The “seamount effect” as revealed by organic matter dynamics around a shallow seamount in the Tyrrhenian Sea (Vercelli Seamount, western Mediterranean).

The effect of a shallow seamount in the Tyrrhenian sea on the surrounding ecosystem was studied during spring 2009, taking account of the variables related to organic-matter (OM) production and turnover. A clear “seamount effect” could not be found, due to the complex hydrodynamic features of the area. Nevertheless, the accumulation of autotrophic biomass and semi-labile OM and fast turnover of labile OM was found on the seamount summit. OM fluxes were observed downstream, in the surface and subsurface layers as well as at greater depths along the seamount’s flank, thus extending the effect of the seamount for at least 20 Km from its summit. Changes in the availability of OM for consumption were observed, especially in the deeper layers, due to mixing with bottom sediments. The OM turnover processes also suggested a flux of labile OM upstream from the seamount. The evaluation of the OM turnover-related processes highlighted the extent of the influence of the seamount in the study area.