The discovery reveals yet another deadly threat of the toxin, domoic acid, which has put the otherwise lucrative California crab season on hold now for weeks.
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This behavioral test entails comparing the memory of sea lions to rats where they are both subjected to a T shaped maze, where the animals are rewarded with treats if they remember which way to go around the maze. “People thought it was mercury poisoning”, said Kathi Lefebvre, a National Oceanic and Atmospheric Administration scientist who was not involved in the new research. Cook conducted the sea lion research while a graduate student at the University of California, Santa Cruz, and he is continuing to expand on it at Emory. The hippocampus is a part of the brain associated with spatial navigation and memory. Results of this study may be applicable to other wild animals naturally exposed to DA, including sea birds and cetaceans, the researchers say. Their blooms – a term used to describe rapid spread of algae – have grown more frequent and severe. The species blooms each year. “What we’re most concerned about right now is this year we have had the likely largest ever recorded algal bloom producing domoic acid ever on the U.S. west coast, spanning the largest geographic range”.
“In this study, we were able to correlate the extent of hippocampal damage to specific behavioural impairments relevant to the animals’ survival in the wild”. However, due to various factors, such as global warming and this year’s El Nino phenomenon, scientists are anxious that the algal bloom might last for months. Domoic acid gradually builds up in shellfish, anchovies, sardines and other small fish that feed on algae filtered from the water. Animals with damage to the hippocampus showed impaired performance on short- and long-term spatial memory tasks. And it could eventually help in the diagnosis of humans poisoned by domoic acid, she said.
The neurotoxin is hurting sea lions’ spatial memory and making them prone to getting confused and forgetting their path, according to the study.
That causes the mammals to lose their ability to navigate and, more importantly to find food. Therefore, those sea lions exposed to less-lethal doses of this neurotoxin may only experience seizures and disorientation.
Temporal lobe epilepsy, one of the most common forms of epilepsy in humans, typically begins with a seizure caused by head trauma, high fever or loss of oxygen, and progresses to full-blown epilepsy. There are thousands of California sea lions with varying degrees of exposure to domoic acid out there. Three other Canadians who ate the mussels died from domoic acid poisoning. This may explain why sea lions are increasingly found disoriented on California beaches, and are being found in areas where sea lions are rarely seen. Scientists then carried out behavioral tests including MRI scans to search for evidence between this algae toxin and the mysterious beach strandings.
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The poisoning affects hundreds of sea lions a year, and can limit the animal’s ability to forage and navigate.
