Biomass of benthic invertebrates unaffected by industrial damage to lakes despite effects on species composition

Historic metal mining and smelting in the area of Sudbury, Ontario, has resulted in lakes with elevated levels of metals in the sediment, low inputs of terrestrial organic material, and unusual fish communities which led to severe changes in the benthic invertebrate community. Using broad-scale surveys of lakes from Sudbury and an undisturbed reference area, we used multivariate methods to tease apart potential influences of predation by fish, habitat availability, and toxicity of the environment on the biomass of benthic invertebrates. In contrast to many other studies, our response variable is benthic invertebrate biomass-a more relevant factor in food web processes than the numeric densities that are more typically studied. Despite differences in species composition, we observed very similar total benthic invertebrate biomass in Sudbury lakes and reference lakes. Redundancy analysis revealed that different factors shaped invertebrate biomass in the two study areas. Sudbury benthos was strongly influenced by the fish community and metal toxicity with only slight effects of habitat quality. Overall, the fact that benthic invertebrate biomass was similar to reference systems suggests that Sudbury communities may be able to function normally despite the strong direct and indirect effects of multiple stressors.