MEPS 353:41-53 (2008)  -  DOI: https://doi.org/10.3354/meps07198

ABSTRACT: The metabolism of the pelagic ecosystem of the Ría de Vigo (NW Spain) was studied during July and September 2002. Measurements of primary production (Pg) and respiration (R) were performed at a single site twice a week at 5 depths, from surface to bottom. In July, the net community production (NCP = Pg – R) decreased along with Pg, from 0.73 under strong upwelling to 0.14 g N m^–2 d^–1 under weak upwelling conditions. In September, NCP increased from –0.10 under downwelling to 0.00 g N m^–2 d^–1 under weak upwelling conditions. Microzooplankton grazing and sedimentation rates were also measured. The high grazing rates observed (58 to 115% of Pg) raises doubts about the previously assumed efficiency of the ría to transfer phytoplankton biomass directly to the metazoans. Our results suggest that phytoplankton biomass is probably imported from the shelf to support the metabolic requirements of the microheterotrophs in September. A comparison of the metabolic state of the ría derived from these measurements with the geochemical budget generated different results in some cases. Both approaches were complementary and their simultaneous application may offer a better understanding of ecosystem functioning.

KEY WORDS: Primary production · Respiration · Grazing · Sedimentation · Upwelling · Downwelling · Rías Baixas (NW Spain)