• E-mail
• Print
• Comment
• Font Size
• Digg
• del.icio.us
• Discuss article

Distribution, Habitat Use and Life History of Stream-Dwelling Crayfish in the Spring River Drainage of Arkansas and Missouri With a Focus on the Imperiled Mammoth Spring Crayfish (Orconectes Marchandi)

Posted on: Wednesday, 26 October 2005, 09:01 CDT

By Flinders, C A; Magoulick, D D

ABSTRACT.-

The Mammoth Spring crayfish (Orcanectes marchandi) is listed as endangered by the American Fisheries Society's Endangered Species Committee and globally impaired by the Missouri Natural Heritage Database. Recorded at only three locations in the Spring River watershed (southern Missouri and northern Arkansas), little information exists on its range, associations with other crayfish and habitat selection. We sampled stream-dwelling crayfish with kicknets and quadrat samplers during spring-summer over 2 y in the Spring River drainage to determine distribution, relative density, habitat use, species associations, and life history characteristics of O. marchandi and other associated crayfish species. Nine crayfish species were collected in the Spring River watershed including a previously unrecorded invasive species, O. neglectus chaenodactylus, that appears to have replaced the native O. eupunctus from a portion of the watershed where it was previously abundant. The known distribution of O. marchandi was expanded from three streams in three sub-watersheds to 20 streams in eight sub-watersheds. Orconectes marchandi was found mainly in smaller streams (order 1- 3) in habitats consisting of slower moving, shallow water with gravel, pebble and cobble substrates. Oronectes marchandi was not significantly associated with any crayfish species by site. Orconectes eupunctus was found exclusively in the main-channel South Fork and Spring rivers. Current velocity, water depth and substrate were related to crayfish densities, but were crayfish species- and size-dependent. Growth rates differed among species with O. punctimanus showing the greatest growth in carapace length from winter to summer and O. marchandi showing the greatest increase in weight with carapace length. Sex ratios differed among crayfish species and by season. Additional research is needed to gain a better understanding of factors affecting habitat selection by crayfish species and to determine potential impacts of O. neglectus chaenodactylus on native populations.

INTRODUCTION

Crayfish are an important component in the function and energy flow of freshwater systems (Lorman and Magnuson, 1978; Momot, 1995; Whitledge and Rabeni, 1997). Crayfish have been shown to act as keystone species by directly and indirectly influencing populations at several trophic levels in aquatic food webs (Momot, 1995) including algae (Hart, 1992; Creed, 1994; Charlebois and Lamberti, 1996), macrophytes (Lodge and Lorman, 1987; Hanson and Chambers, 1995), macroinvertebrates (Hanson et al., 1990; Hart, 1992; Creed, 1994; Charlebois and Lamberti, 1996) and fish (Probst et al., 1984). Additionally, crayfish have been shown to be an important component in energy transfer in stream food webs, consuming substantial amounts of animal matter and algae and processing as much coarse particulate organic matter (CPOM) as all other shredders combined (Whitledge and Rabeni, 1997).

Despite their importance in aquatic systems, 51% of the 400 known crayfish species in Canada and the United States are at risk and there is relatively little information on range, life history and species associations of most species (Taylor et al, 1996; Lodge et al, 2000). The Mammoth Spring crayfish (Orconectes marchandi Hobbs) is considered imperiled in Missouri and globally (S1/S2, G2; Missouri Natural Heritage Database, 2003) and classified as endangered by the American Fisheries Society Endangered Species Committee (Taylor et al, 1996). Populations of O. marchandi were thought to be limited to the Spring River drainage of southern Missouri and northern Arkansas (Pflieger, 1996), but little quantitative information exists on distribution, habitat use or life history of this species. Described by Hobbs, Jr. (1948), the known distribution of O. marchandi was limited to three locations in south central Missouri and north central Arkansas (Williams, 1954; Pflieger, 1996). Within this range, Pflieger (1996) observed that O. marchandi was often associated with the ozark crayfish (O. ozarkae Williams), the spothanded crayfish (O. punctimanus Greaser), the coldwater crayfish (O. eupunctus Williams) and Hubbs' crayfish (Cambarus hubbsi Greaser). All of these species are endemic to the Ozarks region. Additionally, O. eupunctus was thought to be limited to the Spring River drainage and has been listed as rare in Missouri and imperiled globally (Pflieger, 1996; Missouri Natural Heritage Program, 2001). Pflieger (1996) also noted that O. marchandi was often the most abundant crayfish species where it was found, and qualitative examination of habitat use has suggested that O. marchandi occurs under rocks and rubble in shallow water (Williams, 1954) and in riffles (Pflieger, 1996). In a study examining effects of stream permanence on crayfish community structure, Flinders and Magoulick (2003) found that densities of O. marchandi were greater in intermittent than in permanent streams. However, no other studies have examined distribution, habitat use or life history of O. marchandi.

The objectives of this study were to: (1) determine distribution, relative abundance and environmental relationships of the Mammoth Spring crayfish and other associated species within the Spring River drainage basin and (2) examine selected life history characteristics of these crayfish species, including growth and length-weight relationships, with a focus on Orconectes marchandi.

