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Post topic aquatic habitat. Main components of the habitat

What does it take to survive? Food, water, shelter? Animals need the same things and live in habitats that can provide them with everything they need. Each organism has a unique habitat that satisfies all its needs. Animals and plants that live in a certain area and share resources form different communities within which the organisms occupy their niche. There are three main habitats: aquatic, air-terrestrial and soil.

Ecosystem

An ecosystem is an area in which all living and nonliving elements of nature interact and depend on each other. An organism's habitat is a place that is home to a living thing. This environment includes all the necessary conditions for survival. For the animal, this means that here it can find food and a partner for reproduction and procreation.

For a plant, a good habitat must provide the right combination of light, air, water and soil. For example, the prickly pear cactus, adapted to sandy soils, dry climates and bright sunlight, grows well in desert areas. It would not be able to survive in wet, cool places with a lot of rainfall.

Main components of the habitat

The main components of a habitat are shelter, water, food and space. The habitat, as a rule, includes all these elements, but in nature you can also find the absence of one or two components. For example, the habitat of an animal such as a cougar provides the right amount of food (deer, porcupines, rabbits, rodents), water (lake, river) and shelter (trees or burrows). However, this large predator sometimes lacks space, space to establish its own territory.

Space

The amount of space an organism requires varies widely from species to species. For example, a simple ant requires only a few square centimeters, but a single large animal, a panther, needs a large amount of space, which can be about 455 square kilometers, in which to hunt and find a mate. Plants also need space. Some trees reach more than 4.5 meters in diameter and 100 m in height. Such massive plants require more space than ordinary trees and shrubs in a city park.

Food

The availability of food is the most important part of the habitat of a particular organism. Too little or, conversely, too much food can disturb the habitat. In a sense, it is easier for plants to find food for themselves, since they themselves are able to create their own food through photosynthesis. Aquatic habitats generally require the presence of algae. A nutrient such as phosphorus helps them spread.

When there is a sudden increase in phosphorus in a freshwater habitat, it means a rapid proliferation of algae, called a bloom, which turns the water green, red or brown. Algal blooms can also suck oxygen from the water, destroying habitat for organisms such as fish and plants. Thus, excess nutrients for algae can negatively affect the entire food chain of aquatic life.

Water

Water is essential for all forms of life. Almost every habitat must have some form of water supply. Some organisms need a lot of water, while others need very little. For example, a dromedary camel can go without water for quite a long time. Dromedary camels (North Africa and the Arabian Peninsula), which have one hump, can walk 161 kilometers without drinking a sip of water. Despite rare access to water and a hot, dry climate, these animals are adapted to such living conditions. On the other hand, there are plants that grow best in damp places such as swamps and swamps. Aquatic habitats are home to a variety of organisms.

Shelter

The body needs shelter that will protect it from predators and bad weather. These animal shelters can take many forms. A single tree, for example, can provide a safe habitat for many organisms. The caterpillar may hide under the underside of leaves. A cool, damp area near tree roots can provide shelter for the chaga mushroom. The bald eagle finds its home in the canopy, where it builds a nest and looks out for future prey.

Aquatic habitat

Animals that use water as a habitat are called aquatic. Depending on what nutrients and chemical compounds are dissolved in water, the concentration of certain types of aquatic inhabitants is determined. For example, herring live in salty sea waters, while tilapia and salmon live in fresh water.

Plants need moisture and sunlight to carry out photosynthesis. They obtain water from the soil through their roots. Water carries nutrients to other parts of the plant. Some plants, such as water lilies, need a lot of water, while desert cacti can go months without moisture.

Animals also need water. Most should drink regularly to avoid dehydration. For many animals, aquatic habitats are their home. For example, frogs and turtles use water sources to lay eggs and reproduce. Some snakes and other reptiles live in water. Fresh water often carries a lot of dissolved nutrients, without which aquatic organisms would not be able to continue to exist.

Aquatic life environment

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

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

Aquatic life environment

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

Specific properties of water as a habitat

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

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

The following factors also influence the bionta of aquatic ecosystems:

1. concentration of dissolved oxygen;

2. water temperature;

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Water covers 71% of the globe's area and makes up 1/800th of the land volume. The bulk of water is concentrated in the seas and oceans - 94–98%, polar ice contains about 1.2% of water and a very small proportion - less than 0.5%, in fresh waters of rivers, lakes and swamps. These relationships are constant, although in nature the water cycle continues without ceasing.

