the rivers and lakes of the region, as well as aquarium fish in our homes. As you can see, they feel great among aquatic plants... Fish breathe with gills, extracting oxygen from the water. Some fish species, such as macropods, breathe atmospheric air, therefore, they periodically rise to the surface.
Water is the habitat of many aquatic plants and animals. Some of them spend their whole life in water, while others are in the aquatic environment only at the beginning of their life. You can be convinced of this by visiting a small pond or swamp. In the water element, you can find the smallest representatives - single-celled organisms, for which a microscope is required. These include numerous algae and bacteria. Their number is measured in millions per cubic millimeter of water.
Another interesting property of water is the acquisition of a very dense state at temperatures above the freezing level for fresh water, these parameters are 4 ° C and O ° C, respectively. It is critical for the survival of aquatic organisms during the winter. Thanks to this same property, ice floats on the surface of the water, forming a protective layer on lakes, rivers and coastal zones. And this property contributes to the thermal stratification of water layers and the seasonal circulation of water masses in lakes in areas with a cold climate, which is very important for the life of aquatic organisms. The density of the water provides the ability to rely on it, which is especially important for skeletal forms. The support of the environment serves as a condition for soaring in water, and many aquatic organisms are adapted to this particular way of life. Suspended, floating in water organisms are combined into a special ecological group of aquatic organisms - plankton.
Fully purified water exists only under laboratory conditions. Any natural water contains many different substances. In "raw water" it is basically a so-called defense system or a carbonic complex consisting of salt carbonic acid, carbonate and bicarbonate. This factor allows you to determine the type of water acidic, neutral or basic - based on its pH value, which from a chemical point of view means the proportion of hydrogen ions contained in water. For neutral water, pH = 7, lower values indicate increased acidity of the water, and higher values indicate that it is alkaline. In limestone areas, the water of lakes and rivers usually has higher pH values compared to water bodies of those places where the content of limestone in the soil is insignificant.
If the water of lakes and rivers is considered fresh, then sea water is called salty or brackish. There are many intermediate types between fresh and salt water.
3. Ecological groups of aquatic organisms.
Ecological groups of aquatic organisms. The greatest variety life is distinguished by warm seas and oceans (40,000 species of animals) in the equator and the tropics, to the north and south the flora and fauna of the seas is depleted by hundreds of times. As for the distribution of organisms directly in the sea, their bulk is concentrated in the surface layers (epipelagic) and in the sublittoral zone. Depending on the mode of movement and stay in certain layers, marine life is divided into three ecological groups: nekton, plankton and benthos.
Necton (nektos - swimming) - actively moving large animals that can overcome long distances and strong currents: fish, squid, pinnipeds, whales. In fresh waters, amphibians and many insects belong to nekton.
Plankton (planktos - wandering, soaring) - a set of plants (phytoplankton: diatoms, green and blue-green (only fresh water bodies) algae, plant flagellates, peridineas, etc.) and small animal organisms (zooplankton: small crustaceans, from larger ones - pteropods, jellyfish, ctenophores, some worms), living at different depths, but not capable of active movement and resisting currents. The plankton also includes the larvae of animals, forming a special group - neuston. This is a passively floating "temporary" population of the uppermost layer of water, represented by various animals (decapods, barnacles and copepods, echinoderms, polychaetes, fish, molluscs, etc.) in the larval stage. As the larvae mature, they move to the lower layers of the pelagel. Above the neuston, there is a pleiston - these are organisms in which the upper part of the body grows above the water, and the lower one - in the water (duckweed - Lemma, siphonophores, etc.). Plankton plays important role in the trophic links of the biosphere, because is food for many aquatic life, including the main food for baleen whales (Myatcoceti).
Benthos (benthos - depth) - bottom hydrobionts. It is mainly represented by attached or slowly moving animals (zoobenthos: foraminophores, fish, sponges, coelenterates, worms, brachiopods, ascidians, etc.), more numerous in shallow water. In shallow waters, plants also enter the benthos (phytobenthos: diatoms, green, brown, red algae, bacteria). At a depth where there is no light, phytobenthos is absent. On the coasts meet flowering plants zostera, rupee. The richest in phytobenthos are rocky bottom areas.
In lakes, zoobenthos is less abundant and less diverse than in the sea. It is formed by protozoa (ciliates, daphnia), leeches, molluscs, insect larvae, etc. The phytobenthos of lakes is formed by free-floating diatoms, green and blue-green algae; brown and red algae are absent.
Rooting coastal plants in lakes form distinct belts, the species composition and appearance of which are consistent with the environmental conditions in the land-water border zone. In the water near the coast, hydrophytes grow - plants semi-submerged in the water (arrowhead, calla, reeds, cattail, sedges, tricetae, reed). They are replaced by hydatophytes - plants immersed in water, but with floating leaves (lotus, duckweed, egg capsules, chilim, takla) and - further - completely submerged (rdesta, elodea, hara). Hydatophytes also include plants floating on the surface (duckweed).
The high density of the aquatic environment determines the special composition and nature of changes in life-supporting factors. Some of them are the same as on land - heat, light, others are specific: water pressure (with depth increases by 1 atm. For every 10 m), oxygen content, salt composition, acidity. Due to the high density of the medium, the values of heat and light with a gradient of altitude change much faster than on land.
4. Modes.
Temperature regime water bodies are more stable than on land. This is due to the physical properties of water, primarily high specific heat, thanks to which receiving or giving significant amount heat does not cause too drastic temperature changes. Amplitude annual fluctuations temperatures in the upper layers of the ocean are not more than 10-150C, in continental water bodies - 30-350C. Deep water layers are characterized by constant temperature. In equatorial waters, the average annual temperature of the surface layers is +26 ... + 270C, in polar waters - about 00C and below. Thus, there is a fairly significant variety of temperature conditions in water bodies. Between the upper layers of water with seasonal temperature fluctuations expressed in them and the lower ones, where the thermal regime is constant, there is a zone of a temperature jump, or thermocline. The thermocline is more pronounced in warm seas where the temperature difference between the external and deep waters is stronger.
Due to the more stable temperature regime of water among aquatic organisms, stenotherm is widespread to a much greater extent than among the land population. Eurythermal species are found mainly in shallow continental water bodies and in the littoral of the seas of high and temperate latitudes, where daily and seasonal temperature fluctuations are significant.
HABITATS AND THEIR CHARACTERISTICS
Habitat conditions different types organisms are very diverse. Depending on where representatives of different species live, they are affected by various complexes environmental factors. On our planet, several main living environments can be distinguished, which are very different in terms of the conditions of existence:
Aquatic habitat
· Ground-air environment a habitat
Soil as a habitat
In the process of historical development, living organisms have mastered four habitats. The first is water. Life in water originated and developed for many millions of years. The second - ground-air - on land and in the atmosphere arose and rapidly adapted to the new conditions of plants and animals. Gradually transforming the upper layer of land - the lithosphere, they created a third habitat - soil, and they themselves became the fourth habitat.
Aquatic habitat - hydrosphere
Water covers 71% of the earth's area and makes up 1/800 of the land volume or 1370 m 3. The bulk of the water is concentrated in the seas and oceans - 94-98%, polar ice contains about 1.2% of water and a very small share - less than 0.5%, in the fresh waters of rivers, lakes and swamps. These ratios are constant, although in nature, the water cycle goes on without ceasing.
The aquatic environment is home to about 150,000 species of animals and 10,000 plants, which is respectively only 7 and 8% of the total number of species on Earth. Based on this, it was concluded that evolution on land was much more intense than in water.
