Size-mass relationships in Trichodactylus fluviatilis Latreille, 1828 (Decapoda: Brachyura: Trichodactylidae), a macroconsumer in coastal streams of the Atlantic Forest, southeastern Brazil

We determined the size-mass relationships for two populations of the freshwater crab Trichodactylus fluviatilis Latreille, 1828 in the Atlantic Forest along the southeastern coast of Brazil. Different mathematical models (linear, exponential, and power) and body variables (carapace length (CL) and width (CW)) were used to determine the best relationships to estimate the biomass of males, females, and all individuals sampled. The values of the body variables and biomasses did not differ between the sexes or the populations studied. Considering data for all individuals and for males only, the best relationships to estimate the biomass of T. fluviatilis were determined using the power model and CW in the Macuco population and the power model and CL in Mestre Alvaro (model selection using small-sample corrected Akaike's Information Criteria). The best relationships in females were calculated using the linear and power models and CW in the two streams. The slopes of the power model equations determined by both body variables did not differ between the sexes in either stream, but differences were observed when all individuals of the populations were considered. The results support the use of carapace length and width as predictors of the biomass of T. fluviatilis and the population-specificity of size-mass relationships, which requires the determination of one specific equation for each population studied. The biomass estimation of T. fluviatilis through size-mass relationships contributes to the evaluation of the role of these macroconsumers in the detritus-based food webs of Atlantic Forest streams.