Targeted microhabitat sampling and its role in conserving endemic freshwater taxa

North America harbors a rich freshwater fauna, but many of its taxa are narrowly-distributed and threatened with future range reductions from invasive species, habitat alterations, and water quality degradation. The importance of conserving narrowly-distributed freshwater species is well documented, but mechanisms responsible for their distributions are often poorly understood. Developing approaches to better address these species and their unique habitat requirements is critical for providing adequate conservation. We demonstrate the value of fine-scale sampling for narrowly-distributed taxa through a case study of the Coldwater Crayfish (Faxonius eupunctus), a species endemic to the upper Eleven Point River drainage in Arkansas and Missouri, USA. We targeted the upper Eleven Point River drainage for sampling based on results from previously-constructed classification and regression tree species presence models. We estimated F. eupunctus presence and density in shallow, wadeable habitats where lotic crayfishes are often surveyed (i.e., riffles), and we developed a novel approach to estimate F. eupunctus presence and density in deeper, non-wadeable habitats (i.e., pools) where traditional crayfish sampling techniques can be difficult and have rarely been used. We quantified relationships between local F. eupunctus density and surrounding physical microhabitat features in both pools and riffles to provide insights on the species’ habitat use and potential for future conservation. Our targeted sampling approach allowed us to detect a previously-undocumented spatial pattern in F. eupunctus site density throughout the upper Eleven Point River drainage, and we identified important microhabitat variables for F. eupunctus in both habitat types sampled. Our study highlights the benefits of fine-scale sampling in multiple habitat types for conserving narrowly-endemic species, and our methods provide a flexible framework for studying other benthic taxa at fine spatial scales.