A toxin in marine algae is causing sea lions to suffer from memory loss. Once inflicted, the mammals are unable to navigate or forage for food after suffering neurological and behavioral changes.
The toxin is causing symptoms of brain damage in sea lions along California's coast. Suffering from neurological and behavioral changes, these mammals are then unable to navigate their way in the sea risking their survival, said scientists studying their behavior. Sea lions exposed to the toxin are washing ashore by the hundreds off the coast of California. These dazed and confused creatures often suffer seizures and die. Until now, this annual phenomenon has baffled scientists for a long time.
Detailed analysis of the brains of sea lions that died of the mysterious cause has revealed the connection. Brain scans of over 30 affected sea lions in California revealed damage to the hippocampus, a soft brain tissue responsible for holding memory and spatial information such as navigation routes. All the animals were naturally exposed to the toxin, identified as domoic acid, shared the researchers, reported Yahoo News.
At the heart of the problem are the microscopic algae, called Pseudo-nitzschia. These algae have been in existence for a long time, and they always produced the toxin. However, their blossoms have traditionally been infrequent, thus posing no significant risk. Worryingly, their blossoms have become more frequent and severe in recent years, producing the toxin in ever larger quantities. According to the researchers, this year's bloom was the largest on record and extended from Santa Barbara, California, all the way to Alaska.
Domoic acid is produced naturally by these marine algae, but it can severely harm sea lions' brain, more specifically the region that allows them to navigate the sea and remember where to forage for food, according to the report published in the journal Science. The study was conducted by scientists at the University of California Santa Cruz, UC Davis and the Marine Mammal Center in Sausalito, California.
How do sea lions get the toxins? Sea lions don't eat the algae but feed on the small creatures that consume the toxic algae. Domoic acid gradually builds up in shellfish, anchovies, sardines, and other small fish that feed on algae filtered from the water. Sea lions prey on these creatures and ingest the toxin in the process, shared Peter Cook, then a graduate student at UC Santa Cruz and now at Emory University.
"This is the first evidence of changes to brain networks in exposed sea lions, and suggests that these animals may be suffering a broad disruption of memory, not just spatial memory deficits. The behavioral deficits accompanying brain damage with domoic acid is severe, and may negatively impact foraging and navigation in sea lions, driving strandings and mortality."
Researchers added that humans are the ones who are endangering sea lions by ensuring the algae's growth gets bigger every year. Rising ocean pollution due to excessive use of fertilizers and steadily warming water temperatures due to global warming are active contributing factors for the algae's growth and the subsequent rise in the amount of toxin produced, continued Cook.
"Domoic acid-producing blooms have been in the environment for a very long time, but the current pattern of much larger and more frequent blooms causing more visible damage to marine animals has been going on since the 1980s."
After getting exposed to the toxin, sea lions steadily lose connectivity between the hippocampus and the thalamus, a brain structure associated with sensory perception and the regulation of motor functions, reported Yahoo News.
The unusual mortality rate in the thousands of sea lions is quite alarming and the number is 10 times as many in the first five months of this year compared to the same five-month period from 2004 to 2012, according to the National Oceanic and Atmospheric Administration, reported the Daily Mail.
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