|Impact of appendicularians on detritus and export fluxes: a model approach at DyFAMed site |
(Article) Publié: Journal Of Plankton Research, vol. p. (2010)
Ref HAL: hal-00655066_v1
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So far, appendicularians role in the biogeochemical cycling of organic matter has been overlooked. Appendicularians represent only a fraction of total mesozooplankton biomass, however these ubiquitous zooplankters have very high filtration and growth rates compared to copepod, and produce numerous fecal pellets and filtering houses contributing to the export production by aggregating small marine particles. To study their quantitative impact on biogeochemical fluxes, we have included this group in the Biogeochemical Flux Model (BFM), using a recently developed ecophysiological model. One dimensional annual simulations of the pelagic ecosystem including appendicularians were conducted with realistic surface forcing for year 2000, using data from the DyFAMed open ocean station. The appendicularian grazing impact was generally low, but appendicularians increased detritus production by 8% and export production by 55% compared to a simulation without appendicularians. Therefore present biogeochemical models lacking appendicularians probably under, or misestimate the detritus and export production by omitting the pathway from small sized plankton to fast sinking detritus. Detritus production and export rates are 60% lower than estimates from mesotrophic sites, showing that appendicularians' role is lower but still significant in oligotrophic environments. The simulated annual export at 200 m exceeds sediment trap values by 44%, suggesting an intense degradation during the sinking of appendicularian detritus, supported by observations made in other sites. Thus degradation and grazing of appendicularians detritus need a better quantification if we are to accurately assess the appendicularian role in the export flux.