Photosynthesis, respiration and calcification in the Mediterranean crustose coralline alga Lithophyllum cabiochae (Corallinales, Rhodophyta)

Abstract

Primary production and calcification responses to irradiance were investigated in Lithophyllum cabiochae, a crustose coralline alga from Mediterranean coralligenous communities, collected at c. 25 m 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 0.2–0.3 µmol cm⁻² thallus h⁻¹ in terms of both O₂ consumption and CO₂ release and maximal gross photosynthesis averaged 1.0 µmol cm⁻² h⁻¹ in terms of both O₂ production and CO₂ uptake. Mean rate of net calcification was 0.1 µmol CaCO₃ cm⁻² h⁻¹ in the dark and reached 0.4 µmol CaCO₃ cm⁻² h⁻¹ in the light. Diel net and gross organic C productions were estimated to be 3 and 7 µmol C cm⁻² thallus d^−1, respectively. Diel net inorganic C production was estimated to be 3 µmol CaCO₃ cm⁻² thallus d⁻¹. Despite the low light conditions experienced by the algae at c. 25 m 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.

Key words:

• calcification
• carbon
• carbonate
• coralligenous
• coralline algae
• irradiance
• Mediterranean Sea
• oxygen
• primary production

Acknowledgements

We thank D. Luquet, J.-Y. Carval and J.-L. Prevost for assistance in the field and M.-D. Pizay for assistance in the laboratory. We also thank M. Verlaque and A. Meinesz for their help with species determination. The Service d'Observation en Milieu Littoral, INSU-CNRS is gratefully acknowledged for its kind permission to use in situ temperature data. The Service National d'Analyse des Paramètres Océaniques du CO₂ performed the weekly measurements of A _T and C _T in the bay. The two anonymous referees as well as the editor are gratefully acknowledged for their constructive comments and suggestions. This work was supported by the CarboOcean IP of the European Commission (grant 511176-2) and is a contribution to the ‘European Project on Ocean Acidification’ (EPOCA) and MedSeA which received funding from the European Community (grant agreements 211384 and 265103).