Measuring the effects of salmon presence on freshwater macroinvertebrate communities in streams in Thurston County, WA

Abstract

Salmon carcasses provide marine-derived nutrients and carbon to freshwater ecosystems, enhancing the diets of benthic macroinvertebrate communities. Reciprocally, freshwater macroinvertebrates provide sustenance for juvenile salmon. In this study, we collected benthic macroinvertebrate samples and measured key water quality variables for 20 streams (10 salmon- bearing and 10 non-salmon streams). We hypothesized that macroinvertebrate total abundance, taxa diversity, and taxa richness would be greater in salmon-bearing versus non-salmon streams, and that community structure would differ between sites. We found that anadromous salmon presence or absence in streams had a significant influence on the structure of benthic macroinvertebrate communities and their taxa diversity. Taxa richness and Shannon’s Diversity Index values in salmon-bearing streams were both significantly greater than in non-salmon streams. Together, these results suggest salmon presence is a strong influence on macroinvertebrate communities in our study area.