Distribution and abundance of water impacts population dynamics and habitat structure within a wetland ecosystem. It is known that drought can interfere with trophic dynamics and temporarily free crayfish from the threat of predation by population limiting fish predators in seasonal freshwater wetlands. Less is known about wet season water depths, and their effect on predator prey interactions. In order to address this, I conducted a two-and-a-half-year study in which I experimentally manipulated the wet season water depth in four 8 ha replicate wetlands of the central Everglades, allowing two wetlands to be flooded as natural rainfall patterns would allow (unconstrained hydro-pattern) and two wetlands to experience a constrained hydro-pattern in which the maximum depths to which they were flooded was limited. I discovered that crayfish, small marsh fish, and large bodied predatory fish populations were unaffected by the water depth difference between the hydro-pattern treatments. Unlike fauna, flora did respond to the hydro-pattern treatments with stem densities increasing in the wetlands under the constrained hydro-pattern treatment. / Includes bibliography. / Thesis (MS)--Florida Atlantic University, 2021. / FAU Electronic Theses and Dissertations Collection

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Organismal invasions have repeatedly been cited as both a driving force behind global change and beneficiaries of that change. Although many drivers of these invasions have been well studied, few studies have addressed invasions through the perspective of native symbiont communities. In the Mountain Lake region of Virginia, crayfish host diverse assemblages of obligate cleaning symbionts known as branchiobdellida. This cleaning symbiosis has been found to result in significant fitness benefits for native crayfish. Historical survey work showed that invasive crayfish, known to be intolerant of symbionts, were introduced into the region by the 1960s. I carried out an extensive regional survey to determine how this invasion has progressed and what impacts it is having on the native crayfish-branchiobdellida symbiosis. Survey results show that invasive crayfish have successfully spread throughout the region, resulting in the displacement of native crayfish. Additionally, findings suggest that invasion results in significantly reductions in abundance and richness in native symbiont communities. To determine mechanisms contributing to observed impacts on native symbionts, I carried out a study that simulated displacement of native crayfish by invasive crayfish in a controlled setting. This study found that as native crayfish are increasingly displaced by invasive crayfish, both symbiont dispersal and survival are negatively affected. This potential loss of symbiosis caused by invasion may reduce symbionts on native crayfish below abundances necessary for fitness benefits, exacerbating the negative impacts of invasions and presenting a major conservation issue in invaded systems. / M. S. / Introductions of non-native organisms are widely recognized for the negative impacts they have on native biodiversity. Although ongoing study has been directed at understanding many of the factors contributing to invasions, few studies address invasion through the perspective of native symbionts. In the Mountain Lake region of Virginia, crayfish host multiple species of small worms, known as crayfish worms, that provide cleaning services to their crayfish host. These services have been found to provide health benefits to native crayfish. Historical surveys found that invasive crayfish, known to be intolerant of crayfish worms, were introduced into the region by the 1960s. To determine how far invasive crayfish have spread and what impacts they are having on native organisms, I carried out a survey of the region. This survey found that invasive crayfish are now widespread in the region. Additionally, findings suggest that the introduction of invasive crayfish results in reductions in both the number of worms and worm species present. These reductions may be significant enough to prevent health benefits given to native crayfish from occurring. In addition to this survey, I carried out a study under controlled settings to determine what causes negative impacts on native crayfish worms. This study found that as invasive crayfish displace native crayfish, crayfish worms are increasingly killed due to the intolerance of invasive crayfish to the worms. These findings suggest symbiosis should be included in studies of invaded systems if we are to fully understand the introduction and spread of invasive species.

The regulatory emigration hypothesis was tested experimentally using the crayfish Orconectes causeyi Jester. Varying amounts of food and shelter were provided to crayfish in tanks with escape routes. O. causeyi rapidly adjusted its numbers in harmony with available resources through density-dependent emigration. Shelter influenced the distribution and abundance of O. causeyi most. Response to food occurred but less and took longer than the response to shelter. The small amount of variance between numbers of crayfish that emigrated during both short-term and long-term replicate tests strongly supports the regulatory emigration hypothesis.

Thesis (M.Sc. Biological Sciences)--University of Waikato, 2009. / Title from PDF cover (viewed October 2, 2009) Includes bibliographical references.

The aim of this study was to investigate growth and reproduction of the noble crayfish (Astacus astacus L.) in polyculture with plant-feeding fish: grass carp (Ctenopharyngodon idella), and bighead carp (Aristhichthys nobilis) in crayfish ongrowing ponds system. For the first time this experiment was conducted in Simnas crayfish breeding farm (Alytus distr.) during 2002 summer and autumn seasons. The effects of plant-feeding fish on abundance of the aquatic macrophytes, crayfish survival, growth rate and reproduction in semi-intensive culture conditions were investigated. After this experiment we have found, that grass carp and bighead carp community effectively regulates quantity of aquatic macrophytes in small (80 m²) ponds system. Moreover plant feeding fish had no negative impacts on survival and growth of the noble crayfish, so it might be used in polyculture with crayfish for reducing aquatic vegetation in crayfish ongrowing pounds. To assess the reproduction efficiency of noble crayfish in semi-intensive culture conditions the number of mature and ready for reproduction females crayfish was identified. The research was carried out measuring the development level of cement glands.

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