BIO INVADERS!(non-native species)

• Author: Bailey, Ronald

Are we under attack by "non-native" species? Should we care?

"That kind of information is dangerous," scolded Jodi Cassell. Cassell, who works with the California Sea Grant Extension program, was speaking at a symposium on "Alien Species in Coastal Waters: What Are the Real Ecological and Social Costs?" at the February American Association for the Advancement of Science meeting in Washington, D.C. She wasn't alone in her alarm. "We have members of the press here," warned a member of the audience. "I am very concerned that they might think that his view is the dominant view."

The target of this shushing was Mark Sagoff, a philosopher from the University of Maryland who has worked with Maryland's Sea Grant program to determine how the Chesapeake Bay's unique ecology defines a sense of place. Sagoffs sin? He'd had the temerity to point out the benefits that the much-loathed zebra mussels had brought to the Great Lakes.

Introduced via discharged ballast water from European freighters in the mid-1980s, zebra mussel populations have been exploding in the Great Lakes. Tens of thousands of the tiny, striped shellfish can occupy a square meter of any hard surface--like rocks, docks, and boat hulls. Observers initially feared that zebra mussels would clog water-intake pipes for municipalities and power plants and perhaps out-compete native shellfish for food. However, it turns out that the things are voracious "filter feeders." They strain algae and nutrients like fertilizer runoff from the lakes' waters. As a result, zebra mussels have played a significant role in improving water quality by clearing the lakes of polluting organic matter.

"There has been a striking difference in water clarity improving dramatically in Lake Erie, sometimes six to four times what it was before the arrival of the zebra mussels," according to the U.S. Geological Survey's Nonindigenous Aquatic Species Database. "With this increase in water clarity, more light is able to penetrate deeper allowing for an increase in macrophytes (aquatic plants). Some of these macrophyte beds have not been seen for many decades due to changing conditions of the lake mostly due to pollution. The macrophyte beds that have returned are providing cover and acting as nurseries for some species of fish." What's more, zebra mussels provide food and habitat for all sorts of native fish and ducks.

Having Sagoff point out such positive developments was more than his colleagues on the AAAS panel could bear. To them--and to...