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

Abstract

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 10 844 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.

Co-occurrence of multiple classes of harmful algal toxins in bottlenose dolphins (Tursiops truncatus) stranding during an unusual mortality event in Texas, USA

“…However, low levels of brevetoxins similar to that reported here (<30 ng/g) are routinely detected in dolphin feces sampled during non-bloom conditions in regions that experience frequent K. brevis blooms (S. Fire, unpublished data). This is likely an indication of background exposure from residual brevetoxin in the food web long after dissipation of a K. brevis bloom, or from yearround, low-level toxin production from background levels of K. brevis in the water column Fire et al, 2008).…”

Effects of Karenia brevis harmful algal blooms on nearshore fish communities in southwest Florida

“…Brevetoxin can persist in the environment for extended periods. Fire et al (2008) discovered brevetoxins more than 2 mo following a K. brevis bloom and Naar et al (2007) detected brevetoxins more than a year post-bloom. Thus, K. brevis cell count is a crude measure of a fish's potential exposure to PbTx.…”

“…During the entire red-tide event of 2005, the town of Longboat Key, 1 of 5 municipalities bordering the study area, removed 121 tons of dead fish from its beaches and residential canals (Cooper 2005). Fishes collected from the Sarasota Bay study area during these red-tide periods had high brevetoxin concentrations in their tissues (Fire 2006, Fire et al 2008.…”

“…Our sampling methods were unable to discriminate between these 2 potential mechanisms. However, the occurrence of extremely large fish kills and high PbTx concentrations in fish tissues (Fire 2006, Fire et al 2008) suggests brevetoxininduced mortality was a significant factor underlying the community-level changes. Brevetoxins are known to be lethal to fishes (Steidinger et al 1973, Baden & Mende 1982, reviewed by Landsberg 2002 and have also recently been demonstrated to accumulate in tissue of living specimens (Flewelling et al 2005, Naar et al 2007, Fire et al 2008.…”

“…However, the occurrence of extremely large fish kills and high PbTx concentrations in fish tissues (Fire 2006, Fire et al 2008) suggests brevetoxininduced mortality was a significant factor underlying the community-level changes. Brevetoxins are known to be lethal to fishes (Steidinger et al 1973, Baden & Mende 1982, reviewed by Landsberg 2002 and have also recently been demonstrated to accumulate in tissue of living specimens (Flewelling et al 2005, Naar et al 2007, Fire et al 2008. Brevetoxins can be detected in fish tissues more than a year following red tides (Naar et al 2007) and were found in fish tissues several months following these particular red-tide events in Sarasota Bay (Fire et al 2008), indicating that they remain in the food web for substantial periods of time.…”