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Habitat Associations of Three Crayfish Endemic to the Ouachita Mountain Ecoregion
Joseph J. Dyer and Shannon K. Brewer

Southeastern Naturalist, Volume 17, Issue 2 (2018): 257–269

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Southeastern Naturalist 257 J.J. Dyer and S.K. Brewer 22001188 SOUTHEASTERN NATURALIST 1V7o(2l.) :1275,7 N–2o6. 92 Habitat Associations of Three Crayfish Endemic to the Ouachita Mountain Ecoregion Joseph J. Dyer1 and Shannon K. Brewer2,* Abstract - Many crayfish are of conservation concern because of their use of unique habitats and often narrow ranges. In this study, we determined fine-scale habitat use by 3 crayfishes that are endemic to the Ouachita Mountains, in Oklahoma and Arkansas. We sampled Faxonius menae (Mena Crayfish), F. leptogonopodus (Little River Creek Crayfish), and Fallicambarus tenuis (Ouachita Mountain Crayfish) from wet and dry erosional channel units of 29 reaches within the Little River catchment. We compared channel-unit and microhabitat selection for each species. Crayfish of all species and life stages selected erosional channel units more often than depositional units, even though these sites were often dry. Accordingly, crayfish at all life stages typically selected the shallowest available microhabitats. Adult crayfish of all species and juvenile Little River Creek Crayfish selected patches of coarse substrate, and all crayfish tended to use the lowest amount of bedrock available. In general, we showed that these endemic crayfish used erosional channel units of streams, even when the channel units were dry. Conservation efforts that protect erosional channel units and mitigate actions that cause channel downcutting to bedrock would benefit these crayfish, particularly during harsh, summer drying periods. Introduction Approximately 80% of the world’s crayfish species occur in North America (Taylor et al. 2007), and crayfish diversity is highest in the southeastern US (66% of North American crayfishes; Simon 2011). These species are often endemic to portions of small ecoregions, making them exceptionally vulnerable to human stressors (e.g., habitat destruction, habitat loss, and pollution; Simon 2011, Taylor et al. 2007). Even as new species are still being described (e.g., Jones 2016, Schuster et al. 2015, Thoma and Fetzner 2015), our knowledge of previously documented species remains limited, making monitoring and conservation efforts for these endemic populations difficult and often reactive (Loughman and Fetzner 2015, Simon 2011). The Ouachita Mountain ecoregion is home to several endemic crayfishes, including 4 stream-dwelling species in Oklahoma. Faxonius saxatilis (Bouchard and Bouchard) (= Orconectes saxatilis) (Kiamichi Crayfish; Crandall and De Grave 2017) occurs only in the upper reaches of the Kiamichi River, where it primarily occupies riffles despite seasonal intermittence of the streams (Jones and Bergey 2007). When streams become intermittent, Kiamichi Crayfish burrow into the moist substrate under boulders and cobbles in the riffles to avoid desiccation (Jones 1Oklahoma Cooperative Fish and Wildlife Research Unit, Oklahoma State University, Stillwater, OK 74074. 2US Geological Survey, Oklahoma Cooperative Fish and Wildlife Research Unit, Oklahoma State University, Stillwater, OK 74074. *Corresponding author - Manuscript Editor: Bronwyn Williams Southeastern Naturalist J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 258 and Bergey 2007). Jones and Bergey (2007) also collected Fallicambarus tenuis (Hobbs) (= Procambarus tenuis) (Ouachita Mountain Crayfish; Ainscough et al. 2013, Crandall and De Grave 2017), but it was too rare to include in their habitat analysis. However, this species was found to occupy small (1st and 2nd order; Strahler 1957) spring-fed streams and cool, clear perennial streams, where it excavates shallow, simple burrows or seeks shelter under rocks (Jones and Bergey 2007, Robison and McAllister 2008). Faxonius leptogonopodus (Hobbs) (= O. leptogonopodus) (Little River Creek Crayfish; Crandall and De Grave 2017) and F. menae (Creaser) (= O. menae) (Mena Crayfish; Crandall and De Grave 2017) habitats are typically small to medium, clear, permanent streams with swift flow and rocky substrates (Robison et al. 2009, Williams 1954). Our study broadens the knowledge of habitat associations of 3 of the aforementioned species (Ouachita Mountain Crayfish, Little River Creek Crayfish, and Mena Crayfish) by investigating habitat use at fine spatial scales (i.e., channel unit and microhabitat). Jones and Bergey (2007) documented habitat associations of the Kiamichi Crayfish in the Kiamichi River catchment, and we did not repeat their efforts. Instead, we focused our sampling efforts in the adjacent Little River catchment where the other 3 species are distributed (Dyer et al. 2013). We compared observed habitat use