What to know about the toxic algae bloom killing marine life in Southern California

An "unprecedented" toxic algae bloom has overrun the coast of Southern California, sickening marine animals and staining the shoreline, according to marine scientists. The toxin it produces is domoic acid.

The National Oceanic and Atmospheric Administration began seeing an uptick in domoic acid toxicity cases in Los Angeles County in February, Jeni Smith, a rescue supervisor at SeaWorld San Diego, told ABC News. Other West Coast marine mammal stranding facilities -- which rescue and rehabilitate marine animals -- have reported seeing the same.

Since then, the algae blooms have been spreading to San Diego County, Orange County, Santa Barbara County and beyond.

Toxic algae blooms have always been a been a naturally occurring event in the region, but more regular occurrences began in 1998, Smith said.

For the past four years, there have been annual incidents of ocean waters showing high concentrations of domoic acid and algae blooms, according to NOAA.

And the levels measured in recent weeks have been "especially toxic," Alexis Fischer, an aquatic scientist at EutroPHIX -- a company focusing on restoring water quality -- and a former NOAA researcher, told ABC News. In addition, marine scientists in Southern California are accustomed to seeing the blooms start in the summer, when the waters are warmer -- not when it is still technically winter, Smith said.

Recent water testing off of the Scripps Memorial Pier in San Diego indicated concentrations of domoic acid so high that the event will likely persist for some time before it's filtered out -- and it's unclear how long that could take, Smith said.

Marine mammals such as whales, pinnipeds such as sea lions and pelicans are among the species that have been impacted by the toxin this year.

Sea World San Diego has rescued over 100 animals suspected of suffering from domoic acid poisoning since February. That includes 44 birds, 57 California sea lions and 14 dolphins that were actively seizing or dead on arrival.

Rescue centers along the coast have rescued more than 1,000 animals total in that same period, Smith said.

Partners of the West Coast Marine Mammal Stranding Network are receiving 100 calls a day on average for reports of animals poisoned by the toxic algae bloom, according to NOAA.

At rescue facilities, marine biologists attempt to flush out the toxins using fluid therapy. During necropsies, biologists can determine whether domoic acid was the cause of death by examining the brain and heart.

"It does take an emotional toll in the field," John Warner, chief executive officer of the Marine Mammal Care Center in Los Angeles, said in a statement. "Year after year, it's getting tough. Each of our organizations is trying hard to get to as many animals as we can, but we don't have the resources to rescue every one that is out there."

What are toxic algae blooms?

Harmful blooms occur when colonies of algae grow out of control and produce toxic or harmful effects, according to NOAA.

Pseudo-nitzschia, a needle-like group of single-celled algae that is capable of producing domoic acid, has been present in San Diego for years -- but its role in wildlife mortality has been increasing in recent years, according to researchers.

Marine biologists at the University of Southern California announced in 2018 that the region's coast was emerging as a "hot spot" for toxic algae, with concentrations of domoic acid at the highest level ever recorded at the time.

Manmade sources of nutrients, such as nitrogen and phosphorus, can seep into ocean waters and encourage the growth of algae blooms, according to the Centers for Disease Control and Prevention. Another contributing factor is human wastewater.

But a warming ocean appears to be helping to spread them farther north as well, researchers say. While the toxic algae blooms typically only form every four to seven years, warming temperatures and an increase of pollution can drive the growth and occurrences, according to the CDC.

"I do think that these animals are definitely telling the bigger-picture story," Smith said. "With warming water and the climate getting warmer, we may see this more often."

Wind-driven upwelling of deep ocean water can also feed rapid growth of the algae and the toxin it produces, according to NOAA. This phenomenon occurs when factors like wind push surface waters away, allowing for colder and more nutrient-dense waters to rise.

Domoic acid in shellfish has been found to occur at high concentrations off the coast of San Diego, Orange and Los Angeles counties, according to USC researchers. But the toxin tends to be more prevalent in Ventura and Santa Barbara counties, due to more favorable environmental conditions for growing Pseudo-nitzschia -- including wind-driven upwelling, among other factors.

What does domoic acid do?

Domoic acid, the neurotoxin produced by the algae species Pseudo-nitzschia, can stain the ocean -- a phenomenon commonly known as "red tide" that appears as foam, scum, mats or paint on the surface of the water, according to the Centers for Disease Control and Prevention. However, the stains from this particular species tends to be brown, according to USC.

The acid accumulates in shellfish before creeping up the food chain. Once ingested by fish, birds, seals and sea lions, the toxin attacks the nervous system.

"It does change their brain, and it can affect their heart," Smith said.

Changes in animal behavior include "abnormally aggressive" behavior or lethargy, Smith said. Some animals appear to not be aware of their surroundings and others have been seen having seizures on the beach, she added.

Sea lions suffering from domoic acid poisoning have been observed exiting their habitat and moving toward urban areas, such as freeways, due to the toxins' effect on the brain, Smith said.

"It affects each animal differently based off of how much of the fish that they have consumed," Smith said.

Domoic acid can also cause amnesic shellfish poisoning in humans. Symptoms depend on the type of bloom, but acute cases with ingestion in high doses can include vomiting, cramping, coma and death -- as well as neurological impacts such as hallucinations, confusion and memory loss. However, human fatalities from domoic acid exposure are rare, scientists say.

The CDC advises people to stay out of "discolored, scummy or smelly" water and to keep pets away.

Humans or animals that come into contact with a toxic algae bloom should rinse off with tap water right after, according to the CDC.

Several toxic algae incidents have been recorded in Southern California

A number of recent incidents involving marine life have been blamed on the harmful toxic algae.

The cause of death of a juvenile humpback whale stranded on Huntington Beach on Jan. 24 and a minke whale stranded on Long Beach on April 6 was determined to be domoic acid toxicosis, necropsies performed by the Pacific Marine Mammal Center and the Ocean Animal Response & Research Alliance found.

In March, a man who was surfing at Oxnard State Beach in Ventura County reported he was attacked by a "demonic" sea lion that bit him and dragged him off his board. The mammal was "devoid" of curiosity and playfulness, personality traits typically associated with sea lions, the surfer wrote on Facebook.

A similar attack occurred on March 30, when a 15-year-old girl was bitten by an aggressive sea lion on Long Beach, Capt. Jack Crabtree, public information officer for the Long Beach Fire Department, told ABC News. The junior lifeguard candidate was swimming about 25 yards from shore during tryouts for the junior lifeguard cadet program when the sea lion emerged from the water and bit her, Crabtree said.

Dozens of dolphins have also washed ashore since February, ABC Los Angeles station KABC reported.

"It's the worst we've ever seen here in Southern California on many different fronts, but dolphin strandings, it's unprecedented," Warner told KABC. "It's unprecedented."

Alfred Hitchcock's 1963 horror film "Birds" is thought to have been inspired by a domoic acid incident, according to the Scripps Institution of Oceanography. In the summer of 1961, thousands of frenzied seabirds were seen in Monterey, California, when Hitchcock was visiting.

"Dead and stunned seabirds littered the streets and roads in the foggy early dawn," the Santa Cruz Sentinel reported on Aug. 18, 1961.