Marine Animal Encyclopedia
Some red-tide organisms such as Gymnodinium pulchellum produce toxins that affect the nervous system and the clotting properties of the blood, causing high mortality among fish as well as invertebrates. The cause of red tides is not well understood, but some scientists think they may be influenced by coastal pollution providing nutrients that might otherwise be in short supply and so normally limit the population size. Rapid reproduction by simple cell division results in huge numbers of Gymnodinium pulchellum being present in the water, turning it a characteristic brown-red color, as shown here in the seas around Hong Kong. Unlike many other types of dinoflagellates, Gymnodinium pulchellum lacks a test and also produces food by photosynthesis.