aka: Troglobitic Crayfishes
Crayfishes belong to the Phylum Arthropoda, Subphylum Crustacea, Class Malacostraca, Order Decapoda, and Family Cambaridae. Crayfishes are a taxonomically diverse cosmopolitan group with more than 669 species worldwide. There appear to be two centers of geographic diversity, one in southeastern Australia (Southern Hemisphere center) and one in the southeastern United States (Northern Hemisphere center) in the southeastern Appalachian Mountains. Obligate cave-dwelling taxa in the United States occur in five main karst (limestone) geographic regions: (1) the Cumberland Plateau of the southern Appalachians of eastern Kentucky, eastern Tennessee, and northern Alabama; (2) the Interior Lowlands of southern Indiana, western Kentucky, and northwestern Tennessee; (3) the Greenbrier Valley of West Virginia; (4) the Ozark Plateau of southwestern Missouri, northern Arkansas, and eastern Oklahoma; and (5) the Florida Lime Sinks. The Ozarks contain around 9,200 caves, and Arkansas has approximately 3,000. Three species of crayfishes inhabit caves in northern Arkansas.
Ecologically, crayfishes belong to one of two ecological categories—1) those that live in the epigean or surface waters, and 2) those that live in the subsurface water (hypogean). The epigean water dwellers are further broken down into those found in lotic (running water) or lentic (standing water) environments. On the other hand, hypogean crayfishes live either in burrows or caves. Generally speaking, cave organisms can be thought of as troglophilic (stygophilic) or those simply associated with caves, or troglobitic (stygobiotic) or those organisms that are restricted to caves. In Arkansas, crayfishes occupy four main habitat types: (1) primary burrowers (those crayfish that spend their entire life cycles in burrows), (2) stream-dwellers, (3) pond/lake/large river dwellers, including secondary burrowers (which do require connectivity of burrows with freshwater), and (4) stygobitic species (obligate cave dwellers). Interestingly, the first troglobitic crayfish reported in the literature was Orconectes pellucidus described in 1844 from Mammoth Cave, Kentucky.
Several crayfishes have adapted to living in caves. These troglobites have adapted to cave life, which often portends a limited energy (food) supply. As a result, they typically have reduced, energy-efficient metabolisms. A good example is the southern cave crayfish (Orconectes australis), which has been known to live for 175 years, making it one of the world’s oldest living organisms. However, unlike many cave forms that are endemic, this species is the widest-ranging cave species of Orconectes occurring in Mississippian limestone caves from Jackson and Madison counties, Alabama, to the western edge of the Cumberland Plateau in nine counties of Tennessee. Conversely, the Shelta Cave crayfish (Orconectes sheltie) occurs only in Shelta Cave, which is located at the southern end of the Cumberland Plateau in northern Alabama.
In general, crayfishes are classified as crustaceans because of the two pairs of antennae they possess and the fact they breathe using gills. Their body is made up of twenty segments grouped into two main regions: the cephalothorax or domelike carapace, and the abdomen or segmented part of the hindbody. There is a triangular extension of the carapace between the eyes, and it is referred to as the rostrum. Each segment may possess one pair of appendages (up to ten) depending on the group. Individuals are protected by a heavily armored exoskeleton and have five pairs of walking legs, the first of which functions as enlarged pincers (chelipeds) and the others with a small claw at the end. Those adapted to caves typically have a total lack of pigment (albinistic) with reduced eyes. First form males have fully formed and hardened first pleopods (gonopods), or reproductive appendages, that assist taxonomists in differentiating crayfish species.
Crayfishes serve as keystone species and are an integral component of aquatic ecosystems, including those in caves. They also contribute to the maintenance of food webs by processing vegetation and leaf litter, which increases the availability of nutrients and organic matter to other aquatic and terrestrial organisms. Cave crayfish ingest a variety of organic materials, including living and dead organisms, bat guano deposited in caves, cave amphipods, isopods, and other invertebrates that live in the streams of caves. In turn, crayfish, alive or dead, are an important food for many other cave inhabitants.
