Biological Resting in the Dinoflagellate Gonyaulax excavata

Abstract

The Peridiniales, dinoflagellates, are a far more diverse group of organisms than their notoriety as the causative organisms of tides' indicates. Dinoflagellates are found in freshwater, coastal marine, and oceanic habitats, and there are single-celled planktonic, benthic, and symbiotic forms. The fossil record indicates that dinoflagellates existed in geologic time as far back as the Precambrian in the Proterozoic Era, some 450 million years ago (Figure 1). They have been a dominant group of phytoplankton since the Silurian in the Paleozoic Era. Paleontologists have studied these forms as hystrichospheres, and they are welldocumented the world over. In the early 1960s, it was recognized that some hystrichospheres were indistinguishable from organisms found living in modern marine sediments. When these organisms were taken into the laboratory and observed, they were found to be resting cysts of present-day dinoflagellate species (Evitt 1961, Evitt and Davidson 1964, Wall 1965, Wall and Dale 1966), which excysted (hatched) to become motile dinoflagellates. Thus, dinoflagellate resting cysts are synonymous with hystrichospheres. This connection between palynology and neontology has revolutionized thinking in both fields. Modern dinoflagellates are a cosmopolitan group of organisms that live in all of the world's oceans. They provide an important food source for many filter feeders and zooplankton. Dinoflagellates in general contribute some 30% of total oceanic productivity. In cases such as red tides, the organisms reach concentrations of more than one million cells per liter. Red tides have been documented in waters off Japan, the east and west coasts of North America, northwestern and southwestern Europe, northwest Africa, the Indian Ocean, and the western coast of South America, and their effects are as diverse as the organisms that cause them. Some nontoxic dinoflagellates are associated with conditions of anoxia in the water masses, which can result in fish kills. Toxic blooms cause fish and shellfish mortalities and respiratory ailments in humans when the organisms release toxin into the water, as with Ptychodiscus brevis (= Gymnodinium breve) (Steidinger 1979) off the Florida coast. Paralytic shellfish poisoning (PSP) results when humans consume shellfish