The Red Tide

Torpey, John; Ingle, Robert

1. Florida Red Tide is caused by the microscopic organism, Gymnodinium breve Davis. Normally present in seawater along the Florida west coast in small concentrations., they may suddenly reproduce at a rapid rate, resulting in astronomically high numbers of individuals. The water then becomes characteristically discolored. The organism produces toxic substances which, during a bloom, are sufficiently potent to kill marine animals. 2. G. breve is a very delicate and fastidious organism. Its requirements and optima must be met on precise levels for it to survive and multiply. Temperature, light, stability of surrounding media, organic nutritional substances., and metals must all be at the correct level for blooms to develop. 3. Since 1844, Florida Red Tide has occurred at least 16 times in major proportions. There may have been outbreaks that were unreported due to sparse population in the coastal areas and inadequate communication. 4. When Red Tide appears., a slightly irritating gas may be noticed. It has been suggested that this may have man-made origin but biological evidence indicates the causative factor is the breakdown of the Red Tide organism. The irritant effects of the gas are restricted to the sea or beach areas and are temporary. The slight coughing and other symptoms disappear when Red Tide diminishes. 5. Fishes which are not killed or whose behavior is not noticeably affected by Red Tide are apparently safe for human consumption. 6. Mollusks such as mussels, clams, and oysters that are removed from Red Tide waters must be regarded with suspicion. There is a definite relationship between toxicity in these filterfeeding animals and high concentrations of G. breve. 7. Recent studies have indicated that the addition of EDTA (ethylenediamine tetra-acetic acid) and iron to seawater samples containing G. breve promotes survival and growth. 8. An extensive sampling program in North and South Florida has revealed that streams entering the Gulf contain high concentrations of iron and humic acids (coffee-colored substances). The latter may assist in making iron and other metals soluble in seawater just as EDTA does in the laboratory. It is hoped that the present sampling program will provide information on the relationship of land runoff to Red Tide. 9. Financial support for Red Tide investigations for many years was inadequate and undependable. In 1963 the Florida legislature appropriated funds sufficient for a large scale research project. This support was again provided in the 1965 session. As a result of this assistance much has been learned. Scientists of the Board of Conservation have suggested a method of control. Work now is concerned with verifying the practicality of this method. 10. The control suggested involves the construction of dams across major streams of afflicted areas.