Water has long been not only a necessary condition for life, but also the habitat of many organisms. She has a number unique properties, which we will talk about in our article.
Aquatic habitat: characteristics
In each habitat, the action of a number of environmental factors is manifested - the conditions in which populations of different species live. Compared to the land-air environment, the aquatic habitat (grade 5 studies this topic in a biology course) is characterized by high density and noticeable pressure differences. Her distinctive feature is a low oxygen content. Aquatic animals, called hydrobionts, have adapted to life in such conditions in different ways.
Ecological groups of aquatic organisms
Most living organisms are concentrated in the thickness. They are divided into two groups: planktonic and nektonic. The first includes bacteria, blue-green algae, jellyfish, small crustaceans, etc. Despite the fact that many of them can swim independently, they are not able to withstand strong currents. Therefore, planktonic organisms move with the flow of water. Their adaptation to the aquatic environment is manifested in their small size, low specific gravity and the presence of characteristic outgrowths.
Nektonic organisms include fish and aquatic mammals. They do not depend on the strength and direction of the current and move in the water independently. This is facilitated by the streamlined shape of their body and well-developed fins.
Another group of hydrobionts is represented by peripheton. It includes aquatic inhabitants that are attached to the substrate. These are sponges, some algae, on the border of water and ground-air environment Neuston lives. These are mainly insects that are associated with the water film.
Properties of aquatic habitat
Illumination of reservoirs
Another main feature of aquatic habitats is that the amount of solar energy decreases with depth. Therefore, organisms whose life depends on this indicator cannot live at significant depths. First of all, this concerns algae. Below 1500 m, light does not penetrate at all. Some crustaceans, coelenterates, fish and mollusks have the property of bioluminescence. These deep-sea animals produce their own light by oxidizing lipids. With the help of such signals they communicate with each other.
Water pressure
The increase in water pressure is especially noticeable as you dive. At 10 m this figure increases by atmosphere. Therefore, most animals are adapted only to a certain depth and pressure. For example, annelids live only in the intertidal zone, while coelacanths descend to 1000 m.
Movement of water masses
The movement of water can have different natures and reasons. Thus, the change in the position of our planet in relation to the Sun and Moon determines the presence of ebbs and flows in the seas and oceans. The force of gravity and the influence of wind causes currents in rivers. The constant movement of water plays an important role in nature. It causes migratory movements of various groups of aquatic organisms, sources of food and oxygen, which is especially important. The fact is that the content of this vital gas in water is 20 times lower than in the ground-air environment.
Where does oxygen come from in water? This occurs due to diffusion and the activity of algae, which carry out photosynthesis. Since their number decreases with depth, the oxygen concentration also decreases. In the bottom layers this indicator is minimal and creates almost anaerobic conditions. The main feature of the aquatic habitat is that the oxygen concentration decreases with increasing salinity and temperature.
Water salinity indicator
Everyone knows that bodies of water can be fresh or salty. The last group includes seas and oceans. The salinity indicator is measured in ppm. This is the amount of solids that are found in 1 g of water. The average salinity of the World Ocean is 35 ppm. The seas located near the poles of our planet have the lowest rates. This is due to the periodic melting of icebergs - huge frozen blocks of fresh water. The saltiest sea on the planet is the Dead Sea. There is not a single type of living organism in it. Its salinity approaches 350 ppm. The predominant chemical elements in water are chlorine, sodium and magnesium.
So, the main feature of the aquatic habitat is its high density, viscosity, and low temperature difference. The life of organisms with increasing depth is limited by the amount of solar energy and oxygen. Aquatic inhabitants, called hydrobionts, can be moved by water currents or move independently. To live in this environment, they have a number of adaptations: the presence of gill breathing, fins, a streamlined body shape, a small relative body weight, and the presence of characteristic outgrowths.
