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First published online May 2, 2008
Journal of Experimental Biology 211, 1579-1586 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.016345

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Photosynthetic response of the Mediterranean zooxanthellate coral Cladocora caespitosa to the natural range of light and temperature

Riccardo Rodolfo-Metalpa^1,*, Yannick Huot² and Christine Ferrier-Pagès¹

¹ Centre Scientifique de Monaco, MC-98000, Principality of Monaco
² Observatoire Océanologique de Villefranche, BP 28, 06230 Villefranche-sur-Mer, France

^* Author for correspondence at present address: Marine Biology and Ecology Research Centre, PL4 8AA Plymouth, UK (e-mail: riccardo.rodolfo-metalpa{at}plymouth.ac.uk)

Accepted 20 March 2008

We investigated photoacclimation in the symbiotic Mediterranean coral Cladocora caespitosa by exposing it to three light levels (30, 80 and 250 µmol m^–2 s^–1), which are in the range of those recorded for this species. The coral response to a change in both light and temperature was also assessed, by subjecting coral to two treatments corresponding to winter (14°C and 30 µmol m^–2 s^–1) and summer (23°C and 250 µmol m^–2 s^–1) conditions, as measured in the Ligurian Sea. Photosynthesis, measured using both respirometry and pulse amplitude modulated (PAM) fluorometry, revealed a linear relationship only at low light levels. At higher irradiance, relative electron transport rate (rETR) approached saturation more slowly than rates of oxygen production. At constant temperature, a change in light did not induce any change in zooxanthellae (zoox) and chlorophyll (Chla+c₂) concentrations (mean 3.7x10⁶ zoox cm^–2 and 14.1 µg cm^–2, respectively); however, chlorophyll concentrations significantly increased under low light and temperature, probably in order to maintain a sufficient level of autotrophy. Maximal gross photosynthesis (Pg_max) as well as the saturation irradiance (E_k) and the respiration rate (R) were, however, significantly higher at 250 µmol m^–2 s^–1 compared to the lower light treatments, independently of temperature conditions. Acclimation to high light appeared to be partly driven by a change in the non-photochemical quenching (NPQ) capacity of the algal cells, and to a maximal rate of photon utilization. Conversely, under low light conditions, coral polyps presented a lower E_k, but also lower respiration rates, which correspond to a decrease in the energy expenditure. This ability to acclimate to different light conditions, might allow C. caespitosa to rapidly regulate its autotrophic rate in the different light conditions encountered in its natural habitats.

Key words: photoacclimation, photosynthesis, light, temperature, Cladocora caespitosa, temperate coral