Measuring a juvenile coho salmon.
Sockeye salmon aggregating near their spawning stream.
Temperature controls the metabolic rates of organisms across all levels of food webs, from microbes to fish, and therefore influences many ecosystem processes. In high latitude regions such as Alaska, cold temperatures constrain feeding and growth rates of aquatic consumers, limiting their ability to capitalize on abundant but ephemeral food resources. Using fatty acid and stable isotope tracers coupled with multiple years of growth data, I found that stream temperature strongly affected the ability of juvenile coho salmon to benefit from marine resource subsidies (sockeye salmon eggs). Fish in warm streams grew significantly larger with access to energy-rich salmon eggs, but fish in cold streams attained the same size at the end of the growing season regardless of the presence of eggs.
In a second study, I tested the effect of inter-annual variations in climate and competition (con-specific density) on juvenile salmon growth in six SW Alaska lakes. I used multivariate auto-regressive state space (MARSS) models to analyze forty year time series of size data, and found that longer ice-free seasons during warmer years allowed juvenile sockeye to attain larger sizes. In addition, regional climate had a synchronizing effect on growth dynamics across populations. However, the negative effect of competition on fish growth was as strong as the positive effect of temperature, and lake populations displayed independent dynamics despite close spatial proximity. These results highlight the importance of local environmental and ecological conditions in determining the effects of climate on freshwater species. Both these studies suggest that local conditions within lakes and streams can strongly ‘filter’ the effects of rising temperatures on freshwater food webs.
Adrianne P. Smits, D. E. Schindler, J. B. Armstrong, M. T. Brett, J. L. Carter, and B. S. Santos. 2016. Thermal constraints on stream consumer responses to a marine resource subsidy. In Press at Canadian Journal of Fisheries and Aquatic Sciences