WAMSI Node 1.1.3 - Rates of Ecological Processes (Controlled Feeding Experiments)

We attempted to asses the potential for using stable isotopes as a tool for rapid assessment of trophic interactions in a nearshore benthic ecosystem in Western Australia. The information gained from this experiment will help us to refine our use of stable isotopes, and contribute to efforts to develop "sharper" tools to achieve the ultimate goal of providing accurate characterisation of food webs, information sorely needed by managers of marine resources. A controlled laboratory scale feeding experiment with the gastropod, Turbo torquatus was conducted to assess the suitability of stable isotope analyses for diet inference. Seventy eight T.torquatus were fed enriched macroalgae (Ulva lactuca) to alter their natural isotopic profile (ä13C and ä15N) and then fed three locally occurring macroalgae (Ulva lactuca, Carpopeltis phyllophora, and Ecklonia radiate) over 17 weeks to assess how their isotopic profile reflected that of their diet. Feeding the enriched macroalgae (Ulva lactuca) to Turbo torquatus increased their carbon and nitrogen isotope ratios to very high levels after just 72 hours. Unfortunately even after 17 weeks of feeding on natural macroalgae (not enriched) the heavier isotope for both carbon and nitrogen was still retained in the muscle tissue of the gastropods. This suggests that the enrichment of Ulva lactuca appears to have been for too long or the concentration of 98% ä13C NaHCO3 and 98% ä15N NH4Cl was much too high.