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Growth and photosynthesis of two Mediterranean corals, Cladocora caespitosa and Oculina patagonica, under normal and elevated temperature

TitleGrowth and photosynthesis of two Mediterranean corals, Cladocora caespitosa and Oculina patagonica, under normal and elevated temperature
Publication TypeJournal Article
Year of Publication2006
AuthorsRodolfo-Metalpa R, Richard C, Allemand D, Ferrier-Pagès C
JournalThe Journal of Experimental Biology
Keywordsbenthos, biodiversité, biodiversity, blanchiment, bleaching, Cladocora caespitosa, climate change, corail, coral, gène, Genoa, injury, Italie, Italy, La Spezia, Ligurian Sea, mass mortality, Mediterranean sea, Méditerranée nord-occidentale, Méditerrannée occidentale, Mer Ligure, Mer Méditerranée, mortalité massive, nécrose, north-western Mediterranean, Oculina patagonica, photosynthèse, photosynthesis, physiologie, réchauffement, scleractinian, sea water temperature, temperature, température de l'eau de mer, thermotolerance, transport, warming, western Mediterranean, zooxanthellae, zooxanthelle

The Ligurian Sea (NW Mediterranean) experienced warm summers in 1998, 1999 and from 2003 to 2005. The temperature was 1-3°C higher than the mean summer value (24°C) and remained high over a long period. During these summers, mass-mortality events, affecting several sessile benthic species, were reported. In the present study, we tested the long-term (3-7 weeks) effect of different temperatures (20°C measured in spring and autumn, 24°C observed in summer, and 26°C and 28°C abnormal summer values) on two Mediterranean corals, Cladocora caespitosa and Oculina patagonica. Growth rate, photosynthetic efficiency (Fv/Fm), relative electron transport rate (ETR), zooxanthellae and chlorophyll (chl) contents were measured during 48 days incubation. At 20°C, all parameters remained constant during the whole experiment for both species. At higher temperatures, most physiological parameters were affected by only 2-5 weeksat 24°C, and were severely depressed at higher temperatures. Small replicate samples (nubbins) of O. patagonica significantly decreased their zooxanthellae and chl concentrations at all temperatures, after 2 weeks of incubation. Their Fv/Fm values, as well as their growth rates, were also gradually reduced during the incubation at all temperatures. However, only a few nubbinsmaintained at 28°C showed signs of tissue necrosis after 34 days, and these gradually recovered tissue when temperature was returned to normal. In nubbins of C. caespitosa, chl and zooxanthellae concentrations decreased only after 34 days of incubation at 26°C and 28°C. At the same time, tissue necrosis was observed, explaining the loss of the symbionts. Fv/Fm was reduced only after 34 days of incubation at the different temperatures, and growth rate was first enhanced, before collapsing by 30% at 24°C and by 90-100% at 26°C and 28°C. All samples maintained at 26°C and 28°C had died, due to tissue necrosis, by the end of the experiment. Results obtained suggest that O. patagonica is more able than C. caespitosa to resist high temperature conditions because of its rapid bleaching capacity. In contrast, it seems that C. caespitosa is living close to its thermal limit during the summer period; therefore, a long-term increase at 24°C or above could be lethal for this coral, just as was observed in situ during the recent warm summers.

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