All aquatic inhabitants, despite differences in lifestyle, must be adapted to the main features of their environment. These features are determined, first of all, physical properties of water:
Density,
Thermal conductivity,
The ability to dissolve salts and gases
· Vertical movement of water,
Light mode
Concentration of hydrogen ions (pH level)
Density water determines its significant buoyancy. This means that the weight of organisms is lightened in water and it becomes possible to lead permanent life in the water column, without sinking to the bottom. The aggregate of small species that are not capable of rapid active swimming and are suspended in water is called plankton.
Plankton(planktos - wandering, soaring) - a set of plants (phytoplankton: diatoms, green and blue-green (only fresh water bodies) algae, plant flagellates, peridineas, etc.) and small animal organisms (zooplankton: small crustaceans, of the larger ones - pterygopods molluscs, jellyfish, comb jellies, some worms), living at different depths, but not capable of active movement and resisting currents.
Due to the high density of the environment and the presence of plankton in the aquatic environment, the filtration type of feeding is possible. It is developed in both swimming (whales) and sedentary aquatic animals (sea lilies, mussels, oysters). Straining the suspension out of the water provides such animals with food. A sedentary lifestyle would be impossible for aquatic inhabitants if it were not for the sufficient density of the environment.
The density of distilled water at a temperature of 4 ° C is equal to 1 g / cm 3. The density of natural waters containing dissolved salts can be higher, up to 1.35 g / cm 3.
Due to the high density of water, pressure increases strongly with depth. On average, for every 10 m depth, the pressure increases by 1 atmosphere. Deep-sea animals are able to withstand pressure, which is thousands of times higher than ground pressure (flounder, rays). They have special adaptations: a body shape flattened on both sides, massive fins. The density of the water makes it difficult to move in it, so fast-swimming animals must have strong muscles and a streamlined body (dolphins, sharks, squid, fish).
Thermal conditions... The aquatic environment is characterized by a lower heat input, because a significant part of it is reflected, and an equally significant part is spent on evaporation. Water has a high heat capacity. Consistent with the dynamics of terrestrial temperatures, the water temperature has less fluctuations in daily and seasonal temperatures. Therefore, aquatic inhabitants do not face the need to adapt to severe frosts or 40 degree heat. Only in hot springs can the water temperature approach the boiling point. Moreover, reservoirs substantially equalize the course of temperatures in the atmosphere. coastal areas... In the absence of an ice shell, the seas in the cold season have a warming effect on the adjacent land areas, in summer - cooling and moisturizing.
A characteristic feature of the aquatic environment is its mobility, especially in flowing, fast-flowing streams and rivers. The seas and oceans are ebb and flow powerful currents, storms. In lakes, the temperature of the water moves under the influence of temperature and wind. The change in temperature in flowing waters follows its changes in the surrounding air and has a smaller amplitude.
In lakes and ponds of temperate latitudes, the water is clearly divided into three layers:
| During periods of stagnation, three layers are clearly distinguished: the upper (epilimnion) with the sharpest seasonal fluctuations in water temperature, the middle (metalimnion or thermocline), in which there is a sharp jump in temperatures, and the bottom (hypolimnion), in which the temperature changes weakly throughout the year. In summer, the warmest layers are located at the surface, and the coldest ones at the bottom. This type of layer-by-layer temperature distribution in a reservoir is called DIRECT STRATIFICATION. In winter, with a decrease in temperature, REVERSE STRATIFICATION occurs. The surface layer has a temperature close to zero. At the bottom, the temperature is about 4 0 C. Thus, the temperature rises with depth. As a result, vertical circulation is disturbed and a period of temporary stagnation sets in - winter STAGNATION. |
With a further increase in temperature, the upper layers of water become less dense and no longer go down - summer stagnation sets in. In autumn, surface waters are cooled down to 4 ° C again and sink to the bottom, causing secondary mixing of water masses with temperature equalization.
The range of water temperature values in the World Ocean is 38 ° (from -2 to + 36 ° С), in fresh water bodies - 26 ° (from -0.9 to + 25 ° С). With depth, the water temperature drops sharply. Up to 50 m, daily temperature fluctuations are observed, up to 400 m - seasonal, deeper it becomes constant, dropping to + 1-3 ° С (in the Arctic it is close to 0 ° С).
Thus, in water as a life environment, on the one hand, there is a fairly significant variety of temperature conditions, and on the other, the thermodynamic features of the aquatic environment (high specific heat capacity, high thermal conductivity, expansion during freezing) create favorable conditions for living organisms.
Light mode. The intensity of light in water is greatly weakened due to its reflection by the surface and absorption by the water itself. This greatly affects the development of photosynthetic plants. The less transparent the water is, the more light is absorbed. The transparency of the water is limited by mineral suspensions, plankton. It decreases with rapid development small organisms in summer, and in temperate and northern latitudes - also in winter, after the establishment of the ice cover and covering it from above with snow.
In oceans, where the water is very transparent, 1% of light radiation penetrates to a depth of 140 m, and only tenths of a percent penetrate in small lakes at a depth of 2 m. Beams different parts spectra are not uniformly absorbed in water, red rays are absorbed first. With depth, it becomes darker and darker, and the color of the water becomes first green, then blue, blue and finally blue-violet, turning into complete darkness. Accordingly, hydrobionts also change color, adapting not only to the composition of light, but also to its lack - chromatic adaptation. In light zones, in shallow waters, green algae (Chlorophyta) predominate, the chlorophyll of which absorbs red rays, with depth they are replaced by brown (Phaephyta) and then red (Rhodophyta).
Light penetrates only to a relatively shallow depth; therefore, plant organisms (phytobenthos) can exist only in the upper horizons of the water column. There are no plants at great depths, and deep-sea animals live in complete darkness, in a peculiar way adapting to this way of life.
Daylight hours are much shorter (especially in deeper layers) than on land. The amount of light in the upper layers of reservoirs varies with both the latitude of the area and the season. For example, long polar nights severely limit the time suitable for photosynthesis in the Arctic and Antarctic, and ice cover makes it difficult for light to access all freezing water bodies in winter.
Gas mode... The main gases in water are oxygen and carbon dioxide. The rest are of secondary importance (hydrogen sulfide, methane).
A limited amount of oxygen is one of the main difficulties in aquatic life. The total oxygen content in the upper layers of water (what is it called?) Is 6-8 ml / l or in 21 times lower than in the atmosphere (remember the numbers!).
The oxygen content is inversely proportional to temperature. With increasing temperature and salinity of water, the oxygen concentration in it decreases. In layers heavily populated by animals and bacteria, oxygen deficiency can be created due to increased oxygen consumption. Thus, in the World Ocean, depths from 50 to 1000 meters rich in life are characterized by a sharp deterioration in aeration. It is 7-10 times lower than in surface waters inhabited by phytoplankton. Near the bottom of water bodies, conditions can be close to anaerobic.
In bodies of water, sometimes zamora- mass death of inhabitants due to lack of oxygen. The reasons are stagnant conditions in small reservoirs. Ice covering the surface of a reservoir in winter, pollution of a reservoir, an increase in water temperature. At oxygen concentration below 0.3-3.5 ml / l, life of aerobes in water is impossible.
Carbon dioxide... Ways of entry of carbon dioxide into water:
· Dissolution of carbon contained in the air;
· Respiration of aquatic organisms;
· Decomposition of organic residues;
· Release from carbonates.
General characteristics. The hydrosphere as an aquatic life environment occupies about 71% of the area and 1/800 of the volume of the globe. The main amount of water, more than 94%, is concentrated in the seas and oceans (Fig. 5.2).
Rice. 5.2. Oceans versus land (according to N.F. Reimers, 1990)
In fresh waters of rivers and lakes, the amount of water does not exceed 0.016% of the total volume of fresh water.