HABITAT AND THEIR CHARACTERISTICS
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 environment a habitat
Water covers 71% of the earth's area. The bulk of water is concentrated in the seas and oceans - 94-98%, in polar ice contains about 1.2% water and a very small proportion - less than 0.5%, in fresh waters of rivers, lakes and swamps.
About 150,000 species of animals and 10,000 plants live in the aquatic environment, which is only 7 and 8% of the world's population, respectively. total number species of the Earth.
In the seas-oceans, as in the mountains, vertical zoning is expressed. The pelagic - the entire water column - and the benthic - the bottom - differ especially greatly in ecology. The water column, the pelagic zone, is vertically divided into several zones: epipeligal, bathypeligal, abyssopeligal and ultraabyssopeligal(Fig. 2).
Depending on the steepness of the descent and the depth at the bottom, several zones are also distinguished, which correspond to the indicated pelagic zones:
Littoral - the edge of the coast that is flooded during high tides.
Supralittoral - the part of the coast above the upper tidal line where surf splashes reach.
Sublittoral - a gradual decrease in land up to 200m.
Bathial - a steep depression of land (continental slope),
Abyssal - a gradual decrease in the bottom of the ocean floor; the depth of both zones together reaches 3-6 km.
Ultra-abyssal - deep-sea depressions from 6 to 10 km.
Ecological groups of hydrobionts. 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 life are divided into three ecological groups: nekton, plankton and benthos.
Nekton (nektos - floating) - actively moving large animals that can overcome long distances and strong currents: fish, squid, pinnipeds, whales. In fresh water bodies, nekton includes amphibians and many insects.
Plankton (planktos - wandering, soaring) - a collection of plants (phytoplankton: diatoms, green and blue-green (fresh water bodies only) algae, plant flagellates, peridineans, etc.) and small animal organisms (zooplankton: small crustaceans, of the larger ones - pteropods mollusks, jellyfish, ctenophores, some worms) living at different depths, but not capable of active movement and resistance to currents. Plankton also includes animal larvae, forming a special group - Neuston . This is a passively floating “temporary” population of the uppermost layer of water, represented by various animals (decapods, barnacles and copepods, echinoderms, polychaetes, fish, mollusks, etc.) in the larval stage. The larvae, growing up, move into the lower layers of the pelagel. Above the neuston is located plaiston - these are organisms in which top part The body grows above water, and the lower one grows in water (duckweed - Lemma, siphonophores, etc.). Plankton plays an important role in the trophic relationships of the biosphere, because is food for many aquatic inhabitants, including the main food for baleen whales (Myatcoceti).
Benthos (benthos – depth) – bottom hydrobionts. It is represented mainly by attached or slowly moving animals (zoobenthos: foraminephores, fish, sponges, coelenterates, worms, mollusks, ascidians, etc.), more numerous in shallow water. In shallow water, benthos also includes plants (phytobenthos: diatoms, green, brown, red algae, bacteria). At depths where there is no light, phytobenthos is absent. Rocky areas of the bottom are richest in phytobenthos.
In lakes, zoobenthos is less abundant and diverse than in the sea. It is formed by protozoa (ciliates, daphnia), leeches, mollusks, insect larvae, etc. The phytobenthos of lakes is formed by free-floating diatoms, green and blue-green algae; brown and red algae are absent.
The high density of the aquatic environment determines the special composition and nature of changes in life-supporting factors. Some of them are the same as on land - heat, light, others are specific: water pressure (increases with depth by 1 atm for every 10 m), oxygen content, salt composition, acidity. Due to the high density of the environment, the values of heat and light change much faster with an 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°C), in fresh water bodies – 26° (from -0.9 to +25°C). With depth, the water temperature drops sharply. Up to 50 m there are daily temperature fluctuations, up to 400 – seasonal, deeper it becomes constant, dropping to +1-3°C. Since the temperature regime in reservoirs is relatively stable, their inhabitants tend to stenothermicity.
