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Ecology of Cambarus dubius (Upland Burrowing Crayfish) in North-central West Virginia
Zachary J. Loughman

Southeastern Naturalist, Volume 9, Special Issue 3 (2010): 217–230

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Conservation, Biology, and Natural History of Crayfishes from the Southern US 2010 Southeastern Naturalist 9(Special Issue 3):217–230 Ecology of Cambarus dubius (Upland Burrowing Crayfish) in North-central West Virginia Zachary J. Loughman* Abstract - The ecology of primary burrowing crayfishes is poorly understood, especially for high-elevation species. An ecological study of Cambarus (Jugicambarus) dubius (Upland Burrowing Crayfish) was conducted at Terra Alta, Preston County, WV (elevation 781 m). The study sought life-history information including size at sexual maturity, age cohort designation, and age estimation. The density and distribution of burrow portals of C. dubius were examined within and near seeps in forested and disturbed habitats. Data were also collected on intraspecific usage of burrows by commensal species. Size at maturity did not differ significantly for males and females. The average age of C. dubius was 1.5 years, and the oldest individuals were estimated at 7 years. Form change of C. dubius occurred synchronously within the population, a phenomenon not previously documented with primary burrowing Cambarus. Burrow portals had highest densities within 5 m of the center of seeps in forested habitats, but reached highest densities between 10 and 25 m from the center of seeps in disturbed habitats. Many commensal species of invertebrates and vertebrates used C. dubius burrows, data that demonstrates a community-level contribution of C. dubius. Information from this study represents most of the available ecological data from the northern range of this species, and is directly relevant for management and conservation of high-elevation populations of C. dubius. Introduction Given dramatic declines of crayfish populations during the past two decades, ecological studies are needed for management and conservation of cambarid crayfishes (Fielder 1972; Schuster 1997; Taylor et al. 1996, 2007). Cambarid crayfishes comprise species with several burrowing strategies, including primary, secondary, and tertiary burrowers (Taylor and Schuster 2005). Most research studies on cambarid crayfishes have focused on the ecology of secondary and tertiary burrowers (Baker et al. 2008, Corey 1988, Hamr and Berrill 1985, Jezerinac 1982, Muck et al. 2002, Payne 1971, Prins 1968, Riggert et al. 1999, Smart 1962, Smith 1953, Tack 1941, Van Deventer 1937), but the ecology of primary burrowing crayfishes is poorly understood. Primary burrowing cambarid crayfishes occur in several genera: Cambarus, Distocambarus, Fallicambarus, and Procambarus. Researchers have mostly studied the genus Fallicambarus (Hobbs and Whiteman 1991, Johnston and Figiel 1997, Robison and Crump 2004, Welch et al. 2008), particularly F. *Department of Natural Sciences and Mathematics, West Liberty University, West Liberty, WV 26074; zloughman@westliberty.edu. 218 Southeastern Naturalist Vol. 9, Special Issue 3 fodiens (Cottle) (Digger Crayfish) (Bovjberg 1952, Norrocky 1991, Williams et al. 1974). The ecology of P. gracilis (Bundy) (Prairie Crayfish) was investigated by Hobbs and Rewolinksi (1985). Others have examined Cambarus batchii Schuster (Bluegrass Crayfish; Tertuliani 1991), Cambarus carolinus (Erichson) (Red Burrowing Crayfish; Dewees 1972), Cambarus diogenes Girard (Devil Crayfish; Grow 1981, Grow and Merchant 1980), and Cambarus dubius Faxon (Upland Burrowing Crayfish; Dewees 1972). This study focused on the ecology of C. dubius (Fig. 1), a montane species present in central and southern Appalachia (Dewees 1972, Jezerinac et al. 1995, Taylor and Schuster 2005). Work performed in the present study builds on previous research of Dewees (1972). Dewees (1972) critically reviewed the biology of C. dubius in its southern range, documented its social behavior, and provided information on its natural history. Jezerinac et al. (1995) reported on morphometric data as well as anecdotal observations of C. dubius from a few populations in West Virginia. The objectives of my study were to document life-history