Toxic Algae Are Leaving Sea Lions Unable to Find Food—or Their Homes
The record number of emaciated sea lions stranded off the West Coast of the United States this year could have been triggered by more than just fish shortages owing to unusually high ocean temperatures. Now, scientists have found that the marine mammals could also be losing their ability to find food and their way home.
The culprit, according to researchers at the University of California, Santa Cruz, is the persistent toxic algal blooms that engulfed much of the northeast Pacific Ocean in 2015. The naturally occurring blooms produce domoic acid, a neurotoxin known to cause seizures and death in birds, sea lions, and other marine animals.
A study published Monday in the journal Science shows that as the oceans warm from climate change and produce longer-lasting and more toxic algal blooms, domoic acid is inhibiting adult sea lions’ ability to forage for food and hindering simple memory tasks.
“The animals exposed to domoic acid in either short durations, like during a single algal bloom event, or over a long period, from multiple events, showed massive disruptions in both short-term and long-term memory functions,” said Peter Cook, a graduate student at U.C. Santa Cruz, who led the study.
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Over the past three years, researchers have been studying rescued sea lions at The Marine Mammal Center in Sausalito, California, to see how animals recovering from domoic acid poisoning handle simple tasks in their enclosures.
In one test, Cook said, the team hid food in one of four buckets in the animal’s pen—the same bucket every time—to see how quickly it would notice the fish. Sea lions that hadn’t been exposed to high levels of the toxin recognized the food bucket within three days. The domoic acid–exposed sea lions took nearly twice as long to see the pattern.
“We’d put the food out there, and the healthy sea lions are nailing it. But five, six, seven days in, and the sea lions exposed to the poison aren’t getting it,” Cook said.
Brain scans showed poisoned sea lions had lesions on their hippocampus, a part of the brain involved in memory processing. The impacts can leave adult sea lions incapable of finding food and unable to locate their home colony and could possibly impair the females’ ability to feed their young.
The results raise concerns for Cook about the future of the species as algal blooms off the West Coast occur more frequently and over a greater expanse of ocean.
“The algal blooms aren’t going away—they’re increasing in frequency—and sea lions are really our best window into seeing how the rest of the marine world could be impacted by this phenomenon,” he said.
The algal bloom that stretched from Alaska to California this year was the longest lasting and most toxic recorded by the National Oceanic and Atmospheric Administration, resulting in hundreds of reports of poisoned marine mammals and birds.
Small shellfish and fish species such as sardines and anchovies feed on toxic algae, and then larger birds and marine mammals eat those toxin-laced fish, leaving sea lions with a gut full of domoic acid.
“Warmer waters are more favorable for blooms. That’s not rocket science,” said Kathi Lefebvre, lead research biologist for NOAA’s Wildlife Algal Toxin Research and Response Network. “And that’s a scary thought. As our oceans warm due to climate change, there’s absolutely no doubt we’ll see a change in the dynamics of the ocean’s ecosystems.”
Lefebvre has been studying the effects of algal blooms on marine life since 1998, when she connected a sea lion poisoning event in California to an algal bloom that year that was partly related to an El Niño–influenced rise in water temperatures.
As algal blooms have increased in frequency and size over the past 17 years, so have the impacts to marine life, Lefebvre noted. This summer, Washington’s $20 million Dungeness crab fishery and mussel, clam, sardine, and anchovy fisheries in Oregon and California were closed or delayed because of domoic acid concerns. Also, for the first time, a sea lion suffering from toxin-induced seizures was confirmed on Washington’s coast.
“It’s the first one ever reported north of California,” Lefebvre said. “The typical blooms we would see stay in California waters are spreading much farther north.”
This year, more than 3,000 sea lion pups washed up on California’s shore in the first five months of the year—a rate more than 15 times higher than normal.
Researchers blamed the unusually warm offshore water temperatures for moving schools of sardines and anchovies—important food sources for nursing sea lion mothers—farther offshore. The lack of food meant the sea lions were fishing more than feeding and weaning pups before they could fend for themselves.
Lefebvre said Cook’s new research shows the problem might not have had so much to do with a food shortage as it did with sea lion behavioral changes.
“The value of Peter’s findings shows that it’s not just warmer waters and moving fish; it’s the behavioral impacts that the toxin can have on the animals,” she said. “There are multiple factors. If sea lions aren’t able to find food or are not feeding as often, that’s going to quickly throw the species out of balance with a rapidly changing environment.”