Recolonization by Warmwater Fishes and Crayfishes after Severe Drought in Upper Coastal Plain Hill Streams

-Extreme hydrologic disturbance, such as a supraseasonal drought, can dramatically influence aquatic communities. Documentation of the responses of aquatic communities after such disturbances provides insight into the timing, order, and mechanisms of recolonization. Postdisturbance recolonization of streams depends on many factors, including the region and characteristics of the disturbance relative to the disturbance regime. A supraseasonal drought that ended in the fall of 2000 resulted in the desiccation of numerous small streams or stream segments in northern Mississippi that were normally perennial. We repeatedly sampled fish and crayfish during predrought and postdrought periods in seven stream reaches that dried and five that remained flowing during the drought. From immediately after the drought until early summer of 2001, postdrought fish and crayfish assemblages differed from predrought assemblages in dry sites but not in flowing sites. The initially slow recolonization rates increased considerably during early spring 2001 so that by June 2001 fish catch per unit effort, species composition, and species richness in dry sites no longer differed significantly from predrought values. The fish recolonization process was highly ordered, as indicated by significant patterns of species nestedness over time in dry sites. Crayfish numerical recovery followed a pattern similar to that for fish, and we captured more crayfish in June 2001 than in the predrought period. Patterns in fish and crayfish population size structures over time indicated that repopulation was due to both immigration and reproduction. Recolonization was indicative of high mobility, particularly during spring and early summer. Although the fauna was quite resilient to stream desiccation, the effects on fish species composition and fish and crayfish size structure persisted 1 year after the drought. Disturbance, often in the form o f floods or droughts, can be influential in structuring lotic communities. The extent o f the influence depends in part on the nature, severity, and return intervals o f disturbances (Meffe and Minckley 1987; Resh et al. 1988; Poff and Allan 1995; Dodds et al. 2004). Extreme, or supraseasonal, drought (Lake 2003) can completely desiccate perennial stream segments, temporarily eliminating entire fish assemblages from affected segments (Bayley and Osborne 1993). Because supraseasonal drought is not a predictable disturbance to which animals must respond regularly, patterns o f recovery after supraseasonal droughts can differ dramatically from those occurring after seasonal or periodic droughts (Lake 2003). Nonetheless, resistance and resilience to supraseasonal drought are expected to differ among regions based on different degrees o f adaptation to seasonal drought (Poff and Ward 1990; Dodds et al. 2004). The rates and mechanisms o f stream recolonization after drought depend on many factors, in* Corresponding author: sadamsol @fs.fed.us. Received May 27, 2004; accepted April 21, 2005 Published online August 10, 2005 cluding the species pool (Larimore et al. 1959; Lonzarich et al. 1998), presence o f refugia (Sedell et al. 1990; Meador and Matthews 1992; Taylor and Warren 2001; Magoulick and Kobza 2003), size and distribution o f source populations (Sheldon and Meffe 1995; Lonzarich et al. 1998), and recruitment (Larimore et al. 1959; Bayley and Osborne 1993). Typically, species richness recovers before fish abundance (Detenbeck et al. 1992; Sheldon and Meffe 1995; Lonzarich et al. 1998). The timing and spatial scale o f the disturbance strongly influence short-term (e.g., <5 years) recovery (Detenbeck et al. 1992). For example, the seasonal timing o f disturbance relative to fish spawning periods influenced postdisturbance recovery o f fish densities by 6 months or more (Niemi et al. 1990; Detenbeck et al. 1992). Far less is known about crayfish resistance and resilience to drought (Dodds et al. 2004), and no published work addresses disturbance responses by the species common in this study. Interspecific variation in crayfish response to drought appears to be partly attributable to differences in resistance arising from varying burrowing habits (Taylor 1983, 1988). Some species are well adapted to routine stream desiccation, but differences in tol1174 ADAMS AND WARREN TABLE 1.-Locations of sample sites (D = sites that were dry during drought, F = flowing sites) in Benton and Lafayette counties, Mississippi (for more location detail, see Warren et al. 2002). Stream and reach sizes, including lowflow wetted width and streamflow (represented by June 2001 values), predrought (pre) and postdrought (post) reach lengths, postdrought electrofishing effort, and hydrologic conditions (water status) during the drought (Oct 6-Nov 7 2000) are shown. Sampling dates are presented, and column headings indicate how groups of sample dates are referred to in the text. Site Creek Coordinates June 2001 Reach length Watershed Stream Aow Mean area (ha) (m3/s) width (m) Pre (m) Post (m)