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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 a type of algae called Pseudo-nitzschia australis. This neurotoxin accumulates in small fish, like sardines and anchovies, which are then eaten by sea lions in large quantities. So the hearty meals that should be nourishing sea lions instead make them deathly ill.

Domoic acid primarily attacks the brain, causing lethargy, disorientation, seizures and, if not treated, eventually death. 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.

comparison of normal California sea lion brain and a brain affected by domoic acid
Left: normal California sea lion brain -- Right: California sea lion brain affected by domoic acid exposure
(Note the shrunken hippocampus in the center of the brain) Photo © The Marine Mammal Center

Produced by a type of algae called Pseudo-nitzschia australis, this toxin accumulates in small fish, like sardines and anchovies, which are then eaten by sea lions in large quantities.

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 try to reduce the amount of inflammation and damage the brain experiences while the animal is recovering, to hopefully minimize permanent brain damage.

For example, our researchers are testing the effectiveness of adding alpha lipoic acid to our domoic acid toxicity treatment regimen. This powerful antioxidant may help protect against damage to the brain by preventing the toxin from binding to certain receptors in the tissue. And because it is both water- and fat-soluble, alpha lipoic acid is absorbed into a greater variety of tissue types, which means it can pass easily into the brain tissue as well as help prevent cell damage throughout the whole body.

Our veterinary experts are monitoring our patients on this new protocol, anticipating faster recovery times and reduced brain injury. When they see marked changes in behavior over time, they know the animal is ready to go back to the ocean. A sea lion that was once lethargic, disoriented and uninterested in fish will become alert, active and eager to eat—a visual reminder of the importance of the work we’re doing.

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 shellfish, 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, we alert the public health department when we see an outbreak, which helps them to better target their surveillance to protect human 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 one 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.


How the Public Can Help:

  • Report sick marine mammals to The Marine Mammal Center by calling our 24-hour hotline at 415-289-SEAL(7325).
  • Maintain a safe distance of at least 50 feet and keep dogs away.
  • Support this life-saving work by making a gift today.


Domoic Acid Research at The Marine Mammal Center

The Marine Mammal Center diagnosed the first case of domoic acid poisoning in marine mammals because of a large outbreak in California sea lions in 1998. Since then, our veterinarians and scientists have contributed to a number of scientific papers on domoic acid poisoning, some of which can be viewed here:

Lefebvre, K.A., Hendrix, A., Halaska, B., Duignan, P., Shum, S., Isoherranen, N., Marcinek, D.J. and Gulland, F.M., 2018. Domoic acid in California sea lion fetal fluids indicates continuous exposure to a neuroteratogen poses risks to mammals. Harmful Algae 79:53-57.

De Maio, L.M., Cook, P.F., Reichmuth, C., Gulland, F.M.D. 2018. The evaluation of olfaction in stranded California sea lions (Zalophus californianus) and its relevance to domoic acid toxicosis. Aquatic Mammals. 44(3): 231-238.

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

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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