Print PageNutrient recycling by consumers in streams can influence nutrient availability, the assemblage and growth of photoautotrophs, and ultimately ecosystem productivity. In tributaries of the Pacific Northwest, Coastal Giant Salamanders (Dicamptodon tenebrosus) often occur at high densities with Steelhead trout (Oncorhynchus mykiss) as top predators. The relative importance of nutrient excretion (ammonia, total dissolved phosphorous) by these two predators has not been examined. We evaluated the role of consumer identity and the importance of their relative abundance for nutrient recycling by combining surveys of body size distributions and abundance with nutrient excretion experiments and models. We estimated mass-specific excretion rates from a field experiment for D. tenebrosus, and estimated excretion rates for O. mykissusing a bioenergetics model parameterized with field-collected data from the same system.
Results/Conclusions
We found that D. tenebrosus occurred at ~2.5 times higher biomass than O. mykiss within a 1 km reach of stream. Despite these differences, mass-specific excretion rates of O. mykiss were 1.7 times higher for total nitrogen, and 1.2 times higher for phosphorous than D. tenebrosus. The N:P ratio recycled by O. mykiss was significantly higher (8.7) than that of D. tenebrosus (6.0), and of the total recycled nutrients by the two species combined (7.5). This work suggests that continued anthropogenic impacts to stream ecosystems in the Pacific Northwest (increasing temperature, water withdraw, harvest of salmonids) has the potential to alter stream nutrient dynamics by changing the relative abundance of these two top predators.
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