Some can even produce a chemical light called bioluminescence . Dinoflagellates change form during their life cycle. Most go through an active, swimming stage of life and a more stationary stage. In the stationary period, some dinoflagellates develop into thick-walled, seedlike forms called cysts . Scientists believe that cysts settle at the bottom of oceans and lakes, enabling dinoflagellates to survive when water conditions are unfavorable for growth.
Dinoflagellates make up part of plankton, a drifting mass of water organisms.
Plankton provides food for much sea life. However, a few dinoflagellates produce powerful poisons that kill fish. When dinoflagellates become abundant, they may discolor the water, causing red tides . Red tides can harm marine life if they contain poisonous dinoflagellate species, or if the dinoflagellates remove all oxygen from the water. Harmful red tides often occur in coastal waters.