Many dinoflagellates are photosynthetic, manufacturing their own food using the energy from sunlight, and providing a food source for other organisms. The photosynthetic dinoflagellates are important primary producers in coastal waters. Some photosynthetic dinoflagellates are symbiotic, living in the cells of their hosts, such as corals. Called zooxanthellae, they are found in many marine invertebrates, including sponges, corals, jellyfish, and flatworms, as well as within protists, such as ciliates, foraminiferans, and colonial radiolarians. Approximately half of all species are heterotrophic, eating other plankton, and sometimes each other, by snaring or stinging their prey.
Some species are parasites on algae, zooplankton, fish or other organisms.
The most form of reproduction is asexual, where daughter cells form by simple mitosis and division of the cell. The daughter cells will be genetically identical to that of the original cell. The thecal plates may either be divided, or completely shed and then reformed. Under some conditions sexual reproduction may occur. Motile gametes are formed as a result of mitosis, because dinoflagellates are usually haploid.