Scientists have gleaned fresh insight into the havoc wreaked by a microscopic culprit that has disrupted marine life this year along the Pacific Coast, not only tainting Northern California’s delicious supply of Dungeness crab but also sickening or killing hundreds of sea lions.
It’s long been known that a tiny toxin called domoic acid, produced by marine algae known as pseudo-nitzschia, kills brain cells. But new research by a University of California, Santa Cruz, team illuminates the relationship between damage to the brain and sea lions’ profound loss of memory and navigational skills. In recent years, biologists have increasingly observed a high number of California sea lions struggle onto beaches, weak, confused and trembling.
“They have a lot of difficulty navigating and finding food,” said Peter Cook, who presented the findings Monday at the biannual Conference on the Biology of Marine Mammals in San Francisco. “They have no sense of which way to go.”
While harmful algal blooms are not unusual, this year’s phenomenon was the largest ever recorded, lasting through the summer and extending from Santa Barbara to Alaska. Blooms of the toxic algae typically occur in the spring and last just a few weeks.
They have a lot of difficulty navigating and finding food. They have no sense of which way to go.
Peter Cook, who presented the findings Monday at the biannual Conference on the Biology of Marine Mammals in San Francisco
This year’s bloom caused the unprecedented shutdown of the commercial Dungeness and rock crab fisheries throughout most of California. But the toxin has affected other marine life as well, working its way up the food chain from razor clams to anchovies and other small fish to sea lions, one of the top predators in coastal waters.
For the first time ever, sick sea lions have been documented in Oregon and Washington, not just California, said Kathi Lefebvre, of the Northwest Fisheries Science Center, part of the National Oceanic and Atmospheric Administration.
An estimated one-third of stranded sea lions suffer from domoic acid poisoning, Cook said. The research is published in this week’s issue of the journal Science.
Using dog crates and a truck, the team picked up 30 California sea lions undergoing veterinary care and rehabilitation at the Marine Mammal Center in Sausalito. Some had poisoning, while others had infections or other physical ailments.
The sea lions were delivered to a psychology lab at UCSC, where their healing continued and they underwent behavioral tests.
Animals with healthy brains were able to quickly master the pattern of a maze and adjust to last-minute changes in its route. In contrast, animals with poisoning lacked the short-term memory to recall or adapt to the changed maze.
They showed differences in long-term memory as well, with poisoned animals incapable of remembering where buckets of fish were hidden.
Magnetic resonance imaging showed the poisoned animals had a damaged and shrunken hippocampus, a region of the brain responsible for memory and navigation. The greater the damage, the worse their skills.
The study “has very profound implications for an animal that to survive has to forage,” said Lefebvre, who was not involved in the work. And it could eventually help in the diagnosis of humans poisoned by domoic acid, she said. Human cases are rare but may rise if warming ocean temperatures continue to support toxic algal blooms.
“If we continue to see increasing concentrations in the food web, we’re going to need to be more vigilant to protect human health,” said Lefebvre, adding that research by Cook and others could provide “a learning tool for studying the effects of domoic acid in not only marine mammals but also humans.”
More than 3,400 sea lions were brought into the state’s rehabilitation facilities between January and June – and the final tally, still being calculated, will likely surpass 4,000 animals, said Justin Viezbicke, the California stranding coordinator for NOAA fisheries. Additional animals likely died out at sea.
“There were a lot that we just couldn’t get to, once our facilities reached capacity,” Viezbicke said.
When healthy, female sea lions are very focused, “storming up the beach to crawl, interact and look for their pups,” said Sharon Melin, a wildlife biologist with the U.S. National Marine Fisheries Service who specializes in sea lion health.
In contrast, poisoned animals look disoriented, she said.
“They look like they are relieved to be there and just lay down and rest,” Melin said. “If they have seizures, you'll notice their head kinked back and their flippers flapping up and down.”
A different problem – also caused by record-breaking warm temperatures in the Pacific Ocean – is threatening sea lion pups.
Melin’s research reveals that California sea lion pups are emaciated, weighing 31 percent below normal, the lowest average weight in 41 years of testing. A lack of food appears to be the chief problem, as sardines, anchovies and other cold-water creatures are in scarce supply. Mother sea lions aren’t providing enough milk, and the pups are too young and weak to find food on their own, she said.
While the problem is unlikely to threaten the thriving population of California sea lions – estimated at 300,000 and growing – it is an indicator of challenging environmental conditions and could affect future generations, Melin said. “It is an ecosystem health issue, driven by great global processes” such as climate change and other factors, Melin said. Although the phenomenon is not directly linked to El Nino, “El Nino is not helping the situation,” she said. “There is something in the environment that has changed, so it is a less healthy place.”