Biota of Oceans - Ecosystem
Life in the sea is not particularly abundant, though the diversity of organisms is very high. Almost every major group of animals and every major group of algae occur-somewhere in the oceans, with the exception of vascular plants and insects. These two have a few marine representatives though they are abundant in estuaries. On the basis of depth-wise differences in life forms, the expanse of marine ecosystems has been divided into littoral, neritic, pelagic and benthic zones.