Current Status and Historical Trends of Brown Tide and Red Tide ...

Along with favorable salinity levels, sufficient light and an adequate carbonsource like carbon dioxide are necessary for any photosynthetic organism. Aldrich(1962) noted a correlation between red tide outbreaks involving Gymnodinium breve onthe Florida Gulf coast and extended periods of heavy rainfall and subsequent organicinput to the sea from river discharge. After unsuccessfully testing a multitude oforganic substances as potential direct energy sources and discovering that theorganism did not grow in the dark in spite of growth additives, he determined that G.breve was not heterotrophic and that sunlight and carbon dioxide were its principalgrowth requirements. He suggested that vitamins, trace metals and chelators fromFlorida river waters may facilitate photoautotrophy and thus bloom formation in G.breve (cf. Collier, 1958) and should be studied further.Ten years later, Steidinger and Ingle (1972) included in their summary ofinformation on G. breve red tides the facts that pollution does not catalyze blooms inFlorida and that dinoflagellate blooms may initiate from seed populations well offshore.Steidinger (1975b) postulated that the offshore seed populations could be either restingpelagic cells or benthic resting cysts (hypnozygotes) from which blooms could initiateand be transported inshore with the aid of physical factors. For instance, Roberts(1979) confirmed that, in 1976, surface concentrations of G. breve increased graduallyoffshore and were then transported inshore due to winds and currents. Initiation inWest Florida, therefore, may well be an offshore phenomenon that accelerates whenand if transport to depth and toward shore concentrates red tide cells in the photiczones of shallow waters (Seliger et al.,1979). That a process similar to West Floridaoccurs for the initiation of blooms off South Texas is quite possible, particularly giventhe prevailing onshore winds in the western Gulf of Mexico.Temperature is another likely significant factor, supported in part by theapparently strong correlation between surface water temperature patterns and majorbloom initiation reported by Baldridge (1975), who claimed that simple indicatorpatterns of water temperatures from mid-January to early April could predict red tideoutbreaks twelve months in advance near Tampa Bay, Florida. He stated that suchpatterns had already shown strong correlation with five major red tides between 1957and 1974 at Egmont Key, Florida, but had no desire to claim cause-effect dependencynor to diminish the importance of other environmental conditions favoring bloominitiation. His claim of the strong predictive power of certain surface temperaturepatterns, however, has not been substantiated since 1974 (K. A. Steidinger, pers.comm.). Though Baldridge's predictive model may not be acceptable, a necessarytemperature range may still be required for initiation. Rounsefell and Nelson (1966)cite results of studies that examined temperature effects on G. breve which, whencombined, defined the survival range from 7 o -32 o C, the range of possible growth from