“Dolphins, other marine mammals weakened by pollution, scientists say.”

Christine Dell’Amore

National Geographic News

Published April 12, 2013

Part of our weekly “In Focus” series—stepping back, looking closer.

The dead sea otters arrived at Melissa Miller’s Santa Cruz, California, lab with bright-yellow eyes and gums, their livers destroyed.

“One by one, Miller, a marine-wildlife veterinarian, eliminated the potential causes of death until “the last thing I was left with seemed so implausible that I thought I was going crazy.”

The otters had been poisoned by a “nasty toxin” called microcystin, which is produced by cyanobacteria, or blue-green algae. Such toxins can appear when human sewage and fertilizers run into lakes and rivers, adding nutrients that spur the growth of algae “superblooms,” Miller said.

But sea otters stick to the ocean, never entering the polluted lakes and rivers where these blooms occur.

“I said, OK, we have to figure out how the otters are getting into this,” said Miller, of the California Department of Fish and Wildlife and the University of California, Davis.

Miller’s sleuthing led her to California’s Pinto Lake (map), a water body about 2.5 miles (4 kilometers) from the ocean and so prone to superblooms that Miller said “it’ll blow your mind—it looks like fluorescent green paint.”

Sure enough, she found that Pinto Lake eventually drains into the Pacific Ocean—close to where the dead otters were found in 2007.

Later experiments revealed the algae’s toxins can live for long periods of time in shellfish—otters’ main diet. Toxins from the polluted lake were traveling downstream into the ocean, Miller concluded, where they were getting into shellfish and killing otters. (See pictures of threatened marine species.)

Of course, the toll that some types of water pollution take on marine mammals has long been documented. For example, cancer-causing chemicals called PCBs and pesticides like DDT are known to accumulate in marine mammals’ fatty tissues and cause serious harm.

But scientists are just now beginning to understand how these and other toxins in the water are spurring the resurgence of some diseases and the creation of others, largely by weakening animals’ immune systems. And with more development and pollution in coastal areas, the problem appears to be accelerating.”

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