<P> Phytoplankton are the main primary producers at the bottom of the marine food chain . Phytoplankton use photosynthesis to convert inorganic carbon into protoplasm . They are then consumed by microscopic animals called zooplankton . </P> <P> Zooplankton comprise the second level in the food chain, and includes small crustaceans, such as copepods and krill, and the larva of fish, squid, lobsters and crabs . </P> <P> In turn, small zooplankton are consumed by both larger predatory zooplankters, such as krill, and by forage fish, which are small, schooling, filter - feeding fish . This makes up the third level in the food chain . </P> <P> The fourth trophic level consists of predatory fish, marine mammals and seabirds that consume forage fish . Examples are swordfish, seals and gannets . </P>

How does deep-sea biomass compare to the biomass of surface waters