and demographic data of C. dubius from the northern part of its distribution. Additional objectives included the estimation of burrow density and distribution, and documenting the use of burrows by commensal species. Methods Study site Study sites were located at Oglebay Institutes’ Field Station, Terra Alta, Preston County, WV. The field station is at an elevation of 781 m and is Figure 1. Adult form I male Cambarus dubius from Terra Alta, WV. 2010 Z.J. Loughman 219 approximately 2 km from the type locality of C. dubius. Six study sites were comprised of two habitat types: three seeps in forested habitat and three seeps in disturbed habitat. Forested habitats contained mostly native floral associations, mature forest canopies, and moderate human impacts. Disturbed habitats were characterized by nonnative floral associations, manipulated forest canopies, and moderate to extreme human use. Disturbed habitats were primarily comprised of residential yards and adjacent roadside ditches. Capture methods Nocturnal searches for C. dubius were conducted within and near seeps in forested and disturbed habitats, and began at dusk and concluded when crayfish surface activity ceased (usually between 23:00–1:00 h). Crayfish cruising on the ground or resting at burrow portals were collected by hand during nocturnal searches. Active burrows were excavated for capture of underrepresented demographics and juveniles, and were identified by recently exhumed mud in the form of organized pellets or mud aprons at burrow portals. Burrows were first excavated to a common resting chamber. Once the resting chamber was breached, the resting chamber was filled with water and plunged vigorously (by hand with closed fist) to dislodge the crayfish or elicit its movement to the surface (Hobbs 1942, 1981; Jezerinac et al. 1995; Simon 2001; Taylor and Schuster 2005). The burrow was completely excavated if plunging failed to produce the crayfish. Life history and demographics Immediately following capture, total carapace length (TCL), palm length (PL), and areola lengths (AL) were measured to the nearest mm using dial calipers. Additionally, abdominal length (AbL) and width (AbW) were measured on females. Crayfish were marked by uropod clips and released at the point of capture. For ovigerous females, eggs were counted and measurements were obtained for the mean egg diameter and mean egg number per compliment. Additionally, a correlation analysis examined the relationship between TCL and total egg compliment. Collecting efforts occurred sporadically throughout the spring and summer season in 2005 and 2006, and monthly during the 2007 activity season (April–October). Total carapace lengths were used to produce age histograms for males, females, and a pooled sample of the overall population. Mean TCL values were estimated for form I and form II males and for ovigerous and nonovigerous females. Minimum size at maturity was estimated as TCL values of the smallest form I male and the smallest female with active glair glands. Data on growth of neonates were collected by repeat measurements on individuals from a single clutch. For this study, a female carrying eyed instars was captured, marked, and released at her burrow in April 2007. Neonates were captured and measured for five consecutive months, ending in August 2007. Total carapace lengths were used to calculate growth rates and molt increments for the first 5 months after hatching for this clutch of neonates. 220 Southeastern Naturalist Vol. 9, Special Issue 3 Using these data in conjunction with molt frequencies from Dewees (1972) and the methods of Hamr and Berrill (1985), a growth curve was generated for C. dubius. Density and distribution of burrow portals The density and distribution of burrow portals were estimated at seeps in three forested habitats and three disturbed habitats. Densities of burrow portals (and standard errors) were estimated at 0, 5, 10, 15, 20, 25, and 30 m from the center of each seep using T-square sampling and analysis (Greenwood 1996). For each habitat type, densities at 5-m intervals were estimated from pooled distances between 18 random points and the nearest burrow portal locations following methods of Greenwood (1996). Greenwood (1996) indicates that the T-square method is relatively robust to deviations