Influence of marine-derived nutrients from spawning salmon on aquatic insect communities in south-east Alaskan streams (Alaska).

摘要

Alaska is the last region along the Pacific coast of the United States that still enjoys large runs of spawning salmon. Salmon runs provide these oligotrophic systems with a huge pulse of nutrients from the ocean. The retention of these nutrients in streams potentially sustain this pulse of nutrients over many months. Annual nutrient delivery from salmon to Alaskan streams range into the millions of tons of carbon, nitrogen, phosphorous. These nutrients are termed marine-derived nutrients (MDN) and may be tightly linked to secondary production in streams. The most important link between MDN and production is in the production of juvenile salmon. In providing a positive feedback mechanism to ensure viability of subsequent generations, intermediate steps that connect MDN and juvenile salmon production include alterations of dissolved nutrients, biofilm production and alterations to the macroinvertebrate community. Changes due to MDN have far reaching implications in watersheds that receive salmon and may shape the dynamics of stream communities seasonally.; This research focused on aquatic insect community responses to MDN in multiple natural stream systems in southeast Alaska. The objectives were quantify insect abundance, biomass, functional group proportions, richness, diversity, growth and secondary production in relation to MDN inputs. These community attributes were studied to establish if stream communities with exposure to MDN are organized differently from non-anadromous streams in that region. This research will help to elucidate the effect that MDN has on stream insect communities and will also help to better understand the link between MDN and fish production.; Mayfly standing stock and secondary production was higher in control reaches. Chironomid production was higher in stream sections that do receive large annual runs of salmon. Richness, diversity and functional group composition was not impacted by MDN over most of the year. These results suggest that the disturbance of salmon spawning creates a dichotomy of response to MDN so that larger, univoltine taxa have lower population levels in salmon spawning areas. Smaller, multivoltine taxa, however, have higher populations levels, most likely due to their ability to recover and respond to MDN. The links between MDN and juvenile salmon production may be more simplified than many models predict.