An extraordinarily large mass of toxic algae off the West Coast of the United States has prompted state agencies to shut down crab and clam fisheries in at least two states, and is posing risks to recreational fishing and marine life.
The so-called "red tide" bloom doesn't pose a health risk to people who eat commercially caught fish, according to experts. But the Washington Department of Fish and Wildlife has shut down all crab fishing in its waters, and authorities in Oregon have closed that state's coast to digging for clams.
Such halts will likely have no significant impact on commercial fisherman, who have moved on to harvesting other species. But crabs or clams caught and eaten by recreational fishers pose a significant health risk, possibly causing seizures or even death.
Blooms are common, but some of the data suggest the current one may be the biggest in at least a decade. Scientists are concerned about domoic acid, a compound produced by a species of algae that can cause a variety of harmful symptoms.
The bloom is "geographically quite extensive," said Vera Trainer, an oceanographer with the Marine Biotoxins Program at the National Oceanic and Atmospheric Administration's Northwest Fisheries Center in Seattle. "We have reports of high domoic acid levels from Monterey Bay, California, all the way up to Homer, Alaska."
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The NOAA announced this week that it will be sending scientists out to study the bloom, to determine its size and take samples for further research. Samples taken off the coast of Monterey Bay and the Central Oregon coast revealed the highest concentration of domoic acid ever recorded, according to a press release issued by NOAA.
Scientists such as Trainer say the bloom may be connected to a large patch of warm water in the Pacific, but they cannot yet say for sure.
The phenomenon is sometimes called "red tide" since algae can give the water a rust-like color. But the term "red tide" is actually a misnomer, Trainer said. The blooms are not always red, and they are not associated with tides.
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That said, they are dangerous to marine animals and humans who are exposed to high levels of domoic acid.
It has been responsible for seizures and deaths in California sea lion populations that eat contaminated fish. The number of sea lions affected by "sea lion sickness" has increased dramatically in recent years, according to NOAA.
Domoic acid is produced by a particular species of algae—called Pseudo-nitzschia—that is just one of the many species of algae making up the bloom.