Natural and anthropogenic factors predict the presence of two freshwater mussels (Bivalvia: Unionidae) in Illinois, USA

摘要

Over half of the 80 freshwater mussel species that historically occupied Illinois are now extinct, extirpated, endangered, or threatened. Two species of conservation concern that warrant further investigation are Ellipse (Venustaconcha ellipsybrmis) and Spike (Eurynia dilatata). Ellipse have experienced a 30% range contraction in Illinois and are a focal species for a regional conservation initiative in the state. Spike have experienced a range contraction of 55% in Illinois, despite remaining relatively common in bordering states. Several stressors have been proposed as causes of declines in both species, such as habitat fragmentation, hydrologic alteration, pollutants, and availability of fish hosts to aid mussel dispersal. Ultimately, developing effective conservation and management actions for these species requires identifying the environmental conditions that most strongly influence their persistence. Our objective was to identify the habitat features and environmental conditions that best explain patterns in Ellipse and Spike presence in northeastern Illinois. We found that number of pollution dischargers in a watershed was a strong predictor of presence in both species. However, host fish richness, total number of upstream dams, and duration of extreme low flows were also strong predictors of Ellipse presence, whereas distance to the nearest mainstem downstream dam and variation in the number of high flow pulses predicted Spike presence. Our analysis also revealed that different mussel species may respond to the same stressors in an opposite manner, suggesting that conservation actions should either be devised on a species-specific basis or balance the needs of multiple species simultaneously. The specific predictors of mussel distribution we found represent a starting point for developing restoration strategies for these species in northeastern Illinois.