Aquatic habitat

HABITAT AND THEIR CHARACTERISTICS

In progress historical development living organisms have mastered four habitats. The first is water. Life originated and developed in water for many millions of years. The second - ground-air - plants and animals arose on land and in the atmosphere and rapidly adapted to new conditions. Gradually transforming the upper layer of land - the lithosphere, they created a third habitat - soil, and themselves became the fourth habitat.

Aquatic habitat

Water covers 71% of the earth's area. The bulk of water is concentrated in the seas and oceans - 94-98%, in polar ice contains about 1.2% water and a very small proportion - less than 0.5%, in fresh waters of rivers, lakes and swamps.

About 150,000 species of animals and 10,000 plants live in aquatic environments, representing only 7 and 8% of the total number of species on Earth, respectively.

In the seas-oceans, as in the mountains, vertical zoning is expressed. The pelagic - the entire water column - and the benthic - the bottom - differ especially greatly in ecology. The water column, the pelagic zone, is vertically divided into several zones: epipeligal, bathypeligal, abyssopeligal and ultraabyssopeligal(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 pelagic zones:

Littoral - the edge of the coast that is flooded during high tides.

Supralittoral - the part of the coast above the upper tidal line where surf splashes reach.

Sublittoral - a gradual decrease in land up to 200m.

Bathial - a steep depression of land (continental slope),

Abyssal - a gradual decrease in the bottom of the ocean floor; the depth of both zones together reaches 3-6 km.

Ultra-abyssal - deep-sea depressions from 6 to 10 km.

Ecological groups of hydrobionts. Greatest variety Life is distinguished by warm seas and oceans (40,000 species of animals) in the equator and tropics; to the north and south, the flora and fauna of the seas is hundreds of times depleted. As for the distribution of organisms directly in the sea, the bulk of them are concentrated in the surface layers (epipelagic) and in the sublittoral zone. Depending on the method of movement and stay in certain layers, Marine life are divided into three ecological groups: nekton, plankton and benthos.

Nekton (nektos - floating) - actively moving large animals that can overcome long distances and strong currents: fish, squid, pinnipeds, whales. In fresh water bodies, nekton includes amphibians and many insects.

Plankton (planktos - wandering, soaring) - a collection of plants (phytoplankton: diatoms, green and blue-green (fresh water bodies only) algae, plant flagellates, peridineans, etc.) and small animal organisms (zooplankton: small crustaceans, of the larger ones - pteropods mollusks, jellyfish, ctenophores, some worms) living at different depths, but not capable of active movement and resistance to currents. Plankton also includes animal larvae, 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, mollusks, etc.) in the larval stage. The larvae, growing up, move into the lower layers of the pelagel. Above the neuston is located plaiston - these are organisms in which the upper part of the body grows above water, and the lower part in water (duckweed - Lemma, siphonophores, etc.). Plankton plays an important role in the trophic relationships of the biosphere, because is food for many aquatic inhabitants, including the main food for baleen whales (Myatcoceti).

Benthos (benthos – depth) – bottom hydrobionts. It is represented mainly by attached or slowly moving animals (zoobenthos: foraminephores, fish, sponges, coelenterates, worms, mollusks, ascidians, etc.), more numerous in shallow water. In shallow water, benthos also includes plants (phytobenthos: diatoms, green, brown, red algae, bacteria). At depths where there is no light, phytobenthos is absent. Rocky areas of the bottom are richest in phytobenthos.

In lakes, zoobenthos is less abundant and diverse than in the sea. It is formed by protozoa (ciliates, daphnia), leeches, mollusks, insect larvae, etc. The phytobenthos of lakes is formed by free-floating diatoms, green and blue-green algae; brown and red algae are absent.

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 (increases with depth by 1 atm for every 10 m), oxygen content, salt composition, acidity. Due to the high density of the environment, the values ​​of heat and light change much faster with the altitude gradient than on land.

Thermal mode. The aquatic environment is characterized by less heat gain, because a significant part of it is reflected, and an equally significant part is spent on evaporation. Consistent with the dynamics of ground temperatures, water temperature has smaller daily and seasonal temperatures. Moreover, bodies of water significantly equalize the temperature in the atmosphere. coastal areas. In the absence of an ice shell, the seas have a warming effect on the adjacent land areas in the cold season, and a cooling and moistening effect in the summer.

The range of water temperatures in the World Ocean is 38° (from -2 to +36°C), in fresh water bodies – 26° (from -0.9 to +25°C). With depth, the water temperature drops sharply. Up to 50 m there are daily temperature fluctuations, up to 400 – seasonal, deeper it becomes constant, dropping to +1-3°C. Since the temperature regime in reservoirs is relatively stable, their inhabitants tend to stenothermicity.

Due to to varying degrees heating of the upper and lower layers throughout the year, ebbs and flows, currents, and storms constantly mix the water layers. The role of water mixing for aquatic inhabitants is extremely important, because at the same time, the distribution of oxygen and nutrients within reservoirs is equalized, ensuring metabolic processes between organisms and the environment.

In stagnant bodies of water (lakes) temperate latitudes In spring and autumn, vertical mixing takes place, and during these seasons the temperature throughout the entire reservoir becomes uniform, i.e. comes homothermy. In summer and winter, as a result of a sharp increase in heating or cooling of the upper layers, the mixing of water stops. This phenomenon is called temperature dichotomy, and the period of temporary stagnation is stagnation(summer or winter). In summer, lighter warm layers remain on the surface, located above heavy cold ones (Fig. 3). In winter, on the contrary, in the bottom layer there is more warm water, since directly under the ice the temperature surface waters less than +4°С and they are in effect physical and chemical properties waters become lighter than water with a temperature above +4°C.

During periods of stagnation, three layers are clearly distinguished: the upper (epilimnion) with the most dramatic seasonal fluctuations in water temperature, the middle (metalimnion or thermocline), in which there is a sharp jump in temperature, and bottom ( hypolimnion), in which the temperature varies little throughout the year. During periods of stagnation, oxygen deficiency occurs in the water column - in the bottom part in summer, and in the upper part in winter, as a result of which fish kills often occur in winter.

