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• Reciprocal transplant experiment reveals multiple factors influencing changes in coral microbial communities across climate zones.

  Ya-Fan Chan, Yu-Hsiang Chen, Sheng-Ping Yu, Hsing-Ju Chen, Yoko Nozawa, Sen-Lin Tang

  The Science of the total environment   907   167929 - 167929   2024.01 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Previous studies have demonstrated the influence of external factors (environmental factors and the coral host factors) on the community structure of coral-associated bacteria. However, the internal factors, e.g. the interaction within the bacterial community or bacteria itself, have often been overlooked in studies of the coral microbiome. Hence, we performed a reciprocal transplant of corals between two different climate zones to examine the resultant alterations in coral-associated bacterial communities. The findings highlight the significance of environmental factors, host selection, and highly resilient bacteria in shaping the coral microbial composition. The results support that coral species consistently harbor specific predominant bacterial groups influenced by host selection, while locations display unique bacterial taxa due to environmental variations. The transplantation of corals into new environments leads to a gradual shift in the bacterial community, from initially resembling that of the native location to eventually resembling that of the transplanted location, emphasizing the crucial role of bacterial community composition for coral survival under changing ambient conditions. Furthermore, highly resilient bacteria that persisted throughout the reciprocal transplant experiment demonstrated their adaptability to environmental and host changes, suggesting the presence of robust adaptation or resistance mechanisms in bacterial communities. Genetic adaptations within the prevalent bacterial group, Endozoicomonas, were also observed, suggesting variations in resilience and adaptation capabilities among different phylotypes. This study highlights the need to conduct further investigations into the coral-associated bacteria themselves, as they may hold some key insights into understanding the dynamics of coral-associated microbial communities. These data also highlight some key species of coral-associated bacteria which could benefit coral in response to alterations in ambient environment.

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• Molecular Phylogeny and Taxonomy of the Coral Genus Cyphastrea (Cnidaria, Scleractinia, Merulinidae) in Japan, With the First Records of Two Species

  Thanapat Chukaew, Naoko Isomura, Takuma Mezaki, Hisashi Matsumoto, Yuko F Kitano, Yoko Nozawa, Hiroyuki Tachikawa, Hironobu Fukami

  Zoological science   40 ( 4 ) 326 - 340   2023.06 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  The scleractinian coral genus Cyphastrea is widely distributed in the Indo-Pacific region and is common from the subtropical to the warm-temperate regions in Japan. Three new species in this genus have recently been reported from south-eastern Australia or the Red Sea. However, taxonomic and species diversity have been little studied so far in Japan. In this study, we analyzed 112 specimens of Cyphastrea collected from the subtropical to the warm-temperate regions in Japan to clarify the species diversity in the country. This analysis was based on skeletal morphological and molecular analyses using three genetic markers of the nuclear 28S rDNA, histone H3 gene, and the mitochondrial noncoding intergenic region between COI and tRNAmet. The molecular phylogenetic trees showed that our specimens are separated mainly into four clades. Considering the morphological data with the molecular phylogenetic relationships, we confirmed a total of nine species, including two species, C. magna and C. salae, recorded for the first time in Japan. Although eight out of nine species were genetically included within Cyphastrea, one species, C. agassizi, was genetically distant from all other species and was closely related to the genus Leptastrea, suggesting the return of this species to the genus to which it was originally ascribed. Two newly recorded species were reciprocally monophyletic, while the other six species (excluding C. agassizi) clustered in two clades without forming species-specific lineages, including three polyphyletic species. Thus, the species boundary between species in Cyphastrea remains unclear in most species using these three sequenced loci.

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• The influence of seawater temperature on the timing of coral spawning

  Lin C.H.

