All species are zooxanthellate, that is, they contain symbiotic, single-celled photosynthetic dinoflagellates that live in the tissues and provide the coral with nutrients produced by photosynthesis during the day. At night, the tentacles of the polyps expand and capture zooplankton.
The text describes how coral reefs rely on a symbiotic relationship with photosynthetic dinoflagellates, which are responsible for providing nutrients to the coral polyps. The process of capturing zooplankton occurs at night when the coral's tentacles extend.