In the ocean with the seas entering it, first of all, two ecological regions are distinguished: the water column - pelagial and the bottom - benthal. Depending on the depth, the benthal is divided into sublittoral zone - area of smooth descent of land to a depth of 200 m, bathyal - steep slope area and abyssal zone - oceanic bed with an average depth of 3-6 km. Deeper areas of the benthal, corresponding to the depressions of the oceanic bed (6-10 km), are called ultraabyssal. The edge of the coast, flooded during high tides, is called littoral. The part of the coast above the tide level, moistened by the spray of the surf, was named supralittoral.
The open waters of the World Ocean are also divided into vertical zones according to the benthal zones: epipelagic, bathypelagic, abyssopelagic(fig. 5.3).
Rice. 5.3. Vertical ecological zoning of the ocean
(according to N.F. Reimers, 1990)
The aquatic environment is home to about 150,000 animal species, or about 7% of their total number (Fig. 5.4) and 10,000 plant species (8%).
Attention should also be paid to the fact that representatives of most groups of plants and animals remained in the aquatic environment (their "cradle"), but the number of their species is much less than that of terrestrial ones. Hence the conclusion - evolution on land was much faster.
The diversity and richness of flora and fauna are distinguished by the seas and oceans of the equatorial and tropical regions, primarily the Pacific and Atlantic oceans. North and south of these belts qualitative composition is gradually becoming impoverished. For example, at least 40,000 animal species are widespread in the East India Archipelago, while there are only 400 in the Laptev Sea. The bulk of the world's oceans is concentrated in a relatively small area of sea coasts temperate zone and among the mangroves of tropical countries.
The share of rivers, lakes and swamps, as noted earlier, is insignificant in comparison with the seas and oceans. However, they create a supply of fresh water necessary for plants, animals and humans.
Rice. 5.4. Distribution of the main classes of animals on Wednesdays
habitat (according to G.V. Voitkevich and V.A.Vronsky, 1989)
Note animals placed below the wavy line live in the sea, above it - in the ground-air environment
It is known that not only the aquatic environment has a strong effect on its inhabitants, but also the living matter of the hydrosphere, acting on the habitat, processes it and involves it in the circulation of substances. It has been established that the water of oceans, seas, rivers and lakes decomposes and is restored in the biotic cycle in 2 million years, that is, all of it has passed through living matter on Earth more than one thousand times.
Consequently, the modern hydrosphere is a product of the vital activity of living matter, not only of the modern, but also of the past geological eras.
A characteristic feature of the aquatic environment is its mobility, especially in flowing, fast-flowing streams and rivers. In the seas and oceans, there are ebb and flow, powerful currents, storms. In lakes, water moves under the influence of temperature and wind.
Ecological groups of aquatic organisms. The water column, or pelagial(pelages - sea), is inhabited by pelagic organisms that have the ability to swim or stay in certain layers (Fig.5.5).
Rice. 5.5. Ocean profile and its inhabitants (after N.N. Moiseev, 1983)
In this regard, these organisms are divided into two groups: nekton and plankton. The third ecological group - benthos - form the inhabitants of the bottom.
Nekton(nektos - swimming) is a collection of pelagic actively moving animals that do not have a direct connection with the bottom. They are mainly large animals that are able to travel long distances and strong currents of water. They have a streamlined body and well-developed organs of movement. Typical nekton organisms include fish, squid, whales, pinnipeds. In addition to fish, nekton in fresh waters includes amphibians and actively moving insects. Many marine fish can move in the water column with great speed: up to 45-50 km / h - squid (Oegophside), 100-150 km / h - sailboats (Jstiopharidae) and 130 km / h - swordfish (Xiphias glabius).
Plankton(planktos - wandering, hovering) is a collection of pelagic organisms that do not have the ability to move quickly. As a rule, these are small animals - zooplankton and plants - phytoplankton, which cannot resist the currents. The plankton also includes the larvae of many animals "hovering" in the water column. Planktonic organisms are located both on the surface of the water, at depth, and in the bottom layer.
Organisms located on the surface of the water constitute a special group - neuston. The composition of neuston also depends on the stage of development of a number of organisms. Passing the larval stage, growing up, they leave the surface layer that served them as a refuge, move to live on the bottom or in the underlying and deep layers. These include the larvae of decapods, barnacles, copepods, gastropods and bivalves, echinoderms, polychaetes, fish, etc.
The same organisms, part of whose body is above the surface of the water, and the other in the water, are called playston. These include duckweed (Lemma), siphonophores (Siphonophora), etc.
Phytoplankton plays an important role in the life of water bodies, as it is the main producer of organic matter. Phytoplankton primarily include diatoms (Diatomeae) and green (Chlorophyta) algae, plant flagellates (Phytomastigina), peridineas (Peridineae) and coccolithophorids (Coccolitophoridae). In fresh waters, not only green, but also blue-green (Cyanophyta) algae are widespread.
Zooplankton and bacteria can be found at various depths. In fresh waters, poorly swimming relatively large crustaceans (Daphnia, Cyclopoidea, Ostrocoda), many rotifers (Rotatoria) and protozoa are common.
The marine zooplankton is dominated by small crustaceans (Copepoda, Amphipoda, Euphausiaceae) and protozoa (Foraminifera, Radiolaria, Tintinoidea). Large representatives are winged molluscs (Pteropoda), jellyfish (Scyphozoa) and floating ctenophores (Ctenophora), salps (Salpae), some worms (Aleiopidae, Tomopteridae).
Planktonic organisms are important food component for many aquatic animals, including such giants as baleen whales (Mystacoceti), fig. 5.6.
Fig 5.6. Diagram of the main directions of the exchange of energy and matter in the ocean
Benthos(benthos - depth) is a collection of organisms that live on the bottom (on the ground and in the ground) of water bodies. It is subdivided into zoobenthos and phytobenthos. For the most part, it is represented by animals attached, or slowly moving, or burrowing in the ground. In shallow water, it consists of organisms that synthesize organic matter (producers), consume it (consumers) and destroy it (decomposers). At depths where there is no light, phytobenthos (producers) are absent. The marine zoobenthos is dominated by foraminiphores, sponges, intestinal cavities, worms, brachiopods, molluscs, ascidians, fish, etc. Benthic forms are more numerous in shallow waters. Their total biomass here can reach tens of kilograms per 1 m 2.
The phytobenthos of the seas mainly includes algae (diatoms, green, brown, red) and bacteria. Flowering plants such as Zostera, Ruppia, Phyllospadix are found along the coast. The richest in phytobenthos are rocky and stony bottom areas.
In lakes, as in the seas, they distinguish plankton, nekton and benthos.
However, in lakes and other fresh water bodies, zoobenthos is less than in the seas and oceans, and its species composition is uniform. These are mainly protozoa, sponges, ciliary and small-bristle worms, leeches, molluscs, insect larvae, etc.
Freshwater phytobenthos is represented by bacteria, diatoms and green algae. Coastal plants are located inland from the coast in clearly defined belts. First belt - semi-submerged plants (reeds, cattails, sedges and reeds); second belt - submerged plants with floating leaves (water paint, egg capsules, water lilies, duckweed). V third belt dominated by plants - pond, elodea, etc. (Figure 5.7).
Rice. 5.7. Plants rooting at the bottom (A):
1-cattle; 2- sitnik; 3 - arrowhead; 4 - water lily; 5, 6 - rdesta; 7 - hara. Free floating algae (B): 8, 9 - filamentous green; 10-13 - green; 14-17 - diatoms; 18-20 - blue-green
According to their lifestyle, aquatic plants are divided into two main ecological groups: hydrophytes - plants immersed in water only with their lower part and usually rooting in the ground, and hydatophytes - plants that are completely submerged in water, sometimes floating on the surface or having floating leaves.
In the life of aquatic organisms, the vertical movement of water, density, temperature, light, salt, gas (oxygen and carbon dioxide) modes, concentration of hydrogen ions (pH).
