Just as human consumers of seafood contaminated with biotoxins of algal origin are at risk, many animals at higher levels of the marine food web are impacted by HABs. Some toxins are fat soluble and bioaccumulate in higher trophic levels. Others still transfer through successive stages, sometimes having lethal impacts where they are least expected, such as with this humpback whale (right), one of 14 that died near Cape Cod, MA in a one-month period due to saxitoxin in mackerel that they had consumed.
It has now been confirmed that more than 150 deaths of the Florida manatees occurred in 1996 due to affects of algal toxins produced by Karenia brevis. Estimates suggest that about 10% of the endangered population was killed by an extensive and intense HAB event. Both stomach contents and lung tissue contained the toxins suggesting that the toxins entered through the food web as well as from direct contact of the toxic aerosols when the animals broke the surface to breathe.
Between March and April 2003, 107 bottlenose dolphns (Tursiops truncatus) were found dead together with hundreds of fish and marine invertebrates along the Florida Panhandle. Despite the absence of a concurrent bloom of Karenia brevis, high levels of brevetoxin were measured in all stranded dolphins examined (tissues and stomach contents), as well as in their fish prey (undigested menhaden recovered in dolphin stomach contents). Although brevetoxins were suspected in a dolphin mortality event in the same area in 2000, this was the first time that brevetoxin involvement was unequivocally confirmed in all tested animals and that the role of vectors in the poisoning was umambiguously identified. This event has indicated that lethal doses of brevetoxin can be transferred through the food web and that marine mammal mortalities can occur in the absence of a bloom.
Last updated: July 31, 2012