MEPS 334:37-45 (2007)  -  doi:10.3354/meps334037

Community primary production and calcification in a NW Mediterranean ecosystem dominated by calcareous macroalgae

Nathaniel Bensoussan1,*, Jean-Pierre Gattuso2

1Laboratoire Diversité, évolution et écologie fonctionnelle marine, CNRS—Université de la Méditerranée, Centre d’Océanologie de Marseille, Station Marine d’Endoume, rue Batterie des Lions, 13007 Marseille, France
2Laboratoire d’Océanographie de Villefranche, CNRS—Université de Paris 6, BP 28, 06234 Villefranche-sur-mer Cedex, France

ABSTRACT: The community metabolism of a shallow infralittoral ecosystem dominated by the calcareous macroalgae Corallina elongata was investigated in Marseilles (NW Mediterranean), by monitoring hourly changes of seawater pH and total alkalinity over 6 d in February 2000. Fair weather conditions prevailed over the study period as indicated by oceanographic (temperature, salinity, and current velocity and direction) and meteorological variables, which validated the standing water hypothesis. This temperate ecosystem exhibited high community gross primary production (GPP = 519 ± 106 mmol C m–2 d–1, n = 6) and also supported high rates of community respiration (R). As a result, the system was slightly autotrophic (net community production, NCP = 20 mmol C m–2 d–1), with a GPP/R ratio of 1.06. NCP exhibited circadian variations with 2- to 3-fold changes in community respiration, both in the light and in the dark. Rates of net community calcification also exhibited circadian variations, with positive rates (up to 24 mmol CaCO3 m–2 h–1) for irradiance values >300 W m–2 (about 1380 µmol photon m–2 s–1). Below this irradiance threshold, net community dissolution prevailed. Daily net calcification (G) was on average 8 mmol CaCO3 m–2 d–1. CO2 fluxes generated by primary production, respiration, and calcification suggest that the study site was a potential atmospheric CO2 sink of 15 mmol CO2 m–2 d–1 at the time of measurement.

KEY WORDS: Ecosystem metabolism · Primary production · Respiration · Calcification · Calcareous macroalgae · Corallina elongata · pH · Total alkalinity · TA

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