Domoic Acid and California Sea Lions
If you visit the beaches within Santa Barbara or Ventura counties, you may be lucky enough to catch a glimpse of marine wildlife. Perhaps you’ll even encounter a California sea lion resting on the beach. These animals are gregarious and social animals by nature and the mostpredominate species of pinnipeds (seals and sea lions) along the coast of Southern California. They are alsosentinel species - animals that can help identify environmental risks to humans.
If you encounter a California sea lion, or any marine mammal, exhibiting strange behaviors such as head swaying back and forth, foaming at the mouth, or seizure activity, please keep your distance! The animal is most likely suffering from domoic acid toxicity.
What is Domoic Acid?
Domoic acid (DA) is a neurotoxin produced by the microscopic marine algae, Pseudo-nitzschia. This phytoplankton grows when our coastal ecosystem provides favorable conditions, such as when upwelling of water causes the nutrients from deeper water to rise to the surface where sunlight is present which proliferates algal growth. This typically occurs during transitional periods in the spring and fall.
When filter-feeders (e.g., small fish, shellfish, and bivalves) consume the toxic algae, they are not affected. But when predators like sea lions and sea birds eat these filter-feeders, they are negatively impacted by the toxin accumulated in their prey. This phenomenon of increased pollutant concentration from the bottom of the food chain to the top is called biomagnification. Because the predators at higher levels in the food chain, such as sea lions, eat larger amounts of prey, they ingest a higher level of domoic acid.
Harmful algal bloom (HAB) events have occurred in Southern California in 2002, 2006, 2007, 2017, and 2022. By monitoring toxic blooms, researchers are devising early warning systems to protect wildlife, marine ecosystems, and even prevent human illness.
Symptoms and Diagnosis in California Sea Lions
California sea lions are the most common pinniped exposed to domoic acid due to the location of their habitats and foraging sites. Pregnant sea lions are especially susceptible because of their increased food intake. Domoic acid has been associated with premature births and prenatal mortality (stillbirths and death within the first week of life) as the toxin is passed through the placenta in utero to the developing fetus, and then through nursing after birth.
Within 24 hours of consuming contaminated fish, sea lions may develop the following symptoms:
Lethargy
Disorientation
Unresponsiveness
Head bobbing/weaving
Foaming at the mouth
Vomiting
Bulging eyes
Involuntary muscle spasms
Inability to move
Seizures
Death (in severe cases)
In order to diagnose a sea lion with domoic acid poisoning, presence of the toxin in the blood serum, urine, or feces of the affected animal as well as detection of harmful algal bloom in the environment must be present. Typically, symptoms of domoic acid toxicity subside within 72 hours as the toxin is eliminated from the body in urine. In many cases, sea lions with domoic acid can recover and successfully forage in the wild.
The domoic acid neurotoxin causes brain lesions and shrinking of the hippocampus, a part of the brain associated with long-term memory and spatial navigation. Damage to the hippocampus can lead to loss of memory, difficulty in establishing new memories, and inability to learn or store new information. The degree of impact that domoic acid has on a sea lion depends on the amount of contaminated fish they consume. Consuming too much of the contaminated prey could result in death.
Rescue and Rehabilitation
Organizations like CIMWI have rescued and rehabilitated sea lions affected by domoic acid during harmful algal blooms. In 2022, CIMWI responded to a total of 262 marine mammals suspected of suffering from domoic acid toxicosis. When a call for a sea lion potentially affected by domoic acid comes into CIMWI’s Hotline, trained volunteers are dispatched to the reported site. They set up a perimeter around the animal to allow for monitoring while educating the public about sea lions and domoic acid toxicity. For the safety of all parties, it is very important that the public keeps a distance from the animal — a minimum of 50 feet (about the length of a school bus) is ideal.
Oftentimes, affected sea lions will rest on the beach for 24-72 hours as they experience the acute phase of the toxin. Afterwards, they will return to the ocean on their own. If rehabilitation is deemed necessary for the sea lion, additional trained volunteers are dispatched. The animal is netted and put into a kennel for transport to CIMWI’s rehabilitation facility. This process can be very stressful for the animal which could impact the animal’s response and health. In some cases, CIMWI will sedate the animal to ease the stress. Upon arriving at the rehabilitation center, the veterinary team evaluates the patient and determines the best course of action for that particular animal.
Supportive care treatment for sea lions with domoic acid include flushing the toxin out of the animal’s body with subcutaneous fluids, administering anti-seizure medication, and feeding the sea lion uncontaminated fish. There is currently no known cure for domoic acid. In many cases, sea lions with domoic acid can recover, forage, and survive in the wild.
