Conservation, Biology, and Natural History of Crayfishes from the Southern US 2010 Southeastern Naturalist 9(Special Issue 3):245–256 Macrohabitat Partitioning of Crayfish Assemblages in Wadeable Streams in the Coastal Plains of Southeastern Alabama Paul M. Stewart1,*, Jonathan M. Miller1, William H. Heath1, and Thomas P. Simon2 Abstract - Habitats provide food sources, cover, concealment, and a place to reproduce; thus, habitat selection is an important aspect of an organism’s ecology. The objectives of this study were to investigate habitat preferences of crayfish and to determine if there was habitat partitioning among different species of crayfish in wadeable streams. Data were collected while collecting crayfish at 50 sites throughout southeastern Alabama. Data collected along with species and relative abundance were: sex, stream position, type of instream cover, and type of substrate. The 3 dominant aquatic species found in the study area were Procambarus suttkusi (Choctawhatchee Crayfish), P. versutus (Sly Crayfish), and Cambarus graysoni (Twospot Crayfish). These 3 species were most often found in woody debris, on sandy substrate, and in stream runs. In addition, there was a significant difference in abundance in pools where P. suttkusi was found alone and where P. suttkusi was found along with other crayfish species. In contrast to other reported studies, these 3 crayfish species appeared to have no preference among habitat types, but were found in the habitat most available. This result may be due to the limited habitat found in the sandy-bottomed streams of the southeastern coastal plains, and their lack of variety in cover and substrates. Introduction The majority of crayfish inhabiting the United States are found in the Southeast (Helfrich and DiStefano 2003, Holdich 2002, Taylor et al. 1996). Crayfish are omnivorous and often have the largest biomass of any invertebrate group within the stream. They play a key role in stream ecosystems through the exchange of energy between trophic levels. This exchange is accomplished by feeding on aquatic plants, insects, and detritus and by being consumed by predatory fish (Cronin et al. 2002, DiStefano et al. 2003). DiStefano et al. (2003) reported that crayfish occur in most major instream macrohabitats and divide macrohabitats within the stream. Juveniles are thought to inhabit slower waters such as stream edges, vegetation, and backwaters, which likely affords them a better chance of predator avoidance and allows them to maintain their position in the stream. Adult crayfish are more abundant in deeper riffles and runs due to greater cover that allows them to feed with less chance of predation from predators such as Micropterus 1Department of Biological and Environmental Sciences, Troy University, Troy, AL 36081. 22364 East Linden Hill Drive, Bloomington, IN 47401. *Corresponding author - mstewart@troy.edu. 246 Southeastern Naturalist Vol. 9, Special Issue 3 salmoides (Lacepéde) (Largemouth Bass), terrestrial mammals, and birds (Holdich 2002, DiStefano et al. 2003). Key factors that could potentially influence habitat selection within these macrohabitats are predation, availability and permanence of instream cover, abundance of food sources, age, body design, and competition among crayfish (DiStefano et al. 2003, Kershner and Lodge 1995). For crayfish assemblages as a whole, predation is the major factor driving habitat selection in streams, especially those with large numbers of crayfish predators. In streams with few crayfish predators, food availability is probably the major factor driving habitat selection (DiStefano et al. 2003). Behavioral and physiological conditions, such as fight or flight, are additional factors that may drive habitat selection (Jordan et al. 2000). Competition among species plays a role in habitat selection. Some species have the ability to make use of any available habitat, while others are habitat-specific. For example, species in the genus Cambarus divided the available habitat to reduce competition, while other species will take over the area and force out less competitive species (Ratcliff and DeVries 2004). Kershner and Lodge (1995) found that competition between sexes of Orconectes rusticus (Girard) (Rusty Crayfish) will also occur, and males tended to be of higher hierarchical order than females. In general, larger crayfish with larger chela outcompeted congeners for the habitat that afforded the best cover and food supply (Klocker and Strayer 2004). The objective of this research was to examine habitat use by crayfish species and assemblages. The