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

In the World Ocean, as in the mountains, vertical zoning is pronounced. The pelagic - the entire water column - and the benthic - the bottom - differ especially greatly in ecology. Zoning is especially clearly manifested in lakes of temperate latitudes (Fig. 2.1). In the water mass as a habitat for organisms, 3 vertical layers can be distinguished: epilimnion, metalimnion and hypolimnion. The waters of the surface layer, the epilimnion, warm up and mix in summer under the influence of wind and convection currents. In autumn, surface waters, cooling and becoming denser, begin to sink, and the temperature difference between the layers equalizes. With further cooling, the waters of the epilimnion become colder than the waters of the hypolimnion. In spring, the reverse process occurs, ending with a period of summer stagnation. The bottom of lakes (benthal) is divided into 2 zones: a deeper zone - profundal, approximately corresponding to the part of the bed filled with waters of the hypolimnion, and a coastal zone - littoral, usually extending inland to the limit of macrophyte growth. According to the transverse profile of the river, a coastal zone is distinguished - ripal and an open zone - medial. In the open zone, current speeds are higher and the population is quantitatively poorer than in the coastal zone.

Ecological groups of hydrobionts.

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

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

Plankton (planktos - wandering, soaring) is a collection of plants (phytoplankton: diatoms, green and blue-green (fresh water bodies only) algae, plant flagellates, peridinea, etc.) and small animal organisms (zooplankton: small crustaceans, of the larger ones - pteropods, jellyfish, ctenophores, some worms), living at different depths, but not capable of active movement and resistance to currents. Plankton also includes animal larvae, forming a special group - neuston. This is a passively floating “temporary” population of the uppermost layer of water, represented by various animals (decapods, barnacles and copepods, echinoderms, polychaetes, fish, mollusks, etc.) in the larval stage. The larvae, growing up, move into the lower layers of the pelagel. Above the neuston is pleiston - these are organisms in which the upper part of the body grows above the water, and the lower part in the water (duckweed, egg capsules, water lilies, etc.). Plankton plays an important role in the trophic relationships of the biosphere, because is food for many aquatic inhabitants, including the main food for baleen whales.

Benthos (benthos – depth) – hydrobionts of the bottom. It is represented mainly by attached or slowly moving animals (zoobenthos: foraminephores, fish, sponges, coelenterates, worms, brachiopods, ascidians, etc.), more numerous in shallow water. In shallow water, benthos also includes plants (phytobenthos: diatoms, green, brown, red algae, bacteria). At depths where there is no light, phytobenthos is absent. Along the coasts there are flowering plants of zoster, rupiah. Rocky areas of the bottom are richest in phytobenthos. In lakes, zoobenthos is less abundant and diverse than in the sea. It is formed by protozoa (ciliates, daphnia), leeches, mollusks, insect larvae, etc. The phytobenthos of lakes is formed by free-floating diatoms, green and blue-green algae; brown and red algae are absent. Taking root coastal plants in lakes form clearly defined zones, the species composition and appearance of which are consistent with the environmental conditions in the land-water boundary zone. Hydrophytes grow in the water near the shore - plants semi-submerged in water (arrowhead, whitewing, reeds, cattails, sedges, trichaetes, reeds). They are replaced by hydatophytes - plants immersed in water, but with floating leaves (lotus, duckweed, egg capsules, chilim, takla) and - further - completely submerged (pondweed, elodea, hara). Hydatophytes also include plants floating on the surface (duckweed).

The high density of the aquatic environment determines the special composition and nature of changes in life-supporting factors. Some of them are the same as on land - heat, light, others are specific: water pressure (increases with depth by 1 atm for every 10 m), oxygen content, salt composition, acidity. Due to the high density of the environment, the values of heat and light change much faster with the altitude gradient than on land.

Thermal mode.

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

The range of water temperatures in the World Ocean is 38° (from –2 to +36°С), in fresh water bodies – 26° (from –0.9 to +25°С). With depth, the water temperature drops sharply. Up to 50 m there are daily temperature fluctuations, up to 400 – seasonal, deeper it becomes constant, dropping to +1–3°C (in the Arctic it is close to 0°C). Since the temperature regime in reservoirs is relatively stable, their inhabitants are characterized by stenothermism. Minor temperature fluctuations in one direction or another are accompanied by significant changes in aquatic ecosystems. Examples: a “biological explosion” in the Volga delta due to a decrease in the level of the Caspian Sea - the proliferation of lotus thickets (Nelumba kaspium), in southern Primorye - the overgrowth of whitefly in oxbow rivers (Komarovka, Ilistaya, etc.) along the banks of which woody vegetation was cut down and burned.

