Energy density of patagonian aquatic organisms and empirical predictions based on water content

We measured the energy density for key species in the freshwater and marine ecosystems of Patagonia, providing the first database of such information for poorly known fauna, including fish, cephalopods, crustaceans, gastropods, annelids, and insects. We then considered an empirical model linking energy density (which is costly to estimate) to water content (which is easy to estimate) and compared the fit of the model with data from different taxonomic groups. Finally, we evaluated the predictive power of models with different levels of taxonomic aggregation to estimate energy density from water content. Fish (7,148-3,443 J/g of wet weight) had the highest energy density, followed by crustaceans (5,906-2,507 J/g), insects (5,794-1,334 J/g), mollusks (5,014-1,661 J/g), and annelids (4,542-1,954 J/g). The use of water content as a predictor of energy density provided greatly improved predictions as compared with use of the mean energy density value. As expected, the predictive power improved when more specific levels of taxonomic aggregation were employed. Nevertheless, we were able to identify levels of aggregation that provided high levels of predictive power. We regard the data generated as primary products for future research on energy fluxes in Patagonian aquatic ecosystems.