Prevalence of brevetoxins in prey fish of bottlenose dolphins in Sarasota Bay, Florida

Blooms of the brevetoxin-producing dinoflagellate Karenia brevis have been linked to high mortality of bottlenose dolphins Tursiops truncatus on Florida’s Gulf of Mexico coast. A clear understanding of trophic transfer of brevetoxin from its algal source up the food web to top predators is needed to assess exposure of affected dolphin populations. Prey fish constitute a means of accumulating and transferring brevetoxins and are potential vectors of brevetoxin to dolphins frequently exposed to K. brevis blooms. Here we report results of brevetoxin analyses of the primary fish species consumed by long-term resident bottlenose dolphins inhabiting Sarasota Bay, Florida. Fish collected during K. brevis blooms in 2003 to 2006 were analyzed by competitive enzyme-linked immunosorbent assay (ELISA) and had brevetoxin concentrations ranging from 4 to 10844 ng PbTx-3 eq g–1 tissue. Receptor binding assay (RBA) and liquid chromatography–mass spectrometry (LC-MS) analysis confirmed toxicity and the presence of parent brevetoxins and known metabolites. Fish collected in the absence of K. brevis blooms tested positive for brevetoxin by ELISA and RBA, with concentrations up to 1500 ng PbTx-3 eq g–1 tissue. These findings implicate prey fish exposed to K. brevis blooms as brevetoxin vectors for their dolphin predators and provide a critical analysis of persistent brevetoxin loads in the food web of dolphins repeatedly exposed to Florida red tides.