METHODS

The study was conducted in the Spring River drainage in north- central Arkansas and south-central Missouri (36N 91W). Located in the Salem Plateau physiographic region of the Ozark Plateaus, the Spring River drains a total area of 3926 km^sup 2^ from Oregon and Howell counties in south-central Missouri and Fulton, Sharp, Randolph and Lawrence counties in north-central Arkansas, USA. The underlying bedrock consists predominantly of rapidly permeable dolomites, cherts and limestone, leading to a Karst topography (Adamski et al., 1995). Numerous springs ranging from small seeps to large sinkholes feed small intermittent and larger permanent streams. Stream channels generally contain well-defined riffles and pools with streambeds consisting largely of coarse gravel and pebble, cobble, boulder and bedrock. Land use in the Spring River drainage is predominantly pasture for livestock, and forestland consisting mainly of oak (Quercus spp.) and hickory (Carya spp.) trees. No major urban areas are located within the drainage.

FIG. 1.-Distribution and relative densities of the six most common crayfish species collected via kicknet sampling in 1998 and 1999. Relative densities are based on the total crayfish collected at a site. Mean densities were used at sites sampled in both years

Field sampling.-Sampling was conducted to determine the distribution and habitat use of Orconectes marchandi and associated crayfish species at 65 sites in 54 streams in the Spring River watershed from 13 February-31 May 1998 and 16 March-25 April 1999 (henceforth, small streams 1998 and 1999) (Fig. 1). Some streams were sampled in both years. Crayfish were collected using a quantitative kicknet method in which organisms were dislodged from a 1-m^sup 2^ area by thoroughly kicking and disturbing the substrate directly upstream of a 1.5 1.0-m seine net (3-mm mesh) (Mather and Stein, 1993). Crayfish dislodged from the substrate were washed into the seine net with the aid of the current and by pulling the seine through the sample area.

During the 1998 small stream survey, crayfish were collected from a minimum of three riffle, run and pool habitats in each of 36 streams. Streams and habitats sampled were selected based on accessibility but sample locations within habitats were randomly chosen. Habitat types were delineated by qualitatively assessing depth and flow rate of the stream. Riffles were classified as relatively fast flowing and shallower water with noticeable surface aeration. Runs consisted of fast to moderately flowing water with unbroken surface flow. Slow moving, deeper water was classified as pool habitat.

Because sampling during 1998 showed that greater numbers of crayfish were found in runs than in pools and riffles (Flinders and Magoulick, 2003), we focused on sampling run habitats during the 1999 small stream survey. A total of 27 kicknet samples were collected from each of 22 streams in 1999. Three kicknet samples were collected from each of three consecutive runs in a given reach of stream. A reach was defined as an area of stream consisting of three runs separated by riffle or pool habitats. Reach and run locations were selected based on accessibility, but sample locations within runs were randomly selected. This procedure was replicated in three reaches within a stream with reaches being at least 500 m apart for a total of 27 samples per stream. We deviated from 1998 sampling methods as part of a larger project to determine the effect of spatial scale on crayfish community structure. However, in this study, collected data were analyzed to investigate species associations and species-habitat relationships of Spri\ng River crayfish rather than the effect of spatial scale.

We also sampled the three main river channels draining the Spring River watershed; the West Fork, South Fork and Spring rivers; to determine distribution and habitat use of crayfish in these systems. High water precluded sampling in these rivers during spring, so kicknet sampling was conducted in the South Fork and West Fork rivers from 16-22 June 1998, and in the Spring River on 9 July 1998 and from 13-14June 1999 (henceforth, large river 1998 and 1999). Sampling locations were selected based on accessibility, and a minimum of three random kicknet samples were collected in the available habitats at each site. In 1998 riffle, run and pool habitats were sampled in the South and West Fork Rivers, whereas riffle, run, stream margin and backwater habitats were sampled in the Spring River. In 1999 the Spring River was sampled by kicknetting in riffle, run, stream margin and submerged vegetation habitats. Riffle, run and pool habitats were defined in the same manner as the small stream surveys. Stream margins were shallow areas (typically <35 cm deep) within 5 m of stream-side edges of pools and runs, backwaters were low flow coves removed from the main channel, and vegetated habitat contained ≥50% cover of submerged vegetation.

To determine growth and length-weight relationships, crayfish were collected intensively from Jane's Creek in Arkansas (Lat: 3622'00'', Long: 9114'00''; Lat: 3618'00'', Long: 9114'00'') and the Warm Fork River in Missouri (Lat: 3637'15'', Long: 9133'00''; Lat: 3632'00'', Long: 9132'00'') during June-August 1998 and 1999 using a quadrat sampler (Flinders, 2000) (henceforth, intensive survey). Jane's Creek and the Warm Fork River were selected for intensive sampling based on high densities of Orconectes marchandi determined in preliminary sampling.

All collected crayfish were identified to species, sexed and measured [carapace length (CL) to nearest 0.1 mm measured from the tip of rostrum to posterior carapace] prior to release. Collected crayfish were also weighed (to nearest 0.01 g) during the 1998 small stream and both intensive survey periods. Crayfish were weighed after being air-dried in enamel pans for several minutes. Reproductive status was determined during the 1999 small stream- and intensive surveys. Males were classified as Form I (able to reproduce) or Form II (unable to reproduce). Reproductive activity of females was assessed through the presence of a sperm plug, active glair glands (white tissue at the bases of pleopods and on the uropods), eggs or hatchlings.

At all sampling locations, physical characteristics of habitats were collected. Substrate size composition within the habitat was quantified by visually estimating percent area of silt (<0.02 cm diameter), sand (0.02-0.1 cm), gravel (0.1-3 cm), pebble (3-6 cm), cobble (6-25 cm) and boulder (≥26 cm) within the 1 m^sup 2^ sample area (Platts, 1976). Following collection of crayfish, stream depth and mean (0.6 depth) current velocity in front of the sample area were determined using a meter stick and Marsh-McBirney flow meter.

