| The influence of marine-derived nutrients (MDN), delivered by spawning salmon, on Alaskan streams was determined by measuring the carbon and nitrogen isotopic composition of stream biota (fishes, macroinvertebrates, biofilm). Our main study site, Fish Creek (FC), was divided into two reaches, separated by a salmon barrier, and sampled before, during, and after spawning for two years. In Salmon Creek, we assessed the upstream-downstream study design by comparing two sites also separated by a barrier, but with no MDN influence. Isotopic differences in taxa from these two sites were negligible. All lower FC consumers demonstrated MDN incorporation during and after spawning and a "legacy" effect from previous subsidies. Moreover, primary consumers exhibited a rapid MDN response and an increased MDN incorporation downstream. Macroinvertebrate isotope values are an ideal tool for tracking MDN dynamics, but spatial and temporal variability in MDN incorporation should be considered before isotopes are utilized in fisheries management. |
