Trophic web and carrying capacity in a pearl oyster farming lagoon (Takapoto, French Polynesia)

Data concerning the planktonic food web and the fanned pearl oysters of the lagoon of Takapoto Atoll were assembled into a steady state model of carbo n flows. A method of optimisation, using constraints from the literature, c alled 'inverse analysis' was chosen as the numerical tool for estimating th e missing how values. The resulting food web is characterised by: 1) high p rimary production, achieved by low phytoplankton biomass, 2) high productio n of non-living matter, especially as dissolved organic carbon, 3) low bact erial production, 4) zooplankton dominated by protozoa (biomass and process es) and mesozooplankton (processes), and 5) very low consumption of plankto n by farmed bivalves compared to planktonic fluxes. When considering the wh ole lagoon, the farmed oysters (Pinctada margaritifera) and associated biva lves (Pinctada maculata) consume 0.24% of the planktonic gross primary prod uction. In addition, the consumption by natural populations of the main ben thic bivalves in this lagoon (Chama iostoma, Area ventricosa, Pinctada marg aritifera and Pinctada maculata) is also low compared to the high planktoni c primary production (4.1%). The oyster farming in this lagoon is thus very far from being food-limited. (C) 2001 Ifremer/CNRS/lnra/IRD/Cemagref/Editi ons scientifiques et medicales Elsevier SAS.