Temperature conditions. It differs in water, firstly, in a smaller inflow of heat, and secondly, in greater stability than on land. Part of the thermal energy entering the water surface is reflected, part is spent on evaporation. Evaporation of water from the surface of reservoirs, in which about 2263x8 J / g is spent, prevents overheating of the lower layers, and the formation of ice, in which the heat of fusion is released (333.48 J / g), slows down their cooling.
The change in temperature in flowing waters follows its changes in the surrounding air, differing in a smaller amplitude.
In lakes and ponds of temperate latitudes, the thermal regime is determined by a well-known physical phenomenon - the water has a maximum density at 4 ° C. The water in them is clearly divided into three layers: the upper one - epilimnion, the temperature of which is experiencing sharp seasonal fluctuations; transitional, temperature jump layer, -metalimnion, where there is a sharp temperature drop; deep-sea (near-bottom) - hypolimnion reaching the very bottom, where the temperature is throughout the year changes insignificantly.
In summer, the warmest layers of water are located at the surface, and the coldest ones - at the bottom. This type of layer-by-layer temperature distribution in the reservoir is called direct stratification In winter, with a decrease in temperature, there is reverse stratification. The surface layer of water has a temperature close to 0 ° C. At the bottom, the temperature is about 4 ° C, which corresponds to its maximum density. Thus, the temperature rises with depth. This phenomenon is called temperature dichotomy. It is observed in most of our lakes in summer and winter. As a result, the vertical circulation is disrupted, the density stratification of water is formed, a period of temporary stagnation begins - stagnation(fig. 5.8).
With a further increase in temperature, the upper layers of water become less and less dense and no longer sink - summer stagnation sets in. "
In autumn, the surface waters again cool down to 4 ° C and sink to the bottom, causing a secondary mixing of the masses during the year with temperature equalization, that is, the onset of autumn homothermy.
In the marine environment, there is also thermal stratification determined by depth. The following layers are distinguished in the oceans Surface- the waters are subject to the action of the wind, and by analogy with the atmosphere, this layer is called troposphere or sea thermosphere. Daily fluctuations in water temperature are observed here to about 50 meters depth, and seasonal ones are noted even deeper. The thickness of the thermosphere reaches 400 m. Intermediate - represents constant thermocline. The temperature in it in different seas and the oceans drops to 1-3 ° C. It extends to a depth of approximately 1,500 m. Deep sea - characterized by the same temperature of about 1-3 ° C, with the exception of the polar regions, where the temperature is close to 0 ° C.
V On the whole, it should be noted that the amplitude of annual temperature fluctuations in the upper layers of the ocean is no more than 10 - 15 "C in continental waters 30-35 ° C.
Rice. 5.8. Stratification and mixing of water in the lake
(after E. Gunther et al., 1982)
Deep water layers are characterized by constant temperature. In equatorial waters, the average annual temperature of the surface layers is 26-27 ° C, in polar waters - about 0 ° C and below. Exceptions are thermal springs, where the temperature of the surface layer reaches 85-93 ° C.
In water as a life environment, on the one hand, there is a fairly significant variety of temperature conditions, and on the other, there are thermodynamic features of the aquatic environment, such as high specific heat capacity, high thermal conductivity and expansion during freezing (in this case, ice is formed only from above, and the main the water column does not freeze), create favorable conditions for living organisms.
Thus, for the wintering of perennial hydrophytes in rivers and lakes, the vertical distribution of temperatures under the ice is of great importance. The densest and least cold water with a temperature of 4 ° C is located in the bottom layer, where wintering buds (turions) of hornwort, pemphigus, vodokras, etc., as well as whole leafy plants, such as duckweed and elodea, descend.
Rice. 5.9. Vodokras (Hydrocharias morsus ranae) in autumn.
Wintering buds are visible, sinking to the bottom
(from T.K. Goryshinoi, 1979)
It was believed that immersion is associated with the accumulation of starch and the weight of plants. By spring, starch is converted to soluble sugars and fats, which makes the kidneys lighter and allows them to float.
Organisms in water bodies of temperate latitudes are well adapted to seasonal vertical movements of water layers, to spring and autumn homothermy, to summer and winter stagnation. Insofar as temperature regime reservoirs are characterized by great stability, among hydrobionts to a greater extent than among land organisms, stenotherm is widespread.
Eurythermal species are found mainly in shallow continental water bodies and in the littoral of the seas of high and temperate latitudes, where daily and seasonal fluctuations are significant.
Density of water. Water differs from air in its greater density. In this respect, it is 800 times greater than the air environment. The density of distilled water at a temperature of 4 ° C is 1 g / cm 3. The density of natural waters containing dissolved salts can be higher: up to 1.35 g / cm 3. On average, in the water column, for every 10m depth, the pressure increases by 1 atmosphere. The high density of water is reflected in the structure of the body of hydrophytes. So, if in terrestrial plants mechanical tissues are well developed, ensuring the strength of trunks and stems, the arrangement of mechanical and conductive tissues along the periphery of the stem creates a "pipe" structure that resists kinks and bends well, then in hydrophytes the mechanical tissues are greatly reduced, since the plants are supported by themselves. water. Mechanical elements and conductive bundles are quite often concentrated in the center of the stem or leaf petiole, which gives the ability to bend when the water moves.
Submerged hydrophytes have good buoyancy created by special devices (air sacs, bulges). So, the leaves of the paddling pool lie on the surface of the water and have a floating bubble filled with air under each leaf. Like a tiny life jacket, the bubble allows the leaf to float on the surface of the water. Air chambers in the stem keep the plant upright and deliver oxygen to the roots.
Buoyancy also increases with increasing body surface. This is clearly seen in microscopic planktonic algae... Various outgrowths of the body help them to freely "soar" in the water column.
Organisms in the aquatic environment are distributed throughout its thickness. For example, in oceanic trenches, animals have been found at depths of over 10,000 m, and can withstand pressures from several to hundreds of atmospheres. Thus, freshwater inhabitants (swimming beetles, slippers, suvoy, etc.) in experiments withstand up to 600 atmospheres. Holothurians of the genus Elpidia, Priapulus caudatus worms inhabit from the coastal zone to the ultraabyssal. At the same time, it should be noted that many inhabitants of the seas and oceans are relatively stenobathic and confined to certain depths. This applies primarily to shallow and deep-water species. Only in the littoral zone live annelid worm sandworm Arenicola, molluscs - sea saucers(Patella). At great depths at a pressure of at least 400-500 atmospheres, fish from the angler group, cephalopods, crustaceans, sea stars, pogonophores and others.
The density of water provides an opportunity for animal organisms to rely on it, which is especially important for skeletal forms. The support of the medium serves as a condition for floating in water. It is to this lifestyle that many aquatic organisms are adapted.
Light mode. Aquatic organisms are greatly influenced by the light regime and the transparency of the water. The intensity of light in water is greatly weakened (Fig. 5.10), since part of the incident radiation is reflected from the surface of the water, the other is absorbed by its thickness. The attenuation of light is due to the transparency of the water. In oceans, for example, with high transparency to a depth of 140 m, about 1% of radiation still falls, and in small lakes with somewhat confined water already at a depth of 2 m - only tenths of a percent.
Rice. 5.10. Illumination in the water during the day.
Tsimlyansk reservoir (according to A.A. Potapov,
Depth: 1 - at the surface; 2-0.5m; 3 - 1.5m; 4-2m
Due to the fact that the rays of different parts of the solar spectrum are not equally absorbed by water, the spectral composition of light also changes with depth, and red rays are weakened. Blue-green rays penetrate to considerable depths. The twilight in the ocean deepening with depth is at first green, then blue, blue, blue-violet, giving way in the future to constant darkness. Accordingly, living organisms replace each other with depth.