Data analysis.-Habitat use by crayfish can differ with crayfish size (Stein and Magnuson, 1976; Flinders, 2000) so crayfish of all species collected were classified as either small (CL < 15.0 mm) or large (CL > 15.0 mm) based on size-frequency histograms. Small and large size classes of each species were considered to be separate species in the analyses. Prior to all analyses, species data was logio (x + 1) transformed. We determined stream order from 1:100,000 USGS topographic maps.

Canonical Correspondence Analyses (CCA) were used to determine species-environment relationships for small stream 1998 and 1999, and large river 1998 and 1999 crayfish data. Unimodal model CCA's were appropriate because preliminary Detrended Correspondence Analyses (DCA) indicated that species gradient lengths were greater than four standard deviations (ter Braak, 1995). Preliminary Principle Component Analyses (PCA) were conducted separately for each survey period to determine correlations among environmental variables. Percent sand was excluded in the crayfish-environment CCA because it was strongly correlated with percent silt. Substrate diversity was calculated for each sample using the Shannon-Wiener diversity index (Krebs, 1989) with each substrate type treated as a group. Diversity values obtained were included as a separate environmental variable in species-environment analyses.

Because we were interested in relationships among species, scaling of ordination scores was focused on inter-species correlations rather than inter-sample distances and the species scores were standardized to prevent species with large variances from unduly influencing ordination diagrams (ter Braak and Smilauer, 1998). Monte Carlo permutations testing the significance of canonical axes together were then performed for each CCA to determine the overall importance of remaining environmental variables in influencing crayfish density. In the spring species- environment CCAs, sampling date was used as a covariable which effectively removed potential variation due to seasonal effects associated with different sampling dates. Analyses of species- environment relationships were performed separately for each year because sampling was conducted at different sites.

Growth of crayfish was determined using the length-frequency method (France et al, 1991 ). We used ANCOVA to determine effect of species and sex on crayfish CL-weight relationships and Tukey's test to determine differences among species. Lengths and weights were Intransformed prior to analysis to produce a linear relationship. Spearman rank correlations of crayfish species densities determined associations among species. Kolmogorov-Smirnov tests were used to determine species differences among length-frequency distributions. Speciesand sex-related differences in the size (CL) of reproductively active crayfish collected in the 1999 small stream survey was examined using ANOVA. Only 2 reproductively active Cambarus hubbsi were collected and, therefore, not included in the ANOVA.

RESULTS

Distribution and relative density.-Nine species of crayfish were collected from 65 sites in 54 streams in the Spring River drainage. Orconectes punctimanus was the most widely distributed species, found at 53 of the 65 sites sampled, followed by O. ozarkae (32 sites) and O. marchandi (21 sites) (Fig. 1, Table 1). Orconectes neglectus chaenodactylus (Faxon), a recently introduced species to the western portion of the Spring River drainage, was found at five sites in the West Fork River drainage, in the West Fork River main channel, and at its confluence with the South Fork River. Orconectes neglectus chaenodactylus was the dominant species in the run habitats from which it was collected in 1999 (Table 1). Orconectes eupunctus was found exclusively in the main-channel South Fork and Spring Rivers and Cambarus hubbsi was often collected from the larger, permanent streams, especially the Spring River, where it was the most abundant crayfish species (Table 1 ). Orconectes eupunctus and C. hubbsi were significantly positively associated (Spearman correlation , n = 65, r = 0.39, P < 0.05), and O. punctimanus was significantly negatively associated with O. eupunctus (n = 65, r = - 0.32, P < 0.05) and C. hubbsi (n = 65, r = -0.37, P < 0.05). Orconectes marchandi showed positive associations with Cambarus hubbsi (n = 65, r = 0.21, P < 0.10) and negative associations with O. neglectus chaenodactylus (n = 65, r = -0.22, P < 0.10) that approached significance. No other species showed significant associations. Cambarus diogenes (Girard), Procambarus acutus (Girard) and P. viaeveridus (Faxon) were rarely collected during the study with 4, 4 and 1 individuals collected, respectively.

TABLE 1.-Crayfish densities (individuals m^sup -2^) and site characteristics at sites sampled in 1998 (1), 1999 (2) or both (3) in the Spring River drainage. Names were noted for stream orders ≥3. see Figure 1 for site number locations

TABLE 1.-Crayfish densities (individuals m^sup -2^) and site characteristics at sites sampled in 1998 (1), 1999 (2) or both (3) in the Spring River drainage. Names were noted for stream orders ≥3. see Figure 1 for site number locations

Orconectes marchandivtas collected mainly from small streams (found at 16 of 41 order 1-2 sites; Table 1) in the eastern portion of the Spring River drainage (Fig. 1) and habitats consisting of slower moving, shallow water with gravel, pebble, and cobble substrates. Orconectes marchandi was absent in the larger South Fork and West Fork Rivers and rare in the Spring River with only four individuals collected at the mouth of a small tributary stream where O. marchandi populations were present.

