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. The publication of this manuscript
was supported, in part, by the US Geological Survey Cooperative Research Unit
Program, including the West Virginia Cooperative Fish and Wildlife Research Unit.
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