Species Specific Session Abstract

Current and Projected Distribution of Zebra Mussels in the Chesapeake Bay Watershed and their Potential Impacts

Tom Horvath
SUNY at Oneonta

Zebra mussels (Dreissena polymorpha) have been present in waters on three of four sides of the Chesapeake Bay watershed for nearly a decade. Within a few years of their establishment in the Laurentian Great Lakes, zebra mussels dispersed into waterways directly connected to the Great lakes. Among these was the Mohawk River, which is connected to the Great Lakes via the Erie Canal. The Mohawk then provided access to the Hudson River, which was colonized by zebra mussels around 1990-1991. To the west of the Chesapeake Bay watershed, the Monongahela, Allegheny, Ohio river system was colonized around 1993-1994. Despite this near surrounding of the Chesapeake, the watershed itself has remained zebra mussel free until very recently. Larval zebra mussels (veligers) reportedly were collected from the Susquehanna River at Johnson City in 1991-1993; however, no adult mussels were ever found, and no further veligers have been reported since then. In 2000, the first adult mussels in the watershed were collected in Eaton Brook Reservoir (Madison County, N.Y.) by researchers from the Biological Field Station (Cooperstown, N.Y.). Based on shell-length distributions of mussels collected in 2001, zebra mussels likely were established in the reservoir in 1999.

Zebra mussel population in streams and rivers most likely are not self-sustaining because the veligers produced are carried downstream and away from the parent population. Lakes, reservoirs or other impoundments provide the appropriate habitat for a self-sustaining source population. These source populations then can provide a continuous supply of veligers for recruitment into outflowing streams and to all downstream waters. Unfortunately, Eaton Brook Reservoir is located in a headwater region of the watershed. The reservoir is connected to the Chenango River by Eaton Brook (about 10 km from the reservoir outflow to the Chenango River). If zebra mussels successfully disperse through Eaton Brook and the Chenango River, they have the potential to colonize large stretches of the Susquehanna River.

Very limited data suggest that zebra mussels do not achieve the high densities required for significant ecological impact in small streams. However, these streams can function as avenues for dispersal. Although options exist for controlling zebra mussel colonization of man-made systems, no analogous control options exist for natural waterways. The best management plan for protecting these waterways is to educate the public on actions they can take to to prevent further dispersal.

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