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

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

During periods of stagnation, three layers are clearly distinguished: the upper (epilimnion) with the sharpest seasonal fluctuations in water temperature, the middle (metalimnion or thermocline), in which a sharp jump in temperature occurs, and the bottom (hypolimnion), in which the temperature changes little throughout the year. During periods of stagnation, oxygen deficiency occurs in the water column - in the bottom part in summer, and in the upper part in winter, as a result of which fish kills often occur in winter. In stagnant reservoirs (lakes) of temperate latitudes, vertical mixing takes place in spring and autumn, and during these seasons the temperature throughout the reservoir becomes uniform, i.e. homothermy occurs. In summer and winter, as a result of a sharp increase in heating or cooling of the upper layers, the mixing of water stops. This phenomenon is called temperature dichotomy, and the period of temporary stagnation is called stagnation (summer or winter). In summer, lighter warm layers remain on the surface, located above heavy cold ones. In winter, on the contrary, there is warmer water in the bottom layer, since directly under the ice the temperature of surface waters is less than +4°C and, due to the physicochemical properties of water, they become lighter than water with a temperature above +4°C.

Light mode.

The intensity of light in water is greatly weakened due to its reflection by the surface and absorption by the water itself. This greatly affects the development of photosynthetic plants. The less transparent the water, the more light is absorbed. Water transparency is limited by mineral suspensions and plankton. It decreases with the rapid development of small organisms in summer, and in temperate and northern latitudes even in winter, after the establishment of ice cover and covering it with snow on top. In small lakes, only tenths of a percent of light penetrates to a depth of 2 m. With depth it becomes darker, and the color of the water first becomes green, then blue, indigo and finally blue-violet, turning into complete darkness. Hydrobionts also change color accordingly, adapting not only to the composition of light, but also to its lack - chromatic adaptation. In light zones, in shallow waters, green algae (Chlorophyta) predominate, the chlorophyll of which absorbs red rays, with depth they are replaced by brown (Phaephyta) and then red (Rhodophyta). At great depths, phytobenthos is absent. Plants have adapted to the lack of light by developing large chromatophores, which provide a low point of compensation for photosynthesis, as well as by increasing the area of assimilating organs (leaf surface index). For deep-sea algae, strongly dissected leaves are typical, the leaf blades are thin and translucent. Semi-submerged and floating plants are characterized by heterophylly - the leaves above the water are the same as those of land plants, they have a solid blade, the stomatal apparatus is developed, and in the water the leaves are very thin, consisting of narrow thread-like lobes. Animals, like plants, naturally change their color with depth. In the upper layers they are brightly colored in different colors, in the twilight zone (sea bass, corals, crustaceans) they are painted in colors with a red tint - it is more convenient to hide from enemies. Deep-sea species lack pigments.

The water shell of our planet(the totality of oceans, seas, continental waters, ice sheets) is called the hydrosphere. In a broader sense, the hydrosphere also includes groundwater, ice and snow in the Arctic and Antarctic, as well as atmospheric water and water contained in living organisms.

The bulk of the water in the hydrosphere is concentrated in the seas and oceans, the second place is occupied by groundwater, the third is the ice and snow of the Arctic and Antarctic regions. The total volume of natural waters is approximately 1.39 billion km 3 (1/780 of the planet's volume). Water covers 71% of the globe's surface (361 million km2).

Water reserves on the planet (% of the total) were distributed as follows:

Water- an integral part of all elements of the biosphere, not only bodies of water, but also air, living beings. This is the most abundant natural compound on the planet. Without water, neither animals, nor plants, nor humans can exist. For the survival of any organism, a certain amount of water is required daily, so free access to water is a vital necessity.

The liquid shell covering the Earth distinguishes it from its neighboring planets. The hydrosphere is important for the development of life not only in a chemical sense. Its role is also great in maintaining a relatively constant climate, which has allowed life to reproduce for more than three billion years. Since life requires that the prevailing temperatures be in the range from 0 to 100 °C, i.e. within the limits that allow the hydrosphere to remain largely in the liquid phase, we can conclude that the temperature on Earth has been relatively constant throughout most of its history.

The hydrosphere serves as a planetary accumulator of inorganic and organic matter, which is brought into the ocean and other bodies of water by rivers, atmospheric flows, and is also formed by the reservoirs themselves. Water is the great distributor of heat on Earth. Heated by the Sun at the equator, it transfers heat through giant streams of sea currents in the World Ocean.

