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 (Fig. 5.2).

Rice. 5.2. The world's oceans in comparison with land (according to N. F. Reimers, 1990)

In the 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 its constituent seas, two ecological areas are primarily distinguished: the water column - pelagic and the bottom - benthal. Depending on the depth, benthal is divided into sublittoral zone - area of ​​gradual decline of land to a depth of 200 m, bathyal - steep slope area and abyssal zone - ocean floor 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 ultraabyssal. The edge of the shore that is flooded during high tides is called littoral The part of the coast above the tide level, moistened by the spray of the surf, is called supralittoral.

The open waters of the World Ocean are also divided into vertical zones corresponding to the benthic zones: epipelagic, bathypelagic, abyssopelagic(Fig. 5.3).

Rice. 5.3. Vertical ecological zonation of the ocean

(according to N.F. Reimers, 1990)

The aquatic environment is home to approximately 150,000 animal species, or about 7% of the total (Fig. 5.4) and 10,000 plant species (8%).

It should also be noted that representatives of most groups of plants and animals remained in the aquatic environment (their “cradle”), but the number of their species is much smaller than that of terrestrial ones. Hence the conclusion - evolution on land took place much faster.

The seas and oceans of the equatorial and tropical regions, primarily the Pacific and Atlantic oceans, are distinguished by the diversity and richness of flora and fauna. To the north and south of these belts, the quality composition gradually becomes depleted. For example, in the area of ​​the East Indian archipelago there are at least 40,000 species of animals, while in the Laptev Sea there are only 400. The bulk of the organisms of the World Ocean are concentrated in a relatively small area sea ​​coasts temperate zone and among the mangroves of tropical countries.

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.

Rice. 5.4. Distribution of the main classes of animals by environment

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 land-air environment

It is known that not only the aquatic environment has a strong influence on its inhabitants, but also living matter The hydrosphere, affecting the habitat, processes it and involves it in the cycle of substances. It has been established that the water of oceans, seas, rivers and lakes decomposes and is restored in the biotic cycle over 2 million years, i.e. 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 modern, but also of past geological eras.

A characteristic feature of 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 groups of hydrobionts. Water thickness, or pelagic(pelages - sea), inhabited by pelagic organisms that have the ability to swim or stay in certain layers (Fig. 5.5).

Rice. 5.5. Profile of the ocean and its inhabitants (according to N. N. Moiseev, 1983)

In this regard, these organisms are divided into two groups: nekton And plankton. The third environmental group - benthos - form the inhabitants of the bottom.

Nekton(nektos - floating) is a collection of pelagic actively moving animals that do not have a direct connection with the bottom. These are mainly large animals that are able to overcome long distances and strong water currents. They have a streamlined body shape and well-developed organs of movement. Typical nektonic organisms include fish, squid, whales, and pinnipeds. In addition to fish, nekton in fresh waters includes amphibians and actively moving insects. Many marine fish can move through the water at enormous speeds: up to 45-50 km/h for squid (Oegophside), 100-150 km/h for sailfish (Jstiopharidae) and 130 km/h for swordfish (Xiphias glabius).

Plankton(planktos - wandering, soaring) is a set of pelagic organisms that do not have the ability for rapid active movements. As a rule, these are small animals - zooplankton and plants - phytoplankton, who cannot resist the currents. Plankton also includes the larvae of many animals “floating” 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 make up special group - Neuston. The composition of neuston also depends on the developmental stage of a number of organisms. Passing through the larval stage and growing up, they leave the surface layer that served them as a refuge and move to live on the bottom or in the underlying and deeper layers. These include the larvae of decapods, barnacles, copepods, gastropods and bivalves, echinoderms, polychaetes, fish, etc.

The same organisms, part of the body of which is above the surface of the water, and the other in the water, are called plaiston. These include duckweed (Lemma), siphonophores (Siphonophora), etc.

Phytoplankton plays an important role in the life of reservoirs, as it is the main producer organic matter. Phytoplankton primarily includes diatoms (Diatomeae) and green algae (Chlorophyta), plant flagellates (Phytomastigina), peridineae (Peridineae) and coccolithophorids (Coccolitophoridae). Not only green algae, but also blue-green algae (Cyanophyta) are widespread in fresh waters.

Zooplankton and bacteria can be found at various depths. In fresh waters, mostly poorly swimming, relatively large crustaceans (Daphnia, Cyclopoidea, Ostrocoda), many rotifers (Rotatoria) and protozoa are common.

Marine zooplankton is dominated by small crustaceans (Copepoda, Amphipoda, Euphausiaceae) and protozoa (Foraminifera, Radiolaria, Tintinoidea). Large representatives include winged molluscs (Pteropoda), jellyfish (Scyphozoa) and swimming ctenophora (Ctenophora), salps (Salpae), and some worms (Aleiopidae, Tomopteridae).

Planktonic organisms serve as an important food component for many aquatic animals, including such giants as baleen whales (Mystacoceti), fig. 5.6.

Figure 5.6. Scheme of the main directions of energy and matter exchange in the ocean

Benthos(benthos - depth) is a set of organisms that live at the bottom (on the ground and in the ground) of reservoirs. It is divided into zoobenthos And phytobenthos. Mostly represented by attached, or slowly moving, or burrowing animals. 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) is absent. The marine zoobenthos is dominated by foraminiphores, sponges, coelenterates, worms, brachiopods, mollusks, ascidians, fish, etc. Benthic forms are more numerous in shallow waters. Their total biomass here can reach tens of kilograms per 1 m2.

The phytobenthos of the seas mainly includes algae (diatoms, green, brown, red) and bacteria. Along the coasts there are flowering plants - Zostera, Ruppia, Phyllospadix. Rocky and stony areas of the bottom are richest in phytobenthos.

In lakes, as in seas, there are plankton, nekton And benthos.

However, in lakes and other fresh water bodies there is less zoobenthos than in seas and oceans, and its species composition is uniform. These are mainly protozoa, sponges, ciliated and polychaete worms, leeches, mollusks, insect larvae, etc.

Freshwater phytobenthos is represented by bacteria, diatoms and green algae. Coastal plants are located from the shore inland in clearly defined belts. First belt - semi-submerged plants (reeds, cattails, sedges and reeds); second belt - submerged plants with floating leaves (water lilies, egg capsules, water lilies, duckweeds). IN third belt plants predominate - pondweed, elodea, etc. (Figure 5.7).

Rice. 5.7. Bottom-rooting plants (A):

1 - cattail; 2- rushwort; 3 - arrowhead; 4 - water lily; 5, 6 - pondweed; 7 - hara. Free floating algae (B): 8, 9 - filamentous green; 10-13 - green; 14-17 - diatoms; 18-20 - blue-green

Based on their lifestyle, aquatic plants are divided into two main ecological groups: hydrophytes - plants that are immersed in water only with their lower part and usually root in the ground, and hydatophytes - plants that are completely submerged in water and sometimes float on the surface or have floating leaves.

In life aquatic organisms a major role is played by the vertical movement of water, density, temperature, light, salt, gas (oxygen and carbon dioxide content) regimes, and the concentration of hydrogen ions (pH).

Temperature regime. It differs in water, firstly, by less heat influx, and secondly, by greater stability than on land. Part of the thermal energy arriving at the surface of the water is reflected, while part is spent on evaporation. The evaporation of water from the surface of reservoirs, which consumes about 2263x8 J/g, prevents overheating of the lower layers, and the formation of ice, which releases the heat of fusion (333.48 J/g), slows down their cooling.

Temperature changes in flowing waters follow its changes in the surrounding air, differing in smaller amplitude.

In lakes and ponds of temperate latitudes, the thermal regime is determined by a well-known physical phenomenon - water has a maximum density at 4°C. The water in them is clearly divided into three layers: upper - epilimnion, whose temperature experiences sharp seasonal fluctuations; transitional, temperature jump layer, -metalimnion, where there is a sharp temperature change; deep-sea (bottom) - hypolimnion reaching to the very bottom, where the temperature is throughout the year changes insignificant.

In summer, the warmest layers of water are located at the surface, and the coldest ones are located at the bottom. This type of layer-by-layer temperature distribution in a reservoir is called direct stratification In winter, as the temperature drops, 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 increases with depth. This phenomenon is called temperature dichotomy. It is observed in most of our lakes in summer and winter. As a result, vertical circulation is disrupted, density stratification of water is formed, and 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, surface waters cool again to 4°C and sink to the bottom, causing a second mixing of masses in the year with temperature equalization, i.e., the onset of autumn homothermy.

In the marine environment there is also thermal stratification determined by depth. The oceans have the following layers Surface- waters are exposed to the action of wind, and by analogy with the atmosphere this layer is called troposphere or sea thermosphere. Daily fluctuations in water temperature are observed here to approximately 50 meters depth, and seasonal fluctuations are observed even deeper. The thickness of the thermosphere reaches 400 m. Intermediate - represents constant thermocline. The temperature in different seas and oceans drops to 1-3°C. Extends to a depth of approximately 1500 m. Deep-sea - characterized by a uniform temperature of about 1-3°C, with the exception of the polar regions, where the temperature is close to 0°C.

IN In general, 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 it is 30-35 °C.

Rice. 5.8. Stratification and mixing of water in a lake

(after E. Gunter et al., 1982)

Deep layers of water are characterized by constant temperature. In equatorial waters average annual temperature In the surface layers it is 26-27°C, in the polar layers it is about 0°C and below. The exception is thermal springs, where the temperature of the surface layer reaches 85-93°C.

In water as a living environment, on the one hand, there is a fairly significant variety of temperature conditions, and on the other hand, 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 forms only on top, 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 the wintering buds (turions) of hornwort, bladderwort, waterwort, etc. sink (Fig. 5.9), as well as whole leafy plants, such as duckweed and elodea.

