A natural marine toxin is now affecting sea lion's ability to navigate, causing them to get lost and stranded ashore, according to scientists.

This toxin known as domoic acid is produced by marine algae and excessive exposure to this can cause disorientation and worse, seizures to sea lions. 

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Researchers from the University of California, Santa Cruz, discovered how sea lions that are stranded on the beach are apparently suffering from domoic acid poisoning, that can cause serious damage to the hippocampus part of their brain. The hippocampus controls emotions and acts as a memory storage in the brain.

According to lead researcher, Peter Cook of the Emory University, this new study reveals how hippocampal damage can be linked to behavioral impairments that can affect the sea lions' ability to survive in the wild. This also marks the first evidence of the significant changes in the brain networks for sea lions that are exposed to this toxin, suggesting how these creatures are suffering from memory disruption and loss, not just spatial memory deficits. 

The team investigated 30 sea lions that are taken care of the Marine Mammal Center, Sausalito in northern San Francisco. Scientists then carried out behavioral tests including MRI scans to search for evidence between this algae toxin and the mysterious beach strandings.

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. MRI scans also revealed the damage to the brain which were noticeable in the hippocampus region.

According to researcher Charan Ranganath, there are indeed obvious structural differences where the team obtained more functional data from the MRI.

Researchers then discovered that the interaction of the hippocampus with the other brain regions had significant impairments due to domoic acid poisoning. The link to the thalamus was most affected which controls sensory and motor signals and sleep regulation.

With this new study, researchers can now investigate the effects of dosage on sea lions, in regards to how much is needed to have this effect on the hippocampus, causing beach strandings.

In California, record numbers of sea lion strandings were seen this year as sea lion populations increased 30 times from the 1950s where sea lion pups became stranded 20  times more than the average rate from January to February this year.

This new study is published in the journal, Science.

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