Using stage-structured food webs to assess the effects of contaminants and predators on aquatic–terrestrial linkages

Aquatic insects are routinely used to measure the biological responses of streams and lakes to contaminants and predators, but assessments often focus only on benthic larval stages. However, like many organisms on earth, aquatic insects have complex life histories in which ontogenetic stages vary in their ecology, habitat, and susceptibility to stressors like contaminants and predators. Here, I summarize the differential responses of aquatic insect life stages (e.g., larva, pupa, adult) to fish predation and contaminants, 2 common and well-studied sources of mortality for aquatic insects. I then examine how stage-structured mortality may alter the link between larval aquatic insect densities and flux of emerging aquatic insects to terrestrial food webs. The most important finding is that predictions of aquatic insect responses based on stage structured food webs deviate strongly from predictions that do not include life stages, implying that larval responses to predation or contaminants may not be appropriate in predicting adult responses. Larval-based bioassessment continues to be an important tool for stream conservation and management. However, failure to account for variation in stage-specific responses may limit the utility of current bioassessment tools to predict aquatic insect emergence, potentially underestimating the impact of freshwater stressors on linked aquatic–terrestrial ecosystems.