Stable isotopes and mercury as tools to depict aquatic food webs

The structure of food webs is a fundamental attribute of ecosystems, and their characterization provides an intrinsic knowledge of the trophic interactions among organisms and of nutrient and energy transfer within ecosystems. Over the last few decades, several chemical and biogeochemical approaches have been proposed to explore different aspects of food webs. In this sense, this study reviews the application of stable isotopes and mercury as main auxiliary tools to the characterization and modeling of aquatic food webs, including analytical and modeling advances, strengths and limitations. The metanalysis performed showed that the most used tools for trophic ecology studies are stable isotopes, and that they can provide better results when combined with mercury and specific chemical molecules such as amino and fatty acids. In addition, the statistical methods applied in the interpretation of results, such as isotope mixing models, have witnessed significant advances in the last two decades. All approaches have premises and limitations when applied to aquatic ecosystems, which must be well understood prior to results interpretation. The use of multiple tracers in trophic studies provides complementary information and in many cases is an appropriate alternative to overcome some limitations, allowing to expand the knowledge of the food webs.