Marine ecosystem consists of the pattern of relationship between organism and the sea environment. It is well known that about 75% of the earth’s surface is covered by ocean and with salinity and about 90% of which is sodium chloride. Marine ecology is of singular ecological significance.
The sea is deep and continuous and not separated as are land and fresh water. All oceans are connected together. Temperature, salinity and depth are the chief barriers to free movement of marine organisms. The sea is in continuous circulation mainly due to wind stress set up by air temperature differences between poles and equator. The sea is dominated by waves of many kinds and tides produced by pull of sun and moon. The chief salts are in the form of chlorides, sulphates, bicarbonates, carbonates and bromides at sodium, magnesium, calcium and potassium.
1. Zones:
Like ponds and lakes, sea also exhibits different zones. They are mentioned as under:
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(a) The Littoral Zone:
This is the shore line between land and the open sea. In this zone waves and tides have maximum effect. This is because sometimes extremes of temperature, moisture and intensity of height are felt by this zone. Such a kind of behaviour results in a diversity of species. In rocky shores organisms like algae and starfish are found. In bays, algae are found on the surface. Sometimes photosynthetic bacteria are found beneath the algae along with abundance of worms.
(b) The Naritic Zone:
This region is shallow enough to support plants rooted to the sea floor. Below this region is the continental shelf, extending to a water depth of about 200 metres. This zone constitute about 75% of the total ocean area and is relatively rich in species and high productivity due to depth of light penetration and the presence of nutrients washed from land. Extensive communities of grant kelps as well as smaller uni and multicellular forms along with snails, worms, dominate the ocean bottom. Phytoplankton’s and zooplanktons are relatively abundant which support some of the greatest fishing grounds in the world.
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(c) The Pelagic Zone:
This consists of open sea which is about 90% of the total ocean surface. Photosynthesis on the surface of this zone is mainly carried out by various types of phytoplankton. Although largest in size, this zone is low in nutrients and hence low in productivity.
Blue whales and fin are also found in this zone. The organisms in this zone below the level of light penetration are completely dependent on the rain of detritus of upper regions for their nutrients. In deeper water many animals have poor visions, others including fishes are bioluminescent and some deep water fish have light producing organs.
(d) The Benthic Zone:
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This forms the floor of ocean. It extends from the edge of the continental shelf to the deepest ocean trenches. Organisms here are heterotrophic. Rooted animals are sea fan, sponges etc. Snails remain embedded in the mud white star fish, sea cucumbers and sea urchins move on the surface.
As compared to aquatic ecosystems which are essentially a single phase system, a terrestrial ecosystems as a three phase system, where the characteristics of the habitat are a function of the atmosphere and climate, the soil as well as the biotic community.
The distribution of biomes is governed by annual variation of rainfall and availability of sunlight. Forests are generally associated with heavy rainfall but the type is influenced by temperature and sunlight and the same is applicable for deserts which occur in regions where rainfall is very low.