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. Dinoflagellates belong to the kingdom Protista.