The Everglades crayfish (Procambarus alleni) was first described by Hobbs (1942). P. alleni is found in a variety of Everglades fresh and brackish water habitats ranging from the short-hydroperiod Rocky Glades to perennially flooded sloughs, and from cypress forests to brackish mangrove swamps. The ubiquitous nature of P. alleni in South Florida wetlands demonstrates its ability to colonize and persist in very different habitat types and to play an important role in food webs within those environments. Because crayfish can assimilate detritus into biomass (Momot, 1984), they are efficient providers of energy to higher trophic levels should be considered. In Everglades National Park (ENP), many predators have been shown to consume P. alleni. The original proposal to study the Everglades crayfish (Procambarus alleni) was of limited scope and duration, and formed part of a MasterĖs program for a student. The scope included the collection of density and biomass data for the crayfish across a hydrological gradient from the rocky glades into the Big Cypress Swamp, and the description of selected recruitment parameters for an ATLSS model. The most dramatic finding has been the discovery of a second species of crayfish, Procambarus fallax, in the study marshes. This species was previously known to range southward into Palm Beach County, but had never been identified from the Everglades. We are now studying the ecological interactions between the two species.

The purpose of this project is to provide empirical data in support of the ATLSS modeling program, which is the major tool used to measure ecological effects of proposed Everglades restoration activities. This study is providing needed estimates of crayfish abundance, size-frequency, fecundity, size at first reproduction, seasonality of gravid females, and the timing of movements and disappearance from the surface into burrows or solution holes as the habitats dry. Because two species of crayfish inhabit diverse surface environments throughout the Everglades region, we expect habitat partitioning to be expressed by behavioral or life-history adaptations in specific habitats, and to respond to ambient hydrological conditions. We have described characteristics of life-history and demographic to document adaptations to habitat type. This study has also provided the first, baseline database of the relative abundance and standing stocks of the two species in several habitat types from south Florida. This has been accomplished by obtaining seasonal abundance information in habitats spanning a hydrological gradient in Everglades National Park and Big Cypress National Preserve.

In the first segment of this study, we collected the first records for Procambarus fallax in south Florida wetlands. We amassed life-history data for the Everglades crayfish, P. alleni, as well as P. fallax, by collecting 790 throw-trap samples. We tested the throw-trap method for crayfish capture efficiency to estimate an average efficiency by location (based on data collected in July of 1997). The rates were Shark Slough spikerush 56 percent (± 15 percent) Shark Slough sawgrass 49 percent (± 24 percent), BICY domes 60 percent (± 13 percent), BICY prairie 59 percent (± 24 percent) and East Slough 75 percent (± 22 percent). We examined data collected by this project, and from archived samples back to 1985, to understand the habitat requirements (particularly hydrological requirements) of each species. Results of that effort included:

1. Indications of a strong link between species-specific requirements and hydrology: P. fallax inhabited long hydropattern locations while P. fallax inhabited short hydroperiod locations. The two species overlapped in areas that are intermediate in hydroperiod.

2. Species distributions at sites changed in relation to short-term changes in hydrology, then reversed when normal hydropatterns return.

We collected ovigerous P. fallax in sawgrass, spikerush and cypress domes; however, field observations suggested that the ovigerous females are using sawgrass habitat preferentially. Additionally, it appeared that newly detached crayfish are also found in higher numbers in sawgrass versus spikerush habitats. The lack of information on growth for either P. fallax or P. alleni led us to attempt to raise newly detached crayfish under laboratory conditions. While laboratory aquaria in no way simulated field conditions, molt increment has been reported to be somewhat stable irrespective of habitat. These molt increments in captivity averaged 0.94 mm/molt in P. fallax and 1.368 mm/molt in P. alleni.

Activities in 1999 are incorporating the following areas of study:

• Initiation of caged-crayfish experiments in the field in 1999. Through placement of individually marked animals in the field, we intend to simulate field growth rates without an extensive mark-recapture scheme.
• Collection of the two crayfish species, and potential prey items, for stable isotope analysis. The mastication process of crustaceans results in the gut contents being unrecognizable. Stable-isotope analysis, while not a quantitative method for assessing diet contents, has proven useful in assessing trophic links, placement, and food-web pathways.
• Determination of species-specific hydrology requirements through additional analysis of archived samples, including samples collected in 1996 and 1997 in Shark Slough, BICY, East Slough, Taylor Slough, and Conservation Area 3, and archived samples collected from 1975- 1997 in ENP.
• Incorporate crayfish hydrology requirements into a spatially explicit coverage through ARC/INFO. Using existing coverages of water depth provided by ENP hydrologists, and field samples collected during the period matching the water depth coverages, we plan to create a species-distribution map. In 1999 we plan to ground-truth predicted distribution maps through field collections.
• Initiation of pilot study of mechanisms that are responsible for creating the patterns of species distribution. Using mesocosms, we will attempt to simulate various drying conditions, which might favor one species over another in microhabitats such as marsh, cypress prairie, and cypress domes. We will examine the survival of each species, its strategy for coping with falling water depths, and related factors.

Funding for this project was provided by the U.S. Department of Interior South Florida Restoration Program "Critical Ecosystems Studies Initiative" (administered by the National Park Service).

REFERENCES

Hendrix, A.N., and Loftus, W.F., in review, Distribution and relative abundances of the crayfishes Procambarus alleni and related to hydropattern: Wetlands.

Hendrix, A.N., and Loftus, W.F., in preparation, Life-history parameters for Procambarus fallax in the Everglades system: J. Crustacean Biology.

(This abstract was taken from the Proceedings of the South Florida Restoration Science Forum Open File Report)