Species-environment relationships.-Canonical correspondence analyses (CCA) showed a significant relationship between physical environmental variables and crayfish densities in small streams in 1999 (F = 2.30, P < 0.001), but not in 1998 (F =1.48, P = 0.073). In small streams, the first two CCA axes explained 75.6% and 67.4% of the variation in crayfish densities with environmental variables in 1998 and 1999, respectively. In 1998 most crayfish species-size classes showed a negative association with current velocity. In 1999 Orconectes marchandi and small O. punctimanus showed a positive association with percent pebble and gravel (Fig. 2). Orconectes neglectus chaenodactylus was positively associated with current velocity and O. ozarkae was positively associated with substrate diversity, water depth and percent boulder, cobble and bedrock. Large O. punctimanus and Cambarus hubbsi were positively associated with percent silt.

FIG. 2.-Relationship between crayfish species-size class relative densities (circles) and physical environmental variables (arrows) in small str\eams during 1999 based on Canonical Correspondence Analysis. Abbreviations are as follows: March= Orconectes marchandi, Neg= O. neglectus chamodactylus, Oz= O. ozarkae, Puncl=O.punctimanus,Hubbs=Cambarushubbsi, L=Large (> 15.0 mm CL) and S = Small (< 15.0 mm CL); Diversity=substrate diversity, Br=bedrock, B=boulder, C = cobble, P=pebble, G=gravel, Si = silt. Angles of arrows indicate associations and length of arrows indicate strength of the relationship

In the large rivers, there was a significant relationship between physical environmental variables and crayfish densities in 1998 (F = 2.80, P < 0.001), but not in 1999 (F =1.67, P = 0.075). Variation in crayfish densities with environmental variables explained by the first two CCA axes was 76.7% in 1998 and 80.1% in 1999. In 1998 both size classes of Cambarus hubbsi and small Orconectes eupunctus were positively associated with current velocity, whereas both size classes of O. ozarkae were negatively associated with current velocity and positively associated with percent silt (Fig. 3). Large O. eupunctus and small O. punctimanus were positively associated with water depth, whereas both size classes of O. negkctus chaenodactylus showed negative associations with water depth. In 1999 large and small C. hubbsi were positively associated with current velocity, whereas both size classes of O. ozarkae, and large O. punctimanus showed a positive association with percent vegetation.

Life history.-Carapace length-weight relationships of Orconectes marchandi and O. ozarkae, the two species found in each stream, showed a significant stream species year interaction (ANCOVA P < 0.001). In both streams, the crayfish CL-weight regression slopes differed significantly among species (Table 2; ANCOVA species weight P < 0.001). In both Janes Creek and the Warm Fork River during both years, Orconectes marchandi became heavier than O. ozarkae as crayfish grew in length (Fig. 4). In the Warm Fork River, Cambarus hubbsi was consistently heavier than any of the Orconectes species, whereas O. punctimanus grew in a similar fashion to O. ozarkae (Fig. 4).

FIG. 3.-Relationship between crayfish species-size class relative densities (circles) and physical environmental variables (arrows) in large rivers during 1998 based on Canonical Correspondence Analysis. see Figure 2 for abbreviations

In the Warm Fork River in 1998, CL-weight regression slopes differed significantly by sex for all species except Orconectes ozarkae (ANCOVA sex weight P=0.785), whereas in 1999 Cambarus hubbsi was the only species that showed sex-dependent CL-weight regression slopes (ANCOVA sex weight P = 0.008). In Janes Creek in 1998, crayfish CL-weight regression slopes differed significantly by sex for O. marchandi (ANCOVA sex weight P < 0.001), but not for O. ozarkae (ANCOVA sex weight P < 0.578), whereas in 1999 sex did not have a significant affect on CLweight regression slopes for either species (ANCOVA sex weight P > 0.058). In all cases where slopes were not parallel, females became heavier than males as crayfish CL increased.

Growth rates of Orconectes marchandi appeared to be lower than those of O. ozarkae and O. punctimanus (Fig. 5). During the 1998 small stream surveys, male and female O. marchandi CL-frequencies did not differ significantly from O. ozarkae and O. punctimanus CLfrequencies in winter (Kolmogorov-Smirnov test, P > 0.141). Male O. marchandi CLfrequencies did differ significantly from O. ozarkae and O. punctimanus in spring (P < 0.001 ) and summer (P < 0.016), whereas female O. marchandi CL-frequencies differed significantly from O. punctimanus in spring (P < 0.016) and from both O. ozarkae and O. punctimanus in summer (P < 0.004).

TABLE 2.-Linear regression coefficients for relationships between In CL (dependent variable) and In wet weight (independent variable) of crayfish collected during July and August of 1998 and 1999 in Janes Creek and the Warm Fork River

In the 1998 small stream survey, the number of female Orconectes marchandi and Cambarus hubbsi was greater than the number of males collected (Table 3). Orconectes ozarkae showed the opposite trend, whereas O. punctimanus showed approximately 1 male:l female sex ratio. During the 1998 intensive survey, sex ratios were close to 1 for most species in both streams (Table 3). Exceptions were O. ozarkae in Janes Creek with a male:female ratio of 1:1.4 and O. punctimanus in the Warm Fork River with a male:female ratio of 1:1.3.

During the 1999 small stream survey, Orconectes punctimanus, O. neglectus chaenodactylus and Cambarus hubbsi showed approximately 1 male:l female sex ratios, whereas O. marchandi and O. ozarkae showed nearly 2 male:l female sex ratios (Table 4). For all crayfish species, we found fewer Form I males than Form II males. However, Form I males made up 36% of O. marchandi males and 40% of O. ozarkae males that were collected, whereas the percentage of Form I males for all other species was less than 20 (Table 4). Similar patterns were observed for females. Reproductively active females comprised 36% of O. marchandi females, and 25% of O. ozarkae females that were collected, whereas all other species showed lower percentages (Table 4).

