Red Tides and Domoic Acid Toxicity

Domoic acid is produced during certain harmful algal bloom events by a type of algae called Pseudo-nitzschia australis. This neurotoxin accumulates in small fish, like sardines and anchovies, which are then eaten by marine mammals like sea lions in large quantities.

Domoic acid attacks the brain and the heart causing seizures and heart failure. If left untreated, it usually causes permanent brain damage. The toxin will naturally flush from an animal’s system over time, but sea lions repeatedly exposed to the toxin will suffer longer-lasting and more serious effects.

If these animals come into our care before significant damage occurs, we are often able to help flush the toxin from their systems by giving them fluids. We also provide them with a fish source that is free of domoic acid. To control any seizures, our veterinarians give these patients anti-seizure medications that are also used in humans.

The Center’s veterinary team is investigating new therapies to reduce the amount of inflammation and damage the brain experiences while the animal is recovering.

Although most of the patients we treat for domoic acid toxicity are California sea lions, other marine mammals are susceptible to its effects as well. Domoic acid has been reported in a number of other seal and sea lion species, as well as cetaceans such as blue and humpback whales. In 2014, researchers at the Center were the first to detect domoic acid in Guadalupe fur seals, a threatened species.

Domoic acid can also affect humans who eat contaminated crab, shellfish and fish, causing a life-threatening condition known as amnesiac shellfish poisoning. Because sea lions are often the first to be affected by a toxic algal bloom, the Center provides data to the public health department when domoic acid poisonings are detected. This helps public health officials determine whether seafood warnings should be issued and allows scientists to better understand local ecosystem health.

Through testing and closing dangerous fisheries, we’ve gotten better at preventing humans from getting sick from domoic acid, but these efforts don’t work for marine mammals. And there’s still a lot we don’t know about what causes massive algal blooms like the ones we’ve seen in recent years—or even why the Pseudo-nitzschia algae produces the toxin.

One thing we do know is that the algae thrives in unusually warm waters off the West Coast—ocean conditions that have become more frequent in recent years as we see the impacts of climate change increase. Center scientists collaborate with other oceanographers and climate scientists to investigate the links with climate change and other environmental factors.