Effects of changing seawater temperature on photosynthesis and calcification in the scleractinian coral Galaxea fascicularis , measured with O 2 , Ca 2+ and pH microsensors

By FFuad A. Al-Horani. 2005

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Single polyps of Galaxea fascicularis were fixed to glass vials with underwater epoxy resin. After regeneration into microcolonies they were used for microsensor measurements of photosynthesis and calcification under different incubating temperatures. Gross photosynthesis was found highest at temperatures of 23 and 26°C (ca. 0.022 mole O2 m -3 s –1 ), close to the ambient temperature (i.e. 26°C). At 35°C, gross photosynthesis was irreversibly inhibited as the microcolonies bleached. The net photosynthesis rapidly decreased with temperature and became negative at temperatures higher than 29°C. Profiles of O 2 and Ca 2+ showed a strong effect of temperature on them. The concentrations of Ca 2+ measured on the polyp surface also showed temperature dependence of Ca 2+ uptake. In the dark and below 29°C, the surface Ca 2+ concentration was temperature independent. During illumination, the surface Ca 2+ concentration showed a dip at 26°C (ca. 8.7 mM), indicating maximum uptake rates at ambient temperature. However, at 32°C and higher, Ca 2+ was slightly higher at the tissue surface than in the seawater, in both light and dark, resulting from calcium dissolution. The surface pH in light increased gradually from 8.3 to 8.6 with increasing temperature to 23°C, and thereafter remained constant to 29°C. At 32°C, the pH became slightly acidic compared with the water phase, probably due to a decrease in the uptake of CO 2 by photosynthesis. The largest difference in pH between light and dark incubations was at temperatures between 23 and 29°C (7.5-7.7 in dark versus 8.6-8.7 in light), which indicate high rates of photosynthesis and respiration in this temperature range. It is concluded that photosynthetic activity in the coral is maintained up to rather high temperatures (32°C), but corals at super-optimum temperatures (above 26°C) consume more O 2 than they produce, decalcify and produce CO 2

Subfields: Ecology, Global and Planetary Change, Nature and Landscape Conservation

View Paper: https://www.semanticscholar.org/paper/692678ce677b62f1d224a4b08037319741de07c1

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Citations in the corpus

Decline in skeletal growth of the coral Porites lutea from the Andaman Sea, South Thailand between 1984 and 2005 (2009, result): “This result is consistent with other experimental studies, where the optimum temperature for calcification was *27 C (Clausen and Roth 1975; Highsmith 1979; Marshall and Clode 2004; Al-Horani 2005).”
Effects of temperature, light and heterotrophy on the growth rate and budding of the temperate coral Cladocora caespitosa (2008, background): “Enzyme activity is maximal at the optimal temperature of the organism and decreases at high (Marshall and Clode 2004; Al-Horani 2005) and low temperatures (Jacques et al. 1983).”
A modeling tool to evaluate regional coral reef responses to changes in climate and ocean chemistry (2008, background): “2B shows the two empirically derived curves (Gulf of Aqaba and O’ahu HI-N), plus two curves generated by COMBO.”