Spatial distribution of Trichoptera larvae in the sediments of an Austrian mountain brook

Abstract

SUMMARY 1. A set of thirty‐six permanently installed standpipc traps was used over 2 years to sample caddis larvae at various depths in the gravel bed of an Austrian brook. From a total of 805 specimens caught, the most abundant species were Sericostoma sp. (Sericostomatidae), and the three limnephilids Potamophylax cingulatus Steph., Allgamus auricollisPictet and Allogamus uncatus Brauer.2. Sericostoma sp. and Ecclisopteryx guttulata Pictet were collected down to a seditnent depth of l m. In Sericostoma sp., a burrowing species, tiny larvae were found in sediments at 20–60 em, where most of the life cycle is spent; fully grown larvae were mostly collected at a depth of 0–20 em. All instars of Potamophylax cingulatus, Allogamus auricollis and Allogamus uncatus larvae were most abundant at the sediment surface.3. The horizontal distribution of the most abundant species was studied at the 20 cm depth stratum. Larvae were most abundant in midstream areas.4. Factors probably responsible for the observed spatial distribution pattern are briefly diseussed.