Alien Invaders Approach the Upper Chesapeake

by Margaret Clune Giblin

December 11, 2008

Although it might not quite be the stuff of a Hollywood blockbuster, the tale of the lowly zebra mussel has a critical mass of the ingredients needed for a horror movie – or at least a seriously disturbing documentary. They’re creatures from a different world (that is, ecosystem), they’re amazingly prolific (each female produces 1 million eggs per year), they colonize both non-living and living surfaces (including turtles, crustaceans, other mollusks, and even other members of their own species), they harm the environment and impose billions of dollars in costs, and, as Land Letter put it, they’re “impossible to eradicate using current technologies.” (Click here for pictures of the unwelcome invaders.)

Most recently, they’ve been discovered in Maryland, near the uppermost reaches of the Chesapeake Bay. First, officials confirmed that a zebra mussel had been scooped from inside a water intake pipe at the Conowingo Hydroelectric Plant, just northeast of where the Susquehanna River flows into the Chesapeake Bay. Then, several days later, officials confirmed that additional zebra mussels had been found, this time on a boat in Harford County, Maryland.

Native to Europe’s Black and Caspian seas, zebra mussels were first sighted in the United States in 1988 in Lake St. Clair, a small body of water that connects Lake Erie and Lake Huron. Since then, they have spread as far south as Louisiana, as far west as Oklahoma, and as far northeast as Vermont. (Click here for a great interactive map that documents their spread.) Along the way, they’ve wreaked environmental and economic havoc.

From an environmental perspective, zebra mussels compete with native species for food. They eat by filtering water (adults filter up to a quart each day), from which they strain algae and microscopic animals. Their filtering can cause an increase in water clarity – Lake Erie experienced a 600 percent increase in clarity after its zebra mussel infestation. Sounds great, but the filtering can be all too effective, leaving nothing to sustain other filter-feeders such as native mollusks and larval fish. Large populations of these fingernail sized invaders can cause a decline in native species, including fish, mollusks and birds. Also, because zebra mussels attach themselves not only to non-living surfaces but also to other living things, they can have significant impacts on native mussels and clams by interfering with such basic functions as feeding, respiration and movement.

Zebra mussels also colonize a variety of manmade surfaces, and removing them and dealing with the damage costs money. They can attach to and damage boats, docks and navigational buoys. Most significantly, zebra mussels clog water intake and outflow pipes at hydroelectric and other facilities. The cost of scraping zebra mussels from pipes in the Great Lakes region is estimated at $50-$100 million per year. Nationwide, the federal government estimates that the total cost of programs to control zebra mussels in the United States is about $5 billion per year. For a sense of scale, consider that the EPA’s annual budget about $7.5 billion – which isn’t to say that EPA is scraping off the zebra mussels, just that controlling the mussels is very expensive.

Now it appears that the black and white horror show is coming soon to a theater near the already beleaguered Chesapeake Bay: the mussels appear poised to begin colonization of the Bay, the nation’s largest estuary. Because they are freshwater mollusks, the coming infestation may be limited to the Bay’s upper reaches, where the Susquehanna River dilutes salinity levels. Unfortunately, this geographic limitation does not serve to limit the alien’s potential impact on the Bay. The upper Chesapeake provides important nursery areas for native fish, including striped bass, herring and shad. That is, zebra mussels may be able to colonize areas important to larval fish, their chief competitors for food. Native crayfish and mussels could also suffer, and the impact that zebra mussels could have on blue crabs is unclear. (Blue crabs can survive in low-salinity and even fresh water, and male blue crabs typically favor the lower-salinity waters of the upper Bay.) For all those reasons, Maryland’s invasive species task force plans to meet in January to develop a comprehensive plan for dealing with the zebra mussels.

So how did these alien invaders make their way into U.S. waters in the first place? After being transported in the ballast water of a transatlantic freighter, the first zebra mussels to take up residence in North America were discharged into Lake St. Clair. Ballast water is water that is taken in by cargo ships in one port – to attain additional weight and thus stability – and then discharged in another port. Organisms make the journeys in the ballast water, and when able to survive where discharged, become invasive species.

Invasive species pose the second-largest threat to native biodiversity, after loss of habitat. Yet, as CPR Member Scholar and University of Nebraska Associate Professor of Law Sandra B. Zellmer pointed out in an article published in 2000, the lack of federal regulatory mandates aimed at stopping the introduction and spread of invasive species “suggests a glaring omission in U.S. environmental law.” While the complexity of many of the causes of species invasions translates into difficulty identifying a regulatory target, ballast water (and the vessels that discharge it) is surely the “low-hanging fruit” in the invasive species context.

The federal Clean Water Act prohibits discharges of pollutants from point sources without a permit. It defines pollutants to include “biological materials” and point sources to include “vessels.” Yet for decades, EPA has not required ships discharging ballast water filled with exotic organisms to obtain a permit, having exempted these and other discharges from Clean Water Act permit requirements by regulation. The United States Court of Appeals for the Ninth Circuit recently upheld a federal district court decision invalidating that rule, and EPA is currently in the process of finalizing a “Vessel General Permit,” which would incorporate requirements previously imposed by the Coast Guard, establish requirements for other discharge types, include requirements for corrective actions and inspections, and impose monitoring, recordkeeping and reporting requirements.

As Professor Zellmer argued in her 2000 article (which called on EPA to rescind the very regulation it has now been ordered by the court to invalidate), this general permit approach will be an important step towards reducing—and eventually eliminating—discharge of ballast water containing invasive species. Specifically, general permits allow for public participation, require EPA to focus on the effect of a category of activities, and require EPA to revisit the issue every five years or less – all an improvement over the categorical exemption previously in place.

Although the action comes 20 years too late to prevent the infestation of zebra mussels in U.S. waters, regulation of ballast water discharges under the Clean Water Act may just prevent the next alien invader from taking hold.

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