from a random distribution. We examined the distribution of burrow portals at each 5-m interval with a measure for random distribution (t'), where a t' value > 1.96 indicates a uniform distribution and a t' value < -1.96 supports a clumped distribution (Greenwood 1996). Utilization of burrows by other species During all search events, data were collected on commensal taxa utilizing C. dubius burrows including species identification, behaviors, and demographics. Although not the primary study objective, these data documented a community-level contribution of C. dubius, and are relevant to the management and conservation of the species. Results The TCL measurements of form I and form II males (n = 116) ranged from 5.5 mm to 39.7 mm (Fig. 2A). For 51 form I males, TCL ranged from 21.4 mm to 39.7 mm, with the mean TCL = 30.0 mm (Table 1). For form II males (n = 65), TCL ranged from 5.5 mm to 32.8 mm, with a mean of 22.8 mm (Table 1). Non-ovigerous females (n = 146) had a mean TCL of 25.9 mm (Table 1) and ranged from 5.5 mm to 44.3 mm (Fig. 2B). Pooled TCL measurements of males and females ranged from 5.5 mm to 44.3 mm, with a mean of 25.8 mm (Fig. 3). In addition to TCL, means of measurements of PL, AL, AbL, and AbW of ovigerous females exceeded those of non-ovigerous Table 1. Means (standard deviations in parentheses) and sample sizes (n) of total carapace lengths (TCL), palm length (PL), areola length (AL), abdominal length (AbL), and abdominal width (AbW) of Cambarus dubius from Terra Alta, WV (asterisks denote measurements not taken). Non-ovigerous Ovigerous Form I Form II Female female male male Measurement n = 146 n = 7 n = 51 n = 65 TCL 25.9 (9.0) 32.8 (3.9) 30.0 (2.9) 22.8 (6.0) PL 5.2 (1.9) 6.0 (1.9) 5.9 (0.86) 4.5 (1.0) AL 12.2 (2.3) 13.2 (2.1) 12.8 (0.55) 10.2 (0.22) AbL 25.6 (6.5) 27.1 (9.1) * * AbW 11.1 (1.8) 15.9 (17.8) * * 2010 Z.J. Loughman 221 females (Table 1). Mean values for PL and AL of form I males were larger than those of form II males (Table 1). Males underwent seasonal shifts in form change during spring, summer, and fall. Based on a pooled dataset (2005–2007), the form I condition represented less than 70% of the male sample size during April, May, August, September, October, and November (Fig. 4A). During June, July, and August, less than 65% of Figure 2. Length-frequency histograms of total carapace length in male (A) and female (B) Cambarus dubius from Terra Alta, WV. 222 Southeastern Naturalist Vol. 9, Special Issue 3 Figure 3. Length frequency histogram of total carapace length for a pooled sample of male and female Cambarus dubius from Terra Alta, WV. Figure 4. Seasonality of the frequency of (A) form I and form II males and (B) ovigerous females, non-ovigerous females, and glair presence in females of Cambarus dubius from Terra Alta, WV. 2010 Z.J. Loughman 223 males were in form II condition. Molting between forms occurred primarily in June and September (Fig. 4A). The minimum TCL size at maturity for males was 21.4 mm. Reproductive stage seasonality was documented for females of C. dubius as well. Females with active glair glands were observed primarily during April, May, and June, and occasionally in July and November (Fig. 4B). A TCL of 20.7 mm was recorded for the smallest female with active glair glands. During August through October, females were in a non-reproductive state, lacking glair or pleopodal eggs (Fig. 4B). Though zero individuals were captured during winter months, the high percentage of females with active glair glands in April provides evidence of glair maturation during winter. Ovigerous females (n = 10) were collected on 21 May; 9, 19, and 26 June; and 9 July (Fig. 4b). Mean TCL for six ovigerous females was 32.8 mm, and ranged from 30.3 to 39.9 mm (Table 2). Egg counts ranged from 12 to 56, and averaged 33 eggs per compliment. Mean egg diameter was 2.1 mm. No relationship existed in this population between TCL and total egg compliment (r2 = 0.008, P = 0.864). Growth data for individuals from a single clutch of neonates were measured monthly from May–August 2007. From repeated measurements of a minimum of 16 neonates per month, mean TCL increased from 5.5 mm in April to 12.6 mm in August, with an average monthly increase of 1.78 mm. Molt frequency slowed during September and October, with