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Planet Earth

The Year in Science: Environment 1997

The Jaws You Can't See

By Catherine DoldJanuary 1, 1998 6:00 AM

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Consider the following movie pitch: An army of all-but-invisible one-celled creatures arises from the muddy bottom of an estuary to inflict hideous carnage. Although normally quiet and nontoxic, the beasts start releasing potent poisons into the water, paralyzing fish that happen to pass by and leaving them gasping for air. The poison also disrupts the internal salt balance of the fish in a matter of seconds so that they soon develop bleeding skin sores. The microscopic killers feast on the tissues sloughed off by the dying fish. Then they encase themselves in protective cysts and sink out of sight, leaving thousands of fish inexplicably dead.

Though it sounds like grade-B horror, the story could actually be made into a cold-sober documentary. This past summer on the coasts of North Carolina, Virginia, and Maryland, a tiny toxic organism with the singable name of Pfiesteria piscicida was implicated in large-scale fish kills and poisonings in nine rivers. All but unknown only a decade ago, it has been making a pest of itself in North Carolina waters in recent years, killing over a billion fish since 1991. In 1997 it turned into a regional crisis. Fearing a threat to public health, officials closed sections of three rivers that feed into the Chesapeake Bay—the Chicamacomico, Pocomoke, and Manokin—inciting near-panic in the fishing and tourism industries.

Pfiesteria is a mystery of biology. It is a species of dinoflagellate, a type of plankton that sits on an obscure branch of the evolutionary tree not far from amoebas and slime molds. Most dinoflagellates depend on photosynthesis for survival, but Pfiesteria, which passes through more than 20 radically different life stages, feeds on other organisms. No one can say for sure why it is emerging now, but prime suspects are the agricultural operations—particularly hog and chicken farms—that send nutrient-rich runoff into estuaries in quantities that may far exceed the capacity of harmless plants in those ecosystems to absorb. We have been pouring millions and million of tons of nutrients into these poorly flushed systems for years, says JoAnn Burkholder, a North Carolina State University botanist who is leading the research on Pfiesteria. Perhaps we were inadvertently doing an experiment and slowly shifted the balance in favor of these organisms going into toxic mode.

The dangers from the poisons that Pfiesteria manufactures aren’t limited to fish. Research has shown that Pfiesteria can kill shellfish such as crabs, oysters, clams, and scallops and may also harm marine mammals. People who have crossed paths with Pfiesteria have suffered memory loss and impaired cognitive skills. We have to begin to take better care of our coastal areas not just for the sake of fish resources but for our own health as well, advises Burkholder. It isn’t just a fish kill anymore.

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