Toxic Algae Is a Natural Occurrence—With Some Man-Made Origins

David Caron, a researcher with the USC Wrigley Institute for Environmental Studies

The researchers at the University of Southern California have recently confirmed what the marine mammal rescue team at the California Wildlife Center has observed over the last 20 years—that domoic acid poisoning from toxic algae is a recurring theme off the Malibu coastline. Every few years, an unusually high number of stricken sea lions, brown pelicans and other marine mammals and birds are rescued from Malibu’s beaches and taken in for rehabilitation. Until this study came out, scientists had no idea what was causing the periodic toxic algae blooms and no proof as to what conditions caused them. 

The Malibu Times reported outbreaks of domoic acid poisoning that resulted in sick sea lions and even a few dolphins, as well as seabirds like pelicans, cormorants, grebes and loons stranded on local beaches in 2002, 2005, 2007 and 2011. Domoic acid is a neurotoxin that often causes affected birds and mammals to become disoriented and lethargic, with loss of muscle control, seizures and eventual death.

USC researchers have been studying the problem over the last 15 years and now say their findings can help improve methods for monitoring and managing toxic algae blooms. The research was conducted from 2003 to 2017 from Santa Barbara to the San Diego/Tijuana border, including new samples and tests collected the past three years. 

Whereas scientists in the past surmised that the toxic algae blooms stemmed from natural causes, the new study suggested for the first time that, while natural processes may lead to the formation of blooms, they could be made worse with nutrients discharged from man-made sources, like runoff and sewage outfalls.

“We’re seeing an increase in harmful algal blooms and an increase in severity,” co-author David Caron, also a researcher with the USC Wrigley Institute for Environmental Studies, said in a statement provided by the university. “The Southern California coast really is a hot spot and our study also shows that the concentrations of particulate domoic acid measured in the region are some of the highest—if not the highest—ever reported.”

The world’s highest domoic acid measurement in water occurred in March 2011 near San Pedro. It was 52.3 micrograms per liter—measuring about five times higher than the minimum level to raise concern.

Scientists now know domoic acid is produced by specific microscopic diatoms in the ocean that stain the water red or brown, a condition sometimes called “red tide.” It then accumulates in shellfish and fish, moving up the food chain to poison the birds, seals and sea lions—and sometimes humans—that eat the fish and shellfish. 

It can cause amnesic shellfish poisoning in people, with headaches, abdominal pain, cramping, nausea or vomiting. Severe symptoms include permanent short-term memory loss, seizures, coma or shock within 48 hours. Although human fatalities are rare, the California Department of Public Health monitors coastal waters and shellfish for the toxin, and issues warnings when necessary.

The USC researchers say domoic acid is always present offshore, either in shellfish or the water, but is more abundant some years than others. The toxin usually peaks in the spring due to seasonal upwelling of nutrients; and is less abundant in summer and winter. 

The acid diminishes on the West Coast when water temperatures get above 68 degrees (as of Tuesday, the ocean was 72 degrees off the Malibu coast). Therefore, because of global warming, the toxin may be moving farther up the West Coast toward the Pacific Northwest.

The researchers observed that from 2014 to 2016, years of extreme drought in the U.S. Southwest, there were very low concentrations of domoic acid off the Southern California coast—implying a link between the amount of surface water or runoff flowing into the ocean and coastal algal blooms.