Habitat is a part of an ecosystem. The climate, plants and animals are the identities of a habitat. Mainly ecosystem has two domains: Terrestrial/ Land ecosystem and Aquatic/Water ecosystem. Aquatic ecosystem includes freshwater habitats (lakes, ponds, rivers and streams, wetlands, swamp, etc) and marine habitats (oceans, intertidal zone, reefs, seabed and so on). The aquatic ecosystem is the habitat for water dependent animals, plants and microbes.
Water supports many lives. Organisms which survive in water are called aquatic organisms. They depend on water for their food, shelter, reproduction and all other life activities. Different types of aquatic ecosystems are as follow:
Freshwater: They cover only a small portion of earth nearly 0.8 percent. Freshwater involves lakes, ponds, rivers and streams, wetlands, swamp, bog and temporary pools. Freshwater habitats are classified into lotic and lentic habitats. Water bodies such as lakes, ponds, pools, bogs and other reservoirs are standing water and known as lentic habitats. Whereas lotic habitats represent flowing water bodies such as rivers, streams.
Marine: Marine ecosystem covers the largest surface area of the earth. Two –third of earth is covered by water and have the major share (about 71 percent). They constitute of oceans, seas, intertidal zone, reefs, seabed, estuaries, hydrothermal vents and rock pools.
Each life form is unique and native to its habitat. This is because they have adaptations according to their habitat. In the case of aquatic animals, they can’t survive outside water. Exceptional cases are still there which shows another example of adaptations (e.g. mudskippers). Marine ecosystem is more concentrated with salts which make it difficult for freshwater organisms to live in. Also, marine animals cannot survive in fresh water. Their body is adapted to live in salt water; if they are placed in less salty water, their body will swell (osmosis).
Plants and animals in an aquatic ecosystem show a wide variety of adaptations which may involve life cycle, physiological, structural and behavioral adaptations. Majority of aquatic animals are streamlined which helps them to reduce friction and thus save energy. Fins and gills are the locomotory and respiratory organs respectively. Special features in freshwater organisms help them to drain excess water from the body. Aquatic plants have different types of roots which help them to survive in water. Some may have submerged roots; some have emergent roots or may be floating plants like water hyacinths.
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