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

Fate of food nitrogen in marine copepods

Toru Hasegawa1,*, Isao Koike1, Hiroshi Mukai2

1Ocean Research Institute, University of Tokyo, 1-15-1, Minamidai, Nakano, Tokyo 164-8639, Japan
2Akkeshi Marine Biological Station, Hokkaido University Akkeshi, Hokkaido 088-1113, Japan

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

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