Photosynthesis, respiration and calcification in the Mediterranean crustose coralline alga Lithophyllum cabiochae (Corallinales, Rhodophyta)
Résumé
Primary production and calcification responses to irradiance were investigated in Lithophyllum cabiochae, a crustose coralline alga from Mediterranean coralligenous communities, collected at c. 25m depth in the Bay of Villefranche. Algae were maintained in aquaria at temperature and irradiance levels close to in situ conditions. Physiological measurements were performed using incubation chambers in the dark and in the light at different irradiance levels within the range of those measured in situ. Both photosynthesis and calcification rates in L. cabiochae were strongly related to irradiance. Dark respiration averaged 0.20.3 mu molcm(2) thallus h(1) in terms of both O-2 consumption and CO2 release and maximal gross photosynthesis averaged 1.0 mu molcm(2) h(1) in terms of both O-2 production and CO2 uptake. Mean rate of net calcification was 0.1 mu mol CaCO3 cm(2) h(1) in the dark and reached 0.4 mu mol CaCO3 cm(2) h(1) in the light. Diel net and gross organic C productions were estimated to be 3 and 7 mu molC cm(2) thallus d(1,) respectively. Diel net inorganic C production was estimated to be 3 mu mol CaCO3 cm(2) thallus d(1). Despite the low light conditions experienced by the algae at c. 25m depth, L. cabiochae can be considered as a major contributor to primary productivity and calcium carbonate deposition, making coralligenous communities a major carbon and carbonate producer in the Mediterranean Sea.