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Domoic Acid Presents a Puzzle for Marine Mammal Experts

The central California coast is experiencing harmful algae blooms that produce the toxin domoic acid, a threat to sea lions and other marine life.

September 10, 2013

It's always great when a story has a happy ending, and such was the case with Perfume, a California sea lion who was one of a number of sea lions being treated for domoic acid toxicity at The Marine Mammal Center over the past few weeks. Perfume was released back to the ocean on Saturday, September 7, at Scotty Creek Beach near Bodega Bay. A crowd of onlookers and well wishers watched as she joyously made her way back home.

Perfume returns home to the ocean, at Scotty Creek Beach in Sonoma County


September 5, 2013

Currently, The Marine Mammal Center has a large number of patients affected by domoic acid:  Marilou, Vuronica, Shia, Perfume, Lumi, Surfer, Jerika, Late Night, Bautista, and Whirley. Several others have been released following successful treatment, and two have died during treatment. These patients, all of them California sea lions, were rescued in the past few weeks along the San Luis Obispo and Santa Barbara County coast.

Perfume is a California sea lion who was rescued in San Luis Obispo County, suffering from domoic acid toxicity (acute)
© The Marine Mammal Center


What is domoic acid?
Domoic acid is a neurotoxin associated with algal blooms which can have serious effects on marine mammals and humans when it gets into the food chain. It was first discovered in the red algae known as "doumoi" in Japanese, hence the origin of the name, although this algae is not traditionally related to the toxicities that we see. Domoic acid is often referred to as “red tide,” although this is a misnomer, since the algae is often colorless, or has colors other than red. It is also not typically associated with the movement of the tides. Scientists prefer the term “harmful algal bloom.”

Domoic acid is produced by the algae Pseudo-nitzschia and accumulates in shellfish, sardines, and anchovies. These fish are then eaten by sea lions, otters, cetaceans, and humans, among others. If consumed in significant quantities, domoic acid can cause seizures and other central nervous problems. Exposure to the biotoxin affects the brain, causing those affected to become lethargic and disoriented. In humans, domoic acid toxicity manifests itself as “Amnesic Shellfish Poisoning,” which can cause short-term memory loss, brain damage, and even death in some cases.

Shia is another California sea lion patient suffering from domoic acid toxicity (acute)
© The Marine Mammal Center

Diagnosis of domoic acid toxicity is based on clinical signs and the known presence of Pseudo-nitzschia algae in the environment. The toxin itself is often long gone from the animals by the time they are examined. The Center’s researchers diagnosed the first case of domoic acid toxicosis in marine mammals in 1998, and have conducted extensive studies of the condition since then.


Why is this information so important? 
Marine mammals are like canaries in the coal mine -   they warn us of potentially serious environmental conditions in the ocean that can affect not only marine mammals, but humans and other animals as well.

This information also provides critical data for scientists conducting research on global health, and it contributes vital information to resource managers who monitor human activities that impact marine mammals in the area.  Equally important, it provides substantive evidence to help inspire protection and conservation of the ocean and those creatures that call it home.

What causes harmful algal blooms?
No one knows for sure, but Pseudo-nitzschia (and most microorganisms, for that matter) really like nitrogenous waste products/nitrates, and other fertilizers (being plants of a sort).  There are a lot of maps that show algal blooms forming at major river mouths or other waste outfall areas. Also, when the algal cells die or are consumed by animals, domoic acid is released.  Thus there is ample evidence that human activity can lead to worsening blooms of harmful algae and affect the health of our sea lion patients.

Phytoplankton monitoring carried out by the CDPH Marine Biotoxin Monitoring Program along the California coast
© California Department of Public Health

The California Department of Public Health website currently shows that Pseudo-nitzschia is common or abundant at every phytoplankton sampling site throughout the 600-mile rescue range covered by The Marine Mammal Center. However, high concentrations of Pseudo-nitzschia do not always mean high levels of domoic acid are present because phytoplankton don’t always produce the toxin.  So sometimes there are Pseudo-nitzschia blooms without any increase in sea lions stranding with domoic acid toxicity.

Since the first sea lions affected by these blooms began coming into The Marine Mammal Center about two weeks ago, we’ve noticed that the more recently rescued animals are showing more intense symptoms. The puzzle confronting our veterinarians is why the severity is increasing. They are trying to determine if it is caused by a longer exposure time, an increasing amount of toxin in the water, or simply that these particular animals had previously been exposed to the toxin and are now experiencing an acute poisoning, with the combination of previous exposures causing more severe illness.

Stay tuned as our research and veterinary science teams learn more.




Learn about Domoic Acid Toxicity

Learn about California sea lions

Read about Domoic acid in Pacific harbor seals (PDF file)


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