Adaptations for a cave life include a lowered metabolism, reduced energy consumption, better food usage efficiency, decrease or loss of eyesight, and depigmentation—thus, the white coloration of many cave animals. In addition, true cave crayfishes often have evolved elongated antennal and locomotory appendages in order to better move around and respond to environmental stimuli. These structures are also full of chemical, tactile, and humidity receptors. Because cave crayfishes do not survive well outside caves, they generally cannot travel between cave systems, thus limiting many endemic organisms to a single cave or a small region of caves that may be interconnected through passageways. Many crayfishes frequenting cave habitats are facultative species (= troglophiles) (although none in Arkansas are) and commonly live in both cave and surface waters, especially those that are influenced by spring sources. Some cave crayfishes that are known only from subterranean habitats do not possess the well-developed morphological adaptations to their subterranean environment as do highly specialized troglobites. The troglophiles and less modified troglobites probably represent transitional phases through initial behavioral and physiological adaptations toward becoming highly adapted to compete in and more efficiently utilize the underground environment.
Three species of crayfishes inhabit caves in northern Arkansas; all have evolutionary adaptations to living in caves, and all are protected by state and federal laws. They include the Benton County cave crayfish (Cambarus aculabrum), Bristly Cave crayfish (C. setosus), and Hell Creek Cave crayfish (C. zophonastes).
The Benton County cave crayfish was described in 1987 and is currently known from subterranean streams in four caves (Bear Hollow, Elm Springs, Logan, and Old Pendergrass) in and around Benton and Washington counties. It is not considered an Arkansas endemic species because fifty-eight percent of one of the Benton County cave zones is actually within the neighboring state of Missouri. It is a small crayfish with an overall body length of about 48 mm (1.8 in.) and is a federally endangered cave troglobitic crayfish that is also listed as critically imperiled (S1) in the state according to NatureServe, with an IUCN Red List Status of Critically Endangered. The type locality—Logan Cave (Benton County), part of the federally protected Logan Cave National Wildlife Refuge—is a dendritic stream channel cave located in the Mississippian cherty-limestone, Boone Formation of the Springfield Plateau. Since 2004, extensive survey efforts in and around the site have revealed no additional specimens. The primary rationale for federal listing of C. aculabrum is that habitat degradation from groundwater pollution still remains a serious threat at the type locality. Very little is known about the life history and ecology of C. aculabrum. This crayfish feeds on organic matter washed into the cave from the surface, and on bat guano. It has been reported to be preyed on by the banded sculpin (Cottus carolinae). Life history and ecology studies have not been conducted due to the imminent harm that such studies pose to a cryptic species with very low population numbers. Males are reproductively active during October through February. In addition, females carrying eggs and young have been observed during surveys. Threats to this species include direct mortality when they are trampled on by cave explorers and trespassers. Gates have been put in place at the caves to protect them, but vandalism is still a threat. Pollution of the groundwater in the caves was the main reason the organism was federally listed. Individuals are sometimes washed out of caves during floods, leading to mortality. Genetic studies conducted on C. aculabrum in the 1990s suggest that this crayfish is genetically distinct from the other cave crayfish species.
The Bristly Cave crayfish was added to the state list in 2006. This troglobitic species is known in the state from only two widely separated caves in Benton and Independence counties. However, it is also known from at least nine counties in southwestern Missouri and has been found in extreme northeastern Oklahoma, many with declining populations. The population in Benton County may be at risk because the habitat is located in a watershed that contains several municipal sewage treatment outflows and numerous confined animal feeding operations (livestock and poultry) that produce nitrates. This crayfish is listed as S1 (critically imperiled) in Arkansas according to NatureServe with an IUCN Red List Status of Near Threatened.
The Hell Creek Cave crayfish was the first cave crayfish discovered in Arkansas, and it was described in 1964 from Hell Creek Cave (Stone County) by the world’s expert on crayfishes, Dr. Horton H. Hobbs Jr. (1914‒1994) of the Smithsonian Institution. Hobbs described about 168 species of crayfishes, including twenty-nine genera and subgenera. Cambarus zophonastes is a true Arkansas endemic that was later discovered in a second Stone County locality, Nesbitt Spring Cave. Within the cave environment, it has been observed on the sides of steep rocks and on the mud bottom of the cave stream. It is threatened by a variety of negative factors, including groundwater pollution, human disturbance, and a reduction in nutrient availability. This species was designated in 1987 as federally endangered in the United States, listed as S1 (critically imperiled) in Arkansas by NatureServe, and has an IUCN Red List Status of Critically Endangered.
