Evaluating the Ecological Conditions of a Semi-Arid River Basin: A Multimetric Index Incorporating Fish and Macroinvertebrate assemblages

The health and integrity of freshwater ecosystems are significantly affected by anthropogenic pressures. Understanding the ecological conditions of freshwater ecosystems is crucial for effective conservation and management strategies. In this study, we developed a new multimetric index, the Karun Fish-Macroinvertebrate Index (KFMI), that incorporates data on fish and macroinvertebrate assemblages to assess the ecological conditions of the Karun River basin, in Iran. We sampled 53 sites and collected data on fish and macroinvertebrate communities, physicochemical parameters, and habitat characteristics. We used physicochemical and physical habitat characteristics data to identify reference conditions using the concept of least-disturbed condition and based on Principal Component Analysis (PCA). We calculated 54 fish and 363 macroinvertebrate metrics to represent different aspects of ecosystem health. We created multiple KFMIs by combining specific core metrics through a stepwise process that assessed metric stability, responsiveness to environmental variables, and redundancy. The final KFMI consisted of seven metrics (3 fish and 4 macroinvertebrate) related to taxa richness, community composition, functional diversity indices, functional feeding groups, reproduction status, and habitat preferences. The index showed good discrimination efficiency (92%) and precision in classifying sites into different ecological health categories and highlights the value of incorporating multiple biological assemblages in multimetric indices to support ecosystem assessment and management strategies.