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TIDE TROUBLE Poisonous brevetoxins produced by the dinoflagellate Karenia brevis (shown) can accumulate in fish and sea grass. |
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FLORIDA FISH & WILDLIFE CONSERVATION COMMISSION |
Algal blooms of the dinoflagellate Karenia brevis produce poisonous brevetoxins, killing large numbers of fish and rendering shellfish populations unfit for human consumption. Biologists now link the deadly blooms, so-called red tides, to several “unusual mortality events” in the past few years in which manatees and dolphins along the Florida coast died in droves (Nature 2005, 435, 755).
The mysterious deaths occurred during lulls in algal blooming. Autopsies revealed high concentrations of brevetoxins in the stomach contents of the manatees and dolphins, however.
The researchers from the Fish & Wildlife Research Institute in St. Petersburg, Fla., and the University of North Carolina, Wilmington, found high levels of brevetoxins in sea grass eaten by manatees. They also demonstrated that brevetoxins could accumulate to harmful levels in small fish, commonly eaten by dolphins, without killing the fish. The small fish accumulated brevetoxins by feeding on red-tide alga and contaminated shellfish.
The findings suggest that brevetoxins can climb the food chain and pose a threat to marine mammals, even when algal blooms are not immediately present.
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