Freshwater algae might be killing Monterey Bay otters.

Death by Algae: Scientists believe freshwater blooms have led to liver failure and death in nearly two dozen otters.

Findings from a recent study show that a toxin produced by algal blooms in freshwater lakes is poisoning otters in the Monterey Bay, evidence of a land-to-sea pollution flow not previously identified. 

Melissa Miller, Senior Wildlife Veterinarian Specialist in the California Department of Fish and Game and Research Associate at the University of California Santa Cruz, identified severe liver damage in otters beginning in 2007, and brought together a diverse team of marine, freshwater, public health, and veterinary researchers to explore the possibility that freshwater events might be killing otters in the bay. 

Blue-green algae can include a species that produces the toxin microcystin. The toxin destroys the structure of liver cells, and has been linked to at least 11 dog deaths in Humboldt County after dogs licked their wet fur. 

After Miller autopsied several otters with livers so damaged they “would literally fall apart in my hands,” she started looking for sources of microcystin. Large blooms in Pinto Lake in Watsonville were identified, and Miller’s team undertook a “low-tech, under-budget study” to see whether a freshwater toxin could indeed be responsible for killing saltwater mammals. 

Otters are a sentinel species in that they magnify impending health concerns in oceans, because of their position in the food chain and their unique anatomy. Unlike other marine mammals that rely on blubber for warmth, otters have a high metabolism and eat 25 to 30 percent of their body weight daily, so dietary changes can have a particularly acute effect. When Miller found that shellfish popular among Monterey Bay otters pick up and store the toxin, her lab began testing dead otters. 

At $450 per otter, the testing is expensive, but Miller has been able to confirm microcystin in 22 liver-damaged dead otters. The toxin has subsequently been identified in the Pajaro, Salinas and San Lorenzo Rivers, all of which drain into the Monterey Bay. 

Miller, who has autopsied more than 1,000 otters in her career, sees the threat of harmful algal blooms as worthy of increased attention. Gregg Langlois, a senior environmental scientist at the state Department of Public Health and co-author of the study, oversees a marine biotoxin monitoring program. Commercial fishermen and volunteers gather shellfish and water samples to test for toxins and potentially toxin-producing algae. Microcystis, the culpable organism in this study, is not included in such testing because it grows only in fresh water. 

“The best thing we can do for public health protection is maintain a really strong monitoring program,” says Langlois, because blooms can be unpredictable.

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Miller’s findings suggest that humans could be at risk if they eat shellfish from microcystin-contaminated waters. Currently, no formal regulatory system exists for monitoring the toxin in saltwater and saltwater species. 

Blooms are influenced by natural events such as warm temperatures. They can be exacerbated by nutrient-dense pollutants like fertilizer or sewage that help create the perfect environment for some algae to thrive. “As we try to make our freshwater do more and more things, like catch our waste,” algal blooms will become an increasingly significant problem, says Miller. “Pinto Lake is really an example of an international problem.” 

Miller hopes a collaborative process will address the problem. Otters are a perfect species for studying issues that ecosystems face because of their role as a “sentinel species,” says Miller, but as a result, “They’re in the line of fire of everything coming down the road, or down the stream or down the gutter.”

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