Zooxanthellae coat the outside of a coral polyp. This curious little dinoflagellate performs as a symbiote to a coral in this fashion: the carbon derived from photosynthesis is then transferred from the zooxanthellae to the coral. In turn, the coral can supply nitrogen to the dinoflagellate from one-celled organisms it catches as food. Nitrogen is the nutrient required by algae and phytoplankton to be transmuted to energy.