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 absorption of light is stronger, the lower the transparency of the water, which depends on the number of particles suspended in it (mineral suspensions, plankton). It decreases with rapid development small organisms in summer, and in temperate and northern latitudes– also in winter, after the ice cover has been established and covered with snow on top.

Transparency is characterized by the maximum depth at which a specially lowered white disk with a diameter of about 20 cm (Secchi disk) is still visible. The clearest waters are in the Sargasso Sea: the disk is visible to a depth of 66.5 m. In the Pacific Ocean, the Secchi disk is visible up to 59 m, in the Indian Ocean - up to 50, in shallow seas- up to 5-15m. The transparency of rivers is on average 1-1.5 m, and in the muddiest rivers only a few centimeters.

In the oceans, where the water is very transparent, 1% of light radiation penetrates to a depth of 140 m, and in small lakes at a depth of 2 m only tenths of a percent penetrates. Rays different parts spectrum are absorbed differently in water; red rays are absorbed first. With depth it becomes darker, and the color of the water first becomes green, then blue, indigo and finally blue-violet, turning into complete darkness. Hydrobionts also change color accordingly, 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). On great depths phytobenthos is absent.

Plants adapted to the lack of light by developing large chromatophores, as well as increasing the area of ​​assimilating organs (leaf surface index). For deep-sea algae, strongly dissected leaves are typical, the leaf blades are thin and translucent. Semi-submerged and floating plants are characterized by heterophylly - the leaves above the water are the same as those of land plants, they have a solid blade, the stomatal apparatus is developed, and in the water the leaves are very thin, consisting of narrow thread-like lobes.

Animals, like plants, naturally change their color with depth. In the upper layers they are brightly colored in different colors, in the twilight zone (sea bass, corals, crustaceans) they are painted in colors with a red tint - it is more convenient to hide from enemies. Deep-sea species lack pigments. In the dark depths of the ocean, organisms use light emitted by living beings as a source of visual information. bioluminescence.

High density(1 g/cm3, which is 800 times the density of air) and water viscosity ( 55 times higher than that of air) led to the development of special adaptations of aquatic organisms :

1) Plants have very poorly developed or completely absent mechanical tissues - they are supported by water itself. Most are characterized by buoyancy due to air-carrying intercellular cavities. Characterized by active vegetative reproduction, the development of hydrochory - the removal of flower stalks above the water and the distribution of pollen, seeds and spores by surface currents.

2) In animals living in the water column and actively swimming, the body has a streamlined shape and is lubricated with mucus, which reduces friction when moving. Developed devices to increase buoyancy: accumulations of fat in tissues, swim bladders in fish, air cavities in siphonophores. In passively swimming animals, the specific body surface due to outgrowths, spines, appendages; the body is flattened, and skeletal organs are reduced. Different ways locomotion: bending of the body, with the help of flagella, cilia, reactive mode of locomotion ( cephalopods).

In benthic animals, the skeleton disappears or is poorly developed, body size increases, vision reduction is common, and tactile organs develop.

Currents. A characteristic feature of the aquatic environment is mobility. It is caused by ebbs and flows, sea currents, storms, and different levels of elevations of river beds. Adaptations of hydrobionts:

1) In flowing reservoirs, plants are firmly attached to stationary underwater objects. The bottom surface is primarily a substrate for them. These are green and diatom algae, water mosses. Mosses even form a dense cover on fast riffles of rivers. In the tidal zone of the seas, many animals have devices for attaching to the bottom (gastropods, barnacles), or hide in crevices.

2) In fish of running waters, the body is round in diameter, and in fish that live near the bottom, as in benthic invertebrate animals, the body is flat. Many have attachment organs to underwater objects on the ventral side.

Salinity of water.

Natural bodies of water have a certain chemical composition. Carbonates, sulfates, and chlorides predominate. In fresh water bodies, the salt concentration is no more than 0.5 ‰ (and about 80% are carbonates), in the seas - from 12 to 35 ‰ (mainly chlorides and sulfates). When the salinity is more than 40 ppm, the water body is called hypersaline or oversaline.

1) B fresh water(hypotonic environment) osmoregulation processes are well expressed. Hydrobionts are forced to constantly remove water penetrating into them; they are homoyosmotic (ciliates “pump” through themselves an amount of water equal to its weight every 2-3 minutes). In salt water (isotonic environment), the concentration of salts in the bodies and tissues of hydrobionts is the same (isotonic) with the concentration of salts dissolved in water - they are poikiloosmotic. Therefore, the inhabitants of salt water bodies do not have developed osmoregulatory functions, and they were unable to populate fresh water bodies.

2) Aquatic plants are able to absorb water and nutrients from water - “broth”, with their entire surface, therefore their leaves are strongly dissected and conductive tissues and roots are poorly developed. The roots serve mainly for attachment to the underwater substrate. Most freshwater plants have roots.

Typically marine and typically freshwater species, stenohaline, do not tolerate significant changes in water salinity. There are few euryhaline species. They are common in brackish waters (freshwater pike perch, pike, bream, mullet, coastal salmon).

Within the biosphere we can distinguish four main habitats. These are the aquatic environment, the terrestrial air environment, the soil and the environment formed by living organisms themselves.

Water environment

Water serves as a habitat for many organisms. From water they obtain all the substances necessary for life: food, water, gases. Therefore, no matter how diverse aquatic organisms are, they all must be adapted to the main features of life in the aquatic environment. These features are determined by physical and chemical properties water.

Hydrobionts (inhabitants of the aquatic environment) live in both fresh and salt water and are divided into \(3\) groups according to their habitat:

• plankton - organisms living on the surface of water bodies and passively moving due to the movement of water;
• nekton - actively moving in the water column;
• benthos - organisms that live at the bottom of reservoirs or burrow into silt.

Many small plants and animals constantly hover in the water column, living in a suspended state. The ability to soar is ensured not only by the physical properties of water, which has a buoyant force, but also by special adaptations of the organisms themselves, for example, numerous outgrowths and appendages that significantly increase the surface of their body and, therefore, increase friction with the surrounding liquid.

The body density of animals such as jellyfish is very close to that of water.

Moreover, their characteristic body shape, reminiscent of a parachute, helps them stay in the water column.

