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Red Tides and Domoic Acid Toxicity

In 1998, The Marine Mammal Center diagnosed the first case of domoic acid toxicosis in marine mammals. This condition is caused by harmful algal blooms, sometimes referred to as "red tides."

Domoic acid is produced by algae and accumulates in shellfish, sardines, and anchovies which are then eaten by sea lions, otters, cetaceans, and humans, among others. Exposure to the biotoxin affects the brain, causing the marine mammal to become lethargic, disoriented, and have seizures that sometimes result in death.


It is becoming increasingly clear that marine mammals are sentinels of potentially dangerous environmental changes in the ocean environment. Sick and stranded marine mammals warn us of changing ocean conditions in El Niño years, and poisoned marine mammals have protected human health by demonstrating the need for the screening of shellfish and other seafood for fatal biotoxins. The Center’s Veterinary Science program, under the direction of Dr. Shawn Johnson, Director of Veterinary Science at The Marine Mammal Center, lays the foundation for a deeper understanding of human behaviors that may affect marine mammal survival for the long term.

Research outcomes lead to a clear understanding of overall risk factors contributing to disease in marine mammals, and provide vital information to resource managers in the San Francisco Bay Area that can be used for informed mitigation of human activities impacting marine mammals. Additionally, our research program directly informs our education initiatives, which provide resources for the public to deepen its understanding of threats to the health of California’s coast and how to participate in protecting this environment.   

domoic acid, sea lion, The Marine Mammal Center
Left: normal California sea lion brain section. Right: a not so normal one that has been affected by domoic acid exposure; notice the shrunken hippocampus in the center of the brain section.
© The Marine Mammal Center


Investigation into Domoic Acid Toxicity

Often referred to as “Red Tide,” domoic acid (DA) is produced by a harmful algal bloom. DA can have devastating effects on marine mammals and humans that consume toxic prey species. Severe cases of seizures and other central nervous system problems, as well as hippocampal degeneration and amnesiac shellfish poisoning in humans, have been documented as caused by DA. Further study may reveal potential risk factors that cause DA poisoning outbreaks amongst California sea lions, and help point the way toward preventative measures.

Domoic acid is a neurotoxin produced by phytoplankton, specifically a microscopic diatom (Pseudonitzschia australis, pictured at the top of the page) in the ocean. This toxin causes seizures in higher vertebrates as it concentrates up the food chain by targeting the brain, specifically the hippocampus. California sea lions and other marine mammals become affected when they eat prey, like anchovies, that have been feeding during toxin-producing algal blooms. The effect of DA on sea lions depends on the amount they eat. Diagnosis depends on detection of the poison in serum, urine, or feces of affected animals, coupled with detection of P. australis in the environment and prey of affected sea lions. As DA is water-soluble and rapidly excreted in urine following ingestion, urine is the most useful fluid for diagnostic purposes. Because of the variable toxicity of algal blooms and the unpredictable timing of DA “outbreaks,” diagnoses are typically difficult to establish definitively and many other factors must be ruled out in the process.

The Marine Mammal Center was the first group to definitively diagnose DA poisoning in marine mammals because of a large outbreak in California sea lions in 1998. Our veterinarians and scientists have contributed to a number of papers on the subject, some of which can be viewed here:

Anderson, Clarissa R., Kudela, Raphael M., Kahru, Mati, Chao, Yi, Rosenfeld, Leslie K., Bahr, Frederick L., Anderson, David M., Norris, Tenaya A. 2016. Initial skill assessment of the California Harmful Algae Risk Mapping (C-HARM) system. Harmful Algae. 59(2016): 1-18

Cook, P. F., Reichmuth, C., Rouse, A., Dennison, S., Van Bonn, B., Gulland, F. 2016. Natural exposure to domoic acid causes behavioral perseveration in Wild Sea lions: Neural underpinnings and diagnostic application. Neurotoxicology and Teratology. 57(2016): 95-105

Lefebvre, K.A., Quakenbush, L., Frame, E., Burek Huntington, K., Sheffield, G., Stimmelmayr, R., Bryan, A., Kendrick, P., Ziel, H., Goldstein, T., Snyder, J.A., Gelatt, T., Gulland, F., Dickerson, B., Gill, V. 2016. Prevalence of algal toxins in Alaskan marine mammals foraging in a changing arctic and subarctic environment. Harmful Algae. 55(2016): 13-24.

McCabe, R.M., Hickey, B.M., Kudela, R. M., Lefebvre, K. A., Adams, N.G., Bill, B.D., Gulland, F.M.D., Thomson, R.E., Cochlan, W.P., Trainer, V.L. 2016. An unprecedented coastwidwide toxic algal bloom linked to anomalous ocean conditions. Geophysical Research Letters. 43. doi: 10.1002/2016GL070023

Cook, P.F., Reichmuth, C., Rouse, A.A., Libby, L.A., Dennison, S.E., Carmichael, O.T., Kruse-Elliott, K.T., Bloom, J., Singh, B., Fravel, V.A., Barbosa, L., Stuppino, J.J., Van Bonn, W.G., Gulland, F.M.D., Ranganath, C. 2015.Algal toxin impairs sea lion memory and hippocampal connectivity, with implications for strandings. Science. 350(6267): 1545-1547.

