SPATIO-TEMPORAL AND ENVIRONMENTAL GRADIENT EFFECTS ON MOLLUSC COMMUNITIES IN A UNIQUE WETLAND HABITAT (TURLOUGHS) Christopher D. Williams and Michael J. Gormally Applied Ecology Unit Centre For Environmental Science, National University of Ireland, Galway, Ireland E-mail: chris.david.williams@gmail.com Abstract: Turloughs are karst wetlands unique to Ireland. We sought to elucidate mollusc community composition across a broad range of turloughs and to establish the major factors determining spatial distribution and community composition to better inform management decisions. Quantitative pond-net surveys for molluscs were conducted on Carex nigra dominated vegetation zones at each of eight turloughs. Surveys were conducted at each site twice – once just after flooding (early) and once before emptying (late). Thirteen other homogeneous zones were surveyed in the same way once, to assess relationships with environmental variables over the full hydrological gradient. The abundance of temporary-wetland specialists was significantly higher in the early as compared to the late samples, but late samples were more dissimilar to each other than early ones. Site was a more effective grouping variable than time of sampling for the Carex nigra community, and this effect was even higher when considering the whole hydrological gradient. The idiosyncratic nature of the turlough mollusc fauna was notable in both the indicator species analysis and the nestedness analysis. Results suggest a blanket approach to the conservation of turlough molluscan faunas is not appropriate and that turloughs should be considered individually when developing management recommendations. Key Words: biogeographic patterns, community structure, karst wetlands INTRODUCTION Turloughs are temporary lakes unique to the karstic limestone regions in the west of Ireland (Sheehy Skeffington et al. 2006). Turloughs fill and empty through changes in ground-water level either through specific swallow-holes and estavelles or directly through the porous basin floor (Coxon 1986). This results in zones of vegetation from grassy communities on the turlough edge, through sedge dominated communities, to tall stands of emergent aquatic vegetation in some cases (Praeger 1932). As a unique habitat, most turloughs are protected as Special Areas of Conservation (SAC) under the EU Habitats Directive (Council Directive 92/43/EEC). Much work has dealt with the geomorphology, hydrology, and vegetation of turloughs (see Sheehy Skeffington et al. 2006 for a comprehensive review) and a recent multivariate analysis of the available data suggests that a dry-wet continuum is more appropriate than a classificatory system of turloughs (Visser et al. 2006). Furthermore, on turloughs it appears that both pH and nutrient status are correlated with a dry-wet gradient, wetter sites have water which is less acidic and relatively more nutrient poor. This is in contrast to Wheeler and Proctor’s (2000) study of European peatlands, where these variables act independently (Visser et al. 2006). Despite the relatively comprehensive data on hydrology and vegetation, work on invertebrate communities of turloughs has remained scanty (Sheehy Skeffington et al. 2006). Turloughs are thus important from two perspectives: firstly as an internationally important wetland in their own right, and secondly as a model habitat for terrestrial- aquatic ecotones – analogous habitats occur throughout the world, e.g., autumnal pools and sloughs in North America, flood meadows and dew ponds throughout Europe (Whiles and Goldowitz, 2001 and Williams, 2006), and most especially the karst areas of Slovenia with poljes that closely resemble turloughs (Sheehy Skeffington et al. 2006). The international importance of temporary wetlands has been highlighted by Williams (1997) and Boix et al. (2001); both authors note the importance of the distinctive faunas of temporary waters and the latter suggest that the richness is comparable to permanent water bodies. The factors governing mollusc com- munities in turloughs may help guide future studies in other temporary wetland sites of international conservation importance. Certain mollusc species are of considerable conservation importance (Watson and Ormerod 2004; Watson and Ormerod 2005) and wetland mollusc communities have been widely used as bioindicators in both lotic (Foekler et al. 2006 and WETLANDS, Vol. 29, No. 3, September 2009, pp. 854–865 ’ 2009, The Society of Wetland Scientists 854