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 relations. 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, terrestrial-air, soil and organismal (i.e., formed by living organisms themselves).

Aquatic life environment

The aquatic environment of life 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 1 g/cm3. With an increase in salinity, the density increases and can reach 1.35 g/cm 3 . All aquatic organisms experience high pressure, increasing by 1 atmosphere for every 10 m of depth. Some of them, for example, anglerfish, cephalopods, crustaceans, starfish and others, live at great depths at a pressure of 400...500 atm.

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

The biont of aquatic ecosystems is also affected by the following factors:

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. the 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, depth, but increases with increasing flow velocity. Among hydrobionts, there are many species belonging to euryoxybionts, that is, organisms that can tolerate low oxygen content in water (for example, some types of mollusks, carp, crucian carp, tench, and others).

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

The lack of oxygen in water leads to catastrophic deaths (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 a depth in fresh water bodies, the temperature is constantly equal to 4 ... 5 ° C.

The light regime of the aquatic environment differs significantly from the ground-air environment. There is little light in water, as it is partially reflected from the surface and partially absorbed when passing through the water column. The passage of light is also hindered by particles suspended in water. In deep reservoirs, in connection with this, three zones are distinguished: light, twilight and the zone of eternal darkness.

According to the degree of illumination, the following zones are distinguished:

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

limnic zone (water column 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, hygrophytes, mesophytes and xerophytes are distinguished.

Hygrophytes are plants of moist habitats that do not tolerate water deficiency. These include, for example: pondweed, water lily, reed.

Xerophytes plants of dry habitats, able to 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 storage tissue is developed. Sclerophytes are xerophytic plants with hard shoots, due to which, with a water deficit, they do not have an external wilting pattern (for example, feather grass, saxaul).

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

About 150,000 species of animals live in the aquatic environment (which is about 7% of their total number) and 10,000 plant species (which is about 8% of their total number). Organisms that live in water are called hydrobionts.

Aquatic organisms according to the type of habitat and lifestyle are combined into the following ecological groups.

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

Nekton Animals actively moving in the water (fish, amphibians, cephalopods, turtles, cetaceans, etc.). 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 in the presence of a streamlined body shape and highly developed muscles.

Benthos are organisms living on the bottom and in the ground, it is divided into phytobenthos (attached algae and higher plants) and zoobenthos (crustaceans, mollusks, starfish, etc.).

Water as a habitat has a number of specific properties, such as high density, strong pressure drops, relatively low oxygen content, strong absorption of sunlight, etc. Reservoirs and their individual sections differ, in addition, in the salt regime, the speed of horizontal movements (currents) , the content of suspended particles. For the life of benthic organisms, the properties of the soil, the mode of decomposition of organic residues, etc. are important. Therefore, along with adaptations to the general properties of the aquatic environment, its inhabitants must also be adapted to a variety of particular conditions. The inhabitants of the aquatic environment received a common name in ecology hydrobionts. They inhabit the oceans, continental waters and groundwater. In any reservoir, zones can be distinguished according to the conditions.

Consider the basic properties of water as a habitat.

Density of water - this is a factor that determines the conditions for the movement of aquatic organisms and pressure at different depths. The density of natural waters containing dissolved salts may be higher, up to 1.35 g/cm 3 . Pressure increases with depth by approximately 101.3 kPa (1 atm) on average for every 10 m.

In connection with a sharp change in pressure in water bodies, hydrobionts are generally more easily tolerated than terrestrial organisms by pressure changes. Some species, distributed at different depths, endure pressure from several to hundreds of atmospheres. For example, holothurians of the genus Elpidia inhabit the area from the coastal zone to the zone of greatest ocean depths, 6-11 km. However, most of the inhabitants of the seas and oceans live at a certain depth.

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). Plankton includes unicellular and colonial algae, protozoa, jellyfish, various small crustaceans, larvae of bottom animals, fish eggs and fry, and many others.

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.

1. 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.

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. 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 (bloodworms) sway the body, leaning out of the ground.

