Algae bloom killing marine mammals in California could ‘absolutely’ happen in La Jolla, scientist says

Sea lions hang out on Boomer Beach in La Jolla.
Sea lions hang out on Boomer Beach in La Jolla.
(Robyn Davidoff)

Sea lions sickened by the algae also have bitten beach-goers in Southern California recently.


A toxic algae bloom like the one believed to be behind the deaths of hundreds of California sea lions and about 60 dolphins in June in Ventura and Santa Barbara counties could “absolutely” happen in La Jolla, a local expert says.

The danger can spread to humans as well. Sea lions sickened by the algae bit and injured at least two people recently at beaches in Orange County, and the Channel Islands Marine and Wildlife Institute, which serves Santa Barbara and Ventura counties, recorded five recent incidents of animals biting beach-goers both in the water and on the beach.

Sea lions experiencing seizures or sickness due to an ongoing bloom of toxic algae have bitten or behaved aggressively toward beachgoers across Southern California, according to experts.

June 29, 2023

NOAA Fisheries reported that the Channel Islands institute fielded more than 1,000 reports of sick and dead marine mammals between June 8 and 14 that were thought to have been exposed to the algae bloom.

“The rapid growth of the algae pseudo-nitzschia causes the production of a neurotoxin called domoic acid,” according to the National Oceanic and Atmospheric Administration. “Responders believe domoic acid is behind the deaths, given the neurological symptoms exhibited by the animals. They have collected tissue samples for testing to confirm.”

Dr. Alissa Deming of the Pacific Marine Mammal Center in Laguna Beach told the Los Angeles Times that sickened sea lions may experience seizures, disorientation and hyper-reactivity and may bite as a result.

William Gerwick, a professor at La Jolla’s Scripps Institution of Oceanography who contributed to the recently published book “Oceans and Human Health: Opportunities and Impacts,” said harmful algae blooms that produce domoic acid occur when the right combination of ocean conditions and “a bit of randomness” cause micro-algae to accumulate, or “bloom.”

“They bloom ... when the temperature goes up, nutrient availability goes up and currents create the right conditions,” Gerwick said. “Sometimes currents mix the water and cause the algae to disperse, and other times it allows them to reach high density. But there is a bit of randomness in that sometimes the conditions are perfect and they don’t bloom and other times the conditions are less than perfect and they bloom.”

Gerwick said such blooms are typical in Southern California and “have been recorded for a long time.”

“If a bloom develops, there is not a whole lot we can do to terminate it. We have to learn how to live with them.”

— William Gerwick, professor at Scripps Institution of Oceanography

Though harmless blooms have resulted in the bioluminescence of 2020 and 2021, they can cause red tides like the one La Jolla saw in 2020 that can be toxic to some marine animals.

“The toxicity can happen because when you have that many cells in the water, they can use oxygen and deplete the water of oxygen and can cause fish to die. Sub-species can also produce toxins that can be harmful to fish,” Gerwick said.

With algae blooms like the latest one, the toxic domoic acid is transferred to fish in the area, which are then eaten by sea lions.

“The toxins work their way through the food web,” Gerwick said. “There are different toxins produced by different species [of algae] that can affect neurotransmission and can cause aberrations in behavior.”

In this case, the animals have been stranding themselves on land or experiencing disorientation and the inability to move, leading to their deaths.

Though the effects have been north of San Diego, a similar event can happen in La Jolla, Gerwick said.

“We’re at the whim of the phenomena of the sea; we can’t mitigate it,” he said. “If a bloom develops, there is not a whole lot we can do to terminate it. We have to learn how to live with them.”

Recording the turtle’s measurements is important to see if she’s outgrowing her exhibit space.

June 23, 2023

Though La Jolla has fewer sea lions than colonies up the coast, many go on land to rest at places such as Point La Jolla, Boomer Beach and La Jolla Cove. Their presence has caused controversy over the years, especially in light of the city of San Diego’s closure of Point La Jolla during sea lion pupping season, which it plans to make year-round. Supporters of the closure say it is needed to keep people and sea lions apart for the safety of both. ◆