Water environment.
Distribution of organisms by living environments
In the course of a long historical development living matter and the formation of more and more perfect 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 her that life arose. With historical development, many organisms began to populate the ground-air environment. As a result, terrestrial plants and animals appeared, which rapidly evolved, adapting to new conditions of existence.
In the process of functioning of living matter on land, the surface layers of the lithosphere gradually transformed into soil, into a peculiar, according to V. I. Vernadsky, bio-inert body of the planet. The soil began to be inhabited by both aquatic and terrestrial organisms, creating a specific complex of its inhabitants.
Thus, on the modern Earth, four environments of life are clearly distinguished - water, ground-air, soil and living organisms, which differ significantly in their conditions. Let's consider each of them.
General characteristics. The aquatic environment of life, the hydrosphere, occupies up to 71% of the area of the globe. 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 ice in the polar regions; in fresh waters of rivers, lakes and swamps, the amount of water does not exceed 0.45%.
About 150,000 animal species (about 7% of their total number on the globe) and 10,000 plant species (8%) live in the aquatic environment. 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 much less than that of terrestrial ones. This means that evolution on land was much faster.
The most diverse and rich in plant and animal world 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 is gradually depleted. About 40,000 species of animals are distributed in the area of the East Indies Archipelago, and only 400 in the Laptev Sea. At the same time, the bulk of the organisms of the World Ocean is concentrated in a relatively small area of the sea coasts of the temperate zone and among the mangroves of tropical countries. In vast areas far from the coast, there are desert areas that are practically devoid of life.
The share of rivers, lakes and swamps in comparison with that of the seas and oceans in the biosphere is insignificant. Nevertheless, they create a 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 substance of the hydrosphere affects the environment, processes it, involving it in the circulation of substances. It has been calculated that the water of the seas and oceans, rivers and lakes decomposes and is restored in the biotic cycle in 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 epochs.
A characteristic feature of the aquatic environment is its mobility even in stagnant water bodies, not to mention flowing, fast-flowing rivers and streams. Ebb and flow, powerful currents, storms are observed in the seas and oceans; 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, leads to an equalization (decrease) in temperature throughout the reservoir.
The inhabitants of water bodies 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 plume of processes, diatoms (Diatomeae), water mosses (Fontinalis), forming a dense cover even on stones in stormy river rifts .
Animals have 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 towards 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 themselves to underwater objects. In the seas, organisms of the tidal and surf zones experience the strongest influence of moving masses of water. Barnacles (Balanus, Chthamalus), gastropods (Patella Haliotis), and some species of crustaceans hiding in the crevices of the shore are common on rocky shores in the surf zone.
In the life of aquatic organisms in temperate latitudes, the vertical movement of water in stagnant water bodies 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 there is a sharp temperature drop; bottom deep layer, hypolimnion - here the temperature varies slightly throughout the year.
In summer, the warmest layers of water are located at the surface, and the coldest - at the bottom. Such a layered distribution of temperatures in a reservoir is called direct stratification. In winter, with a decrease in temperature, reverse stratification is observed: surface cold waters with a temperature 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 the temperature dichotomy, a density stratification of water is formed in the reservoir, its vertical circulation is disturbed, and a period of temporary stagnation sets in.
In spring, surface water, due to heating to 4 °C, becomes denser and sinks deeper, and warmer water rises in its place from the depth. As a result of such vertical circulation, homothermia sets in in the reservoir, i.e., for some time, the temperature of the entire water mass equalizes. With a further increase in temperature, the upper layers of water become 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 happens before the onset of autumn homothermy. When surface waters are cooled below 4 °C, they again become less dense and again remain on the surface. As a result, water circulation stops and winter stagnation sets in.
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 of tropical latitudes, the water temperature on the surface never drops below 4 °C, and the temperature gradient in them is clearly expressed to the deepest layers. Mixing of water, as a rule, occurs here irregularly in 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 for aquatic organisms only as a more or less solid substrate, performing mainly a mechanical-dynamic function. In this regard, the sizes of soil particles, the density of their fit to each other and resistance to washout by currents acquire the greatest ecological significance.
Abiotic factors of the aquatic environment. Water as a living medium 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 about 36 ° C. The oscillation amplitude here, therefore, is within 38 °C. The temperature of the oceans drops with depth. Even in tropical regions at a depth of 1000 m, it does not exceed 4–5°С. At the depths of all oceans there is a layer of cold water (from -1.87 to +2°C).
In fresh inland water bodies of temperate latitudes, the temperature of the surface water layers ranges from -0.9 to +25°C, in deeper waters it is 4–5°C. Thermal springs are an exception, where the temperature of the surface layer sometimes reaches 85–93 °C.
Such thermodynamic features of the aquatic environment as high specific heat capacity, high thermal conductivity and expansion during freezing create especially 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 highest density at 4 ° C, and expands when it freezes, in winter ice forms only from above, while the main thickness does not freeze through.
Since the temperature regime of water bodies is characterized by great stability, the organisms living in it are distinguished by a relatively constant body temperature and have a narrow range of adaptability to fluctuations in environmental temperature. Even minor deviations in the thermal regime can lead to significant changes in the life 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. Behind last decade the area of lotus thickets has increased almost 20 times and now occupies over 1500 hectares of water area. Such a 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. During the hot summer months, the water here warmed up more than before, and this contributed to the growth of lotus thickets.
Water is also characterized by a significant density (in this respect it is 800 times greater than air) and viscosity. These features affect plants in that they develop very little or no mechanical tissue at all, so their stems are very elastic and easily bent. Most aquatic plants are inherent in buoyancy and the ability to be suspended in the water column. They then rise to the surface, then again fall. In many aquatic animals, the integument is abundantly lubricated with mucus, which reduces friction during movement, and the body acquires a streamlined shape.
Organisms in the aquatic environment are distributed throughout its entire thickness (in oceanic depressions, animals have been found at depths of more than 10,000 m). Naturally, at different depths they experience different pressures. Deep-sea are adapted to high pressure (up to 1000 atm), while the inhabitants of the surface layers are not subject to it. On average, in the water column, for every 10 m of depth, the pressure increases by 1 atm. All hydrobionts are adapted to this factor and, accordingly, are divided into deep-sea and living at shallow depths.
The transparency of water and its light regime have a great influence on aquatic organisms. This especially affects the distribution of photosynthetic plants. In muddy water bodies, they live only in the surface layer, and where there is great transparency, they penetrate to considerable depths. A certain turbidity of water is created by a huge amount of particles suspended in it, which limits the penetration of sunlight. Turbidity of water can be caused by particles of mineral substances (clay, silt), small organisms. The transparency of water also decreases in summer with the rapid growth of aquatic vegetation, with the mass reproduction of small organisms that are in suspension 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 is still covered with snow from above, the penetration of light into the water column is severely limited.
The light regime is also determined by the regular decrease in light with depth due to the fact that water absorbs sunlight. At the same time, rays with different wavelengths are absorbed differently: red ones are the fastest, while blue-green ones penetrate to considerable depths. The ocean gets darker with depth. The color of the environment at the same time changes, gradually moving from greenish to green, then to blue, blue, blue-violet, replaced by constant darkness. Accordingly, with depth, green algae (Chlorophyta) are replaced by brown (Phaeophyta) and red (Rhodophyta), whose pigments are adapted to capture sunlight with different wavelengths. With depth, the color of animals also naturally changes. In the surface, light layers of water, brightly and diversely colored animals usually live, while deep-sea species are devoid of pigments. In the twilight zone of the ocean, animals are painted in colors with a reddish tint, which helps them hide from enemies, since the red color in the blue-violet rays is perceived as black.
