Effects of disturbance at two spatial scales on macroinvertebrate and fish metrics of stream health

We analyzed macroinvertebrate and fish assemblage data collected from the upper southeastern coastal plain of the USA to (1) assess the relative sensitivities of bioassessment metrics to in-stream habitat quality, catchment scale land disturbance, and the presence of a reservoir in the catchment and (2) determine whether fish differ from macroinvertebrates in their responses to these variables. Fish and macroinvertebrates responded differently to anthropogenic disturbance: macroinvertebrates were affected most strongly by in-stream habitat quality and fish by the presence of a reservoir in the catchment. Neither taxonomic group were significantly affected by the catchment scale disturbance, probably because the proportions of disturbed land in the study areas were low. Fish may be particularly sensitive to the presence of reservoirs because of their need to cover relatively large distances to complete life cycles and maintain viable populations and because of their sensitivity to the effects of invasive reservoir species, particularly predator fishes. Although not an important predictor in itself, disturbance at the watershed scale was significantly and positively related to in-stream habitat quality, indicating that watershed disturbance had an important indirect effect on aquatic organisms. Direct and indirect ordination showed that the metric data were more strongly related to the disturbance variables than the taxonomic data from which the metrics were derived, possibly because the metrics were less sensitive than the taxon-specific abundances to nondisturbance-related factors. Other factors that may have contributed to this result include greater statistical tractability of the metric data and the relatively high sensitivity of the collective properties represented by the metrics to disturbance-related environmental changes.