Monterey sea otters killed by toxic algae

Monterey sea otters killed by toxic algae

A toxic algae that forms in reservoirs, lakes and stagnant freshwater ponds was responsible for the deaths of at least 21 threatened California sea otters in the Monterey Bay area, a scientific study revealed Friday.

The discovery, reported in the scientific journal PLoS ONE, is alarming because the toxin, called microcystin, had never been linked to the death of a marine mammal and was not believed to be capable of surviving for long periods in saltwater.

"Based on what we know, this is the first documentation of a freshwater algal bloom being transmitted to upper-level marine mammals, specifically a federally listed species," said Melissa Miller, a senior wildlife veterinarian and pathologist for the California Department of Fish and Game and the study's lead author.

The three-year average population of California otters, also known as southern sea otters, declined 3.6 percent this year, the second consecutive drop after a decade of increases. The reason for the decline is a mystery, but scientists believe a variety of causes are at play, including toxic runoff.

There are 2,711 sea otters along the California coast, according to a U.S. Geological Survey study, which also reported an 11 percent drop in the number of otter pups compared with last year.

Study points to algae
Microcystin, which is commonly referred to as blue-green algae, can cause liver damage when ingested. All 21 sea otters that tested positive for the bacteria died from liver failure, according to the study, which was completed with the help of experts from UC Santa Cruz and a variety of state and federal agencies.

It is believed the toxins flowed to the ocean off the coast of Monterey in rivers and creeks. Sea urchins and shellfish near the outflow filtered the water and the poison accumulated in their bodies, which were, in turn, eaten by otters.

It has not yet been determined whether poisoning from blue-green algae is playing a major or minor role in the overall otter decline, but it was at least a factor, the researchers said. The 21 sea otters represent only a fraction of the number of mammals found dead from unknown causes along the Central California coast since 1999. Miller said the full extent of the problem will not be known until further studies can be conducted.

Microcystis is a naturally occurring algae. Its bright green blooms have long been found behind dams, particularly along the Klamath River, and in stagnant pools.

Global concern
But researchers say the microcystin toxin appears to be multiplying in the environment to the point that it is becoming a global health concern. That's because cyanobacteria, as scientists call bacterial blooms, thrive in warm water that is rich in nutrients from lawn, city and agricultural runoff. The warmer the temperatures, the more bacteria there are

Global warming, scientists say, has increased the frequency of deadly green "super-blooms."

Microcystins have been detected in brackish water before, including in the Sacramento-San Joaquin River Delta and San Francisco Bay, scientists say. The bacteria has been linked to the death of cattle and even dogs that drank the water or swam through the green slime and then licked their fur. It is also potentially dangerous to humans.

"What's really astonishing to us is that it had not been on anyone's radar as a problem in the marine environments until now," said co-author Tim Tinker, a research biologist with the U.S. Geological Survey and an adjunct professor of ecology and evolutionary biology at UC Santa Cruz.

The problem was discovered largely by mistake. In 2007, Miller kept running across the bloated, bright yellow corpses of otters near Monterey Bay, indicating acute liver failure. She searched medical journals for things that might have caused the problem and found nothing that fit until she came across blue-green algae.

Suspicions confirmed
Tissue samples confirmed her suspicion. The team of scientists she recruited eventually found high concentrations of microcystin in lakes bordering Monterey Bay and in adjacent rivers.

Blooms were also found in Pinto Lake in Watsonville, which drains into Corralitos Creek and flows into the Pajaro River. Microcystin contamination was eventually detected in the Salinas, Pajaro and San Lorenzo rivers and in the ocean at the Santa Cruz wharf.

The study found that the algae remains extremely toxic for two weeks in the ocean and that the poison can become 107 times more concentrated in shellfish. That means it is a risk to humans who consume shellfish harvested near river mouths. There are no state or federal regulations for exposure to microcystin.

"This definitely highlights the importance of monitoring water quality," Tinker said. "Here is a toxin coming into the ocean, probably affecting a lot of species, and the first indication we have of it is the death of sea otters. It is an early warning for an emerging problem."