The role of the environment in the distribution and composition of Trichoptera assemblages in streams

We investigated how diversity and distribution of more than 11000 Trichop- tera larvae in streams of central Portugal were related to chemical and physical envi- ronmental variables. Sixty-six sites were sampled in 2001, by kicknet, in 55 streams of the Mondego River basin, the largest entirely Portuguese river. Simultaneously 43 environmental variables were evaluated for each site. We identified 18 families and 70 species and genera of caddisflies, representing ≈ 20 % of all trichopteran taxa recorded for the Iberian Peninsula. The species Calamoceras marsupus, Cheumatopsyche lepida, Hydropsyche bulbifera, Hydropsyche siltalai, Hydroptila sp., Lepidostoma hir- tum, Mystacides azurea, Chimarra marginata, Polycentropus flavomaculatus, Tinodes waeneri, Rhyacophila adjuncta and Sericostoma sp. were found to be the most impor- tant taxa in the Mondego River basin. Stream order, substrate quality, altitude, current velocity and alkalinity explained 41 % of the taxa distribution suggesting that at a wi- der (catchment) scale physical and hydrological parameters are more important for the distribution of Trichoptera assemblages than chemical parameters. Six significantly different groups of sites with similar Trichoptera assemblages were identified in the catchment and related to altitudinal, hydrological and substrate gradients. Our findings allow us to predict Trichoptera assemblages in streams of the Mondego catchment based on few environmental characteristics.