Aquatic macroinvertebrate and microbial community responses to salmon carrion introduction into a headwater stream

Aquatic insect communities in headwater streams are heavily influenced by outside sources of organic matter, primarily relying on these allochthonous inputs as a food resource and habitat. Therefore, decomposing salmon carrion may serve as a significant organic matter resource to benthic aquatic insects and microorganisms, such as bacteria. Our objective in this study was to determine the effect of salmon carrion introduction on aquatic macroinvertebrate and microbial communities over time. Chinook and Coho salmon carcasses were introduced to Hunt Creek, Michigan, downstream of a migration barrier. Upstream of that barrier served as a control reach, where salmon carrion was not present. Macroinvertebrate and microbial (benthic epilithic biofilm, salmon carrion surface and the internal portion of surface decontaminated macroinvertebrates, such as Trichoptera larvae) communities were sampled before (September 2014), during (October 2014), and after (November 2014 to September 2015) carcass introduction along both reaches. Initial results indicate overall macroinvertebrate diversity (Simpson’s Diversity Index at the genera level) was similar between control and salmon sites, with a trend of increased diversity in salmon sites over time. Epilithic biofilm communities were variable over time, with higher diversity in carcass addition reaches. Stamenophiles, an order of bacteria that decomposes a variety of aquatic detritus, had significantly higher relative abundance in biofilms after salmon introduction (t=3.2472, df=4, p=0.0315). These trends are related to shifts in the salmon carrion surface and insect microbial communities. Our results provide some of the first information documenting salmon carcass biotic effects in Michigan headwater streams.