Toxic Algae Bloom Sickens Sea Lions, Overwhelms Rescuers in California
A toxic algae bloom off Southern California is overwhelming marine rescue teams as sea lions and dolphins suffer seizures and alarming behavior due to domoic acid poisoning.
Marine life experts at NOAA, SeaWorld, the Pacific Marine Life Center, and the Marine Mammal Center have been inundated with calls to rescue sea lions and dolphins experiencing seizures, aggression, and zombie-like behavior for the past five weeks. Some of the animals have attacked beachgoers, while others fell into a deep sleep before rescuers could arrive.
Researchers have traced the cause to a toxic algae bloom off the Southern California coast. The bloom produces a neurotoxin called domoic acid, which is poisoning local marine life.
Domoic acid is a naturally occurring toxin produced by algae during blooms. It accumulates in shellfish, sardines, and anchovies, causing amnesic shellfish poisoning in humans and domoic acid toxicosis in marine mammals. While shellfish can tolerate high levels of the toxin, animals that eat them often cannot.
Exposed sea lions may suffer seizures, heart attacks, or permanent brain damage. Other symptoms include disorientation, foaming at the mouth, vomiting, bulging eyes, and lethargy. Some display unusual behaviors such as head bobbing or stargazing. Approximately 50% to 60% of affected sea lions can recover with care, but dolphins are much more likely to die. Pregnant sea lions are also at risk of miscarriages.
This is not an isolated event.
According to Jeni Smith, head of the rescue unit at SeaWorld, cases of domoic acid toxicosis have increased in recent years. A similar outbreak in 2023 killed more than 1,000 sea lions, and this year may be worse. SeaWorld San Diego told the San Diego Union-Tribune it receives around 100 daily calls and emails from people reporting sick sea lions.
There is currently no cure for domoic acid poisoning. However, staff at the Marine Mammal Center have been able to flush the toxins from some animals, providing uncontaminated food and antiseizure medication with varying success.
While NOAA and other agencies have tracked domoic acid levels for years, cases have surged in the past five. The toxin is naturally present in the Pacific Ocean, but wind-driven upwelling appears to push it into the food chain. Cold water brings nutrient-rich sediment to the surface, feeding algae that smaller marine life—and subsequently birds, fish, and mammals—consume.
Fertilizers used in agriculture can also enter the water supply and feed algae blooms in the ocean, just as they do on land. Some researchers also believe wildfires could be a contributing factor. One thing scientists agree on is that the waters off California’s coast are becoming more toxic.
With funding and staffing changes at NOAA that include layoffs, the ability to respond to these types of toxicity events appropriately and effectively is concerning. As Southern California’s beaches grow increasingly toxic for marine life, the response from scientists, rescuers, and policymakers may determine whether these recurring events become seasonal catastrophes or containable incidents. For now, with no cure in sight and limited resources, the best defense remains vigilance — from both marine professionals and the public.
Whales in Long Beach and Huntington Beach both died of domoic acid toxicity
Researchers from the Pacific Marine Mammal Center and the Ocean Animal Response & Research Alliance confirmed that domoic acid toxicity led to the deaths of a juvenile humpback whale and a subadult minke whale found stranded along the Southern California coast. Necropsies revealed elevated levels of the neurotoxin in the whales’ stomach contents, feces, and urine.
Sources:
https://www.theguardian.com/us-news/2025/apr/12/california-sea-lions-domoic-acid-poisoning
https://www.latimes.com/california/story/2025-03-24/domoic-acid-sea-lions-dolphins-stranded-southern-california-coast
https://www.cnn.com/2025/04/06/climate/sea-lion-attacks-california/index.html
https://www.nationalgeographic.com/animals/article/poisoned-sea-lions
https://www.newsweek.com/donald-trump-noaa-job-cuts-california-sea-lion-deaths-2054360
https://www.fisheries.noaa.gov/feature-story/early-bloom-toxic-algae-southern-california-sickens-hundreds-sea-lions-and-dolphins
https://www.marinemammalcenter.org/science-conservation/research-library/domoic-acid-toxicosis#:~:text=What%20Is%20Domoic%20Acid?,sea%20lions%20in%20large%20quantities
https://www.sandiegouniontribune.com/2025/03/28/sea-lions-and-birds-sickened-as-toxic-algae-bloom-reaches-san-diego/
