marine ecosystem

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Marine ecosystem which are of singular ecological significance occupy 70% of Earth's surface,with average depth of 3750m & salinity averaging 3.5%.unlike fresh water ecosystems ,marine ecosystems are continuous & is in continuous circulation via major surface currents , waves , tidal action, upwelling etc. In the absence of vertical mixing of the deep waters which constitute 60% of ocean stay permanently at 3(degrees)celcius. the concentration of nutrients in ocean is low.Hydrogen & oxygen form 96% of total ocean elements.
 
The major zones in marine ecosystems are litoral,neritic,pelagic benthic.
 
a)The litoral or inter-tidal zone:-It is subjected to physical violence of waves & tides & to fluctuations of temperature ,moisture & light intensity. Along rocky shores we find sandy shores organisms are adapted to burrowing in or adhering to sand like- ghost crabs, sand dollars etc. Mud flats occurring in Bays houses algae on the surface & photosynthetic bacteria right beneath it along with abundance of clams, worms etc. Coral reefs may be regarded as litoral ecosystems & is highly productive.

b)The Neritic zone:It constitutes 70% of total ocean area & is rich in species.It has high productivity due to deposition of nutrients washed from land & depth of light penetration. Richness & productivity decreases towards deeper water of this zone.It houses algael communities uni-cellular & multi-cellular organisms apart from snails,worms etc.Phytoplanktons & zooplanktons are abundant & support some of the greatest fishing grounds of the world.

c)Pelagic zone:- It's the open sea & constitute 90% of total ocean surface. Photosynthesis occurs in the surface by planktonic diatoms & dinoflagellates. Copepods & arrow worms are the major types of zooplanktons. 

The zone is low in nutrients & also in primary & secondary productivity. Most plankton live between 75m - 200m from surface. The top milimeter plays an important role in global carbon-di-oxide regulations.The organisms of this zone live below the light penetration are dependent upon detrius & are heterotropic. Carnivores copepods & other crustacea are abundant in upper water of this non-photosynthetic zone. Many animals have reduced vision & others are bio-luminescent, while fishes have light producing organs.

d)Benthic zone:- Extends from the edge of continental shelf to deep ocean trenches. Organisms of this zone are heterotropic. It encompasses 94% of ocean bottom. It is like sea lilies, sponges, other organisms like star fish, sea urchins, clams, snails, diatoms, siliceous & calcerious shelled Forminifera etc.

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