Stable isotope analysis in fisheries food webs

Stable isotope analysis has been used as a technique to analyse fisheries food webs for a quarter of a century, and remains the principal method for determining energy and nutrient pathways from primary producers to consumers in aquatic ecosystems. Carbon isotope analysis has been used to distinguish autotrophs at the base of inshore and offshore fisheries food webs. The combination of nitrogen and carbon isotope analysis has established the contributions of different food items to the energy and protein requirements of fish. Methodological issues with stable isotope analysis are being solved using new laboratory and mathematical modelling techniques. For example, compound-specific isotope analysis of phytol (the side-chain of chlorophyll), can be used to obtain a carbon isotope signature of benthic microalgae without interference from contamination. Advanced mixing models help distinguish among sources even in situations such as estuaries where potential sources are numerous. The addition of sulphur analysis can help to separate the contribution of sources indistinguishable using carbon and nitrogen. Ultimately, when natural abundance isotopes cannot separate sources, the addition of enriched isotope material in pulse-chase tracer experiments is effective in testing among alternate food web models.