Invertebrate Fauna of the Carapaces of the Texas River Cooter (Pseudemys texana) and the Red-Eared Slider (Trachemys scripta elegans)

Abstract

Symbiotic relationships occur between many pairs of species of organisms. The relationship between algae and turtles recently has been quantified. The relationship between turtles and aquatic invertebrates is less known. This study described quantitatively the invertebrate fauna inhabiting the algal covering of the carapaces of 2 species of freshwater turtles, the Texas river cooter (Pseudemys texana) and the Redeared slider (Trachemys scripta elegans) at Spring Lake, Hays County, Texas. Turtles were captured from August through November 2002 using hoop nets, basking traps, and dip nets. Invertebrate samples were obtained by scraping a small area of the carapace to completely remove the algae and accompanying invertebrates and by brushing through the algal covering to remove invertebrates from the entire carapace. Invertebrates from each sample were identified using dissecting stereomicroscopes and quantified by subsampling. Taxa of aquatic invertebrates identified included species of Rotifera, Nematoda, Crustacea, Gastropoda, Insecta, and Hirudinea. A comparison of the similarity and diversity of invertebrates on the carapaces of P. texana and T. s. elegans revealed similar communities. A positive correlation occurred between carapace size and number of invertebrate taxa, indicating that larger turtles may support more invertebrate taxa than smaller turtles, in accordance with Island Biogeoraphy Theory. Turtle carapaces represent a substrate type to be considered in studies of freshwater systems because they possess ecological variables providing space, food, and protection for aquatic invertebrates. Due to their mobile lifestyle, turtles may contribute to the spread of invasive exotic organisms between bodies of water and river drainage systems.