Contrasting associations between habitat conditions and stream aquatic biodiversity in a forest reserve and its surrounding area in the Eastern Amazon

Streams of protected areas should be subjected to less environmental degradation than surrounding areas and consequently support greater aquatic biodiversity. To test this, 186 environmental and landscape variables were measured in 34 streams within the Caxiuanã National Forest (CNF) and its surrounding zone in the eastern Amazon. We expected that streams inside the CNF protected area would have more riparian forest cover and large woody debris (LWD) that increase instream habitat complexity and aquatic biodiversity. Several environmental variables differed between streams in the CNF and surrounding zone; however, the major difference was greater LWD, leaf litter, and channel depth in CNF streams. Richness of fish, Chironomidae, EPT (Ephemeroptera + Plecoptera + Trichoptera), and all-groups combined were positively associated with LWD. Assemblage taxonomic composition was correlated with several variables, but most groups revealed no clear differentiation between the two areas. This lack of differentiation may be explained by relatively minor environmental impacts in areas surrounding the CNF given the region’s small human population. The most notable impact to streams outside of the CNF was removal of LWD to facilitate boat passage. To conserve aquatic biodiversity, we recommend expansion of protected areas and adoption of policies governing land use in surrounding zones.