The effect of flow and mussel species traits on the occurrence of rare mussels: A case study within selected rivers of the West Gulf Coastal Plain

Abstract

1. Mussel-flow relationships are not well defined and studies linking behavioural, physiological and life-history traits to hydrological conditions remain scant. This lack of information hinders not only understanding of how flow shapes population and community processes but the development of evidence-based flow recommendations to mitigate mussel declines. 2. Mussel-flow relationships were evaluated for Potamilus amphichaenus (Texas heelsplitter), Pleurobema riddellii (Louisiana pigtoe) and Truncilla macrodon (Texas fawnsfoot) from the Sabine, Trinity, Neches and Cypress River basins of East Texas using Indicators of Hydraulic Alteration and random forest models.These species were chosen because all three are currently being evaluated for listing under the US Endangered Species Act.3. Analyses were performed on US Geological Survey stream gauge stations and mussel records within 20 km of each other. Only gauges with at least 15 years of continuous data and ≥70% overlap of flow records from 1968 to 2018 were included. For selected 28 gauges, Indicators of Hydraulic Alteration were used to calculate 47 hydrological parameters that describe the magnitude, frequency and duration of high and low flow events. Random forest classification models across species were significant and had low error rates (3.57-21.43%), moderate to high sensitivity (0.81-0.93) and moderate to high specificity (0.71-1.00).4. Life-history theory was useful for explaining how mussel species cope with hydrological variation. Potamilus amphichaenus and T. macrodon/Truncilla donaciformis, considered r-selected or opportunistic strategists, were more likely to occur in basins characterized by significant changes in flow and land use compared with P. riddellii, considered a K-selected or equilibrium strategist.5. The analytical framework presented in this study should be helpful to managers and conservationists interested in determining how the flow regime is shaping aquatic communities in their region and developing reference points that could serve for ecological research, conservation and management.