The Temperate Shelf and Seas are highly productive regions of great biological importance, supporting resident as well as migratory species during various life cycle stages. The relative shallowness of these regions (the continental shelf extends to an average maximum depth of 150 meters) leads to warmer temperatures and seasonal stratification of the water column based on temperature.
Seasonal variability, along with freshwater influxes from coastal streams and tidal action, contribute to very heterogeneous habitats and a corresopondingly high diversity of organisms: fish, invertebrates (productive benthic communities), marine mammals, and numerous marine bird species. Some of the most productive marine ecosystems occur in the Grand Banks and New Zealand plus the Patagonia ecoregions. The South Australian coastal waters are remarkable for unusually high levels of endemism in invertebrates, in addition to the diverse marine mammal assemblage found there.
Two of the world's largest temperate estuaries, the Chesapeake and Delaware Bays and the Northeast Atlantic Shelf are elevated to the Global Ecoregions due to their size, productivity, and habitat diversity. Two of the most distinctive enclosed temperate seas, the Mediterranean Sea and the Yellow and East China Seas, are recognized in the Global Ecoregions.