Seasonal influence and local factors affecting macroinvertebrate structure in a high-altitude Andean stream

Small water bodies are critical for maintaining freshwater biodiversity, but are among the least investigated aquatic environments. We examined physical and chemical variables at two reaches in Arroyo Tambillos, a small, high-elevation Andean stream, in NW Mendoza province, Argentina,across four seasons to examine how local factors and seasonality affected the structure of the macroinvertebrate community. The Arroyo Tambillos community was numerically dominated by ephemeropterans(mainly Massartellopsis irarrazavali) while the dipteran Chironomidae were the most species rich. Total macroinvertebrate abundance was highest in summer, driven mainly by taxa that were secondary in dominance(Austrelmis sp. and Andesiops peruvianus), while richness did not differ between seasons. However, benthic composition was different in Fall 2013(March)compared to other seasons, largely because of the increased abundance of Chironomidae. Canonical correspondence analysis discriminated Chironomidae species distributions in Fall 2013 by substrate type(i.e., big and small boulder substrate). By contrast,discharge, velocity, and depth were the variables which most affected the macroinvertebrate abundance and distributions. Contrary to our expectations, most community changes observed occurred in fall instead of summer. Nivo-kryal stream communities like the one described here have become increasingly important for conserving mountain stream biodiversity as anthropogentic impacts and climate change increasingly impact lower stream reaches. Therefore, monitoring high-altitude streams like the Arroyo Tambillos may be critical for preventing the future loss of unique and sensitive stream biota.