Dunn, C.G., M.J. Moore, N.A. Sievert, C.P. Paukert, and R.J. DiStefano. 2021. Co-occuring lotic crayfishes exhibit variable long-term responses to extreme-flow events and temperature. Freshwater Science 40:626-643: https://doi.org/10.1086/717486
Crayfish serve critical roles in aquatic ecosystems as engineers, omnivores, and prey. It is unclear how increasingly frequent extreme-flow events and warming air temperatures will affect crayfish populations, partly because there are few long-term crayfish monitoring datasets. Using a unique 10-year dataset, we asked: 1) whether recruitment of crayfish in summer responded to extreme-flow events and air temperature during spring brooding and summer growing periods, and 2) whether responses were similar among 3 co-occurring crayfish species. Golden Faxonius luteus (Creaser, 1933), Ozark Faxonius ozarkae (Williams, 1952), and Spothand Faxonius punctimanus (Creaser, 1933) crayfishes were sampled in quadrats at 2 sites each in the Big Piney (1993–2000) and Jacks Fork (1992–2001) rivers (Missouri, USA; n = 3355 1-m2 quadrats). We used zero-inflated generalized linear models to relate variability in quadrat-level age-0 counts to mean daily maximum air temperatures and flow metrics (variability, magnitude, and frequency of extreme high- and low-flow events). Species ranged from a small-bodied, abundant, habitat generalist (Golden Crayfish) to large-bodied, uncommon, habitat specialists (Ozark, Spothand crayfishes). Golden Crayfish occurred in higher-velocity habitats (riffles, runs) and had variable recruitment that increased during years with few spring and summer high-flow events and summers with lower flows and warmer temperatures. In contrast, annual recruitment variability of Ozark and Spothand crayfishes was low and explained by positive effects of cooler summers and by varying flow metrics. Spothand Crayfish recruitment decreased in years with frequent spring and summer high-flow events, whereas lower summer minimum flow was the only flow metric that explained slight increases in Ozark Crayfish recruitment. Relationships with the preceding year’s recruitment were quadratic for Ozark and Spothand crayfishes, suggesting potential density dependence at higher recruitment levels. Species-specific responses suggest that closely related crayfishes could respond idiosyncratically to changes in temperature and flow. Temperature- and flow-related disturbances may be key mechanisms mediating competition and, thus, may help maintain crayfish diversity. However, warming air temperatures and increasingly frequent extreme-flow events could disadvantage some species, thereby altering future crayfish assemblages.