Assessing effects of stress across levels of biological organization using an aquatic ecosystem health index.

Multimetric approaches typically consider only one level of biological organization to assess the effects of environmental stressors on the health of aquatic ecosystems. The present study applied integrative star-plot analysis to evaluate effects of stressors over several levels of biological organization ranging from the sub-organism to the community level at study sites subjected to different levels of contaminant stress. An aquatic ecosystem health index (AEHI), based on the sum of all the star-plot areas over these levels of biological organization, was developed to reflect an integrative and holistic assessment of stressors on ecosystem health. Star-plot areas ranged from 1.96 at a reference site to 0.79-1.08 at sites located at increasing distances downstream from a pulp mill discharge. The values of the AEHI were positively correlated with the index of biotic integrity (IBI) scores (Pearson's r=0.824). The AEHI can be used to evaluate the overall health status of aquatic systems, to identify those levels of biological organization that have the greatest response to environmental stressors, and to help identify possible causes of observed effects. Results from this study suggest that the AEHI approach can avoid false-negative responses that can occur from assessing effects at only one level of biological organization.