Comparing responses of freshwater fish and invertebrate community integrity along multiple environmental gradients

Multimetric indices of biotic integrity provide a quantitative measure of biological quality and have been developed for several taxonomic groups. Community integrity for fish is typically represented by the multimetric Index of Biotic Integrity (IBI), while for macroinverterates the Invertebrate Community Index (ICI) can be applied. Given the considerable sampling efforts required for biomonitoring, it is important to know the extent to which indices based on particular taxonomic groups respond differently to (anthropogenic) stressors in the environment. The three goals of our study were (1) to assess the concordance of freshwater fish and macroinvertebrate communities, (2) to derive stressor–response relationships for IBI and ICI pertaining to multiple environmental factors and (3) to compare the responses of IBI and ICI to these environmental factors in the state of Ohio (USA). We used a database containing abiotic as well as biotic information for 545 local catchments located across Ohio (USA). Our 22 environmental factors covered physiography, water chemistry, physical habitat quality and toxic pressure. Concordance between the fish and invertebrate communities was assessed using a Mantel test. Response patterns of IBI and ICI to each of the environmental factors were analyzed by constructing stressor–response curves with Boosted Regression Trees (BRT). Fish community integrity was primarily related to physical characteristics of the stream (channel- and riffle quality) and latitude, whereas invertebrate community integrity mainly responded to the phosphorus concentration. Response curves showed that the two indices responded similarly to most of the water chemistry variables, while responses differed for physiographical and physical habitat quality variables.