Salinity 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 water bodies have 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 6Distribution of basic salts in various water bodies (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 their shells and 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 the flowing rivers and streams), differ greatly both in composition and in the concentration of salts dissolved in them. Marine waters are more stable in this respect. Almost all known elements have been found in them. However, in terms of importance, the first place is occupied by table salt, then magnesium chloride and sulfate and potassium chloride.
Freshwater plants and animals live in a hypotonic environment, that is, in 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 fresh water hydrobionts are forced to intensively remove it. In this regard, they have well-defined processes of osmoregulation. The concentration of salts in 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. Difficulties in osmoregulation are one of the reasons why many marine plants and especially animals failed to populate fresh water bodies and turned out, with the exception of individual representatives, to be typical marine inhabitants (intestinal - Coelenterata, echinoderms - Echinodermata, pogonophores - Pogonophora, sponges - Spongia, tunicates – Tunicata). At that same time, 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 numbers, in brackish waters. These are freshwater pike-perch (Stizostedion lucioperca), bream (Abramis brama), pike (Esox lucius), and the family of mullet (Mugilidae) can be called from the marine ones.
In fresh waters, plants are common, fortified at the bottom of the reservoir. Often their photosynthetic surface is located above the water. These are cattails (Typha), reeds (Scirpus), arrowhead (Sagittaria), water lilies (Nymphaea), egg capsules (Nuphar). In others, the photosynthetic organs are submerged in water. These include pondweeds (Potamogeton), urut (Myriophyllum), elodea (Elodea). Some higher plants of fresh waters are deprived of roots. They are either free-floating or grow on underwater objects or algae attached to the ground.
If oxygen does not play a significant role for the air environment, then for the water it is the most important environmental factor. 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 water bodies and especially for fast-flowing rivers and streams, the oxygen content also increases.
Different animals exhibit different oxygen requirements. For example, trout (Salmo trutta), minnow (Phoxinus phoxinus) are very sensitive to its deficiency and therefore live only in fast-flowing cold and well-mixed waters. Roach (Rutilus rutilus), ruff (Acerina cernua), common carp (Cyprinus carpio), crucian carp (Carassius carassius) are unpretentious in this respect, and chironomid mosquito larvae (Chironomidae) and oligochaete tubifex worms (Tubifex) live at great depths, where there is no oxygen at all or very little of it. Aquatic insects and lung molluscs (Pulmonata) can also live in waters with low oxygen content. However, they systematically rise to the surface, storing fresh air for a while.
Carbon dioxide is about 35 times more soluble in water than oxygen. There is almost 700 times more of it in water than in the atmosphere where it comes from. The source of carbon dioxide in water, in addition, are carbonates and bicarbonates of alkali and alkaline earth metals. Carbon dioxide contained in water provides photosynthesis of aquatic plants and takes part in the formation of calcareous skeletal formations of invertebrates.
Of great importance in the life of aquatic organisms is the concentration of hydrogen ions (pH). Freshwater pools with a pH of 3.7–4.7 are considered acidic, 6.95–7.3 are neutral, and those with a pH greater than 7.8 are considered 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 an important role in the distribution of hydrobionts. At a pH of less than 7.5, half-grass (Isoetes), burrweed (Sparganium) grows, at 7.7–8.8, i.e., in an alkaline environment, many types of pondweeds and elodea develop. Sphagnum mosses (Sphagnum) predominate in the acidic waters of the marshes, but there are no lamella-gill mollusks of the genus Toothless (Unio), other mollusks are rare, but shell rhizomes (Testacea) are abundant. Most freshwater fish can withstand a pH of 5 to 9. If the pH is less than 5, there is a mass death of fish, and above 10, all fish and other animals die.
Ecological groups of hydrobionts. The water column - pelagial (pelagos - sea) is inhabited by pelagic organisms that can actively swim or stay (soar) in certain layers. In accordance with this, pelagic organisms are divided into two groups - nekton and plankton. The inhabitants of the bottom 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. Basically, these are large animals that can travel long distances and strong water currents. They are characterized by a streamlined body shape and well-developed organs of movement. Typical nekton 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 in the water column at great speed. Some squids (Oegopsida) swim very quickly, up to 45–50 km/h, sailboats (Istiopharidae) reach speeds of up to 100 km/h, and swordfish (Xiphias glabius) up to 130 km/h.
Plankton (planktos– hovering, wandering)– this is a collection of pelagic organisms that do not have the ability for fast active movement. Planktonic organisms cannot resist currents. These are mainly small animals - zooplankton and plants - phytoplankton. The composition of plankton periodically includes the larvae of many animals soaring 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 former constitute a special group - the neuston. Organisms, on the other hand, part of the body of which is in the water, and part is above its surface, are called pleuston. These are siphonophores (Siphonophora), duckweed (Lemna), etc.
Phytoplankton has great importance in the life of water bodies, since it is the main producer of organic matter. It primarily includes diatoms (Diatomeae) and green (Chlorophyta) algae, plant flagellates (Phytomastigina), Peridineae (Peridineae) and coccolithophores (Coccolitophoridae). In the northern waters of the World Ocean, diatoms predominate, and in the tropical and subtropical waters, the armored flagellates. In fresh waters, in addition to diatoms, green and blue-green (Cuanophyta) algae are common.
Zooplankton and bacteria are found at all depths. Marine zooplankton is dominated by small crustaceans (Copepoda, Amphipoda, Euphausiacea), protozoa (Foraminifera, Radiolaria, Tintinnoidea). More major representatives his are winged mollusks (Pteropoda), jellyfish (Scyphozoa) and floating ctenophores (Ctenophora), salps (Salpae), 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 plankton of tropical waters reaches the highest species diversity.
Groups of planktonic organisms are distinguished by size. Nannoplankton (nannos - dwarf) are the smallest algae and bacteria; microplankton (micros - small) - most algae, protozoa, rotifers; mesoplankton (mesos - medium) - copepods and cladocerans, shrimps and a number of animals and plants, not more than 1 cm in length; macroplankton (macros - large) - jellyfish, mysids, shrimps and other organisms larger than 1 cm; megaloplankton (megalos - huge) - very large, over 1 m, animals. For example, the floating comb jelly venus belt (Cestus veneris) reaches a length of 1.5 m, and the cyanide jellyfish (Suapea) has a bell up to 2 m in diameter and tentacles 30 m long.
Plankton organisms are an important food component of many aquatic animals (including such giants as baleen whales - Mystacoceti), especially considering that they, and above all phytoplankton, are characterized by seasonal outbreaks of mass reproduction (water bloom).
Benthos (benthos– depth)– a set of organisms living at the bottom (on the ground and in the ground) of water bodies. It is subdivided into phytobenthos and zoobenthos. It is mainly represented by animals attached or slowly moving, as well as burrowing in the ground. Only in shallow water does it consist of organisms that synthesize organic matter (producers), consume it (consumers) and destroy it (decomposers). At great depths where light does not penetrate, phytobenthos (producers) are absent.
Benthic organisms differ in their way of life - mobile, inactive and immobile; according to the method of nutrition - 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 (Zostera), phyllospodix (Phyllospadix), ruppia (Rup-pia). Phytobenthos is richest on rocky and rocky bottom areas. Along the coasts, kelp (Laminaria) and fucus (Fucus) sometimes form a biomass of up to 30 kg per 1 sq. km. m. On soft soils, where plants cannot be firmly attached, phytobenthos develops mainly in places protected from waves.
