Secondary production of benthic communities at the habitat scale as a tool to assess ecological integrity in mountain streams

Secondary production of the benthic community was estimated in the four functional habitats identified in the pristine Pioverna stream (Northern Italy): riffle, pool, transition and bedrock habitats. The instantaneous growth, removal-summation and size-frequency methods were used to estimate production. Twelve taxa reached appreciable densities and presumably accounted for most of total benthic production. Three of them belong to the Plecoptera, seven to the Ephemeroptera and one each to Diptera and Trichoptera. The riffle habitat had the highest secondary production, while bedrock habitat had the lowest. Pool and transition habitats showed intermediate production values. Shredders and predators were the major component of production in pools, with a low contribution of gathering collectors. In riffles, this last category and scrapers had the highest production, with shredders, predators and filtering collectors showing decreasing production values. In general terms, shredders, gathering collectors and scrapers contributed most to total production. The rank-production curves for the habitats are reported. In riffles, a proportionally high evenness of the most productive taxa was noted. In contrast, in the pool habitat a steep curve was recognised. The potential of comparing rank/production curves and changes in reference species production between unaltered and impacted stream habitats and sites is discussed as a means to estimate ecological integrity. For site comparisons of secondary production in the alpine area, the riffle habitat is suggested as the most adequate, as it shows a lower dominance and more taxa contributing to overall production. The calculation of secondary production for indicator and dominant taxa in the different habitats should constitute an effective way to describe some functional aspects of the community to assess the ecological integrity of mountain streams.