only a 0.5-mm increase in size during these months. A growth curve (Fig. 5) was generated using TCL data from neonates and the three peaks in the TCL distribution of pooled male and female data (Fig. 3). Based on the growth curve, an age of 17 months (± 1 month) was estimated for individuals with a 21-mm TCL. Individuals with 29-mm TCL and 38-mm TCL were estimated at 30 months (± 2 months) and 41 months (± 8 months), respectively (Fig. 5). Eighteen months (± 2 months) was the mean age for the mean TCL (25.8 mm) within the population. Median age of the population was 21 months (± 2 months). An age of 83 months (± 10 months) was estimated for the largest members of the population. Table 2. Estimates of burrow portal density (standard error in parentheses) and test statistics (t') for burrow portal distributions of Cambarus dubius within seeps in forested and disturbed habitats at Terra Alta, WV. A t' value between -1.96 and 1.96 indicates a random distribution, whereas those above 1.96 and below -1.96 indicate uniform and clumped distributions, respectively (Greenwood 1996). Distance (m) from center of seep Seep habitat Estimate 0 5 10 15 20 25 30 Forested Burrow portals per m2 11.6 3.0 0.28 0.24 0.15 0.30 0.13 (0.04) (0.12) (1.7) (2.5) (3.0) (2.8) (3.0) t' value -2.14 -2.00 1.56 1.22 1.23 2.28 3.79 Disturbed Burrow portals per m2 0.47 0.88 4.09 4.38 2.64 3.73 0.37 (1.6) (0.56) (0.07) (0.79) (0.14) (0.05) (1.6) t' value -1.19 1.8 1.02 1.41 1.37 1.83 -0.32 224 Southeastern Naturalist Vol. 9, Special Issue 3 The estimates of density and distribution of burrow portals differed for seeps within forested and disturbed habitats. Densities of burrow portals were highest within 5 m of the central area of seeps in forested habitats, but were highest within 10 to 25 m of the central seep area in disturbed habitats (Fig. 6). The highest density of burrow portals (11.6 portals m-2) was in the center of forested seeps, and drastically declined with distance from the seep center. Burrow portal densities in disturbed habitat did not follow a declining trend with increasing distance from the seep, and peaked (4.38 portals m-2) at 15 m from the seep center (Fig. 6). The distributions of burrow portals were clumped in forested seeps at distances of 0 m and 5 m (0 m: t' = -2.14, 5 m: t' = 2.00), distributed randomly at 10 m and 20 m (10 m: t'= 1.56, 15 m: t' = 1.22, 20 m: t' = 1.23) and uniformly distributed at 25 m and 30 m (25 m: t' = 2.28, 30 m: t' = 3.79). The distributions of burrow portals were randomly distributed at all 5-m intervals within disturbed habitats. Several commensal species were observed utilizing burrows of C. dubius. Plethodontid salamanders were documented multiple times within inactive burrows. Plethodon glutinosus (Green) (Northern Slimy Salamander), in particular large adult males, utilized burrows frequently and were observed with the first third of their bodies protruding from burrow portals. Desmognathus ochrophaeus Cope (Allegheny Mountain Dusky Salamander) were noted resting within burrows, though with less frequency. Thamnophis s. sirtalis Brown (Eastern Garter Snake) used burrows on two occasions to avoid capture. When we excavated a C. dubius burrow, a Peromyscus maniculatus (Wagner) (Deer Mouse) was encountered in the resting chamber with an Figure 5. Estimated growth curve of a population of Cambarus dubius from Terra Alta, WV. Thinner plotted lines are 95% confidence intervals (y = 11.61 ln (x) -8.6319). 2010 Z.J. Loughman 225 active nest. Terrestrial invertebrates were observed in burrow portals during this study. Female wolf spiders (lycosidae) carrying young were documented in burrows more often than any other species of arthropod. Cambarus carinirostris Hay (Rock Crawfish) and C. dubius occurred sympatrically at the Terra Alta site, but rarely occurred syntopically. Syntopy between the two species occurred during inundation of seeps and roadside ditches following rain. During these events, headwater streams flooded into seeps, at which time C. carinirostris gained access to C. dubius habitats. On the few occasions C. carinirostris were observed in direct association with C. dubius, interactions appeared to be benign in nature. Discussion Morphometrics of the Terra Alta population were similar to those of southern populations (Dewees 