Fresh water phytobenos is represented by bacteria, diatoms and green algae. Coastal plants are abundant, located from the coast deep into clearly defined belts. Semi-submerged plants (reeds, reeds, cattails and sedges) grow in the first belt. The second belt is occupied by submerged plants with floating leaves (pods, water lilies, duckweeds, vodokras). In the third belt, submerged plants predominate - pondweed, elodea, etc.
All aquatic plants according to their lifestyle can be divided into two main ecological groups: hydrophytes - plants immersed in water only with their lower part and usually rooting in the ground, and hydatophytes - plants completely immersed in water, but sometimes floating on the surface or having floating leaves.
The marine zoobenthos is dominated by foraminifera, sponges, coelenterates, nemerteans, polychaetes, sipunculids, bryozoans, brachiopods, mollusks, ascidians, and fish. The most numerous are benthic forms in shallow waters, where their total biomass often reaches tens of kilograms per 1 sq. km. m. With depth, the number of benthos drops sharply and at great depths is milligrams per 1 sq. km. m.
There are fewer zoobenthos in fresh water bodies than in the seas and oceans, and the species composition is more uniform. These are mainly protozoa, some sponges, ciliary and oligochaete worms, leeches, bryozoans, molluscs 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, stony corals cannot withstand even weak water desalination and live only in the seas, moreover, on solid ground at a temperature of at least 20 °C. These are typical stenobionts. However, there are species with increased ecological plasticity. For example, the rhizopod Cyphoderia ampulla is a typical eurybiont. It lives in the seas and fresh waters, in warm ponds and cold lakes.
Freshwater animals and plants tend to be much more flexible than marine ones because freshwater is a more variable environment. The most plastic are 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 the ecological plasticity of hydrobionts is assessed in relation not only to the whole complex of factors (eury- and stanobiontness), but also to any one of them. Coastal plants and animals, in contrast to the inhabitants of open areas, are mainly eurythermal and euryhaline organisms, since near the coast the temperature conditions and salt regime are quite variable (heating 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 water bodies. For the same reasons, the inhabitants of the surface layers turn out to be more eurythermal and euryhaline in comparison with the deep-water forms.
Ecological plasticity serves as an important regulator of the dispersal of organisms. As a rule, hydrobionts with high ecological plasticity are quite widespread. This applies, for example, Elodea. However, the Artemia crustacean (Artemia salina) is diametrically opposed to it in this sense. It lives in small reservoirs 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 occurs everywhere in salt water bodies.
Ecological plasticity depends on the age and phase of development of the organism. So, the marine gastropod mollusk Littorina in its adult state daily at low tide long time does without water, and its larvae lead a purely planktonic lifestyle and do not tolerate desiccation.
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 environment reflected in their morphological and physiological organization. For aquatic plants, first of all, the weak development of the conductive tissue and the root system is characteristic. 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 rooting aquatic plants are devoid of root hairs. They are fed by the entire surface of the body. Powerfully developed rhizomes in some of them serve for vegetative propagation and storage of nutrients. Such are many pondweeds, water lilies, egg capsules.
The high density of water makes it possible for plants to live in its entire thickness. To do this, lower plants that inhabit different layers and lead a floating lifestyle have special appendages that increase their buoyancy and allow them to stay in suspension. In higher hydrophytes, mechanical tissue develops poorly. In their leaves, stems, roots, as noted, air-bearing intercellular cavities are located. This increases the lightness and buoyancy of organs suspended in water and floating on the surface, and also promotes flushing of 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 intensive gas exchange with 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 ranunculus - Ranunculus aquatilis, urt - Myriophyllum spicatum, hornwort - Ceratophyllum dernersum).
A number of aquatic plants have developed heterophilia (diversity). For example, in Salvinia (Salvinia) immersed leaves perform the function of mineral nutrition, and floating - organic. In water lilies and egg capsules, the floating and submerged leaves differ significantly from each other. The upper surface of floating leaves is dense and leathery with a large number of stomata. This contributes to better gas exchange with air. There are no stomata on the underside of floating and underwater leaves.
An equally important adaptive feature of plants for living in an aquatic environment is the fact 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 an increase in the intensity of photosynthesis in low light conditions. Such anatomical and morphological features are most clearly expressed in many pondweeds (Potamogeton), Elodea (Helodea canadensis), water mosses (Riccia, Fontinalis), Vallisneria (Vallisneria spiralis).
Protection of aquatic plants from leaching of mineral salts from cells (leaching) 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 the vegetative parts of plants immersed in water after the formation of winter buds, as well as the replacement of summer tender ones. thin leaves tougher and shorter winter ones. At the same time, low water temperature adversely affects the generative organs of aquatic plants, and its high density hinders the transfer of pollen. Therefore, aquatic plants reproduce intensively by vegetative means. The sexual process in many of them is suppressed. Adapting to the characteristics of the aquatic environment, most of the plants submerged and floating on the surface take out flowering stems into the air and reproduce sexually (pollen is carried by wind and surface currents). The resulting fruits, seeds and other primordia are also spread by surface currents (hydrochoria).
Not only aquatic, but also many coastal plants belong to hydrochoirs. Their fruits are highly buoyant and can stay in water for a long time without losing their germination. Fruits and seeds of chastukha (Alisma plantago-aquatica), arrowhead (Sagittaria sagittifolia), susak (Butomusumbellatus), pondweeds and other plants are carried by water. The fruits of many sedges (Cageh) are enclosed in peculiar sacs with air 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 due to the buoyancy of their fruits - coconuts. Along the Vakhsh River, the humai weed (Sorgnum halepense) spread through the canals in the same way.
Adaptive features of aquatic animals. Adaptations of animals to the aquatic environment are even more diverse than those of plants. They can distinguish anatomical, morphological, physiological, behavioral and other adaptive features. Even a simple enumeration of them is difficult. Therefore, we will name in general terms only the most characteristic of them.
Animals living in the water column, first of all, have adaptations that increase their buoyancy and allow them to resist the movement of water, currents. Bottom organisms, on the contrary, develop devices that prevent them from rising into the water column, that is, they reduce buoyancy and allow them to stay on 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, the flint needles of the skeleton are hollow inside. The specific density of jellyfish (Scyphozoa) and ctenophores (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 (night-lighters - 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, air chambers in mollusk shells. Many fish have gas-filled swim bladders. The siphonophores of 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 of the body. The fact is that the greater the viscosity of the medium and the higher the specific surface area of the organism's body, the slower it sinks into the water. As a result, the body flattens in animals, all kinds of spikes, outgrowths, and appendages are formed on it. This is characteristic of many radiolarians (Chalengeridae, Aulacantha), flagellates (Leptodiscus, Craspedotella), and foraminifers (Globigerina, Orbulina). Since the viscosity of water decreases with increasing temperature and increases with increasing salinity, adaptations to increased friction are most pronounced at high temperatures and low salinities. For example, the flagellar Ceratium from the Indian Ocean are armed with longer horn-like appendages than those found in the cold waters of the East Atlantic.
Active swimming in animals is carried out with the help of cilia, flagella, body bending. This is how protozoa, ciliary worms, and rotifers move.
Among aquatic animals, swimming is common in a jet way due to the energy of the ejected jet of water. This is typical for protozoa, jellyfish, dragonfly larvae, and some bivalves. The jet mode of locomotion reaches its highest perfection in cephalopods. Some squids, when throwing out water, develop a speed of 40-50 km / h. In larger animals, specialized limbs are formed (swimming legs in insects, crustaceans; fins, flippers). The body of such animals is covered with mucus and has a streamlined shape.
A large group of animals, mostly freshwater, use the surface film of water (surface tension) when moving. On it run freely, for example, beetles (Gyrinidae), water strider bugs (Gerridae, Veliidae). Small Hydrophilidae beetles move along the lower surface of the film, pond snails (Limnaea) and mosquito larvae also hang on it. All of them have a number of features in the structure of the limbs, and their covers are not wetted by water.