Rice. 5.9. Watercolor (Hydrocharias morsus ranae) in autumn.

Overwintering buds are visible, sinking to the bottom

(from T.K. Goryshinoya, 1979)

The opinion has been established that immersion is associated with the accumulation of starch and the weighting of plants. By spring, starch is converted into soluble sugars and fats, which makes the buds lighter and allows them to float.

Organisms in water bodies of temperate latitudes are well adapted to seasonal vertical movements of water layers, spring and autumn homothermy, and summer and winter stagnation. Since the temperature regime of water bodies is characterized by great stability, stenothermy is common among aquatic organisms to a greater extent than among terrestrial organisms.

Eurythermal species are found mainly in shallow continental reservoirs and in the littoral zone of seas of high and temperate latitudes, where daily and seasonal fluctuations are significant.

Density of water. Water differs from air in being more dense. In this respect, it is 800 times superior to the air. The density of distilled water at a temperature of 4 °C is 1 g/cm3. Density natural waters containing dissolved salts may be more: up to 1.35 g/cm3. On average, in the water column, for every 10 m of depth, pressure increases by 1 atmosphere. The high density of water is reflected in the body structure of hydrophytes. Thus, if in terrestrial plants mechanical tissues are well developed, providing the strength of trunks and stems, the arrangement of mechanical and conductive tissues along the periphery of the stem creates a “pipe” structure that is well resistant to kinks and bends, 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 it the ability to bend with water movements.

Submerged hydrophytes have good buoyancy created by special devices (air sacs, swellings). Thus, the frog leaves lie on the surface of the water and under each leaf they have a floating bubble filled with air. 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 area. This is clearly visible in microscopic planktonic algae. Various outgrowths of the body help them “float” freely in the water column.

Organisms in the aquatic environment are distributed throughout its entire thickness. For example, in oceanic depressions, animals are found at depths of over 10,000 m and endure pressure from several to hundreds of atmospheres. So, freshwater inhabitants(swimming beetles, slippers, suvoikas, etc.) can withstand up to 600 atmospheres in experiments. Holothurians of the genus Elpidia and worms Priapulus caudatus live from the coastal zone to the ultra-abyssal zone. At the same time, it should be noted that many inhabitants of the seas and oceans are relatively stenobatic and confined to certain depths. This applies primarily to shallow- and deep-sea species. Only the littoral zone is inhabited by the annelid worm Arenicola, mollusks - limpets(Patella). At great depths at a pressure of at least 400-500 atmospheres, fish from the group of anglers, cephalopods, crustaceans, starfish, pogonophora and others.

The density of water allows animal organisms to rely on it, which is especially important for non-skeletal forms. The support of the medium serves as a condition for floating in water. It is to this way of life that many aquatic organisms are adapted.

Light mode. Aquatic organisms are greatly influenced by light conditions and water transparency. 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, while the other is absorbed by its thickness. The attenuation of light is related to the transparency of the water. In oceans, for example, with great transparency, about 1% of radiation still falls to a depth of 140 m, and in small lakes with somewhat closed water, already to a depth of 2 m, only tenths of a percent.

Rice. 5.10. Illumination in water during the day.

Tsimlyansk Reservoir (according to A. A. Potapov,

Depth: 1 - on the surface; 2-0.5m; 3- 1.5 m; 4-2m

Due to the fact that the rays of different parts of the solar spectrum are absorbed differently by water, the spectral composition of light also changes with depth, and the red rays are weakened. Blue-green rays penetrate to considerable depths. The twilight in the ocean, which thickens with depth, is first green, then blue, indigo, blue-violet, later giving way to constant darkness. Accordingly, living organisms replace each other with depth.

Thus, plants living on the surface of the water do not experience a lack of light, while submerged and especially deep-sea plants are classified as “shadow flora”. They have to adapt not only to the lack of light, but also to changes in its composition by producing additional pigments. This can be seen in the known pattern of coloration in algae living at different depths. In shallow water zones, where plants still have access to red rays, which are absorbed to the greatest extent by chlorophyll, green algae tend to predominate. In deeper zones there are brown algae, which, in addition to chlorophyll, contain brown pigments phycaffeine, fucoxanthin, etc. Red algae containing the pigment phycoerythrin live even deeper. The ability to capture sunlight with different lengths waves. This phenomenon is called chromatic adaptation.

Deep-sea species have a number of physical traits characteristic of shade plants. Among them, it should be noted the low point of compensation for photosynthesis (30-100 lux), the “shadow nature” of the light curve of photosynthesis with a low saturation plateau, and in algae, for example, large chromatophores. Whereas for 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. Thus, arrowhead (Sagittaria sagittifolia) forms leaves of different shapes when developing on land and in water.

The hereditary program encodes the possibility of development in both directions. The “trigger mechanism” for the development of “water” forms of leaves is shading, and not the direct action of water.

Often the leaves of aquatic plants, immersed in water, are strongly dissected into narrow thread-like lobes, as, for example, in hornwort, uruti, bladderwort, or have a thin translucent plate - underwater leaves of egg capsules, water lilies, leaves of submerged pondweeds.

These features are also characteristic of algae, such as filamentous algae, dissected thalli of Characeae, and thin transparent thalli of many deep-sea species. This makes it possible for hydrophytes to increase the ratio of body area to volume, and therefore to develop a larger surface area at a relatively low cost of organic mass.

In plants partially submerged in water, the heterophilia, i.e., the difference in the structure of above-water and underwater leaves of the same plant: This is clearly visible in the aquatic buttercup (Fig. 5.11) The above-water ones have features common to the leaves of above-ground plants (dorsoventral structure, well-developed integumentary tissues and stomatal apparatus) , underwater - very thin or dissected leaf blades. Heterophily has also been noted in water lilies and egg capsules, arrowheads and other species.

Rice. 5.11. Heterophily in the aquatic buttercup

Ranunculus diversifolius (from T, G. Goryshina, 1979)

Leaves: 1 - above-water; 2 - underwater

An illustrative example is the caddisfly (Simn latifolium), on the stem of which you can see several forms of leaves, 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 the layer of water, into which the amount of light sufficient for photosynthesis penetrates. The lower boundary of this layer is called the compensation level. Above this depth, plants release more oxygen than they consume, and 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.

Brightly and variously colored animals live in light, surface layers of water, while deep-sea species are usually devoid of pigments. In the twilight zone of the ocean, animals live that are colored with a reddish tint, which helps them hide from enemies, since the red color in blue-violet rays is perceived as black. Red coloring is characteristic of twilight zone animals such as sea bass, red coral, various crustaceans, etc.

The absorption of light in water is stronger, the lower its transparency, which is due to the presence of mineral particles (clay, silt) in it. The transparency of water also decreases with the rapid growth of aquatic vegetation in the summer or with the mass reproduction of small organisms suspended in the surface layers. Transparency is characterized by extreme depth, where a specially lowered Secchi disk (a white disk with a diameter of 20 cm) is still visible. In the Sargasso Sea (the most clear waters) the Secchi disk is visible to a depth of 66.5 m, in the Pacific Ocean - up to 59, in the Indian - 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 the Amu Darya and Syrdarya - a few centimeters. Hence, the boundaries of photosynthesis zones vary greatly in different bodies of water. In the most clean waters the photosynthesis zone, or 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 the time of year. Thus, long polar nights greatly limit the time suitable for photosynthesis in the Arctic and Antarctic basins, and ice cover makes it difficult for light to access all frozen water bodies in winter.

Salt regime. The salinity of water or salt regime plays an important role in the life of aquatic organisms. The chemical composition of waters is formed under the influence of natural historical and geological conditions, as well as anthropogenic impact. The content of chemical compounds (salts) in water determines its salinity and is expressed in grams per liter or in per mile(°/od). According to the general mineralization, waters can be divided into fresh 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 solutes in water are carbonates, sulfates and chlorides (Table 5.1).

Table 5.1

Composition of basic salts in various reservoirs (according to R. Dazho, 1975)

Among fresh waters, there are many that are almost pure, but there are also many that contain up to 0.5 g of dissolved substances per liter. Cations according to 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, sometimes significant, are possible.

An important element in fresh water is calcium content. Calcium may act as a limiting factor. There are “soft” waters, low in calcium (less than 9 mg per 1 liter), and “hard” waters, which contain large amounts of calcium (more than 25 mg per 1 liter).

In sea water, the average content of dissolved salts is 35 g/l, in marginal seas it is much lower. 13 metalloids and at least 40 metals have been found in seawater. In terms of importance, table salt ranks first, 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 dissolved substances 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 fresh water aquatic organisms are forced to intensively remove it. They have well-expressed 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 secrete an amount of water equal to their body volume every 2-2.5 minutes.

With increasing 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 the body fluids and tissues of many marine organisms is isotonic with the concentration of dissolved salts in the surrounding water. In this regard, their osmoregulatory functions are less developed than those of freshwater animals. Osmoregulation is one of the reasons that many marine plants and animals failed to populate fresh water bodies and turned out to be typical marine inhabitants: coelenterata (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 basins are abundantly populated 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 much. They are found, often in large quantities, in brackish waters. These are such as bream (Abramis brama), freshwater pike perch (Stizostedion lucioperca), pike (Ezox lucios), and 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 water regime in plants literally surrounded by water. Such plants do not have transpiration, and therefore there is no “upper engine” that maintains the flow of water in the plant. And at the same time, the current that delivers nutrients to the tissues exists (though much weaker than in land plants), with a clearly defined daily frequency: more during the day, absent at night. An active role in its maintenance belongs to root pressure (in attached species) and the activity of special cells that secrete water - water stomata or hydathodes.