Active swimmers (fish, dolphins, seals, etc.) have a spindle-shaped body and limbs in the form of flippers.

Their movement in the aquatic environment is facilitated, in addition, due to the special structure of the outer covers, which secrete a special lubricant - mucus, which reduces friction with water.

Water has a very high heat capacity, i.e. ability to accumulate and retain heat. For this reason, there are no sharp temperature fluctuations in water, which often occur on land. Very deep waters can be very cold, but thanks to the constant temperature, animals have been able to develop a number of adaptations that ensure life even in these conditions.

Animals can live at vast ocean depths. Plants survive only in the upper layer of water, where the radiant energy necessary for photosynthesis enters. This layer is called photic zone .

Since the surface of the water reflects most of the light, even in the most transparent ocean waters the thickness of the photic zone does not exceed \(100\) m. Animals of great depths feed either on living organisms or the remains of animals and plants that constantly fall down from the upper layer.

Like terrestrial organisms, aquatic animals and plants breathe and require oxygen. The amount of oxygen dissolved in water decreases with increasing temperature. Moreover, oxygen dissolves less well in sea water than in fresh water. For this reason, the waters of the open sea of ​​the tropical zone are poor in living organisms. And, conversely, polar waters are rich in plankton - small crustaceans on which fish and large cetaceans feed.

The salt composition of water is very important for life. The \(Ca2+\) ions are of particular importance for organisms. Clams and crustaceans need calcium to build their shells or shells. The concentration of salts in water can vary greatly. Water is considered fresh if one liter contains less than \(0.5\) g of dissolved salts. Sea water has a constant salinity and contains on average \(35\) g of salts per liter.

Ground air environment

The terrestrial air environment, mastered in the course of evolution later than the aquatic environment, is more complex and diverse, and it is inhabited by more highly organized living organisms.

Most important factor The life of the organisms living here is determined by the properties and composition of the air masses surrounding them. The density of air is much lower than the density of water, so terrestrial organisms have highly developed supporting tissues- internal and exoskeleton. The forms of movement are very diverse: running, jumping, crawling, flying, etc. Birds and some types of insects fly in the air. Air currents carry plant seeds, spores, and microorganisms.

Air masses are constantly in motion. Air temperature can change very quickly and over large areas, so organisms living on land have numerous adaptations to withstand or avoid sudden changes in temperature.

The most remarkable of them is the development of warm-bloodedness, which arose precisely in the terrestrial air environment.
The chemical composition of air (\(78%\) nitrogen, \(21%\) oxygen and \(0.03%\) carbon dioxide is important for the life of plants and animals. Carbon dioxide, for example, is the most important raw material for photosynthesis. Air nitrogen is necessary for the synthesis of proteins and nucleic acids.

The amount of water vapor in the air ( relative humidity) determines the intensity of transpiration processes in plants and evaporation from the skin of some animals. Organisms living in low humidity conditions have numerous adaptations to prevent severe water loss. For example, desert plants have a powerful root system that can pump water into the plant from great depths. Cacti store water in their tissues and use it sparingly. In many plants, to reduce evaporation, the leaf blades are turned into spines. Many desert animals hibernate during the hottest period, which can last for several months.

The soil - this is the top layer of land, transformed as a result of the vital activity of living beings. This is an important and very complex component of the biosphere, closely connected with its other parts. Soil life is unusually rich. Some organisms spend their entire lives in the soil, others spend part of their lives. Between the soil particles there are numerous cavities that can be filled with water or air. Therefore, the soil is inhabited by both aquatic and air-breathing organisms. Soil plays a huge role in plant life.

Living conditions in the soil are largely determined climatic factors, the most important of which is temperature. However, as one goes deeper into the soil, temperature fluctuations become less and less noticeable: daily temperature changes quickly fade, and as the depth increases, seasonal temperature changes also fade away.

Even at shallow depths, complete darkness reigns in the soil. In addition, as you sink into the soil, the oxygen content decreases and the carbon dioxide content increases. Therefore, only anaerobic bacteria can live at a considerable depth, while in the upper layers of the soil, in addition to bacteria, fungi, protozoa, roundworms, arthropods, and even relatively large animals that make passages and build shelters, such as moles, shrews, and mole rats, are found in abundance.

The environment formed by living organisms themselves

It is obvious that the living conditions inside another organism are characterized by greater constancy compared to the conditions of the external environment.

Therefore, organisms that find a place in the body of plants or animals often completely lose the organs and systems necessary for free-living species. They do not have developed sensory organs or organs of movement, but they develop adaptations (often very sophisticated) for retention in the host’s body and effective reproduction.

Sources:

Kamensky A.A., Kriksunov E.A., Pasechnik V.V. Biology. 9th grade // Bustard
Kamensky A.A., Kriksunov E.A., Pasechnik V.V. Biology. General biology (basic level) grades 10-11 // Bustard

Federal Fisheries Agency

Federal State Educational Institution of Higher Professional Education Kamchatka State Technical University

Department of Ecology and Environmental Management

Discipline ecology

Abstract on the topic

“The aquatic environment of life and the adaptation of organisms to it”

Completed Checked

Student of group 11PZhb Associate Professor

Sazonov P.A. Stupnikova N.A.

Petropavlovsk-Kamchatsky

Introduction…………………………………….3

general characteristics……………………...3- 4

Ecological zones of the World Ocean………….4

Basic properties of the aquatic environment………………….5

· Density…………………………………….5- 6

· Oxygen regime…………………………6-7

· Salt regime……………………………….7-8

· Temperature………………………8

· Light mode……………………………..8-9

Specific adaptations of hydrobionts………..10-11

Features of plant adaptation to the aquatic environment………11-12

Features of animal adaptation to the aquatic environment……..12-14

References……………………………………………………15

Introduction

On our planet, living organisms have mastered four main environments

a habitat. The aquatic environment was the first in which arose and

life has spread. Only then did the organisms take over

ground-air, created and populated the soil and themselves became the fourth

specific living environment.

Water as a habitat has a number of specific properties, such as

high density, strong pressure drops, low content

oxygen, strong absorption sun rays. In addition, bodies of water and

their individual areas differ in salt regime, current speed,

also soil properties, decomposition mode of organic residues, etc.

