Environment & Science

Orange County's massive algae bloom is killing pregnant sea lions

File: Sea lions sunning themselves on channel marker Buoy #9 in San Diego as the USS Decatur passes by.
File: Sea lions sunning themselves on channel marker Buoy #9 in San Diego as the USS Decatur passes by.
KPCC/John Ismay

At least seven pregnant sea lions rescued off the coast of Orange County have died this week after a neurotoxin worked its way up the food chain.

Large algae blooms — fed by local fertilizer runoff — have recently appeared along the coast, Pacific Marine Mammal Center spokesperson Krysta Higuchi told KPCC. The blooms are the worst the region has seen since 2002, she said.

The algae contains a lethal neurotoxin — domoic acid — which causes a range of symptoms including lethargic behavior, seizures and hypersensitivity, Higuchi said. When consumed in large amounts, domoic acid can kill large numbers of brain cells.

Sea lions themselves don’t eat the algae, she said. But sardines, which are sea lions' favorite food, do.

As the algae blooms grow, the number of sardines that eat the algae also grows, Higuchi said. Those sardines eventually end up in sea lion stomachs. The presence of domoic acid in the ecosystem is mainly killing expecting sea lion mothers, who are eating for two.

“That large amount is causing the adult females to physically show these clinical symptoms,” Higuchi said. One of those symptoms you can spot: “At the beach, you can see the animals bobbing their heads up and down.”

In the past few weeks, the Pacific Marine Mammal Center has rescued 13 sea lions total, Higuchi said. Of the 13, seven have died. 

Higuchi said the disease is transferrable — even to humans. If you spot lethargic or strangely-acting animals near the beach, call the Pacific Marine Mammal Center.