Plankton include a huge quantity of organisms, which float in different layers of the Ocean and are transported by currents. Belonging to this class are bacteria, cell-like plants (phytoplankton), some kinds of molluscs, crabs, roe and larva of fishes, larva of invertebrate bottom animals and others (zooplankton).

Nekton consist of organisms which swim in deeper waters and are capable of travelling long distances. Fishes, cephalopod molluscs, marine mammals (whales (cetaceans), seals, sea lions and walruses (pinnipeds)), sea turtles and snakes all rely on them for food. Although nekton are important to large animals, the nektonic biomass is approximately 20 times less than that of plankton.

Benthos comprise a group of organisms living near the sea floor, attached to it, dug in or living in it for shelter. Organisms living on top of the sea floor also fit into this category It contains many kinds of molluscs, crabs, worms, echinoderms and sponges. Especially beautiful are the magnificent benthos on coral reefs. The primary plants in the benthos category are multicellular seaweed (green, red, brown), microscopic one-celled plants, wrack grass, thalassia and other grasses.

There are specific communities that confine themselves to the sea surface: birds. There are 240 kinds of birds - albatrosses, frigate-birds, gannets, shearwaters, gulls and many others that live and rely heavily on the Oceanic food chain.
 
 

Wrack grass






Information provided by HDNO:  http://www.oceansatlas.com/unatlas/about/ContactInfoForHDNO.html