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Microdistribution of chironomids (Diptera: Chironomidae) in Alpine streams: an autoecological perspective
Authors:Valeria Lencioni  Bruno Rossaro
Affiliation:(1) Section of Invertebrate Zoology and Hydrobiology, Natural Science Museum, Via Calepina 14, I-38100 Trento, Italy;(2) Department of Biology, Section of Ecology, University of Milan, Via Celoria 26, I-20133 Milan, Italy
Abstract:Chironomid communities from three glacial and three non-glacial high mountain streams in three Alpine river basins were analyzed (Conca, Niscli, Cornisello, NE Italy, 46°thinspN, 10°thinspE). Eighteen sampling reaches belonging to five stream types (kryal, subkryal, glacio-rhithral, kreno-rhithral, outlet) were investigated. At each reach, geomorphological, physical, chemical and biological data were collected. Field surveys were carried out during three periods per year from 1996 to 1998: immediately after spring snowmelt, in mid-summer and in early autumn. In all, 439 zoobenthos samples were collected from 5 to 10 microhabitats of 0.1thinspm2 in each reach and date using a standard pond net (mesh size of 250thinspmgrm). About 50% of individuals collected were chironomids (26thinsp673 specimens, 53 taxa), with densities ranging from 4 to 2652thinspindthinspm–2. With few exceptions, they dominated as number of taxa and individuals in all reaches. Chironomid subfamilies Diamesinae and Orthocladiinae were most abundant, especially in glacial reaches, where Diamesa spp. constituted up to 100% of the total fauna. Chironomid distribution was analyzed in relation to 37 abiotic variables, referring to stream origin, hydrology, geomorphology, physics and chemistry. Diamesa steinboecki, D. latitarsis gr. A and Pseudokiefferiella parva were the taxa best associated with lsquoglacialrsquo conditions (i.e. high channel instability or presence of bedrock, high suspended solids and total phosphorous content, low conductivity and silica content, highly variable diel discharge and low mean temperature), while Pseudodiamesa branickii, Corynoneura spp., Eukiefferiella spp., Parorthocladius nudipennis, Tvetenia calvescens/bavarica, Thienemaniella spp. and Micropsectra atrofasciata were mostly associated with lsquonon-glacialrsquo conditions. Substratum particle size, water depth, current velocity, the presence of riffles/pools and of mosses/algae (Hydrurus foetidus) were the major factors affecting microdistribution of chironomids in the investigated streams.
Keywords:chironomids  glacial streams  water temperature  autoecology  microhabitat  Alps
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