In fresh waters, plants fixed on the bottom of the reservoir are common. Often their photosynthetic surface is located above the water. These include reeds (Scirpus), water lilies (Nymphaea), egg capsules (Nyphar), cattails (Typha), arrowhead (Sagittaria). In others, the photosynthetic organs are submerged in water. These are pondweed (Potamogeton), urut (Myriophyllum), elodea (Elodea). Certain types of higher freshwater plants are rootless and float freely or grow over underwater objects, algae, which are attached to the ground.

Gas mode. The main gases in the aquatic environment are oxygen and carbon dioxide. The rest, such as hydrogen sulfide or methane, are of secondary importance.

Oxygen for the aquatic environment - the most important environmental factor. It enters water from the air and is released by plants during photosynthesis. The diffusion coefficient of oxygen in water is approximately 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. As the temperature and salinity of water increase, the concentration of oxygen in it decreases. In layers heavily populated by animals and bacteria, oxygen deficiency may occur due to increased oxygen consumption. Thus, in the World Ocean, life-rich depths from 50 to 1000 m are characterized by a sharp deterioration in aeration. It is 7-10 times lower than in surface waters inhabited by phytoplankton. Conditions near the bottom of reservoirs can be close to anaerobic.

With stagnation in small bodies of water, the water is also sharply depleted of oxygen. Its deficiency can also occur in winter under ice. At a concentration below 0.3-3.5 ml/l, the life of aerobes in water is impossible. The oxygen content under reservoir conditions turns out to be a limiting factor (Table 5.2).

Table 5.2

Oxygen requirements in different species freshwater fish

Among aquatic inhabitants there are a significant number of species that can tolerate wide fluctuations in 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, and crucian carp can withstand very low oxygen saturation of fish from fish. However, many species are stenoxybiont, 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, the so-called anoxybiosis, and thus experience an unfavorable period.

Respiration of aquatic organisms occurs 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 there is a combination of water and air respiration, for example, lungfishes, siphonophores, discophants, many lung molluscs, crustaceans Yammarus lacustris, etc. Secondary aquatic animals usually retain the atmospheric type of respiration as energetically more favorable, and therefore require 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 water as a result of the dissolution of CO 2 contained in the air, the respiration of aquatic organisms, the decomposition of organic residues and release from carbonates. The carbon dioxide content in water ranges from 0.2-0.5 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 invertebrate animals and ensures photosynthesis of aquatic plants. With intense 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 respond to an increase in CO 2 content in water by increasing photosynthesis.

An additional source of CO for photosynthesis of aquatic plants is also carbon dioxide, which is released during the decomposition of bicarbonate salts and their transformation into carbon dioxide:

Ca(HCO 3) 2 -> CaCO 3 + CO, + H 2 O

The poorly soluble carbonates that form 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.

Hydrogen ion concentration(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, and with a pH of more than 7.8 - alkaline. In fresh water bodies, pH experiences significant fluctuations, often during the day. Sea water is more alkaline and its pH changes less than fresh water. pH decreases with depth.

From plants with a pH less than 7.5, grasshopper (Jsoetes) and hogweed (Sparganium) grow. In an alkaline environment (pH 7.7-8.8), many types of pondweed and elodea are common; at pH 8.4-9, Typha angustifolia reaches strong development. The acidic waters of peat bogs promote the development of sphagnum mosses.

Most freshwater fish can tolerate a pH between 5 and 9. If the pH is less than 5, there is a massive death of fish, and above 10, all fish and other animals die.

In lakes with an acidic environment, larvae of dipterans of the genus Chaoborus are often found, and in the acidic waters of swamps, shell rhizomes (Testaceae) are common, lamellar-branch mollusks of the genus Unio are absent, and other mollusks are rarely found.

Ecological plasticity of organisms in the aquatic environment. Water is a more stable environment, and abiotic factors undergo relatively minor fluctuations, and hence aquatic organisms have less ecological plasticity compared to terrestrial ones. Freshwater plants and animals are more plastic than marine ones, since freshwater as a living environment is more variable. The breadth of ecological plasticity of aquatic organisms is assessed not only as a whole to a complex of factors (eury- and stenobionticity), but also individually.

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 the temperature conditions and salt regime near the shore are quite variable - warming by the sun and relatively intense cooling, desalination by the influx of water from streams and rivers , in particular during the rainy season, etc. An example is the lotus, which is a typical stenothermic species and grows only in shallow, well-warmed reservoirs. Inhabitants of the surface layers, compared to deep-sea forms, for the above reasons, turn out to be more eurythermic and euryhaline.

Ecological 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), which lives in small reservoirs with very salty water and 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 as an adult at low tide daily long time does without water, but its larvae lead a planktonic lifestyle and cannot tolerate drying out.

Features of plant adaptation to the aquatic environment. Water paradise| Sthenias 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. Characteristic of aquatic plants is the poor development of conductive tissue and the root system. The root system serves mainly for attachment to the underwater substratum 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. Lower plants that inhabit various layers and lead a floating lifestyle have special appendages for this purpose that increase their buoyancy and allow them to remain suspended. Higher hydrophytes have poorly developed mechanical tissue. How yni As noted above, 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 contributes to the washing away of the internal cells by water with salts and gases dissolved in it. Hydrophytes are distinguished| They have 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 heterophilia. Thus, in Salvinia, submerged leaves provide mineral nutrition, while floating leaves provide organic nutrition.

An important feature of plant adaptation to living in water | This environment is also due to the fact that leaves immersed in water are usually very thin. Often the chlorophyll in them is located in the epidermal cells, which helps to increase the intensity of photosynthesis in low light. Such anatomical and morphological features are most clearly expressed in water mosses (Riccia, Fontinalis), Vallisneria spiralis, and pondweeds (Potamageton).

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.

Relatively low temperature in 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, tender summer leaves with tougher and shorter winter leaves. Low water temperature negatively affects the generative organs of aquatic plants, and its high density makes it difficult to transfer 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. 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 hydrochoria. 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 transports the fruits and seeds of arrowhead (Sagittaria sagittofolia), commonweed (Butomus umbellatus), and chastukha (Alisma plantago-aguatica). The fruits of many sedges (Carex) are enclosed in peculiar air sacs and are carried by water currents. In the same way, the humai weed (Sorgnum halepense) spread along the Vakht River along the canals.

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 such as anatomical-morphological, behavioral etc.

Animals that live in the water column primarily have adaptations that increase their buoyancy and allow them to resist 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, Rhizopoda), the shells are porous, and the flint spines of the skeleton are hollow inside. The specific density of ctenophora and jellyfish (Scyphozoa) decreases due to the presence of water in the tissues. The accumulation of fat droplets in the body (noctils - Noctiluca, radiolarians - Radiolaria) helps to increase buoyancy. Large accumulations of fat are observed in some crustaceans (Cladocera, Copepoda), fish and cetaceans. The specific density of the body is reduced and thereby increased buoyancy by gas-filled swim bladders, which many fish have. 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 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 (Leptodiscus, Craspeditella), radiolarians (Aulacantha, Chalengeridae), etc.

A large group of animals that live in fresh water use the surface tension of water (surface film) when moving. Water strider bugs (Gyronidae, Veliidae), whirling beetles (Gerridae), 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 (F) 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 mass increases in proportion to the cube of size, and 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. I will achieve the greatest perfection in the jet mode of transportation. cephalopods. Thus, some squids develop speeds of up to 40-50 km/h when throwing out water (Fig. 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 motionless animals leading an attached lifestyle found. 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 (body density is greater than the density of water) and special devices for attachment to substrate.

Aquatic animals are mostly poikilothermic. In homothermal mammals, for example, (cetaceans, pinnipeds), a significant layer of subcutaneous fat is formed, which performs a heat-insulating 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 remove excess water by working hard excretory system, and salts are absorbed through the gill filaments. Marine fish are forced to replenish their water reserves and therefore drink sea water, and excess salts supplied with water are removed from the body through the gill filaments (Fig. 5.13).

Rice. 5.13. Excretion and osmoregulation in freshwater teleosts

fish (A), elasmobranchs (B) and marine bony fish (C)

The abbreviations hypo-, iso- and hyper- indicate the tonicity of the internal environment in relation to the external one (from N. Green et al., 1993)

A number of 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 expenditures of energy in search of prey and is typical for elasmobranch mollusks, sessile echinoderms, ascidians, planktonic crustaceans, etc. Filter-feeding animals play an important role in biological treatment reservoirs.

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 per day through the mantle cavity, precipitating suspended particles.

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 infrasounds. Sound signaling serves most of all for intraspecific relationships: orientation in a flock, attracting individuals of the opposite sex, etc. Cetaceans, for example, look for food and orient themselves 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. A number of fish (electric stingray, electric eel, etc.) use electric fields for defense and attack.

Characteristic of aquatic organisms ancient way orientation - perception of the chemistry of the environment. The chemoreceptors of many hydrobionts (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 (descending into the depths, 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 appear after river floods, heavy rains, snow melting, etc. General Features inhabitants of drying up reservoirs is the ability to give birth to 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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Distribution of organisms by living environment

In the process of the long historical development of living matter and the formation of ever more advanced forms of living beings, organisms, mastering new habitats, were distributed on Earth according to its mineral shells (hydrosphere, lithosphere, atmosphere) and adapted to existence in strictly defined conditions.

The first medium of life was water. It was in it that life arose. As historical development progressed, many organisms began to populate the land-air environment. As a result, land plants and animals appeared, which rapidly evolved, adapting to new living conditions.

In the process of functioning of living matter on land, the surface layers of the lithosphere were gradually transformed into soil, into a kind of, as V.I. Vernadsky put it, a bioinert body of the planet. The soil began to be populated by both aquatic and terrestrial organisms, creating a specific complex of its inhabitants.