So, plants living on the surface of the water do not experience a lack of light, and submerged and especially deep-water plants are referred to as "shadow flora". They have to adapt not only to a lack of light, but also to a change in its composition by the production of additional pigments. This can be traced in the well-known regularity of coloration in algae living at different depths. In shallow water areas, where plants still have access to red rays, which are most absorbed by chlorophyll, as a rule, green algae predominate. In deeper zones there are brown algae which, in addition to chlorophyll, have brown pigments phycofein, fucoxanthin, etc. Red algae, which contain phycoerythrin pigment, live even deeper. The ability to capture sun rays with different wavelengths. This phenomenon is called chromatic adaptation.
Deep sea species have a number of physical traits associated with shade plants. Among them, it should be noted the low point of compensation for photosynthesis (30-100 lx), the "shadow character" of the light curve of photosynthesis with a low saturation plateau, in algae, for example, large sizes of chromatophores. Whereas on the surface and floating forms these curves are of a lighter type.
To use weak light in the process of photosynthesis, an increased area of assimilating organs is required. For example, arrowhead (Sagittaria sagittifolia) forms leaves of different shapes during development on land and in water.
The hereditary program encodes the possibility of development in both directions. The "trigger" for the development of "aquatic" leaf forms is shading rather than the direct action of water.
Often, the leaves of aquatic plants immersed in water are strongly dissected into narrow filamentous lobes, such as in hornwort, uruti, pemphigus, or have a thin translucent plate - underwater leaves of egg capsules, water lilies, leaves of submerged pondweed.
These traits are also characteristic of algae, such as filamentous algae, dissected thalli of charots, thin transparent thalli of many deep-sea species. This makes it possible for hydrophytes to increase the ratio of body area to volume, and, consequently, to develop a large surface at a relatively low cost of organic matter.
In plants partially submerged in water, it is well expressed heterophilia, i.e., the difference in the structure of the above-water and underwater leaves in the same plant: This is clearly seen in the aquatic buttercup varifolia (Fig.5.11) The above-water ones have features that are common for the leaves of aboveground plants (dorsoventral structure, well-developed integumentary tissues and stomatal apparatus) , underwater - very thin or dissected leaf blades. Heterophilia is also noted in water lilies and egg capsules, arrowhead and other species.
Rice. 5.11. Heterophilia in the aquatic buttercup varifolia
Ranunculus diversifolius (from T, G. Goryshina, 1979)
Leaves: 1 - emergent; 2 - underwater
An illustrative example is the hand-warp (Simn latifolium), on the stem of which several leaf shapes can be seen, reflecting all the transitions from typically terrestrial to typically aquatic.
The depth of the aquatic environment also affects animals, their color, species composition, etc. For example, in a lake ecosystem, the main life is concentrated in a layer of water, where enough light penetrates for photosynthesis. The lower boundary of this layer is called the compensation level. Above this depth, plants emit more oxygen than they consume, the excess oxygen can be used by other organisms. Below this depth, photosynthesis cannot provide respiration; therefore, only oxygen is available to organisms, which comes with water from the more surface layers of the lake.
Bright and diversely colored animals live in the light, surface layers of water, while deep-sea species are usually devoid of pigments. The twilight zone of the ocean is inhabited by animals painted in colors with a reddish tint, which helps them to hide from enemies, since the red color in the blue-violet rays is perceived as black. The red color is typical for such animals of the twilight zone as sea bass, red coral, various crustaceans, etc.
The absorption of light in water is the stronger, the lower its transparency, which is due to the presence of particles of mineral substances in it (clay, silt). The transparency of the water decreases and with the rapid growth of aquatic vegetation in summer period or during mass reproduction of small organisms in the surface layers in suspension. The transparency is characterized by extreme depth, where the specially lowered Secchi disc (white disc with a diameter of 20 cm) is still visible. In the Sargasso Sea (the most transparent waters), the Secchi disc is visible to a depth of 66.5 m, in the Pacific Ocean - up to 59, in the Indian Ocean - up to 50, in shallow seas - up to 5-15 m. The transparency of rivers does not exceed 1 -1.5 m, and in the Central Asian rivers Amu Darya and Syrdarya - several centimeters. Hence, the boundaries of the zones of photosynthesis vary greatly in different bodies of water. In the most clean waters the zone of photosynthesis, or the euphotic zone, reaches a depth of no more than 200 m, the twilight (dysphotic) zone extends to 1000-1500 m, and deeper, into the aphotic zone, sunlight does not penetrate at all.
Daylight hours in water are much shorter (especially in deep layers) than on land. The amount of light in the upper layers of reservoirs varies with the latitude of the area and with the season. For example, long polar nights severely limit the time suitable for photosynthesis in the Arctic and Antarctic basins, and the ice cover makes it difficult for light to access all freezing water bodies in winter.
Salt mode. In the life of aquatic organisms, water salinity or salt regime plays an important role. The chemical composition of waters is formed under the influence of natural-historical and geological conditions, as well as under anthropogenic impact. Content chemical compounds(salts) in water determines its salinity and is expressed in grams per liter or in ppm(° / od). According to the total salinity, the waters can be divided into fresh waters with a salt content of up to 1 g / l, brackish (1-25 g / l), sea salinity (26-50 g / l) and brines (more than 50 g / l). The most important of the dissolved substances in water are carbonates, sulfates and chlorides (Table 5.1).
Table 5.1
The composition of basic salts in various water bodies (according to R. Dajo, 1975)
Among fresh waters, there are many that are almost pure, but there are also many that contain up to 0.5 g of solutes per liter. Cations by their content in fresh water are arranged as follows: calcium - 64%, magnesium - 17%, sodium - 16%, potassium - 3%. These are average values, and in each specific case fluctuations are possible, sometimes significant.
An important element in fresh waters is the calcium content. Calcium can act as a limiting factor. Distinguish between "soft" waters, poor in calcium (less than 9 mg per 1 liter), and "hard" waters, its content is large (more than 25 mg per 1 liter).
In seawater, the average content of dissolved salts is 35 g / l, in the marginal seas it is much lower. 13 metalloids and at least 40 metals were found in seawater. In terms of importance, table salt takes the first place, then barium chloride, magnesium sulfate and potassium chloride.
Most aquatic life poikilosmotic. The osmotic pressure in their body depends on the salinity of the environment. Freshwater animals and plants live in environments where the concentration of solutes is lower than in body fluids and tissues. Due to the difference in osmotic pressure outside and inside the body, water constantly penetrates into the body, as a result of which the aquatic organisms of fresh water are forced to intensively remove it. They have well-pronounced osmoregulation processes. In protozoa this is achieved by the work of excretory vacuoles, in multicellular organisms - by removing water through the excretory system. Some ciliates release an amount of water equal to the volume of the body every 2-2.5 minutes.
With an increase in salinity, the work of vacuoles slows down, and at a salt concentration of 17.5% it stops working, since the difference in osmotic pressure between cells and external environment disappears.
The concentration of salts in body fluids and tissues of many marine organisms isotonic to the concentration of dissolved salts in surrounding water... In this regard, their osmoregulatory functions are less developed than in freshwater ones. Osmoregulation is one of the reasons that many marine plants and animals were unable to colonize fresh water bodies and turned out to be typical marine inhabitants: intestinal cavity (Coelenterata), echinoderms (Echinodermata), sponges (Spongia), tunicates (Tunicata), pogonophora (Pogonophora) ... On the other hand, insects practically do not live in the seas and oceans, while freshwater pools are abundantly inhabited by them. Typically marine and typically freshwater organisms do not tolerate significant changes in salinity and are stenohaline. Euryhaline organisms, in particular animals, freshwater and marine origin not so much. They meet, often in large quantities, in brackish waters. These are such as bream (Abramis brama), freshwater pike perch (Stizostedion lucioperca), pike (Ezox lucios), from the sea - the mullet family (Mugilidae).
