Historically, hermatypic corals are defined as a symbiotic system composed of an animal host, corals belonging to the taxa Cnidarian, and a photosynthetic organism, the dinoflagellate Symbiodinium spp., also known as zooxanthellae. The high gross productivity and stability of coral reefs have been explained by the efficiency of the coral-algal symbiotic system in using the low nutrient concentrations found in the surrounding water and their rapid recycling in the water. Although several studies have reported the presence of bacteria closely associated with corals, the mechanisms of the relationships among them, the host and the zooxanthellae, remain to be shown. In this study, evidence for the importance of coelenteric bacteria in corals as a component of the coral symbiotic complex was shown by using a new approach. Vitamin B₁₂, which is produced only by prokaryotes, was chosen as a chemical tool to clarify the symbiotic relationships among bacteria, coral, and zooxanthellae, which require vitamin B₁₂. High vitamin B₁₂ concentrations (up to 700pmol l^-1 compared with max. 20pmol l^-1 in the surrounding water) and high bacteria abundances (100 times higher than surrounding water) were found in the coelenteron of live corals using a new sampling method. The results led to the hypothesis that prokaryotes are the drivers of internal processes, such as vitamin B₁₂ production, occurring directly inside the coral, forming a semi-closed system. Furthermore, most maintenance of the symbiotic complex is due to internal processes rather than the supply from outside the coral.

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The relative contributions of larval recruitment and post-settlement mortality to the establishment of the zonation of Acropora communities, a dominant group in reef corals, remain unknown. Our field research revealed that the relative abundances of juveniles between two morphological categories of acroporid corals were different on shallow and deep slopes: tabular species dominated in shallow waters (1.5-2.5m), whereas arborescent species dominated in deep waters (5.5-11m). These abundances were consistent with the distributional patterns of the adults, suggesting that the zonation structure is formed during the initial life stages of settlement and early post-settlement periods. To determine to what extent Acropora zonation is determined by depth-related differences in initial mortality among species, a transplant experiment using artificially settled corals (10 days after settlement) of four dominant species (the shallow-dominants Acropora digitifera and A. selago and the deep-dominants A. muricata and A. tenuis) was performed at four depths (1.5, 2.5, 5.5, and 11m). Survivorship of all four species was lower at 5.5m than the other depths and that the survival rate of A. muricata was much higher than that of other species at all depths. However, there was no species-specific survival related to adaptation to a particular habitat (i.e., depth), implying that Acropora spats do not possess species-specific tolerance for the environmental stresses of their own particular habitat, at least during the first 6 months after settlement. Post-settlement survival rate during this period is therefore not a major factor in forming the vertical zonation pattern of these Acropora species in subtropical reefs around Japan.

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Phylogenetic relationships within Hexacorallia (Cnidaria, Anthozoa) have long been debated. Recently, complete mitochondrial (mt) genomes for all the hexacorallian orders have been obtained by different research groups, but no global analyses including all these data have yet been performed. Here we present the partial genome of the antipatharian Leiopathes glaberrima and the result of the first phylogenetic analyses including complete mitochondrial genomes of the five hexacorallian orders (Ceriantharia not being considered as true hexacorallian). Moreover, we report for the first time the presence of an intron in COI in the an antipatharian mt genome.

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Despite increased efforts in coral-reef monitoring and coral-disease research, reports on rapid recovery of diseased corals are rare. Here, I report fast recovery of Porites cylindrica colonies from live tissue loss, a reported and yet unnamed disease, at Shiraho, Ishigaki Island, Japan. Loss of live tissue and exposure of skeleton in P. cylindrica were first observed in August and September 2007. At the end of January 2008, recovery from the tissue loss was quantified. Mean proportion (±SD) of affected P. cylindrica branches decreased from 0.52±0.16 in September 2007 to 0.08±0.06 in January 2008. The majority of branches in the September sample had multiple, especially small, lesions; whereas in January, branches with multiple lesions were absent and most branches had no lesions. These results indicate that, by the end of January 2008, P. cylindrica colonies in the study area had almost fully recovered from the summer tissue loss by re-growth of live tissue over the denuded skeletons. Except in cases of coral bleaching, the rapid recovery from a disease observed in this study has not previously been reported. The observed quick recovery suggests that some coral-disease outbreaks may have been overlooked in the past and, without proper monitoring, will be overlooked in the future as well. Effects of overlooked diseases may accumulate and can have long-lasting impacts on reef communities, suggesting a need for frequent monitoring.

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