Pacific Salmon, Marine-Derived Nutrients, and the Characteristics of Aquatic and Riparian Ecosystems
Robert J. Naiman, James M. Helfield, Krista K. Bartz, Deanne C. Drake, and Jon M. Honea
Abstract.—We review the current understanding of major pathways, mechanisms, and consequences of salmon-borne marine-derived nutrients (MDN) in estuarine, freshwater, and riparian ecosystems. Semelparous Pacific salmon Oncorhynchus spp. acquire most of their body mass while at sea before returning to spawn and die in natal streams. The annual spawning migrations transport substantial quantities of MDN from the fertile North Pacific Ocean to relatively nutrient-poor coastal freshwater and terrestrial ecosystems. People have been long aware of the importance of salmon-borne MDN for the productivity of freshwater ecosystems in western North America, and the rapidly increasing knowledge base supports this notion. Nevertheless, many details associated with nutrient pathways, cycling processes, and the ecosystem-scale consequences of MDN transfer remain to be elucidated. The collective data suggest that freshwater portions of the salmon production system, as well as the dynamics of local terrestrial plant and animal communities, are intimately linked to MDN in complex ways. At the same time, the ecological importance of MDN, relative to other major nutrient sources, is temporally and spatially dependent and influenced by the life histories and abundances of salmonid stocks. Although interactions among climate cycles, salmon, riparian vegetation, predators, and MDN flowpaths and feedbacks are complex, they also form a wonderfully integrated ecological system with a high degree of resilience and productivity. Understanding this complex system and its inherent temporal and spatial variability requires a holistic scientific perspective that values important interactions among the salmonid life cycle, the physical setting, and the numerous linkages to other ecosystem components.