Comparing Macroinvertebrate Assemblages Across Reservoirs

Comparing Macroinvertebrate Assemblages Across Reservoirs

Brent Johnson¹, Margaret Whitmore¹, Christina A. Murphy¹, Ivan Arismendi¹, Brendan Coffin¹,

 Sherri Johnson²,

¹Oregon State University

Department of Fisheries & Wildlife, Corvallis, OR 97331

johnbren@onid.orst.edu

²U. S. Forest Service, Pacific Northwest Research Station, Corvallis, Oregon 97331

As a part of a larger study examining impacts to reservoir ecology and food webs in Pacific Northwest reservoirs under modified drawdown regimes, we developed a method for sampling littoral benthic macroinvertebrates. We sampled across three high-head central Willamette reservoirs, Hills Creek, Fall Creek, and Lookout Point, with samples standardized by effort. Here we illustrate how this sampling method can be used to compare abundance and biomass of macroinvertebrate assemblages across reservoirs over time. We found that community composition was strongly associated with environmental variables (Biomass P < 0.05; Abundance P < 0.05). We observed unique and strong clustering of macroinvertebrate assemblages by reservoir and season. We conclude that this method is comparable across sites and able to capture seasonal variation in macroinvertebrate communities within each reservoir. Continuing research will further investigate the role of productivity and water management regimes in the seasonal variation of macroinvertebrate community composition.