The distribution of marine biodiversity varies widely throughout ocean basins. The abundance and diversity of most taxa tends to be highest near continental and island margins that are less than 2,000 meters deep.
These areas experience nutrient enrichment from upwelling processes and terrestrial runoff. Areas where significant upwelling occurs are often extraordinarily productive in tropical, temperate, and polar regions. Within major habitat types, species richness and endemism also vary enormously around the globe.
Species endemism tends to be less pronounced in marine ecosystems than in terrestrial or freshwater ecoregions, but several regional centers of endemism are recognized, including the southern coast of Australia, New Caledonia, Lord Howe and Norfolk Islands, the northern coast of South America, the Yellow and East China Seas, the Red Sea, the Mediterranean Sea, the Sea of Cortez, the Great Barrier Reef, and tropical Pacific Islands such as Hawaii, Marquesas, the Tuamotus and Societies, and Easter Island.
In general, marine ecoregions associated with isolated islands and enclosed seas tend to display higher levels of endemism.