Morphophysiological variations of symbiotic dinoflagellates in hermatypic corals from a fringing reef at Sesoko Island

Three types of symbiotic dinoflagellates L (large), B (brown) and G (green) found in hermatypic corals from a fringing reef of Sesoko Island (Okinawa, Japan) differed morphologically, physiologically and biochemically. Colonies of the hydrocoral Millepora intricata hosted symbionts of type L only; scleractinian corals containing type B only were Pocillopora damicornis, type G only were Seriatopora caliendrum and S. hystrix, and both types B and G were found living together in Stylophora pistillata and Echinopora lamellosa. The symbiotic dinoflagellates (SD) differed considerably in cell size, shape and structural elements in coccoid state in hospite. SD of these types also differed in photosynthetic capacities, primary production, pigment accumulation and maximum rates of cell division and degradation.Corals hosting various types of SD significantly differed in light-resistance. Scleractinian corals with symbionts of both types B and G, in the same colony, acclimated to bright light by increasing the relative number of symbionts of type G and acclimated to dim light by increasing the SD number of type B. It was shown that scleractinian corals can photo-acclimate through formation of optimal composition of SD types under various light intensities.