Thus, on modern Earth Four environments of life are clearly distinguished - aquatic, ground-air, soil and living organisms - which differ significantly in their conditions. Let's look at each of them.

General characteristics. The aquatic environment of life, the hydrosphere, occupies up to 71% of the globe's area. In terms of volume, water reserves on Earth are estimated at 1370 million cubic meters. km, which is 1/800 of the volume of the globe. The main amount of water, more than 98%, is concentrated in the seas and oceans, 1.24% is represented by the ice of the polar regions; in fresh waters of rivers, lakes and swamps, the amount of water does not exceed 0.45%.

About 150,000 species of animals live in the aquatic environment (approximately 7% of their total number in globe) and 10,000 plant species (8%). Despite the fact that representatives of the vast majority of groups of plants and animals remained in the aquatic environment (in their “cradle”), the number of their species is significantly less than that of terrestrial ones. This means that evolution on land took place much faster.

The most diverse and rich flora and fauna of the seas and oceans of the equatorial and tropical regions (especially the Pacific and Atlantic oceans). To the south and north of these belts, the qualitative composition of organisms gradually becomes depleted. In the area of ​​the East Indian archipelago, there are about 40,000 species of animals, and in the Laptev Sea there are only 400. Moreover, the bulk of the organisms of the World Ocean are concentrated in a relatively small area of ​​the sea coasts of the temperate zone and among the mangroves of tropical countries. In vast areas of water far from the coast there are desert areas, practically devoid of life.

The share of rivers, lakes and swamps in the biosphere is insignificant compared to that of the seas and oceans. Nevertheless, they create the supply of fresh water necessary for a huge number of plants and animals, as well as for humans.

The aquatic environment has a strong influence on its inhabitants. In turn, the living matter of the hydrosphere affects the habitat, processes it, involving it in the cycle of substances. It is estimated that the water of the seas and oceans, rivers and lakes decomposes and is restored in the biotic cycle within 2 million years, i.e. all of it has passed through the living matter of the planet more than one thousand times*. Thus, the modern hydrosphere is a product of the vital activity of living matter not only of modern, but also of past geological eras.

A characteristic feature of the aquatic environment is its mobility even in stagnant bodies of water, not to mention flowing, fast-flowing rivers and streams. The seas and oceans experience ebbs and flows, powerful currents, and storms; In lakes, water moves under the influence of wind and temperature. The movement of water ensures the supply of aquatic organisms with oxygen and nutrients and leads to an equalization (decrease) in temperature throughout the entire reservoir.

The inhabitants of reservoirs have developed appropriate adaptations to the mobility of the environment. For example, in flowing water bodies there are so-called “fouling” plants firmly attached to underwater objects - green algae (Cladophora) with a trail of shoots, diatoms (Diatomeae), water mosses (Fontinalis), forming a dense cover even on stones in rapid river riffles .

Animals also adapted to the mobility of the aquatic environment. In fish that live in fast-flowing rivers, the body is almost round in cross section (trout, minnow). They usually move against the current. Invertebrates of flowing water bodies usually stay at the bottom, their body is flattened in the dorso-ventral direction, many have various fixation organs on the ventral side, allowing them to attach to underwater objects. In the seas, the strongest influence of moving masses of water is experienced by organisms in the tidal and surf zones. On rocky shores in the surf, barnacles (Balanus, Chthamalus), gastropods (Patella Haliotis), and some species of crustaceans hiding in the crevices of the shore are common.

In the life of aquatic organisms in temperate latitudes, the vertical movement of water in standing reservoirs plays an important role. The water in them is clearly divided into three layers: the upper epilimnion, the temperature of which experiences sharp seasonal fluctuations; temperature jump layer – metalimnion (thermocline), where a sharp temperature difference is observed; bottom deep layer, hypolimnion, where the temperature changes slightly throughout the year.

In summer, the warmest layers of water are located at the surface, and the coldest ones are located at the bottom. This layer-by-layer distribution of temperatures in a reservoir is called direct stratification. In winter, with a decrease in temperature, a reverse stratification is observed: cold surface waters with temperatures below 4 °C are located above relatively warm ones. This phenomenon is called temperature dichotomy. It is especially pronounced in most of our lakes in summer and winter. As a result of temperature dichotomy, a density stratification of water is formed in a reservoir, its vertical circulation is disrupted and a period of temporary stagnation begins.

In spring, surface water, due to heating to 4 °C, becomes denser and sinks deeper, and warmer water rises from the depths to take its place. As a result of such vertical circulation in the reservoir, homothermy occurs, i.e., for some time the temperature of the entire water mass leveled out. 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 layer cools, becomes denser and sinks deeper, displacing warmer water to the surface. This occurs before the onset of autumn homothermy. When surface waters cool below 4 °C, they again become less dense and again remain on the surface. As a result, water circulation stops and winter stagnation occurs.

Organisms in water bodies of temperate latitudes are well adapted to seasonal vertical movements of water layers, to spring and autumn homothermy and to summer and winter stagnation (Fig. 13).

In lakes at tropical latitudes, the surface water temperature never drops below 4 °C and the temperature gradient in them is clearly expressed down to the deepest layers. Mixing of water, as a rule, occurs here irregularly during the coldest time of the year.

Peculiar conditions for life develop not only in the water column, but also at the bottom of the reservoir, since there is no aeration in the soils and mineral compounds are washed out of them. Therefore, they do not have fertility and serve only as a more or less solid substrate for aquatic organisms, performing mainly a mechanical-dynamic function. In this regard, the size of soil particles, the density of their contact with each other and resistance to washout by currents acquire the greatest environmental significance.

Abiotic factors of the aquatic environment. Water as a living environment has special physical and chemical properties.

The temperature regime of the hydrosphere is fundamentally different from that in other environments. Temperature fluctuations in the World Ocean are relatively small: the lowest is about –2 °C, and the highest is approximately 36 °C. The amplitude of oscillations here, therefore, falls within 38 °C. With depth, the temperature of water in the oceans drops. Even in tropical areas at a depth of 1000 m it does not exceed 4–5°C. At the depths of all oceans there is a layer of cold water (from -1.87 to +2°C).

In fresh inland reservoirs of temperate latitudes, the temperature of the surface layers of water ranges from – 0.9 to +25 ° C, in deeper waters it is 4–5 ° C. The exception is thermal springs, where the temperature of the surface layer sometimes reaches 85–93 °C.

Thermodynamic features of the aquatic environment, such as high specific heat capacity, high thermal conductivity and expansion upon freezing, create particularly favorable conditions for life. These conditions are also ensured by the high latent heat of fusion of water, as a result of which in winter the temperature under the ice is never below its freezing point (for fresh water about 0 ° C). Since water has the greatest density at 4° C, and when it freezes it expands, in winter ice forms only on top, but the main thickness does not freeze.

Since the temperature regime of water bodies is characterized by great stability, the organisms living in it are characterized by a relative constancy of body temperature and have a narrow range of adaptability to fluctuations in environmental temperature. Even minor deviations in thermal mode All can lead to significant changes in the lives of animals and plants. An example is the “biological explosion” of the lotus (Nelumbium caspium) in the northernmost part of its habitat - in the Volga delta. For a long time this exotic plant inhabited only a small bay. Over the last decade, the area of ​​lotus thickets has increased almost 20 times and now occupies over 1,500 hectares of water area. This rapid spread of the lotus is explained by the general drop in the level of the Caspian Sea, which was accompanied by the formation of many small lakes and estuaries at the mouth of the Volga. On hot days summer months The water here warmed up more than before, which contributed to the growth of lotus thickets.

Water is also characterized by significant density (in this regard, it is 800 times greater than the air medium) and viscosity. These features affect plants in the fact that their mechanical tissue develops very weakly or not at all, so their stems are very elastic and bend easily. Most aquatic plants are characterized by buoyancy and the ability to be suspended in the water column. They rise to the surface and then fall again. In many aquatic animals, the integument is abundantly lubricated with mucus, which reduces friction during movement, and the body takes on a streamlined shape.

Organisms in the aquatic environment are distributed throughout its entire thickness (in oceanic depressions, animals were found at depths of over 10,000 m). Naturally, at different depths they experience different pressures. Deep sea creatures are adapted to high blood pressure(up to 1000 atm), the inhabitants of the surface layers are not susceptible to it. On average, in the water column, for every 10 m of depth, pressure increases by 1 atm. All hydrobionts are adapted to this factor and are accordingly divided into deep-sea and those living at shallow depths.

Water transparency and its light regime have a great influence on aquatic organisms. This especially affects the distribution of photosynthetic plants. In muddy reservoirs they live only in the surface layer, and where there is greater transparency, they penetrate to significant depths. A certain turbidity of water is created by a huge number of particles suspended in it, which limits the penetration of sunlight. Turbidity in water can be caused by particles of mineral substances (clay, silt) and small organisms. The transparency of water also decreases in summer with the rapid growth of aquatic vegetation and the mass reproduction of small organisms suspended in the surface layers. The light regime of reservoirs also depends on the season. In the north in temperate latitudes When water bodies freeze and the ice on top is still covered with snow, the penetration of light into the water column is greatly limited.

The light regime is also determined by the natural decrease in light with depth due to the fact that water absorbs sunlight. In this case, rays with different wavelengths are absorbed differently: red ones are absorbed most quickly, while blue-green ones penetrate to significant depths. The ocean becomes darker with depth. The color of the environment changes, gradually moving from greenish to green, then to blue, blue, blue-violet, giving way to constant darkness. Accordingly, with depth, green algae (Chlorophyta) are replaced by brown (Phaeophyta) and red (Rhodophyta), the pigments of which are adapted to capture sunlight of different wavelengths. The color of animals also naturally changes with depth. In the surface, light layers of water, brightly and variously colored animals usually live, while deep-sea species are devoid of pigments. In the twilight zone of the ocean, animals live that are colored with a reddish tint, which helps them hide from enemies, since the red color in blue-violet rays is perceived as black.

