Seasonal variability in glacial influence affects macroinvertebrate assemblages in North-Andean Patagonian glacier-fed streams

Abstract

Macroinvertebrate communities of glacial streams are affected by melting mountain glaciers, which in turn are influenced by landscape and local and global climate change. We analyzed macroinvertebrate communities in 2 North-Andean Patagonian glacier-fed streams. The significant difference in glacial influence between the 2 streams was due to differences in glacier flow velocity and to the presence of a proglacial lake in one of the streams. Our main aim was to analyze whether temporal variations in physical and chemical parameters of meltwater produced shifts in macroinvertebrate taxon richness and community composition. We applied the glaciality index (GI) to consider the combined effect of suspended solids, water temperature, conductivity, and streambed stability. On each stream we established one sampling station; we sampled during the melting season (spring–summer) of 3 consecutive years on 12 occasions. Macroinvertebrate taxon richness, diversity, and evenness increased as glacial influence decreased. Scrapers were the dominant functional feeding group in the stream with the lower glacial influence while detritivores-gathers dominated under high glacial influence. We further analyzed how temporal changes in the GI affected compositional differences among communities using Bray-Curtis dissimilarities. Under a stable GI, communities showed no substantial compositional changes (low Bray-Curtis), whereas under change in glacial influence (ΔGI ≠ 0) the communities decreased in similarity.