A toxic bloom of microscopic algae is once again turning Southern California’s coastal waters into a killing field for marine life — and this year, it arrived early.
For the fourth consecutive year, domoic acid, a neurotoxin produced by a fast-growing group of algae called Pseudo-nitzschia, is causing widespread poisonings.
Sea lions, dolphins and seabirds have washed up on beaches — many convulsing, disoriented or already dead.
“We’re receiving over a hundred [calls] a day,” said Jeni Smith, curator of SeaWorld Rescue in San Diego. “Oftentimes there are multiple calls for the same animal, but we’re logging 20 or more distinct rescues per day, all along the coastline.”
According to SeaWorld Rescue, an estimated 50% of marine mammals treated for chronic domoic acid exposure are successfully rehabilitated and returned to the wild. While long-term post-release data is limited, they say this event will offer valuable insight into recovery outcomes over time.
The bloom, which started near Los Angeles and drifted south, has been detected just off the San Diego County coast.
Domoic acid is often associated with “Red Tide.”
According to the National Institute of Enviornmental Health Sciences, algal blooms can sometimes be seen as green, blue-green, red or brown patches on the water’s surface, depending on the type of algae.
Its timing — first spotted in February — marks a shift from the typical summer peak.
“[The blooms] this year have been somewhat consistent with the last three years… We’ve had three summertime events, followed by this [year’s] springtime event,” said Clarissa Anderson, director of the Southern California Coastal Ocean Observing System (SCCOOS) and the NOAA Cooperative Institute for Marine, Earth and Atmospheric Systems at Scripps Institution of Oceanography. “This springtime event is possibly, very probably, explained by the fact that we’re in a La Niña year, which has a larger impact on the physics of the ocean, and when you have these blooms.”
Marked by cooler-than-average ocean temperatures in the central and eastern Pacific, a La Niña year can shift weather patterns and ocean conditions. In Southern California, it often leads to increased upwelling — a process that brings nutrient-rich water to the surface and can fuel toxic harmful algal blooms (HAB).
Warmer waters, seasonal upwelling and runoff typically create ideal breeding grounds for these toxic harmful algal blooms (HAB) during summer, but the early arrival this year could reflect deeper oceanic changes.
“We had an inkling,” Smith said. “We’re constantly talking to other stranding network partners and water sampling organizations. This bloom is earlier than usual — but not completely unheard of.”
SeaWorld’s rescue center has been treating mostly California sea lions but also seabirds like pelicans and common dolphins.
Smith said once the toxin makes its way up the food chain — from contaminated sardines or anchovies to larger predators — the effects can be fatal.
“The fish will eat the algae and then the sea lions eat the fish,” Smith explained, “and depending on how many they eat, they start showing signs. It’s a neurological toxin that affects their brain and can affect their heart. The sea lions will have seizures. They might appear lethargic, stargazing or they’ll wander off beaches and onto roads…they lose that inhibition to be in their natural habitat.”
The rescue
“When we bring an animal in, we’re immediately administering fluids to try to flush out the toxin,” she continued. “If they’re having seizures, we’ll give them anti-seizure medication. We monitor them. If, within about seven days, they’re eating again and responsive, we know we’ve caught it in time.”
But not all cases recover. Chronic domoic acid exposure can lead to permanent brain and heart damage.
As of April 10, SeaWorld’s rescue team has rescued three sea lions in Imperial Beach, two in Silver Strand and one in Coronado.
Smith said SeaWorld’s team is in triage mode, mapping reports to prioritize rescues.
“We have to consider how large the animal is, the surrounding area, and whether the animal is in a safe area to access,” she said. “We also take care of the in-house animals and ensure that they are indeed getting the treatment that they need. We have to go at it at all angles.”
Meanwhile, Anderson said SCCOOS is working to detect and forecast blooms using a multi-pronged monitoring system: water samples, ocean sensors, robotic microscopes and advanced models that combine satellite and ocean circulation data.
Based at Scripps Institution of Oceanography and funded by NOAA, the system is one of 11 regional groups in a national ocean monitoring network.
One of the main goals is detecting harmful algal blooms, and SCCOOS has built one of the country’s earliest and most advanced alert systems for it, Anderson said.
But even with these tools, toxic blooms are hard to track.
“Many of these blooms start offshore or in the subsurface, where large marine animals feed,” Anderson said. “Often, the first real indicator is the animals themselves coming ashore sick, and we see it tick up at the shore stations themselves.”
This year’s strandings include many pregnant female dolphins.
“That’s going to have longer-term ramifications on their population growth,” Anderson said.
Onshore, the public is also at risk.
Multiple harmful algal blooms at once
Officials have issued shellfish advisories in Santa Barbara, Los Angeles and San Diego counties due to domoic acid and another toxin that causes paralytic shellfish poisoning.
“We’re currently experiencing multiple harmful algal blooms at once,” Anderson said. “Domoic acid is responsible for amnesic shellfish poisoning, but another plankton is producing paralytic shellfish toxin. It’s a big concern for public health managers.”
Commercial shellfish harvesters must submit weekly shellfish samples to the California Department of Public Health for testing for paralytic shellfish toxins and domoic acid.
Anderson said California doesn’t require testing for other types of fish off the coast. Monitoring mainly focuses on bivalve shellfish like oysters, mussels, clams and scallops.
On the commercial side, shellfish served in restaurants are tested weekly, and aquaculture farms are closely monitored for domoic acid. Since the bloom began, many commercial shellfish farms — especially in Santa Barbara — have been shut down or placed on hold.
As domoic acid sinks into marine sediments, it can contaminate bottom-dwelling organisms for months.
“We used to see [toxic HABs] every three to five years. In 2015-2016, we had the largest blooms we’d ever seen, and from that point forward, we’re pretty much in a gauntlet of them,” Anderson said.
Scientists are still working to understand what’s driving the shift. Anderson and her colleagues are investigating how warming waters and changing nutrient profiles — possibly linked to human activity — could be fueling more frequent and intense toxic blooms.
For now, both Smith and Anderson urge the public to remain vigilant.
“If you see a sea lion acting oddly or a dolphin stranded, don’t approach it,” Anderson said. “Call the marine mammal stranding network. These animals are sick, and they’re telling us something important about the state of the ocean.”
Smith added: “Stay back 150 feet — that’s the federal recommendation — and if you see a stranded animal, call the 24/7 SeaWorld hotline: 1-800-541-SEAL.”
