Organic carbon metabolism and carbonate dynamics in a Mediterranean seagrass (Posidonia oceanica) meadow

in a Posidonia oceanica meadow and unvegetated sediments of Magalluf Bay (Mallorca Island, Spain) to
determine gross primary production (GPP), community respiration (R), and net community production (NCP). From June
2001 to October 2002, we also measured fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TAlk). The yearly
integrated metabolic rates based on DO changes show that the P. oceanica communities are net autotrophic while the
metabolic rates in the unvegetated benthic communities are nearly balanced. Higher calcium carbonate (CaCO3) cycling, both
in terms of production and dissolution, was observed in P. oceanica communities than in unvegetated benthic communities. In
the P. oceanica meadow, the annual release of CO2 from net CaCO3 production corresponds to almost half of the CO2 uptake
by NCP based on DIC incubations. In unvegetated benthic communities, the annual uptake of CO2 from net CaCO3
dissolution almost fully compensates the CO2 release by NCP based on DIC incubations. CaCO3 dynamics is potentially
a major factor in CO2 benthic fluxes in seagrass and carbonate-rich temperate coastal ecosystems.