Red tides and marine mammal mortalities: Brevetoxicosis

Unexpected brevetoxin vectors may account for deaths long after or remote from an algal bloom. Red alert A string of recent reports have claimed that the deaths of groups of dolphins and manatees off the Florida coast have been caused by red tides (toxic algal blooms). It has been hard to verify the true cause of these deaths. But the discovery that algal toxins accumulate in fish and seagrass, food for dolphins and manatees, respectively, suggests that the red tides are indeed to blame. Potent marine neurotoxins known as brevetoxins are produced by the ‘red tide’ dinoflagellate Karenia brevis . They kill large numbers of fish and cause illness in humans who ingest toxic filter-feeding shellfish or inhale toxic aerosols 1 . The toxins are also suspected of having been involved in events in which many manatees and dolphins died, but this has usually not been verified owing to limited confirmation of toxin exposure, unexplained intoxication mechanisms and complicating pathologies 2 , 3 , 4 . Here we show that fish and seagrass can accumulate high concentrations of brevetoxins and that these have acted as toxin vectors during recent deaths of dolphins and manatees, respectively. Our results challenge claims that the deleterious effects of a brevetoxin on fish (ichthyotoxicity) preclude its accumulation in live fish, and they reveal a new vector mechanism for brevetoxin spread through food webs that poses a threat to upper trophic levels.