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 effect of a number of environmental factors is manifested - the conditions in which populations of various species live. Compared with the ground-air, the aquatic habitat (Grade 5 studies this topic in a biology course) is characterized by a high density and noticeable pressure drops. Its distinguishing feature is its low oxygen content. Aquatic animals called hydrobionts have adapted differently to life under such conditions.
Ecological groups of aquatic organisms
Most living organisms are concentrated in the water column of the oceans. They are combined 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 on their own, they are not able to withstand strong currents. Therefore, planktonic organisms move with the flow of water. Adaptation to the aquatic habitat is manifested in them in small sizes, small specific gravity and the presence of characteristic outgrowths.
Nectonic organisms include fish, cephalopods, and aquatic mammals. They do not depend on the strength and direction of the flow and move independently in the water. This is facilitated by the streamlined shape of their body and well-developed fins.
Peripheton is another group of hydrobionts. It includes aquatic inhabitants that attach to the substrate. These are sponges, some algae, coral polyps. At the border of the water and airborne environments, a neuston lives. These are mainly insects that are associated with a water film.
Properties of the aquatic habitat
Among the environmental factors of the aquatic environment, the leading role belongs to the temperature regime and illumination. They can be considered limiting. So, the maximum depth at which plants are found is about 270 m. It is there that red algae absorb scattered light. There are simply no deeper conditions for photosynthesis.
The aquatic habitat, the characteristic of which is very extensive, also differs in such an indicator as pressure. Thanks to its influence, animals can live only at certain depths.
Temperature mode
The main feature of the aquatic habitat is that, compared with air, temperature differences are less noticeable here. For example, in the surface oceanic layers this indicator does not exceed 10-15 degrees above zero. And at depth, the water temperature is constant. Its lower limit reaches -2 degrees Celsius. This temperature regime is ensured by the high specific heat of water.
Illumination of water bodies
Another major feature of the aquatic habitat is that the amount of solar energy decreases with depth. Therefore, organisms whose life depends on this indicator can not dwell at considerable depths. First of all, this applies to algae. Deeper than 1,500 m, light does not penetrate at all. Some crustaceans, gastrointestinal, fish and mollusks have the property of bioluminescence. These deep-sea animals themselves produce light by oxidizing lipids. With the help of such signals, they communicate with each other.
Water pressure
Especially strongly with immersion is an increase in water pressure. At 10 m, this figure increases by the atmosphere. Therefore, most animals are adapted only to a certain depth and pressure. For example, annelids live only in the tidal zone, and the coelacanth drops to 1000 m.
Water movement
The movement of water can have different nature and causes. Thus, a change in the position of our planet in relation to the Sun and Moon determines the presence of tides in the seas and oceans. The force of gravity and the influence of wind causes a flow in rivers. The constant movement of water plays an important role in nature. It causes migratory movements of various groups of aquatic organisms, food sources 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 is due to the diffusion and activity of algae that carry out photosynthesis. As 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
Everyone knows that ponds 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 lowest indicator are the seas located at the poles of our planet. 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. There are no species of living organisms in it. Its salinity approaches 350 ppm. Of the chemical elements in the water, chlorine, sodium and magnesium predominate.
So, the main feature of the aquatic environment 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, called hydrobionts, can be moved by streams of water or move independently. For life in this environment, they have a number of devices: the presence of gill breathing, fins, streamlined body shape, small relative body weight, the presence of characteristic outgrowths.