The scheme used to find out these ecoregions is more or less the same as that for terrestrial ecoregions. Major habitat types are identified: polar, temperate shelfs and seas, temperate upwelling, tropical upwelling, tropical coral, pelagic, abyssal, and hadal (ocean trench) — which correspond to the terrestrial biomes. Major biogeographic realms, analogous to the seven terrestrial ecozones, represent large regions of the ocean basins: North Temperate Atlantic, Eastern Tropical Atlantic, Western Tropical Atlantic, South Temperate Atlantic, North Temperate Indo-Pacific, Central Indo-Pacific, Eastern Indo-Pacific, Western Indo-Pacific, South Temperate Indo-Pacific, Southern Ocean, Antarctic, Arctic, and Mediterranean.