specific questions asked were: will habitat use differ among crayfish species? and will habitat use by P. suttkusi Hobbs (Choctawhatchee Crayfish) differ when found by itself versus found along with other species? It is hypothesized that crayfish will partition the various macrohabitats of the stream according to species (DiStefano et al. 2003, Englund and Krupa 2000, Ratcliffe and DeVries 2004). Methods Study area The major streams of southeastern Alabama include the Choctawhatchee River, Pea River, Patsaliga Creek, and Yellow River (Fig. 1), and these generally flow in a south by southwest direction. The dominant sediments include sand, marl, gravel, limestone, clay, and chalk (Mettee et al. 1996). The Choctawhatchee River watershed covers about 8107 km2 of Alabama and includes both the Choctawhatchee and Pea Rivers (Mettee et al. 1996, US Department of Agriculture 1995). The Choctawhatchee watershed originates near Clayton, AL and exits Alabama south of Geneva. The Pea River originates in Bullock County, drains the west region of the Choctawhatchee watershed, and meets the Choctawhatchee south of Geneva, AL. The Patsaliga Creek originates south of Montgomery, AL and flows generally south, until emptying into the Conecuh River in Covington County. The Yellow River watershed begins in Crenshaw County, AL and flows through 2010 P.M. Stewart, J.M. Miller, W.H. Heath, and T.P. Simon 247 Covington County draining 1313 km2. The major land uses of the study area are forests (54%), crops (25%), and pastures (13%). Urbanization only comprises 4% of the land-use area, 0.7% is ponds and lakes, 0.3% mines, and 3% other (US Department of Agriculture 1995). Site selection Fifty sites were selected within the Choctawhatchee River, Pea River, Yellow River, and Patsaliga Creek watersheds (Fig. 1; See Appendix A in Heath et al. 2010). Thirty-one sites were selected based on accessibility, wadeability, and the presence of available crayfish instream cover. Nineteen sites were selected because they coincided with another study on candidate mussel species being conducted within the same watershed. Representative instream cover included, but were not limited to the following: presence of woody debris, rocky areas, stream edges with vegetation, roots, and leaf packs. Figure 1. Map of southeastern Alabama showing the major watersheds and study sites for the 2004 summer collection in the Choctawhatchee River, Pea River, Yellow River, and Patsaliga Creek watersheds. 248 Southeastern Naturalist Vol. 9, Special Issue 3 Habitat partitioning Crayfish sampling began at bridge crossings and proceeded upstream for 150 m. If the upstream portion of the stream was inaccessible, 150 m were sampled downstream. A backpack electrofisher (Smith-Root, Inc., Model 12-B®) was used to agitate crayfish from their cover so they could be captured in dip nets. At the point of capture, pertinent information was recorded on individual habitat characteristics, including position in the stream, type of instream cover, and substrate type. If multiple instream cover or substrate types were present, all were recorded. For example, if 10 individuals of the same species were collected at a site, and 9 were found in both woody debris and leaf pack while the other was found in rootwad, then percent occurrence would be 90% in woody debris, 90% in leaf pack, and 10% in rootwad (allowing habitats characteristics preferred to equal over 100%). Individual crayfish characteristics recorded included species and sex. Position where the crayfish were first observed in the stream was broken down into riffle, run, or pool. Instream cover recorded in the immediate vicinity of where the crayfish was first observed included rootmat, rootwad, woody debris, logs, undercut bank, bank, overhanging vegetation, aquatic vegetation, rocks, cobble, boulder, leaf pack, trash, and shallows. Specimens were placed in 95% ethyl alcohol for transportation to the laboratory. After identification, the specimens were transferred to a solution of 70% ethyl alcohol. A reference collection was made and is housed in the aquatic laboratory at Troy University. Data analysis We first analyzed data for the 3 dominant species collected. Totals and averages of habitat variables were computed for each of these 3 species (Table 1). Normality was determined by Q-Q plot, and Levene’s test was used to determine equality of variance. The program SPSS® 11.0 was used to perform one-way analysis of variance (ANOVA; α < 0.05) for each habitat variable and were run using the percentage of occurrence of each of the 3 Table 1. Occurrence (%) of the three dominant aquatic crayfish species in relationship to instream habitat during the 2004 summer collection in the Choctawhatchee River, Pea River, Yellow River, and Patsaliga Creek watersheds in the southeastern coastal plains of Alabama. P. suttkusi P. versutus C. graysoni Habitat n = 1126 n = 343 n = 105 Riffle 27 21 44 Run 50 51 34 Pool 23 28 21 Woody debris 60 58 70 Leafpack 27 31 58 Rootmat 28 30 28 Log 21 15 27 Sand 96 94 99 Clay 6 5 8 Gravel 6 10 4 Hardpan 4 9 2 2010 P.M. Stewart, J.M. Miller, W.H. Heath, and T.P. Simon 249 most common species at each site to identify differences in habitat preference of those species. The second set of data compared habitat data at sites that were inhabited only by P. suttkusi to sites that contained P. suttkusi and other species. An independent sample t-test was used to determine if P. suttkusi at a site occurred in the same habitat when found alone as when found with other species of crayfish. Results During this study, 1611 aquatic crayfish were collected from 50 sites (see Table 1 in Heath et al. 2010). The number of crayfish collected at each site ranged from 0 to 87 individuals, and the number of species per site ranged from 0 to 4. Most of the time, only one aquatic species was found at a site, and when additional species were found, the number was always very low and these were often burrowers (Heath et al. 2010). A total of 8 aquatic species were collected: P. suttkusi (n = 1126), P. versutus (Hagen) (Sly Crayfish; n = 343), P. okaloosae Hobbs (Okaloosa Crayfish; n = 4), P. acutus (Girard) (White River Crawfish; n = 7), Procambarus sp. (n = 2), Cambarus latimanus (LeConte) (Variable Crayfish; n = 6), C. graysoni Faxon (Twospot Crayfish; n = 105), and Cambarus sp. (n = 18). Three most common species Comparisons were made among the three dominant species (P. suttkusi, P. versutus, and C. graysoni) and their occurrence in riffles, runs, and pools and their selection of instream cover and substrate types (Table 1; Figs. 2–4). No significant difference was found between the 3 dominant species and the habitat variables in which they were found, such as run (F = 0.144, P = 0.866), woody debris (F = 0.139, P = 0.870), leafpack (F = 2.85, P = 0.66), rootmat (F = 1.928, P = 0.153), log (F = 0.426, P = 0.655), and sand (F = 0.058, P = 0.943). Since no significant differences were found, only the magnitude of means were used from the graphs to determine in which habitats the 3 dominant species were most commonly associated. The Procambarus species selected habitats, such as runs and woody debris, that were different than those selected by the Cambarus species. Comparisons showed that P. suttkusi was found in riffles 27% of the time, runs 50% of the time, and in pools 23% of the time (Fig. 2). Procambarus suttkusi selected woody debris 60%, leafpack 27%, rootmat 28%, and log 21% of the time (Fig. 3). Procambarus suttkusi was found on sand substrate 98% of the time. Other substrates selected by this species included clay (4%), gravel (3%), and hardpan (2%) (Fig. 4). Procambarus versutus, the second-most common species found (n = 343), selected riffle 21%, run 51%, and pool 28% of the time (Fig. 1). Procambarus versutus selected woody debris 58%, leafpack 31%, rootmat 30%, and log 15% of the time (Fig. 3). Procambarus versutus was found on sand 96% of the time (Fig. 4). Others substrates that this species selected were clay (3%), gravel (7%), and hardpan (6%) (Fig. 4). The least common of the 250 Southeastern Naturalist Vol. 9, Special Issue 3 3 dominant species found was C. graysoni (n = 105). Cambarus graysoni selected riffle 44%, run 33%, and pool 21% of the time (Fig. 2). Cambarus graysoni selected woody debris 70%, leafpack 58%, rootmat 28%, and log 26% of the time (Fig. 3). Cambarus graysoni was found on sand 98% of the time (Fig. 4). Other substrates on which C. graysoni were found included clay (5%), gravel (2%), and hardpan (1%) (Fig. 4). Sites with P. suttkusi An additional comparison was made at sites where P. suttkusi occurred alone and at sites where P. suttkusi occurred along with P. versutus and C. graysoni. A significant difference was found to exist in pool preferences at sites where P. suttkusi occurred with other species (t = -2.439, P = 0.021; Fig. 5). Procambarus suttkusi occurred more frequently in pool habitats when other species were present than when P. suttkusi occurred in the stream alone. Discussion Organisms use their habitat to meet daily energy requirements, avoid predators, and aid in reproduction (Scheel 2002). Urabe and Nakano (1999) F i g