Toxic Algae Blooms Killing Scores of Central Coast Marine Mammals

More than 150 Dolphins and Sea Lions Found Dead in Santa Barbara County Since February

Since March 1, CICRU has responded to 50 dead dolphins along the Central Coast due to domoic acid poisoning. | Credit: CICRU

Waves of poisoned animals are washing up across the Central Coast, marking the fourth year in a row that toxic algae blooms have led to a mass die-off of marine mammals.

Domoic acid, a potent neurotoxin produced by algae, has been killing sea lions and dolphins along California’s coastline for years. However, large toxic algal blooms are becoming more frequent, causing recent spikes in domoic acid deaths.

Reports of animals suffering from domoic acid poisoning on Santa Barbara County beaches are flooding local marine wildlife organizations — including the Channel Islands Marine Wildlife Institute (CIMWI) and the Channel Islands Cetacean Research Unit (CICRU). These animals, if alive, exhibit symptoms such as disorientation, foaming at the mouth, and seizures.

One “feral” sea lion even attacked a surfer off Ventura County on Friday, according to the L.A. Times. The surfer, RJ LaMendola, said the animal bit him and dragged him off his surfboard. When he later contacted CIMWI, they told him it was likely due to domoic acid poisoning.

“Domoic acid harmful algal bloom events are now occurring annually,” said Ruth Dover, managing director of CIMWI. “The neurotoxin is crippling and killing sea lions and dolphins. It is heartbreaking for beachgoers to witness.”

While sea lions are able to survive the toxin about 50 percent of the time if treated early enough, dolphins usually don’t make it. It’s a harrowing sight, explained Michelle Berman Kowalewski, founder and director of CICRU.

She said common dolphins are accustomed to deeper waters, so they panic when they come close to shore, being too weak from the toxin to fight the current.

“If they’re too sick to do anything, then they end up on the beach, and it’s their worst case scenario — they know they don’t belong there,” she said. Dolphins overheat on the sand, too, since their bodies are insulated to withstand colder ocean temperatures.

“Really, they start to degrade,” Kowalewski continued. “They almost start to cook on the inside because they can’t dump their heat enough to cool them off. They’re already sick, they’re panicked, they’re overheating, and there’s just very little chance for survival at that stage.”

Kowalewski said they see domoic acid poisoning every year, but concentrations and mortality rates differ. The main vector of the toxin for dolphins is anchovies — the fish ingest the harmful toxin and pass it on to the dolphins that eat them for lunch.

She said the average number of dolphins they respond to in a year is 30 to 40. So far, during this domoic acid season, starting in February, the group has responded to 50 dead dolphins. CIMWI, too, has seen an unusually high number of dolphins, responding to 10 this month.

In 2023, which saw the worst domoic acid bloom in California’s recorded history, CICRU responded to 120 dead dolphins in one month (up to 20 a day).

This year isn’t as bad for the Central Coast, but it’s not looking good. The current bloom has killed more than 200 animals in Santa Barbara County since February. CIMWI is getting at least 150 reports of marine mammals in distress each day, and the death rate is more than 90 percent.

“Many animals are dying despite care,” CIMWI posted on their Instagram on Friday, along with a video of a female sea lion that had to be humanely euthanized.

“Domoic acid cases are not easy for our rescue rehabilitation team members. They take a toll on our hearts, emotions, and physical well-being.”

However, since February, CIMWI has successfully rehabilitated 10 animals suffering from domoic acid toxicity, including a seal pup from Hendry’s Beach, which was taken to rehab for treatment last week.

Historically, these large domoic acid blooms only occurred every four to seven years. But this is the fourth instance in Santa Barbara in four years. And while February blooms have happened in the past, they are uncommon (they usually begin in April or May).

The blooms usually last from four to eight weeks.

Alyson Santoro, a marine microbiologist at UC Santa Barbara, is involved in a lab that coordinates sampling of harmful algal blooms at Stearn’s Wharf for the Southern California Coastal Ocean Observing System.

Domoic acid is a naturally occurring consequence of changing water temperatures, but Santoro said the “why” behind the rise in big-blooms in recent years is hard to pin down.

With science experiments, it helps to have a control, or an unchanging sample that can be used for comparison.

“But we don’t have that with the ocean, and we’re changing so many things at the same time,”
Santoro said. “It’s hard to nail down any one thing.”

Rising ocean temperatures, alterations in ocean currents and upwelling cycles, and ocean acidification due to climate change and nitrate runoff, however, are likely suspects. Organic runoff from recent storms, and, potentially, phosphorus-based fire retardants from the Los Angeles wildfires, could also be feeding the beastly blooms this year.

In other words: Humans are definitely making it worse.

“If the ocean as a whole is warming up, we might expect these blooms to be more prevalent,” Santoro said. “I also can’t rule out the effects on the animals that are getting sick. Are they more susceptible because they’re dealing with other stressors? It’s hard to know.”

Researchers are monitoring the blooms, she said. However, coastal monitoring is largely funded by the National Oceanic and Atmospheric Association, which is facing major cuts from the Trump administration.

“We’re constantly struggling to keep the monitoring program alive,” she said. “The only way you can really understand these things is sustained observations over a lot of years, and that’s not a very sexy thing. People want a solution now, and so these programs are always on the chopping block.”

If you come across a sea lion exhibiting signs of domoic acid poisoning, do not touch it; instead, observe it from a distance of at least 50 feet, determine its location, and call the CIMWI Rescue Hotline at (805) 567-1505. Provide your name, phone number, specific information about the animal, and its location. Dolphins, which are especially vulnerable to stress and should be given a wide berth, can be reported to CIMWI, or CICRU’s stranding hotline at (805) 500-6220.