The habitat of plants in the aquatic environment, in addition to the features listed above, leaves an imprint on other aspects of life, especially on the water regime of plants, literally surrounded by water. Such plants do not have transpiration, and, consequently, there is no "upper engine" supporting the flow of water in the plant. And at the same time, the current that delivers nutrients to the tissues exists (although it is much weaker than in land plants), with a clear diurnal periodicity: more during the day, absent at night. An active role in its maintenance belongs to the root pressure (in attached species) and the activity of special cells that release water - water stomata or hydatodes.
Plants fixed at the bottom of the reservoir are widespread in fresh waters. Often their photosynthetic surface is located above water. These include reeds (Scirpus), water lilies (Nymphaea), egg capsules (Nyphar), cattails (Typha), arrowheads (Sagittaria). In others, photosynthetic organs are submerged in water. These are pondweed (Potamogeton), urut (Myriophyllum), elodea (Elodea). Separate types higher plants of fresh water are devoid of roots and freely float or overgrow underwater objects, algae, which are attached to the ground.
Gas mode. The main gases in the aquatic environment are oxygen and carbon dioxide. Others, such as hydrogen sulfide or methane, are of secondary importance.
Oxygen for the aquatic environment - the most important environmental factor. It enters the water from the air and is excreted by plants during photosynthesis. The diffusion coefficient of oxygen in water is about 320 thousand times lower than in air, and its total content in the upper layers of water is 6-8 ml / l, or 21 times lower than in the atmosphere. The oxygen content in water is inversely proportional to temperature. With increasing temperature and salinity of water, the concentration of oxygen in it decreases. In layers heavily populated by animals and bacteria, oxygen deficiency can be created due to increased oxygen consumption. Thus, in the World Ocean, depths from 50 to 1000 m rich in life are characterized by a sharp deterioration in aeration. It is 7-10 times lower than in surface waters inhabited by phytoplankton. Near the bottom of water bodies, conditions can be close to anaerobic.
Under stagnant conditions in small reservoirs, water is also sharply depleted in oxygen. Its deficit can also arise under ice in winter. At a concentration below 0.3-3.5 ml / l, the life of aerobes in water is impossible. The oxygen content under the conditions of the reservoir turns out to be the limiting factor (Table 5.2).
Table 5.2
Oxygen Demand of Various Freshwater Fish Species
Among aquatic inhabitants, there are a significant number of species that can tolerate wide fluctuations in the oxygen content in water, close to its absence. These are the so-called euryoxybionts. These include freshwater oligochaetes (Tubifex tubifex), gastropods (Viviparus viviparus). Carp, tench, crucian carp can withstand very weak water saturation with oxygen from fish. However, many species are stenoxybiontic, that is, they can exist only with a sufficiently high saturation of water with oxygen, for example, rainbow trout, brown trout, minnow, etc. Many species of living organisms are capable of falling into an inactive state with a lack of oxygen, the so-called anoxybiosis, and thus experience an unfavorable period.
Respiration of aquatic organisms is carried out both through the surface of the body and through specialized organs - gills, lungs, trachea. Often, the integument of the body can serve as an additional respiratory organ. In some species, a combination of water and air respiration is found, for example, lungfish, siphonophores, discophants, many pulmonary molluscs, crustaceans Yammarus lacustris, etc. Secondary aquatic animals usually retain the atmospheric type of respiration as energetically more beneficial, and therefore need contact with the air environment. These include pinnipeds, cetaceans, water beetles, mosquito larvae, etc.
Carbon dioxide. In the aquatic environment, living organisms, in addition to a lack of light and oxygen, may lack available CO 2, for example, plants for photosynthesis. Carbon dioxide enters the water as a result of the dissolution of CO 2 contained in the air, respiration of aquatic organisms, decomposition of organic residues and release from carbonates. The carbon dioxide content in water ranges from 0.2 to 0.5 ml / l, or 700 times more than in the atmosphere. CO 2 dissolves in water 35 times better than oxygen. Sea water is the main reservoir of carbon dioxide, as it contains from 40 to 50 cm 3 of gas per liter in free or bound form, which is 150 times higher than its concentration in the atmosphere.
Carbon dioxide contained in water takes part in the formation of calcareous skeletal formations of invertebrates and ensures photosynthesis of aquatic plants. With intensive photosynthesis of plants, there is an increased consumption of carbon dioxide (0.2-0.3 ml / l per hour), which leads to its deficiency. Hydrophytes react to an increase in CO2 content in water by increasing photosynthesis.
An additional source of CO for the photosynthesis of aquatic plants is also carbon dioxide, which is released during the decomposition of bicarbonate salts and their transition to carbon dioxide:
Ca (HCO 3) 2 -> CaCO 3 + CO, + H 2 O
The slightly soluble carbonates that are formed in this case settle on the surface of the leaves in the form of a limescale or crust, which is clearly visible when many aquatic plants dry out.
Concentration of hydrogen ions(pH) often affects the distribution of aquatic organisms. Freshwater pools with a pH of 3.7-4.7 are considered acidic, 6.95-7.3 neutral, with a pH of more than 7.8 alkaline. In fresh water bodies, pH fluctuates significantly, often during the day. Sea water is more alkaline and its pH changes less than fresh water. The pH decreases with depth.
From plants with a pH of less than 7.5, a half-cress (Jsoetes), a hedgehog (Sparganium) grow. In an alkaline environment (pH 7.7-8.8), many species of pondweed and elodea are widespread; at pH 8.4-9, Typha angustifolia reaches strong development. The acidic waters of the peatlands contribute to the development of sphagnum mosses.
Most freshwater fish can withstand a pH of 5 to 9. If the pH is less than 5, there is massive fish death, and above 10, all fish and other animals die.
In lakes with an acidic environment, diptera larvae of the genus Chaoborus are often found, and in acidic waters of bogs shell-shaped rhizopods (Testaceae) are common, lamellar-gill mollusks from the genus Toothless (Unio) are absent, and other mollusks are rare.
Ecological plasticity of organisms in the aquatic environment. Water is a more stable environment, and abiotic factors undergo relatively insignificant fluctuations, and hence aquatic organisms have less ecological plasticity than terrestrial ones. Freshwater plants and animals are more flexible than marine ones, since fresh water as a living environment is more changeable. The latitude of the ecological plasticity of aquatic organisms is assessed not only as a whole to a complex of factors (eury- and stenobionticity), but also separately.
Thus, it has been established that coastal plants and animals, in contrast to the inhabitants of open zones, are mainly eurythermal and euryhaline organisms, due to the fact that temperature conditions and the salt regime near the coast are quite variable - warming up by the sun and relatively intense cooling, desalination by the influx of water from streams and rivers, in particular during the rainy season, etc. in shallow, well-warmed water bodies. The inhabitants of the surface layers, in comparison with deep-sea forms, for the above reasons, are more eurythermal and euryhaline.
Environmental plasticity is an important regulator of the dispersal of organisms. It has been proven that aquatic organisms with high ecological plasticity are widespread, for example, elodea. The opposite example is the brine shrimp (Artemia solina), living in small reservoirs with very salty water, is a typical stenohaline representative with narrow ecological plasticity. In relation to other factors, it has significant plasticity and is found quite often in salt water bodies.
Environmental plasticity depends on the age and developmental phase of the organism. For example, the marine gastropod mollusk Littorina in its adult state at low tides daily does without water for a long time, but its larvae lead a planktonic lifestyle and do not tolerate drying out.
Features of adaptation of plants to the aquatic environment. Aquatic paradise | plants have significant differences from terrestrial plant organisms. Thus, the ability of aquatic plants to absorb moisture and mineral salts directly from the surrounding environment is reflected in their morphological and physiological organization. A weak development of the conductive tissue and root system is characteristic of aquatic plants. The root system serves mainly for attachment to the underwater sub stratum and does not function mineral nutrition and water supply, like that of terrestrial plants. The nutrition of aquatic plants is carried out by the entire surface of their body.
