Macroinvertebrate-based index of biotic integrity for protection of streams in west-central Mexico

The water and habitat quality of many streams in west-central Mexico are influenced by municipal and industrial effluent, as well as water diversion for irrigation, livestock, and deforestation. Restoration efforts have been hampered by a lack of clear standards against which to judge the degree and trend in environmental degradation. We describe the development and characteristics of a macroinvertebrate-based index of biotic integrity (IBI) designed to provide such standards. Eight metrics chosen a priori comprised the IBI: catch per unit effort, generic richness, % Ephemeroptera-Plecoptera-Trichoptera genera, % Chironomidae individuais, Hilsenhoff Biotic Index, % depositional individuais, % predator individuais, and % gatherer genera. Each metric distinguished sites with minimum or moderate human influence from sites with severe influence. The IBI was developed with data from 27 sites and validated with 6 others. Values from the development data set correlated well with the measures of human influence based on qualitative assessment of habitat and water quality (Pearson's r = 0.86). IBI values for 7 sites on Río Ayuquila corresponded with a documented longitudinal pattern of human influence and the existing fish-based IBI (Pearson's r = 0.87). This macroinvertebrate IBI shows promise for developing biological standards, facilitating long-term monitoring, and improving ecological integrity of streams in west-central Mexico