Toxic Algal Bloom Affecting California Sea Lions and Dolphins

Upwelling of nutrient-laden ocean water is fueling the algal bloom which produces domoic acid, which can poison marine mammals.

Strong upwelling of nutrient-laden water from the deep ocean is driving a bloom of harmful algae along the Southern California coast. It produces a toxin that can poison sea lions and other marine mammals. The neurotoxin, domoic acid, does not appear to harm fish or pose a risk to swimmers. It can accumulate in shellfish such as mussels, oysters, and Dungeness crabs.

The deep waters are rich in nutrients, so the wind-driven upwelling subsequently kicked in and fueled growth of the algae. In particular, it encouraged growth of the toxin-producing diatom Pseudo-nitzschia spp, which thrives in such conditions. Satellite maps of sea surface temperature anomalies display the upwelled water as blue streaks off the California Coast that are colder than usual this time of year. The same nutrients also nourish California’s rich coastal ecosystem, including many fish and shellfish species that support commercial and recreational fisheries.

Domoic acid not only contaminates shellfish, but can poison marine mammals such as California sea lions that consume contaminated fish. The toxin accumulates in their bodies—causing seizures, other unpredictable behavior, brain damage, and death. Beachgoers and their pets should stay a safe distance from affected animals on shore and report them to the West Coast Marine Mammal Stranding Network at (866) 767-6114.

Another Outbreak Begins

The phone began ringing off the hook in late July 2024 for Channel Islands Marine & Wildlife Institute.

read more at fisheries.noaa.gov.