Only in the aquatic environment are immobile animals leading an attached lifestyle. They are characterized by a peculiar body shape, slight buoyancy (the density of the body is greater than the density of water) and special devices for attaching to the substrate. Some are attached to the ground, others crawl on 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), sea lilies (Crinoidea), bivalves (Bivalvia), barnacles (Cirripedia), etc.
Among the burrowing animals, there are especially many worms, insect larvae, and also molluscs. Certain fish spend considerable time in the ground (spike - Cobitis taenia, flatfish - Pleuronectidae, stingrays - Rajidae), lamprey larvae (Petromyzones). The abundance of these animals and their species diversity depend on the type of soil (stones, sand, clay, silt). On stony soils, they are usually less than on silty ones. Invertebrates that inhabit silty bottoms 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 ambient temperature. In homoiothermic mammals (pinnipeds, cetaceans) a powerful layer of subcutaneous fat is formed, which performs a heat-insulating function.
For aquatic animals, environmental pressure matters. In this regard, stenobate animals are distinguished, which cannot withstand large fluctuations in pressure, and eurybat 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, pogonophores, sea lilies 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 weak development of the calcareous skeleton; often - reduction of the organs of vision; increased development of tactile receptors; lack of body pigmentation or, conversely, dark coloration.
Maintaining a certain osmotic pressure and ionic state of solutions in the body of animals is provided 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 crayfish, insects and their larvae are homoiosmotic - they maintain a constant osmotic pressure in the body, regardless of the salinity of the water.
Marine invertebrates basically do not have mechanisms of water-salt exchange: anatomically they are closed to water, but osmotically open. However, it would be wrong to speak about the absolute absence of mechanisms that control water-salt metabolism in them.
They are simply imperfect, and this is because the salinity of sea water is close to the salinity of body juices. Indeed, in fresh water hydrobionts, the salinity and ionic state of the mineral substances of the body juices are, as a rule, higher than those of the surrounding water. Therefore, they have well-defined mechanisms of osmoregulation. The most common way to maintain a constant osmotic pressure is to regularly remove incoming water with the help of pulsating vacuoles and excretory organs. In other animals, impenetrable covers of chitin or horn formations develop for these purposes. Some produce mucus on the surface of the body.
The difficulty of regulating the osmotic pressure in freshwater organisms explains their species poverty in comparison with the inhabitants of the sea.
Let us follow the example of fish how osmoregulation of animals is carried out in marine and fresh waters. Freshwater fish remove excess water by the increased 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 in depth, raising to the surface). During horizontal migrations, aquatic animals can travel hundreds and thousands of kilometers. Such 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 of a large number of small particles of organic matter - detritus, formed due to dying plants and animals. Huge masses of these particles settle on bacteria and, due to the gas released as a result of the bacterial process, are constantly suspended in the water column.
For many aquatic organisms, detritus is a high-quality food, so some of them, the so-called biofilter feeders, have adapted to extract it using specific microporous structures. These structures, as it were, filter out water, retaining particles suspended in it. This way of eating is called filtering. Another group of animals deposits detritus on the surface either of their own bodies or on special trapping devices. This method is called sedimentation. Often the same organism feeds by both filtration and sedimentation.
Biofiltering animals (lamellagill molluscs, sessile echinoderms and polychaetes, bryozoans, ascidians, planktonic crustaceans, and many others) play an important 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 settling suspended particles. An almost microscopic crustacean calanus (Calanoida) cleans up to 1.5 liters of water per day. If we take into account the huge number of these crustaceans, then the work they do in the biological purification of water bodies seems truly grandiose.
In fresh waters, barley (Unioninae), toothless (Anodontinae), zebra mussels (Dreissena), daphnia (Daphnia) and other invertebrates are active biofilter feeders. Their significance as a kind of biological "cleansing system" of reservoirs is so great that it is almost impossible to overestimate it.
Zoning of the aquatic environment. The aquatic environment of life is characterized by a clearly defined horizontal and especially vertical zonality. All hydrobionts are strictly confined to living in certain zones, which differ in different living conditions.
In the World Ocean, the water column is called the pelagial, and the bottom is called the benthal. Accordingly, the ecological groups of organisms living in the water column (pelagic) and at the bottom (benthic) are also distinguished.
The bottom, depending on the depth of its occurrence from the water surface, is divided into sublittoral (the area of smooth decrease to a depth of 200 m), bathyal (steep slope), abyssal (oceanic 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 is also distinguished - the edge of the coast, periodically flooded during high tides (Fig. 16).
The open waters of the World Ocean (pelagial) are also divided into vertical zones according to the benthal zones: epipelagial, bathypelagial, abyssopelagial.
The littoral and sublittoral zones are most rich in plants and animals. There is a lot of sunlight, low pressure, significant temperature fluctuations. The inhabitants of the abyssal and ultra-abyssal depths live at a constant temperature, in darkness, and experience enormous pressure, reaching several hundred atmospheres in oceanic depressions.
A similar, but less clearly defined zonality is also characteristic of inland freshwater bodies.
| Parameter name | Meaning |
| Article subject: | Water environment. |
| Rubric (thematic category) | Ecology |
Water is the first medium of life: life arose in it and most groups of organisms were formed. All inhabitants of the aquatic environment are called hydrobionts. A characteristic feature of aquatic environments is the movement of water, ĸᴏᴛᴏᴩᴏᴇ manifests itself in the form currents(transfer of water in one direction) and unrest(evasion of water particles from the initial position with subsequent return to it). The Gulf Stream transports 2.5 million m^3 of water per year, which is 25 times more than all the rivers of the Earth combined. In addition, tidal fluctuations in sea level occur under the influence of the attraction of the Moon and the Sun.
In addition to the movement of water towards the number important properties The water environment includes density and viscosity, ghosting, dissolved oxygen, and mineral content.
Density and viscosity determine, first of all, the conditions for the movement of hydrobionts. The higher the density of water, the more supporting it becomes, the easier it is to stay in it. Another value of density is its pressure on the body. With a deepening of 10.3 m into fresh water and 9.986 m into sea water, the pressure increases by 1 atm. With an increase in viscosity, the resistance to the active movement of organisms increases. The density of living tissues is higher than the density of fresh and sea water, in connection with this, in the process of evolution, aquatic organisms have developed various structures that increase their buoyancy - a general increase in the relative surface of the body due to a decrease in size; flattening; development of various outgrowths (setae); decrease in body density due to the reduction of the skeleton; accumulation of fat and the presence of a swim bladder. Water, unlike air, has a greater buoyancy force, and therefore the maximum size of aquatic organisms is less limited.
Thermal properties water differ significantly from the thermal properties of air. The high specific heat capacity of water (500 times higher) and thermal conductivity (30 times higher) determine a constant and relatively uniform temperature distribution in the aquatic environment. Temperature fluctuations in water are not as sharp as in air. Temperature affects the rate of various processes.
Light and light mode. The sun illuminates the surface of the land and the ocean with the same intensity, but the ability of water to absorb and scatter is quite large, which limits the depth of penetration of light into the ocean. Moreover, rays with different wavelengths are absorbed differently: red is scattered almost immediately, while blue and green go deeper. The zone in which the intensity of photosynthesis exceeds the intensity of respiration is called euphotic zone. The lower limit at which photosynthesis is balanced by respiration is commonly called compensation point.
