Maine lobster observed in Puget Sound. Japanese crab found in Long Island Sound. Zebra mussels discovered in a Connecticut lake.

These headlines may seem harmless, but to marine scientists they are cause for alarm.

Pesky critters from foreign lands and sea are invading in growing numbers. Many of them hitch a ride in the ballast water of ocean-going ships. Some have been purposefully introduced, but quickly spread out of control.

A recent Connecticut Sea Grant study found that 15,000 new species are moved around the world by ballast water every week, though the vast majority of them never become established.

"Biological invasions can dramatically alter community composition and ecosystem function. Not only is it a growing ecological problem, it's a significant economic issue as well," says Robert Whitlatch, a marine biologist and head of the marine sciences department at the Avery Point campus.

Whitlatch has been studying invasive marine species for about 15 years. He points to the zebra mussel as an example of how just one organism can cause widespread damage. The black-and-white striped bivalve is native to the Black and Caspian Seas and first appeared in the U.S. in 1988. Two years ago, the damaging mollusk showed up in a Connecticut lake.

The mussels rapidly form large reefs. They prevent fish from laying eggs, wipe out bottom-dwelling species, and clog water intake pipes at power plants. The price tag for damage in the states and Canada is estimated in the billions of dollars.

Given the seriousness of the problem, Whitlatch and two colleagues are working to gain a better understanding of why some species are more invasive than others, and why some ecosystems are more vulnerable than others to invasion.

Since the 1940s, many scientists have operated under the assumption that the more diverse an ecological community is, the more resistant it is to exotic species. Until recently, observational studies brought conflicting results. Whitlatch says no one had ever tested the theory in the marine environment - that is, until now.

He and two colleagues - John Stachowicz, a post doctoral student, and Richard Osman of the Academy of Natural Sciences in St. Leonard, Md. - conducted experiments in Long Island Sound to test the diversity theory.

Slabs of tile were used as platforms to create marine communities. Each tile, or experimental community, was composed of up to four native species. The invader chosen for the study was the Pacific colonial tunicate (a plant-like creature that affixes itself to rocks). The sea squirt, as it is more commonly known, first made its appearance in Long Island Sound about 20 years ago.

As the researchers increased the number of native species on the tile, the sea squirt's ability to survive decreased.

"It's evidence that we need to preserve naturally occurring biodiversity, because the loss of it promotes invasion," Stachowicz says.

To illustrate his point, he compares it to the game "Jenga". Picture a tower of interconnected blocks. The tower becomes less stable as blocks from different sections of the tower are removed. Eventually the tower crumbles and is destroyed.

"Diversity represents a kind of biological insurance, in that having a lot of species provides a buffer against loss of any one of those species," Stachowicz says. "And it ensures ecosystems are more likely to function in a healthy and productive manner."

Their findings were recently reported in the journal Science.

The focus of their work is applauded by Edward Monahan, director of Connecticut Sea Grant. "We feel that the study by Whitlatch and his colleagues will provide important insights into the alteration of ecosystems by bio-invaders and, perhaps, may pave the way for possible control strategies," he says.

With $155,000 of funding from Connecticut Sea Grant, the researchers are expanding their study. During the next two years they will test other invaders - first in Long Island Sound and then in Narragansett Bay and Cape Cod.

And as an added twist, Whitlatch says, they'll also be looking at the potential positive roles some invasive species may play. For instance, the sea squirt, a native of California, may actually come to the rescue of blue mussels. By attaching to the mussel's hard outer shell (which causes no damage to the mussel), the sea squirt may actually hide and protect the mussel from other

Janice Palmer