Toxic algae bloom causes surge in sick sea lions along San Diego coast
Mar 21, 2025
SAN DIEGO (FOX 5/KUSI) — As a harmful algae bloom continues to spread along California’s coastline, more animals are falling ill in San Diego.
Weekly monitoring stations operated by Scripps and NOAA have recorded significant concentrations of the diatom Pseudo-nitzschia (specifically the P-n
seriata group) at Stearns Wharf in Santa Barbara (66,880 cells/Liter as of last week) and Santa Monica Pier, where levels were extremely high at 1,528,442 cells/L, according to a spokesperson for Scripps Institution of Oceanography. They also noted that anything above 10,000 c/L is considered concerning. Pseudo-nitzschia has been detected at Scripps Pier, but not at the elevated concentrations observed at sites further north.
Pseudo-nitzschia is a type of plankton that can produce a neurotoxin known as domoic acid. When these plankton are consumed, domoic acid can accumulate in tissues of shellfish and fish. When consumed by larger mammals, like sea lions or even humans, domoic acid can cause memory loss, seizures, and even death, although the risk to humans is low.
Dr. Clarissa Anderson, a biological oceanographer and the director of Southern California Coastal Ocean Observing System at Scripps, said the bloom likely started offshore, so researchers didn't see many domoic acid-producing diatoms in any of their coastal phytoplankton monitoring stations. In the last 2-3 weeks, however, they have recorded a substantial increase, likely because the bloom is finally making its way to the coast.
“I saw a sick sea lion down at the beach around 9th Street and it didn’t look very good and then on the way back I saw another one by 18th," said Del Mar resident, Maris Laipenieks.
A few times this week he’s spotted sea lions on the beach and he's not alone.
"We’re getting hundreds of calls. Concerned citizens, lifeguards, sheriff’s department," said Jeni Smith, Rescue Program Curator, SeaWorld San Diego.
Smith said she and her team are seeing sea lions with symptoms from domoic acid poisoning.
“You could see these animals on the coastline exhibiting behaviors like having seizures, looking dazed, stargazing, lethargic. They can be abnormally aggressive. They can also be in areas that are not their natural habitat," Smith said.
SeaWorld San Diego has so far treated 15 sea lions for suspected domoic acid poisoning and has seen one death.
"Our veterinarians will take a look at them and some of the animals that are having seizures they may prescribe some anti-seizure medication," Smith said.
Lifeguard Sgt. Scott Henson said it's not unusual to run into sea lions on the beach from time to time, but he offered advice for anyone that does.
“Just stay away and give us a call. Give SeaWorld a call. Let us know that there’s an animal on the beach and we can come investigate and see if there’s further action that needs to be taken," Henson said.
SeaWorld recommends people keep the distance of a school bus, or about 50 feet, away from a sea lion if you see one. If you have seen an animal in distress or in need of help, please contact their rescue team.
Phone: 1-800-541-SEAL (7325)
Email: SWC.Rescue@seaworld.com
Helpful information to give the Rescue Team:
Date animal was last seen
Time animal was last seen
Location (name of beach, address, landmark etc.)
Size of the animal compared to a dog breed
Is the animal thin? Can you see its ribs, hips or spine?
Is the animal entangled in fishing gear?
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