Transparency water depends on the content of suspended particles in it. Transparency is characterized by the maximum depth at which a specially lowered white disc with a diameter of 30 cm is still visible. clear waters in the Sargasso Sea (the disk is visible at a depth of 66 m), in the Pacific Ocean (60 m), Indian Ocean(50 m). In shallow seas, transparency is 2-15 m, in rivers 1-1.5 m.
Oxygen- Needed for breathing. In water, the distribution of dissolved oxygen is subject to sharp fluctuations. At night, the oxygen content in the water is less. Respiration of hydrobionts is carried out either through the surface of the body, or through special organs (lungs, gills, trachea).
Mineral substances. Sea water mainly contains sodium, magnesium, chloride, and sulfate ions. Fresh calcium ions and carbonate ion.
Ecological classification aquatic organisms. More than 150 thousand animal species and about 10 thousand plant species live in the water. The main biotopes of hydrobionts are: the water column ( pelagial) and the bottom of reservoirs ( benthal). A distinction is made between pelagic and benthic organisms. Pelagial is divided into groups: plankton(a set of organisms that are not capable of active movement and move with water flows) and nekton(large animals, the motor activity of which is sufficient to overcome water currents). Benthos- a set of organisms that inhabit the bottom.
Water environment. - concept and types. Classification and features of the category "Aquatic environment." 2017, 2018.
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You already know such concepts as "habitat" and "environment of life". You need to learn to distinguish between them. What is a "living environment"?
The living environment is a part of nature with a special set of factors, for the existence in which different systematic groups of organisms have formed similar adaptations.
On Earth, four main environments of life can be distinguished: water, land-air, soil, living organism.
Water environment
The aquatic environment of life is characterized by high density, special temperature, light, gas and salt regimes. Organisms that live in the aquatic environment are called hydrobionts(from Greek. hydro- water, bios- life).
Temperature regime of the aquatic environment
In water, the temperature changes to a lesser extent than on land, due to the high specific heat capacity and thermal conductivity of water. An increase in air temperature of 10 °C causes an increase in water temperature of 1 °C. The temperature gradually decreases with depth. At great depths, the temperature regime is relatively constant (not higher than +4 °C). In the upper layers there are daily and seasonal fluctuations (from 0 to +36 °C). Since the temperature in the aquatic environment varies within a narrow range, most hydrobionts require a stable temperature. For them, even small temperature deviations are detrimental, caused, for example, by the discharge of warm Wastewater. Hydrobionts that can exist at large fluctuations in temperature are found only in shallow water bodies. Due to the small volume of water in these reservoirs, significant daily and seasonal temperature fluctuations are observed.
Light regime of the aquatic environment
There is less light in water than in air. Part of the sun's rays are reflected from its surface, and part is absorbed by the water column.
The day underwater is shorter than on land. In summer, at a depth of 30 m, it is 5 hours, and at a depth of 40 m, it is 15 minutes. The rapid decrease in light with depth is due to its absorption by water.
The boundary of the photosynthesis zone in the seas is at a depth of about 200 m. In rivers, it ranges from 1.0 to 1.5 m and depends on the transparency of the water. The transparency of water in rivers and lakes is greatly reduced due to pollution with suspended particles. At a depth of more than 1500 m, there is practically no light.
Gas regime of the aquatic environment
In the aquatic environment, the oxygen content is 20-30 times less than in the air, so it is a limiting factor. Oxygen enters the water due to the photosynthesis of aquatic plants and the ability of atmospheric oxygen to dissolve in water. When water is stirred, the oxygen content in it increases. The upper layers of water are richer in oxygen than the lower ones. With oxygen deficiency, deaths are observed (mass death of aquatic organisms). Winter freezes occur when water bodies are covered with ice. Summer - when, due to the high temperature of the water, the solubility of oxygen decreases. The reason may also be an increase in the concentration of toxic gases (methane, hydrogen sulfide), formed during the decomposition of dead organisms without access to oxygen. Due to the variability of oxygen concentration, most aquatic organisms in relation to it are eurybionts. But there are also stenobionts (trout, planaria, larvae of mayflies and caddis flies) that cannot tolerate a lack of oxygen. They are indicators of water purity. Carbon dioxide dissolves in water 35 times better than oxygen, and its concentration in it is 700 times higher than in air. In water, CO2 accumulates due to the respiration of aquatic organisms, the decomposition of organic residues. Carbon dioxide provides photosynthesis and is used in the formation of calcareous skeletons of invertebrates.
Salt regime of the aquatic environment
Salinity of water plays an important role in the life of hydrobionts. According to the salt content, natural waters are divided into groups presented in the table:
In the World Ocean, salinity averages 35 g/l. Salt lakes have the highest salt content (up to 370 g/l). Typical inhabitants of fresh and salt waters are stenobionts. They do not tolerate fluctuations in salinity of the water. There are relatively few eurybionts (bream, pike perch, pike, eel, stickleback, salmon, etc.). They can live in both fresh and salt water.
Plant adaptations to life in water
All plants in the aquatic environment are called hydrophytes(from Greek. hydro- water, phyton- plant). Only algae live in salty waters. Their body is not divided into tissues and organs. Algae adapted to the change in the composition of the solar spectrum depending on the depth by changing the composition of their pigments. When moving from the upper layers of water to the deep ones, the color of the algae changes in the sequence: green - brown - red (the deepest algae).
Green algae contain green, orange and yellow pigments. They are capable of photosynthesis with a sufficiently high intensity of sunlight. Therefore, green algae live in small fresh water bodies or in shallow sea water. These include: spirogyra, ulotrix, ulva, etc. Brown algae, in addition to green, contain brown and yellow pigments. They are able to capture less intense solar radiation at a depth of 40-100 m. Representatives of brown algae are fucus and kelp, which live only in the seas. Red algae (porphyra, phyllophora) can live at a depth of more than 200 m. In addition to green, they have red and blue pigments that can capture even slight light at great depths.
In freshwater bodies, the stems of higher plants have poorly developed mechanical tissue. For example, if you take a white water lily or a yellow water lily out of the water, then their stems droop and are not able to support the flowers in an upright position. Water serves as a support for them due to its high density. An adaptation to a lack of oxygen in water is the presence of aerenchyma (air-bearing tissue) in plant organs. Minerals are in the water, so the conductive and root systems are poorly developed. Roots may be completely absent (duckweed, elodea, pondweed) or serve to fix in the substrate (cattail, arrowhead, chastukha). There are no root hairs on the roots. The leaves are often thin and long or strongly dissected. The mesophyll is not differentiated. The stomata of floating leaves are on the upper side, while those immersed in water are absent. Some plants are characterized by the presence of leaves of different shapes (heterophilia) depending on where they are located. In water lily and arrowhead, the shape of the leaves in the water and in the air is different.
Pollen, fruits and seeds of aquatic plants are adapted to be dispersed by water. They have cork outgrowths or strong shells that prevent water from getting inside and rotting.
Animal adaptations to life in the water
In the aquatic environment, the animal world is richer than the plant world. Thanks to their independence from sunlight, animals inhabited the entire water column. According to the type of morphological and behavioral adaptations, they are divided into the following ecological groups: plankton, nekton, benthos.
Plankton(from Greek. planktos- soaring, wandering) - organisms that live in the water column and move under the influence of its current. These are small crustaceans, coelenterates, larvae of some invertebrates. All their adaptations are aimed at increasing the buoyancy of the body:
- an increase in the surface of the body due to flattening and elongation of the shape, the development of outgrowths and setae;
- a decrease in body density due to the reduction of the skeleton, the presence of fat drops, air bubbles, and mucous membranes.
