Original paper

Trichoptera assemblages and environmental features in a large arid Patagonian river

Miserendino, Marí a Laura; Brand, Cecilia

Abstract

The longitudinal distribution of Trichoptera species and environmental variables was analyzed in a large, regulated river from the arid area in Patagonia (Argentina). We examined caddisfl y abundance and richness patterns across a 1000 m altitudinal gradient. Samples were collected seasonally at 13 sites in the upper, middle and lower Chubut River basin. Fifteen species were recorded in the study. Smicridea annulicornis, Cailloma sp., Neoatopsyche chilensis, Neopsilochorema tricarinatum and Parasericostoma ovale were the most common species in tributaries and main channel upper basin sites, S. dithyra appeared mostly at the middle basin sites and Metrichia neotropicalis was the most ubiquitous species. Species richness and density were signifi cantly higher in the upper basin sites than in those on the middle and lower basin. Canonical Correspondence Analysis indicated altitude, stream order and total suspended solids as the stronger factors determining Trichoptera distribution patterns. However, variables that changed seasonally such as discharge and temperature explained the observed temporal changes in the most abundant species, with density being higher during a period of stable flow and high temperature. The analysis also revealed a clear gradient of eutrophication at the lower basin, with sites having higher chlorophyll-a and soluble reactive phosphorus values. This contrasted with upper basin sites showing lower nutrient concentration and caddisfl y species depending on the particulate organic matter supply.

Keywords

caddisfl ylongitudinal gradientenvironmental relationshipspomchlorophylldamarid area