Chesapeake Quarterly
The Ecological Numbers Game
Potomac River with snakehead & hydrilla
While the Potomac may be known as "the nation's river," it's now home to several species from far away, including snakehead and hydrilla from Asia. Credits: Photo of Potomac River by Michael W. Fincham; inset photo of snakehead (left) by The U.S. Geological Survey; inset of hydrilla (right) by Michael Naylor.

It was the summer of 2002, and an invasion by an airbreathing fish from Asia that could walk on land spurred a media frenzy. Though the most sensational stories proved to be nothing but fish tales, the snakehead soon became a poster species for how easily non-native animals and plants can set up shop in the Chesapeake. No sooner had officials eradicated the toothy invader in a Crofton, Maryland pond than it showed up in the Potomac. The snakehead quickly established what appears to be a firm finhold in the river.

Less able to grab the headlines are scores of other non-native species — plants, animals, and microbes introduced from somewhere else and now in the Bay. Some of these species have taken hold without notice and without apparent harm. Others have killed our oysters, smothered our grasses, degraded our shorelines.

And there are thousands of other non-native species that could yet come to the Chesapeake. That's according to experts like Greg Ruiz, head of the Marine Invasions Research Laboratory at the Smithsonian Environmental Research Center. We don't know which species will come and when, where they will end up, or whether they will cause real harm. It's a numbers game, says Ruiz. An ecological roulette of sorts.

What do we do when we lose the game — when an unwanted species shows up on our doorstep? This past year Maryland Sea Grant helped draft a plan for the Mid-Atlantic states to use when faced with an unintended introduction of a non-native species. The plan outlines necessary steps for a "rapid response" — from deciding whether to take action, to determining control methods, to monitoring results. The idea was to keep the plan short and simple. It still turned out to be over 40 pages. The plan's unexpected length speaks to the complexity of controlling an invasive species once it's arrived. An effective response effort is, unfortunately, seldom short. Or simple.

While working on the plan, I kept thinking about Ben Franklin's well-worn adage, "An ounce of prevention is worth a pound of cure." Though it's important to respond rapidly to a species invasion, the better goal is to avoid that situation in the first place.

This is where understanding pathways for invasions becomes critical — what scientists call vector ecology. Whether by commercial cargo ship or a weekend warrior's Boston Whaler, bait buckets or fly-fishing gear, how we spread invasive species may be just as important as what we do once they get here.

The Maryland Department of Natural Resources convened a meeting over the winter to discuss the discovery of several zebra mussels near the lower portion of the Susquehanna River. One attendee lamented that the public might grow weary of hearing about another "new" invasive species. Snakeheads. Mitten crabs. Now zebra mussels. Another biologist responded that this march of new invaders shows that focusing on pathways rather than individual species is key. One set of preventive measures — properly cleaning boat hulls, for example — could avoid the introduction of a whole host of organisms.

In this issue of Chesapeake Quarterly we explore pathways that invasive species can take to get here, from commercial shipping to the actions of everyday citizens.

We also tell the stories of two non-native species, one that's had devastating consequences for the Chesapeake, and one that hasn't lived up to its initial threat.

Some argue that the introduction of non-native species is a natural turn of events. Plants and animals have been coming and going for millennia. Why should we try to stop them? The short answer may be, it's a numbers game. Is it worth the gamble?

— Jessica Smits

Current Issue Contents
Blocking Species
Invasions in the Bay
June 2009
vol. 8, no. 2
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