Whole-system metabolism and CO2 fluxes in a Mediterranean Bay dominated by seagrass beds (Palma Bay, NW Mediterranean)
1Unité d’Océanographie Chimique (B5), MARE, Université de Liège, B-4000 Sart Tilman, Belgium
2Laboratoire d’Océanographie de Villefranche, CNRS-Université de Paris 6, B. P. 28, F-06234 Villefranche-sur-mer Cedex, France
3IMEDEA (CSIC-UIB), Grupo de Oceanografia Interdisciplinar, Instituto Mediterráneo de Estudios Avanzados, C/Miquel Marqués 21, 07190 Esporles (Islas Baleares), Spain
4Département des sciences biologiques, Université du Québec à Montréal, Case postale 8888, succ. Centre-Ville, Montréal, H3C 3P8, Canada
*present address: Netherlands Institute of Ecology (NIOO-KNAW), Postbus 140, 4400 AC Yerseke, The Netherlands
**present address: Área de Biodiversidad y Conservación, ESCET, Universidad Rey Juan Carlos, C/ Tulipán s/n, Móstoles 28933, Madrid, Spain
***present address: CLS Space Oceanography Division, Parc technologique du Canal, 8-10 Rue Hermès, 31526 Ramonville Cedex, France
Abstract. Planktonic and benthic incubations (bare and Posidonia oceanica vegetated sediments) were performed at monthly intervals from March 2001 to October 2002 in a seagrass vegetated area of the Bay of Palma (Mallorca, Spain). Results showed a contrast between the planktonic compartment, which was on average near metabolic balance (−4.6±5.9 mmol O2 m-2 d-1) and the benthic compartment, which was autotrophic (17.6±8.5 mmol O2 m-2 d-1). During two cruises in March and June 2002, planktonic and benthic incubations were performed at several stations in the bay to estimate the whole-system metabolism and to examine its relationship with partial pressure of CO2 (pCO2) and apparent oxygen utilisation (AOU) spatial patterns. Moreover, during the second cruise, when the residence time of water was long enough, net ecosystem production (NEP) estimates based on incubations were compared, over the Posidonia oceanica meadow, to rates derived from dissolved inorganic carbon (DIC) and oxygen (O2) mass balance budgets. These budgets provided NEP estimates in fair agreement with those derived from direct metabolic estimates based on incubated samples over the Posidonia oceanica meadow. Whereas the seagrass community was autotrophic, the excess organic carbon production therein could only balance the planktonic heterotrophy in shallow waters relative to the maximum depth of the bay (55 m). This generated a horizontal gradient from autotrophic or balanced communities in the shallow seagrass-covered areas, to strongly heterotrophic communities in deeper areas of the bay. It seems therefore that, on an annual scale in the whole bay, the organic matter production by the Posidonia oceanica may not be sufficient to fully compensate the heterotrophy of the planktonic compartment, which may require external organic carbon inputs, most likely from land.
Gazeau, F., Duarte, C. M., Gattuso, J.-P., Barrón, C., Navarro, N., Ruiz, S., Prairie, Y. T., Calleja, M., Delille, B., Frankignoulle, M., and Borges, A. V.: Whole-system metabolism and CO2 fluxes in a Mediterranean Bay dominated by seagrass beds (Palma Bay, NW Mediterranean), Biogeosciences, 2, 43-60, doi:10.5194/bg-2-43-2005, 2005.