  Coral Reefs ( Coral Reefs )  42 ( 2 ) 417 - 426   2023.04 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  We report the influence of seawater temperature on the timing of coral spawning for three time-scales; months, days, and hours for four scleractinian coral species (Acropora hyacinthus, Acropora gemmifera, Dipsastraea speciosa, and Favites pentagona). We monitored the timing of in situ coral spawning in Lyudao (Green Island), Taiwan from 2010 to 2020, at two sites (Gonggan and Dabaisha) that had an average seawater temperature difference of 0.1-2.1 degrees C due to upwelling. We also conducted a reciprocal transplantation experiment between the two sites using A. hyacinthus in March 2015 (1-2 months before the expected spawning). Results indicated consistent patterns among the four coral species. Annual spawning always occurred between April and June, when seawater temperature was rapidly rising and reached the monthly average between similar to 26-29 degrees C. Spawning days (days after full moon) were negatively correlated with average seawater temperatures over the 1 week prior to spawning, as were spawning hours with average seawater temperatures between sunset and spawning time. Spawning tended to occur on earlier days and hours at the warmer site (Dabaisha). Transplants of A. hyacinthus to the warmer site spawned in May, compared to those at the cooler site that spawned in June. Our results demonstrated the pervasive influence of temperature on the timing of coral spawning at three relevant time-scales. This can probably be attributed to temperature influencing the time course of various reproductive processes that operate on different time-scales; e.g., gametogenesis (months), the final gamete maturation (days), and the preparation of spawning (hours).

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• An External Coincidence Model for the Lunar Cycle Reveals Circadian Phase-Dependent Moonlight Effects on Coral Spawning

  Hideyuki Komoto, Che-Hung Lin, Yoko Nozawa, Akiko Satake

  JOURNAL OF BIOLOGICAL RHYTHMS ( SAGE PUBLICATIONS INC )  38 ( 2 ) 148 - 158   2023.04 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Many marine organisms synchronously spawn at specific times to ensure the success of external fertilization in the ocean. Corals are famous examples of synchronized spawning at specific lunar phases, and two distinct spawning patterns have been observed in two dominant taxa: merulinid corals spawn at regular lunar phases, several days after the full moon, whereas Acropora corals spawn at more irregular lunar phases around the full moon. Although it has been suggested that the two coral taxa have different responses to moonlight and seawater temperature, their spawning times have never been analyzed by integrating the two environmental factors, resulting in an incomplete understanding of the regulatory mechanisms of spawning. In this study, we developed a new predictive model of coral spawning days by integrating moonlight and temperature effects based on the external coincidence model for the lunar cycle. We performed model fitting using a 10-year monitoring record of coral spawning time in Taiwan. Our model successfully demonstrated the synergistic effects of moonlight and temperature on coral spawning time (days) and provided two testable hypotheses to explain the different spawning patterns regarding the preparation (maturation) process for spawning and the sensitivity to moonlight at different circadian phases: (1) Acropora corals may have an earlier onset and longer period of preparation for spawning than merulinid corals; and (2) merulinid corals may use moonlight signals near sunset, while Acropora corals may have a similar onset at approximately midnight. This is the first study to indicate the difference in circadian phase-dependent moonlight sensitivities between coral taxa, providing a basis for underlying coral spawning mechanisms for rhythmic studies.

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• Timing of final oocyte maturation in Acropora and merulinid corals

  Tzu-Yu Lai, Vianney Denis, Yoko Nozawa

  CORAL REEFS ( SPRINGER )  41 ( 5 ) 1379 - 1387   2022.10 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Final oocyte maturation is a gametogenic process that occurs at the end of oogenesis, which includes germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD). This process is essential for oocytes to become competent for fertilization and occurs just before spawning. Timing of GVM and GVBD has been extensively studied to understand reproductive timing in various marine organisms. For corals, however, such information remains scarce. Here, we examined the timing of GVM and GVBD in broadcast-spawning corals: two Acropora and six merulinid species, from around the full moon until spawning day(s), at Lyudao, Taiwan in 2019 and 2020. The proportion of oocytes that had completed GVM around the full moon varied among species (14-64%), while the proportion increased to > 80% by 6-7 d after the full moon when many sampled colonies spawned. By contrast, although data are limited, the timing of GVBD indicated a more uniform pattern among species, and the onset of GVBD in the majority of oocytes occurred within 3-10 h before spawning. As GVM and GVBD are prerequisites for fertilization, and probably the spawning itself, the interspecific variation in the timing of GVM likely reflects an interspecies variation in spawning timing. This hypothesis may partially explain the different spawning timing (days) among coral species observed at the study location. Further research is needed to test such a hypothesis, given the limitation of our study with regard to the number of observations, annual variation, and examined coral taxa.

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