Due to 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 is extremely important, because this evens out the distribution of oxygen and nutrients inside reservoirs, providing 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. comes homothermy. In summer and winter as a result of a sharp increase in heating or cooling upper layers mixing of water stops. This phenomenon is called temperature dichotomy, and the period of temporary stagnation is stagnation(summer or winter). In summer, lighter warm layers remain on the surface, located above heavy cold ones (Fig. 3). In winter, on the contrary, in the bottom layer there is more warm water, since directly under the ice the temperature 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 most dramatic seasonal fluctuations in water temperature, the middle (metalimnion or thermocline), in which there is a sharp jump in temperature, and bottom ( hypolimnion), in which the temperature varies little throughout the year. During periods of stagnation, oxygen deficiency occurs in the water column - in the bottom part in summer, and in the upper part in winter, as a result of which fish kills often occur in winter.
Light mode. The intensity of light in water is greatly weakened due to its reflection by the surface and absorption by the water itself. This greatly affects the development of photosynthetic plants.
The absorption of light is stronger, the lower the transparency of the water, which depends on the number of particles suspended in it (mineral suspensions, plankton). It decreases with 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.
Transparency is characterized by the maximum depth at which a specially lowered white disk with a diameter of about 20 cm (Secchi disk) is still visible. The clearest waters are in the Sargasso Sea: the disk is visible to a depth of 66.5 m. Pacific Ocean the Secchi disk is visible up to 59 m, in the Indian Sea - up to 50 m, in shallow seas - up to 5-15 m. The transparency of rivers is on average 1-1.5 m, and in the muddiest rivers only a few centimeters.
In the oceans, where the water is very transparent, 1% of light radiation penetrates to a depth of 140 m, and in small lakes at a depth of 2 m only tenths of a percent penetrates. Rays 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). At great depths, phytobenthos is absent.
Plants adapted to the lack of light by developing large chromatophores, as well as increasing the area of assimilating organs (leaf surface index). For deep-sea algae, strongly dissected leaves are typical, the leaf blades are thin and translucent. Semi-submerged and floating plants are characterized by heterophylly - the leaves above the water are the same as those of land plants, they have a solid blade, the stomatal apparatus is developed, and in the water the leaves are very thin, consisting of narrow thread-like lobes.
Animals, like plants, naturally change their color with depth. In the upper layers they are brightly colored different colors, V twilight zone (sea bass, corals, crustaceans) are painted in colors with a red tint - it is more convenient to hide from enemies. Deep-sea species lack pigments. In the dark depths of the ocean, organisms use light emitted by living beings as a source of visual information. bioluminescence.
High density(1 g/cm3, which is 800 times the density of air) and water viscosity ( 55 times higher than that of air) led to the development of special adaptations of aquatic organisms :
1) Plants have very poorly developed or completely absent mechanical tissues - they are supported by water itself. Most are characterized by buoyancy due to air-carrying intercellular cavities. Characteristically active vegetative propagation, the development of hydrochory - the removal of flower stalks above the water and the distribution of pollen, seeds and spores by surface currents.
2) In animals living in the water column and actively swimming, the body has a streamlined shape and is lubricated with mucus, which reduces friction when moving. Developed devices to increase buoyancy: accumulations of fat in tissues, swim bladders in fish, air cavities in siphonophores. In passively swimming animals, the specific surface area of the body increases due to outgrowths, spines, and appendages; the body is flattened, and skeletal organs are reduced. Different ways locomotion: bending of the body, with the help of flagella, cilia, reactive mode of locomotion (cephalopods).
In benthic animals, the skeleton disappears or is poorly developed, body size increases, vision reduction is common, and tactile organs develop.
Currents. A characteristic feature of the aquatic environment is mobility. It is caused by ebbs and flows, sea currents, storms, at different levels elevation marks of river beds. Adaptations of hydrobionts:
1) In flowing reservoirs, plants are firmly attached to stationary underwater objects. The bottom surface is primarily a substrate for them. These are green and diatom algae, water mosses. Mosses even form a dense cover on fast riffles of rivers. In the tidal zone of the seas, many animals have devices for attaching to the bottom (gastropods, barnacles), or hide in crevices.