to habitat availability at both the channel unit (e.g., erosional and depositional) and microhabitat scales. Knowledge of habitat use at multiple spatial scales allows managers to focus conservation efforts in areas where suitable habitat naturally occurs and can be protected or rehabilitated. Methods Study area We conducted crayfish sampling in the Little River catchment of the Ouachita Mountain Ecoregion, OK (Fig. 1). Dominant lithology of the Little River catchment is sandstone and shale (Woods et al. 2005). The landscape vegetation is a mixture of hardwood and coniferous forest, and land-use practices include recreation (e.g., horseback riding), logging, and poultry or cattle agriculture. The Ouachita National Forest is located in the northeast portion of the catchment, encompassing much of the headwaters of the Mountain Fork River. Ouachita National Forest streams are somewhat protected from the effects of agriculture and industrial timber-harvest practices (Woods et al. 2005). Field sampling During summer 2011 and 2012, we sampled 29 study reaches that comprised a series of erosional and depositional channel units. We defined each sample reach as a length of stream with 3 pool–riffle sequences. In each reach, we sampled crayfish from both erosional and depositional channel units. Erosional channel units were characterized as having a swift current or steep streambed gradient relative to adjacent habitat. Erosional channel units could be wet but were commonly dry during our study. Depositional units had relatively slow-moving or stagnant water, and were typically depressions in the streambed or pools, but also included some Southeastern Naturalist 259 J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 backwater and vegetated edges of the main channel. The channel units we sampled were typically less than 10 m wide and ~5–30-m in length. We quantitatively sampled crayfish using 1–3 haphazardly placed 1-m2 quadrat samples (Dyer et al. 2016, modified from DiStefano et al. 2003) in both wet and dry erosional and depositional channel units. Some sampled channel units were relatively small, and we were only able to place a single quadrat in those locations, whereas we took up to 3 quadrat samples in larger channel units. We did not take multiple samples from channel units that were too small to accommodate them without overlap. We placed the quadrat sampler haphazardly within each channel unit. In wetted channel units, we employed a quadrat sampler with 3-mm mesh and a 0.5 m x 1 m x 1.2 m downstream bag to sample crayfish (see figure 2 of Dyer et al. 2016). After placement of the quadrat, we removed coarse particles within the quadrat sampler. Any remaining substrate in the quadrat was disturbed to a depth of 15 cm as water was swept into the downstream bag. We sampled dry-channel units by delineating 1-m2 plots within each channel unit and excavated and searched for crayfish to a depth of 30 cm in the substrate within plots (DiSt efano et al. 2009). We measured microhabitat parameters at each quadrat-sample location prior to sampling to represent unaltered habitat conditions. We visually classified substrate Figure 1. Crayfish sampling locations: Solid circles indicate sites where we detected 1 of our species of interest and open circles indicate sites where none of our species of interest were detected. We conducted our sampling in the Ouachita Mountain Ecoregion of Oklahoma (from west to east, the mainstem rivers are Little, Glover, and Mountain Fork rivers). Southeastern Naturalist J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 260 using the modified Wentworth scale (Cummins 1962). In each quadrat, we estimated the percent cover of each of 4 substrate categories: bedrock (solid, mostly subterranean shale or sandstone), coarse substrate (>64 mm), gravel (4–64 mm), and fine substrate (less than 4 mm). We measured depth (to the nearest 1.0 cm) and employed an electromagnetic flow-meter (Model 2000 Portable Flow Meter; Marsh– McBirney, Fredrick, MD) to determine average water-column velocity (at 0.6 of depth to the nearest 0.1 m s-1) in the center of each quadrat. We identified captured crayfish to species and measured carapace lengths (CL) to determine life stage. We used vernier calipers to measure the carapace— from anterior tip of the rostrum to the posterior edge of the carapace—to the nearest 0.5 mm. We completed preliminary sampling in November and December 2012 to determine the CL of both juveniles and adults. We used the smallest CL of Form I males of each species to delineate the CL of juveniles. We determined that individuals of all species with a CL of ≥17 mm were adults, and individuals with a CL of less than 17 mm were juveniles. However, juvenile Ouachita Mountain Crayfish were rare in our samples, so we did not differentiate adult and juvenile life stages for that species. Selected habitat We determined available habitat at