Ecological Requirements of Chironomids (Diptera: Chironomidae) on the Soft Bottom of the River Arrone, Central Italy

Abstract

ABSTRACT The distribution and abundance of soft bottom chironomids in an organically polluted lowland river of Central Italy were investigated relative to correlations with physicochemical parameters of the water and sediments. Chironomus were the dominant tribe in the river with the highest density at the most polluted stations. Chironomus riparius showed the highest annual mean densities at the very highly polluted station, where it was the dominant species in late spring and summer. At the same station, Micropsectra sp., Polypedilum breviantennatum, Cryptochironomus sp., Harnischia sp. and Cricotopus bicinctus replaced C. riparius in winter, when the environmental conditions improved slightly. Densities of all the above mentioned taxa generally showed a positive correlation with the orthophosphate and BOD5 contents and a negative correlation with the oxygen content. C. riparius, Micropsectra sp. and Harnischia sp. preferred fine sediments (silt/clay and very fine sand) with high organic matter content, whereas P. breviantennatum was mostly confined to sandy stations. Robackia demejerei, Acalcarella sp., Rheosmittia spinicornis and Paracladopelma cloris group were present and/or abundant exclusively at unstable sandy stations with summer regulation of the water. Principal Component Analyses based on chironomid densities seems to provide an integrated response to the effects of both physical (hydraulic stress and granulometric composition of the sediment) and chemical characteristics (organic pollution) of the river.