1972) and other West Virginia populations (Jezerinac et al. 1995). Mean TCL of females was larger than that reported by Dewees (1972; mean = 22.6), but smaller than other West Virginia specimens (mean = 33.7, n = 124; Jezerinac et al. 1995). The mean TCL of form I males was larger than reported by Dewees (1972; mean = 21.4) and smaller than that reported by Jezerinac et al. (1995; mean = 33.7, n = 30). The same trends were observed with form II males. In Tennessee, Dewees (1972) collected ovigerous females between 2 and 31 May. Jezerinac et al. (1995) collected ovigerous females on 26 and 28 May; 22, 25, and 29 June; and 6 July; which are congruent with collection dates of ovigerous females in this study. Figure 6. Estimates of burrow portal densities of Cambarus dubius at distances from seep centers in forested (black line) and disturbed (gray line) habitat. 226 Southeastern Naturalist Vol. 9, Special Issue 3 Cambarus dubius populations at Terra Alta molt in relation to female reproductive state. Form change of C. dubius occurred synchronously within the population, a phenomenon not previously documented with primary burrowing Cambarus. The relationship of male form state (Fig. 4a) to female reproductive condition (Fig. 4b) is more indicative of seasonal form changes encountered with Orconectes (Fieldner 1972, Jezerinac 1982, Jezerinac et al. 1995, Taylor and Schuster 2005). Others have reported the male reproductive condition of Cambarus as asynchronous with gross seasonal changes during summer and fall rather than male form change associated with specific months (Hamr and Berrill 1985, Smart 1962). Hamr and Berrill (1985) observed this seasonal form change in C. bartonii bartonii (Fabricius) (Common Crayfish) and C. robustus Girard (Big Water Crayfish) in Ontario. Form change in males occurred in late summer with a consistent rate of molting over a 3-month period. Smart (1962) documented a mass form change in male Cambarus longulus Girard (Atlantic Slope Crayfish), following youngof- the-year’s molt into sexual maturity. After this molt, male form became asynchronous, spanning a 3-month period. Mating likely occurs during fall, winter, and spring in the population of C. dubius at Terra Alta, and was observed in captive individuals on 1 March 2006 (Z. Loughman, pers. observ.). Surface activity begins in late March and April following seasonal warming. Interestingly, the presence of females with neonates in April indicates egg extrusion and hatching during fall or winter months. Females with pleopodal instars occurred rarely during this time in collections and likely represent the exception rather than the norm. Age-TCL relationships were similar to that reported for C. dubius in Tennessee (Dewees 1972), where the mean age was estimated to be 1.5 years, with oldest individuals estimated at less than 7 years. With the exception of Dewees (1972), the literature lacks detailed studies of age-TCL relationships for primary burrowing Cambarus. Norrocky (1991) recaptured individuals of F. fodiens over a 7-year period in northwestern Ohio, which represents the oldest documented age for individuals of any burrowing species; however, he did not calculate the relationship between TCL and age. Norrocky’s data (1991) are mirrored by age estimates of the largest C. dubius collected during this study. If the lower confidence interval of the age curve is extrapolated, the largest individuals of the Terra Alta population could be in excess of 8 years in age. These estimates of C. dubius age are greater than the maximum for most epigean species. Hamr and Berill (1985) estimated a maximum age of 4 years for C. robustus and C. b. bartonii. Corey (1990) documented a maximum age of 3 years for C. robustus in the Kawartha Lakes region of Ontario, and Smart (1962) documented the life history of C. longulus in Virginia and indicated a maximum age of 3 years for both sexes. Parental females tolerated neonates for months after detachment, with neonates observed in female burrows on 9 occasions. In one instance, neonates resided within their mother’s burrow throughout the activity season (April–October), with no evidence of mass dispersion from the burrow. Why 2010 Z.J. Loughman 227 tolerance is warranted by females remains unknown, but potential explanations could include