PARENT SESSION
Oral Session #7: Aquatic Ecology: Stream ecosystems. Presiding: T. Ehlinger.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.
Marine nutrients in freshwater ecosystems: role of salmon migrations in supporting stream food webs.
Lamberti, Gary1, Chaloner, Dominic1, Merritt, Richard2, Ostrom, Peggy2, Wipfli, Mark3, 1 2 3
ABSTRACT- Stream ecosystems are believed to import much of their energy from adjacent ecosystems and to export considerable energy downstream. A different paradigm, however, may exist in streams in which anadromous fishes spawn. In Southeast Alaska streams, we studied the ecological importance of marine-derived nutrients (MDN) transported into fresh waters by Pacific salmon (Oncorhynchus spp.) during spawning migrations. We predicted that dissolved nutrients released with salmon excretion during migration and decomposition after migration would stimulate primary production. In the presence of spawning salmon, concentrations of ammonium and soluble reactive phosphorus increased by 4x and net primary production increased by 0.5x. We also hypothesized that salmon carcasses, which can exceed 1 carcass per m2 of streambed, would be a direct food resource for invertebrate consumers. Submerged carcasses increased the growth of detritivorous invertebrates by 70-100%. Benthic invertebrate abundance was not increased, however, possibly because of massive sediment disturbance by spawning activities and increased fish predation. Stable isotope analyses of nitrogen and carbon indicated that MDN permeated all major components of the stream food web, including juvenile salmon, which grew at faster rates in the presence of decomposing salmon. Our results suggest that MDN delivered by returning salmon can enhance freshwater productivity, but factors such as disturbance, retention, and size of salmon runs modulate the overall effect of MDN on stream food webs.
KEY WORDS: stream, salmon, subsidy, foodweb