2) In fish of running waters, the body is round in diameter, and in fish that live near the bottom, as in benthic invertebrate animals, the body is flat. Many have attachment organs to underwater objects on the ventral side.
Salinity of water.
Natural reservoirs are characterized by a certain chemical composition. Carbonates, sulfates, and chlorides predominate. In fresh water bodies, the salt concentration is no more than 0.5 ‰ (and about 80% are carbonates), in the seas - from 12 to 35 ‰ (mainly chlorides and sulfates). When the salinity is more than 40 ppm, the water body is called hypersaline or oversaline.
1) In fresh water (hypotonic environment), osmoregulation processes are well expressed. Hydrobionts are forced to constantly remove water penetrating into them; they are homoyosmotic (ciliates “pump” through themselves an amount of water equal to its weight every 2-3 minutes). In salt water (isotonic environment), the concentration of salts in the bodies and tissues of hydrobionts is the same (isotonic) with the concentration of salts dissolved in water - they are poikiloosmotic. Therefore, the inhabitants of salt water bodies do not have developed osmoregulatory functions, and they were unable to populate fresh water bodies.
2) Aquatic plants are able to absorb water and nutrients from water - “broth”, with their entire surface, therefore their leaves are strongly dissected and conductive tissues and roots are poorly developed. The roots serve mainly for attachment to the underwater substrate. Most freshwater plants have roots.
Typically marine and typically freshwater species, stenohaline, do not tolerate significant changes in water salinity. There are few euryhaline species. They are common in brackish waters (freshwater pike perch, pike, bream, mullet, coastal salmon).
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 puma provides required quantity 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 small or, conversely, a large number of 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 accommodate the most different shapes. A single tree, for example, can provide a safe habitat for many organisms. The caterpillar may hide under the underside of leaves. Cool temperatures can serve as shelter for chaga mushrooms. wet zone near tree roots. 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 many dissolved nutrients, without which aquatic organisms would not be able to continue to exist.
Minsk Educational Institution “Gymnasium No. 14”
Abstract on biology on the topic:
“ WATER - HABITAT”
Prepared by a student of grade 11 “B”
Maslovskaya Evgenia
Teacher:
Bulva Ivan Vasilievich
1. Aquatic habitat – hydrosphere.
2. Water is a unique environment.
3. Ecological groups of hydrobionts.
4. Modes.
5. Specific adaptations of hydrobionts.
6. Filtration as a type of nutrition.
7. Adaptation to life in drying up water bodies.
8. Conclusion.
1. Aquatic environment - hydrosphere
In the process of historical development, living organisms have mastered four habitats. The first is water. Life originated and developed in water for many millions of years. 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 (Fig. 1).
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.
In the seas-oceans, as in the mountains, vertical zoning is expressed. The pelagic - the entire water column - and the benthic - the bottom - differ especially greatly in ecology.
The water column, the pelagial, is vertically divided into several zones: epipeligal, bathypeligal, abyssopeligal and ultraabyssopeligal (Fig. 2).
Depending on the steepness of the descent and the depth at the bottom, several zones are also distinguished, which correspond to the indicated pelagic zones:
Littoral - the edge of the coast that is flooded during high tides.
Supralittoral - the part of the coast above the upper tidal line where surf splashes reach.
Sublittoral - a gradual decrease in land up to 200m.
Bathial - a steep depression of land (continental slope),
Abyssal - a gradual decrease in the bottom of the ocean floor; the depth of both zones together reaches 3-6 km.
Ultra-abyssal - deep-sea depressions from 6 to 10 km.
2. Water is a unique environment.
Water is a completely unique medium in many respects. The water molecule, consisting of two hydrogen atoms and one oxygen atom, is surprisingly stable. Water is a unique compound that exists simultaneously in gaseous, liquid and solid states.