limited resources within the finite area of forested seeps, lack of proper dispersal conditions over the course of the activity period, and possible social behavior. Several authors have hypothesized that social behavior exists in C. dubius. Dewees (1972) observed multiple demographics and sexes within a single burrow. Jezerinac et al. (1995) did not observe both sexes occurring within individual burrows, but did observe neonates occurring in burrows with females. At Terra Alta, multiple adults occurred occasionally in the same burrow, but only in forested seep habitats. Given the high number of burrow portals distributed centrally in seeps of forested habitat (11.6 burrow portals per m2), it is likely that individuals excavate into burrows of conspecifics, ultimately occupying the same burrow. Though disturbed habitats (yards and roadside ditches) were used by C. dubius, highest densities of burrow portals occurred in centers of forested seeps, the only habitat with clumped distribution of burrow portals (Table 2). Forested areas promote seep persistence during summer months (Colburn 2004), and likely desiccate at a slower rate than that of disturbed habitats (March and Robson 2006). At ground level, relative humidity levels were considerably lower in disturbed versus forested seeps (Z. Loughman, unpubl. data). The density of burrow portals declined with distance from the seep center suggesting a relationship between water availability and burrow density. Higher burrow densities were distant from seep centers in disturbed habitats, and possibly reflect drainage alteration and the use of ditch habitats. Surface behavior in C. dubius was positively correlated to relative humidity (Z. Loughman, unpubl. data). Given that forested seeps maintain humidity levels longer into the activity season, populations present within forests are granted longer surface activity than those in disturbed settings. This may explain forested seep use by C. dubius and denser burrow portal per m2 counts occurring in this habitat. Similar preference for forested habitat over disturbed habitat was observed in the Australian burrowing crayfishes Engaeus sericatus Clark and Geocherax gracilis Clark (March and Robson 2006). Burrow densities in both species were twice as high in forested environs than disturbed habitats, indicating forest preference in burrowing species is not just limited to cambarids. Cambarus dubius burrows provided habitat for many species. Interspecific cohabitation between C. dubius and other taxa was not observed; all observations involved commensals utilizing abandoned burrows. Among vertebrates present at the study site, salamanders appear to use C. dubius burrows more than any other taxa, and were observed using C. dubius burrows in southern West Virginia (Z. Loughman, unpubl. data) and in Tennessee (Dewees 1972). Crayfish burrows may represent important moisture refugia for salamanders during periods of drought. Further studies of commensal relationships with burrows are warranted to further define the communitylevel contribution of C. dubius. 228 Southeastern Naturalist Vol. 9, Special Issue 3 In conclusion, C. dubius life history differs from that of previously studied primary burrowers. Habitat specialization was observed in this species, with marked preference for forested seep habitats. Within these environments, C. dubius undergo a multi-year life cycle, creating microhabitats that are used by a myriad of species. Behavioral ecology, foraging ecology, and population biology still remain unknown for this species, and represent important avenues of future research, research that will aid the conservation of this and other primary burrowing crayfishes. Acknowledgments I would like to thank Nicole Garrison, Christopher Hearn, Kathleen Loughman, Matthew McKinney, Natalie Mancusso, Cody Rosettii, and Christopher Vopal for assistance in the field. I am also appreciative of manuscript reviews by Sarah Brammer, Melinda Kreisberg, and Stuart Welsh. Three anonymous reviewers’ comments and concerns increased the quality of the manuscript as well. Stuart Welsh provided publication support. Thanks are also expressed to Oglebay Institute and West Liberty University for financial support of this project. 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