PARENT SESSION
Poster Session 3: Aquatic Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 210 D, Level 2, Palais des congrès de Montréal

Assessing the role of salmon-derived nutrients in shaping algal composition, biomass and quality as forage in Alaskan sockeye salmon nursery lakes.

Taranu, Zofia^*,1, Finney, Bruce², Gregory-Eaves, Irene¹, ¹ Dept. of Biology, McGill University, Montreal² Institute of Marine Science, University of Alaska Fairbanks, Fairbanks

ABSTRACT- The impact of variable salmon abundances on freshwater and terrestrial communities is a field that has received considerable attention over the past decade. Salmon accumulate most of their biomass in the marine environment (>95%) and then return to their natal freshwaters to spawn and subsequently die. Accordingly, they have been identified as significant nutrient transport vectors. Substantial effort has been directed towards identifying and quantifying salmon-derived nutrient (SDN) inputs, but little is known about the spatial and temporal movement of salmon-derived nutrients in freshwaters, or how these nutrient dynamics influence the community composition or biomass of lake biota. The goal of this study is to investigate the influence of SDN and other chemical, biological and physical characters on the seasonal algal dynamics. To address this objective we are conducting a comparative three-year study of a sockeye salmon nursery lake and a reference lake (a lake not receiving adult spawners). High densities of spawners return to our salmon lake, Karluk Lake, and thus this system represent a "best case" scenario for nutrient feedback among generations of salmon. Our phytoplankton results from the first year's worth of sampling show that algal biomass was consistently at least twice as great in the salmon lake compared to the control lake. The timing of sockeye salmon spawners returning to Karluk Lake is bimodal, where there is a large number of returns in mid June and then again in early to mid-September. Over the last century, there has been a shift from a larger early return to a larger late run. Based on our data, however, we did not detect a strong phytoplankton biomass response to the second wave of spawner returns in our October sampling. In future years, we will conduct a lengthier field season to assess the degree to which such nutrients are incorporated into the freshwater food web. We will also conduct a mesocosm experiment to assess the effect of the timing of SDN delivery on phytoplankton biomass and composition. Overall, this work will address the degree to which the timing and quantity of salmon-derived nutrients explains algal biomass, composition and quality.

Key words: salmon, nutrients, phytoplankton