AB 17:107-117 (2012)  -  DOI: https://doi.org/10.3354/ab00465

ABSTRACT: Allochthonous inputs can be an important contribution of organic matter in lake ecosystems. Yet, our understanding of the patterns of energy dependence of littoral invertebrates and fish is poor. We measured carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope values for primary producers, terrestrial detritus, benthic macroinvertebrates, zooplankton and brook trout Salvelinus fontinalis in 8 oligotrophic Canadian Boreal Shield lakes to determine food sources that support benthic consumers and brook trout. Mixing models used to determine animal diets from stable isotope analysis showed leaf litter to be the principal food source for benthic primary consumers in 6 out of 8 lakes. Brook trout derived its carbon mainly from benthic predatory macroinvertebrates in all lakes, with a contribution ranging from 60 to 90%. Zooplankton also contributed to brook trout diet in 3 of 8 lakes, ranging from 28 to 37%. δ¹⁵N increased from primary producers to consumers at different trophic positions in all lakes. Nitrogen isotopic signatures of brook trout became more positive with increasing fish length, indicating a change in fish foraging strategy related to size. Our study (1) suggests that carbon from terrestrial habitat (leaf litter) may contribute significantly to the food web of oligotrophic Canadian Boreal Shield lakes and (2) highlights the importance of carbon originating from benthic habitats in supporting brook trout in these lakes.

KEY WORDS: Allochthonous subsidies · Benthic macroinvertebrates · Zooplankton · Brook trout · Diet breadth · Size-related diet shift · Stable isotopes · Boreal lakes