ABSTRACT
Temperature governs the distribution of marine biological communities more than any other factor. Water masses are defined by homogenous temperature and salinity regimes and are analogous to the major terrestrial regions. High biological productivity is found in areas where water masses converge or diverge. The great majority of phyla of multicellular animals are found only in the marine environment. Phytoplankton are responsible for > 95 per cent of the annual primary production in the ocean. While the ocean’s habitable volume is hundreds of times greater than that of the land, only the upper 50–200 metres of the oceans - the photic zone - will support the growth of primary producers. In terrestrial ecosystems, primary producers (mainly vascular plants such as trees and grass) constitute the great majority of biomass, and individual organisms are often large. In contrast, the dominant primary producers in marine ecosystems - the phytoplankton - are generally microscopic and can reproduce rapidly and are rapidly processed, either by consumers or reducers (e.g. bacteria). In the oceans, species and communities can be passively transported long distances, whereas on land, colonization of distant areas generally requires active migration and passive dispersal. Species diversity decreases from west to east in both the Atlantic and Pacific Oceans. Furthermore, faunas in the Pacific Ocean (e.g. coral reefs) are on the whole more diverse than in the Atlantic Ocean. Water motion in the surface waters of the oceans (down to a depth of about 600m) is driven primarily by winds and tides. Below approximately 600m, water motion and horizontal currents are much slower and driven primarily by density differences.
