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Biological Chemistry

Neurotoxin Scuttles Crab Season

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

by Elizabeth K. Wilson
November 12, 2015 | A version of this story appeared in Volume 93, Issue 45

Credit: California Department of Public Health
A lab worker tests Dungeness crabs for domoic acid (structure shown above).
A lab worker handles a crab.
Credit: California Department of Public Health
A lab worker tests Dungeness crabs for domoic acid (structure shown above).

Officials have postponed the West Coast’s Dungeness crab season indefinitely because of 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 Niño-induced warm ocean temperatures off the West Coast have nurtured a massive bloom.

California monitors toxins in seafood year-round and recently detected high levels of domoic acid in Dungeness and rock crabs.

On Nov. 6, the California Department of Fish & Wildlife called off the crab season which was slated to start Nov. 15, from the Oregon border to Santa Barbara.

“Crab is an important part of California’s culture and economy, and I did not make this decision lightly,” Charlton Bonham, 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 can have devastating effects, including seizures, permanent short-term memory loss, coma, and even death. It is odorless and colorless, and it can’t be inactivated by cooking or freezing.

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 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.



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