 The lower trophic layers are very well-represented with about 500 species of copepods, 2500 species of gastropods, and 2500 species of crustaceans on average.At the apex and near-apex trophic levels, there are usually about 100 species of marine mammals and about 50 species of marine birds.The vital intermediate trophic species however are small pelagic fish that usually feed on phytoplankton.