Synergistic effects of regional climate patterns and local water management on freshwater mussel communities

Abstract

Human alterations to aquatic ecosystems are leading to decreases in species richness and biomass and subsequent changes in community composition. In many cases species losses are non-random: species with traits poorly adapted to the new environmental conditions suffer greater losses. We used long-term data from a southern US river, the Kiamichi River, to evaluate the synergistic effects of regional climate patterns coupled with water management practices on freshwater mussel communities. Mussel communities in the river changed over the 15 year period of this study, with overall densities and species richness decreasing and community structure shifting from assemblages dominated by thermally sensitive to thermally tolerant species. These changes corresponded with a period of very low flows in the river caused by a combination of climate patterns (a regional drought) and local water management practices (decreased reservoir releases). These low flows, coupled with high summer air temperatures, changed the river in many locations from a continuously flowing river to a series of shallow, isolated pools where water temperatures sometimes exceeded 40 °C. Altered conditions led to higher mortality rates of thermally sensitive compared to tolerant species. We predict future shifts in river ecosystem function as mussel communities change in response to changing climate and water management.