Species assemblages of Chironomidae (Diptera) in acidic Welsh streams

Abstract

Despite their speciose nature and potential role as ecological indicators, there are few data on the chironomids that characterise upland streams at risk from acidification. Nor has the use of pupal exuviae for typing upland streams been appraised. Therefore, in conjunction with the second Acid Waters Survey for Wales, sixty-one sites on acid-sensitive streams were sampled for chironomid pupal exuviae in June 1995. No exuviae were found at nine of the sites but the remainder produced seventy-three species, the majority of which belonged to the sub-family Orthocladiinae. Sites with three or more species were subjected to two-way indicator species analysis (TWINSPAN). This analysis produced thirteen species assemblages and eight site groups at Level 6, The concepts of constancy and fidelity were used to establish the relative strengths of the relationships between the species assemblages and the site groups. Almost all the species assemblages showed a strong fidelity to one or two site groups. Habitat data collected for each site from October 1994 to September 1995 were used to explore the relationships between the species assemblages and the habitat characteristics of the site groups. It was apparent that pH was only one of several environmental variables that correlated with the distribution of the species assemblages. However, the robustness of these species assemblages and their ecology require further investigation.