Consumers should not eat rock crabs from Half Moon Bay or rock crabs, mussels, oysters, clams and scallops from Monterey Bay, according to the California Department of Public Health. High levels of domoic acid, a neurotoxin, have been found in the organisms, making them unsafe for human consumption.
Domoic acid is a naturally occurring byproduct of algal blooms and can get into the tissue of the animals that we eat. They can particularly accumulate in crabs and shellfish because they filter water for food.
Besides the public health implications, these events can also have economic implications as fishermen can't catch and sell seafood with high levels of domoic acid.
"At least somewhere in California, you're going to have a domoic acid problem," said Clarissa Anderson, a phytoplankton expert at University of California Santa Cruz. "It'll come, and it will go throughout the spring and parts of summer."
The blooms have become yearly events linked with warming waters off of the western U.S. They've gotten particularly bad in recent years. Last year saw the worst algal bloom on record. It stretched from Santa Barbara to Alaska and lasted five months. Such algae blooms usually last no longer than one month.
Last year's record-breaking event was linked to the "the Blob," the gigantic pool of warm water that lingered off of the coast of the western coast of the U.S. for more than a year. The Blob has mostly broken up, but pockets of warmer water remain. Last winter's El Niño also contributed to warmer ocean temperatures.
Similar to last year, this year's toxic algae bloom started in Northern California.
It's not certain that it'll move down to southern waters, Anderson said, but it's a possibility that we'll see one pop up in Santa Barbara as well. That could have impact on fisheries there.
"Considering the fact that the El Niño has a large effect on Southern California, increasing water temperatures down there, there is a likelihood we can start to see more blooms... south of [the] Santa Barbara channel," she said.
"It has been seeming like the new normal for a long time. We've been watching levels of domoic acid march up steadily each year for the most part of the last ten years in California," Anderson said. "And given the fact that we had the biggest event on record last year, and we're starting to see high levels again, it may just be we are in the normal now."
Shellfish and crabs are frequently tested for domoic acid, so consumers should not worry about seafood in restaurants and markets, Anderson said.