Nekton(from Greek. nektos- floating) - organisms that live in the water column and lead an active lifestyle. Representatives of the nekton are fish, cetaceans, pinnipeds, cephalopods. To resist the current, they are helped by adaptations to active swimming and a decrease in body friction. Active swimming is achieved due to well-developed muscles. In this case, the energy of the ejected jet of water, bending of the body, fins, flippers, etc. can be used.
skin scales and mucus.
Benthos(from Greek. benthos- depth) - organisms that live at the bottom of a reservoir or in the thickness of the bottom soil.
Adaptations of benthic organisms are aimed at reducing buoyancy:
- weighting of the body due to shells (molluscs), chitinous covers (crayfish, crabs, lobsters, spiny lobsters);
- fixation at the bottom with the help of fixation organs (suckers in leeches, hooks in caddis larvae) or a flattened body (stingrays, flounder). Some representatives burrow into the ground (polychaete worms).
In lakes and ponds, another ecological group of organisms is distinguished - neuston. Neuston- organisms associated with the surface film of water and living permanently or temporarily on this film or up to 5 cm deep from its surface. Their body is not wetted because its density is less than that of water. Specially arranged limbs allow you to move on the surface of the water without sinking (water strider bugs, whirlwind beetles). A peculiar group of aquatic organisms is also periphyton— organisms that form a fouling film on underwater objects. Representatives of the periphyton are: algae, bacteria, protists, crustaceans, bivalves, oligochaetes, bryozoans, sponges.
On planet Earth, there are four main environments of life: water, land-air, soil and living organism. In the aquatic environment, oxygen is the limiting factor. According to the nature of adaptations, aquatic inhabitants are divided into ecological groups: plankton, nekton, benthos.
Density of water is a factor that determines the conditions for the movement of aquatic organisms and pressure at different depths. For distilled water, the density is 1 g/cm3 at 4°C. The density of natural waters containing dissolved salts may be higher, up to 1.35 g/cm 3 . The pressure increases with depth by approximately 1 10 5 Pa (1 atm) for every 10 m on average.
Due to the sharp pressure gradient in water bodies, hydrobionts are generally much more eurybatic than land organisms. Some species, distributed at different depths, endure pressure from several to hundreds of atmospheres. For example, holothurians of the genus Elpidia and worms Priapulus caudatus inhabit from the coastal zone to the ultraabyssal. Even freshwater inhabitants, such as ciliates-shoes, suvoys, swimming beetles, etc., withstand up to 6 10 7 Pa (600 atm) in the experiment.
However, many inhabitants of the seas and oceans are relatively wall-to-wall and confined to certain depths. Stenobatnost most often characteristic of shallow and deep-sea species. Only the littoral is inhabited by the annelid worm Arenicola, mollusk molluscs (Patella). Many fish, for example from the group of anglers, cephalopods, crustaceans, pogonophores, starfish, etc., are found only at great depths at a pressure of at least 4 10 7 - 5 10 7 Pa (400-500 atm).
The density of water makes it possible to lean on it, which is especially important for non-skeletal forms. The density of the medium serves as a condition for soaring in water, and many hydrobionts are adapted precisely to this way of life. Suspended organisms floating in water are combined into a special ecological group of hydrobionts - plankton ("planktos" - soaring).
Rice. 39. An increase in the relative surface of the body in planktonic organisms (according to S. A. Zernov, 1949):
A - rod-shaped forms:
1 - diatom Synedra;
2 - cyanobacterium Aphanizomenon;
3 - peridinean alga Amphisolenia;
4 - Euglena acus;
5 - cephalopod Doratopsis vermicularis;
6 - copepod Setella;
7 - larva of Porcellana (Decapoda)
B - dissected forms:
1 - mollusk Glaucus atlanticus;
2 - Tomopetris euchaeta worm;
3 - cancer larva Palinurus;
4 - fish larva of monkfish Lophius;
5 – copepod Calocalanus pavo
Plankton includes unicellular and colonial algae, protozoa, jellyfish, siphonophores, ctenophores, winged and keeled mollusks, various small crustaceans, larvae of bottom animals, fish eggs and fry, and many others (Fig. 39). Planktonic organisms have many similar adaptations that increase their buoyancy and prevent them from sinking to the bottom. These adaptations include: 1) a general increase in the relative surface of the body due to a decrease in size, flattening, elongation, the development of numerous outgrowths or bristles, which increases friction against water; 2) a decrease in density due to the reduction of the skeleton, the accumulation in the body of fats, gas bubbles, etc. In diatoms, reserve substances are deposited not in the form of heavy starch, but in the form of fat drops. The night light Noctiluca is distinguished by such an abundance of gas vacuoles and fat droplets in the cell that the cytoplasm in it looks like strands that merge only around the nucleus. Siphonophores, a number of jellyfish, planktonic gastropods, and others also have air chambers.
Seaweed (phytoplankton) hover passively in the water, while most planktonic animals are capable of active swimming, but to a limited extent. Planktonic organisms cannot overcome currents and are transported by them over long distances. many kinds zooplankton however, they are capable of vertical migrations in the water column for tens and hundreds of meters, both due to active movement and by regulating the buoyancy of their body. A special kind of plankton is the ecological group neuston ("nein" - to swim) - the inhabitants of the surface film of water on the border with the air.
The density and viscosity of water greatly affect the possibility of active swimming. Animals capable of fast swimming and overcoming the force of currents are combined into an ecological group. nekton ("nektos" - floating). Representatives of nekton are fish, squid, dolphins. Rapid movement in the water column is possible only in the presence of a streamlined body shape and highly developed muscles. The torpedo-shaped form is developed by all good swimmers, regardless of their systematic affiliation and the method of movement in the water: reactive, by bending the body, with the help of the limbs.
Oxygen mode. In oxygen-saturated water, its content does not exceed 10 ml per 1 liter, which is 21 times lower than in the atmosphere. Therefore, the conditions for the respiration of hydrobionts are much more complicated. Oxygen enters the water mainly due to the photosynthetic activity of algae and diffusion from the air. Therefore, the upper layers of the water column, as a rule, are richer in this gas than the lower ones. With an increase in temperature and salinity of water, the concentration of oxygen in it decreases. In layers heavily populated by animals and bacteria, a sharp deficiency of O 2 can be created due to its increased consumption. For example, in the World Ocean, depths rich in life 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. Near the bottom of water bodies, conditions can be close to anaerobic.
Among the aquatic inhabitants there are many species that can tolerate wide fluctuations in the oxygen content in the water, up to its almost complete absence. (euryoxybionts - "oxy" - oxygen, "biont" - inhabitant). These include, for example, freshwater oligochaetes Tubifex tubifex, gastropods Viviparus viviparus. Among fish, carp, tench, crucian carp can withstand very low saturation of water with oxygen. However, a number of types stenoxybiont - they can exist only at a sufficiently high saturation of water with oxygen (rainbow trout, brown trout, minnow, ciliary worm Planaria alpina, larvae of mayflies, stoneflies, etc.). Many species are capable of falling into an inactive state with a lack of oxygen - anoxybiosis - and thus experience an unfavorable period.
Respiration of hydrobionts is carried out either through the surface of the body, or through specialized organs - gills, lungs, trachea. In this case, the covers can serve as an additional respiratory organ. For example, loach fish consumes on average up to 63% of oxygen through the skin. If gas exchange occurs through the integument of the body, then they are very thin. Breathing is also facilitated by increasing the surface. This is achieved in the course of the evolution of species by the formation of various outgrowths, flattening, elongation, and a general decrease in body size. Some species with a lack of oxygen actively change the size of the respiratory surface. Tubifex tubifex worms strongly elongate the body; hydras and sea anemones - tentacles; echinoderms - ambulacral legs. Many sedentary and inactive animals renew the water around them, either by creating its directed current, or by oscillatory movements contributing to its mixing. For this purpose, bivalve mollusks use cilia lining the walls of the mantle cavity; crustaceans - the work of the abdominal or thoracic legs. Leeches, larvae of ringing mosquitoes (bloodworm), many oligochaetes sway the body, leaning out of the ground.