The salinity of water plays an important role in the life of aquatic organisms. As you know, water is an excellent solvent for many mineral compounds. As a result, natural reservoirs are characterized by a certain chemical composition. Highest value have carbonates, sulfates, chlorides. The amount of dissolved salts per 1 liter of water in fresh water bodies does not exceed 0.5 g (usually less); in the seas and oceans it reaches 35 g (Table 6).

Table 6.Distribution of basic salts in various reservoirs (according to R. Dazho, 1975)

Calcium plays an essential role in the life of freshwater animals. Mollusks, crustaceans and other invertebrates use it to build shells and the exoskeleton. But fresh water bodies, depending on a number of circumstances (the presence of certain soluble salts in the soil of the reservoir, in the soil and soil of the banks, in the water of inflowing rivers and streams) vary greatly both in composition and in the concentration of salts dissolved in them. Sea waters are more stable in this regard. Almost all known elements were found in them. However, in terms of importance, table salt takes first place, then magnesium chloride and sulfate and potassium chloride.

Freshwater plants and animals live in a hypotonic environment, that is, an environment in which 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, and freshwater hydrobionts are forced to intensively remove it. In this regard, their osmoregulation processes are well expressed. The concentration of salts in the body fluids and tissues of many marine organisms is isotonic with the concentration of dissolved salts in the surrounding water. Therefore, their osmoregulatory functions are not developed to the same extent as in freshwater animals. Difficulties in osmoregulation are one of the reasons that many marine plants and especially animals were unable to populate fresh water bodies and turned out, with the exception of certain representatives, to be typical marine inhabitants (coelenterata - Coelenterata, echinoderms - Echinodermata, pogonophora - Pogonophora, sponges - Spongia, tunicates – Tunicata). At that same Insects practically do not live in the seas and oceans, while freshwater basins are abundantly populated by them. Typically marine and typically freshwater species do not tolerate significant changes in water salinity. All of them are stenohaline organisms. There are relatively few euryhaline animals of freshwater and marine origin. They are usually found, and in significant quantities, in brackish waters. These are freshwater pike perch (Stizostedion lucioperca), bream (Abramis brama), pike (Esox lucius), and the sea mullet family (Mugilidae).

In fresh waters, plants fixed on the bottom of the reservoir are common. Often their photosynthetic surface is located above the water. These are cattails (Typha), reeds (Scirpus), arrowheads (Sagittaria), water lilies (Nymphaea), egg capsules (Nuphar). In others, the photosynthetic organs are submerged in water. These include pondweed (Potamogeton), urut (Myriophyllum), and elodea (Elodea). Some higher plants fresh waters are devoid of roots. They either float freely or grow over underwater objects or algae attached to the ground.

While oxygen does not play a significant role in the air environment, it is the most important environmental factor in the water environment. Its content in water is inversely proportional to temperature. With decreasing temperature, the solubility of oxygen, like other gases, increases. The accumulation of oxygen dissolved in water occurs as a result of its entry from the atmosphere, as well as due to the photosynthetic activity of green plants. When water is mixed, which is typical for flowing reservoirs and especially for fast-flowing rivers and streams, the oxygen content also increases.

Different animals have different needs for oxygen. For example, trout (Salmo trutta) and minnow (Phoxinus phoxinus) are very sensitive to its deficiency and therefore live only in fast-flowing, cold and well-mixed waters. Roach (Rutilus rutilus), ruffe (Acerina cernua), carp (Cyprinus carpio), crucian carp (Carassius carassius) are unpretentious in this regard, and the larvae of chironomid mosquitoes (Chironomidae) and tubifex worms (Tubifex) live at great depths, where there is no oxygen at all or very little. Aquatic insects and mollusks (Pulmonata) can also live in bodies of water with low oxygen levels. However, they systematically rise to the surface, storing fresh air for some time.

Carbon dioxide is approximately 35 times more soluble in water than oxygen. There is almost 700 times more of it in water than in the atmosphere from where it comes. In addition, carbonates and bicarbonates of alkali and alkaline earth metals are a source of carbon dioxide in water. Carbon dioxide contained in water ensures photosynthesis of aquatic plants and takes part in the formation of calcareous skeletal structures of invertebrate animals.

The concentration of hydrogen ions (pH) is of great importance in the life of aquatic organisms. Freshwater pools with a pH of 3.7–4.7 are considered acidic, 6.95–7.3 are considered neutral, and those with a pH greater than 7.8 are alkaline. In fresh water bodies, pH even experiences daily fluctuations. Sea water is more alkaline and its pH changes much less than fresh water. pH decreases with depth.

The concentration of hydrogen ions plays a large role in the distribution of aquatic organisms. At a pH of less than 7.5, grasshopper (Isoetes) and burberry (Sparganium) grow; at 7.7–8.8, i.e., in an alkaline environment, many types of pondweed and elodea develop. In the acidic waters of swamps, sphagnum mosses (Sphagnum) predominate, but elasmobranch mollusks of the genus Unio are absent; other mollusks are rare, but shell rhizomes (Testacea) are abundant. Most freshwater fish can withstand a pH between 5 and 9. If the pH is less than 5, there is a massive death of fish, and above 10, all fish and other animals die.

Ecological groups of hydrobionts. The water column - pelagic (pelagos - sea) is inhabited by pelagic organisms that can actively swim or stay (float) in certain layers. In accordance with this, pelagic organisms are divided into two groups - nekton and plankton. Bottom inhabitants form the third ecological group of organisms - benthos.

Nekton (nekios–· floating)– This is a collection of pelagic actively moving animals that do not have a direct connection with the bottom. These are mainly large animals that can overcome long distances and strong water currents. They are characterized by a streamlined body shape and well-developed organs of movement. Typical nektonic organisms are fish, squid, pinnipeds, and whales. In fresh waters, in addition to fish, nekton includes amphibians and actively moving insects. Many marine fish can move through the water at great speed. Some squids (Oegopsida) swim very quickly, up to 45–50 km/h, sailfish (Istiopharidae) reach speeds of up to 100–10 km/h, and swordfish (Xiphias glabius) reach speeds of up to 130 km/h.

Plankton– soaring, wandering)– This is a set of pelagic organisms that do not have the ability for rapid active movements. Planktonic organisms cannot resist currents. These are mainly small animals - zooplankton and plants - phytoplankton. The plankton periodically includes the larvae of many animals floating in the water column.

Planktonic organisms are located either on the surface of the water, or at depth, or even in the bottom layer. The first form a special group – neuston. Organisms, part of whose body is located in water, and part of which is above its surface, are called pleuston. These are siphonophores (Siphonophora), duckweed (Lemna), etc.

Phytoplankton is of great importance in the life of water bodies, since it is the main producer of organic matter. It includes primarily diatoms (Diatomeae) and green algae (Chlorophyta), plant flagellates (Phytomastigina), peridineae (Peridineae) and coccolithophorids (Coccolitophoridae). IN northern waters The world's oceans are dominated by diatoms, and in tropical and subtropical regions - armored flagellates. In fresh waters, in addition to diatoms, green and blue-green algae (Suanophyta) are common.

Zooplankton and bacteria are found at all depths. Marine zooplankton is dominated by small crustaceans (Copepoda, Amphipoda, Euphausiacea) and protozoa (Foraminifera, Radiolaria, Tintinnoidea). Its larger representatives are pteropods (Pteropoda), jellyfish (Scyphozoa) and swimming ctenophora (Ctenophora), salps (Salpae), and some worms (Alciopidae, Tomopteridae). In fresh waters, poorly swimming, relatively large crustaceans (Daphnia, Cyclopoidea, Ostracoda, Simocephalus; Fig. 14), many rotifers (Rotatoria) and protozoa are common.

The greatest species diversity is achieved by plankton in tropical waters.

Groups of planktonic organisms are differentiated by size. Nannoplankton (nannos - dwarf) are the smallest algae and bacteria; microplankton (micros – small) – most algae, protozoa, rotifers; mesoplankton (mesos - middle) - copepods and cladocerans, shrimp and a number of animals and plants, no more than 1 cm in length; macroplankton (macros - large) - jellyfish, mysids, shrimp and other organisms larger than 1 cm; megaloplankton (megalos – huge) – very large, over 1 m, animals. For example, the swimming ctenophore (Cestus veneris) reaches a length of 1.5 m, and the cyanea jellyfish (Suapea) has a bell with a diameter of up to 2 m and tentacles 30 m long.

Planktonic organisms are an important food component of many aquatic animals (including such giants as baleen whales - Mystacoceti), especially considering that they, and especially phytoplankton, are characterized by seasonal outbreaks of mass reproduction (water blooms).

Benthos– depth)– a set of organisms living at the bottom (on the ground and in the ground) of water bodies. It is divided into phytobenthos and zoobenthos. Mainly represented by attached or slowly moving animals, as well as burrowing animals. Only in shallow water does it consist of organisms that synthesize organic matter (producers), consume (consumers) and destroy (decomposers) it. At great depths, where light does not penetrate, phytobenthos (producers) is absent.

Benthic organisms differ in their lifestyle - mobile, sedentary and immobile; by feeding method - photosynthetic, carnivorous, herbivorous, detritivorous; by size – macro-, meso-microbenthos.

The phytobenthos of the seas mainly includes bacteria and algae (diatoms, green, brown, red). Flowering plants are also found along the coasts: Zostera, Phyllospadix, and Rup-pia. The richest phytobenthos is in rocky and stony areas of the bottom. Along the coasts, kelp (Laminaria) and fucus (Fucus) sometimes form a biomass of up to 30 kg per 1 sq. m. On soft soils, where plants cannot firmly attach, phytobenthos develops mainly in places protected from waves.

