Effects of small changes in riparian forest complexity on aquatic insect bioindicators in Brazilian subtropical streams

Riparian forests have positive effects on water quality and biodiversity. However, most studies have only tested the effects of distinct vegetation types or streams with and without forests, despite the fact that riparian forests differ in degrees of complexity. The aim of the present study was to test whether riparian forest complexity affected the composition and abundance of the Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa across a small environmental gradient. We also measured whether EPT genera or feeding groups responded to changes in riparian forest complexity. The study was conducted in two protection areas (i.e. Lagoa do Peri Municipal Park, PERI; and the Permanent Protection Area of Ratones, RAT) of Santa Catarina Island, Brazil. Primary production increased in streams with lower canopy percentage, and EPT assemblages differed among streams with different riparian forest complexity. In RAT, the water quality and forest variables affected EPT composition; however, in PERI, only water quality variables were important. Indicator species analysis based on genera suggested Kempnyia (Plecoptera) and Zelusia (Ephemeroptera) to be indicative of streams with greater forest complexity, whereas Farrodes (Ephemeroptera) was significant in streams of intermediate riparian forest complexity; however, no one functional group dominated. The results of the present study show that small changes in riparian forest complexity influence the composition of EPT insects in subtropical streams.