The number of marine mammals in California affected by a neurological toxin from algae has surged in the past week, in what could be another deadly year for animals such as sea lions, seals, dolphins and larger whales.
According to the Marine Mammal Care Center, a rescue facility based in Sausalito, California, the facility is treating more than 30 animals affected by a toxic algal bloom, with eight animals admitted on Wednesday. The algae bloom off the California coast has been on the rise in recent years, producing a neurological toxin called domoic acid.
“Since about 2015 we really saw kind of a steep change in how intense these blooms are and how long they last,” said Clarissa Anderson, a biological oceanographer at the Scripps Institution of Oceanography. “They’re definitely longer lasting in general than they were prior to about 2014.”
Anderson added: “In the last four years, the impacts have been really heavy on the marine mammal side, both sea lions, some fur seals, and quite a few long-beaked common dolphins.”
Domoic acid is a neurotoxin that accumulates in small fish such as sardines and anchovies, creatures that serve as common food sources for marine mammals such as sea lions. This toxin can affect animals and humans.
When ingested in large quantities, domoic acid attacks the animal’s brain and heart, which can lead to seizures and heart failure. It often causes permanent brain damage if left untreated. Although the toxin can naturally leave an animal’s system over time, repeated exposure results in more severe and lasting effects.
If sea lions receive care before any serious damage occurs, veterinarians can help flush the toxin from their system by administering fluids and providing domoic acid-free fish. Anti-seizure medications, similar to those used in humans, are also given to control seizures.
Climate change seems to be leading to higher levels of domoic acid amid changing water temperatures. The first diagnosed case of domoic acid toxicosis in California sea lions was made in 1998 at the Marine Mammal Center, and cases of affected sea lions have been on the rise ever since.
“The 25 to 30 years of data we have now is suggesting that something’s changing. They do appear to be getting more intense,” Anderson said of the blooms. She suggested that changes in nutrient supply, possibly propelled by global climate change, could be having ripple effects on the ecosystem.
The extent of the current domoic acid outbreak remains uncertain, but the MMCC, for example, warned that if they continue to receive three to five new patients daily, their resources may become strained in the coming weeks.
“On the science side we’re trying to really study these blooms and understand what causes them and whether they are increasing in frequency,” Anderson said, “and that’s primarily all federally funded, and that is in huge jeopardy right now considering what’s happening on the Hill and with Doge, so we’re struggling I think from all ends on the resource end of this.”
To make matters worse, this is also the time of year when malnourished elephant seal pups begin stranding along Los Angeles county beaches, which could further hinder the ability for rescue centers to intake new animals.
On Thursday, the MMCC reminded beachgoers in an Instagram post not to approach stranded marine mammals.
“While it is always dangerous to approach a marine mammal on the beach, sea lions affected by domoic acid can be especially aggressive, often awaking from a seizure with little notice,” reads the post.
Anderson said predicting domoic acid events is more complex than it looks, not only because it’s hard to forecast when the organism will bloom and produce toxins, but also because the impact on animals varies.
“If the anchovies are swimming more at the surface, then you can imagine pelicans being more impacted because they don’t dive too deep,” Anderson said.
She added that multiple factors must align – bloom location, the feeding patterns of anchovies (which transfer the toxin), and the presence of top predators – to create the kinds of effects seen in recent years.
