The New York Times reports...
A distressed, possibly pregnant sea lion was wheeled recently into the Marine Mammal Care Center here, just as two other lions were herded into cages in preparation for their return to the ocean.
“That’s just the way it is,” said Lauren Palmer, the chief veterinarian at the center. “Two go out and more come in.”
Peter Wallerstein of the Whale Rescue Team, a private group authorized by Los Angeles to rescue whales and other marine mammals, said he had found the sea lion on the sand in nearby Manhattan Beach. Mr. Wallerstein said he feared she could have been poisoned by domoic acid, a toxin released by large blooms of algae that causes seizures in sea lions.
Southern California marine mammal hospitals have been overwhelmed by sea lions sick from the acid, which appeared in record levels off the coast of Los Angeles in April. Domoic acid poisoning has killed hundreds of the animals across Southern California this spring.
“In over 22 years of marine mammal rescues, I’ve never seen such distress of marine mammals,” Mr. Wallerstein said. “The stress and the fright, it’s kind of shocking.”
Domoic acid poisoning is not a new phenomenon-- it is responsible for marine mammal strandings and deaths that occur every year in California in the springtime as waters warm up and marine phytoplankton proliferate, giving rise to "algal blooms." It is produced by certain species of marine planktonic algae, most notably one called Pseudonitzschia australis.
Domoic acid is toxic to particular neurons in the brain that express a receptor for the common excitatory neurotransmitter, glutamate. Glutamate receptors come in several forms with different properies and the type that is activated by domoic acid is called the "kainate receptor." Domoic acid mimics that action of glutamate on kainate receptors, but it is not subject to the natural systems in the brain that remove glutamate. Unfortunately, the kainate receptor is a dangerous receptor to activate artifically. It is one of a class of receptors that, when activated, allow the net flux of positive ions into the neuron, producing excitation. Most receptors of this type, when exposed to continuous levels of neurotransmitter, rapidly "desensitize", that is, they flux ions for a few hundredths of a second, and then snap shut. Not so, for kainate receptors. When continuously activated by domoic acid, these receptors will continue to allow the influx of positive ions, literally exciting the neurons to death.
While kainate receptors are widely distributed in the brain, one place they are highly concentrated is the medial temporal lobe, a structure where damage can produce both seizures and profound memory loss. In fact, there are a number of cases where humans has suffered profound amnesias, including an inability to store new memories for facts and events, after consuming shellfish (usually mussels) that have fed on toxic phytoplankton and have thereby concentrated domoic acid in their tissues.
So, like the mussel-poisoned humans, these poor sea lions, even if they survive the acute effects of domoic acid poisoning, are likely to be amsnesiacs thereafter.