Abstract
Organisms transporting nutrients from highly productive ecosystems can subsidize food webs and alter ecosystem processes. For example, the carcasses and eggs of migratory Pacific salmon (Oncorhynchus spp.) provide a high‐quality food source that could potentially benefit other species of salmon rearing in fresh water. We investigated relationships between spawning chum (O. keta) and pink (O. gorbuscha) salmon density, and the body size and age of juvenile coho salmon (O. kisutch) in 17 streams on the central coast of British Columbia, Canada. Chum salmon density was the most consistently important and positive correlate of coho body size, in comparison with pink salmon density, juvenile coho salmon density, and numerous characteristics of habitats. This was shown by comparisons both among and within streams, and between sites above and below natural barriers to spawning chum and pink salmon. In addition, streams that had higher chum and pink salmon spawning densities had a higher proportion of age 0 coho (less age 1), suggesting earlier juvenile coho salmon migration to the ocean with increased spawning salmon nutrient availability. Most of the coho salmon sampled had little or no direct contact with spawning chum and pink salmon, which suggests an indirect, time‐delayed influence on coho salmon body size.
Highlights
Geophysical processes and organisms can transport nutrients across ecological boundaries, linking an array of environments, such as above- and below-ground terrestrial systems (Scheu 2001), sea ice and arctic islands (Roth 2002), and streams and forests (Nakano and Murakami 2001)
We examined the effect of spawning chum and pink salmon density on the proportion of age 0 compared to age 1 juvenile coho salmon across the 17 streams
Chum density 0.24 0.52 0.14 0.59 0.15 0.71 Pink density 0.43 0.57 0.21 0.52 0.02 0.47 natural barriers to spawning chum and pink salmon compared to above barriers at high spawning salmon density streams
Summary
Geophysical processes and organisms can transport nutrients across ecological boundaries, linking an array of environments, such as above- and below-ground terrestrial systems (Scheu 2001), sea ice and arctic islands (Roth 2002), and streams and forests (Nakano and Murakami 2001). Productive systems can subsidize nutrient-limited ones (Gravel et al 2010), such as when nutrients move from the marine environment to desert islands (Spiller et al 2010) and freshwater streams (Richardson et al 2010). These subsidies can have a wide range of effects, including the growth and body size of organisms in recipient food webs (Marczak and Richardson 2008, Young et al 2011). Transport and concentration of nutrients can occur both spatially, such as in avian nesting colony aggregation, and temporally, such as through annual migrations. One example that constitutes both a spatial and temporal aggregation of nutrients occurs through the annual migration of spawning salmon
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