A pelagic ecosystem model simulating production and sedimentation of biogenic particles: role of salps and copepods

Production and sedimentation of biogenic particles are investigated by a depth-dependent model of a Mediterranean coastal pelagic ecosystem during spring. The model considers living and dead phytoplankton (chiefly diatoms) and its sedimentation, 2 herbivores, salps and copepods, and sedimentation of their fecal pellets and carcases; a sediment trap is assumed to be set up at 200 m depth. Results underline the major role played by fecal pellets and by both living and dead salps in vertical matter flux. Fecal pellets of salps and copepods constitute 65 % of the material in the trap after a 40 d simulation period. Although salp and copepod biomasses are similar, the magnitude and composition of the particle flux are much more influenced by salps than by copepods: salp fecal pellets and carcases account for 72 % of the maximum overall flux. The fluxes calculated by this model are in good agreement with those generally recorded in the field: at 200 m depth, up to 72.3 mgC m 2 d ' and a mean of 44.7 mgC m 2 d over 40 d.