Mammals that have passed in the process of evolutionary development from a land to aquatic way of life, for example, pinnipeds, cetaceans, water beetles, mosquito larvae, usually retain an atmospheric type of breathing and therefore need contact with the air.

Lack of oxygen in water sometimes leads to catastrophic phenomena - death, accompanied by the death of many aquatic organisms. Winter freezes are often caused by the formation of ice on the surface of water bodies and the termination of contact with air; summer - by an increase in water temperature and a decrease in the solubility of oxygen as a result.

• 2. 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. Therefore, freshwater forms cannot exist in the seas, marine ones cannot tolerate desalination. If the salinity of the water is subject to change, the animals move in search of a favorable environment.
• 3. Temperature regime water bodies, as already noted, is more stable than on land. The amplitude of annual temperature fluctuations in the upper layers of the ocean is no more than 10-15 °С, in continental water bodies - 30-35 °С. Deep layers of water are characterized by constant temperature. In equatorial waters, the average annual temperature of the surface layers is +26-27 °С, in polar waters - about 0 °С and lower. In hot terrestrial 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. But along the vertical, the temperature regime is diverse, for example, seasonal temperature fluctuations appear in the upper layers, and the thermal regime is constant in the lower layers.
• 4. 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. The rapid decrease in the amount of light with depth is due to its absorption by water. Rays with different wavelengths are absorbed differently: red ones disappear close to the surface, while blue-green ones penetrate much deeper. This affects the color of hydrobionts, for example, with depth, the color of algae changes: green, brown and red algae, which specialize in capturing light with different wavelengths. The color of animals changes with depth in the same way. Many deep organisms do not have pigments.

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.

Thus, the properties of the environment largely determine the ways of adaptation of its inhabitants, their way of life and ways of using resources, creating chains of cause-and-effect dependencies. Thus, the high density of water makes the existence of plankton possible, and the presence of organisms hovering in the water is a prerequisite for the development of a filtration type of nutrition, in which a sedentary lifestyle of animals is also possible. As a result, a powerful mechanism of self-purification of water bodies of biospheric significance is formed. It involves a huge number of hydrobionts, both benthic (living on the ground and in the soil of the bottom of water bodies) and pelagic (plants or animals living in the water column or on the surface), from unicellular protozoa to vertebrates. For example, only planktonic marine copepods (Calanus) are able to filter the waters of the entire World Ocean in a few years; approximately 1.37 billion km 3. Disturbance of the activity of filter feeders by various anthropogenic influences poses a serious threat to maintaining the purity of waters.

Questions and tasks for self-control

• 1. List the main properties of the aquatic habitat.
• 2. Explain how the density of water determines the shape of animals capable of fast swimming.
• 3. Name the reason for blockages.
• 4. What phenomenon is called "bioluminescence"? Do you know living organisms that have this property?
• 5. What ecological role do filter feeders play?

The inhabitants of the aquatic environment received a common name in ecology hydrobionts. They inhabit the oceans, continental waters and groundwater. In any reservoir, zones can be distinguished according to the conditions.

In the ocean and its constituent seas, two ecological areas are primarily distinguished: the water column - pelagial and the bottom benthal. The inhabitants of the abyssal and ultra-abyssal depths exist in darkness, at constant temperature and enormous pressure. The entire population of the ocean floor was named benthos.

Basic properties of the aquatic environment.

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 approximately by 1 · 10 5 Pa (1 atm) for every 10 m on average. 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 hovering in water are combined into a special ecological group of hydrobionts - plankton("planktos" - soaring). Plankton is dominated by 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. Seaweed (phytoplankton) hover passively in the water, while most planktonic animals are capable of active swimming, but to a limited extent .. 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).

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. 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, gastropods. 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 with a sufficiently high saturation of water with oxygen (rainbow trout, trout, minnow).

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, the main way for aquatic organisms to maintain their salt balance is to avoid habitats with unsuitable salinity. Freshwater forms cannot exist in the seas, marine forms cannot tolerate desalination. Vertebrates, higher crayfish, insects and their larvae living in water belong to homoiosmotic species, maintaining a constant osmotic pressure in the body, regardless of the concentration of salts in the water.

