Impact of Bank Protection Work on Chironomid Fauna (Diptera: Chironomidae) in the Middle Reaches of the Chikuma River in Central Japan

Abstract

ABSTRACT In order to assess the short term impact of bank protection work on species composition and abundance of aquatic insects, we sampled adult insects by light trap from April 19 to September 30 in 2001 and 2002 before and after habitat alteration. A large bank protection project was undertaken during winter (from late October in 2001 to late March in 2002) in the middle reaches of the Chikuma River. Prior to construction, the collected insect community comprised predominately Trichoptera (31.4%), Chironomidae (28.5%), and Tipulidae (17.1%). After construction, 50.1% of insects collected were chironomid midges. Although Cricotopus sylvestris was the most abundant chironomid species in both years, the number of species and the species diversity index (H′) were affected. Sixty-six species (H′ = 3.9) of chironomids were sampled in 2001, whereas only 44 species (H′ = 2.7) were collected in 2002. The patterns of temporal succession of H′ in the occurrence of chironomid fauna throughout the investigation periods were very different in 2001 and 2002. After construction in 2002, it took about 150 days to recover the same H′ level as in 2001 as the season progressed.