Red Tide in Sarasota

Red tides occur throughout the world, drastically affecting Scandinavian and Japanese fisheries, Caribbean and South Pacific reef fishes, and shellfishing along U.S. Coasts. These red tides are caused by several species of marine phytoplankton, microscopic plants that produce potent chemical toxins.

The Florida red tide is caused by blooms of a dinoflagellate that produce potent neurotoxins. These toxins cause extensive fish kills, contaminate shellfish and create severe respiratory irritation to humans along the shore.

Florida red tide blooms typically begin in the Gulf of Mexico 40-80 miles offshore and move slowly southeast with the prevailing ocean currents toward the Tampa Bay area. As the bloom progresses, the density of red tide organisms increases to several million cells in each liter of seawater, and the affected area expands to many square miles. The result is a mass of deadly toxin-containing water sweeping toward the southwest Florida coast, leaving a wake of dead and dying fish.

As the bloom approaches the shoreline, we begin to see and feel the obvious effects: dead fish, the characteristic burning sensation of the eyes and nose, and dry, choking cough. When the bloom is severe, fish die rapidly from the neurotoxic effects of the red tide which enter their bloodstream through the gills. Because the fish die so quickly, these toxins do not have time to build up in their tissue. Fish exposed to lower (sublethal) concentrations, however, may accumulate these toxins in their body.

Red tide populations well below the fish kill level can pose a problem for public health through shellfish contamination. Bivalve shellfish, especially oysters, clams, and coquinas, accumulate so much toxin that they become toxic to humans. Public health concerns also emerge from studies of airborne toxins that show the presence of bacteria impacting our respiratory system along with the red tide toxins.

Because of the severe economic and public health effects of red tides, much consideration has been given to controlling the blooms. Control is feasible within confined areas, such as fish hatchery and aquaculture ponds, and research is underway to assess various control methods. Control in the broad expanses of the Gulf of Mexico, however, is neither feasible nor desirable at this time.

Although coastal pollution has enhanced red tide bloom in other areas, the Florida red tides represent a natural process, not caused by pollution. These blooms serve a purpose in the ecology of the Florida Gulf coastal regions. Our responsibility is to understand the purpose and function of red tides, directing our efforts toward alleviating the adverse effects without causing further ecological damage.

The more we learn about red tide, the more intriguing this natural phenomenon appears. There is much more to this event than is detected by our eyes and nose. The red tide organism plays a very important role in the conversion of solar energy to chemical energy (photosynthesis), a process that is essential to the survival of most marine animals. Why this little menace also produces neurotoxins is still a mystery, but how toxins are produced and how they affect marine life as well as humans is the focus of much intensive research.

Information provided by Mote Marine Laboratory