There was a significant species difference in the size of reproductively active crayfish (F^sub 4,380^ = 58.6, P < 0.001), but no difference with sex (F^sub 1,380^ < 0.001, P = 0.990) or interaction effect (F^sub 1,380^ = 0.740, P = 0.565) (Fig. 6). Mean CL of sexually mature crayfish was significantly lower for Orconectes marchandi (Tukey's test P < 0.004) and greater for O. punctimanus (Tukey's test P < 0.001) than all other Orconectes species (Fig. 6). Orconectes marchandi had the smallest sexually mature individual with a CL of 11.2 mm for male and 12.0 mm for female crayfish. Only 1 reproductively active male (Form I, 22.6 mm CL) and female (active glair glands, 24.8 mm CL) C. hubbsi were collected during the 1999 small stream survey. By midjune (1999 intensive survey), most species showed sex ratios slightly skewed toward females and almost all crayfish were reproductively inactive (Table 5).

Few Orconectes marchandi females were collected with active glair glands (n = 19), eggs (n = 26) or hatchlings (n = 10) during the 1999 small stream survey. Females were collected with active glair glands in early March and began to exude eggs (35-85 eggs/female) in mid-March. Eggs were deep purple and ranged from 1.5-1.7 mm in diameter. Hatching began in early April and independent young-of- the-year were collected by the third week in April. By midjune, males had molted into Form II and females were in the process of molting into a non-reproductive stage.

FIG. 4.-Carapace length-wet weight relationships for the most common crayfish species collected in Janes Creek and the Warm Fork River during 1998 and 1999

DISCUSSION

We have expanded the known distribution of Orconectes marchandi within the Spring River drainage from three streams to 20 streams. We found O. marchandi almost exclusively in smaller tributary streams of the Spring River, predominantly in shallow, slow-moving water in gravel and pebble substrates. In contrast, Pflieger (1996) found that O. marchandi was common in faster-flowing riffle habitats. This apparent contradiction is likely due to the high spatial variation common in crayfish communities and few previously recorded observations of this organism.

Previous studies reported Orconectes marchandi in association with O. eupunctus and O. nais (Faxon) (Williams, 1954; Pflieger, 1996). We found that O. marchandi was not significantly associated with any other crayfish species found in our study, but O. marchandi was weakly positively associated with Cambarus hubbsi and negatively associated with O. neglectus chaenodactylus. Orconectes eupunctus was limited to the Spring and South Fork Rivers and showed no association with O. marchandi. Crayfish collections were made at nine locations along the Spring River including the location previously documented to contain O. marchandi (Williams, 1954). This site was located at the confluence of the Spring River and a small stream containing populations of O. marchandi with the dominant species consisting of O. ozarhae and O. eupunctus, and a low abundance of O. marchandi. These findings indicate that populations of O. marchandi are limited to the smaller tributaries of the Spring River with any populations in the main channel restricted to marginal areas near the confluence of tributaries and the main channel.

FIG. 5.-Length-frequency histograms of Orconectes marchandi, O. ozarkae and O. punctimanus during winter, spring and summer seasons. Winter = February, March; Spring = April, May; Summer = June, July, August. Upper bars = female, lower bars = male

Williams (1954) identified Orconectes nais as a crayfish associated with O. marchandi, Bouchard and Robison (1980) suggested that populations of O. nais in Arkansas are most likely O. virilis. However, no evidence of O. virilis (or O. nais) was seen in the Spring River drainage during this study. Previously occurring populations of O. virilis may have been extirpated as a result of competitive exclusion by other crayfish (Flynn and Hobbs III, 1984) or differential predation by fish and terrestrial predators (Garvey et a., 1994).

It should be noted that the area sampled was not completely enclosed and it may have been possible for crayfish to escape the sampling net. We attempted to prevent this by sweeping the net through the water column, but we likely still had crayfish escapes. More active and stronger swimmers may have been better able to avoid capture. Therefore, our crayfish density estimates should be viewed as conservative estimates, and potentially biased toward weaker swimmers. We may have missed species with our sampling technique, but as we collected several crayfish species in relatively high numbers, it seems unlikely that w\e missed any common species.

TABLE 3.-Number of males and females of common crayfish species collected during the 1998 small stream (13 February-31 May) and intensive (June-August) surveys

Crayfish in the Spring River watershed showed specific associations with environmental variables that correspond with stream size. For example, Orconectes marchandi was negatively associated with current velocity and positively associated with percent gravel and pebble and were collected predominantly in small, slow moving streams. In contrast, O. eupunctus and Cambarus hubbsiv/ ere positively associated with current velocity and collected predominantly in faster flowing, permanent streams. Orconectes neglectus chaenodactylus, O. ozarkae and O. punctimanus showed no distribution or density relationship with stream size. These differences may be the result of adaptations to the habitat conditions found in these stream types. Additionally, biotic factors such as interspecific competition and differential predation by fish predators can play a significant role in determining crayfish habitat use (Capelli and Munjal, 1982; Flynn and Hobbs III, 1984; Butler and Stein, 1985; DiDonato and Lodge, 1993; Mather and Stein, 1993; Hill and Lodge, 1999). It is likely that an interaction of biotic factors and crayfish environmental tolerances are responsible for determining the distribution and structure of crayfish communities in Spring River watershed streams.

