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Subterranean ecosystems harbor globally important yet highly threatened biodiversity. Unfortunately, subterranean biodiversity is often neglected in regional and global conservation initiatives, including conservation assessments. We reviewed the conservation status and threats to subterranean species based on the two most popular conservation assessment protocols in North America, NatureServe and International Union for Conservation of Nature (IUCN) Red List, as well as federal and state/provincial protection status of the 1,460 described cave-obligate species occurring in the United States and Canada. Only 9.3% of species have been assessed under IUCN Red List criteria compared to 77.9% of species assessed under NatureServe criteria; notably, 1,065 and 116 of species are assessed at an elevated risk of extinction by NatureServe and IUCN Red List, respectively. Just 41 species are listed or proposed to be listed under the U.S. Endangered Species Act and none of the 10 species that occur in Canada are federally listed. Vertebrates (fishes and salamanders), decapods (crayfishes and shrimps), and U.S. federally listed species are overrepresented on the list of species with IUCN Red List assessments compared to other taxonomic groups, particularly arachnids, millipedes, and insects. Most species assessed under IUCN Red List criteria as well as federally listed species occur in the Edwards Plateau and Balcones Escarpment karst region of Texas. Major threats frequently reported in conservation assessments include habitat degradation, pollution/contamination, recreational activities, climate change, and groundwater exploitation; however, information on threats was lacking for most species for nearly all major taxonomic groups, except decapods, fishes, and salamanders. The intrinsic vulnerability of subterranean biodiversity coupled with the many potential threats facing species and extensive biodiversity knowledge gaps makes assessing their conservation status and ultimately their protection a challenging endeavor. We highlight several limitations of implementing current conservation assessment approaches while offering recommendations to improve our ability to assess the conservation status of subterranean biodiversity to better inform sound local to global conservation policies and actions. 

Most cave-obligate species (troglobionts) have small ranges due to limited dispersal ability and the isolated nature of cave habitats. The troglobiontic linyphiid spiderPhanetta subterranea(Emerton, 1875), the only member of its genus, is a notable exception to this pattern; it has been reported from more counties and caves than any other troglobiont in North America. As many troglobionts exhibit significant genetic differentiation between populations over even small geographic distances, it has been hypothesized thatPhanettamay comprise multiple, genetically distinct lineages. To test this hypothesis, we examined genetic diversity inPhanettaacross its range at the mitochondrial cytochrome c oxidase subunit I gene for 47 individuals from 40 caves, distributed across seven states and 37 counties. We found limited genetic differentiation across the species’ range with haplotypes shared by individuals collected up to 600 km apart. Intraspecific nucleotide diversity was 0.006 +/- 0.005 (mean +/- SD), and the maximum genetic p-distance observed between any two individuals was 0.022. These values are within the typical range observed for other spider species. Thus, we found no evidence of cryptic genetic diversity inPhanetta. Our observation of low genetic diversity across such a broad distribution raises the question of how these troglobiontic spiders have managed to disperse so widely. 

The Crystal-Wonder Cave System developed in the Western Escarpment of the southern Cumberland Plateau in the Interior Low Plateau karst region of south-central Tennessee, USA is a global hotspot of cave-limited biodiversity. We combined historical literature, museum accessions, and database occurrences with new observations from bio-inventory efforts conducted between 2005 and 2022 to compile an updated list of troglobiotic and stygobiotic biodiversity for the Crystal-Wonder Cave System. The list of cave-limited fauna includes 31 species (23 troglobionts and 8 stygobionts) with 28 and 18 species documented from the Crystal and Wonder caves, respectively, which represents five phyla, ten classes, nineteen orders, and twenty-six families (six arachnids, three springtails, two diplurans, three millipedes, six insects, three terrestrial snails, one flatworm, five crustaceans, and two vertebrates, respectively). The Crystal-Wonder Cave System is the type locality for six species—Anillinus longiceps, Pseudanophthalmus humeralis, P. intermedius, Ptomaphagus hatchi, Tolus appalachius, and Chitrella archeri. The carabid beetle Anillinus longiceps is endemic to the Crystal-Wonder Cave System. Sixteen species are of conservation concern, including twelve taxa with NatureServe conservation ranks of G1–G3. The exceptional diversity of the Crystal-Wonder Cave System has been associated with several factors, including a high dispersal potential of cave fauna associated with expansive karst exposures along the Western Escarpment of the southern Cumberland Plateau, a high surface productivity, and a favorable climate throughout the Pleistocene.