Massive blooms of toxic algae, also known as red tides, might have led to brain damage contributing to the stranding of thousands of sea lions on California beaches, researchers say.
The algal bloom that has spread from California waters all the way to northern Washington is releasing domoic acid, which can be toxic to humans and to marine mammals who consume concentrations of it in crabs, oysters, mussels, sardines and anchovies, they explain.
Sea lions exposed to the neurotoxin can suffer damage to their spatial memory, leading to them becoming confused and lost as they search for increasingly diminishing sources of food, the researchers report in the journal Science.
They conducted a series of tests on 30 sea lions that had been rescued after being stranded on state beaches, putting them through a simple maze to see if they could navigate it to find a food reward.
The animals exhibited a significant loss in spatial memory, the researchers found.
"The [study] results inform us of brain-behavior linkages that influence the survival of sea lions," said Colleen Reichmuth from the University of California, Santa Cruz's Long Marine Laboratory.