In adjacent Oklahoma, the Delaware County cave crayfish (C. subterraneus) and Oklahoma cave crayfish (C. tartarus) occur. The former is known only from four sites in three separate caves (Jail, Star, and Twin [type locality]) in Delaware County, while the latter is endemic to three subterranean waterways in the northeastern part of the state, the Stansberry-January cave system of the Spavinaw Creek drainage, Delaware County. Extensive searches have been conducted to locate additional C. subterraneus populations in other caves, but as of 2020 none have been recorded. The cave system in which C. setosus occurs is under the protection of the U.S. Fish and Wildlife Service as part of its Ozark Plateau National Wildlife Refuge. The species was also recently reported from Long’s Cave (an additional cave but fragmented system). Both are ranked S1 (critically imperiled) by NatureServe, and they are vulnerable to groundwater pollution or alteration or other forms of habitat degradation.
Other Arkansas crayfishes are known to enter caves in the state. Because crayfishes are negatively phototropic, epigean species do not hesitate to enter caves. Any decapod crustacean could be a visitor to subterranean waters (= trogloxene), and therefore any epigean species that finds the stenothermal habitat near or in a spring source an affable residence could enter the subterranean waters but usually only to the twilight zone of caves. Examples of crayfishes that are not considered “cave crayfishes” but have been collected in caves include the longpincered crayfish (Faxonius longidigitus) and ringed crayfish (F. neglectus).
Some noteworthy examples of other North American cave crayfishes include the Caney Mountain cave crayfish (Faxonius stygocaneyi), Cumberland Plateau cave crayfish (O. barri), Dougherty Plain cave crayfish (C. cryptodytes), Salem cave crayfish (C. hubrichti), Alabama cave crayfish (C. jonesi), Tennessee cave crayfish (O. incomptus), Appalachian cave crayfish (O. packardi), and White Spring cave crayfish (C. veitchorum). Most, if not all, are protected species and are found in just a few caves within their range.
For additional information:
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Bouchard, Raymond W., and Henry W. Robison. “An Inventory of the Decapod Crustaceans (Crayfishes and Shrimps) of Arkansas with a Discussion of their Habitats.” Proceedings of the Arkansas Academy of Science 34 (1980): 22‒30. Online at https://scholarworks.uark.edu/jaas/vol34/iss1/9/ (accessed January 10, 2020).
Crandall, Keith A., and Jennifer E. Buhay. “Global Diversity of Crayfish (Astacidae, Cambaridae, and Parastacidae: Decapoda) in Freshwater.” Hydrobiologica 595 (2008): 295‒301.
Crandall, Keith A., and S. De Grave. “An Updated Classification of the Freshwater Crayfishes (Decapoda: Astacidea) of the World, With a Complete Species List.” Journal of Crustacean Biology 37 (2017): 1‒39.
Graening, G. O., Horton H. Hobbs III, Michael E. Slay, William R. Elliott, and Arthur V. Brown. “Status Update for Bristly Cave Crayfish, Cambarus setosus (Decapoda: Cambaridae) and Range Extension into Arkansas.” Southwestern Naturalist 51 (2006): 382–391.
Graening, G. O., Danté B. Fenolio, and Michael E. Slay. Cave Life of Oklahoma and Arkansas: Exploration and Conservation of Subterranean Biodiversity. Norman: University of Oklahoma Press, 2011.
Graening, G. O., J. B. Koppelman, Brian K. Wagner, Michael E. Slay, and C. L. Brickey. “Range Extension and Status Update of the Endangered Hell Creek Cave Crayfish, Cambarus zophonastes (Decapoda: Cambaridae).” Southwestern Naturalist 51 (2006): 392–396.
Graening, G. O., Michael E. Slay, Arthur V. Brown, and J. B. Koppelman. “Status and Distribution of the Endangered Benton Cave Crayfish, Cambarus aculabrum (Decapoda: Cambaridae).” Southwestern Naturalist 51 (2006): 376–381.
