The Red Tide

Red Tide is a reddish brown color of sea water caused by an organism, Gymnodinium breve, which is a member of the Dinoflagellate family. When water temperature, salinity, and nutrients reach certain levels, a massive increase in the number of dinoflagellates occurs. This is called a bloom and may lead to high mortalities among marine animals..

Fresh water has a zero (0) ppt (parts per thousand) salinity, normal sea water has 36.3 ppt. The optimum salinity for red tide to grow is 30 to 40 ppt. This makes our Tampa Bay area prime for red tide. High temperatures together with a lack of wind and adequate rainfall are usually at the root of an outbreak.

A count of 250,000 red tide organisms per liter of sea water is lethal to fish and other marine animals. At times, we have had triple that figure. Although it has not killed humans, shellfish harvesting is banned in areas that are affected. Swimming in infested water is not harmful but is unpleasant. Nose and throat irritation and burning eyes are a side effect. The smell of dead fish alone is enough to keep most people away.

Most of the fish that die are "bottom" fish such as catfish, grunt, shiner, pin fish, drum, and dog fish. At times, game fish are victim to the tide also.

G. breve red tide blooms begin offshore in a zone approximately 12 to 50 miles from shore. Because most red tides are shoreward in movement we eventually find our beaches littered with the problem.

 

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