What are plaguing sea lions stranded on California beaches?

What are plaguing sea lions stranded on California beaches?

What are plaguing sea lions stranded on California beaches?

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The calls in question began in mid-August. Sea lions – mostly adult females – were popping up along the southern California coast with signs of poisoning: bewildered and agitated, heads swaying and mouths foaming.

Marine animal organizations say they have been inundated with requests from alarmed swimmers. “We answer 50-100 calls a day,” the Channel Islands Marine and Wildlife Institute, which operates in the island region off the coast of Los Angeles, wrote on Instagram.

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The cause was quickly determined by poisoning with domoic acid, a naturally occurring neurotoxin produced by a tiny single-celled seaweed. The neurotoxin accumulates in crustaceans, small fish and squid, then is passed on to larger predators, such as sea lions.

While most animals usually recover within a few days of their worst symptoms after passing the acid through their urine, the Channel Islands Institute said more than 60 sea lions have been trapped in the past few weeks. One died after suffering a seizure on a crowded beach near the Ventura pier.

Scientists are now working to understand exactly what happened and what made this particular algal bloom so bad. They are also exploring how ocean warming is altering the behavior of domoic acid, which is found in abundance along the California coast.

Clarissa Anderson, a scientist who heads Southern California’s coastal ocean observation system, was among those who received messages about sick sea lions. She immediately checked the observation stations that take weekly samples on the piers up and down the California coast.

Man holding a crab above a yellow bucket

Neurotoxins from algal blooms can accumulate in animals such as Dungeness crabs and have even forced the closure of fishing seasons. Photography: Jane Tyska / AP

None of the near-shore samples showed any blooms, he says, indicating that the event appeared to take place in the deeper waters near the Channel Islands, where most of the sick sea lions were showing up.

Neurotoxin-creating algae blooms are a natural seasonal occurrence in California, Anderson says, but having one this late in the summer is unusual. “We expect a major peak in April or May,” says Anderson, because the organism is highly responsive to coastal upwelling – when strong winds cause deep waters to rise to the surface, bringing in the nutrients the algae need to thrive. – which usually occurs in spring.

Southern California is emerging as a hot spot for domoic acid: the world’s highest measurement of neurotoxin in water occurred near San Pedro, southern Los Angeles County, in March 2011. It was 52.3 micrograms per liter, about five times higher than a concern level.

It is indeed a crisis in Ventura and Santa Barbara counties for these sentinel species

Clarissa Anderson

Acid can be passed from animals to humans who eat toxic seafood: 30 minutes to 24 hours after eating, people can experience vomiting, diarrhea, abdominal cramps, headaches, and dizziness. Crustaceans, fish, and crustaceans can all have high levels of domoic acid without showing symptoms, according to the California Department of Public Health. Also known as red tide, the toxin threat previously disrupted razor clam and crab fishing seasons from Monterey Bay to Alaska, costing the fishing industry millions in lost revenue.

Vera Trainer, a scientist at Noaa Northwest Fisheries Science Center, says scientists studying large blooms in the Pacific Northwest have discovered how resilient the organism is. “I can withstand very intense and stressful environments,” she says, falling like sea snow to the ocean floor and waiting in a hibernating state for the right nutrients to recover and come back to the surface.

A group of sea lions swim in the kelp forest around the Channel Islands in California.

A group of sea lions swim in the kelp forest around the Channel Islands in California. Photography: Antonio Busiello / Alamy

This could mean that the domoic acid adapts well as ocean waters warm up. “We have evidence that these cells perform well when the water is warm and we have evidence that they perform well in nutrient-poor environments, followed by a rapid nutrient supply,” says Trainer. “And it is likely to happen more and more as the climate changes.”

Blooms like this are likely more likely in a future warmer ocean, but the science is complex because algae species actually perform better in colder waters, Anderson says, making it difficult to predict exactly how it will behave. “Temperature is just one of the many factors that trigger these blooms,” he says. “They need nutrients in a certain combination to activate the toxin.”

Researchers are also trying to figure out whether new algae strains could evolve to thrive at higher temperatures. Anderson says some strains are moving further north, to places that were previously too cold for them. One thing is clear though, he says, “Over the past 20 years they have become more prevalent and more toxic.”

Anderson says he’s still trying to investigate and find out what happened to kickstart the bloom. Most affected sea lions will recover, but repeated exposure to the toxin can have more severe and lasting effects – and sea lions are particularly at risk because they eat so many sardines and anchovies, that they build up the toxin in their bodies.

Channel Islands Institute staff continue to treat sick and stranded sea lions, they say, but worry about what lies ahead. “It’s really a crisis in Ventura and Santa Barbara counties for these sentinel species.”

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