Land use effects on the field metabolic rate of stream crayfish

The effects of land development on stream ecosystems is often measured in terms of changes in primary productivity, contaminant concentrations, and community composition. In contrast, how humans and their activities in the catchment alter the physiological processes of key stream invertebrates has received less study. Field metabolic rates (FMR) of crayfish were assessed in seven southern Ontario streams ranging in agricultural land use. Site-specific regressions between log-mass and log-FMR revealed slopes (hereafter called the scaling exponent) that varied widely among streams, from 0.30 (r² = 0.51) to 1.08 (r² = 0.91). This wide range translates into several fold differences in FMR between sites even for individuals of the same mass. Scaling exponent variation among sites was strongly related to the proportion of monoculture-type agriculture within the watershed (r²= 0.90). Preliminary results also suggest that food quality is partly attributable for these differences in the scaling exponent. Our findings suggest: 1) the mass-specific FMR of crayfish can vary widely among streams and 2) this variation is related to human land use in the stream catchment. Human activities thus appear to alter trophic transfer efficiencies of invertebrates and food webs of stream ecosystems.