Stable isotopes and mass-balance trophic models (e.g., ECOPATH) are well-known and widely usedapproximations to describe food-web structure, but their consistency is not properly established. Herewe analyze the food-web structure of a subtropical-temperate coastal lagoon using two approaches:stable isotopic techniques and mass-balance modelling, exploring also the correspondence between theoutputs of both methods. We compared trophic positions (TPs) derived by these two approaches for 14consumersinLagunadeRocha(LR).TPsbasedonstableisotopesweretakenfromarecentstudy.ECOPATHtrophic levels were estimated by a model presented here constructed based on field data for the period2003–2006 and literature data. The model incorporated over 50 species in 27 trophic groups, including primary producers, invertebrate and vertebrate consumers. The origin and quality of data (pedigreerou-tine) indicated that 68% of the information was locally bound, although several un knowns were detected. Birds and mammals represented the highest trophic levels (4.2 and 3.98, respectively). Network analy-sis estimated a size of the system (fluxes and biomasses) of 451twetweightkm −2 year−1, while transferefficiency, primary production/respiration and production/ biomass ratios, and several ecological indexes characterized LR as an under developed system. TPs derived from isotopic analysis were highly correlated with trophic levels estimated by ECOPATH according to a linear regression model through the origin (r 2=0.82, n=14, p≪0.01). The slope of the linear model (0.88±0.019, estimate±SD) indicated that TPsderived from isotopic analyses were slightly higher (∼13.5% on average) than those derived from themass-balance model. Current results support the overall consistency of the use of both stable isotopesand mass balance modelling approaches as descriptors of this aquatic food-web.
Trophic mass-balance model of a subtropical coastal lagoon, including a comparison with a stable isotope analysis of the food-web.
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