Therefore, along with adaptations to the general properties of the aquatic environment, its

the inhabitants must also be adapted to a variety of private

conditions.

All inhabitants of the aquatic environment have received a common name in ecology

hydrobionts.

Hydrobionts inhabit the World Ocean, continental reservoirs and

The groundwater.

general characteristics

The hydrosphere as an aquatic living 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. 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 included in it, first of all, two are distinguished: environmental areas: the water column is pelagic and the bottom is benthic. Depending on the depth, the benthal is divided into a sublittoral zone - an area of ​​smooth decline of land to a depth of 200 m, a bathyal zone - an area of ​​a steep slope and an abyssal zone - the oceanic bed with an average depth of 3-6 km. The deeper benthic regions corresponding to the depressions of the ocean floor (6-10 km) are called ultra-abyssal. The edge of the coast that is flooded during high tides is called the littoral zone. The part of the coast above the tide level, moistened by the spray of the surf, is called the superlittoral.

The open waters of the World Ocean are also divided into zones vertically corresponding to the benthic zones: epipeligal, bathypeligal, abyssopeligal.

The aquatic environment is home to approximately 150,000 animal species, or about 7% of the total, and 10,000 plant species (8%).

The share of rivers, lakes and swamps, as noted earlier, is insignificant compared to seas and oceans. However, they create the supply of fresh water necessary for plants, animals and humans.

Characteristic feature The aquatic environment is its mobility, especially in flowing, fast-flowing streams and rivers. The seas and oceans experience ebbs and flows, powerful currents, and storms. In lakes, water moves under the influence of temperature and wind.

Ecological zones of the World Ocean

In any body of water, zones with different conditions can be distinguished. In the ocean

together with the seas entering it, there are, first of all, two

ecological areas: pelagic - water column and benthic -

Depending on the depth, the benthic zone is divided into the sublittoral zone - an area of ​​gradual decline of land to depth

approximately 200 m, bathyal - steep slope area and abyssal

zone - the ocean floor with an average depth of 3-6 km. Even more

deep benthic regions corresponding to the depressions of the ocean floor,

called ultrabenthal. The edge of the coast, flooded during high tides,

called the littoral zone. Part of the coast above the tide level, wetted

splashes, called supralittoral.

Naturally, for example, the inhabitants of the sublittoral zone live in conditions

relatively low pressure, daytime sunlight, often

quite significant changes in temperature. Inhabitants

abyssal and ultra-abyssal depths exist in darkness, with

constant temperature and pressure of several hundred, and sometimes about

thousands of atmospheres. Therefore, just an indication of which zone

benthal inhabited by one or another species of organisms already indicates what

it must have general environmental properties.

The entire population of the ocean floor is called benthos. Organisms,

those living in the water column, or pelagic zone, belong to the pelagos.

The pelagic zone is also divided into vertical zones corresponding in depth

Benthic zones: epipelagic, bathypelagic, abyssopelagic. Lower

the epipelagic boundary (no more than 200 m) is determined by the penetration

sufficient sunlight for photosynthesis. Greens

plants cannot exist deeper than these zones. In the twilight

bathyal and dark abyssal depths live only

microorganisms and animals. Different ecological zones are distinguished in

all other types of reservoirs: lakes, swamps, ponds, rivers, etc.

The diversity of aquatic organisms that have colonized all these habitats is very

Basic properties of the aquatic environment

1. Density of water

This is a factor that determines the conditions for the movement of aquatic organisms and

pressure at different depths. For distilled water the density is

1 g/cm 3 at +4 0 C. Density natural waters containing dissolved

salt, maybe more, up to 1.35 g/cm3. Pressure increases with

approximately 1 atmosphere deep for every 10 m.

Due to the sharp pressure gradient in water bodies, aquatic organisms in general

significantly more eurybathous compared to land organisms.

Some species, distributed at different depths, carry

pressure from several to hundreds of atmospheres.

However, many inhabitants of the seas and oceans are relatively stenobatic and

confined to certain depths. Stenoticness is usually characteristic

shallow and deep water species.

The density of water makes it possible to rely on it, which

especially important for non-skeletal forms. The support of the environment serves as a condition

hovering in water, and many aquatic organisms are adapted to this

way of life. Suspended, floating organisms in water are combined into a special

environmental group hydrobionts plankton.

Plankton consists of unicellular algae, protozoa, jellyfish,

siphonophores, ctenophores, pteropods and keelfoot mollusks, various

small crustaceans, larvae of bottom animals, eggs and fry of fish and many

other. Planktonic organisms have many similar adaptations,

increasing their buoyancy and preventing them from settling to the bottom. To such

adaptations include: 1) a general increase in body surface over

due to size reduction, flattening, elongation, development

numerous outgrowths and bristles, which increases friction with water; 2)

decrease in density due to reduction of the skeleton, accumulation in the body

fats, gas bubbles, etc.

Single-celled algae, phytoplankton, float passively in water.

Most planktonic animals are capable of active swimming, but

within limited limits. Planktonic organisms cannot overcome

currents and are carried over long distances. Many types

zooplankton are capable, however, of vertical migrations in the thickness

water for tens and hundreds of meters due to both active movement and

and by regulating the buoyancy of its body. A special variety

plankton constitutes the ecological group of neuston inhabitants

surface film of water at the border with air environment.

The density and viscosity of water greatly influence the possibility of active

swimming. Animals capable of fast swimming and overcoming force

currents, are combined into the ecological group nekton. Representatives

nekton fish, squid, dolphins. Rapid movement in the water column

perhaps only if there is a streamlined body shape and a highly developed

muscles. The torpedo shape is developed in all good

swimmers, regardless of their systematic affiliation and method

movement in water: reactive, due to bending of the body, with the help

limbs.

2. Oxygen regime

The diffusion coefficient of oxygen in water is approximately 320 thousand times lower,

than in the air, and general content it does not exceed 10 ml in 1 liter

water, this is 21 times lower than in the atmosphere. Therefore, breathing conditions

hydrobionts are significantly more complicated. Oxygen enters water at

mainly due to the photosynthetic activity of algae and diffusion

from the air. Therefore, the upper salts of the water column are, as a rule, richer

oxygen than the lower ones. With increasing temperature and salinity of water

the oxygen concentration in it decreases. In layers heavily populated

bacteria and animals, a severe oxygen deficiency can be created

due to its increased consumption.

