Sea Lions Getting Brain Damage from Climate-Fueled Toxic Algae

December 17,2015 at 05:48 am

A new study is providing a window into how our warming oceans are putting marine mammals at risk.

Toxic algal blooms, which have grown to record levels in the Pacific Ocean, are causing brain damage and a loss of memory in California sea lions, according to a new report published in Science. The study exhibits the "first neurobiological evidence" for how domoic acid, a neurotoxin derived from the algal bloom known as pseudo-nitzschia, impacts the "brains and behavior" of the sea lions, which makes them get lost or confused when they`re out looking for food. 

“We knew already from work that had been done that this toxic exposure could cause pretty specific damage to a part of the brain that we know is really important for spatial memory," lead author Peter Cook, post-doctoral fellow in the Center for Neuropolicy at Emory University, told "We know a lot about it in humans and small rodents, certainly it had never been studied in sea lions functionally before, but we did know they got damage to this part of the brain, so the question for us really was, `okay, so they’re getting brain damage to a part of the brain that is probably important for spatial memory. That is having a measurable negative impact on their ability to navigate.`"

Cook and his team looked at 30 different California sea lions impacted by domoic acid and scanned their brains with magnetic resonance imaging (MRI) machines. The researchers then had the animals perform several spatial tests, one involving a maze that led to food after following a pattern, and another placing buckets of fish in different locations. The sea lions that had brain damage on the right side of their brains had trouble finding the fish.

Cook explained that sea lions, perhaps more than many other marine mammals, rely on their memories to find food and take care of their young.

"If you’re a sea lion, you go out looking for fish, you will find fish in a good region, if you can remember. Or you take care of a pup, you go back to the rookery to find your pup," Cook said. "Wait a minute, where is it?"

"The domoic acid impacts (with atrophying lesions) the hippocampus of the brain, the area where long term memory is processed," explained Robert DeLong, pinniped researcher at the National Marine Mammal Laboratory.

Shawn Johnson, director of veterinary sciences at the Marine Mammal Center, praised Cook`s report, saying it was a really ingenious study design (which involved using blinds, buckets and ropes), and the results validated what marine scientists had suspected for a long time, that certain amounts of domoic acid exposure causes memory loss in the animal.

The neurotoxin has caused sea lions to have seizures on the beach and forget the location of their colonies. Johnson told that he`s gotten many reports of sea lions ranging far outside of their rookeries with sightings in fields, or even on people`s decks.

"It`s completely bizarre, but it happens pretty regularly," Johnson said.

So far this year, the center admitted 224 California sea lions with domoic acid poisoning, as well as four Guadalupe fur seals.

Kathi Lefebvre, a marine biologist at NOAA`s Northwest Fisheries Science Center, told that the study raises concerns for other marine life.

"It`s not just sea lions, other marine mammals are likely impacted for sure, and many of those are endangered or threatened," Lefebvre said. Lefebvre remembered when the toxin was first detected in 1998 on the West Coast and being there to study the then-mysterious sea lion strandings.

"It`s a strange thing for me to come full circle," Lefebvre said. "What does the future hold? If we get more toxins in the food web, are we going to see this move further north towards Alaska?"

Sharon Melin, a wildlife biologist at the National Marine Mammal Laboratory, told that populations of sea lions are at a healthy level at the moment, with approximately 300,000 of them living in California, but toxic algal blooms raise significant worries if they continue to be stressors to their habitat each year.

"It`s something that probably impacts them in their ability to survive," Melin said. "If an animal has a disease like this, it`s unlikely they will have a successful life. They have predators; there`s boats, people shooting at them, and if they`re not fully there mentally, then I think it would hurt their chances at long-term survival."

"This is the type of thing that having a rapidly changing environment might result in," Johnson added. "If you think of all the things warming water will do, this is a wake up call when you get your system out of balance."

Cook hopes that his study can lead to further understanding of the neurological impacts of toxic algal blooms.

"The scary thing is how much more frequent it`s becoming and how much more we`re seeing the effects in these animals," Cook said.