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Neurotoxin Scuttles Crab Season

Enviroment: Domoic acid contamination due to algal bloom caused by El Nino-warmed waters in Pacific

by Lisa Wilson
November 10, 2015

Credit: California Department of Public Health
Lab workers test Dungeness crabs for domoic acid.
A scientist handling a crab.
Credit: California Department of Public Health
Lab workers test Dungeness crabs for domoic acid.

Officials have postponed the West Coast’s Dungeness crab season indefinitely, due to a massive contamination of the toxin domoic acid. The drastic event not only will disappoint fans of the delicacy, but also could cost the commercial crab fishing industry $60 million.

The potent neurotoxin, discovered only in recent decades, is produced by the marine alga Pseudo-nitzschia, which is eaten by shellfish and some small fish. Domoic acid becomes more concentrated, and more dangerous, in organisms further up the food chain, as larger animals eat the contaminated smaller creatures.

Although the algae bloom seasonally, this year’s El-Nino-induced warm ocean temperatures off the West Coast have nurtured a massive bloom.

California monitors toxins in seafood year around, and recently detected high levels of domoic acid in Dungeness and rock crabs. Safe limits are set at 20 ppm; but one yellow rock crab showed a level of 190 ppm, according to the California Department of Fish and Wildlife.

On Nov. 6, the CDFW called off the crab season which was slated to start Nov. 15, from the Oregon border to southern Santa Barbara County.

“Crab is an important part of California’s culture and economy, and I did not make this decision lightly,” Chuck Bonham, the CDFW’s director, said in a Nov. 6 statement. “But doing everything we can to limit the risk to public health has to take precedence.”

In small quantities, domoic acid may cause nausea vomiting, diarrhea, and dizziness. But in higher concentrations, domoic acid’s effects are devastating, and include seizures, permanent short term memory loss, coma, and even death. It is odorless and colorless, and can’t be inactivated by cooking or freezing.

Scientists first isolated domoic acid from marine algae in 1959. But it wasn’t until 1987 that domoic acid was identified as a culprit in shellfish poisoning. In a case that year, over 250 people in Prince Edward Island were sickened, and three killed, by contaminated mussels.

In 1961, in the California town of Capitola, hundreds of disoriented birds crashed into buildings and to the ground. Scientists now believe the cause was domoic acid poisoning. The event inspired Alfred Hitchcock to make his horror movie “The Birds.”

Domoic acid wreaks havoc on an animal’s nervous system by mimicking glutamate, and activating a subset of glutamate receptors, explains Justin Brower, a forensic toxicologist with North Carolina’s office of the chief medical examiner and who also pens the blog “Nature’s Poisons.”

Cells in the brain and nervous system are loaded with glutamate receptors. By binding these receptors, the toxin overexcites the cells, creating a massive influx of calcium into the cells, which kills them.

Still unexplained is why the algae produce the poison, Brower says. It’s not clear what the algae are defending themselves against when they synthesize domoic acid. Some researchers have suggested that domoic acid binds iron and copper, scavenging the metals as nutrients for the algae.

Meanwhile, the California crustaceans will remain off limits until domoic acid drops to safe levels. And up in Oregon, where the Dungeness crab season doesn’t start until Dec. 1, state scientists will be rigorously testing the crabs in their waters.


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