Salmon runs serve as an important annual input of organic matter into headwater streams, which may be utilized by stream organisms as an energy source. In Michigan, salmon have been introduced into the Great Lakes for recreational use, with their carcasses having unknown effects on the microbial and macroinvertebrate communities residing in headwater streams. 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 in the collector-filtering, collector-gathering and predator functional feeding groups) communities were sampled before (September), during (October), and after (November to August) carcass introduction along both reaches. The study was conducted for two years (September 2014-August 2016), and salmon carrion introduction occurred in October of both years.
Results/Conclusions
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. There was a significant difference in the biofilm microbial communities in the control and carcass areas two weeks after the 2014 salmon introduction, and again six months later in May 2015. Contributing to this community shift were Stamenophiles, an order of bacteria that decomposes a variety of aquatic detritus, which had significantly higher relative abundance in biofilms two weeks 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.