Incorporation of nitrogen and carbon from spawning coho salmon into the trophic system of small streams: evidence from stable isotopes

• Published in: Canadian journal of fisheries and aquatic sciences 1996-01, Vol.53 (1), p.164-173
• Main Authors: Bilby, Robert E, Fransen, Brian R, Bisson, Peter A
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Fresh water ecosystems; Freshwater; Fundamental and applied biological sciences. Psychology; Marine; Oncorhynchus kisutch; Synecology
• ISSN: 0706-652X; 1205-7533
• DOI: 10.1139/f95-159

Nitrogen-15 and carbon-13 ratios were compared in epilithic organic matter, all aquatic macro-invertebrates except shredders and fish from 4 tributaries of the Snoqualmie river, where spawning coho salmon (Oncorhynchus kisutch), were present. Riparian vegetation adjacent to salmon-bearing streams and shredding macro-invertebrates were enriched with nitrogen-15 but not carbon-13. The greatest enrichment by heavy isotopes was in early spring following carcass decomposition. The weight and growth rate of juvenile O. kisutch increased following the appearance of spawning salmon in the stream. Age-0 cutthroat trout (Oncorhynchus clarki), in a nearby stream without salmon showed no changed in growth rate during the winter. Salmon-derived organic matter was incorporated into the stream biota through direct consumption of eggs, carcasses and fry and by sorption onto the streambed substrate of dissolved organic matter from decomposing carcasses. Pathways other than autotrophic uptake were primarily responsible for incorporation of salmon-derived organic matter into the trophic systems. The proportion of nitrogen contributed by spawning salmon ranged from about 17 per cent in collector-gatherers to more than 30 per cent in juvenile O. kisutch. Carbon contribution ranged from 0 per cent in the foliage of riparian plants and shredders to 34 per cent in juvenile O. kisutch.