It appears that Orconectes eupunctus may be at greater risk of displacement than O. marchandi due to the invasion of O. neglectus chaenodactylus into the West Fork River. Previously unreported in the watershed, O. neglectus chaenodactylus was collected in the main channel of the West Fork River, three intermittent headwater streams and at the confluence of the West Fork and South Fork rivers. Orconectes neglectus chaenodactylus appears to have replaced the previously dominant species in these systems, O. eupunctus, an endemic to the Spring River drainage (Pflieger, 1996). Native to the White River basin in southwestern Missouri and northwestern Arkansas, and usually the most dominant crayfish in its range (Williams, 1952, 1954; Hobbs Jr., 1972; Pflieger, 1996), O. neglectus chaenodactylus was most often associated with O. ozarkae and O. punctimanus in its native range.

Introduced crayfish can have detrimental effects on native crayfish populations (Light et al, 1995; Hill and Lodge, 1999; Lodge et al., 2000). Anthropogenic introduction has been cited as the cause of many crayfish species introductions (Capelli, 1982; Hobbs et al., 1989) and this is the likely source of Orconectes neglectus chaenodactylus in the West Fork drainage. While it is possible for headwater streams to undergo stream capture events allowing for natural crayfish migration (Greaser, 1934), this seems an unlikely avenue of invasion by O. neglectus chaenodactylus into the West Fork drainage given no known stream capture events in this drainage. Further study is needed to determine the extent to which O. neglectus chaenodactylus has affected native populations, evaluate risk to downstream drainages, and develop potential mitigation efforts.

TABLE 4.-Percentage by reproductive status and total number for male and female crayfish collected during the 1999 small stream survey (16 March-25 April)

FIG. 6.-Mean carapace length for reproductively active male and female Orconectes marchandi, O. neglectus chaenodactylus, O. ozarkae and O. punctimanus

We found that crayfish species differed in their growth rates and carapace length-weight relationships. Orconectes punctimanus showed the greatest growth in carapace length from winter to summer and O. marchandi showed the greatest increase in weight with carapace length. Faster growth rates may be important in determining the distribution and relative abundance of species because size can affect the outcomes of biotic interactions. Juvenile crayfish with slower growth rates have an increased vulnerability to predation for longer periods of time (Sderbck, 1992) and are less likely to successfully compete against larger crayfish for resources (Bovberg, 1970; Hill and Lodge, 1994). We did not collect enough O. negkctus chaenodactylus to examine growth rate, but Price and Payne (1984) found that O. negkctus chaenodactylus molted more and grew faster than other species in the genus Orconectes. This trait may contribute to the displacement of native crayfish in the West Fork and South Fork drainages and warrants further study.

TABLE 5.-Percentage by reproductive status and total number for male and female crayfish collected during the 1999 intensive surveys on Janes Creek and the Warm Fork River (June-August)

Orconectes marchandi became reproductively active at smaller sizes than other crayfish in this study and other Orconectes species studied elsewhere (Prins, 1968; Fielder, 1972; Boyd and Page, 1978; Smith, 1981; Corey, 1987; Muck et al., 2002). Crayfish that are able to reproduce at smaller sizes may have an advantage because they are able to reproduce at a younger age. However, in a study of four closely related crayfish species, Corey (1987) found no significant difference in overall fecundity despite significant differences in the size of ovigerous females. Given the mean size of sexually mature male (16.4 mm CL) and female (16.2 mm CL) Orconectes marchandi, 26.1% of males and 41.6% of females had the potential to be Form I or reproductively active during our 1999 small stream survey. However, we observed 36.1% Form I males and 36.2% reproductively active females. These differences in abundance, and the male-dominated sex ratios, may be due to behavioral differences related to life cycle. Several researchers have observed similar male-dominated sex ratios from late winter through spring and suggested that females sought different habitats to protect eggs or young (Fielder, 1972; Corey, 1988). Additionally, Weagle and Ozburn (1972) suggested that larger females are more likely to be successful in biotic interactions, and therefore, be more active than smaller females.

The results of this study indicate that Orconectes marchandi is limited to smaller 1-3 order streams and has a greater distribution than initially thought. Orconectes eupunctus may be of greater concern than O. marchandi due to displacement by the introduced crayfish O. neglectus chaenodactylus that was newly discovered in the West Fork River sub-drainage. The size of sexually mature O. marchandi was significantly smaller than that of other species in this study. Further research is needed to establish the extent and mechanism of displacement of O. eupunctus by O. negkctus chaenodactylus, crayfish habitat selection, and processes driving selection of crayfish size and sexual maturity.

Acknowledgments.-We thank the numerous landowners that provided stream access for this study. W. A. Fisher, H. Dukat, B. Gasper, C. Spicer, K Johnson and B. Gibson provided field assistance over the course of the study. The Arkansas Game and Fish Commission provided canoeing equipment in 1999. J. Wilson and N. Myatt provided assistance in producing the distribution maps. R. J. DiStefano and C. Taylor provided advice and confirmation of crayfish identification. Comments from R. J. DiStefano, M. Rabalais, R. Creed and E. Bergey improved the quality of the manuscript. This research was supported by a grant from the Missouri Department of Conservation and a grant from the University of Central Arkansas Research Council. The Academy of Natural Sciences (C.A.F.) and U.S. Geological Survey, Arkansas Cooperative Fish and Wildlife Research Unit (D.D.M.) provided support to the authors during portions of writing.

