Benthic consumers and autotrophs in recovering acidified lakes: Patterns and processes

The relative importance of grazing and abiotic factors to benthic autotrophs was examined in six recovering acidified boreal lakes. Chemical variables (pH, DOC, phosphorus) were significant predictors of biomass and taxonomic composition of autotrophs and consumers. A nonsignificant relationship between autotrophic and consumer biomass, and stable isotopic evidence of detrital and planktonic food sources, suggested grazing pressure was weak. A 2-factor (stress x consumer size) experiment tested if grazing pressure was maintained across three acid-stressed and recovered lakes owing to a compensatory grazer size shift. Abiotic stress suppressed autotrophic biomass and altered community composition. Consumers did not affect autotrophic biomass, but large grazers influenced composition in recovered lakes. Differential impacts of consumers and abiotic stress on autotrophic communities highlighted their capacity to compensate for weak natural disturbances (e.g., grazing), but not chronic stress (e.g., anthropogenic acidification). The primacy of abiotic factors in structuring benthic communities suggested biological recovery remained incomplete.