Causes of Domoic Acid
Domoic acid is a neurotoxin produced by naturally occurring harmful algal bloom (HAB). HAB occurs when colonies of toxic microscopic algae grow out of control. In small quantities, the toxin is not dangerous. But when there is an extensive bloom, the toxin is consumed through the food chain. This causes harm to fish, marine mammals, birds, humans, and ecosystems.
The particular algae that produce domoic acid, Pseudo-nitzschia, typically blooms during the transitional periods in the spring and fall when upwelling is either starting or winding down. The upwelling of cold water causes the nutrients from deeper water to rise to the surface where sunlight is present. This produces favorable conditions for the growth of phytoplankton in our coastal ecosystem. Additionally, the warm-water anomaly known as the “warm blob” increases algal blooms — the warm water interacts with coastal upwelling creating favorable conditions for a toxic bloom of Pseudo-nitzschia.
The coastal ocean is changing rapidly as it responds to natural and human-induced change. The frequency and severity of harmful algal bloom events along Southern California’s coast has been increasing in recent decades. Climate change and rise of nutrient pollution are environmental circumstances that are potentially causing HABs to occur more often and in locations not previously affected. El Niño brings warm water conditions that can promote higher toxic algae blooms. Unusual oceanographic conditions that are not related to El Niño can also lead to algal bloom. For example, eutrophication is the excessive richness of nutrients in bodies of water which causes a dense growth of plant life. This leads to death of animal life due to lack of oxygen, and it is frequently associated with fertilizers, agricultural and urban runoff, aquaculture activity, and coastal development.
Does Domoic Acid Affect Humans?
Marine mammals are sentinels of ocean health, meaning they can alert us to potentially dangerous environmental changes in the ocean. Sick and stranded marine mammals warn us about changing ocean conditions. Marine mammals that have been poisoned by domoic acid help protect human health by demonstrating the need for screening shellfish and other seafood for biotoxins.
In humans, domoic acid is referred to as Amnesic Shellfish Poisoning (ASP) which is caused by the consumption of contaminated shellfish. ASP causes a range of signs and symptoms (with varying severity) including vomiting and diarrhea within 24 hours of eating the contaminated shellfish, dizziness, headache, disorientation and short-term memory loss. In severe cases seizures, weakness, paralysis and death can occur.
For information regarding seafood advisories, visit the Environmental Protection Agency’s (EPA) “Choose Fish and Shellfish Wisely” web page, as well as the California Department of Fish and Wildlife’s “Health Advisories and Closures for California Finfish, Shellfish and Crustaceans” web page.
2022 Domoic Acid Event – An Unprecedented Crisis
For 37 consecutive days, August 15 through September 21, 2022, Channel Islands Marine & Wildlife Institute (CIMWI) experienced a domoic acid (DA) event of immense proportions. It started suddenly on the afternoon of August 15th with reports of two adult female California sea lions acting erratically within one mile of each other at San Buenaventura State Beach. The first sea lion was reported by a lifeguard at Tower #7 and was observed swimming abnormally before beaching itself on the rock jetty. The animal expired while CIMWI was enroute. Upon visual examination, CIMWI did not find any external signs of injury or trauma and the animal had good body condition. The second animal reported was by Lifeguard Tower #11 and CIMWI observed traditional signs of DA. The animal was acting disoriented, exhibiting lack of control of motor skills, moving in circles, and had a grand-mal seizure before expiring on the beach.
This harmful algal bloom event of domoic acid started in Ventura and spread to Santa Barbara, Los Angeles, and San Luis Obispo counties. CIMWI responds to Ventura and Santa Barbara counties and the information in this summary pertains to animals in this geographic area. This was an unprecedented event for CIMWI with the volume of animals exhibiting signs of DA, severity of symptoms, and acute mortality in many cases. Probable DA refers to an animal showing signs consistent with traditional domoic acid toxicosis.
On a daily basis, CIMWI responded to two to 15 new probable DA animals with an average of six animals per day. In this 37 day event, CIMWI responded to a total of 262 individual marine mammals exhibiting signs of domoic acid toxicosis. The highest days were on 8/22/22 with 15 new cases, 9/7/22 with 16 new cases and 9/8/22 with 14 new cases. CIMWI also re-checked animals that were placed under observation the previous day. On a daily basis, CIMWI responded to and assessed two to 21 animals exhibiting signs of DA with an average of 9.5 animals a day. At the end of this event, CIMWI had conducted a total of 366 assessments of animals exhibiting signs of domoic acid toxicosis. CIMWI’s Hotline averaged 49 calls a day and the highest number of reports received in a single day was 100. CIMWI managed a total number of 1,816 reports of probable DA animals in 37 days.
During this 37 day period, CIMWI rescued 70 marine mammals suffering from domoic acid and collected 86 biological samples from these animals. CIMWI also rescued seven animals which were not exhibiting signs of domoic acid. During this domoic acid event, CIMWI collected data on 72 dead stranded marine mammals and 33 of these animals were observed exhibiting signs of severe domoic acid toxicosis prior to death on the beach.
