Carcass analogues provide marine subsidies for macroinvertebrates and juvenile Atlantic salmon in temperate oligotrophic streams

摘要

1. Anadromous fish populations entering freshwater ecosystems provide organic matter and marine-derived nutrients during spawning and subsequent mortalities of adults. Dams and other impediments to connectivity in rivers and streams have affected anadromous fish populations in many regions and prevented or reduced this influx of organic materials and nutrients. 2. This study used historical data on the timing of delivery of marine-derived nutrients; we added a carcass analogue (pellets made from the carcasses of Chinook salmon, Oncorhynchus tschawytcha) to simulate potential effects of restored access of anadromous fish to streams. We used stable isotopes to document the extent of nutrient incorporation of nitrogen and carbon from the carcass analogue by macroinvertebrates and juvenile Atlantic salmon (Salmo salar) in salmon nursery streams. We stocked four headwater streams that historically hosted spawning Atlantic salmon and sea lamprey (Petromyzon marinus) in Maine, U.S.A. with Atlantic salmon fry and simulated timing of nutrient addition by spawning sea lamprey in the early summer and Atlantic salmon in the autumn. 3. Macroinvertebrates and Atlantic salmon assimilated nitrogen (12-57% of total N) and carbon (21-65% of total C) from the added pellets, and the magnitude and duration of enrichment varied temporally and with macroinvertebrate functional feeding group. 4. Assimilation of nutrients from carcass analogues was both direct and indirect, and a nutrient legacy was evident in the second year of sampling. Incorporation of nutrients from the pellets at a range of heights in the food web demonstrated the potential for marine-derived subsidies to contribute to freshwater ecosystem processes in Atlantic salmon nursery streams.