Among aquatic inhabitants there are many species that can tolerate wide

absence (euryoxybionts). At the same time, a number of species are stenoxybiont

they can only exist if the water saturation is sufficiently high

oxygen. Many species are capable of going into a state when there is a lack of oxygen.

inactive state of anoxybiosis and thus experience

unfavorable period.

Respiration of hydrobionts occurs 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. If

gas exchange occurs through the integuments of the body, they are very thin. Breath

It is also made easier by increasing the surface area. This is achieved during

evolution of species by the formation of various outgrowths, flattening,

elongation, a general decrease in body size. Some types of

lack of oxygen actively changes the size of the respiratory surface.

Many sessile and sedentary animals renew the water around them,

either by creating its directed current, or by oscillatory movements

promoting its mixing.

In some species there is a combination of water and air

breathing. Secondary aquatic animals usually retain atmospheric respiration

as more favorable energetically and therefore need contacts with

air environment.

Lack of oxygen in water sometimes leads to catastrophic

the phenomena of death, accompanied by the death of many aquatic organisms.

Winter death is often caused by the formation of ponds on the surface of water bodies.

ice and cessation of contact with air; summer temperature rise

water and, as a result, a decrease in oxygen solubility. Zamora

more often occur more often occur in ponds, lakes, rivers. Less frequent deaths

occur in the seas. In addition to lack of oxygen, death can occur

caused by an increase in the concentration of toxic methane gases in water,

hydrogen sulfide and others formed as a result of decomposition

organic materials at the bottom of reservoirs.

3. Salt regime

Maintaining the water balance of aquatic organisms has its own specifics. If

for terrestrial animals and plants, the most important thing is to provide the body

water in conditions of its deficiency, then for hydrobionts it is no less important

maintaining a certain amount of water in the body when there is an excess of it in

environment. Excessive amount of water in cells leads to

changes in osmotic pressure in them and disruption of the most important vital

Most aquatic inhabitants are poikilosmotic: osmotic pressure

in their body depends on salinity surrounding water. Therefore for

hydrobionts main way to maintain their salt balance is

Avoid habitats with unsuitable salinity. Freshwater forms

cannot exist in the seas, seas do not tolerate desalination. If

the salinity of the water is subject to change, animals move in search of

favorable environment. Vertebrates, higher crustaceans, insects and their

larvae living in water belong to homoiosmotic species,

maintaining constant osmotic pressure in the body regardless of

concentration of salts in water.

In freshwater species, body juices are hypertonic in relation to

environment. They are threatened by excessive watering, if not

preventing the entry or removal of excess water from the body. U

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 every 2-2.5 minutes

bodies. The cell spends a lot of money “pumping out” excess water.

energy. With increasing salinity, the work of vacuoles slows down.

If the water is hypertonic in relation to the body juices of hydrobionts, they

risk of dehydration as a result of osmotic losses. Defence from

dehydration is achieved by increasing the concentration of salts also in the body

hydrobionts. Waterproof seals prevent dehydration

integuments of homoyosmatic organisms of mammals, fish, higher crayfish,

aquatic insects and their larvae. Many poikilosmotic species

transition to an inactive state of suspended animation as a result of water deficiency

in the body with increasing salinity. This is typical for species living in

puddles of sea water and in the littoral zone: rotifers, flagellates, ciliates,

some crustaceans, etc. Salt suspended animation is a means of surviving

unfavorable periods in conditions of variable water salinity.

Truly euryhaline species capable of living in an active state

both in fresh and salt water, among aquatic inhabitants there are not so many

a lot of. These are mainly species inhabiting river estuaries, estuaries and other

brackish water bodies.

4. Temperature conditions of reservoirs

more stable than on land. This is due to the physical properties

water, especially its high specific heat capacity, due to which

receiving or giving significant amount does not cause heat

too sudden temperature changes. Amplitude of annual fluctuations

temperatures in the upper layers of the ocean are no more than 10-15 0 C, in

continental reservoirs 30-35 0 C. Deep layers of water differ

constant temperature. In equatorial waters the average annual

temperature of surface layers +26...+27 0 C, in polar layers about 0 0 C

and below. Thus, in reservoirs there is quite a significant

variety of temperature conditions. Between the upper layers of water with

seasonal temperature fluctuations expressed in them and lower ones, where

the thermal regime is constant, there is a zone of temperature jump, or

thermocline. The thermocline is more pronounced in warm seas, where it is stronger

temperature difference between external and deep waters.

Due to the more stable temperature regime of water among

hydrobionts to a much greater extent than among the land population,

Stenothermia is common. Eurythermal species are found mainly

in small continental reservoirs and in the littoral zone of high and

temperate latitudes, where daily and seasonal variations are significant

temperature.

5. Light regime of reservoirs

There is much less light in water than in air. Some of those falling on

the surface of the reservoir of rays is reflected into the air. Reflection of themes

stronger, the lower the position of the Sun, so the day under water is shorter than

on the land. The rapid decrease in the amount of light with depth is associated with

its absorption by water. Rays of different wavelengths are absorbed

not the same: the red ones disappear not far from the surface, while

blue-green ones penetrate much deeper. Twilight deepening with depth

are first green, then blue, indigo and violet,

finally giving way to constant darkness. They replace each other accordingly

with depth green, brown and red algae specialized for

capturing light of different wavelengths. The color of animals changes with depth just as naturally.

The inhabitants of the littoral and

sublittoral zones. Many deep organisms, like cave organisms, do not

have pigments. Red is widespread in the twilight zone

coloration that is complementary to blue violet light on

these depths. Additional color rays are most completely absorbed

body. This allows animals to hide from enemies, since their red

The color in blue-violet rays is visually perceived as black.

The absorption of light is stronger, the lower the transparency of the water, which

depends on the number of particles suspended in it. Transparency

characterized by the maximum depth at which it is still specifically visible

a lowered white disk with a diameter of about 20 cm (Secchi disk).

