We have been investigating the impacts of red tide on Sarasota Bay dolphins, sea turtles, and sea birds over the last several years. Although the Sarasota Bay area did not experience a red tide bloom during 2008, we are still investigating the impacts of Florida red tide blooms during 2005, 2006, and 2007 on these species. We have collected data from stranded dolphins, sea turtles, and sea birds to determine brevetoxin levels and the effects brevetoxin has on increasing morbidity and mortality in these species. In sea turtles and sea birds we have been able to collect blood and/or fecal samples from live animals suffering from brevetoxicosis and determine how quickly or slowly these animals clear the toxin from their blood.
Seventy-six percent of dolphins stranding in Southwest Florida (not necessarily Sarasota Bay residents) during 2006-2007 (n=21) had brevetoxin levels above the detection limit and were classified as brevetoxin positive animals. Of these positive animals, 30% were determined to have died from brevetoxin intoxication or it was implicated as a contributory factor to death. A proportion of sea birds and sea turtles stranding live during 2005-2007 had clinical signs of red tide intoxication including circling, paralysis, and seizures. Red tide intoxication appeared to be the primary cause of stranding in 42 of 78 (54%) live-stranded sea birds and 59 of 71 (83%) live-stranded sea turtles. Sea birds were able to clear the toxin from their blood in 10 days, while it took up to 50 days for some sea turtles to clear the toxin due to their lower metabolic rate.
Findings from this study are only preliminary, but the fact that the majority of the live sea birds and sea turtles sampled during these red tide events were positive for the red tide toxin indicates that red tide intoxication plays a larger role in the morbidity and mortality of sea birds and sea turtles off the west coast of Florida than was previously recognized. In addition, the information that sea birds can clear the red tide toxin from their bodies within 10 days of rehabilitation whereas it may take up to 50 days for sea turtles to clear the toxin can be used by rehabilitators to modify treatment plans for animals suspected of suffering from red tide intoxication. We have just received funding to investigate cholestyramine (Questran), a bile acid binder, which may be a useful treatment for brevetoxicosis in loggerhead sea turtles and double-crested cormorants. Cholestyramine has been used to treat cases of toxin exposure in humans and domestic animals. Use of cholestyramine treatment may lead to quicker elimination of brevetoxin and increased survival in affected animals. If this treatment is successful it would prove useful in future red tide events by increasing treatment success for these and other threatened/endangered species.
Our research was supported by funding from the John H. Prescott Grant Program, Morris Animal Foundation and the Florida Sea Turtle License Plate Sea Turtle Grants Program.