Responses of riparian insects and spiders to experimental additions of salmon carcasses

Riparian insects incorporate marine-derived nutrients from salmon carcasses directly by consuming carcass material, or indirectly when salmon nutrients stimulate primary producers and invertebrate consumers. We hypothesized that addition of salmon carcass and salmon analog would increase abundance, alter species composition, and affect distribution of insects in riparian areas, which would result in higher abundance of predators, in this case riparian spiders (Tetragnathidae). Sticky traps were systematically deployed in and adjacent to 9 streams treated with salmon carcasses, salmon analog and control (n=3 of each). Treatments increased abundance and altered composition of both terrestrial and adult aquatic insects 2 and 4 weeks post-treatment. Carcass additions increased terrestrial dipterans more than analog whereas analog primarily increased aquatic dipteran (midge) abundance. Spider abundance was highest at analog sites three weeks post-treatment, which may have been driven by increases in their prey - adult aquatic insects. The consequences of differential responses of insect taxa to treatments may further affect other predators such as fish or bats, and may improve understanding of bottom-up influences of mitigation tools and subsequent energy flow through food webs