Scientists in California may have an answer for why threatened sea otters are dying along the state's coastline: They're being poisoned.
A study out from the University of California, Santa Cruz, in coordination with the state Department of Fish and Game blames a freshwater toxin for leaking into the Pacific Ocean and contributing to sea otter mortality in bays and estuaries.
Until now, researchers have been puzzled as to why the California sea otter population has been hit hard for the second year in a row. Some have speculated that great white shark attacks, infectious diseases or simple malnutrition could be the culprits (Greenwire, Aug. 17).
But the UC Santa Cruz study, which was published in the online journal PLos One, sees a connection between the toxin microcystin and sea otter deaths.
The toxin is produced by a bacterium called Microcystis, also known as blue-green algae, which thrives in warm, stagnant water. High concentrations have been found in lakes bordering Monterey Bay -- a prime habitat for the iconic sea otter -- and in rivers that flow into the bay.
The researchers say that at least 21 sea otter deaths can be linked to microcystin. Of these, 17 occurred within Monterey Bay, with others found along the Big Sur and south-central California coasts.
The study also suggests that humans could be at risk for microcystin poisoning through consumption of shellfish harvested in the wild near river mouths. The scientists said there are no state or federal regulations governing exposure to the toxin.
Raphael Kudela, a professor of ocean sciences at UC Santa Cruz and co-author of the study, cautioned that blue-green algae may be spreading, at least in part, because of climate change. Their study did not look at the issue directly, but Kudela in an interview cited other research that connects warming with the algae.
"Climate change could be a factor," Kudela said. "These algae like warm, high-nutrient waters."
The sea otter is listed as threatened under the federal Endangered Species Act.
Sullivan reported from San Francisco.