Fresh water phytobenzos is represented by bacteria, diatoms and green algae. Coastal plants are abundant, located inland from the shore in clearly defined belts. In the first zone, semi-submerged plants grow (reeds, reeds, cattails and sedges). The second zone is occupied by submerged plants with floating leaves (water lilies, duckweeds, water lilies). The third zone is dominated by submerged plants - pondweed, elodea, etc.

According to their lifestyle, all aquatic plants can be divided into two main ecological groups: hydrophytes - plants that are submerged in water only with their lower part and usually root in the ground, and hydatophytes - plants that are completely submerged in water, but sometimes float on the surface or have floating leaves.

The marine zoobenthos is dominated by foraminifera, sponges, coelenterates, nemerteans, polychaete worms, sipunculids, bryozoans, brachiopods, mollusks, ascidians, and fish. Benthic forms are most numerous in shallow waters, where their total biomass often reaches tens of kilograms per square meter. m. With depth, the number of benthos drops sharply and at great depths amounts to milligrams per 1 sq. m.

In fresh water bodies there is less zoobenthos than in the seas and oceans, and the species composition is more uniform. These are mainly protozoans, some sponges, ciliated and oligochaete worms, leeches, bryozoans, mollusks and insect larvae.

Ecological plasticity of aquatic organisms. Aquatic organisms have less ecological plasticity than terrestrial ones, since water is a more stable environment and its abiotic factors undergo relatively minor fluctuations. Marine plants and animals are the least plastic. They are very sensitive to changes in water salinity and temperature. Thus, madrepore corals cannot withstand even weak desalination of water and live only in the seas, moreover, on solid ground at a temperature not lower than 20 ° C. These are typical stenobionts. However, there are species with increased ecological plasticity. For example, the rhizome Cyphoderia ampulla is a typical eurybiont. It lives in seas and fresh waters, in warm ponds and cold lakes.

Freshwater animals and plants are generally much more flexible than marine ones, since freshwater as a living environment is more variable. The most flexible are the brackish-water inhabitants. They are adapted to both high concentrations of dissolved salts and significant desalination. However, there are a relatively small number of species, since environmental factors undergo significant changes in brackish waters.

The breadth of ecological plasticity of aquatic organisms is assessed in relation not only to the entire complex of factors (eury- and stanobionticity), but also to any one of them. Coastal plants and animals, in contrast to the inhabitants of open zones, are mainly eurythermic and euryhaline organisms, since near the shore the temperature conditions and salt regime are quite variable (warming by the sun and relatively intense cooling, desalination by the influx of water from streams and rivers, especially during the rainy season, and etc.). A typical stenothermic species is the lotus. It grows only in well-warmed shallow reservoirs. For the same reasons, the inhabitants of the surface layers turn out to be more eurythermic and euryhaline in comparison with deep-sea forms.

Ecological plasticity serves as an important regulator of the dispersal of organisms. As a rule, aquatic organisms with high ecological plasticity are quite widespread. This applies, for example, to elodea. However, the crustacean brine shrimp (Artemia salina) is diametrically opposed to it in this sense. It lives in small bodies of water with very salty water. This is a typical stenohaline representative with narrow ecological plasticity. But in relation to other factors, it is very plastic and therefore is found everywhere in salt water bodies.

Ecological plasticity depends on the age and developmental phase of the organism. Thus, the marine gastropod Littorina, as an adult, goes without water for a long time every day during low tides, and its larvae lead a purely planktonic lifestyle and cannot tolerate drying out.

Adaptive features of aquatic plants. The ecology of aquatic plants, as noted, is very specific and differs sharply from the ecology of most terrestrial plant organisms. The ability of aquatic plants to absorb moisture and mineral salts directly from the environment is reflected in their morphological and physiological organization. Aquatic plants are primarily characterized by poor development of conductive tissue and root systems. The latter serves mainly for attachment to the underwater substrate and, unlike terrestrial plants, does not perform the function of mineral nutrition and water supply. In this regard, the roots of rooted aquatic plants are devoid of root hairs. They feed on the entire surface of the body. The powerfully developed rhizomes of some of them serve for vegetative propagation and storage. nutrients. These are many pondweeds, water lilies, and egg capsules.

The high density of water makes it possible for plants to inhabit its entire thickness. For this purpose, lower plants that inhabit various layers and lead a floating lifestyle have special appendages that increase their buoyancy and allow them to remain suspended. Mechanical tissue is poorly developed in higher hydrophytes. In their leaves, stems, and roots, as noted, there are air-bearing intercellular cavities. This increases the lightness and buoyancy of organs suspended in water and floating on the surface, and also helps to wash away internal cells with water with gases and salts dissolved in it. Hydatophytes are generally characterized by a large leaf surface with a small total plant volume. This provides them with intense gas exchange when there is a lack of oxygen and other gases dissolved in water. Many pondweeds (Potamogeton lusens, P. perfoliatus) have thin and very long stems and leaves, their covers are easily permeable to oxygen. Other plants have strongly dissected leaves (water buttercup – Ranunculus aquatilis, urut – Myriophyllum spicatum, hornwort – Ceratophyllum dernersum).

A number of aquatic plants have developed heterophyly (various leaves). For example, in Salvinia, submerged leaves serve as mineral nutrition, while floating leaves serve as organic nutrition. In water lilies and egg capsules, the floating and submerged leaves are significantly different from each other. The upper surface of the floating leaves is dense and leathery with a large number of stomata. This promotes better gas exchange with air. There are no stomata on the underside of floating or submerged leaves.

An equally important adaptive feature of plants for living in an aquatic environment is that the leaves immersed in water are usually very thin. Chlorophyll in them is often located in the cells of the epidermis. This leads to increased photosynthesis rates under low light conditions. Such anatomical and morphological features are most clearly expressed in many pondweeds (Potamogeton), elodea (Helodea canadensis), water mosses (Riccia, Fontinalis), and Vallisneria spiralis.

The protection of aquatic plants from leaching of mineral salts from cells is the secretion of mucus by special cells and the formation of endoderm in the form of a ring of thicker-walled cells.

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, as well as the replacement of tender thin summer leaves with tougher and shorter winter leaves. At the same time, low water temperature negatively affects the generative organs of aquatic plants, and its high density makes pollen transfer difficult. Therefore, aquatic plants reproduce intensively by vegetative means. The sexual process is suppressed in many of them. Adapting to the characteristics of the aquatic environment, most submerged and floating plants carry flowering stems into the air and reproduce sexually (pollen is carried by wind and surface currents). The resulting fruits, seeds and other rudiments are also distributed by surface currents (hydrochory).

Hydrochorous plants include not only aquatic plants, but also many coastal plants. Their fruits are highly buoyant and can remain in water for a long time without losing their germination. Water carries the fruits and seeds of chastukha (Alisma plantago-aquatica), arrowhead (Sagittaria sagittifolia), sageweed (Butomusumbellatus), pondweed and other plants. The fruits of many sedges (Sagekh) are enclosed in peculiar air sacs and are also carried by water currents. It is believed that even coconut palms spread throughout the archipelagos of the tropical islands of the Pacific Ocean thanks to the buoyancy of their fruits - coconuts. Along the Vakhsh River, along the canals, the gumai weed (Sorgnum halepense) spread in the same way.

Adaptive features of aquatic animals. The adaptations of animals to the aquatic environment are even more diverse than those of plants. They have anatomical, morphological, physiological, behavioral and other adaptive characteristics. Even simply listing them is difficult. Therefore, we will name in general terms only the most characteristic of them.

Animals that live in the water column have, first of all, adaptations that increase their buoyancy and allow them to resist the movement of water and currents. Bottom organisms, on the contrary, develop adaptations that prevent them from rising into the water column, that is, they reduce buoyancy and allow them to stay at the bottom even in fast-flowing waters.

In small forms living in the water column, a reduction in skeletal formations is observed. In protozoa (Rhizopoda, Radiolaria), the shells are porous, and the flint spines of the skeleton are hollow inside. The specific density of jellyfish (Scyphozoa) and ctenophora (Ctenophora) decreases due to the presence of water in the tissues. An increase in buoyancy is also achieved by the accumulation of fat droplets in the body (nightlights - Noctiluca, radiolarians - Radiolaria). Larger accumulations of fat are also observed in some crustaceans (Cladocera, Copepoda), fish, and cetaceans. The specific density of the body is also reduced by gas bubbles in the protoplasm of testate amoebae and air chambers in the shells of mollusks. Many fish have swim bladders filled with gas. The siphonophores Physalia and Velella develop powerful air cavities.

Animals passively swimming in the water column are characterized not only by a decrease in weight, but also by an increase in the specific surface area of ​​the body. The fact is 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. As a result, the animal’s body becomes flattened and all sorts of spines, outgrowths, and appendages form on it. This is characteristic of many radiolarians (Chalengeridae, Aulacantha), flagellates (Leptodiscus, Craspedotella), and foraminifera (Globigerina, Orbulina). Since the viscosity of water decreases with increasing temperature, and increases with increasing salinity, adaptations to increased friction are most pronounced when high temperatures and low salinities. For example, flagellates Ceratium from Indian Ocean armed with longer horn-like appendages than those that live in the cold waters of the Eastern Atlantic.

Active swimming in animals is carried out with the help of cilia, flagella, and body bending. This is how protozoa, ciliated worms, and rotifers move.

Among aquatic animals, reactive swimming is common due to the energy of the ejected stream of water. This is typical for protozoa, jellyfish, dragonfly larvae, and some bivalves. The reactive mode of locomotion reaches its highest perfection in cephalopods. Some squids, when throwing out water, develop a speed of 40–50 km/h. Larger animals develop specialized limbs (swimming legs in insects, crustaceans; fins, flippers). The body of such animals is covered with mucus and has a streamlined shape.