Buckmaster, P.S., Wen, X., Toyoda, I., Gulland, F.M.D., Van Bonn, W. 2014. Hippocampal neuropathology of domoic acid-induced epilepsy in California sea lions (Zalophus californianus). Journal of Comparative Neurology. 522:1691-1706.

Kirkley, K.S., Madl, J.E., Duncan, C., Gulland, F.M., Tjalkens, R.B. 2014. Domoic acid-induced seizures in California sea lions (Zalophus californianus) are associated with neuroinflammatory brain injury. Aquatic Toxicology. 156(2014): 259-268.

Ramsdell, J.S., Gulland, F.M. 2014. Domoic acid epileptic disease. Marine Drugs. 12:1185-1207.

Rust, L., Gulland, F., Frame, E., Lefebvre, K. 2014. Domoic acid in milk of free living California marine mammals indicates lactational exposure occurs. Marine Mammal Science. 30 (3): 1272-1278.

Cook, P., Reichmuth, C., Gulland, F. 2011. Rapid behavioural diagnosis of domoic acid toxicosis in California sea lions. Biology Letters, doi:10.1098/rsbl.2011.0127

Other Domoic Acid Research
On April 20, 2011, domoic acid was a topic of a presentation held at the Center. UCSC doctoral student, Peter Cook, spoke about his investigations into sea lion memory and learning, and how this is impacted by domoic acid intoxication.  Studying the effects of this neurotoxin on marine mammals is helping researchers better understand the disease's effects on the human population. Here is a recent paper on Peter Cook's work. 

Cook, P., Reichmuth, C., Gulland, F. 2011. Rapid behavioural diagnosis of domoic acid toxicosis in California sea lions. Biology Letters, doi:10.1098/rsbl.2011.0127

Oceans and Human Health Initiative
In September 2004, the Center received a grant from the Oceans and Human Health Initiative to study the long term effects of domoic acid in sea lions. This project studied the impact of DA on health, survival, and reproduction.  Part of this project focused on the neurological effects of DA. Effects were evaluated using magnetic resonance imaging (MRI), cognitive behavior tests (how the animal behaves), and histopathology (tissue samples from dead animals). Below are some papers that resulted from this study.

Bargu, S., Silver, M., Goldstein, T., Roberts, K. and Gulland, F. 2010. Complexity of domoic acid-related sea lion strandings in Monterey Bay, California: foraging patterns, climate events, and toxic blooms. Marine Ecology Progress Series 418: 213-222.

Goldstein, T., Zabka, T.S., DeLong, R.L., Wheeler, E.A., Ylitalo, G., Bargu, S., Silver, M., Leighfield, T., Van Dolah, F., Langlois, G., Sidor, I., Dunn, J.L., and Gulland, F.M.D. 2009. The role of domoic acid in abortion and premature parturition of California sea lions (Zalophus californianus) on San Miguel Island, California. Journal of Wildlife Diseases. 45(1): 91-108.

Goldstein, T., Mazet, J.A.K., Zabka, T.S., Langlois, G., Colegrove, K.M., Silver, M., Bargu Ates, S., Van Dolah, F., Leighfield, T., Conrad, P.A., Barakos, J., Williams, D.C., Dennison, S., Haulena, M.A, and Gulland, F.M.D. 2008. Novel symptomatology and changing epidemiology of domoic acid toxicosis in California sea lions (Zalophus californianus): an increasing risk to marine mammal health. Proceedings of the Royal Society B 275: 267-276.

Montie, E.W., Wheeler, E., Pussini, N., Battey, T.W.K., Barakos, J., Dennison, S., Colegrove, K. and Gulland, F. 2010. Magnetic resonance imaging quality and volumes of brain structures from live and postmortem imaging of California sea lions with clinical signs of domoic acid toxicosis. Diseases of Aquatic Organisms 91(3): 243-256. 

Thomas, K., Harvey, J.T., Goldstein, T., and Gulland, F. 2010. Movement, dive behavior, and survival of California sea lions (Zalophus californianus) posttreatment for domoic acid toxicosis. Marine Mammal Science. 26 (1):36-52.

Zabka, T. S., T. Goldstein, C. Cross, R. W. Mueller, C. Kreuder-Johnson, S. Gill, and Gulland, F.M.D. 2009. Characterization of a degenerative cardiomyopathy associated with domoic acid toxicity in California sea lions (Zalophus californianus). Veterinary Pathology. 46: 105-119.

Watch an animated video about Domoic Acid Toxicity, produced for The Marine Mammal Center by the students at the California College of the Arts.


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