u r e 2 . Comparison of mean percentage of P. suttkusi, P. versutus, and C. graysoni found in riffles, pools, and runs. 2010 P.M. Stewart, J.M. Miller, W.H. Heath, and T.P. Simon 251 showed that stream-dwelling fish were influenced by the physical attributes of their environment, and that these attributes varied from stream to stream. Fish studies have also shown that changes to the environment, natural or man-induced, altered assemblage distribution, abundance, and structure (Welker and Scarnecchia 2004). There are few studies representing the influences of the environment on crayfish distribution and habitat selection. However, Butler et al. (2003) showed that impoundments, stream channelization, and pollution affected crayfish environments by limiting the available habitat. In the current study, the dominant Procambarus species, P. suttkusi and P. versutus, were most often found in runs, among woody debris, and on sandy substrate. The dominant Cambarus species, C. graysoni, were most often found in riffles, among woody debris, and on sandy substrate. Crayfish studies have shown that crayfish select habitats that allowed them to avoid predation (Cossette and Rodriquez 2004, Englund and Krupa 2000). The coastal plain is comprised mainly of sand and clay substrates that have eroded from the uplands of the upper half of the State (Lee County Extension Office 1965). Stream substrates other than sand were an infrequent find; thus there was relatively little variety for crayfish to select. This limited variability in stream substrates makes it difficult to formulate generalizations regarding substrate habitat preferences. All 3 dominant species occurred on sandy substrates at least 96% of the time, with gravel the next most common Figure 3. Comparison of mean percentage of P. suttkusi, P. versutus, and C. graysoni found in woody debris, leafpacks, rootmats, and logs. 252 Southeastern Naturalist Vol. 9, Special Issue 3 substrate type at 10%. In contrast, in a study of P. alleni (Faxon) (Everglades Crayfish) in a wetland habitat mosaic, Jordan et al. (1996a) found that P. alleni did not prefer a sandy substrate, and only ventured onto sandy substrate at night when pressure from predation was lessened. The Procambarus species in the current study may not prefer the sandy substrate, but inhabit Figure 4. Comparison of mean percentage of P. suttkusi, P. versutus, and C. graysoni found on sand, clay, gravel, and hardpan substrates. Figure 5. Pool occurrences of sites with only P. suttkusi (alone) and sites where other species (co-habitated) were found. 2010 P.M. Stewart, J.M. Miller, W.H. Heath, and T.P. Simon 253 it due to lack of availability of other choices such as gravel or pebbles. If Procambarus species within southeastern Alabama had a larger selection of substrates, they might choose something other than sand. Coastal plain streams are relatively low gradient with only a minor elevation change throughout the entire ecoregion. With a dominant substrate of sand and little change in elevation, riffles in coastal plain streams are not common and contribute little to stream variability. More Procambarus species preferred runs than riffles or pools (Fig. 2), but in the presence of other species, P. suttkussi occurred more frequently in pools (Fig. 5). Flinders and Magoulick (2005) found that Orconectes species showed positive and negative associations with environmental variables such as current velocity, percent gravel and pebbles, and stream permanence. McGregor et al. (1999) found that the Procambarus species common to southern Alabama preferred flowing water with sandy bottoms and natural debris scattered throughout for cover, concealment, and food. No evidence suggested that the Procambarus species collected during this study showed a preference for one habitat variable, such as stream flow and sandy bottoms, compared to other Procambarus species. Over half of Alabama lands are forested, and timber is a major industry, suggesting that there should be a large amount of woody debris in the streams (US Department of Agriculture 1995). These facts would explain why the crayfish in the current study were found most often in woody debris (Fig. 3). The woody debris provides excellent cover from predators, as well as habitat to scavenge for food. More complex habitat provided more food and more abundant opportunities to hide from predators (Jordan et al. 1996b). Data from the current study confirmed that both of the dominant Procambarus species in this study in the coastal plains were found much more often in flowing water and natural