The significant density of water makes it possible for plants to inhabit its entire thickness. Lower plants, inhabiting various layers and leading a floating lifestyle, have special appendages for this, which increase their buoyancy and allow them to stay in suspension. Higher hydrophytes have poorly developed mechanical tissue. How yni noted above, in their leaves, stems, and roots there are airborne intercellular cavities, which increase the lightness and buoyancy of organs suspended in water and floating on the surface, which also contributes to the flushing of internal cells by water with salts and gases dissolved in it. Hydrophytes are excellent | They have a large leaf surface with a small total volume of the plant, which provides them with intensive gas exchange with a lack of oxygen and other gases dissolved in water.
A number of aquatic organisms are variegated, or geto rofilia. So, in salvinia (Salvinia), submerged leaves provide mineral nutrition, and floating ones - organic.
An important feature of plant adaptation to water habitat | Noisy environment is that the leaves immersed in water are usually very thin. Chlorophyll in them is often located in the cells of the epidermis, which enhances the intensity of photosynthesis in low light. Such anatomical and morphological features are most pronounced in water mosses (Riccia, Fontinalis), Vallisneria spiralis, and pondweed (Potamageton).
From leaching of mineral salts from the cells of aquatic plants or leaching, the protection is the secretion of mucus by special cells and the formation of endoderm from thicker-walled cells in the form of a ring.
The relatively low temperature of the aquatic environment causes the death of vegetative parts of submerged plants after the formation of winter buds and the replacement of summer thin delicate leaves harder and shorter winter ones. Low water temperature negatively affects the generative organs of aquatic plants, and its high density makes it difficult to transport pollen. In this regard, aquatic plants reproduce intensively by vegetative means. Most floating and submerged plants carry flowering stems into the air and reproduce sexually. The pollen is carried by wind and surface currents. The fruits and seeds that form are also spread by surface currents. This phenomenon is called hydrochoria. Hydrochorns include not only aquatic plants, but also many coastal plants. Their fruits have a high buoyancy, stay in water for a long time and do not lose germination at the same time. For example, the fruits and seeds of arrowhead (Sagittaria sagittofolia), susak (Butomus umbellatus), chastuha (Alisma plantago-aguatica) are transported by water. The fruits of many sedges (Carex) are enclosed in peculiar bags of air and carried by water currents. In the same way, the gumay weed (Sorgnum halepense) spread along the Vakht River along the canals.
Features of adaptation of animals to the aquatic environment. In animals living in the aquatic environment, in comparison with plants, adaptive characteristics are more diverse, they include such as anatomical and morphological, behavioral and etc.
Animals living in the water column, first of all, have adaptations that increase their buoyancy and allow them to resist the movement of water, currents. These organisms develop adaptations that prevent them from rising into the water column or reduce buoyancy, which allows them to stay on the bottom, including rapidly flowing waters.
In small forms living in the water column, a reduction in skeletal formations is noted. So, in protozoa (Radiolaria, Rhizopoda), the shells have porosity, the flint spines of the skeleton are hollow inside. The specific gravity of ctenophora (Ctenophora), jellyfish (Scyphozoa) decreases due to the presence of water in the tissues. The accumulation of droplets of fat in the body (night light - Noctiluca, radiolaria - Radiolaria) contributes to an increase in buoyancy. Large accumulations of fat are observed in some crustaceans (Cladocera, Copepoda), fish and cetaceans. The specific gravity of the body is reduced and thereby increased buoyancy by the gas-filled swimbladders that many fish have. The siphonophores (Physalia, Velella) have powerful air cavities.
Animals that passively swim in the water column are characterized not only by a decrease in mass, but also by an increase in the specific surface of the body. This is due to the fact that the higher the viscosity of the medium and the higher the specific surface area of the body, the slower it sinks into water. In animals, the body is flattened, spines, outgrowths, appendages are formed on it, for example, in flagellates (Leptodiscus, Craspeditella), radiolarians (Aulacantha, Chalengeridae), etc.
A large group of animals living in fresh water uses the surface tension of the water (surface film) when moving. Water stripper bugs (Gyronidae, Veliidae), whirligig beetles (Gerridae) and others run freely on the surface of the water. When the lifting force (F), directed upward, is greater than the mass of the animal, the latter will be kept on the water due to surface tension.
Thus, life on the surface of water is possible for relatively small animals, since the mass grows in proportion to the cube of size, and the surface tension increases as a linear quantity.
Active swimming in animals is carried out with the help of cilia, flagella, bending of the body, in a reactive way due to the energy of the ejected stream of water. The greatest perfection of the jet mode of travel is achieved cephalopods... So, some squids develop a speed of up to 40-50 km / h when ejecting water (Figure 5.12).
Rice. 5.12. Squid
Large animals often have specialized limbs (fins, flippers), their body is streamlined and covered with mucus.
Only in the aquatic environment are there motionless animals leading an attached lifestyle. These are such as hydroids (Hydroidea) and coral polyps (Anthozoo), sea lilies (Crinoidea), bivalves (Br / aMa), etc. They are characterized by a peculiar body shape, slight buoyancy (the density of the body is greater than the density of water) and special devices for attaching to substrate.
Aquatic animals are mostly poikilothermic. In home-othermic, for example, mammals (cetaceans, pinnipeds), a significant layer of subcutaneous fat is formed, which performs a heat-insulating function.
Deep sea animals are different specific features organizations: the disappearance or weak development of the calcareous skeleton, an increase in body size, often a reduction in the organs of vision, an increase in the development of tactile receptors, etc.
Osmotic pressure and ionic state of solutions in the body of animals is provided by complex mechanisms of water-salt metabolism. The most common way to maintain a constant osmotic pressure is to regularly remove the water entering the body using pulsating vacuoles and excretory organs. So, freshwater fish remove excess water by the enhanced work of the excretory system, and absorb salts through the gill lobes. Sea fish are forced to replenish water supplies and therefore drink sea water, and the surplus of salts supplied with water is excreted from the body through the gill petals (Fig. 5.13).
Rice. 5.13. Excretion and osmoregulation in freshwater teleosts
fish (A), lamellar (B) and marine bony fish(V)
Abbreviations hypo-, iso- and hyper- indicate tonicity internal environment in relation to the external (from N. Green et al., 1993)
A number of aquatic organisms have a special feeding pattern - it is the straining or sedimentation of particles of organic origin suspended in water, numerous small organisms. This method of feeding does not require large expenditures of energy for the search for prey and is characteristic of lamellar gill mollusks, sessile echinoderms, ascidians, planktonic crustaceans, etc. Filter feeding animals play an important role in the biological purification of water bodies.
Freshwater daphnia, cyclops, as well as the most abundant crustacean in the ocean, Calanus finmarchicus, filter up to 1.5 liters of water per individual per day. Mussels living on an area of 1 m 2 can drive 150-280 m 3 of water through the mantle cavity per day, precipitating suspended particles.
Due to the rapid attenuation of light rays in water, life in constant twilight or in darkness severely limits the possibilities of visual orientation of aquatic organisms. Sound travels faster in water than in air, and aquatic organisms have a better visual orientation to sound. Some species even pick up infrasounds. Sound signaling serves most of all for intraspecific relationships: orientation in a flock, attracting individuals of the opposite sex, etc. Cetaceans, for example, search for food and orient themselves using echolocation - the perception of reflected sound waves. The principle of a dolphin locator is to emit sound waves that propagate in front of a swimming animal. Upon encountering an obstacle, such as a fish, the sound waves are reflected and returned to the dolphin, which hears the resulting echo and thus detects the object causing the sound to be reflected.
