A harmful algae bloom off the California coast created a neurotoxin called domoic acid that killed hundreds of sea lions and about 60 dolphins in a short period last year.

Soon after, scientists at UC San Diego’s Scripps Institution of Oceanography in La Jolla started studying the process of how such masses of algae develop so researchers, industries, officials and communities can be better prepared for future outbreaks.

As part of a study funded by the National Oceanic and Atmospheric Administration, Bradley Moore, a professor of marine biology, marine chemistry and geochemistry at Scripps Oceanography, worked to determine how domoic acid is produced with the hope of creating a predictive model.

Now, a team of researchers from SIO, La Jolla’s J. Craig Venter Institute and other organizations appear to have done it.

In September, the group published a study on predicting harmful algae blooms that contain high levels of domoic acid by tracking a single gene that serves like a canary in a coal mine — an early detector of danger.

The study provides new insights into the mechanisms that drive harmful blooms and offers potential ways to forecast and mitigate their effects.

“We are witnessing a barrage of highly toxic and impactful domoic acid events in California, creating an urgent need for better predictions and forewarning that a harmful algal bloom is imminent,” said Clarissa Anderson, director of the Southern California Coastal Ocean Observing System at Scripps Oceanography and a co-author of the study.

Moore said that while blooms happen nearly annually, not all of them become toxic. According to NOAA, rapid growth of an algae called pseudo-nitzschia causes the production of domoic acid.

“In the last several years, we have had these harmful events in Santa Barbara, which is very disturbing,” Moore said. “Some years it happens, other years it is really minor. The vast majority are not toxic, but some are. And when they are, they really are.

“So we sought out to use our knowledge to make that kind of prediction … so industries and communities that would be affected can prepare accordingly. If there is a bloom coming, will it be toxic? And can I prepare? Because these events can be devastating to fishing industries and communities.”

The minor type of blooms, he said, are needed to produce phytoplankton that serve as part of the ocean food web.

To explore what makes some algae blooms toxic, scientists started studying water conditions before, during and after a harmful bloom. In pouring through tens of thousands of genes and cells appearing in the ocean, they found one — dubbed dabA — that was “highly expressed” about a week before the neurotoxin appeared.

“It was the telltale signal,” Moore said. “We could measure that and there was no toxin in the water, and a week later the toxin would appear. It was a one-week look ahead.”

Armed with that knowledge, “having the ability to forecast these harmful algal blooms is going to happen,” Moore said. “These toxic blooms are global events. We think this … will be impactful.”

Work to develop such a model has been going on since 2015, when the largest recorded harmful algae bloom occurred in the northeast Pacific, causing nearly $100 million in damage to fisheries and killing many marine mammals.

During such blooms, shellfish such as clams, mussels and scallops filter-feed on algae and accumulate the toxin in their tissue.

Contaminated shellfish are dangerous to humans when consumed, often causing vomiting, diarrhea, headache, abdominal cramps, dizziness and disorientation, and in more severe cases, difficulty breathing, seizures, loss of short-term memory, irregular heartbeat and more. The toxin cannot be detected by sight or taste.

Following the 2015 bloom, researchers collected water samples from Monterey Bay nearly every week for a year, recording available nutrients and domoic acid concentrations.

Three years later, a published study first implicated the dabA gene in the production of domoic acid. Though scientists discovered the genetic mechanism for production, they didn’t understand the biological or environmental drivers involved.

With the role of dabA now better understood, and with data from the past three years of water samples, Moore and his collaborators are now working to create a test kit that can identify the gene.

“It is expensive and time-consuming to find the dabA signal, so we are looking to … make diagnostic kits that would simplify things tremendously,” Moore said.

The team also is looking to test the model in other areas of the world.

The issue is important for sea animals that frequent the waters off California.

In 2023, NOAA Fisheries reported that the Channel Islands Marine & Wildlife Institute fielded more than 1,000 reports of sick or dead marine mammals between June 8 and 14 that were thought to have been exposed to the toxic algae bloom.

“Responders believe domoic acid is behind the deaths, given the neurological symptoms exhibited by the animals,” NOAA said. Tissue samples were collected for testing to confirm.

Because the toxin may cause animals to experience seizures, disorientation and hyper-reactivity, the bloom also led to a surge of sick and potentially aggressive sea lions onshore, including in San Diego.

During that time, sea lions sickened by the algae bit and injured at least two people at beaches in Orange County. The Channel Islands institute, which serves Santa Barbara and Ventura counties, recorded five incidents of marine animals biting beach-goers both in the water and on land. ♦