Riparian land-use and in-stream habitat predict the distribution of a critically endangered freshwater mussel

Recent human population growth in North America’s southern Appalachian Mountains has raised concerns about the effects of ex-urban development on its streams and their at-risk biota. The few studies to examine effects of land-use change in this region found that many headwater species require well-forested watersheds. Alasmidonta raveneliana is endemic to montane streams in North Carolina and Tennessee and during the past 20 years populations have declined alarmingly in several former strongholds. In 2015, we conducted surveys for A. raveneliana and quantified in-stream habitat and land-use at 25 current or historically occupied sites in the Nolichucky Drainage. We found that A. raveneliana populations were only detected at sites with well-forested watersheds and low proportions of fine substrates. Thin-sections revealed that A. raveneliana is fast-growing and short-lived (max age ~ 12 years) which may be an adaptation to unpredictable headwater streams. However, like many headwater specialists, A. raveneliana appears sensitive to changes in forest cover. Our results suggest that subtle changes in stream habitats linked to land-use change are a significant threat to the long-term survival of this species. Protection of forested headwaters and restoration of riparian zones appear to be the best strategies for conserving populations of this critically endangered freshwater mussel.