Large group animals, mainly freshwater ones, use a surface film of water (surface tension) when moving. For example, spinning beetles (Gyrinidae) and water strider bugs (Gerridae, Veliidae) run freely on it. Small Hydrophilidae beetles move along the lower surface of the film, and pond snails (Limnaea) and mosquito larvae are suspended from it. All of them have a number of features in the structure of their limbs, and their integuments are not wetted by water.

Only in the aquatic environment are motionless animals leading an attached lifestyle found. 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. Some attach themselves to the ground, others crawl along it or lead a burrowing lifestyle, some settle on underwater objects, in particular the bottoms of ships.

Of the animals attached to the ground, the most characteristic are sponges, many coelenterates, especially hydroids (Hydroidea) and coral polyps (Anthozoa), crinoids (Crinoidea), bivalves(Bivalvia), barnacles (Cirripedia), etc.

Among burrowing animals there are especially many worms, insect larvae, and mollusks. Certain fish (spikefish - Cobitis taenia, flounders - Pleuronectidae, stingrays - Rajidae), and lamprey larvae (Petromyzones) spend significant time in the ground. The abundance of these animals and their species diversity depend on the type of soil (stones, sand, clay, silt). There are usually fewer of them on rocky soils than on muddy soils. Invertebrates that colonize muddy soils en masse create optimal conditions for the life of a number of larger benthic predators.

Most aquatic animals are poikilothermic, and their body temperature depends on the temperature of the environment. In homeothermic mammals (pinnipeds, cetaceans), a thick layer of subcutaneous fat is formed, which performs a thermal insulation function.

For aquatic animals, environmental pressure matters. In this regard, there are stenobathic animals, which cannot withstand large fluctuations in pressure, and eurybathic animals, which live at both high and low pressure. Holothurians (Elpidia, Myriotrochus) live at depths from 100 to 9000 m, and many species of Storthyngura crayfish, pogonophora, crinoids are located at depths from 3000 to 10,000 m. Such deep-sea animals have specific organizational features: an increase in body size; disappearance or poor development of the calcareous skeleton; often – reduction of the visual organs; strengthening the development of tactile receptors; lack of body pigmentation or, conversely, dark coloring.

Maintaining a certain osmotic pressure and ionic state of solutions in the body of animals is ensured by complex mechanisms of water-salt metabolism. However, most aquatic organisms are poikilosmotic, that is, the osmotic pressure in their body depends on the concentration of dissolved salts in the surrounding water. Only vertebrates, higher crustaceans, insects and their larvae are homoiosmotic - they maintain constant osmotic pressure in the body, regardless of the salinity of the water.

Marine invertebrates generally do not have mechanisms for water-salt metabolism: anatomically they are closed to water, but osmotically they are open. However, it would be incorrect to say that they have absolutely no mechanisms that control water-salt metabolism.

They are simply imperfect, and this is explained by the fact that the salinity of sea water is close to the salinity of the body juices. After all, in freshwater hydrobionts, the salinity and ionic state of mineral substances in the body juices are, as a rule, higher than in the surrounding water. Therefore, their osmoregulatory mechanisms are well expressed. The most common way to maintain constant osmotic pressure is to regularly remove water entering the body using pulsating vacuoles and excretory organs. In other animals, impenetrable covers of chitin or horny formations develop for these purposes. Some people produce mucus on the surface of their body.

The difficulty of regulating osmotic pressure in freshwater organisms explains their species poverty compared to sea inhabitants.

Let us use the example of fish to see how osmoregulation of animals occurs in sea and fresh waters. Freshwater fish remove excess water through the intensive work of the excretory system, and absorb salts through the gill filaments. Marine fish, on the contrary, are forced to replenish their water reserves and therefore drink sea water, and the excess salts that come with it are removed from the body through the gill filaments (Fig. 15).

Changing conditions in the aquatic environment causes certain behavioral reactions of organisms. Vertical migrations of animals are associated with changes in illumination, temperature, salinity, gas regime and other factors. In the seas and oceans, millions of tons of aquatic organisms take part in such migrations (lowering into the depths, rising to the surface). During horizontal migrations, aquatic animals can travel hundreds and thousands of kilometers. These are the spawning, wintering and feeding migrations of many fish and aquatic mammals.

Biofilters and their ecological role. One of the specific features of the aquatic environment is the presence in it large quantity fine particles organic matter - detritus formed by dying plants and animals. Huge masses of these particles settle on bacteria and, thanks to the gas released as a result of the bacterial process, are constantly suspended in the water column.

Detritus is a high-quality food for many aquatic organisms, so some of them, the so-called biofilters, have adapted to obtain it using specific microporous structures. These structures, as it were, filter the water, retaining particles suspended in it. This feeding method is called filtration. Another group of animals deposits detritus on the surface of either their own body or on special trapping devices. This method is called sedimentation. Often the same organism feeds by both filtration and sedimentation.

Animal biofilters (elasmobranch mollusks, sessile echinoderms and polychaete annulars, bryozoans, ascidians, planktonic crustaceans and many others) play a large role in the biological purification of water bodies. For example, a colony of mussels (Mytilus) per 1 sq. m passes through the mantle cavity up to 250 cubic meters. m of water per day, filtering it and precipitating suspended particles. The almost microscopic crustacean Calanoida purifies up to 1.5 liters of water per day. If we take into account the enormous number of these crustaceans, the work they perform in the biological purification of water bodies seems truly enormous.

In fresh waters, active biofilters are pearl barley (Unioninae), toothless mussels (Anodontinae), zebra mussels (Dreissena), daphnia (Daphnia) and other invertebrates. Their importance as a kind of biological “cleaning system” of water bodies is so great that it is almost impossible to overestimate it.

Zoning of the water environment. The aquatic living environment is characterized by clearly defined horizontal and especially vertical zoning. All hydrobionts are strictly confined to living in certain zones that differ in different living conditions.

In the World Ocean, the water column is called pelagic, and the bottom is benthic. Accordingly, ecological groups of organisms living in the water column (pelagic) and on the bottom (benthic) are also distinguished.

The bottom, depending on the depth of its occurrence from the water surface, is divided into sublittoral (an area of ​​gradual decline to a depth of 200 m), bathyal (steep slope), abyssal (ocean bed with an average depth of 3–6 km), ultra-abyssal (the bottom of oceanic depressions located at a depth of 6 to 10 km). The littoral zone is also distinguished - the edge of the coast, which is periodically flooded during high tides (Fig. 16).

Open waters The world's oceans (pelagial) are also divided into vertical zones corresponding to the benthic zones: epipelagic, bathypelagial, abyssopelagic.

The littoral and sublittoral zones are most richly populated by plants and animals. There's a lot here sunlight, low pressure, significant temperature fluctuations. The inhabitants of the abyssal and ultra-abyssal depths live at a constant temperature, in the dark, and experience enormous pressure, reaching several hundred atmospheres in the oceanic depressions.

A similar, but less clearly defined zonation is also characteristic of inland fresh water bodies.

Key concepts: environment - living environment - aquatic environment - ground-air environment - soil environment - organism as a living environment

In previous lessons we often talked about “habitat”, “living environment” and did not give this concept an exact definition. Intuitively, we understood by “environment” everything that surrounds the organism and influences it in one way or another. The influence of the environment on the body is the environmental factors that we studied in previous lessons. In other words, the living environment is characterized by a certain set of environmental factors.

The generally accepted definition of the environment is that of Nikolai Pavlovich Naumov:

ENVIRONMENT - everything that surrounds organisms, directly or indirectly affects their condition, development, survival and reproduction.

There is a huge variety of living conditions on Earth, which provides a variety of ecological niches and their “population”. However, despite this diversity, there are four qualitatively different environments lives that have a specific set of environmental factors, and therefore require a specific set of adaptations. These are the living environments:

ground-aquatic (land);

other organisms.

Let's get acquainted with the features of each of these environments.

Aquatic life environment

According to the majority of authors studying the origin of life on Earth, the evolutionarily primary environment for life was the aquatic environment. We find quite a few indirect confirmations 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 occur, obviously still retains the features of the environment in which the evolution of the first organisms took place. Thus, the salt content in human blood (maintained at a relatively constant level) is close to that in ocean water. The properties of the aquatic oceanic environment largely determined the chemical and physical evolution of all forms of life.

Perhaps the main one distinctive feature the aquatic environment is its relative conservatism. For example, the amplitude of seasonal or daily temperature fluctuations in the aquatic environment is much smaller than in the land-air environment. Bottom topography, differences in conditions at different depths, the presence of coral reefs, etc. create a variety of conditions in the aquatic environment.

The characteristics of the aquatic environment stem from the physical and chemical properties of water. Thus, the high density and viscosity of water are of great environmental importance. The specific gravity of water is comparable to that of the body of living organisms. The density of water is approximately 1000 times higher than the density of air. Therefore, aquatic organisms (especially actively moving ones) encounter a large force of hydrodynamic resistance. For this reason, the evolution of many groups of aquatic animals went in the direction of the formation of body shapes and types of movement that reduce drag, which leads to a decrease in energy costs 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 propagate well in the aquatic environment. This was important in the evolution of sensory organs, spatial orientation and communication between aquatic inhabitants. Four times greater than in air, the speed of sound in an aquatic environment determines more high frequency 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 a mandatory connection with the bottom or other substrate, “floating” in the water column.

Electrical conductivity opened up the possibility of the evolutionary formation of electrical sense organs, defense and attack.

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 shaping the conditions of the land-air environment of life, and above all, the gas composition of the atmosphere. Almost all the oxygen earth's atmosphere is of biogenic origin.