Water is not only a life-giving source for all animals and plants on Earth, but is also a habitat for many of them. These include, for example, numerous species of fish, including crucian carp, inhabiting the rivers and lakes of the region, as well as aquarium fish in our homes. As you can see, they feel great among aquatic plants. Fish breathe through gills, extracting oxygen from the water. Some species of fish, for example, macropods, breathe atmospheric air, so they periodically rise to the surface.
Water is the habitat of many aquatic plants and animals. Some of them spend their entire lives in water, while others are in the aquatic environment only at the beginning of their lives. You can verify this by visiting a small pond or swamp. IN water element you can find the smallest representatives - single-celled organisms, which require a microscope to view. These include numerous algae and bacteria. Their number is measured in millions per cubic millimeter of water.
Other interesting property water consists in acquiring a very dense state at a temperature above the freezing level; for fresh water, these parameters are 4 °C and 0 °C, respectively. This is critical for the survival of aquatic organisms during the winter. Thanks to this same property, ice floats on the surface of the water, forming a protective layer on lakes, rivers and coastal areas. And this same property contributes to the thermal stratification of water layers and the seasonal turnover of water masses in lakes in areas with cold climates, which is very important for the life of aquatic organisms. The density of water provides the ability to lean on it, which is especially important for non-skeletal forms. The support of the environment serves as a condition for soaring in water, and many hydrobionts are adapted precisely to this way of life. Suspended, floating organisms in water are combined into a special environmental group hydrobionts - plankton.
Completely purified water exists only in laboratory conditions. Any natural water contains many different substances. In "raw water" this is mainly the so-called protective system or carbonic complex, consisting of a carbonic acid salt, carbonate and bicarbonate. This factor allows you to determine the type of water - acidic, neutral or basic - based on its pH value, which from a chemical point of view means the proportion of hydrogen ions contained in the water. Neutral water has a pH of 7, lower values indicate increased acidity of the water, and higher values indicate that it is alkaline. In limestone areas, the water of lakes and rivers usually has higher pH values compared to reservoirs in places where the limestone content in the soil is insignificant
If the water of lakes and rivers is considered fresh, then sea water is called salty or brackish. There are many intermediate types between fresh and salt water.
3. Ecological groups of hydrobionts.
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 there is a pleiston - these are organisms in which the upper part of the body grows above water, and the lower part in water (duckweed - Lemma, siphonophores, etc.). Plankton plays an important role in the trophic relationships of the biosphere, because is food for many aquatic inhabitants, including the main food for baleen whales (Myatcoceti).
Benthos (benthos – depth) – 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.
Rooted coastal plants in lakes form clearly defined belts, species composition and the appearance of which is 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 an altitude gradient than on land.
4. Modes.
Temperature reservoirs are more stable than on land. It's connected with physical properties water, especially high water specific heat capacity, thanks to which receiving or giving significant amount heat does not cause too sudden changes in temperature. The amplitude of annual temperature fluctuations in the upper layers of the ocean is no more than 10-150C, in continental waters - 30-350C. Deep layers of water are characterized by constant temperature. In equatorial waters the average annual temperature of the surface layers is +26...+270C, in polar waters it is about 00C and below. Thus, there is a fairly significant variety of temperature conditions in reservoirs. Between top layers waters with seasonal temperature fluctuations expressed in them and lower ones, where the thermal regime is constant, there is a zone of temperature jump, or thermocline. The thermocline is more pronounced in warm seas, where the temperature difference between external and deep waters is stronger.
Due to the more stable temperature regime of water, stenothermy is common among aquatic organisms to a much greater extent than among the land population. Eurythermal species are found mainly in shallow continental reservoirs and in the littoral zone of seas of high and temperate latitudes, where daily and seasonal temperature fluctuations are significant.
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, sea stars and others, live at great depths at pressures 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.).