LITERATURE CITED

ADAMSKI, J. C., J. C. PETERSEN, D. A. FREIWALD AND J. V. DAVIS. 1995. Environmental and hydrologie setting of the Ozark Plateaus study unit, Arkansas, Kansas, Missouri, and Oklahoma. U.S. Geological Survey Water-Resources Investigations report 94-4022, 69 p.

BOUCHARD, R. W. AND H. W. ROBISON. 1980. An inventory of the decapod crustaceans (crayfishes and shrimps) of Arkansas with a discussion of their habitats. Ark. Acad. of Sci. Proc., 34:22-30.

BOVBERG, R. V. 1970. Ecological isolation and competitive exclusion in two crayfish (Orconectes virilis and Orconectes immunis). Ecology, 51:225-236.

BOYD, J. A. AND L. M. PAGE. 1978. The life history of the crayfish Orconectes kentuckiensis in Big Creek, Illinois. Am. Midl. Nat., 99:398-414.

BUTLER, M. J., IVAND R. A. STEIN. 1985. An analysis of the mechanisms governing species replacements in crayfish. Oecologia, 66:168-177.

CAPELLI, G. M. 1982. Displacement of northern crayfish by O. rusticus (Girard). Limnol. Oceanogr., 27: 741-745.

_____ AND B. L. MUNJAL. 1982. Aggressive interactions and resource competition in relation to species displacement among crayfish of the genus Orconectes. J. Crust. Biol., 2:486-492.

CHARLEBOIS, P. M. AND G. A. LAMBERTI. 1996. Invading crayfish in a Michigan stream: direct and indirect effects on periphyton and macroinvertebrates. J. N. Am. Benthol. Soc., 15:551-563.

COREY, S. 1987. Comparative fecundity of four species of crayfish in southwestern Ontario, Canada (Decapoda: Astacidea). Crustaceana, 52:276-286.

_____. 1988. Comparative life histories of two populations of the introduced crayfish Orconectes rusticus (Girard, 1852) in Ontario. Crustaceana, 55:29-38.

GREASER, E. P. 1934. A faunistic area of five isolated species of crayfish in southwestern Missouri. Occas. Pap. Mus. Zool, 278:1-8.

CREED, R. P. 1994. Direct and indirect effects of crayfish grazing in a stream community. Ecology, 75(7):2091-2103.

DiDONATO, G. T. AND D. M. LODGE. 1993. Species replacements among Orconectes crayfishes in Wisconsin Lakes: the role of predation by fish. Can. J. Fish. Aquat. Sci., 50:1484-1488.

FIELDER, D. D. 1972. Some aspects of the life histories of three closely related crayfish species, Orconectes obscuru\s, O. sanbomi, and O. propinquus. Ohio J. Sci., 72:129-145.

FLINDERS, C. A. 2000. The ecology of lotie system crayfish in the Spring River watershed in northern Arkansas and southern Missouri. M.S. Thesis, University of Central Arkansas, Conway, Arizona. 107 p.

_____ AND D. D. MAGOULICK. 2003. Effects of stream permanence on crayfish community structure. Am. Midl. Nat., 149:134-147.

FLYNN, M. F. AND H. H. HOBBS, III. 1984. Parapatric crayfishes in southern Ohio: evidence of competitive exclusion? J. Crust. Biol., 4:382-389.

FRANCE, R., J. HOLMES AND A. LYNCH. 1991. Use of size-frequency data to estimate the age composition of crayfish populations. Can. J. Fish. Aquat. Sci., 48:2324-2332.

GARVEY, J. E., R. A. STEIN AND H. M. THOMAS. 1994. Assessing how fish predation and interspecific prey competition influence a crayfish assemblage. Ecology, 75:532-547.

HANSON, J. M., P. A. CHAMBERS AND E. E. PREPAS. 1990. Selective foraging by the crayfish Orconectes virilis and its impact on macroinvertebrates. Freshwater Biol., 24:69-80.

_____ AND _____. 1995. Review of effects of variation in crayfish abundance on macrophyte and macroinvertebrate communities of lakes. ICES Marine Sci. Symp., 199:175-182.

HART, D. D. 1992. Community organization in streams: the importance of species interactions, physical factors, and chance. Oecologia, 91:220-228.

HILL, A. M. AND D. M. LODGE. 1994. Die! changes in resource demand: competition and predation in species replacement among crayfishes. Ecology, 75:2118-2126.

_____ AND _____. 1999. Replacement of resident crayfishes by an exotic crayfish: the roles of competition and prdation. Ecol. Appl, 9:678-690.

HOBBS, H. H., JR. 1948. Two new crayfishes of the genus Orconectes from Arkansas, with a key to the species of the Hylas group (Decapoda, Astacidae). Am. Midl. Nat., 39:139-150.

_____. 1972. Crayfishes (Astacidae) of North and Middle America. U.S. EPA, Cincinnati, Ohio. 173 p.

HOBBS, H. H. JR., J. P. JASS AND J. V. HUNER. 1989. A review of global crayfish introductions with particular emphasis on two North American species (Decapoda, Cambaridae). Crustaceana, 56:299-316.

HURYN, A. D. AND J. B. WALIACE. 1987. Production and litter processing by crayfish in an Appalachian mountain stream. Freshwater Biol., 18:277-286.

KREBS, C. J. 1989. Ecological methodology. Harper Collins Publishers, New York. 620 p.

LIGHT, T., D. C. ERMAN, C. MYRICK AND J. CLARKE. 1995. Decline of the Shasta crayfish (Pacifastacus fortis Faxon) of Northeastern California. Conseru. Biol., 9:1567-1577.

