Diet-tissue discrimination and turnover of δ C and δ N in muscle tissue of a penaeid prawn.

RATIONALE

Stable isotopes are used to study trophic and movement ecology in aquatic systems, as they provide spatially distinct, time-integrated signatures of diet. Stable isotope ecology has been used to quantify species-habitat relationships in many important fisheries species (e.g., penaeid prawns), with approaches that typically assume constant values for diet-tissue discrimination and diet-tissue steady state, but these can be highly variable. Here we provide the first report of these processes in Metapenaeus macleayi (eastern school prawn).

METHODS

Here we explicitly measure and model carbon (δ C) and nitrogen (δ N) diet-tissue discrimination and turnover in eastern school prawn muscle tissue as a function of experimental time following a change in diet to an isotopically distinct food source.

RESULTS

Diet-tissue discrimination factors were 5 and 0.6‰ for δ C and δ N, respectively. Prawn muscle tissue reached an approximate steady state after approximately 50 and 30 days for δ C and δ N. Half-lives indicated faster turnover of δ N (8 days) than δ C (14 days).

CONCLUSIONS

Our diet-tissue discrimination factors deviate from 'typical' values with larger values for carbon than nitrogen isotopes, but are generally similar to those measured in other crustaceans. Similarly, our estimates of isotopic turnover align with those in other penaeid species. These findings confirm muscle tissue as a reliable indicator of long-term diet and movement patterns in eastern school prawn.