Effects of a Freshwater Turtle (Trachemys scripta elegans) on Ecosystem Functioning in Experimental Ponds
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Ecosystem functioning is a broad term, often used to describe intra- and interspecies interactions of organisms and the resulting effects on the ecosystem, these ecosystem functioning processes can encompass a variety of phenomena, including ecosystem properties, ecosystem goods and ecosystem services Christenesen et al. 1996). Many aquatic organisms have significant effects on ecosystem functioning and benthic communities. However little is known if freshwater turtles affect ecosystem processes and benthic community assemblage in pond ecosystems. We conducted a study in order to test the direct effects of the red-eared slider Trachemys scripta elegans on ecosystem functioning and benthic communities in experimental pond systems that have never had turtles. The ecosystem processes, biological community and environmental variables we studied were sediment accumulation, leaf litter breakdown rate, periphyton biomass production, invertebrate richness and abundance and water chemistry including pH, conductivity and dissolved oxygen. These processes were measured in the presence or absence of T . s. elegans in the experimental ponds. A multivariate analysis of variance (MANOVA), two-way MANOVA’s and canonical correspondence analysis (CCA) were used to analyze the treatment effects on biological and environmental variables. Significant treatment effects were found when T . s. elegans had been present in the experimental ponds. The pH, conductivity, sediment accumulation, leaf litter breakdown rate and the abundance of invertebrates all averaged higher in ponds that contained T . s. elegans. The significant results detected when measuring the ecosystem functioning processes from this study support our hypothesis that the presence of freshwater turtles such as T. s. elegans does impact ecosystem functioning by altering ecosystem processes and environmental variables. In addition, our study also investigated the potential of T. s. elegans inoculating water or sediment with the bacteria salmonellae. The turtles used in the study, as well as water and sediment from the experimental ponds, were tested using enrichment techniques and polymerase chain reaction (PCR) in order to detect salmonellae. All turtle swabs, water and sediment samples collected did not detect any salmonellae bacteria. The results from this study support our hypothesis that the presence of a freshwater turtle such as T. s. elegans does influence ecosystem processes and benthic communities. Overall population sizes of freshwater turtles are down in South Texas due to commercial harvest and habitat loss (Brown et al. 2011). Loss of freshwater turtles in pond ecosystems may affect the productivity due to the decreased amounts of nutrients provided by the turtles directly and through their activities in ponds. Thus, this study suggests that freshwater turtles can influence pond ecosystem functioning and pond food webs by increasing resource availability for invertebrate communities.