both the channel unit and microhabitat scales for each reach at the time of sampling. We mapped erosional and depositional channel units at each site. We considered channel units available to each species if the species occupied that sampling reach. In our analysis, if a species occurred in 10 sample reaches, we considered the sum of channel-unit habitat from those 10 reaches to be available. We treated available microhabitat similarly across all occupied reaches, where availability included all microhabitats from reaches occupied by a species. We determined microhabitat availability in each reach by summing the microhabitat data collected from all quadrat samples combin ed. We summarized habitat use and selection at the channel-unit and microhabitat scales using descriptive statistics, graphical methods, and the Strauss selectivity index (Strauss 1982). We calculated occurrence frequencies at the channel-unit scale for the combined life stages of Ouachita Mountain Crayfish and adult and juvenile Little River Creek Crayfish and Mena Crayfish. We calculated the Strauss selectivity index as: Li = ri - pi , where, ri is the proportion of the selected habitat represented by environmental parameter i, and pi is the proportion of available habitat represented by environmental parameter i. Positive or negative values indicate selection or avoidance; whereas, values near zero represent neutrality. At the microhabitat scale, we created density plots to compare the range of habitat conditions used relative to available habitat (i.e., selection) in reaches where each species occurred. We did not calculate selectivity indices for habitat features at this scale because we wanted to maintain continuous data of each habitat element. Southeastern Naturalist 261 J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 Results We collected at least 1 of the 3 species in 20 of the 29 stream reaches sampled (Fig. 1). Little River Creek Crayfish was the most commonly encountered species; 285 individuals were collected from 11 reaches. Adult Little River Creek Crayfish were much less abundant than juveniles, accounting for only 19% of the individuals sampled. We sampled 103 Mena Crayfish from 9 reaches. Observed ratios of adults to juveniles (1:2) were more balanced for Mena Crayfish compared to Little River Creek Crayfish. Ouachita Mountain Crayfish was the rarest species; only 25 individuals were sampled from 6 reaches. We encountered adult Ouachita Crayfish more frequently (68% of catch) than juveniles. Crayfish of all species and life stages selected erosional channel units over depositional channel units (Fig. 2). Juvenile Mena Crayfish and Little River Creek Crayfish were sampled in at least half of all erosional channel units within reaches where a member of either species was present. Similarly, adult Mena Crayfish and Little River Creek Crayfish occurred in nearly half of the erosional units sampled and were rare in depositional units. We found juveniles more commonly in depositional channel units than adults, but juveniles still occupied erosional units twice as often as depositional units. Ouachita Mountain Crayfish occurred exclusively in erosional channel units. Our results suggest that erosional channel units are particularly important to these species during the summer baseflow period, even when surface flows cease. Crayfish associations with water depth and bedrock were consistent among species and life stages; however, associations with other substrates were more variable. Crayfish were most frequently associated with the shallowest depths Figure 2. Proportional use of depositional (gray) and erosional (white) channel units by Faxonius leptogonopodus (Little River Creek Crayfish; FLE) and F. menae (Mena Crayfish; FME) juveniles (J) and adults (A), and by all Fallicambarus tenuis (Ouachita Mountain Crayfish; FTE) sampled. The values of the Strauss index are listed above each bar. Positive values indicate selection and negative values indicate avoidance. Southeastern Naturalist J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 262 sampled (less than 14 cm) and areas with less than 10% bedrock (Figs. 3a, b; 4a, b; 5a, b). Adult and juvenile Mena Crayfish occurred in all available depths, but generally at a slightly lower frequency than expected based on availability when depths exceeded 25 cm (Fig. 3). All species and life stages except juvenile Mena Crayfish were positively associated with coarse substrate (Fig. 3c, 4c, 5c). Adult Mena Crayfish and all Little River Creek Crayfish used gravel in proportion to availability, but juvenile Mena Crayfish and Ouachita Mountain Crayfish tended to select moderate to higher proportions of gravel (Figs. 3d, 4d, 5d). Fine substrate was rare in reaches where we detected crayfish, and all crayfish used it in proportion to avai lability. Discussion We found that the 3 crayfishes frequently occurred in seasonally intermittent