Snail Distributions in Lake Erie: The Influence of Anoxia in the Southern Central Basin Nearshore Zone

The distributions and abundances of gastropods collected in sediment grab samples in 1978 and 1979 in the southern nearshore zone of the central basin of Lake Erie were compared with earlier gastropod records from throughout the lake. Since the 1920s, 34 species in eight families have been reported for the lake proper. Sixteen species have been reported only once, 13 of them in three reports prior to 1950. All but three of the species collected by two or more authors prior to the mid-1950s have also been collected in the past decade. The most frequently reported species are Walvata trkarinata, Bithynia tentaculata, Elimia ( =Goniobasis) livescens, Physella " s p . " , Amnkola limosa, Pleuroceraacuta and V. sincera. Only six of 19 studies reported species densities, and most did not record sample locations, depths or substrates. Thus, only a limited comparison of the gastropod fauna between studies was possible, with the exception of several well documented studies in the western basin up to the early 1960s. Of four introduced species in Lake Erie, only two were found in the present study, and these appear to have no influence on the present distributions of the native species. The absence of snails in the southwestern part of the study area and at the mouths of the Cuyahoga and Black rivers appears to be the result of prolonged anoxia during one or more summers preceding the study. OHIO J. SCI. 85 (5): 230-244, 1985 INTRODUCTION from the composition of the oligochaete Lake quality in the southern nearshore (worm), sphaeriid (clam) and chironomid zone of the central basin of Lake Erie in (midge) communities, which comprised 1978 and 1979 was recently interpreted the most abundant benthic macroinvertebrate groups inhabiting soft substrates 'Manuscript received 12 February 1985 and in revised (Krieger 1984). The fourth most widely form 7 August 1985 (#85-4). distributed and abundant group, the GasOhioJ. Sci. SNAIL DISTRIBUTIONS IN LAKE ERIE 231 tropoda, also has been used to discern conditions of pollution and environmental change (Harman 1974). Detailed records of the gastropods in the southern nearshore zone of the central basin have never been reported. The purposes of this report are to describe the distributions and abundances of the gastropods collected in the 1978 and 1979 samples and to relate this information to previous gastropod records for Lake Erie, with discussion of some ecological factors which may influence snail distributions. STUDY AREA Lake Erie contains three primary basins, the shallowest being the western basin and the deepest the eastern basin (fig. 1). Because of their different morphometries and pollution sources, each basin has responded differently and in different degrees to various types of pollution (e.g., Britt 1955, Internat. Joint Comm. 1981). Researchers have somewhat arbitrarily divided the lake into the wave zone (<2 m deep) (Barton and Hynes 1978), the nearshore zone (generally < 8 km from shore)