Determining the partition of resources of different species of rays using stable isotopes in Shark Bay, Western Australia

Given the large-scale modifications to coastal marine ecosystems, it is important to understand the structure and function of pristine systems in order to draft management strategies and set conservation benchmarks. Stable isotope tracers are already present and circulating in natural systems, and their natural distribution reflects an integrated history of physical and metabolic processes within ecosystems. Stable isotopes are ideally suited to increase our understanding of element cycles in ecosystems. Gaining an understanding of diet, food web, and trophic position of a ray community in a pristine ecosystem is of conservation value. Shark Bay on the western coast of Australia is a World Heritage Area and diverse ecosystem. The study will discuss the interactions of ray species within the bay via biogeochemical markers (stable isotopes) and determine the partition of food resources available. Tissue samples were collected from five ray species non-destructively between September 2005 and May 2007. Primary consumers (e.g. filter feeding clams, detritivores) and primary producers (e.g. plankton, seagrass, macroalgae) were also collected to determine the isotopic baseline of the area and to aid in estimates of trophic position. Stable isotopic signatures were compared and used to determine species, season, and habitat differences. Preliminary results suggest that food resources are shared across species and habitat.