MEPS 210:167-174(2001)  -  doi: 10.3354/meps210167

ABSTRACT: The stable isotope of nitrogen, ¹⁵N, was used to evaluate the nitrogen accumulation efficiency of copepods feeding on natural plankton assemblages from coastal waters over the period March to November 1998. Although allowances have to be made for selective feeding, the clearance rates calculated from the accumulation of ¹⁵N were considerably lower than the rate of removal of the particles labeled with ¹⁵N. The percentage of accumulation/removal varied from 9 to 75%. In 3 out of 5 experiments, the copepods released dissolved nitrogen from their food rather than accumulating it. It appears that, at least on some occasions, copepods may transfer much of the particulate organic nitrogen to the dissolved form, and thus short-circuit the food chain from phytoplankton to carnivores.

KEY WORDS: Copepods · Nitrogen · ¹⁵N tracer