Fish and Mussel Assemblage Patterns during and after Drought Conditions in Tributaries of the Lower Apalachicola-Chattahoochee-Flint Basin

Fish and mussel communities in headwater streams of the Chipola River (Alabama and Florida) and Spring Creek (Georgia) were examined over two years during and following drought conditions to evaluate persistence and colonization in relation to hydrology within an occupancy modeling framework. Four of thirteen sites sampled were intermittent due to hydrologic factors involving groundwater withdrawal and drought. A total of 46 fish and 17 mussel species were quantitatively sampled across sites and seasons. Sites clustered by hydrologic features, with perennial sites having greater fish and mussel abundance and diversity compared to intermittent sites. Occupancy and colonization probabilities of large-bodied fishes increased significantly from drought to post-drought conditions; however, fish sampling design provided low analytical power with occupancy models. Recolonization for some fish species rapidly increased following drought. For mussels six habitat covariates of species occurrence were used to develop 36 a priori occupancy models. The best fit model included minimum discharge, average stream width, and permanence. Mussel abundance and diversity was lowest at intermittent sites. Our results suggest that proximity of intermittent sites to permanently flowing streams, as well as frequency and duration of dewatering cycles, affects fish and mussel assemblage structure, recovery, and persistence.