IN SITU MONITORING OF OXYGEN PRODUCTION AND RESPIRATION IN CNIDARIA WITH AND WITHOUT ZOOXANTHELLAE

Abstract

24h in situ monitoring was carried out on Red Sea corals and other coelenterates with symbiotic zooxanthellae and some species lacking them. The individuals were enclosed in bell jars, and the water stirred continuously. In another experimental series the bell jars were flushed automatically at regular intervals. During a 24h cycle the species having zooxanthellae showed a conspicuous surplus in O2 production at all depths down to 40m. In all species examined there was a maximum production and respiration below 5m depth, with an unexpected decrease of 25–50% in 1m depth. A slight decrease in production appeared following saturation light intensities in the morning if the closed bell jar system was used. In the flushed bell jars production remained constant until the evening saturation level. Xeniids showed a stepwise increase of O2 output caused by diurnal colony contraction. Species lacking symbionts showed remarkable reduced metabolism compared with symbiotic species. It must be concluded that metabolism of symbiotic species is accelerated by the supply of photosynthetic products.