Biological traits and community patterns of Trichoptera at two Patagonian headwater streams affected by volcanic ash deposition

Abstract

Background: Sediment deposition constitutes a major disturbance having negative effects on aquatic ecosystems. The Chaitén Volcano eruption occurred on May 2008. As a consequence, broad areas along the Argentine Andes (40° S to 46° S) were covered with ash. This event provided an excellent opportunity to investigate how a natural and exceptional sedimentation episode affects Trichoptera communities. Results: We assessed changes in caddisfly community attributes (composition, density and diversity) and 11 biological traits, by comparing pre-eruption (May 2007 to April 2008) and post-eruption (July 2008 to March 2010) data at two headwater streams. As a consequence of the event, total suspended solids increased and Trichoptera richness and density significantly diminished. By March 2010, two common species of Hydroptilidae (Metrichia patagonica and Metrichia neotropicalis) were no longer recorded at one site; while species richness and density values were still low indicating that the community had not recovered. Scrapers, shredders, and predators were among the most affected functional feeding groups and changes in their relative abundance were tracked in subsequent years after the ashfall event. Conclusions: In this study, species tolerance to sedimentation was related to certain traits such as poorly synchronized life history, filter-feeding habits, rounded body shape, tegument respiration mode, and poorly sclerotized life forms.