Subterranean Freshwater Gastropod Biodiversity and Conservation in North America.

Many taxonomic groups have successfully exploited groundwater environments and adapted to a subterranean (stygobiotic) existence. Among these groups are freshwater gastropods (stygosnails), which represent a widespread and taxonomically diverse component of groundwater ecosystems in the United States and Mexico; no stygosnails are known from Canada. North American stygosnails have convergently evolved a miniaturized body plan compared to their surface relatives and have independently colonized a variety of groundwater habitats ranging from cave passages to deep, human-inaccessible aquifers. Owing to sampling difficulty and lack of targeted study, stygosnails remain among the most understudied of all subterranean groups. Compared to their surface relatives, of which over 75% are already considered threatened in North America, stygosnails may face additional stressors. As currently understood, most stygosnails exhibit extreme narrow-range endemism, resulting in a high risk of extinction from a single catastrophic event, particularly when combined with increasingly modified underground habitats. Anthropogenically-driven changes to surface environments have led to changes in local hydrology and degradation of groundwater systems through increased sedimentation, introduction of invasive species, groundwater extraction, and/or physical collapse of water-bearing passages. Consequently, 32 of the 39 described North American stygosnail species have been assessed as imperiled under NatureServe criteria, and 10 species have been assessed as threatened under International Union for Conservation of Nature (IUCN) criteria. Although imperilment rates of stygosnails and above-ground freshwater snails in North America are similar, stygosnail conservation is uniquely hindered by difficulties associated with accessing subterranean habitats for monitoring and active management. Furthermore, only three species are afforded federal protection in either U.S. or Mexico, and current law regulating water pollution may be inadequate for protecting stygosnail habitats. Here, we review the biology of stygosnails in North America and discuss conservation needs and policy considerations that will aid in their protection. This article is protected by copyright. All rights reserved.