streams. Like Kiamichi Crayfish (Jones and Bergey 2007), each species selected erosional channel units over depositional channel units, and many of the erosional channel units were dry. Similarly, DiStefano et al. (2009) found that densities of F. williamsi (Fitzpatrick) (= Orconectes williamsi) (Williams’ Crayfish; Crandall and De Grave 2017) in riffles did not differ as these areas dried, indicating that crayfish sought refuge in the hyporheic zone rather than nearby pools. Likewise, we found crayfish typically selected the shallowest available microhabitats. In addition, crayfish typically used habitats with low amounts of bedrock or used bedrock at or below available levels. Given our findings that crayfish in this study selected dry, erosional habitats over wetted pools, the tendency to use areas with greater portions of coarse substrate reflects their burrowing abilities (Dyer et al. 2015, Martin et al. 2012). The selection of relatively dry habitats (i.e., erosional channel units) was interesting given their close proximity to intermittent pools; however, the hyporheic zone below the dry streambed likely offer refugia. One possible benefit of the hyporheic refuge is thermal regulation (Dole-Oliver 2011, Wood et al. 2010). Groundwater temperatures 20 cm below the surface are consistently cooler than Figure 3 (following page). Density plots of habitat associated with the occurrence of Mena Crayfish (gray lines) compared to the available habitat (black lines) in reaches where we encountered the species. The area under each curve accounts for 100% of the observations and the dashed vertical lines represent the median value associated with used (gray) and available (black) habitat. Each panel represents a different environmental parameter: (a) depth (cm), (b) bedrock (%), (c) coarse substrate (%), (d) gravel substrate (%), and (e) fine substrate (%). Figure 4 (see page 264). Density plots of habitat associated with the occurrence of Little River Creek Crayfish (gray lines) compared to the available habitat (black lines) in reaches where we encountered the species The area under each curve accounts for 100% of the observations and the dashed vertical lines represent the median value associated with used (gray) and available (black) habitat. Each panel represents a different environmental parameter: (a) depth (cm), (b) bedrock (%), (c) coarse substrate (%), (d) gravel substrate (%), and (e) fine substrate (%). Southeastern Naturalist 263 J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 Figure 3. [Caption on page 262.] Southeastern Naturalist J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 264 Figure 4. [Caption on page 262.] Southeastern Naturalist 265 J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 Figure 5. Density plots of habitat associated with the occurrence of Ouachita Mountain Crayfish (gray lines) compared to the available habitat (black lines) in reaches where we encountered the species. The area under each curve accounts for 100% of the observations and the dashed vertical lines represent the median value associated with used (gray) and available (black) habitat. Each panel represents a different environmental parameter: (a) depth (cm), (b) bedrock (%), (c) coarse substrate (%), (d) gravel substrate (%), and (e) fine substrate (%). Southeastern Naturalist J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 266 surface water (Wood et al. 2010). Additionally, the loss of herbivorous fishes in the intermittent pools can result in the overgrowth of algae and eventually create anoxic conditions (Dodds 2002). We measured stream temperatures of intermittent pools that exceeded 33 °C (maximum = 34.5 °C) and observed fish kills in some of the pools. Some of the remaining pools appeared to offer suitable habitat, but they were often occupied by Green Sunfish (Rafinesque) (Lepomis cyanellus). Green Sunfish predation can alter crayfish habitat selection (Englund and Krupa 2000). Specifically, Cambarus bartonii (Fabricius) (Common Crayfish) and F. putnami (Faxon) (= Orconectes putnami) (Phallic Crayfish; Crandall and De Grave 2017) with total lengths of less than 40 mm (CL < 20 mm) sought refuge in shallow habitats in the presence of Green Sunfish and other predators (Englund and K rupa 2000). The combined threats of predation and degrading physicochemical condition may make the hyporheic zone more suitable than wetted-surface habitat for crayfish during dry and warm periods. The differential substrate-use by juveniles and adult crayfish could have been related to differences in crayfish size and their ability to occupy interstitial spaces. The adult Mena Crayfish and Little River Creek Crayfish, as well as the Ouachita Mountain Crayfish (which were primarily adults), occurred more frequently in areas with coarser substrate; whereas juveniles appeared less selective. Similarly, a positive relationship between substrate size and