A toxic algae bloom in coastal waters has killed dozens of marine animals, including whales and dolphins, between San Diego and San Luis Obispo, and the area has been labeled an extreme danger zone by health and environmental groups.
A neurotoxin called domoic acid, produced by a type of plankton called pseudo-nitzschia, has been detected in an algae bloom off the coast for the fourth year in a row, and John Warner, chief executive of the Marine Mammal Care Center in Los Angeles, told KABC-TV that this one is “the worst we’ve ever seen here in Southern California on many different fronts.”
The number of dolphin strandings, he said, is “unprecedented.”
More than 50 dead and dying dolphins have been found along the Los Angeles County coast just this week, and 16 were discovered in San Diego County on April 20.
In 2023, more than 1,000 sea lions and over 100 dolphins died from a domoic acid outbreak, scientists said.
Algae blooms are a natural phenomenon and usually occur in spring and summer. The algae can flourish during upwellings, when winds blow from north to south along the coast, pushing water offshore and bringing nutrient-rich deep water to the surface.
“In any given year, when upwelling happens, any number of plankton can respond. Pseudo-nitzschia is a type of plankton that responds readily to upwelling,” said Clarissa Anderson, a biological oceanographer at UC San Diego’s Scripps Institution of Oceanography in La Jolla.
Scientists say this year’s outbreak emerged earlier than some previous algae blooms.
In 2015, the largest toxic algae bloom ever recorded caused massive die-offs from Santa Barbara all the way to Alaska, killing thousands of marine mammals, including sea lions and fin whales.
The toxic algae is eaten by small fish, which are then eaten by marine mammals and birds, leading to potentially deadly overdoses. The toxin can damage the brains and hearts of larger mammals, sometimes causing them to behave aggressively.
Sea lions and birds can be saved, but it is almost always fatal for dolphins, scientists say.
Many of the sick sea lions being rescued along the coastline are pregnant. It is thought they are more susceptible to the toxin because they tend to eat more food.
Some of the animals suffer seizures and tremors, while others seem dazed. When the animals die, necropsies are done to learn more about what killed them.
Domoic acid also can sicken humans who consume shellfish and fish. Last month, regulators advised the public not to consume sport-harvested bivalve shellfish — including mussels, clams and scallops — gathered from waters off Los Angeles and Santa Barbara counties after dangerous levels of domoic acid were detected, according to the California Department of Public Health.
The warning did not apply to commercially sold mussels, clams, scallops or oysters from approved sources. Public health officials said shellfish sold by certified harvesters and dealers are subject to frequent mandatory testing to monitor for toxins.
Soon after the 2023 toxic algae bloom, scientists at Scripps Oceanography started studying the process of how such masses of algae develop so researchers, industries, officials and communities can be better prepared for future outbreaks.
As part of a study funded by the National Oceanic and Atmospheric istration, Bradley Moore, a Scripps Oceanography professor of marine biology, marine chemistry and geochemistry, worked to determine how domoic acid is produced with the hope of creating a predictive model.
Last September, a team of researchers from SIO, La Jolla’s J. Craig Venter Institute and other organizations published a study on predicting harmful algae blooms that contain high levels of domoic acid by tracking a single gene that serves like a canary in a coal mine — an early detector of danger.
The study provided new insights into the mechanisms that drive harmful blooms and offered potential ways to forecast and mitigate their effects, the researchers said.
“One of the really big predictive difficulties for us is even if we are measuring domoic acid in the water, we cannot always say which animals are going to be the ones impacted,” Anderson said. “It just happens to be in the last four years it has been hitting the California sea lion population much harder than other populations of animals.”
Unlike the previous three years, this year’s event also seems to be impacting sea birds, Anderson said.
Birds might be affected more because the anchovies and other fish they are feeding on are “hanging out more at the surface,” she said.
Officials advise beach-goers to stay away from any ailing animals they find on the beach and call SeaWorld San Diego’s rescue hotline at 800-541-7325 or send an email to [email protected].
— San Diego Union-Tribune staff writer Karen Kucher and La Jolla Light staff writer Ashley Mackin-Solomon contributed to this report. ♦