Specific adaptations of aquatic organisms

Methods for orienting animals in the aquatic environment

Living in constant twilight or darkness is very limiting

possibilities of visual orientation of aquatic organisms. Due to the fast

due to the attenuation of light rays in water, even those with well-developed

organs of vision are oriented with their help only at close range.

Sound travels faster in water than in air. Focus on

Sound is generally better developed in aquatic organisms than visual. A number of species

picks up even very low frequency vibrations (infrasounds),

arising when the rhythm of the waves changes, and descends in advance

before a storm from the surface layers to the deeper ones. Many

inhabitants of reservoirs: mammals, fish, mollusks, crustaceans themselves

make sounds. Crustaceans do this by rubbing against each other

different parts of the body; fish using a swim bladder, pharyngeal

teeth, jaws, rays pectoral fins and in other ways. Sound

signaling most often serves for intraspecific relationships

for example, for orientation in the pack, attracting individuals of the other sex, and

especially developed among the inhabitants troubled waters and great depths living in

A number of hydrobionts search for food and navigate using

echolocation perception of reflected sound waves. Many perceive

reflected electrical impulses, producing discharges while swimming

different frequencies. About 300 species of fish are known that can generate

electricity and use it for orientation and signaling. Row

fish also uses electric fields for defense and attack.

For orientation in depth, the perception of hydrostatic pressure is used. It is carried out using statocysts, gas chambers and

other organs.

Most ancient way common to everyone aquatic animals,

perception of the chemistry of the environment. Chemoreceptors of many aquatic organisms have

extreme sensitivity. In thousand-kilometer migrations,

which are characteristic of many species of fish, they are oriented mainly

by smell, with amazing accuracy finding spawning grounds or

Filtration as a power supply

Some hydrobionts have a special feeding pattern:

straining or sedimentation of organic particles suspended in water

origin and numerous small organisms. This way

food that does not require large amounts of energy to search for prey,

characteristic of elasmobranched mollusks, sessile echinoderms,

polychaetes, bryozoans, ascidians, planktonic crustaceans and others. Animals

Filters play a vital role in the biological treatment of water bodies.

The littoral zone of the ocean, especially rich in accumulations of filtering

organisms, works as an effective cleansing system.

Specifics of adaptations to life in drying up water bodies

There are many temporary, shallow bodies of water on Earth,

arising after river floods, heavy rains, snow melting, etc. IN

these reservoirs, despite the brevity of their existence, are settled

various hydrobionts. General characteristics of the inhabitants

drying pools are able to give in a short time

numerous offspring and carry long periods without water.

Representatives of many species bury themselves in the silt, turning into

state of decreased vital activity of hypobiosis. Many small species

form cysts that can withstand drought. Others are worried

unfavorable period in the stage of highly resistant eggs. Some species

drying up reservoirs are inherent unique ability dry until

film condition, and when moistened, resume growth and development.

Ecological plasticity is an important regulator of the distribution of organisms. Hydrobionts with high ecological plasticity are widespread, for example, Elodea. As an opposite example, the crustacean Artemia, 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.

Ecological plasticity depends on the age and developmental phase of the organism. For example, sea gastropod Littorina in its adult state during low tides is daily without water for a long time, but its larvae lead a planktonic lifestyle and cannot tolerate drying out.

Features of plant adaptation to the aquatic environment

Aquatic plants have significant differences from terrestrial plant organisms. Thus, the ability of aquatic plants to absorb moisture and mineral salts directly from environment is reflected in their morphological and physiological organization. Characteristic of aquatic plants is the poor development of conductive tissue and root systems. The root system serves mainly for attachment to the underwater substrate and does not perform the functions of mineral nutrition and water supply, as in terrestrial plants. Aquatic plants feed on the entire surface of their body. The significant density of water makes it possible for plants to inhabit its entire thickness. U lower plants, inhabiting various layers and leading a floating lifestyle, for this there are special appendages that increase their buoyancy and allow them to remain suspended. Higher hydrophytes have a poorly developed mechanical fabric. In their leaves, stems, and roots there are air-bearing intercellular cavities that increase the lightness and buoyancy of organs suspended in water and floating on the surface, which also helps to wash the internal cells with water with salts and gases dissolved in it. Hydrophytes are distinguished by a large leaf surface with a small total volume of the plant, which provides them with intense gas exchange with a lack of oxygen and other gases dissolved in water.

A number of aquatic organisms have developed diversity of leaves, or heterophyly. Thus, in salvinia, submerged leaves provide mineral nutrition, and floating leaves provide organic nutrition.

Important feature The adaptation of plants to living in an aquatic environment is also due to the fact that leaves immersed in water are usually very thin. Often chlorophyll in them is located in the cells of the epidermis, which helps to increase the intensity of photosynthesis during low light. Such anatomical and morphological features are most clearly expressed in aquatic mosses, Valisneria, and pondweeds.

The protection against leaching or leaching of mineral salts from the cells of aquatic plants 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 plants immersed in water after the formation of winter buds and the replacement of thin lower summer leaves with stiffer and shorter winter ones. Low water temperature negatively affects the generative organs of aquatic plants, and its high density makes it difficult to transfer pollen. Due to this aquatic plants reproduce intensively by vegetative means. Most floating and submerged plants carry flowering stems into the air and reproduce sexually. Pollen is carried by wind and surface currents. The fruits and seeds that are produced are also distributed by surface currents. This phenomenon is called hydrochory. Hydrochorous plants include not only aquatic plants, but also many coastal plants. Their fruits are highly buoyant, remain in water for a long time and do not lose their germination. For example, water carries the fruits and seeds of arrowhead, susak, and chastukha. The fruits of many sedges are enclosed in peculiar air sacs and are carried by water currents.

Features of animal adaptation to the aquatic environment

In animals living in an aquatic environment, compared to plants, adaptive features are more diverse, these include anatomical, morphological, behavioral, etc.

Animals that live in the water column primarily have adaptations that increase their buoyancy and allow them to withstand the movement of water and currents. These organisms develop adaptations that prevent them from rising into the water column or reduce their buoyancy, which allows them to stay at the bottom, including fast-flowing waters.

