ANDY COHEN is searching the shoreline of this San Francisco Bay port for aliens. But Mr. Cohen is a marine biologist, not a border guard. The illegal immigrants he seeks are located below the water line, encrusted on dock pilings and ship bottoms - and the source of serious environmental concerns.
The scientist from the University of California at Berkeley pulls up a chain covered with mussels, sea squirts, and tiny marine pillbugs scampering in every direction. "Cool, it's a Japanese nudibranch," he says, pulling out a hand lens to examine a tiny, shell-less snail with polka-dotted pods as it writhes in the air. "I don't have one recorded from this dock before," Cohen says enthusiastically.
This is only one of 212 alien species that have established themselves in the shores, estuaries, and bottom of San Francisco Bay since the days of the Gold Rush. This makes the Bay area "the most invaded aquatic ecosystem in North America," according to a just-released study conducted by Cohen and fellow scientist James Carlton for the United States Fish and Wildlife Service.
The pace of invasions is increasing - since 1970, 1 new organism became established every 24 weeks, and in the last decade, every 12 weeks, according to the study. Most of the species arrive in the ballast water of ships. The water, pumped out in port when the ship takes on cargo, may contain clams, crabs, worms, and other marine animals, as well as smaller organisms numbering in the millions from one ship.
The invasion poses serious threats to the region's ecology, contributing to the possible extinction of native fish and shorebirds. And some of these biological invaders could have substantial economic impacts, including damage to California's vast network of water aqueducts and pipelines.
Similar problems exist in other water bodies around the globe, where introduced organisms have severely disrupted native ecosystems. Two weeks ago Sen. John Glenn (D) of Ohio introduced legislation, supported by an unusual alliance of California environmentalists and water agencies, to try to control this "biological pollution" of the nation's waters.
"It's harder to visualize than an oil spill, even though a biological spill is going to be a lot more enduring," says Allegra Cangelosi of the Washington-based Northwest-Midwest Institute, a regional association supporting the legislation.
THE most infamous case in this country is the European zebra mussel, which after it was accidently introduced into the Great Lakes in 1986 became a major nuisance. The soon-ubiquitous shellfish attached itself to ship hulls and buoys, and clogged and blocked the water pipes of cities and factories, as well as the cooling systems of power plants. The cost of this one invasion has been estimated at $5 billion and the zebra mussel is rapidly spreading south and west.
The Great Lakes problem prompted the passage of a 1990 act sponsored by Senator Glenn setting guidelines for ships to exchange their ballast at sea before entering the freshwater lakes. The new legislation would extend those guidelines to the rest of the nation's ports, as well as funding studies of the extent of the problem and other methods, such as filtration and heating, to control the organisms in the ballast water.
The Bay Area amply demonstrates how quickly such invasive species can spread. The Asian clam arrived via ballast water in 1986 - by the next summer it had become the most common clam in the Bay, reaching densities of 2,000 clams per square foot and sucking up the tiny plants that feed many of the Bay's native species.
The Chinese mitten crab has migrated up the Sacramento and San Joaquin Rivers, burrowing into river banks and levees, destroying rice plants and carrying a fluke (a flat worm) that scientists say can cause health problems in humans.
An Atlantic species of salt marsh cordgrass, deliberately brought in during the 1970s as part of marsh-restoration projects, is now covering large areas of mud flats that harbor the food supplies for millions of migratory birds.
Environmentalists such as Cohen are concerned enough about the impact of these invaders on the native ecology that they have allied with water agencies that have often been their foes. Those agencies manage 1,800 different pipelines in the Sacramento Delta alone, many of them small and readily blocked by clams, mussels, and similar organisms.