Crab fishermen feel the pinch with toxic algae bloom
Local wildlife officials have delayed this year’s recreational and commercial crab fishing season indefinitely, due to a warm-water-induced toxic algae bloom that’s poisoning the food chain. The news has left a lot of us, well, crabbier than normal, and wondering just how dangerous the bloom could really be.
“This year’s bloom was incredibly toxic and is the largest we’ve ever seen on the West Coast,” says Raphael M. Kudela, Ph.D., a phytoplankton expert and professor of Ocean Sciences UCSC. The algae create a toxin called domoic acid. “Basically the toxin works its way into the food web. Once it goes from the algae to the animals that consume them, it spreads rapidly.”
As filter feeders, Dungeness crab and other crustaceans are especially susceptible to the toxin, which bioaccumulates in their flesh. If it’s ingested by humans, domoic acid causes amnesic shellfish poisoning. “In higher vertebrates, a small dose is like food poisoning,” says Kudela. “At higher doses it crosses the blood-brain barrier and puts holes in the brain which can cause death.” Short of death, larger amounts can also cause disorientation and general neurological dysfunction. Even worse, there is no currently known antidote for domoic acid and it is extremely resistant to heat, so cooking the tainted crab will not make it any safer to eat.
A favorite local delicacy, crabs up and down our coast will continue to be tested for the toxin, and no one knows for sure when, or even if, the critters will be safe to eat this year. The season’s cancellation could have a major impact on not only the price and availability of crab in supermarkets and restaurants, but also on California crab fishermen, who rely on the approximately $60 million industry to keep them afloat, so to speak, during the winter months.
“This is the first time crab season has been closed due to domoic acid in California, so this is uncharted territory,” says Kudela. “If [toxicity] is due to the bloom, then the season could re-open in a month or two. But we know that the bloom could settle into the bottom and sediment, which is where the crabs feed, exposing them to an ongoing toxic pool.”
A bit of good news is that the ocean water itself remains uncontaminated. “As long as you follow the warnings, you’ll be safe. It’s not a contact issue, it poses no risk to surfers or swimmers,” says Kudela. Additionally, a strong El Niño this winter could neutralize the toxic algae bloom. “The El Niño will break it up. But, high rains cause large runoffs that bring many nutrients back into the ocean, which can itself create another large bloom.” It’s clearly a complicated issue with a murky outlook.
As it turns out, domoic acid has quite the rap sheet, and this year is not the first time it has tripped out the local ecosystem. In May and June of 1998, also an El Niño year with a large algae bloom, more than 400 local sea lions died and countless others were sick and poisoned by the toxin.
Domoic acid is also the likely culprit for another famous incident in local lore. On the early morning of Aug. 18, 1961, Capitola residents awoke to find a scene straight out of a horror movie that would later actually inspire one. Hundreds upon hundreds of migratory seabirds called sooty shearwaters were flying straight into buildings, cars, and people. Most of the birds died, but the ones that managed to survive were stumbling amongst the corpses of their comrades in the streets, seemingly disoriented and vomiting partially digested anchovies. This incident inspired Scott’s Valley resident Alfred Hitchcock to direct a famous 1963 horror film called The Birds, in which hundreds of birds attack a coastal California town.
Although initially a mystery, scientists later looked back at zooplankton, tiny floating marine animals, taken from Monterey Bay in 1961. Sure enough, most of the samples tested had domoic acid-producing algae in their guts, suggesting that the entire ecosystem at the time may have been poisoned. Apparently the crazed sooty shearwaters had feasted on a school of toxic anchovies, got sick and disoriented, and “attacked” the town of Capitola.
TAINTED CATCH Unsafe levels of the toxin domoic acid have been found in local crab, delaying crab fishing season indefinitely.