The main features of the ground-air environment are the large amplitude of changes in environmental factors, the heterogeneity of the environment, the action of gravitational forces, and low air density. A complex of physical-geographical and climatic factors characteristic of a certain natural area, leads to the evolutionary formation of morphophysiological adaptations of organisms to life in these conditions, the diversity of life forms.

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.

Soil as a living environment

Soil is the result of the activity of living organisms. The organisms that populated the ground-air environment led to the emergence of soil as a unique habitat. Soil is a complex system including a solid phase (mineral particles), a liquid phase (soil moisture) and a gaseous phase. The relationship between 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 death of organisms and is part of their excreta (secretions).

Terms soil environment habitats are determined by such soil properties as its aeration (that is, air saturation), humidity (presence of moisture), heat capacity and thermal regime (daily, seasonal, annual temperature variations). Thermal mode, compared to the ground-air environment, more conservative, especially on great depth. In general, the soil differs quite stable conditions life.

Vertical differences are also characteristic of other soil properties, for example, light penetration naturally depends on depth.

Many authors note the intermediate position of the soil environment between aquatic and ground-air environment. Soil can harbor organisms that have both aquatic and airborne respiration. The vertical gradient of light penetration in soil is even more pronounced than in water. Microorganisms are found throughout the entire thickness of the soil, and plants (primarily root systems) are associated with external 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, volcanic, worm-shaped); durable and flexible covers; reduction of eyes and disappearance of pigments. Among soil inhabitants, saprophagy is widely developed - eating the corpses of other animals, rotting remains, etc.

Organism as a habitat

Glossary

ECOLOGICAL NICHE

position of a species in nature, including not only the species’ place in space, but also its functional role in the natural community, position relative to abiotic conditions of existence, place of individual phases life cycle representatives of a species in time (for example, early spring plant species occupy a completely independent ecological niche).

EVOLUTION

irreversible historical development of living nature, accompanied by changes in the genetic composition of populations, the formation and extinction of species, transformation of ecosystems and the biosphere as a whole.

INTERNAL ENVIRONMENT OF THE ORGANISM

an environment characterized by relative constancy of composition and properties that ensures the flow of life processes in the body. For man internal environment The body is a system of blood, lymph and tissue fluid.

ECHOLOCATION, LOCATION

determination of the position in space of an object by emitted or reflected signals (in the case of echolocation - perception sound signals). They have the ability to echolocate guinea pigs, dolphins, bats. Radar and electrolocation - perception of reflected radio signals and signals electric field. Some fish have the ability for this type of location - Nile longsnout, gimarch.

According to the majority of authors studying the origin of life on Earth, the evolutionarily primary environment for life was 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 occur, obviously still retains the features of the environment in which the evolution of the first organisms took place. Thus, the salt content in human blood (maintained at a relatively constant level) is close to that in ocean water. The properties of the aquatic oceanic environment 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 smaller than in the land-air environment. Bottom topography, differences in conditions at different depths, the presence of coral reefs, etc. create a variety of conditions in the aquatic environment. The characteristics of the aquatic environment stem from the physical and chemical properties of water. Thus, the high density and viscosity of water are of great environmental importance. The specific gravity of water is comparable to that of the body of living organisms. The density of water is approximately 1000 times higher than the density of air. Therefore, aquatic organisms (especially actively moving ones) encounter a large force of hydrodynamic resistance. For this reason, the evolution of many groups of aquatic animals went in the direction of the formation of body shapes and types of movement that reduce drag, which leads to a decrease in energy costs 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 propagate well in the aquatic environment. This was of great importance in the evolution of sensory organs, spatial orientation and communication between aquatic inhabitants. Four times greater than in the air, the speed of sound in the aquatic environment 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 a mandatory connection with the bottom or other substrate, “floating” in the water column. Electrical conductivity opened up the possibility of the evolutionary formation of electrical sense organs, 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 shaping the conditions of the land-air environment of life, and above all, the gas composition of the atmosphere. Almost all the oxygen in the earth's atmosphere is of biogenic origin. The main features of the ground-air environment are the large amplitude of changes in environmental factors, the heterogeneity of the environment, the action of gravitational forces, and low air density. A complex of physical-geographical and climatic factors characteristic of a certain natural zone leads to the evolutionary formation of morphophysiological adaptations of organisms to life in these conditions, a diversity 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 that populated the ground-air environment led to the emergence of soil as a unique habitat. Soil is a complex system including a solid phase (mineral particles), a liquid phase (soil moisture) and a gaseous phase. The relationship between 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 death of organisms and is part of their excreta (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 variations). The thermal regime, compared to the ground-air environment, is more conservative, especially at great depths. In general, the soil has fairly stable living conditions. Vertical differences are also characteristic of 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 land-air environments. Soil can harbor organisms that have both aquatic and airborne respiration. The vertical gradient of light penetration in soil is even more pronounced than in water. Microorganisms are found throughout the entire thickness of the soil, and plants (primarily root systems) are associated with external 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, volcanic, worm-shaped); durable and flexible covers; reduction of eyes and disappearance of pigments. Among soil inhabitants, saprophagy is widely developed - eating the corpses of other animals, rotting remains, etc.

Aquatic living environment.

Hydrosphere occupies approximately 71% of the planet's area. Its main quantity is concentrated in the seas and oceans (94%). In freshwater bodies of water, the amount of water is much less (0.016%).

The aquatic environment is home to about 150 thousand species of animals (7% of the total number on Earth) and 10 thousand species of plants (8%).

Features of the aquatic environment: mobility, density, special salt, light and temperature conditions, acidity (concentration of hydrogen ions), content of oxygen, carbon dioxide and nutrients.

An important feature of the aquatic environment is its mobility. In streams and rivers, the average flow speed usually increases as it moves downstream. Actually fast current plants grow that encrust the substrate, or filamentous algae, mosses and liverworts. In a weak current - plants flow around the flow, and do not offer much resistance to it and are securely attached to a stationary object with an abundant growth of adventitious roots. Unattached, free-floating plants are found in places with slow currents or where there is no current at all.

Invertebrate animals wild rivers have an extremely flattened body.

Water is 800 times stronger than air by density. The density of natural waters is 1.35 g/cm3 due to the salt content. For every 10 m of depth, pressure increases by 1 atmosphere. In hydrobionts, mechanical tissues are greatly reduced. The support of the environment serves as a condition for soaring and maintaining non-skeletal forms in water. Many aquatic organisms are adapted to this way of life.

Salt regime important for aquatic organisms. According to the general mineralization, water can be divided into fresh 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 dissolved substances in water are carbonates, sulfates and chlorides.

Calcium may act as a limiting factor. There are “soft” waters - calcium content less than 9 mg per 1 liter and “hard” waters containing calcium more than 25 mg per 1 liter.

13 metalloids and at least 40 metals have been found in seawater.

Water salinity can have a significant impact on the distribution and abundance of organisms.

The rays of different parts of the solar spectrum are absorbed differently by water, the spectral composition of light changes with depth, and the red rays are weakened. Blue-green rays penetrate to considerable depths. The deepening twilight in the ocean is first green, then blue, indigo, blue-violet, later mixing with constant darkness.

In shallow water zones, plants use 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, contain brown pigments phycaffeine, fucoxanthin, etc. Red algae containing the pigment phycoerythrin live even deeper. This phenomenon is called chromatographic adaptation.

Brightly and variously colored animals live in light, surface layers of water; deep-sea species are usually devoid of pigments. Organisms with a reddish tint live in the twilight zone, which helps them hide from enemies.

The amplitude of annual temperature fluctuations in the upper layers of the ocean is no more than 10-15 0 C , in continental waters 30-35 0 C. Deep layers of water are characterized by constant temperature. In equatorial waters, the average annual temperature of surface layers is 26–27 0 C, in polar waters it is about 0 0 C and lower. The exception is thermal springs, where the temperature of the surface layer reaches 85 – 93 0 C.

Thermodynamic features of the aquatic environment - high specific heat, high thermal conductivity and expansion during freezing, create favorable conditions for living organisms.

With promotion acidity water, the species diversity of animals inhabiting rivers, ponds and lakes usually decreases.

Freshwater bodies of water with a pH of 3.7 - 4.7 are considered acidic, 6.95 - 7.3 - alkaline, and with a pH of more than 7.8 - alkaline. In fresh water bodies, pH experiences significant fluctuations, often during the day. Sea water is more alkaline and its pH changes less than fresh water. pH decreases with depth.

Most freshwater fish can withstand a pH of 5 to 9. If the pH is less than 5, then there is a massive death of fish, and above 10, all fish and other animals die.

The main gases of the aquatic environment are oxygen and carbon dioxide, and hydrogen sulfide or methane are of secondary importance.

Oxygen for the aquatic environment is the most important environmental factor. It enters water from the air and is released by plants during the process of photosynthesis. As the temperature and salinity of water increase, the concentration of oxygen in it decreases. In layers heavily populated by animals and bacteria, oxygen deficiency may occur due to increased oxygen consumption. Conditions near the bottom of reservoirs can be close to anaerobic.

There is 700 times more carbon dioxide than in the atmosphere, because it is 35 times more soluble in water.

In the aquatic environment, three ecological groups of aquatic organisms can be distinguished:

1)nekton (floating) - This is a collection of actively moving animals that do not have a direct connection with the bottom. These are mainly large animals capable of traveling long distances and strong currents.

2)plankton (wandering, floating) is a collection of organisms that do not have the ability for rapid active movement. It is divided into phytoplankton (plants) and zooplankton (animals). Planktonic organisms are located both on the surface of the water, at depth, and in the bottom layer.

3) benthos (depth) is a collection of organisms that live at the bottom (on the ground and in the ground) of water bodies. It is divided into zoobenthos and phytobenthos.