the carapace length of the crayfish seeking refuge has been documented in other field studies (Flinders and Magoulick 2003, Martin et al. 2012). Cambarus hubbsi (Creaser) (Hubbs’ Crayfish) with CL >15 mm selected habitats with boulder substrates and swift currents that would prevent fine-sediment deposition, whereas small Hubbs’ Crayfish were negatively associated with water depth (Flinders and Magoulick 2003). Crayfish can experience difficulty moving into the hyporheic zone in the absence of coarse substrate (Dyer et al. 2015, Martin et al. 2012). In laboratory trials, the burrowing depths of adult F. palmeri longimanus (Faxon) (= Orconectes palmeri longimanus) (Western Painted Crayfish; Crandall and De Grave 2017), Mena Crayfish, Little River Creek Crayfish, Kiamichi Crayfish, and Ouachita Mountain Crayfish were significantly reduced in pebble substrate (32–64 mm) when compared to coarser substrate (Dyer et al. 2015). We found that Mena Crayfish and Little River Creek Crayfish had a broader ecological niche than previously documented; however, Ouachita Mountain Crayfish were rare in our study. We confirmed the presence of Mena Crayfish and Little River Creek Crayfish in small to medium-sized streams with rocky substrate (Robison et al. 2009, Williams 1954), but found that neither species was restricted to permanent streams and often occupied intermittent streams. Despite the wide range of Ouachita Mountain Crayfish and considerable sampling effort, we detected only 25 individuals. Bergey et al. (2005) and Jones and Bergey (2007) documented the rarity of this species, and the International Union for Conservation of Nature lists the species as data deficient (Crandall 2010). We recognize that our results are based on only 25 individuals and should be interpreted with caution. The previous reports of Ouachita Mountain Crayfish as rare within their range (Bergey et al. 2005, Jones and Bergey 2007) may be an artifact of the sampling Southeastern Naturalist 267 J.J. Dyer and S.K. Brewer 2018 Vol. 17, No. 2 methods rather than a small population. Occasional detections of Ouachita Mountain Crayfish using methods targeting lotic-dwelling, tertiary burrowers have led to the assumption that the species was a lotic dwelling, tertiary burrower; however, the Ouachita Mountain Crayfish may actually spend the majority of its time underground. Recent genetic work has placed Ouachita Mountain Crayfish in Fallicambarus, a genus of primary burrowers, rather than Procambarus, a genus in which many burrowing strategies are represented (Ainscough et al. 2013). Although we found Ouachita Mountain Crayfish under large boulders (>500 mm) within the active stream channel, we also made several observations of Ouachita Mountain Crayfish by opportunistic excavation of chimney-capped burrows that were outside of the streambanks and did not fit into our sample design. The chimney-capped burrows were located in ephemeral forest ditches that flowed into the stream, but the substrate appeared similar to the soil type on the forest floor. Further, our failure to detect Ouachita Mountain Crayfish, despite sampling the instream substrate to a depth of 30 cm and successfully detecting sympatric species in instream burrows, suggests that the species may rarely inhabit the active channel. The burrows we found consisted of fine sediment in ephemeral tributaries and were consistent with other members of the genus. Future studies targeting Ouachita Mountain Crayfish would benefit from a sampling design that targets primary or secondary burrowing strategies, rather than stream-dwelling, te rtiary burrowers. Our growing knowledge of the importance of intermittent habitat to native crayfish should be helpful to developing effective conservation strategies. Stream drying is sometimes considered a disturbance (Lake 2000), but under normal conditions, these crayfish are able to make use of these areas despite surface drying. However, intensified water demands that accompany climate change could present interesting challenges for the persistence of aquatic species (Xenopoulos et al. 2005). Crayfish that burrow will be sensitive to excessive water withdrawals and development that promotes sedimentation of instream habitat. We encourage researchers to further examine the role of intermittent stream areas to the persistence of aquatic biota in an effort to highlight the importance of these areas to overall biodiversity. Acknowledgments This research is a contribution of the Oklahoma Cooperative Fish and Wildlife Research Unit (Cooperators: US Geological Survey, Oklahoma Department of Wildlife Conservation, Oklahoma State University, and Wildlife Management Institute). Our work was supported by the Oklahoma Department of Wildlife Conservation (T-60-R). We thank Julia Mueller, Jarrod Powers, Justin Rowland, and Kortney Kowal for technical assistance. 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