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. 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. The reactions used to generate light are varied. But in all cases, this is the oxidation of complex organic compounds (luciferins) using protein catalysts (luciferase).

Ways of orientation of animals in the aquatic environment. Living in constant twilight or darkness greatly limits the possibilities visual orientation hydrobionts. In connection with the rapid attenuation of light rays in water, even the owners of well-developed organs of vision orient themselves with their help only at close range.

Sound travels faster in water than in air. Orientation to sound is generally better developed in hydrobionts than visual. A number of species even pick up very low frequency vibrations (infrasounds) , arising when the rhythm of the waves changes, and descends in advance before the storm from the surface layers to the deeper ones (for example, jellyfish). Many inhabitants of water bodies - mammals, fish, mollusks, crustaceans - make sounds themselves. A number of hydrobionts look for food and navigate using echolocation– perception of reflected sound waves (cetaceans). Many perceive reflected electrical impulses , producing discharges of different frequencies when swimming. A number of fish also use electric fields for defense and attack (electric stingray, electric eel, etc.).

For depth orientation hydrostatic pressure perception. It is carried out with the help of statocysts, gas chambers and other organs.

Filtration as a type of food. Many aquatic organisms have a special nature of nutrition - this is the sieving or sedimentation of particles of organic origin suspended in water and numerous small organisms.

Body shape. Most hydrobionts have a streamlined body shape.

An animal that lives in water for a certain amount of time or its entire life. Many insects, such as mosquitoes, mayflies, dragonflies and caddisflies, begin their life cycle as aquatic larvae before developing into winged adults. Aquatic animals can breathe air or obtain oxygen dissolved in water using specialized organs called gills or directly through their skin. Natural conditions and those that live in them can be divided into two main categories: water or.

Aquatic Animal Groups

Most people only think of fish when asked about aquatic animals. However, there are other groups of animals living in the water:

• mammals such as (whales), sirens (dugongs, manatees) and pinnipeds (true seals, eared seals and walruses). The concept of "aquatic mammal" is also applied to animals with, such as river otters or beavers, leading a semi-aquatic lifestyle;
• shellfish (eg sea snails, oysters);
• (for example, corals);
• (e.g. crabs, shrimp).

The term "aquatic" can be applied to animals that live in both fresh water (freshwater animals) and salt water (marine animals). However, the concept of marine organisms is most often used for animals that live in sea water, that is, in the oceans and seas.

Aquatic life (especially freshwater animals) is often of particular concern to conservationists due to their fragility. They are exposed to overfishing, poaching, and pollution.

frog tadpoles

Most are characterized by an aquatic larval stage, for example, tadpoles in frogs, but adults lead a terrestrial lifestyle near water bodies. Some fish, such as arapaima and walking catfish, also need to breathe air to survive in oxygen-poor water.

Do you know why the hero of the famous cartoon "SpongeBob SquarePants" (or "Spongebob Square Pants") is depicted as a sponge? Because there are aquatic animals called marine. However, sea sponges do not look like a square kitchen sponge like a cartoon character, but have a more rounded body shape.

Fish and Mammals

School of fish near the coral reef

Did you know that there are more species of fish than there are amphibians, birds, mammals and reptiles combined? Fish are aquatic animals because they spend their entire life in water. Fish are cold-blooded and have gills that take oxygen from the water to breathe. In addition, fish are vertebrates. Most fish species can live in either fresh water or sea water, but some fish, such as salmon, live in both environments.

Dugong - an aquatic mammal from the order of sirens

While fish live only in water, mammals can be found on land and in water. All mammals are vertebrates; have lungs; they are warm-blooded and give birth to live young instead of laying eggs. However, aquatic mammals depend on water to survive. Some mammals, such as whales and dolphins, only live in water. Others, such as beavers, are semi-aquatic. Aquatic mammals have lungs but no gills and are unable to breathe underwater. They need to float to the surface at regular intervals to breathe air. If you've ever seen what a fountain of water looks like coming out of a whale's blowhole, then you should know that this is his exhalation, followed by an inhalation before the animal plunges back under the water.

