Dwindling CA Sea Otter Population Linked to Deadly Bacterial Strain
A sea otter lounging in Monterey, CA
Sep 29, 2010 (GreenAnswers) – Historically, sea otters have had a rough time living off the warm coastal waters of Southern and Central California. During the Western expansion characteristic of 19th century America, California sea otters became an unfortunate victim of the burgeoning fur trade, their population dwindling down to nearly nothing by the start of the 1900s. However, following their dramatic rediscovery on an inlet of Big Sur in 1939, the species benefited from extensive efforts made to study and rehabilitate it, and sea otters have been making a steady comeback in California ever since. Until now.
The US Geological Survey recently confirmed a 3.6% drop in California’s sea otter population for 2010, with an even more alarming 11% drop in sea otter pups born this year. This marks the second consecutive yearly drop in sea otter population, something that worries Tim Tinker, head of the USGS otter research program in Santa Cruz, California.
“All the research we have done to date suggests there’s no one single mortality factor,” Tinker says, “but that the deaths are caused by a suite of interacting stressors”. Tinker cites several natural causes for increased sea otter deaths (low genetic diversity; parasites from feral animal excrement; recent increases in shark attacks) as well as distressingly standard human causes (dirty ocean water from urban runoff, agricultural fertilizers, and pesticide traces; poaching; accidental fishing catches).
However, the single most disturbing cause of California’s decreased otter population is a combination of natural phenomenon and human waste. In investigating the irregular deaths of 21 sea otters found off the coast of Monterey, State veterinarian Melissa Miller was left puzzled by a series of chronic liver failures and circulatory problems in young, otherwise healthy otters. Then she found out about microcystin.
Microcystin is an ancient strain of cyanobacteria — a bacterial form of blue-green algae found in large bodies of freshwater. When consumed in large quantities, it causes liver failure and subsequent blood poisoning, which perfectly explained the deaths of the 21 sea otters Miller had examined. The only trouble was figuring out how the marine animals had been exposed to such high levels of an ancient freshwater contaminant.
“Based on what we know, this is the first documentation of a freshwater algal bloom being transmitted to upper-level species mammals,” Miller told the San Francisco Chronicle. She originally postulated that blooms (large formations of bacterial growth in water) of microcystin flowed into the ocean directly from creeks, and was then eaten by urchins and shellfish that were subsequently eaten by sea otters.
An algal bloom in Lake Erie
To confirm her suspicions, Miller conducted a study with members of the California Department of Fish and Game on the nature of microcystin. To their alarm, they found that cyanobacteria, previously though incapable of surviving for long periods in saltwater, can remain extremely toxic for up to two weeks in the ocean. They also discovered that the poison becomes up to 107 times more concentrated in shellfish, which helps to explain why the microcystin was able to poison Miller’s sea otters so quickly.
The study attributes these changes in the nature of cyanobacteria to changing environmental conditions. Global warming, scientist claim, have raised the temperature of coastal seas and inland freshwater reserves, promoting bacterial growth. This warmer water is also rich in waste-related nutrients as a result of city and agricultural runoff. Warm and polluted water provides ideal living conditions for cyanobacteria like microcystin, and the subsequent flow of these waters into the oceans sufficiently alters marine habitats to accommodate the survival of cyanobacteria for longer than ever thought possible.
All of this leaves Tim Tinker very concerned about not just the future of the California sea otter, but about the future of all oceanic life. “Here is a toxin coming into the ocean,” which, he claims, “probably affects a lot of species, and the first indication we have of it is the death of sea otters.”
For the California sea otter, microcystin represents another deadly concern to their population, something the species doesn’t need; with only 2,711 sea otters left in central and Southern California waters, one disastrous epidemic is all it would take to wipe the species out for good. Even more troubling to concerned marine biologists are the implications this problem has for other oceanic species and the people and industries who depend on them. Steve Shimek, executive director of the USGS’s sea otter research project, commented that “The California sea otter is one of the most researched marine mammals on the planet. So if we don’t have enough information to take action on behalf of the sea otter, I would say that 90% of the other endangered species in the world are doomed.”
Shimek and Tinker plan to concentrate all of their energies into boosting the California sea otter population and figuring out how to most effectively of treating the microcystin problem. “This definitely highlights the importance of monitoring water quality,” Tinker says. “It is an early warning sign for an emerging problem.”