Long-term emergence patterns of Chironomidae (Diptera) from an intermittent stream

Abstract

In non-perennial aquatic habitats, dry periods influence the aquatic community by filtering organisms based on their ability to survive periods of drying or to recolonize the habitat quickly. Although intermittent streams often support interesting, specialized species, they often support a less species-rich community compared to perennial habitats. I collected Chironomidae from an intermittent, 3rd order stream biweekly for 6 years using surface floating pupal exuviae. The stream regularly dried in the summer every year, but the duration of the dry period varied among years (15-146 days). In total, 158 non-biting midge taxa were identified, but many species (65) were rare and only occurred in 1-2 samples. Most common taxa had regular seasonal emergence patterns, but some taxa had irregular emergence patterns that differed year to year. Following dry periods, Chironomidae resumed emergence within 2-3 weeks after the stream began flowing again and, in some years, sample richness was higher after flow resumed than before. The length of the dry period in the stream did not affect annual taxa richness, but lower annual taxa richness was observed in years with higher accumulated discharge and more frequent summer spates. Comparison of midge communities from this intermittent site to a downstream perennial site found no difference in taxonomic richness. However, the emergence period was shorter and the number of taxa present in individual samples was lower at the intermittent site. The equivalent richness was achieved in the intermittent site through higher temporal β diversity. This pattern may have been the result of higher disturbance in the intermittent site due to spates and drying which could contribute to greater habitat heterogeneity and promote colonization of new taxa. Most taxa at the perennial site were also found in the intermittent site indicating that many midge taxa in these habitats are facultative. Intermittent streams are usually expected to only support a depauperate community of facultative species, but these habitats can support interesting and diverse communities that should be conserved.