Theses and Dissertations

Defense Date

3-2003

Document Type

Dissertation

Degree Name

Ph.D. Oceanography/Marine Biology

Department

Oceanographic Center

First Advisor

Bart J. Baca

Second Advisor

Patricia Blackwelder

Third Advisor

Curtis M. Burney

Fourth Advisor

Frank Jordan

Abstract

Two species of epigean crayfish, Procambarus alleni (the Everglades crayfish) and Procambarus fallax (slough crayfish), may be keystone species that inhabit wetlands in south Florida and the Everglades. Recent field studies showed that although these two species occur in sympatric and syntopic distribution, Everglades crayfish prefer shallow water and short hydroperiod conditions, whereas slough crayfish prefer areas that are more permanently flooded (Hendrix 2000). Slough crayfish have invaded some areas within the range occupied by Everglades crayfish, and may be the more successful competitor. Because of their critical role throughout the trophic structure of Everglades wetlands, shifts in relative abundance of these two species through water management decisions may have significant effects on wetland communities and the overall availability of crayfish as food for other organisms.

To examine the biology and ecology of Everglades and slough crayfish, three experiments were conducted on juveniles, under laboratory conditions that simulated environmental conditions in wetlands of south Florida. Adult crayfish of both species were obtained mostly from natural areas in south Florida, including wetlands that were historically connected to the northern Everglades. Young crayfish were hatched from berried females captured in the field or bred in the laboratory.

Experiment 1. Growth, survival, and development of Everglades and slough crayfish hatchlings were monitored to three months of age, under stable conditions (water depth and food availability). Weight, total length, survival, and development (presence and size of male gonopods) were recorded at nearly four week intervals. Slough crayfish had significantly higher survival rates than Everglades crayfish, however, statistical analysis indicated that Everglades crayfish grew significantly larger than slough crayfish, at a faster rate. Linear regression showed that juvenile slough crayfish were heavier at a given length, and combined with gonopod development, was used to predict that slough crayfish become mature at an earlier age than Everglades crayfish.

Experiment 2. In this multifactorial experiment, the effects of abiotic (various conditions of food availability and water levels) and biotic (density and competition) factors were examined on the survival and growth of hatchlings of both species up to three months old. Assuming that slough crayfish was an invading species, emphasis was placed on competitive influences of slough crayfish on Everglades crayfish. In conditions simulating different water levels, Everglades crayfish survival was most impacted by low food availability, high density, all three water levels, and intraspecific competition, while highest survival took place in conditions of high food availability, and low density. Lowest survival of slough crayfish occurred in low food availability, high density, and low water levels. slough crayfish had higher survival in all conditions tested. Everglades crayfish grew significantly larger in size than slough crayfish in all conditions tested. Growth of Everglades crayfish was most impacted by low food availability, drying conditions, high density, and intraspecific competition in high and low densities. The best conditions for growth of Everglades crayfish included high food availability, low water levels, low density, and interspecific competition with slough crayfish. The growth of slough crayfish young was most impacted by low food availability, high density, and high density interspecific competition. Slough crayfish grew largest under conditions of high food availability, low density, and low density interspecific competition, but reached the same size in all three water levels tested.

Experiment 3. Patterns of behavior and choice of substrate of juvenile Everglades and slough crayfish, in the presence of an arthropod predator were observed, both day and night, during a 48 hour time period. Juveniles were offered four choices of substrates commonly found in Everglades environments (Utricularia foliosa, Panicum hemitomon, Typha domingensis, and sand), and seven possible behavior choices (feeding, resting, moving, digging, retreating, avoiding, or approaching).With and without the presence of an arthropod predator, both species spent the greatest amount of time in U. foliosa and P. hemitomon, and the least amount of time in T. domingensis and on sand. At night, in the presence of the predator, slough crayfish spent significantly more time secluded in bladderwort than Everglades crayfish, but Everglades crayfish was twice as exposed on sand.

In the absence of the predator, feeding was the primary activity of both species during the day, but at night Everglades crayfish foraged while slough crayfish rested. a greater percent of time Both species were more mobile during the day, whether the predator was present or not. In the presence of an arthropod predator, juveniles of both species fed more during the day, but at night spent more time resting.

Because of its larger size, propensity for burrowing, and probably a more size-structured population, Everglades crayfish may have a competitive advantage in resource holding potential, ability to survive adverse drying conditions, and in reproduction, by producing larger numbers of eggs. Slough crayfish grow more slowly, tend to be heavier than Everglades crayfish at a given length, and reach maturity at a smaller size and younger age than Everglades crayfish. U. foliosa was the preferred substrate at all times by young crayfish, probably due to providing optimal shelter and food. In the presence of an arthropod predator, diurnal activity patterns were followed. If survival and growth strategies of slough crayfish are enhanced by long hydroperiods and appropriate depths in Everglades environments, then slough crayfish could have a considerable competitive advantage over Everglades crayfish in survival, reproduction, and development strategies. However, Everglades crayfish may have size-related advantages over slough crayfish.

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