Water is part of minerals, is found in the cells of plants and animals, influences climate formation, participates in the cycle of substances in nature, contributes to the deposition of sedimentary rocks and soil formation, and is a source of cheap electricity: it is used in industry, agriculture and for domestic needs. .

Despite the seemingly sufficient amount of water on the planet, the fresh water necessary for human life and many other organisms is sorely lacking. Of the total amount of water in the world, 97-98% is salt water of the seas and oceans. Of course, it is impossible to use this water in everyday life, agriculture, industry, or for food production. And yet something else is much more serious: 75% of fresh water on Earth is in the form of ice, a significant part of it is groundwater, and only 1% is available to living organisms. And people mercilessly pollute these precious crumbs and carelessly consume them, while water consumption is constantly increasing. Pollution of the hydrosphere occurs primarily as a result of the discharge of industrial, agricultural and domestic wastewater into rivers, lakes and seas.

Fresh waters- not only an irreplaceable drinking resource. The lands irrigated by them produce about 40% of the world's harvest; Hydroelectric power plants produce approximately 20% of all electricity; Of the fish consumed by people, 12% are river and lake species.

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 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 developing body shapes and types of movement that reduced drag, which led 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 also contributes to the fact that mechanical vibrations (vibrations) propagate well in it. This was important in the evolution of sensory organs, spatial orientation and communication between aquatic inhabitants. The speed of sound in the aquatic environment, four times greater than in air, determines the higher frequency of echolocation signals.

Due to the high density of the aquatic environment, many of its inhabitants are deprived of the obligatory connection with the substrate, which is characteristic of terrestrial forms and is caused by gravitational forces. There is a whole group of aquatic organisms (both plants and animals) that spend their entire lives floating.

Water has an exceptionally high heat capacity. The heat capacity of water is taken as unity. The heat capacity of sand, for example, is 0.2, and that of iron is only 0.107 of the heat capacity of water. The ability of water to accumulate large reserves of thermal energy makes it possible to smooth out sharp temperature fluctuations in the coastal areas of the Earth at different times of the year and at different times of the day: water acts as a kind of temperature regulator on the planet.

HABITAT AND THEIR CHARACTERISTICS

The living conditions of different species of organisms are very diverse. Depending on where representatives of different species live, they are affected by different sets of environmental factors. On our planet, we can distinguish several main living environments, which vary greatly in terms of living conditions:

Aquatic habitat

· Ground-air habitat

· Soil as a habitat

Aquatic habitat - hydrosphere

Water covers 71% of the globe's area and makes up 1/800 of the volume of land or 1370 m3. The bulk of water is concentrated in the seas and oceans - 94-98%, polar ice contains about 1.2% of water and a very small proportion - less than 0.5%, in fresh waters of rivers, lakes and swamps. These relationships are constant, although in nature the water cycle continues without ceasing.

About 150,000 species of animals and 10,000 plants live in aquatic environments, representing only 7 and 8% of the total number of species on Earth, respectively. Based on this, it was concluded that evolution on land was much more intense than in water.

All aquatic inhabitants, despite differences in lifestyle, must be adapted to the main features of their environment. These features are determined, first of all, physical properties of water:

Density,

· Thermal conductivity,

Ability to dissolve salts and gases

· Vertical movements of water,

Light mode

Hydrogen ion concentration (pH level)

Density water determines its significant buoyant force. This means that the weight of organisms in water is lightened and it becomes possible to lead a permanent life in the water column without sinking to the bottom. A collection of small species that are not capable of fast active swimming and are suspended in water is called plankton.

Plankton(planktos - wandering, soaring) - a collection of plants (phytoplankton: diatoms, green and blue-green (fresh water bodies only) algae, plant flagellates, peridineans, etc.) and small animal organisms (zooplankton: small crustaceans, of the larger ones - pteropods mollusks, jellyfish, ctenophores, some worms) living at different depths, but not capable of active movement and resistance to currents.

Due to the high density of the environment and the presence of plankton in the aquatic environment, a filtration type of nutrition is possible. It is developed in both swimming (whales) and sessile aquatic animals (sea lilies, mussels, oysters). Straining suspended matter from water provides such animals with food. A sedentary lifestyle would be impossible for aquatic inhabitants if it were not for the sufficient density of the environment.

The density of distilled water at a temperature of 4 0 C is equal to 1 g/cm 3 . The density of natural waters containing dissolved salts can be greater, up to 1.35 g/cm 3 .

