Now You See Them, Now You Don't

From May, 1995 (Update #24)

AMHERST, N.Y. - Is it possible for an introduced population of zebra mussels to initially survive and spawn in a body of water, then not sustain itself? What constitutes successful zebra mussel colonization? And should some sightings eventually be removed from distribution maps? Questions like these come up when you consider the observations of Cameron Lange, a senior environmental scientist with Acres International Corp., an Amherst, N.Y., consulting firm. Lange has been sampling two New York, water bodies where zebra mussel veligers were detected for several years but subsequently disappeared. Acres conducted a mussel monitoring program from 1991 through 1994 for the New York Power Authority's (NYPA) Hinckley Project in Marcy, N.Y. The program consisted of substrate sampling for adults and pump sampling for veligers. Monthly sampling was conducted from March through November 1991. Veligers were initially observed at a low density (4/m3) in September, but no adults were found. In 1992 veligers were again observed at densities ranging from 5 to 56/m3 during July through September. According to Lange, similar sampling efforts were conducted in 1993 and 1994, but no zebra mussel veligers or adults were found during any of the sampling events. A similar occurrence took place in the Susquehanna River near Johnson City, N.Y. A low density of zebra mussel veligers (63/m3) was collected by the Acres staff at the intake to New York State Electric and Gas Corporation's (NYSEG) Goudey Station in 1991. Because this was the first discovery of veligers in a major non-Great Lakes drainage system, Acres re-sampled the site two weeks later with previously unused equipment. Low densities of veligers were again detected. According to Lange, the veligers were not Corbicula, based on their size and lack of a foot in the D-form veligers. In 1992 and 1993, veligers were detected at the site in a sampling effort conducted by another consulting firm. In 1994 no veligers were detected, although the sampling frequency remained the same as in previous years. Adults have never been collected from the Susquehanna River. What would cause a small introduced population of zebra mussels to disappear? Lange noted a number of similarities between the Hinckley and Susquehanna reports: (1) only veligers were collected and always in low densities; (2) overland transport was the only means of transportation; (3) boating access was available upstream from the sampling sites; and (4) veligers were detected for only two or three years. Lange believes a "clump" of adult mussels could have been introduced upstream from each collection site. This clump of mussels successfully produced veligers, but any settled progeny were too diffuse to successfully spawn in subsequent years. After two or three years, all mussels in the original "clump" probably died. Lange credits NYPA's Arnie Talgo and NYSEG's Ray Tuttle for information and support related to these studies.

ID: 199505-11.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.