N35 2019 Northeastern Naturalist Notes Vol. 26, No. 3 S.M. Hartzell Observation of a Cambarus bartonii bartonii (Common Crayfish) Overwintering in a Terrestrial Winter Microhabitat Sean M. Hartzell* Abstract - In cool climates, crayfish that are not primary burrowing species are typically thought to retreat into deeper waters in winter and may seek refuge in small aquatic burrows or interstitial spaces associated with aquatic substrates. Herein, I report a novel observation of a juvenile Cambarus bartonii bartonii (Common Crayfish) during winter within eastern Pennsylvania occupying a terrestrial microhabitat consisting of moist, terrestrial leaf litter associated with a small depression in an upland forest. I found the crayfish in association with a small aggregation of Plethodon cinereus (Eastern Red-backed Salamander). Requirements of a hibernaculum by the salamanders with sufficient moisture and buffered from freezing may have also provided sufficient conditions for the crayfish to utilize the depression as a winter refugium. During winter in cooler climates, crayfish that occupy surface waters (i.e., tertiary burrowers; Hobbs 1981) are typically thought to respond by moving into deeper waters for overwintering (Crocker and Barr 1968, Ortmann 1906, Prins 1968). Crayfish may remain active in deeper waters throughout the winter, although a number of studies have indicated an association between reduced activity in crayfish and cooler water temperatures during winter, such as studies on crayfish in the genera Faxonius (formerly Orconectes; Crandall and De Grave 2017) and Pacificastus (e.g., Bovbjerg 1952; Bubb et al. 2002, 2004; Flint 1977; Prins 1968). When inactive during winter, crayfish have been found to retreat into interstitial spaces below substrate or burrow into streambanks (Prins 1968). Conversely, some crayfish species could become more active during winter. For instance, Cambarus thomai (Jezerinac) (Little Brown Mudbug), a primary burrowing species, may increase activity during winter, as it has been reported to occupy surface waters only during winter months (Loughman and Simon 2011). This latter observation suggests the winter biology of certain crayfish species is presently understudied, particularly for members of the genus Cambarus. Few observations appear to have been published regarding winter behavior of Cambarus bartonii bartonii (Fabricus) (Common Crayfish), a medium-sized, tertiary burrowing crayfish that typically occupies springs, small to medium-sized streams, and occasionally lentic habitats in eastern North America (Hobbs 1989). This species may retreat to deeper waters in winter and/or burrow into the streambank or seek refugium within interstitial spaces. For instance, Hamr and Berrill (1985) collected Common Crayfish during winter within a larger river, but not within a smaller stream, suggesting that individuals at the latter site may have burrowed or migrated to deeper waters during winter. Common Crayfish often occupy springs and seeps (Hobbs 1989, Ortmann 1906) and may be collected in these habitats during winter (S.M. Hartzell, pers. observ.). However, no previous studies have reported observations of this species occupying a terrestrial refugium during winter, Herein, I describe a novel observation of a young Common Crayfish found during winter in eastern Pennsylvania occupying a terrestrial microhabitat associated with an overwintering aggregation of Plethodon cinereus (Green) (Eastern Red-backed Salamander). *Department of Biological and Allied Health Sciences, Bloomsburg University of Pennsylvania, Bloomsburg, PA 17815; seanhartzell77@gmail.com. Manuscript Editor: David Yozzo Notes of the Northeastern Naturalist, Issue 26/3, 2019 2019 Northeastern Naturalist Notes Vol. 26, No. 3 N36 S.M. Hartzell On 13 December 2016 at 1200 h, I collected a small (~4 cm total length) Common Crayfish underneath moist leaf litter within a small depression along an abandoned roadway ~2 km south of Mechanicsville, Montour County, PA (40°57'05.5"N, 76°34'40.7"W). The feature that contained the crayfish consisted of a depression approximately 1.5 m in length and 1 m in width along a hillside slope within an upland mixed-deciduous forest. The depression did not appear to be immediately associated with any perennial or ephemeral water source such as a stream, spring, or ephemeral runoff channel; however, a small spring was located ~20 m from the site of the depression. The depression contained a dense concentration of moist leaf litter, but was not inundated with water during the observation reported herein. The crayfish was located ~8–10 cm beneath the surface of the leaf litter and associated with a small aggregation of 3 Eastern Red-backed Salamanders. The crayfish was alive but torpid. The temperature of the leaf litter was 4 °C, as measured with a mercury thermometer. Following these observations, I returned the crayfish and salamanders to their initial positions in the leaf pile and covered them with leaves. Although weather data from the general locality of the observation site during the period leading up to the observation are unavailable, data from a regional weather station located ~43 km NW of the site indicate that the weather the proceeding week consisted of mean temperatures varying from -2.2 °C to 4.4 °C, with temperatures typically ≤0 °C (Weather Underground 2019). No precipitation had occurred for 10 d prior to the observation reported herein, with the exception of ~5 cm snowfall the day prior (Weather Underground 2019). To my knowledge, the observation reported herein appears to be unique and may suggest that the crayfish could have been utilizing the moist leaf litter as a refugium to overwinter. This possibility may be supported by the fact that several Eastern Red-backed Salamanders were associated with the leaf litter containing the crayfish. Eastern Red-backed Salamanders are not freeze-tolerant and must hibernate in refugia that do not freeze (Casper 2005). Many terrestrial or semi-terrestrial salamanders overwinter underneath leaf litter (Bishop 1941), suggesting that the Eastern Red-backed Salamanders were utilizing the leaf litter that contained the Common Crayfish as a hibernaculum. Eastern Red-backed Salamanders are lungless and require moist conditions for cutaneous respiration (Casper 2005, Petranka 1998). These requirements by Eastern Red-backed Salamanders may suggest that the leaf litter was sufficiently moist and buffered from freezing to allow the Common Crayfish to utilize this microhabitat as a terrestrial refugium during winter. Given the cold temperatures and lack of heavy precipitation in the proceeding days, the crayfish may have occupied the depression for at least some time prior to the date of its discovery reported herein. Due to the occurrence of the depression in upland habitat and its distance from any permanent streams or ephemeral channels, it is unlikely that the crayfish’s presence at this location was the result of being washed there during a severe precipitation and/or high water event. Further studies could survey similar habitats during winter to elucidate the frequency that Common Crayfish or other crayfish species may occupy terrestrial refugium during winter. Acknowledgments. I thank 2 anonymous reviewers for their time and comments which facilitated the improvement of this manuscript. Additionally, I think the Bloomsburg University College of Science and Technology and Katherine Burke for support during the preparation of this manuscript. Funding towards this publication was generously provided by the Bloomsburg University Office of Graduate Studies and Sponsored Research. Literature Cited Bishop, S.C. 1941. The Salamanders of New York. New York State Museum Bulletin 324:1–365. Bovbjerg, R.V. 1958. Comparative ecology and physiology of the crayfish Orconectes propinquus and Cambarus fodiens. Physiological Zoology 25:34–56. N37 2019 Northeastern Naturalist Notes Vol. 26, No. 3 S.M. Hartzell Bubb, D.H., M.C. Lucas, and T.J. Thom. 2002. Winter movements and activity of Signal Crayfish, Pacifastacus leniusculus, in an upland river, determined by radio telemetry. Hydrobiologia 483:111–1119. Bubb, D.H., T. J. Thom, and M.C. Lucas. 2004. 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