In small forms living in the water column, a reduction in skeletal formations is noted. Thus, in protozoa (radiolaria), the shells are porous, and the flint spines of the skeleton are hollow inside. The specific density of ctenophores and jellyfish decreases due to the presence of water in the tissues. The accumulation of fat droplets in the body increases buoyancy. Large accumulations of fat are observed in some crustaceans, fish and cetaceans. Specific Gravity bodies are reduced and thereby increase buoyancy by gas-filled swim bladders, which many fish have. Siphonophores 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 area of ​​the body. This is due to the fact that the greater the viscosity of the medium and the higher the specific surface area of ​​the body of the organism, the slower it sinks into water. In animals, the body is flattened, spines, outgrowths, and appendages are formed on it, for example, in flagellates and radiolarians.

A large group of animals that live in fresh water use the surface tension of water to move around. Water strider bugs, whirligig beetles, etc. run freely across the surface of the water. Arthropods touching the water with the ends of their appendages covered with water-repellent hairs cause deformation of its surface with the formation of a concave meniscus. When the lifting force directed upward is greater than the mass of the animal, the latter will be held on the water due to surface tension.

Thus, life on the surface of water is possible for relatively small animals, since the mass increases in proportion to the cube of the size, and the surface tension increases as a linear value.

Active swimming in animals is carried out with the help of cilia, flagella, bending of the body, and in a reactive manner due to the energy of the ejected stream of water. The reactive mode of locomotion reached its greatest perfection in cephalopods.

Large animals often have specialized limbs (fins, flippers), their body is streamlined and covered with mucus.

Only in the aquatic environment are motionless animals leading an attached lifestyle found. These are such as hydroids and coral polyps, sea ​​lilies, bivalves, 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 attachment to the substrate.

aquatic animals for the most part poikilotherms. In homeotherms (cetaceans, pinnipeds), a significant layer of subcutaneous fat is formed, which performs a thermal insulation function.

Deep-sea animals are distinguished by specific organizational features: the disappearance or weak development of the calcareous skeleton, an increase in body size, often a reduction in the organs of vision, increased development of tactile receptors, etc.

The osmotic pressure and ionic state of solutions in the body of animals is ensured by complex mechanisms of water-salt metabolism. The most common way to maintain constant osmotic pressure is to regularly remove water entering the body using pulsating vacuoles and excretory organs. So, freshwater fish excess water is removed by increased work of the excretory system, and salts are absorbed through the gill filaments. Marine fish are forced to replenish their water supplies and therefore drink sea ​​water, and excess salts supplied with water are removed from the body through the gill filaments.

Whole line hydrobionts have a special feeding pattern - this is the filtering or sedimentation of particles of organic origin suspended in water, numerous small organisms. This method of feeding does not require large amounts of energy to search for prey and is typical for elasmobranch mollusks, sessile echinoderms, ascidians, planktonic crustaceans, etc. Filter-feeding animals play an important role in the biological purification of water bodies.

Due to the rapid attenuation of light rays in water, life in constant twilight or darkness greatly limits the visual orientation capabilities of aquatic organisms. Sound travels faster in water than in air, and aquatic organisms have a better-developed visual orientation to sound. Some species even detect ultrasound. Sound signaling serves most of all for intraspecific relationships: orientation in a flock, attracting individuals of the opposite sex, etc. Cetaceans, for example, find food and navigate using echolocation - the perception of reflected sound waves. The principle of the dolphin locator is to emit sound waves that travel in front of the swimming animal. When 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 reflection.

About 300 species of fish are known that are capable of generating electricity and using it for orientation and signaling. Row of fish (electric ray, electric eel) use electric fields for defense and attack.

Aquatic organisms are characterized by an ancient method of orientation - the perception of the chemistry of the environment. The chemoreceptors of many aquatic organisms (salmon, eels) are extremely sensitive. In migrations of thousands of kilometers, they find spawning and feeding grounds with amazing accuracy.

Bibliography

1. Akimova T.A. Ecology / T.A. Akimova, V.V. Haskin M.: UNITY, 1998

2. Odum Yu. General ecology / Yu. Odum M.: Mir. 1986

3. Stepanovskikh A.S. Ecology / A.S. Stepanovskikh M.: UNITY - 2001

4. Ecological encyclopedic Dictionary. M.: "Noosphere", 1999

Aquatic life environment

From an ecological point of view, the environment is natural bodies and phenomena with which the organism is in direct or indirect relationships. Habitat is a part of nature that surrounds living organisms (individual, population, community) and has a certain impact on them.

On our planet, living organisms have mastered four main habitats: aquatic, ground-air, soil and organismal (i.e., formed by living organisms themselves).

Aquatic life environment

The aquatic life environment is the most ancient. Water ensures the flow of metabolism in the body and the normal functioning of the body as a whole. Some organisms live in water, others have adapted to a constant lack of moisture. The average water content in the cells of most living organisms is about 70%.

Specific properties water as a habitat

A characteristic feature of the aquatic environment is its high density; it is 800 times greater than the density of the air environment. In distilled water, for example, it is equal to 1 g/cm3. With increasing salinity, the density increases and can reach 1.35 g/cm3. All aquatic organisms experience high pressure, increasing by 1 atmosphere for every 10 m of depth. Some of them, for example, angler fish, cephalopods, crustaceans, starfish and others, live at great depths at a pressure of 400...500 atm.

The density of water provides the ability to rest on it, which is important for non-skeletal forms of aquatic organisms.

The following factors also influence the bionta of aquatic ecosystems:

1. concentration of dissolved oxygen;

2. water temperature;

3. transparency, characterized by a relative change in the intensity of the light flux with depth;

4. salinity, that is, the percentage (by weight) of salts dissolved in water, mainly NaCl, KC1 and MgS0 4;

5. availability of nutrients, primarily compounds of chemically bound nitrogen and phosphorus.

The oxygen regime of the aquatic environment is specific. There is 21 times less oxygen in water than in the atmosphere. The oxygen content in water decreases with increasing temperature, salinity, and depth, but increases with increasing flow speed. Among hydrobionts there are many species that belong to euryoxybionts, i.e. organisms that can tolerate low oxygen content in water (for example, some types of mollusks, carp, crucian carp, tench and others).

Stenoxybionts, for example trout, mayfly larvae and others, can only exist at a sufficiently high saturation of water with oxygen (7...11 cm 3 /l), and therefore are bioindicators of this factor.

