Effects of antecedent drying events on structure, composition and functional traits of invertebrate assemblages and leaf‐litter breakdown in a former perennial river of Central Apennines (Aterno River, Abruzzo, Central Italy)

Because of global change and increasing anthropogenic pressures, non-perennial rivers and streams are predicted to drastically increase in the European-Mediterranean region. Some river basins already subject to reduced levels of available superficial flow may present a further reduction, with a significant increase in intermittence phenomena and complete drought of former perennial rivers. In this context, a sound knowledge of the ecological effects of increasing drying events on these watercourses may help to better predict impacts of the altered flow regime on structure and functions of freshwater ecosystems. In this paper, we assessed the long-term response of invertebrate assemblages and ecosystems processes to antecedent drying events (drying memory) in a Central Apennine river (Italy). We demonstrated that compared to the perennial reach, the 7-km downstream intermittent site, after more than 1 year from a complete superficial flow resumption, still conserved the ‘memory’ of past disturbance with marked differences in structure, composition and functional traits of assemblages which, in turn, negatively influenced the leaf-litter breakdown process. Despite total abundance and taxa richness were on average higher at the intermittent site, antecedent droughts determined a decline of shredders and scrapers and an increase of collectors. In addition, some more sensible, semivoltine and rheophile taxa were replaced by generalist, multivoltine and more resistant taxa. Our findings confirm and extend the ‘drying memory’ hypothesis and suggest that irregular drying events in former perennial Apennine rivers may have dramatic long-term effects on both structure and functions of lotic ecosystems.