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National Committee on Marine Sciences (NCMS)

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Author: search.filters.author.Fortes, Miguel D.Scientific name: search.filters.scientificname.Thalassia hemprichii

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    Vegetative dynamics and sexual reproduction of monospecific Thalassia hemprichii meadows in the Kalayaan Island Group
    Rollon, Rene N.; Cayabyab, Napo M.; Fortes, Miguel D. (Elsevier BV, 2001-11)
    We surveyed eight offshore islands and shoals in the Philippine Kalayaan Island Group. The aims were to (1) map the distribution, (2) evaluate the demographic status, (3) elucidate the vegetative growth dynamics, and (4) quantify the sexual reproductive capacity of Thalassia hemprichii meadows in the region. We combined age reconstruction techniques and in situ estimations to attain such goals. We found T. hemprichii meadows only in Pag-asa Island. These meadows were generally young (mean age <1 year) and rapidly expanding (net recruitment ∼0.8 ln units per year). This was consistent with the horizontal rhizome apices being dense (162–334 apex m−2) and fast-spreading (36–56 cm per apex per year). The results for in situ measurements of plastochron interval (9.2 days), and relative leaf (3.7 cm2 cm−2 per shoot per day) and areal growth rates (2.3–2.7 cm2 per shoot per day) were similar to those of previous studies. The variation in the vertical internodal lengths showed a unimodal annual trend more distinctly in the south than in the north station, suggesting local, small-scale differences in environmental conditions between stations. Flower production was clearly seasonal, peaking around January 1999. Fruiting (128–134 m−2) and seedling recruitment (22–32 m−2) values were high, indicating a substantial contribution of sexual reproduction to the rapid expansion or meadow maintenance. The apparent disjunct occurrence of such young and highly reproductive meadows in the region merits further investigation.
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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.