Visual signs of domoic acid observed by CIMWI volunteers included: disorientation, lethargy, bulging eyes, impaired locomotion (unable to get out of surf), debilitated cognitive ability (unaware of surroundings, agitation), rhythmic head bobbing and weaving, uncontrollable body movements, grand mal seizures, being unresponsive, and continued degradation of these health signs as well as lack of spontaneous recovery and sudden death. The majority of these stranded animals were adult female California sea lions with outliers being two long-beaked common dolphins, one adult female Northern fur seal, one sub adult Northern fur seal, nine adult male California sea lions (the largest one estimated to weigh 600 pounds), three subadult male California sea lions, six subadult female California sea lions, and two yearling female sea lions.
This domoic acid event was very different from previous DA events that CIMWI had experienced. Most animals exhibited severe signs of domoic acid toxicosis and acute mortality was abnormally high. Out of the 70 animals CIMWI rescued with domoic acid during this event, six animals were returned to the wild. Three were returned to the wild after being treated with fluid therapy and anti-seizure medication along with diets of non-contaminated fish. These animals were one yearling female California sea lion, one sub-adult female California sea lion, and one sub-adult female Northern Fur seal. All three only exhibited mild symptoms of domoic acid before rescue and throughout their treatment. The Northern fur seal was transferred to The Marine Mammal Center for long-term rehabilitation care with other Northern fur seals. The two California sea lions exhibited mild neurological deficits at the time of their release however CIMWI’s veterinary team determined prognosis for survival in the wild was good and humane euthanasia was not warranted. These sea lions were returned to the wild at Santa Cruz Island. Three other probable DA California sea lions were returned to the wild without medical treatment. These were two adult females and one adult male that were rescued in “out of habitat” locations and did not show classic external signs of DA other than disorientation. These animals weighed 200 to 600 pounds, had good body condition, and were very responsive. Each animal was given a physical exam, tagged with a roto flipper tag, and marked with a non-toxic grease crayon for identification before being returned to the wild without medical intervention at Hobie Beach in Oxnard. There were no further sightings of these animals.
CIMWI submitted 34 urine, fecal, and stomach contents samples to University California Santa Cruz for DA testing. CIMWI also transferred 13 expired or euthanized animals to the Pacific Marine Mammal Center (PMMC) for full necropsies due to CIMWI’s case load. PMMC collected 22 urine, fecal, stomach, and milk samples on these animals and submitted them for DA testing. Each sample CIMWI submitted was positive for domoic acid toxicosis. The confirmation of DA in 100% of CIMWI’s samples is unprecedented and indicates the dose of the toxin was very high as this toxin is excreted fairly quickly through urine. The adult female Northern fur seal CIMWI rescued had the highest level of DA ever recorded in an individual. A very high level of the toxin is considered to be 20,000 ng/g and the feces of this fur seal tested over 500,000 ng/g. Four animals measured above this 20,000 ng/g threshold and two of them had been under observation at the beach prior to rescue and sample collection. The mean sample average, not including the adult female northern fur seal, was 2,802.35 ng/g. The sample ranges for the California sea lions were:
Stomach Contents: n~10, range 1.12-2,723.69 ng/g, mean average 564.2 ng/g
Urine: n~23, range 2.9-28,372.96 ng/g, mean average 1,767.07
Feces: n~21, range 21.07-47,624.97, mean average 5,133.37
Milk: n~1, 43.77 ng/g
This harmful algal bloom was concentrated in Ventura and Santa Barbara counties and it was much stronger than CIMWI had ever experienced. The strain of this toxin was more potent and attacked the animals in CIMWI’s area of response with greater intensity. The animals suffered from more acute symptoms and higher rates of mortality despite treatment.
CIMWI is a volunteer-based 501(c)(3) nonprofit organization. CIMWI volunteers invested their hearts and time to successfully respond to this domoic acid crisis with resilience, compassion, and skill. We are truly grateful for our amazing team of volunteers. They were beyond exceptional during this crisis and managed to keep up with the relentless pace of this unprecedented event.
CIMWI would like to thank the following organizations for their support, assistance and collaboration during this domoic acid event:
California Marine Mammal Stranding Network
The Marine Mammal Center
Pacific Marine Mammal Center
Ocean Animal Response and Research Alliance
Southern California Coastal Ocean Observing System
Additional Resources
Learn more about domoic acid from these sources:
Southern California Coastal Oceans Observing System
SCCOOS & CENCOOS Harmful Algal Bloom Monitoring Alert Program
NOAA Fisheries article
Toxic Algal Bloom Spreads Along California Coast, Poisoning Sea Lions