MORE THAN MEETS THE EYES AND NOSE

On a sultry Fall morning of 1947, the community of Venice, Florida, awoke to thousands of dead fish along the beaches and a stinging, choking "gas" in the air. Some blamed nerve gas, others a chemical spill, but scientists soon discovered the cause RED TIDE. Although this was the first scientific documentation of this catastrophic event along the Florida Gulf coast, reports of similar events have been recorded as far back as the mid 1800's.

Red tides occur throughout the world, drastically affecting Scandinavian and Japanese fisheries, Caribbean and South Pacific reef fishes, and shell fishing along U.S. coasts. Most recently, it has been implicated in the deaths of hundreds of whales, dolphins, and manatees in North American waters. These red tides are caused by several species of marine phytoplankton, microscopic plant like cells 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 increase to several million cells in each liter of sea water, and the effected 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 (sub lethal) concentrations, however, may accumulate these toxins in their body. New evidence from current research suggests that such bioaccumulation in fish eaten by dolphins may have been a major factor in the deaths of more than 700 of these marine mammals in 1987.

Red tide populations well below the fish kill level pose a serious problem for public heath through shellfish contamination. Bivalve shellfish, especially oysters, clams and coquinas, can accumulate so much toxin that they become toxic to humans. Public health concerns also emerge from studies that show the presence of airborne toxins have an impact on the human respiratory system.

Because of the severe economic and public health effects of red tides, much consideration has been given to controlling the blooms. Control is only feasible within confined areas, such as fish hatcheries 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.  

Historical evidence indicates that red tides have occurred along the Florida Gulf coast for hundreds of years, and probably longer.  Red tide cells occur naturally through out the Gulf and develop into highly concentrated “bloom” conditions as a result of physical, chemical and biological factors that are conducive to bloom formation most frequently along the unique, shallow environment of the west Florida shelf.  Scientists are working very hard to understand the complex combination of these factors that result in a red tide bloom, so that we might predict bloom formation and investigate possible ways to eliminate or reduce their adverse impacts on marine life and public health. One aspect of red tide research investigates the type and source of nutrients that support a red tide bloom.  The extent to which coastal pollution influences red tides is an area of intense interest and considerable effort is being placed toward those investigations. It is important to keep in mind that red tide blooms appear to be a natural part of the phytoplankton community in the Gulf of Mexico.  In this area of research, our responsibility is to determine the natural function of red tides and direct our efforts toward reducing human influences 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 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 essential to the survival of all animals. Why this little menace also produces neurotoxin is still a mystery. Mote is dedicated to research that will help us, not only understand the natural and man made factors that influence red tide, but also to minimize and mitigate the health effects to humans and marine life.

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