Photosynthetic activity of a temperate coral Acropora pruinosa (Scleractinia, Anthozoa) with symbiotic algae in Japan

摘要

Physiological properties of the temperate hermatypic coral Acropora pruinosa Brook with symbiotic algae (zooxanthellae) on the southern coast of the Izu Peninsula, Shizuoka Prefecture, central Japan, were compared between summer and winter. Photosynthesis and respiration rates of the coral with symbiotic zooxanthellae were measured in summer and winter under controlled temperatures and irradiances with a differential gasvolumeter (Productmeter). Net photosynthetic rate under all irradiances was higher in winter than in summer at the lower range of temperature (12-20°C), while lower than in summer at the higher range of temperature (20-30°C). The optimum temperature for net photosynthesis was apt to fall with the decrease of irradiance both in summer and winter, whereas it was higher in summer than in winter under each irradiance. At 25/ 50/100 mu mol photons m~(-2) s~(-1), it was nearly the seawater temperature in each season, Dark respiration rate was higher in winter than in summer, especiallyin the range from 20-30°C. In both seasons the optimum temperature for gross photosynthesis was 28°C under 400 mu mol photons m~(-2) s~(-1) and lowered with decreasing irradiance up to 22°C under 25 (xmol photons m~(-2) s~(-1) in summer, while 20°C under the same irradiance in winter, The optimum temperature for production/respiration (P/R) ratio was higher in summer than in winter under each irradiance. Results indicated that metabolism of coral and zooxanthellae is adapted to ambient temperature condition under nearly natural irradiance in each season.