Hobbs, Horton H., Jr. “Crayfishes (Astacidae) of North and Middle America.” U.S. Environmental Protection Agency Biota of Freshwater Ecosystems Identification Manual 9 (1972): 1–173.
———. “An Illustrated Checklist of the American Crayfishes (Decapoda: Astacidae, Cambaridae, and Parastacidae.” Washington DC: Smithsonian Contributions to Zoology 480 (1989): 1‒236.
———. “A New Cave-Dwelling Crayfish from the Greenbrier Drainage System, West Virginia (Decapoda, Astacidae).” Proceedings of the Biological Society of Washington 77 (1964): 189‒194.
Hobbs, Horton H., Jr., and Thomas C. Barr Jr. “Origins and Affinities of the Troglobitic Crayfishes of North America (Decapoda: Astacidae) II. Genus Orconectes.” Smithsonian Contributions to Zoology 105 (1972): 1‒84.
Hobbs, Horton H., Jr., and M. S. Bedinger. “New Troglobitic Crayfish of the Genus Cambarus (Decapoda, Astacidae) from Arkansas with a Note on the Range of Cambarus cryptodytes.” Proceedings of the Biological Society of Washington 77 (1964): 9–15.
Hobbs, Horton H., Jr., and Arthur V. Brown. “A New Troglobitic Crayfish from Northwestern Arkansas.” Proceedings of the Biological Society of Washington 100 (1987): 1040–1048.
Hobbs, Horton H., Jr., and Martha R. Cooper. “A New Troglobitic Crayfish from Oklahoma (Decapoda: Astacidae).” Proceedings of the Biological Society of Washington 85 (1972): 49‒56.
Hobbs, Horton H., Jr., Horton H. Hobbs III, and M. A. Daniel. “A Review of the Troglobitic Decapod Crustaceans of the Americas.” Smithsonian Contributions to Zoology 244 (1977): 1‒183.
Koppelman, J. B., and D. E. Figg. “Genetic Estimates of Variability and Relatedness for Conservation of an Ozark Cave Crayfish Species Complex.” Conservation Biology 9 (1995): 1288‒1294.
Pflieger, William L. The Crayfishes of Missouri. Jefferson City: Missouri Department of Conservation, 1996.
Reimer, Rollin D. The Crawfish of Arkansas. MS thesis. Fayetteville: University of Arkansas, 1963.
Robison, Henry W., and Robert T. Allen. Only in Arkansas. Fayetteville: University of Arkansas Press, 1995.
Robison, Henry W., Keith A. Crandall, and Chris T. McAllister. “An Annotated Checklist of Crayfishes (Decapoda: Cambaridae) of Arkansas.” Journal of the Arkansas Academy of Science 71 (2017): 17‒34. Online at https://scholarworks.uark.edu/jaas/vol71/iss1/9/ (accessed January 10, 2020).
Robison, Henry W., and Chris T. McAllister. “The Endemic Biota of Oklahoma.” Proceedings of the Oklahoma Academy of Science 92 (2012): 21‒28.
Spanjer, G. R., and M. L. Cipollini. “Relationship Between Physiochemical Factors and Distribution of Stygobitic Crayfishes in Southeastern Caves.” Southeastern Naturalist 5 (2006): 17‒26.
Taylor Christopher A, Guether A. Schuster, John E. Cooper, R. J. DiStefano, A. G. Eversole, P Hamr, Horton H. Hobbs, Jr., Henry W. Robison, C. E. Skelton, and R. F. Thoma. “A Reassessment of the Conservation Status of Crayfishes of the United States and Canada After 10+ years of Increased Awareness.” Fisheries 32 (2007): 272–389.
Taylor, Christopher A., M. L. Warren, J. F. Fitzpatrick Jr., Horton H. Hobbs, III, R. F. Jezerinac, William L. Pflieger, and Henry W. Robison. “Conservation Status of Crayfishes of the United States and Canada.” Fisheries 21 (1996): 25–38.
Williams, A. B. “Speciation and Distribution of the Crayfishes of the Ozark Plateaus and Ouachita Provinces.” University of Kansas Science Bulletin 36 (1954): 803‒918.
Henry W. Robison
Chris T. McAllister
Eastern Oklahoma State College
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