BREVARD COUNTY, Fla. – An algae toxin 1,000 times deadlier than cyanide lingers at trace levels in the livers of bottlenose dolphins in the Indian River Lagoon, a new study shows, remaining there even when the algae is not blooming, News 6 partner Florida Today reported.
The long-term health implications for the lagoon's top predator and other marine life remain uncertain.
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"We're not making any conclusions about what it's doing to them," said Spencer Fire, an assistant professor at Florida Tech.
The study for the first time establishes a baseline level of the toxin in lagoon dolphins by which to compare future toxin levels during dolphin strandings or die-offs.
"This is what we expect to be sort of background levels," Fire said.
The poison, called saxitoxin, comes from the same algae that glows like fairy dust at night in the lagoon. The study, led by Florida Tech, is the first report of saxitoxin being detected in marine mammals absent an algae bloom.
Saxitoxin poisoning from eating lagoon fish has made people sick before. The same toxin has rendered puffer fish off-limits to harvest since 2002 after several people almost died after eating the fish. At least 28 people got sick in 2002 and 2003 after they ate pufferfish caught in the Titusville area, leading to a permanent state ban on harvesting the fish.
Saxitoxin is a natural byproduct of certain species of algae known to bloom in the lagoon and Florida lakes and rivers, including the St. Johns River, a main source of the region’s drinking water. Locally, the toxin is most commonly associated with an algae called Pyrodinium bahamense. The reddish algae, which has haunted the estuary over the past decade, is bioluminescent, making it a popular lure for kayak tours and ecotourists.
Human saxitoxin exposure most commonly occurs from eating certain fish that contain it in their tissues.
The toxin blocks nerve cells from sensing signals. Symptoms of saxitoxin poisoning include numbness in the mouth as quickly as 30 minutes after exposure, according to the Centers for Disease Control and Prevention. In severe poisoning, illness typically progresses rapidly and may include nausea, vomiting, a floating sensation, headache, muscle weakness, burning or prickling sensations and respiratory failure. Death can occur from paralysis, the CDC says.
The Florida Tech study was published online recently in the journalAquatic Toxicology.
Florida Tech graduate student Jeremy Browning and Wendy Noke Durden and Megan Stolen from Hubbs-SeaWorld Research Institute analyzed liver samples from 119 dead dolphins collected from 2002 to 2011. They extracted liver samples from dolphins found dead from 2002 to 2011, mostly from dolphins found in the lagoon, Halifax River and on the beach.
The researcher say their discovery suggests saxitoxin is an emerging threat to any organism living in the lagoon, but to what degree is unknown.
Fire said dolphins get the saxitoxin from the fish they eat, including mullet, sea trout and herring. He and colleagues from Harbor Branch Oceanographic Institute at Florida Atlantic University also recently completed a separate three-year study that found 1 in 4 lagoon fish they examined contained saxitoxin. The toxin levels were a third of the federal action limit at which shellfish are deemed safe to eat, Fire said.
"I think it's too early for us to make any recommendation," he said of whether people should eat lagoon seafood.
Researchers first began to suspect Pyrodinium bahamense’s toxicity in the lagoon in the early 2000s, after 28 people got sick eating lagoon puffer fish in 2002 and 2003.
Some scientists suspect the algae and its saxitoxin could be linked to about 120 dolphin deaths in the lagoon between the summer of 2000 and the summer of 2001. About forty died between U.S. 192 and State Road 520 in one month. Saxitoxin may suppress dolphin immune systems, making them susceptible to disease.
As the lagoon gains excess nutrients via runoff, the algae can bloom more frequently and severely, leading to more toxins into the food chain.
In collaboration with professors Toufiq Reza and Ralph Turingan, Fire has submitted a federal grant proposal to study a way to remove saxitoxins and the algae that produces it from the water. The research would involve harvesting algae during a bloom, converting it into a solid material, and re-introducing that material into the water as a way to knock back the algae.