Parasites that were once the pests of house cats and opossums now infect marine mammals like otters and seals, experts said at a symposium at the AAAS Annual Meeting.

Some of these marine animals have been stranded fatally in large numbers along the coasts, providing researchers with one of the first signs that something new and potentially troubling was flowing from land to sea. Increasingly, land pathogens are washing into the oceans, said marine zoologist Andrew Trites, "and affecting the health of the ecosystems we live next to and depend on."



Trites, a University of British Columbia researcher, was one of many scientists converging on the Vancouver meeting to offer a comprehensive assessment of the world's oceans. International teams of scientists shared their latest data on sea level rise, the mysterious animal communities living in deep seas, and the effects of climate change on ocean acidity.

Among the findings presented were the first reports from the Nereus Program, a massive international study with the goal of predicting the future of the world's fisheries. "We are saying goodbye to the big fish, like cod and grouper, and saying hello to the little fish," said Nereus co-director Villy Christensen. But Christensen said the little fish--"oily little black things" called mesopelagics--are dispersed widely in the open ocean and don't taste as good as cod and grouper.

Climate change is making new "winners and losers" of fishing around the world, although not always in the ways that people have predicted, said University of British Columbia fisheries researcher William Cheung. As oceans warm in the tropics, more fish may migrate north. But warming is also making North Atlantic waters more oxygen-poor and acidic, Cheung said, which could lead to smaller catches in the region's fisheries.

Another loser in the changing oceans is the threatened southern sea otter, which wildlife pathologist Melissa Miller has been tracking along California's central coast for 15 years. "The kinds of things we're seeing in these animals are not what you'd expect to see in a healthy population," she said. Nearly 20% of the dead otters that show up in her wildlife medical examiner's office were killed by brain infections caused by Toxoplasmosis gondii, a parasite found in cat feces.

Mike Grigg, a self-described "bug hunter" at the U.S. National Institutes of Health who tracks the spread of new parasites, said a new strain of Toxoplasmosis was identified first in sea otters. It's unclear whether the new strain is any more infectious or harmful to humans than the family version found in cats. The familiar version infects nearly a quarter of all Americans and perhaps up to half of all Europeans, but most people show no symptoms.

Toxoplasmosis is only one of the parasites found in marine mammals, Grigg said, who said parasites found in opossums, cattle, and raccoons also make the sea animals sick.

The parasites wash down to the shore from city storm drains and agricultural fields, the researchers said. Trities and Grigg said marshlands and other "normal filters" in the ecosystem that would protect the shore from runoff pollution have disappeared rapidly in the past 50 years.

The plight of the otters in California has renewed interest "in changing the way we think about water as a disposal site," Miller said, noting the emergence of new laws to enforce runoff restrictions and increased "greenscaping" to absorb water in place instead of channeling it to the sea.