ABSTRACT: The body size composition of benthic communities is commonly described using abundance-body mass relationships (size spectra). We tested whether the slopes of these relationships in a central North Sea infaunal community could be predicted fromthe energy available to different size-classes of animals. The results showed that the observed slopes were consistent with predictions of slope based on available energy at mass, where available energy was calculated from empirical measurements oftrophic level (using nitrogen stable isotope analysis) and estimated trophic transfer efficiency. If our preliminary findings prove to apply more widely, then our macroecological approach may be refined to validate size-based models of community structureto explain regional differences in size structure and to underpin the development of new disturbance indicators.