US Long-Term Ecological Research Network

North Temperate Lakes LTER: Snail Survey in Northern Wisconsin Lakes 2006

The Chinese mystery snail (Bellamya chinensis) is a large invasive gastropod that achieves high densities in waters across North America, yet little is known about its ecological significance in invaded systems. We surveyed 44 lakes to describe the patterns and determinants of B. chinensis distributions in northern Wisconsin, U.S.A., and to assess the likelihood of effects on native snail communities in the invaded systems. B. chinensis was widespread among surveyed lakes (21 of 42 lakes with snails) and its occurrence was correlated with indicators of lake productivity and anthropogenic dispersal vectors (boat landings, distance to population centers, shoreline housing density). Some native snail species tended not to occur at sites where B. chinensis was abundant; among these was Lymnaea stagnalis, which suffered reduced survival in the presence of B. chinensis in a recently published mesocosm study. However, there was no difference in overall snail assemblage structure at either the site or lake level as a function of B. chinensis presence or abundance. Lake occurrences of many snail species have apparently been lost over time, but a comparison to a 1930's survey showed that there was no increased likelihood of species loss in lakes invaded by B. chinensis (or by the invasive crayfish Orconectes rusticus). Although B. chinensis is widespread and sometimes abundant in northern Wisconsin lakes, it does not appear to have strong systematic impacts on native snail assemblages. Solomon, C.T., J.D.Olden, P.T. J. Johnson, R.T. Dillon Jr., and M. Jake Vander Zanden. 2010. Distribution and community-level effects of the Chinese mystery snail (Bellamya chinensis) in northern Wisconsin lakes. Biological Invasions 12:1591–1605. Number of sites: Sites surveyed within 44 lakes. Sampling Frequency: Each lake surveyed once in summer of 2006
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During the summer of 2006 we collected snails at 4–6 sites in each of 44 focal lakes. Survey lakes ranged in surface area from 14 to 1,400 ha (median = 130 ha), and were selected to span broad gradients of landscape position, water chemistry, human use, and other characteristics, and to maximize overlap with lakes where Morrison (1932) has previously described snail assemblages. For each lake, site locations were chosen randomly within each compass quadrant of the shoreline, using Geographic Information System (GIS) software (ArcGIS 9.2; ESRI, Redlands, California). At each site we placed a 20 m transect line on the lake bottom along the 1 m depth contour. At 2 m intervals along the transect, two snorkelers collected all the snails from within 0.25 m2 quadrats (10 quadrats per site). They then searched the vicinity of the transect haphazardly for 5 minutes to reduce the likelihood that B. chinensis presence at a site escaped detection. Sampling ceased after the fourth site if at least 25 quadrats with non-zero snail abundances had been sampled; otherwise, sampling continued at alternate sites until that threshold was reached or 6 sites had been sampled. At some sites the entire 20-m transect fell in thick macrophyte beds, precluding effective snorkel surveys. In these cases we sampled snails by vigorously sweeping a D-net (500 lm mesh) through the macrophytes in two 1 m2 areas. Collected snails were preserved in 80% ethanol. Identifications were made according to Burch (1989), following the revision of Hubendick (1951) for the Lymnaeidae, Hubendick (1955) for the Planorbidae, and Wethington and Lydeard (2007) for the Physidae. All samples are being curated into the Illinois Natural History Survey Mollusk Collection.We also tested the effectiveness of a rapid assessment protocol for detecting the presence of B. chinensis. Two observers snorkeled around the vicinity of the boat launch (if present) for up to 5 min each, or until B. chinensis was found. We conducted this rapid assessment at 27 of the focal survey lakes, as well as at 8 additional lakes where we did not conduct full quadrat surveys.
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