Virginia biologists in September confirmed that zebra mussels were found in an abandoned quarry in Prince William County. It was the third discovery of the invasive mussel in the Bay watershed in the past two years, and the first reported within the Potomac drainage.
The discovery raises concerns that zebra mussels — which have overrun and dramatically altered the Great Lakes in the last decade — might soon wreak economic and ecological havoc within the Bay region as well.
A special Bay Program panel will begin meeting in October to work on a plan to contain further mussel expansion that can be put in place by next spring.
The Virginia discovery was in an abandoned quarry. Although it had no outlet, it was within a quarter mile of Broad Run, a tributary of the Occoquan River draining into the Potomac.
The state Department of Game and Inland Fisheries was weighing options to eradicate the mussel out of concern that scuba divers — who use the quarry — might accidentally transport the exotic species to other waterways. Zebra mussels can latch onto solid surfaces and survive out of water for several days.
For more than a decade after the Caspian Sea native was accidentally introduced into the Great Lakes by ocean-going ships, the Bay watershed had remained free of the invader, even as it spread through adjacent river systems. But the situation has changed rapidly: In the past two years, the mussels have become firmly established in two lakes in the upper Susquehanna watershed in New York. They were also recently discovered in a quarry just outside the watershed in central Pennsylvania.
Zebra mussels are aggressive water filters. While that can have some positive effects, it also causes problems. In the Hudson River, zebra mussels have been linked to reduced dissolved oxygen levels and increased nutrient export.
In the Great Lakes, the zebra mussels so thoroughly filter algae from the water that scientists believe they are is altering the food web, and potentially affecting fish populations. The mussels have also been a nuisance for water users, as their dense colonies have clogged water intakes for industries, municipalities and others. The U.S. Fish and Wildlife Service has estimated the mussels will cause $5 billion in economic impacts over the next 10 years in the Great Lakes alone.
Because of its high salinities, most of the Bay would be off-limits to zebra mussels, but scientists say the fingernail-size species may be able to establish footholds in slow-moving portions of major rivers, as well as lakes and reservoirs.
Finding ways to step up education efforts aimed at divers, and other members of the public, is likely to be one of the objects of the Bay Program’s new zebra panel, which consists of experts and state officials.
Officials say it’s possible the mussels were intentionally placed in the two quarries where they’ve been found to help clear the water and improve diving conditions. It’s likely the mussels were accidentally introduced into the lakes by boaters.
In addition, the group will look for ways of “re-energizing” monitoring programs that look for zebra mussels, said Leo Dunn, of the Pennsylvania Department of Agriculture, and chair of the Bay Program’s Invasive Species Work Group.
A decade ago, more than 200 sites around the watershed were regularly checked for zebra mussels but — as the mussels went undetected — that number fell to about 60.
Dunn said the group will also need to warn industry, municipalities and other water users about the impact zebra mussels can have on equipment such as water intake pipes.
The group will also be charged with exploring potential eradication techniques that could be used against zebra mussels.
If the stepped-up water monitoring helps to detect small populations, it may be possible to take some action before their numbers get out of control, said Tony Shaw, who oversees zebra mussel programs for the Pennsylvania Department of Environmental Protection and will chair the new panel. “Once they’re established in a waterbody, it’s almost impossible to get rid of them,” he said.