Some species have a combination of water and air respiration. Such are lungfish, discophant siphonophores, many pulmonary molluscs, crustaceans Gammarus lacustris, and others. Secondary aquatic animals usually retain the atmospheric type of breathing as more energetically favorable and therefore need contact with the air, for example, pinnipeds, cetaceans, water beetles, mosquito larvae, etc.
The lack of oxygen in water sometimes leads to catastrophic phenomena - zamoram, accompanied by the death of many hydrobionts. winter freezes often caused by the formation of ice on the surface of water bodies and the termination of contact with air; summer- an increase in water temperature and a decrease in the solubility of oxygen as a result.
The frequent death of fish and many invertebrates in winter is typical, for example, for the lower part of the Ob River basin, whose waters, flowing from the swampy areas of the West Siberian Lowland, are extremely poor in dissolved oxygen. Sometimes zamora occur in the seas.
In addition to a lack of oxygen, deaths can be caused by an increase in the concentration of toxic gases in water - methane, hydrogen sulfide, CO 2, etc., formed as a result of the decomposition of organic materials at the bottom of reservoirs.
Salt mode. Maintaining the water balance of hydrobionts has its own specifics. If for terrestrial animals and plants it is most important to provide the body with water in conditions of its deficiency, then for hydrobionts it is no less important to maintain a certain amount of water in the body when it is in excess in the environment. An excessive amount of water in the cells leads to a change in their osmotic pressure and a violation of the most important vital functions.
Most aquatic life poikilosmotic: the osmotic pressure in their body depends on the salinity of the surrounding water. Therefore, for aquatic organisms, the main way to maintain their salt balance is to avoid habitats with unsuitable salinity. Freshwater forms cannot exist in the seas, marine forms cannot tolerate desalination. If the salinity of the water is subject to change, the animals move in search of a favorable environment. For example, during the desalination of the surface layers of the sea after heavy rains, radiolarians, marine crustaceans Calanus and others descend to a depth of 100 m. Vertebrates, higher crayfish, insects and their larvae that live in water belong to homoiosmotic species, maintaining a constant osmotic pressure in the body, regardless of the concentration of salts in the water.
In freshwater species, the body juices are hypertonic relative to the surrounding water. They are in danger of becoming overwatered unless their intake is prevented or the excess water is removed from the body. In protozoa, this is achieved by the work of excretory vacuoles, in multicellular organisms, by the removal of water through the excretory system. Some ciliates every 2-2.5 minutes release an amount of water equal to the volume of the body. The cell expends a lot of energy on “pumping out” excess water. With an increase in salinity, the work of vacuoles slows down. So, in Paramecium shoes, at a water salinity of 2.5% o, the vacuole pulsates with an interval of 9 s, at 5% o - 18 s, at 7.5% o - 25 s. At a salt concentration of 17.5% o, the vacuole stops working, since the difference in osmotic pressure between the cell and the external environment disappears.
If the water is hypertonic in relation to the body fluids of hydrobionts, they are threatened with dehydration as a result of osmotic losses. Protection against dehydration is achieved by increasing the concentration of salts also in the body of hydrobionts. Dehydration is prevented by water-impervious covers of homoiosmotic organisms - mammals, fish, higher crayfish, aquatic insects and their larvae.
Many poikilosmotic species go into an inactive state - anabiosis as a result of water deficiency in the body with increasing salinity. This is characteristic of species that live in pools of sea water and in the littoral zone: rotifers, flagellates, ciliates, some crustaceans, the Black Sea polychaetes Nereis divesicolor, etc. Salt hibernation- a means to survive unfavorable periods in conditions of variable salinity of water.
Truly euryhaline There are not so many species that can live in an active state in both fresh and salt water among aquatic inhabitants. These are mainly species inhabiting river estuaries, estuaries and other brackish water bodies.
Temperature regime water bodies are more stable than on land. It's connected with physical properties water, especially high specific heat capacity, due to which the receipt or release of a significant amount of heat does not cause too sharp temperature changes. Evaporation of water from the surface of water bodies, which consumes about 2263.8 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.
The amplitude of annual temperature fluctuations in the upper layers of the ocean is no more than 10-15 °C, in continental waters - 30-35 °C. Deep layers of water are characterized by constant temperature. In equatorial waters mean annual temperature surface layers + (26-27) ° С, in polar - about 0 ° C and below. In hot ground springs, the water temperature can approach +100 °C, and in underwater geysers at high pressure on the ocean floor, a temperature of +380 °C has been recorded.
Thus, in reservoirs there is a fairly significant variety of temperature conditions. Between the upper layers of water with seasonal temperature fluctuations expressed in them and the lower ones, where the thermal regime is constant, there is a zone of temperature jump, or thermocline. The thermocline is more pronounced in warm seas, where the temperature difference between the outer and deep waters is greater.
Due to the more stable temperature regime of water among hydrobionts, to a much greater extent than among the population of the land, stenothermy is common. Eurythermal species are found mainly in shallow continental water bodies and in the littoral of the seas of high and temperate latitudes, where daily and seasonal temperature fluctuations are significant.
Light mode. There is much less light in water than in air. Part of the rays incident on the surface of the reservoir is reflected into the air. The reflection is stronger the lower the position of the Sun, so the day under water is shorter than on land. For example, a summer day near the island of Madeira at a depth of 30 m - 5 hours, and at a depth of 40 m - only 15 minutes. The rapid decrease in the amount of light with depth is due to its absorption by water. Rays with different wavelengths are absorbed differently: reds disappear close to the surface, while blue-greens penetrate much deeper. Deepening twilight in the ocean is first green, then blue, blue and blue-violet, finally giving way to permanent darkness. Accordingly, green, brown and red algae replace each other with depth, specialized in capturing light with different wavelengths.
The color of animals changes with depth in the same way. The inhabitants of the littoral and sublittoral zones are most brightly and diversely colored. Many deep-seated organisms, like cave ones, do not have pigments. In the twilight zone, red coloration is widespread, which is complementary to the blue-violet light at these depths. Additional color rays are most fully absorbed by the body. This allows the animals to hide from enemies, since their red color in blue-violet rays is visually perceived as black. Red coloration is typical for such animals. twilight zone like sea bass, red coral, various crustaceans, etc.
In some species that live near the surface of water bodies, the eyes are divided into two parts with different ability to the refraction of rays. One half of the eye sees in the air, the other half in the water. This “four-eyedness” is characteristic of the whirling beetles, the American fish Anableps tetraphthalmus, one of the tropical species of blennies Dialommus fuscus. This fish sits in recesses at low tides, exposing part of its head from the water (see Fig. 26).
The absorption of light is the stronger, the lower the transparency of water, which depends on the number of particles suspended in it.
Transparency is characterized by the maximum depth at which a specially lowered white disk with a diameter of about 20 cm (Secchi disk) is still visible. The most transparent waters are in the Sargasso Sea: the disk is visible to a depth of 66.5 m. In the Pacific Ocean, the Secchi disk is visible up to 59 m, in the Indian Ocean - up to 50, in shallow seas - up to 5-15 m. The transparency of rivers is on average 1-1 .5 m, and in the most muddy rivers, for example, in the Central Asian Amu Darya and Syr Darya, only a few centimeters. The boundary of the photosynthesis zone therefore varies greatly in different water bodies. In the clearest waters euphotic zone, or zone of photosynthesis, extends to depths of no more than 200 m, twilight, or dysphotic, the zone occupies depths up to 1000-1500 m, and deeper, in aphotic zone, sunlight does not penetrate at all.