Due to the high density of water, pressure increases greatly with depth. On average, for every 10 m of depth, pressure increases by 1 atmosphere. Deep-sea animals are able to withstand pressure that is thousands of times higher than land pressure (flounder, stingrays). They have special adaptations: a body shape flattened on both sides, massive fins. The density of water makes it difficult to move in it, so fast-swimming animals must have strong muscles and a streamlined body shape (dolphins, sharks, squids, fish).

Thermal mode. The aquatic environment is characterized by less heat gain, because a significant part of it is reflected, and an equally significant part is spent on evaporation. Water has a high heat capacity. Consistent with the dynamics of land temperatures, water temperatures exhibit smaller fluctuations in daily and seasonal temperatures. Therefore, aquatic inhabitants do not have to adapt to severe frosts or 40 degree heat. Only in hot springs can the water temperature approach the boiling point. Moreover, reservoirs significantly equalize the temperature in the atmosphere of coastal areas. In the absence of an ice shell, the seas have a warming effect on the adjacent land areas in the cold season, and a cooling and moistening effect in the summer.

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, the water temperature moves due to temperature and wind. Temperature changes in flowing waters follow its changes in the surrounding air and have a smaller amplitude.

In lakes and ponds of temperate latitudes, the water is clearly divided into three layers:

With a further increase in temperature, the upper layers of water become less dense and no longer sink down - summer stagnation sets in. In autumn, surface waters cool again to 4 0 C and sink to the bottom, causing secondary mixing of water masses with equalization of temperature.

The range of water temperatures in the World Ocean is 38° (from -2 to +36°C), in fresh water bodies – 26° (from -0.9 to +25°C). With depth, the water temperature drops sharply. Up to 50 m there are daily temperature fluctuations, up to 400 m – seasonal, deeper it becomes constant, dropping to +1-3°C (in the Arctic it is close to 0°C).

Thus, in water as a living environment, on the one hand, there is a fairly significant variety of temperature conditions, and on the other, the thermodynamic features of the aquatic environment (high specific heat, high thermal conductivity, expansion during freezing) create favorable conditions for living organisms.

Light mode. The intensity of light in water is greatly weakened due to its reflection by the surface and absorption by the water itself. This greatly affects the development of photosynthetic plants. The less transparent the water, the more light is absorbed. Water transparency is limited by mineral suspensions and plankton. It decreases with the rapid development of small organisms in summer, and in temperate and northern latitudes even in winter, after the establishment of ice cover and covering it with snow on top.

In the oceans, where the water is very transparent, 1% of light radiation penetrates to a depth of 140 m, and in small lakes at a depth of 2 m only tenths of a percent penetrates. Rays from different parts of the spectrum are absorbed differently in water; red rays are absorbed first. With depth it becomes darker, and the color of the water first becomes green, then blue, indigo and finally blue-violet, turning into complete darkness. Hydrobionts also change color accordingly, adapting not only to the composition of light, but also to its lack - chromatic adaptation. In light zones, in shallow waters, green algae (Chlorophyta) predominate, the chlorophyll of which absorbs red rays, with depth they are replaced by brown (Phaephyta) and then red (Rhodophyta).

Light penetrates only to a relatively shallow depth, so plant organisms (phytobenthos) can exist only in the upper horizons of the water column. At great depths there are no plants, and deep-sea animals live in complete darkness, uniquely adapting to this way of life.

Daylight hours 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, and ice cover makes it difficult for light to reach all frozen bodies of water in winter.

Gas mode. The main gases in water are oxygen and carbon dioxide. The rest are of secondary importance (hydrogen sulfide, methane).

A limited amount of oxygen is one of the main difficulties in the life of aquatic inhabitants. The total oxygen content in the upper layers of water (what is it called?) is 6-8 ml/l or in 21 times lower than in the atmosphere (remember the numbers!).

Oxygen content 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 meters 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.

In bodies of water there can sometimes be freezes– mass death of inhabitants due to lack of oxygen. The reasons are stagnant conditions in small reservoirs. Covering the surface of a reservoir with ice in winter, polluting the reservoir, increasing water temperature. When the oxygen concentration is below 0.3-3.5 ml/l, the life of aerobes in water is impossible.

Carbon dioxide. Ways of carbon dioxide entering water:

· Dissolution of carbon contained in the air;

· Respiration of aquatic organisms;

· Decomposition of organic residues;

· Release from carbonates.

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