Lack of oxygen in water leads to catastrophic phenomena of death (winter and summer), accompanied by the death of aquatic organisms.

The temperature regime of the aquatic environment is characterized by relative stability compared to other environments. In fresh water bodies of temperate latitudes, the temperature of the surface layers ranges from 0.9 °C to 25 °C, i.e. the amplitude of temperature changes is within 26 °C (except for thermal sources, where the temperature can reach 140 °C). At depth in fresh water bodies the temperature is constantly 4...5 °C.

The light regime of the aquatic environment differs significantly from the air-terrestrial environment. There is little light in water, since it is partially reflected from the surface and partially absorbed when passing through the water column. Particles suspended in water also obstruct the passage of light. In this regard, in deep reservoirs, three zones are distinguished: light, twilight and the zone of eternal darkness.

The following zones are distinguished according to the degree of illumination:

littoral zone (the water column where sunlight reaches the bottom);

limnic zone (the thickness of water to a depth where only 1% of sunlight penetrates and where photosynthesis fades);

euphotic zone (the entire illuminated water column, including the littoral and limnic zones);

profundal zone (bottom and water column where sunlight does not penetrate).

In relation to water, the following ecological groups are distinguished among living organisms: hygrophiles (moisture-loving), xerophiles (dry-loving) and mesophiles (intermediate group). In particular, among plants there are hygrophytes, mesophytes and xerophytes.

Hygrophytes are plants of humid habitats that cannot tolerate water deficiency. These include, for example: pondweed, water lily, reed.

Xerophytes are plants in dry habitats that can tolerate overheating and dehydration. There are succulents and sclerophytes. Succulents are xerophytic plants with succulent, fleshy leaves (for example, aloe) or stems (for example, cacti), in which water-storing tissue is developed. Sclerophytes are xerophytic plants with rigid shoots, due to which, in case of water deficiency, they do not exhibit an external pattern of wilting (for example, feather grass, saxaul).

Mesophytes of plants in moderately humid habitats; an intermediate group between hydrophytes and xerophytes.

The aquatic environment is home to about 150,000 species of animals (which is approximately 7% of the total) and 10,000 species of plants (which is about 8% of the total). Organisms that live in water are called hydrobionts.

Aquatic organisms, based on the type of habitat and lifestyle, are grouped into the following ecological groups.

Plankton are suspended, floating organisms that move passively due to currents. There are phytoplankton (single-celled algae) and zooplankton (single-celled animals, crustaceans, jellyfish, etc.). A special type of plankton is the ecological group neuston, inhabitants of the surface film of water at the border with the air (for example, water striders, bugs, and others).

Nekton are animals that actively move in water (fish, amphibians, cephalopods, turtles, cetaceans, etc.). The active swimming of aquatic organisms united in this ecological group directly depends on the density of water. Rapid movement in the water column is possible only if you have a streamlined body shape and highly developed muscles.

Benthos are organisms living at the bottom and in the soil; they are divided into phytobenthos (attached algae and higher plants) and zoobenthos (crustaceans, mollusks, starfish, etc.).

Aquatic habitat characteristics and features, its inhabitants.

Habitat is an element of the world used by living organisms for existence.

It has certain conditions and factors to which organisms living in this area must adapt.

There are 4 types:

• Ground-air
• Soil
• Water
• Organismal

According to one theory, the first organisms formed 3.7 billion years ago, according to another - 4.1 billion. The first forms of life appeared in water. The Earth's surface is 71% covered with water, which is very important for life on the planet as a whole.

Without water, plants and animals cannot exist. This is an amazing liquid that can exist in three stays. Water is part of everything; a certain percentage of it is contained in the atmosphere, soil and living organisms, minerals, and affects weather and climate.

It has the ability to store thermal energy, which prevents sudden temperature changes in coastal areas.

Characteristic

The aquatic environment has limited resources of both light and oxygen. The amount of air can be replenished mainly through photosynthesis. The oxygen level directly depends on the depth of the water column, because... light does not penetrate below 270 meters. It is there that red algae grow, absorbing the scattered rays of the sun and converting them into oxygen. Due to pressure at different depths, organisms can live at certain levels.

Inhabitants and animals

What creatures live in water are greatly influenced by:

• water temperature, its acidity and density;
• mobility (ebb and flow);
• mineralization;
• light mode;
• gas mode (percentage of oxygen content).

A huge number of representatives live in the aquatic environment various types animals and plants. Mammals can live both on land and in water. Among freshwater animals, we can distinguish such as the hippopotamus, which uses water for cooling purposes, Amazonian dolphin, living in the beds of the Amazon River, is a manatee that can live in both salt and fresh waters.

TO marine mammals include whales, the largest animals on the planet, polar bears, which do not spend all their lives in water, but a significant part; sea ​​lions, going ashore for recreation.

Among freshwater amphibians, various species can be distinguished: newts; salamanders; frogs; worms, crayfish, lobsters, and many others. Amphibians do not live in salt water due to the fact that their eggs die even in slightly salty waters, and amphibians live in the same place where they breed, although there are exceptions to the rules.

Also, frogs cannot live in salt water due to the fact that they have very thin skin, and the salts draw moisture from the amphibian, as a result of which it dies. Reptiles inhabit both fresh and salt waters. Some species of lizards, snakes, crocodiles and turtles live there and have adapted to this environment.

aquatic plants photo

For fish, the aquatic environment is their home. They can live in salty or fresh water. Many insects such as mosquitoes, dragonflies, water striders, water spiders and the like live in aquatic environments.

There are also a large number of plants present here. In freshwater bodies of water, lake reeds (along swampy shores), water lilies (swamps, ponds, creeks), and calamus (in shallow waters) grow. In salt water, algae and sea grasses (Posidonia, eelgrass) mostly grow.

Organisms of the aquatic environment

In addition to multicellular animals, simple unicellular animals also live in water. Plankton or “wandering” cannot move independently. That is why it is carried by the currents of both salt and fresh water bodies. The concept of plankton includes both plants (phytoplankton), living on the surface for the sake of sunlight, and animals (zooplankton), living throughout the water column. There are also amoebas, single-celled loners that live wherever there is water.