About 300 species of fish are known to be capable of generating electricity and using it for orientation and signaling. A row of fish ( electric Stingray, electric eel, etc.) use electric fields for defense and attack.
Aquatic organisms are characterized by ancient way orientation - the perception of the chemistry of the environment. The chemoreceptors of many aquatic organisms (salmon, eels, etc.) are extremely sensitive. In migrations of thousands of kilometers, they find spawning and feeding grounds with amazing accuracy.
Changing conditions in the aquatic environment also causes certain behavioral reactions of organisms. Changes in illumination, temperature, salinity, gas regime and other factors are associated with vertical (sinking inland, rising to the surface) and horizontal (spawning, wintering and feeding) migrations of animals. In the seas and oceans, millions of tons of aquatic organisms take part in vertical migrations, and during horizontal migrations, aquatic animals can travel hundreds and thousands of kilometers.
There are many temporary, shallow bodies of water on Earth that arise after the flooding of rivers, heavy rains melting snow, etc. Common features inhabitants of drying up reservoirs is the ability to give numerous offspring in a short time and endure long periods without water, passing into a state of reduced vital activity - hypobiosis.
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Water as a habitat has a number of specific properties, such as high density, strong pressure drops, relatively low oxygen content, strong absorption of sunlight, etc. , the content of suspended particles. For the life of benthic organisms, the properties of the soil, the mode of decomposition of organic residues, etc., are important. Therefore, along with adaptations to general properties the aquatic environment, its inhabitants must be adapted to a variety of private conditions. The inhabitants of the aquatic environment received in ecology common name hydrobionts. They inhabit the oceans, continental bodies of water and groundwater. In any body of water, it is possible to distinguish zones that are different in terms of conditions.
Let's consider the main properties of water as a habitat.
Density of water - it is a factor that determines the conditions of movement of aquatic organisms and pressure at different depths. The density of natural waters containing dissolved salts can be higher, up to 1.35 g / cm 3. The pressure increases with depth by about 101.3 kPa (1 atm) on average for every 10 m.
Due to the sharp change in pressure in water bodies, aquatic organisms, on the whole, tolerate pressure changes more easily than land organisms. Some species, common at different depths, tolerate pressures from several to hundreds of atmospheres. For example, sea cucumbers of the genus Elpidia live in the area from coastal zone to the zone of greatest ocean depths, 6-11 km. However, most of the inhabitants of the seas and oceans live at a certain depth.
The density of the water provides the ability to rely on it, which is especially important for skeletal forms. The density of the environment serves as a condition for soaring in water, and many aquatic organisms are adapted to this particular way of life. Suspended, floating in water organisms are combined into a special ecological group of aquatic organisms - plankton("Planktos" - soaring). The plankton contains unicellular and colonial algae, protozoa, jellyfish, various small crustaceans, larvae of benthic animals, eggs and fish fry, and many others.
The density and viscosity of water greatly affects the ability to swim actively. Animals capable of fast swimming and overcoming the force of currents are united into an ecological group nekton("Nektos" - floating). Representatives of nekton are fish, squid, dolphins. Rapid movement in the water column is possible only if there is a streamlined body shape and highly developed muscles.
1. Oxygen mode. In oxygenated water, its content does not exceed 10 ml per 1 liter, which is 21 times lower than in the atmosphere. Therefore, the conditions for the respiration of aquatic organisms are significantly complicated. Oxygen enters the water mainly through the photosynthetic activity of algae and diffusion from the air. Therefore, the upper layers of the water column, as a rule, are richer in this gas than the lower ones. With increasing temperature and salinity of water, the concentration of oxygen in it decreases.
Respiration of aquatic organisms is carried out either through the surface of the body, or through specialized organs - gills, lungs, trachea. In this case, the integument can serve as an additional respiratory organ. For example, loach fish consumes up to 63% of oxygen through the skin on average. Many sedentary and sedentary animals renew the water around them, either by creating a directed current of it, or by oscillating movements contributing to its mixing. Bivalve molluscs for this purpose, the cilia lining the walls of the mantle cavity serve; crustaceans - the work of the abdominal or thoracic legs. Leeches, larvae of mosquito-bellies (bloodworms) wiggle the body, leaning out of the ground.
Mammals that have passed in the process of evolutionary development from a terrestrial to an aquatic lifestyle, for example, pinnipeds, cetaceans, water beetles, mosquito larvae, usually retain the atmospheric type of respiration and therefore need contact with the air environment.
Lack of oxygen in water sometimes leads to catastrophic phenomena - deaths, accompanied by the death of many hydrobionts. Winter frosts are often caused by the formation of ice on the surface of water bodies and the cessation of contact with air; summer - by an increase in water temperature and a decrease in oxygen solubility as a result.
- 2. Salt mode. Maintaining the water balance of aquatic organisms has its own specifics. If for terrestrial animals and plants it is most important to provide the body with water in conditions of its deficiency, then for aquatic organisms it is equally important to maintain a certain amount of water in the body with its excess in the environment. An excessive amount of water in cells leads to a change in osmotic pressure and disruption of the most important vital functions. Therefore, freshwater forms cannot exist in the seas, and marine ones cannot tolerate desalination. If the salinity of the water is subject to changes, animals move in search of a favorable environment.
- 3. Temperature regime water bodies, as already noted, are more stable than on land. The amplitude of annual temperature fluctuations in the upper layers of the ocean is no more than 10-15 ° C, in continental water bodies - 30-35 ° C. Deep water layers are characterized by constant temperature. In equatorial waters, the average annual temperature of the surface layers is + 26-27 ° С, in polar waters - about 0 ° С and below. In hot ground springs, the water temperature can approach +100 ° С, and in underwater geysers at high pressure at the bottom of the ocean, a temperature of +380 ° C was recorded. But vertically, the temperature regime is diverse, for example, seasonal temperature fluctuations appear in the upper layers, and the thermal regime is constant in the lower layers.
- 4. Light mode. There is much less light in water than in air. Part of the rays falling on the surface of the reservoir is reflected into the air. The lower the position of the Sun, the stronger the reflection, so the day is shorter under water than on land. The rapid decrease in the amount of light with depth is associated with its absorption by water. Rays with different wavelengths are absorbed differently: the red ones disappear already close to the surface, while the blue-green ones penetrate much deeper. This affects the color of aquatic organisms, for example, the color of algae changes with depth: green, brown and red algae, which specialize in capturing light with different wavelengths. The color of animals changes with depth in the same way. Many deep-seated organisms lack pigments.
In the dark depths of the ocean, organisms use the light emitted by living things as a source of visual information. The glow of a living organism is called bioluminescence.
Thus, the properties of the environment largely determine the ways of adaptation of its inhabitants, their way of life and ways of using resources, creating a chain of cause-and-effect relationships. Thus, the high density of water makes possible the existence of plankton, and the presence of organisms floating in the water is a prerequisite for the development of a filtration type of nutrition, in which a sedentary lifestyle of animals is also possible. As a result, a powerful mechanism of self-purification of reservoirs of biospheric importance is formed. It involves a huge number of aquatic organisms, both benthic (living on the ground and in the bottom of the bottom of reservoirs) and pelagic (plants or animals living in the water column or on the surface of the water), from unicellular protozoa to vertebrates. For example, only planktonic sea copepods (Calanus) are able to filter the waters of the entire World Ocean over several years, i.e. approximately 1.37 billion km 3. Disruption of filter feeders by various anthropogenic influences poses a serious threat to maintaining the purity of waters.
Questions and tasks for self-control
- 1. List the main properties of the aquatic habitat.
- 2. Explain how the density of water determines the shape of animals capable of swimming fast.
- 3. What is the reason for the death?
- 4. What phenomenon is called "bioluminescence"? Do you know living organisms that have this property?
- 5. What is the ecological role of filter feeders?
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