Why are oceans least productive? | Class 12 Biology Chapter Ecosystem, Ecosystem NCERT Solutions

Oceans are the largest and most diversified type of ecosystem. It occupies nearly 70- 73% of the earth’s surface. Ocean is categorized in the marine ecosystem and contains high salt content. The chief salts are found: chlorides, sulphates, bicarbonates and bromides of sodium, magnesium, calcium and potassium.

Ocean environment is generally classified into many zones on the basis of light penetration (euphotic, disphotic and aphotic zones), on the basis of distance from shore and water depth (littoral or intertidal, neritic or oceanic zone); in the open water (pelagic zone) or bottom (benthic zones). Oceans are least productive because they do not receive enough sunlight that is necessary for the primary productivity. There is insufficient sunlight decreases with the increasing depth. There is deficiency of nitrogen in the ocean that is important for the plants.

Diagram:

Note*: the epipelagic zone is also known as sunlight zone in the ocean environment and is 200m from the surface; is the region where the photosynthesis occurs and thus contains the large biodiversity.