MEPS 370:199-206 (2008)  -  DOI: https://doi.org/10.3354/meps07653

ABSTRACT: We describe seasonal variation in nitrogen stable isotope ratios of marine animals (zooplankton, benthic infauna, benthic epifauna and fishes) in size-fractionated classes spanning 6 orders of magnitude in body mass. Variation in δ¹⁵N over the course of the seasonal production cycle was significantly greater in smaller animals and declined continuously with increasing body size. The duration and magnitude of a decrease in δ¹⁵N (as observed in the zooplankton community at the start of the production cycle) was reduced and attenuated in larger animals at higher trophic levels (higher mean δ¹⁵N), likely reflecting different rates of energy propagation in different food web pathways and the transfer of energy to animals with slower turnover times. Animals ≥16 g wet body mass integrated seasonal variation in δ¹⁵N of their prey, such that a single annual sampling of animals in size classes ≥16 g was sufficient to determine mean δ¹⁵N. For zooplankton and smaller infauna, very frequent sampling would be required to estimate mean δ¹⁵N, and we show that measurements of food web properties such as trophic position and predator-prey size ratios would be biased when based on single samples of these small animals.

KEY WORDS: Food web · Body size · Stable isotope analysis · Temporal variation · Stoichiometry