VANCOUVER, CANADA—When several sea otters began showing up dead in April 2007 along the coast of California's Monterey Bay, wildlife officials called otter expert Melissa Miller to investigate. The animals' insides, she found, were bright yellow—a sure sign of liver damage. Over the next few years, Miller, a veterinary biologist at the Marine Wildlife Veterinary Care and Research Center in Santa Cruz, California, and colleagues explored the possible culprits. They quickly ruled out the scourge's most likely source: a bacterium known to cause jaundice, as it wasn't found in any of the dead otters. As for other possibilities, “Sea otters don't take drugs, they don't eat toxic mushrooms or plants because they're marine mammals, and California weather isn't so crazy that we'd see 15 sea otters struck by lightning,” Miller said here today at the annual meeting of the American Association for the Advancement of Science (which publishes ScienceNOW). In 2009, one of her colleagues noticed a report that nearby Pinto Lake harbored a particularly nasty blue-green algae called microcystin. Tests confirmed it was indeed the killer. At the meeting, Miller laid out the scenario: After heavy rainfalls, Pinto Lake overflowed, emptying its deadly contents into rivers that flowed into Monterey Bay. Filter feeders such as mussels and clams absorbed the microcystin and concentrated it over time. The otters ate them, their livers failed, and they beached ashore. Since the discovery, California officials have taken measures to control the outbreak at Pinto Lake, but the discovery illustrates how marine mammals like sea otters act as warning signals for near-shore ecosystems, Miller said. “The kinds of things that sea otters eat in California are some of the same things we like to eat, too.”
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