habitats. These Procambarus species have also been observed burrowing into swampy areas in times of drought or low water levels (Hendrix and Loftus 2000). Procambarus species were found occupying burrows just above or below the waterline during lowwater events, but with minimal or no chimneys. During the current study, the abundance of crayfish found in a stream appeared to increase as the amount of stream habitat increased (J.M. Miller, pers. observ.). In support of this observation, Jordan et al. (1996b) found a positive relationship between the abundance of P. alleni and the complex habitats of the wet prairies. They also found a negative relationship between biomass of P. alleni and deeper sloughs that afforded the crayfish less habitat for concealment. Typically, Cambarus species are associated with the Piedmont Region of Alabama. The current study found that C. graysoni was found most often in riffles, woody debris, leafpacks, and sandy substrate. Cambarus graysoni was collected 79% of the time in riffles or runs, and 70% of C. graysoni was found among woody debris, which coincides with historical information. Although rocks were not a dominant feature of these streams, C. graysoni was found among rocks when rocks were present. Historical accounts stated that 254 Southeastern Naturalist Vol. 9, Special Issue 3 the preferred habitats of C. graysoni were rocks and woody debris in lotic environments, but they can become secondary burrowers if low water levels exist (Schuster and Taylor 2004, Taylor and Schuster 2004). A study on an endangered crayfish Cambarus bouchardi Hobbs (Big South Fork Crayfish) in Tennessee showed that C. bouchardi preferred to hide under large flat rocks (Williams et al. 2002). Our results supported the preference of rocks, when present, by C. graysoni. Otherwise, Cambarus sp. in the Williams et al. (2002) study preferred woody debris. Similarly, Austropotamobius pallipes (Lereboullet) (White-clawed Crayfish) was only found at Irish river sites where significant amounts of moss and bedrock were available to provide cover (Gallagher et al. 2005). Mueller and Rothaus (2001) also found a positive relationship between Pacifastacus leniusculus (Dana) (Signal Crayfish) and boulder/bedrock substrates and an inverse relationship between the same Signal Crayfish and sand/silt substrates. The minimal amounts of rocks or gravel and large amount of sandy substrates in the coastal plain may explain why stream-dwelling Cambarus species occur in smaller numbers than Procambarus species in the coastal plain in this current study. Conclusions Crayfish assemblages of the southeastern coastal plains of Alabama showed little habitat preference, but appeared to select habitat based on availability. Procambarus suttkusi, P. versutus, and C. graysoni were the 3 dominant aquatic species found in the study area. Examination of percentages suggests that P. suttkusi and P. versutus were found more often in runs, while C. graysoni was found more often in riffles. In these streams, the most common instream habitats available were woody debris, leafpack, rootmat, and log. Sand dominated the substrates in the streams sampled. When examination of major habitat variables were considered, such as substrate, instream cover, and location within stream, each species was predominately found in the most abundant habitat present, which were generally woody debris and on sandy substrate. Data collected in this study do not suggest that one species out-competed another species for preferred habitat. Holdich (2002) and DiStefano et al. (2003) suggested that particular species of crayfish, size of crayfish, and social class would influence the type of habitat that the crayfish will select. Data collected from the present study do not support these findings, but that crayfish simply assort based on the available habitat or cover with no apparent preferences. This result may be due to the limited habitat found in sandy-bottomed streams of the southeastern coastal plain and their lack of variety in cover and substrates. Acknowledgments We thank two anonymous reviewers for suggestions to the manuscript, Guenter Schuster and Roger Thoma for crayfish verifications, and Stuart Welsh for publication support. 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. 2010 P.M. Stewart, J.M. Miller, W.H. Heath, and T.P. Simon 255 Literature Cited Butler, R.S., R.J. DiStefano, and G.A. Schuster. 2003. Crayfish: An overlooked fauna. Endangered Species Bulletin 28(2):10–11. Cossette, C., and M.A. Rodriquez. 2004. 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