Mollusks, cnidarians, crustaceans

Giant tridacna - the largest representative of bivalve molluscs

Mollusks are invertebrates that have soft muscular bodies without legs. For this reason, many clams have a hard shell to protect their vulnerable body from predators. Sea snails and oysters are examples of shellfish. Squids are also mollusks, but they do not have shells.

swarm of jellyfish

What do jellyfish, sea anemones and corals have in common? All of them belong to cnidarians - a group of aquatic, which are invertebrates, have a special mouth and stinging cells. The stinging cells around the mouth are used to catch food. Jellyfish can move around to catch their prey, but sea anemones and corals are attached to rocks and wait for food to come close to them.

red crab

Crustaceans are aquatic invertebrates with a hard, chitinous outer shell (exoskeleton). Some examples include crabs, lobsters, shrimp and crayfish. Crustaceans have two pairs of antennae (antennae) that help them receive information about their environment. Most crustaceans feed on the floating remains of dead plants and animals.

Conclusion

Aquatic animals live in water and depend on it for survival. There are various groups of aquatic animals, including fish, mammals, molluscs, cnidarians, and crustaceans. They live either in freshwater bodies of water (streams, rivers, lakes and ponds) or in salt water (seas, oceans, etc.), and can be both vertebrates and invertebrates.

Water has long been not only a necessary condition for life, but also the habitat of many organisms. It has a number of unique properties, which we will discuss in our article.

Aquatic habitat: characteristic

In each habitat, the action of a number of environmental factors is manifested - the conditions in which populations of various species live. Compared to the land-air environment, the aquatic habitat (grade 5 studies this topic in the biology course) is characterized by high density and tangible pressure drops. Its distinguishing feature is its low oxygen content. Aquatic animals, which are called hydrobionts, have adapted to life in such conditions in different ways.

Ecological groups of hydrobionts

Most of the living organisms are concentrated in the thickness. They are combined into two groups: planktonic and nektonic. The first includes bacteria, blue-green algae, jellyfish, small crustaceans, etc. Although many of them can swim on their own, they are not able to withstand strong currents. Therefore, planktonic organisms move with the flow of water. Adaptability to the aquatic environment is manifested in their small size, small 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 independently in the water. 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 attach to the substrate. These are sponges, some algae. Neuston lives on the border of the aquatic and terrestrial-air environment. These are mainly insects that are associated with the water film.

Aquatic habitat properties

Illumination of reservoirs

Another main feature of the aquatic habitat 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, it concerns algae. Deeper than 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. They use these signals to communicate with each other.

water pressure

Especially strongly with immersion, an increase in water pressure is felt. At 10 m, this indicator increases by the atmosphere. Therefore, most animals are adapted only to a certain depth and pressure. For example, annelids live only in the intertidal zone, and the coelacanth descends to 1000 m.

Movement of water masses

The movement of water can have a different nature and causes. Thus, the change in the position of our planet in relation to the Sun and the Moon determines the presence of ebbs and flows in the seas and oceans. The force of gravity and the influence of the wind causes the flow in rivers. The constant movement of water plays an important role in nature. It causes migratory movements of various groups of hydrobionts, food and oxygen sources, 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 is 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 the fact that the oxygen concentration decreases with increasing salinity and temperature.

Salinity index

Everyone knows that water bodies are fresh and salty. The last group includes the seas and oceans. Salinity is measured in ppm. This is the amount of solids that are in 1 g of water. The average salinity of the oceans is 35 ppm. The seas located at the poles of our planet have the lowest rate. This is due to the periodic melting of icebergs - huge frozen blocks of fresh water. The most salty on the planet is the Dead Sea. It does not contain any species of living organisms. Its salinity approaches 350 ppm. Of the chemical elements in water, chlorine, sodium and magnesium predominate.

So, the main feature of the aquatic habitat is its high density, viscosity, low temperature difference. The life of organisms with increasing depth is limited by the amount of solar energy and oxygen. Aquatic inhabitants, which are called hydrobionts, can move with water flows or move independently. For life 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.