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Harmful Algal Bloom Toxins Found in Dolphin Diets

Dr. Spencer Fire of NOAA's Marine Biotoxins Program extracts toxin from marine mammal samples. Fire recently served as lead author in a study confirming that toxins from harmful algal blooms impact coastal ecosystems long after the bloom is over. These toxins accumulate in fish and other aquatic life that eat the algae. The animals then pass the toxins on to larger predators when they are eaten.

A new study by NOS researchers finds that harmful algal bloom (HAB) toxins are transferred to dolphins through the fish they eat.

The study, published in the Sept. 25 issue of Marine Ecology Progress Series, shows that the primary prey fish of dolphins in Florida carry the toxic algae long after a HAB event is over.

National Centers for Coastal Ocean Science (NCCOS) researchers and collaborators from multiple institutions in Florida and North Carolina identified accumulated amounts of brevetoxin, produced by the toxic alga Karenia brevis, in the food web of Florida bottlenose dolphins.

The findings point out the need for coastal managers to consider long-term, repeated dietary exposure to harmful algal toxins in their assessments of marine mammal health risks.

Previous NCCOS studies have found that HABs play a significant role in unusual deaths of marine mammals such as seals, sea lions, dolphins, and whales. It is estimated that over 50 percent of these events—referred to as Unusual Mortality Events (UMEs) by scientists—are caused by algal toxins.

A UME is defined as an unexpected marine mammal stranding, or significant die-off of any marine mammal population.

While HABs are often suspect during unexplained marine mammal deaths, they are not always the culprit.

In a separate NCCOS study, researchers recently ruled out the involvement of HAB toxins during an unusual dolphin mortality event that occurred in Feb. and March, 2008, in Virginia, Maryland, and Delaware.

The high numbers of dolphins stranded during this event were thought to be tied to a large HAB outbreak in coastal waters off the Eastern U.S. However, no HAB toxins were found in samples collected from these animals.

The search for the cause of this dolphin stranding remains a mystery.