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National Committee on Marine Sciences (NCMS)

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Author: search.filters.author.Nadaoka, KazuoScientific name: search.filters.scientificname.Thalassia hemprichii

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    Strong genetic structure and limited gene flow among populations of the tropical seagrass Thalassia hemprichii in the Philippines
    Nakajima, Yuichi; Matsuki, Yu; Fortes, Miguel D.; Uy, Wilfredo H.; Campos, Wilfredo L.; Nadaoka, Kazuo; Lian, Chunlan (MDPI AG, 2023-02-05)
    Seagrasses are marine angiosperms, and seagrass beds maintain the species diversity of tropical and subtropical coastal ecosystems. For proper understanding, management and conservation of coastal ecosystems, it is essential to understand seagrass population dynamics. Population genetic studies can cover large geographic scales and contribute to a comprehensive understanding of reproductive dynamics and potential dispersal among locations. The clonal and genetic diversity and genetic connectivity of Thalassia hemprichii in the Philippines were estimated by a population genetics approach. The geographic scale of this study has a direct distance of approximately 1600 km. Although high clonal diversity was found in some sites (R = 0.07–1.00), both sexual and asexual reproduction generally maintains separate populations. Genetic diversity is not definitely correlated with latitude, and genetic differentiation is significant in all pairs of sites (FST = 0.026–0.744). Complex genetic structure was found in some regions, even at a fine geographic scale. The migration of fruits and seedlings was elucidated as an infrequent and stochastic event. These results suggest the necessity for the conservation of this species due to a deficiency in migrants from external regions.
    We thank members of CECAM project.
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    17-year change in species composition of mixed seagrass beds around Santiago Island, Bolinao, the northwestern Philippines
    Tanaka, Yoshiyuki; Go, Gay Amabelle; Watanabe, Atsushi; Miyajima, Toshihiro; Nakaoka, Masahiro; Uy, Wilfredo H.; Nadaoka, Kazuo; Watanabe, Shuichi; Fortes, Miguel D. (Elsevier, 2014)
    Effects of fish culture can alter the adjacent ecosystems. This study compared seagrass species compositions in 2012 with those in 1995, when fish culture was less intensive compared to 2012 in the region. Observations were conducted at the same four sites around Santiago Island, Bolinao: (1) Silaqui Island, (2) Binaballian Loob, (3) Pislatan and (4) Santa Barbara, and by using the same methods as those of Bach et al. (1998). These sites were originally selected along a siltation gradient, ranging from Site 1, the most pristine, to Site 4, a heavily silted site. By 2012, fish culture had expanded around Sites 2, 3 and 4, where chlorophyll a (Chl a) was greater in 2012 than in 1995 by one order of magnitude. Enhalus acoroides and Cymodocea serrulata, which were recorded in 1995, were no longer present at Site 4, where both siltation and nutrient load are heavy.