LODGE, D. M. AND J. G. LORMAN. 1987. Reduction in submersed macrophyte biomass and species richness by the crayfish Orconectes rusticus. Can. J. Fish. Aquat. Sci., 44:591-597.

_____, C. A. TAYLOR, D. M. HOLDICH AND J. SKURDAL. 2000. Nonindigenous crayfishes threaten North American freshwater biodiversity: lessons from Europe. Fisheries, 25:7-20.

LORMAN, A. J. AND J. J. MAGNUSON. 1978. The role of crayfish in aquatic systems. Fisheries, 3:8-10.

MATHER, M. E. AND R. A. STEIN. 1993. Direct and indirect effects offish predation on the replacement of a native crayfish by an invading congener. Can. J. Fish. Aquat. Sci., 50:1279-1288.

MISSOURI NATURAL HERITAGE DATABASE. 2003. Missouri species of conservation concern checklist. Missouri Department of Conservation. Jefferson City, Missouri.

MOMOT, W. T. 1995. Redefining the role of crayfish in aquatic systems. Rev. Fish. Sci., 3:33-63.

MUCK, J. A., C. F. RABENI AND R. J. DISTEFANO. 2002. Reproductive biology of the crayfish Orconectes luteus (Greaser) in a Missouri stream. Am. Midl. Nat., 147:338-351.

PFLIEGER, W. L. 1996. The crayfishes of Missouri. Missouri Department of Conservation, Jefferson City, Missouri. 152 p.

PLATTS, W. S. 1976. Validity of methodologies to document stream environments for evaluating fishery conditions, p. 267-284. In: J. R. Barnes and G. W. Minshall (eds.). Stream ecology: application and testing of general ecological theory. Plenum Press, New York.

PRICE, J. O. AND J. F. PAYNE. 1984. Size, age, and population dynamics in an r-selected population of Orconectes neglectus chaenodactylus (Decapoda, Cambaridae). Crustaceana, 46:29-38.

PRINS, R. 1968. Comparative ecology of the of the crayfishes Orconectes rusticus rusticus and Cambarus tenebrosus in Doe Run, Meade County, Kentucky. Int. Revue. Ges. Hydrobiol, 53:667-714.

PROBST, W. E., C. F. RABENI, W. G. COVINGTON AND R. E. MARTENEY. 1984. Resource use by stream-dwelling rock bass and smallmouth bass. Trans. Am. Fish. Soc., 113:283-294.

RABENI, C. F., M. GOSSETT AND D. D. McCLENDON. 1995. Contribution of crayfish to invertebrate production and trophic ecology of an Ozark stream. Freshwat. Crayfish, 10:163-173.

SMITH, D. G. 1981. Life history parameters of the crayfish Orconectes limosus (Raf.) in southern New England, Ohio. Science, N. Y., 81:169-172.

SDERBCK, B. 1992. Predator avoidance and vulnerability of two co- occurring crayfish species Astacus astacus (L.) and Pacifastacus leniusculus (Dana). Ann. Zool. Fennici, 29:253-259.

STEIN, R. A. AND J. J. MAGNUSON. 1976. Behavioral response of crayfish to a fish predator. Ecology, 57: 751-761.

TAYLOR, C. A., M. L. WARREN, JR., J. R. FITZGERALD, JR., H. H. HOBBS, III, R. F. JEZERINAC, W. L. PFLIEGERAND H. W. ROBISON. 1996. Conservation status of crayfishes of the United States and Canada. Fisheries, 21:25-38.

TER BRAAK, C. J. F. 1995. Ordination, p. 91-173. In: R. H. G. Jongman, C. J. F. ter Braak and O. F. R. VanTongeren (eds.). Data analysis in community and landscape ecology. Cambridge University Press, New York.

_____ ANDP. SMILAUER. 1998. CANOCO reference manual and user's guide to canoco for windows: software for canonical community ordination (version 4). Microcomputer Power, Ithaca, New York. 351 p.

WEAGLE, K. V. AND G. W. OZBURN. 1972. Observations on aspects of the life history of the crayfish, Orconectes virilis (Hagen), in northwest Ontario. Can. J. Zool., 50:366-370.

WHITLEDGE, G. W. AND C. F. RABENI. 1997. Energy sources and ecological role of crayfishes in an Ozark stream: insights from stable isotopes and gut analysis. Can. J. Fish. Aquat. Sci., 54:2555- 2563.

WILLIAMS, A. B. 1952. Orconectes neglectus chaenodactylus Williams. Transactions of the Kans. Acad. Sci., 55:33-40.

_____. 1954. Speciation and distribution of the crayfishes of the Ozark Plateaus and Ouachita Provinces. U. Kans. Sci. Bull., 36:805- 916.

WILLIAMS, D. D. 1996. Environmental constraints in temporary fresh waters and their consequences for the insect fauna. J. N. Am. Benthol. Soc., 15:634-650.

SUBMITTED 19 APRIL 2004 ACCEPTED 5 APRIL 2005

C. A. FLINDERS

Patrick Center for Environmental Research, The Academy of Natural Sciences, 1900 Benjamin Franklin Pkwy, Philadelphia, Pennsylvania 19103

AND

D. D. MAGOULICK1

U.S. Geological Survey, Arkansas Cooperative Fish and Wildlife Research Unit, Department of Biological Sciences, University of Arkansas, Fayetteville 72701

1 Corresponding author

Copyright American Midland Naturalist Oct 2005

Source: American Midland Naturalist, The

More News in this Category