Anthropogenic flow intermittency shapes food-web topology and community delineation in Mediterranean rivers

Anthropogenic flow intermittency is considered a severe disturbance for benthic macroinvertebrates with largely unknown impacts on the organization of benthic communities and their food webs. We analysed the community composition (as taxonomic composition and relative abundance of taxa) and food webs of the macroinvertebrates inhabiting the pools and riffles of two Mediterranean streams with contrasting perennial and anthropogenic intermittent flow regimes. Our analyses comprised monthly measurements in two pools and two riffles of the community composition, food-web topology (the pattern in which specific links are arranged within the network) and food-web complexity indexes (the number of nodes and links regardless of their identity or arrangement) over 1 year. The food webs revealed a significant annual variation in size, complexity, and diversity within pools and under perennial flow (e.g., number of nodes, number of links, link density). Multivariate analysis showed strong differences in the composition and relative abundance of taxa and food-web topology of assemblages inhabiting pools and riffles. However, differences between communities inhabiting pools and riffles varied during the year; periods of great similarity were followed by periods in which communities were very different. This annual sequence of differences between pools and riffles was compressed under the anthropogenic flow intermittency regime. The anthropogenic intermittent flow studied here might represent a moderate stressor for Mediterranean communities well-adapted to dry conditions. Still, the reported deviation of the community composition and food-web topology from the reference status reflect the detrimental effect of this stressor on the benthic community.