Abstract
The relationship between genetically different zooxanthella types and their physiological functions in scleractinian corals has been studied extensively, because decrease in coral abundance is a growing concern at the present and possibilities of changing symbiotic algal partner by corals with more adaptive zooxanthella types against perturbed environment and survival of coral species harboring particular zooxanthella types after environmental changes were suggested. Distribution patterns of algal genotypes have been examined using molecular phylogenetic methods also in the North-West Pacific region, which exhibits a wide latitudinal range (tropical, subtropical, and temperate areas) of scleractinian coral distribution and is an appropriate field to understand adaptive patterns of coral-algae relationship in response to latitudinal changes of environmental factors (e.g. temperature and light intensity). Main clade in the North-West Pacific region is clade C, while clades A and B are dominant in the Caribbean. At a subtype level, several subtypes within clade C are dominant in the North-West Pacific region. Some different algal genotypes have also been found within the same colony or the same species of corals at both clade and subtype levels in the North-West Pacific region. However, some problems have been pointed out in the DGGE (Denatured Gel Gradient Electrophoresis) analysis, which has often been used to determine algal genotypes at a subtype level. Thus the distribution patterns of algal genotypes should be examined further by using the sequence data.
