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    Using Phytoplankton as Bioindicators of Tourism Impact and Seasonal Eutrophication in the Andaman Sea (Koh Yaa, Thailand)
    (2026-01-01)
    Wongsnansilp, Tassnapa
    ;
    Khamcharoen, Manoch
    ;
    Boonrong, Jaran
    ;
    Dejtisakdi, Wipawee
    This study focuses on the diversity of phytoplankton in the Koh Yaa region of Thailand and their relationship with environmental variables, aiming to assess whether human activities (primarily tourism) pose potential threats to the marine ecosystem and provide scientific support for eco-sustainable tourism management decisions in the region. In April, August, and December 2024, corresponding to peak season, off-season, and shoulder season, a total of 156 discrete samples were collected from four coastal sites to analyze water quality parameters such as temperature, pH, total nitrogen (TN), and total phosphorus (TP), along with plankton diversity and abundance. Statistical analyses including two-way ANOVA with Duncan’s Multiple Range Test (DMRT), Pearson correlation analysis, and principal component analysis (PCA) were applied. The results showed a declining trend in plankton abundance over time, peaking at 1009 × 10<sup>6</sup> cells/m<sup>3</sup> in April and dropping to 281 × 10<sup>6</sup> cells/m<sup>3</sup> by December. A total of 15 types of phytoplankton were identified across four phyla: Bacillariophyta, Cyanobacteria, Dinoflagellata, and Chlorophyta. Notably, Chaetoceros from Bacillariophyta accounted for 47% of phytoplankton, while Oscillatoria from Cyanobacteria made up 29.6%. The diversity index and evenness index improved from 1.34 and 0.46 in April to 1.88 and 0.64 in December, respectively. Environmental factors like pH, temperature, and TP significantly affected phytoplankton abundance (p < 0.01), with TP levels ranging from 0.27 to 0.69 mg/L. These results indicate possible pollution in this region, and changes in phytoplankton abundance were linked to seasonal climate variations—especially during peak tourist seasons—which may exacerbate eutrophication affecting community structures.
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    Morphological and molecular insights into diversity of Brevitrygon (Elasmobranchii, Myliobatiformes, Dasyatidae) in Thai waters
    (2026-01-01)
    Wongmanee, Phiphat
    ;
    Khudamrongsawat, Jenjit
    ;
    Krajangdara, Tassapon
    ;
    Senanan, Wansuk
    ;
    Panithanarak, Thadsin
    Stingrays of the genus Brevitrygon in Thailand are captured as bycatch in fisheries, and a proportion of the catch is used for local consumption, but information on their biodiversity remains limited. This study examines the diversity of Brevitrygon species collected from the Gulf of Thailand and the Andaman Sea. A total of 148 specimens were morphologically identified as either Brevitrygon heterura (Bleeker, 1852) or Brevitrygon cf. imbricata, based on diagnostic characters. Morphometric analysis revealed that all specimens more closely resembled B. heterura, with no significant differences between morphotypes or sexes. Genetic analysis based on COI sequences from 39 samples further supported these results. All samples grouped within the B. heterura clade with strong bootstrap support and formed two distinct genetic subgroups corresponding tothe Gulf of Thailand and the Andaman Sea. The mean intraspecific divergence (1.08%) fell within the expected range for population-level variation in elasmobranchs, with interspecific divergence from other Brevitrygon species exceeding 9%. These results indicate that B. heterura in Thai waters likely represents a single species. While both morphometric and genetic data suggest regional differentiation, the observed variation falls within the normal range for a single species, providing no evidence of cryptic diversity. This study underscores the value of integrating morphological and molecular data to better understand population structure and taxonomy in stingrays.