The amount of light in the upper layers of water bodies varies greatly depending on the latitude of the area and the time of year. Long polar nights greatly limit the time available for photosynthesis in the Arctic and Antarctic basins, and the ice cover makes it difficult for light to reach all freezing water bodies in winter.
In the dark depths of the ocean, organisms use the light emitted by living beings as a source of visual information. The glow of a living organism is called bioluminescence. Luminous species are found in almost all classes of aquatic animals from protozoa to fish, as well as among bacteria, lower plants and fungi. Bioluminescence appears to have occurred repeatedly in different groups on different stages evolution.
The chemistry of bioluminescence is now fairly well understood. The reactions used to generate light are varied. But in all cases it is the oxidation of complex organic compounds (luciferins) using protein catalysts (luciferase). Luciferins and luciferases have different structures in different organisms. During the reaction, the excess energy of the excited luciferin molecule is released in the form of light quanta. Living organisms emit light in impulses, usually in response to stimuli coming from the external environment.
Glow may not play a special ecological role in the life of the species, but may be a by-product of the vital activity of cells, as, for example, in bacteria or lower plants. It receives ecological significance only in animals with a sufficiently developed nervous system and organs of vision. In many species, the luminous organs acquire a very complex structure with a system of reflectors and lenses that amplify the radiation (Fig. 40). A number of fish and cephalopods, unable to generate light, use symbiotic bacteria that multiply in special organs of these animals.
Rice. 40. Luminous organs of aquatic animals (according to S. A. Zernov, 1949):
1 - deep-sea angler with a flashlight over the toothed mouth;
2 - distribution of luminous organs in fish of this family. Mystophidae;
3 - the luminous organ of the fish Argyropelecus affinis:
a - pigment, b - reflector, c - luminous body, d - lens
Bioluminescence has mainly a signal value in the life of animals. Light signals can be used for orientation in the flock, attracting individuals of the opposite sex, luring victims, for masking or distraction. The flash of light can be a defense against a predator, blinding or disorienting it. For example, deep-sea cuttlefish, escaping from an enemy, release a cloud of luminous secretion, while species that live in illuminated waters use a dark liquid for this purpose. In some bottom worms - polychaetes - the luminous organs develop by the period of maturation of the reproductive products, and the females glow brighter, and the eyes are better developed in males. In predatory deep-sea fish from the anglerfish order, the first ray of the dorsal fin is shifted to the upper jaw and turned into a flexible "rod" that carries at the end a worm-like "bait" - a gland filled with mucus with luminous bacteria. By regulating the blood flow to the gland and therefore the supply of oxygen to the bacterium, the fish can arbitrarily cause the "bait" to glow, imitating the movements of the worm and luring the prey.
Question 1. What are the main features of the life of organisms in the aquatic environment, in the air-terrestrial environment, in the soil.
The features of the life of organisms in the aquatic environment, the terrestrial-air environment and in the soil are determined by the physical and chemical properties of these living environments. These properties have a significant impact on the action of other factors of inanimate nature - they stabilize seasonal temperature fluctuations (water and soil), gradually change the illumination (water) or completely exclude it (soil), etc.
Water is a dense medium compared to air, which has a buoyant force and is a good solvent. Therefore, many organisms that live in water are characterized by a weak development of supporting tissues (aquatic plants, protozoa, coelenterates, etc.), special methods of locomotion (floating, jet propulsion), breathing patterns, and adaptations to maintain a constant osmotic pressure in the cells that form their bodies.
The density of air is much lower than the density of water, therefore, terrestrial organisms have highly developed supporting tissues - the internal and external skeleton.
Soil is the top layer of land, transformed as a result of the vital activity of living beings. Between soil particles there are numerous cavities that can be filled with water or air. Therefore, the soil is inhabited by both aquatic and air-breathing organisms.
Question 2. What adaptations have developed in organisms to live in the aquatic environment?
The aquatic environment is denser than the air environment, which determines the adaptations for movement in it.
For active movement in the water, a streamlined body shape and well-developed muscles (fish, cephalopods - squids, mammals - dolphins, seals) are necessary.
Planktonic organisms (hovering in water) have adaptations that increase their buoyancy, such as an increase in the relative surface of the body due to numerous outgrowths and setae; decrease in density due to the accumulation in the body of fats, gas bubbles (unicellular algae, protozoa, jellyfish, small crustaceans).
Organisms living in the aquatic environment are also characterized by adaptations to maintain the water-salt balance. Freshwater species have adaptations to remove excess water from the body. This, for example, is the excretory vacuoles in protozoa. In salt water, on the contrary, it is necessary to protect the body from dehydration, which is achieved by increasing the concentration of salts in the body.
Another way to maintain your water-salt balance is to move to places with favorable salinity levels.
And finally, the constancy of the water-salt environment of the body is provided by covers impervious to water (mammals, higher crayfish, aquatic insects and their larvae).
For life, plants need the light energy of the Sun, so aquatic plants live only at those depths where light can penetrate (usually no more than 100 m). With an increase in the depth of habitation in plant cells, the composition of pigments involved in the process of photosynthesis changes, which makes it possible to capture the parts of the solar spectrum penetrating into the depths.
Question 3. How do organisms avoid the negative effects of low temperatures?
At low temperatures, there is a danger of stopping metabolism, so organisms have developed special adaptation mechanisms to stabilize it.
Plants are least adapted to sharp fluctuations in temperature. With a sharp drop in temperature below 0 ° C, the water in the tissues can turn into ice, which can damage them. But plants are able to withstand low negative temperatures by binding free water molecules into complexes incapable of forming ice crystals (for example, by accumulating up to 20-30% of sugars or fatty oils in cells).
With a gradual decrease in temperature in the process of seasonal climatic changes, a dormant period begins in the life of many plants, accompanied by either partial or complete death of terrestrial vegetative organs (herbaceous forms), or a temporary cessation or slowdown of the main physiological processes - photosynthesis and transport of substances.
In animals, the most reliable protection against low ambient temperatures is warm-bloodedness, but not all have it. The following ways of adaptation of animals to low temperatures can be distinguished: chemical, physical and behavioral thermoregulation.
Chemical thermoregulation is associated with an increase in heat production with a decrease in temperature through the intensification of redox processes. This path requires a large amount of energy, so animals in harsh climatic conditions need more food. This type of thermoregulation is carried out reflexively.
Many cold-blooded animals are capable of maintaining optimal temperature body through muscle work. For example, bumblebees in cool weather warm up their body with a shiver to 32-33 ° C, which gives them the opportunity to take off and feed.
Physical thermoregulation is associated with the presence in animals of special body covers - feather or hair, which, due to their structure, form an air gap between the body and the environment, since air is known to be an excellent heat insulator. In addition, many animals living in harsh climatic conditions accumulate subcutaneous fat, which also has thermal insulation properties.
Behavioral thermoregulation is associated with moving in space in order to avoid unfavorable temperatures for life, creating shelters, crowding into groups, changing activity at different times of the day or year.
Question 4. What are the main features of organisms that use the bodies of other organisms as a habitat?
The conditions of life inside another organism are characterized by greater constancy compared to the conditions of the external environment; therefore, organisms that find a place for themselves in the body of plants or animals often completely lose the organs and systems necessary for free-living species (sense organs, organs of locomotion, digestion, etc.). ), but at the same time they have devices for holding in the host's body (hooks, suckers, etc.) and effective reproduction.
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