Environment & Science

Record harmful algae bloom appears to be declining

Screenshot of a map of the West Coast in the summer shows the extent of harmful algal bloom.
Screenshot of a map of the West Coast in the summer shows the extent of harmful algal bloom.
NOAA Climate.gov / NOAA View

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A record-breaking harmful algal bloom that for months stretched from Santa Barbara into Alaska and dumped deadly neurotoxin into the ocean appears to be in decline, according to a government researcher.

“We’re now into a transition time. Water temperatures are colder; we’re going toward winter, and we’re not seeing as many algae showing up at our beaches,” said Vera Trainer, a research oceanographer with NOAA’s Northwest Fisheries Science Center in Seattle. “Very low numbers or none are being seen at our beaches.”

In addition to the absence of appreciable levels of the algae in beach monitoring, Trainer said satellite imaging indicates an overall reduction of off-shore chlorophyll, of which the toxin-producing pseudo-nitzschia species of algae contributed a large part.

The neurotoxin domoic acid collects in the flesh and viscera of several species of seafood. Some of the more severe human reactions to ingesting the tainted seafood include permanent short-term memory loss, coma and death.

The California Department of Public Health still advises residents not to eat rock and dungeness crabs caught in waters from Santa Barbara County to the state’s northern border. It advises against eating recreationally harvested mussels and clams from Humboldt and Del Norte counties.

The dungeness crab season in California remains delayed indefinitely.

The decline of the algal bloom would eventually lead to decreases in the amount of domoic acid in the local marine ecosystem, but Trainer said the toxin can remain in the environment and food chain for months.

“There is toxin in the food chain. Cells sink into the sediments, and they can affect benthic creatures like crabs and so-forth even after a surface bloom is completely gone,” Trainer said.

Some areas of the state are seeing a reduction in the number of test crabs that turn up with too-high levels of domoic acid, according to the Department of Public Health’s most recent summary.

Trainer said that though the bloom appears to have disappeared, its absence might be a brief respite, as El Niño is expected to deliver warmer water to the region. An unusually warm patch of water off the West Coast is believed to have contributed to the algal bloom’s formation and persistence. 

“El Niño years have shown that there are larger domoic acid events, and I think this warmer water that’s anticipated due to the El Niño is sort of our early warning of potential problems again,” Trainer said.

She said researchers will perform monitoring cruises in January to keep tabs on a possible resurgence of the bloom.

She said that, despite the need for caution, seafood that is available for purchase is safe to eat.

“Seafood is tested and is safe, so people, if they have crabs in their freezer, or they’re buying frozen crab, they should be confident that what they’re getting is safe to eat,” Trainer said.