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Morphological and molecular insights into diversity of Brevitrygon (Elasmobranchii, Myliobatiformes, Dasyatidae) in Thai waters
(2026-01-01)
Wongmanee, Phiphat
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Khudamrongsawat, Jenjit
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Krajangdara, Tassapon
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Senanan, Wansuk
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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.
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Decadal and seasonal oceanographic trends influenced by climate changes in the Gulf of Thailand
(2025-06-01)
Lubis, Muhammad Zainuddin
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Ghazali, Muhammad
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Simanjuntak, Andrean V.H.
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Riama, Nelly F.
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Pasma, Gumilang R.
Our study investigates the decadal and seasonal variability of sea surface height (SSH) and sea surface temperature (SST) in the Gulf of Thailand (GoT) using data from CMEMS from 1993 to 2021. We employed statistical analyses utilizing GLM and GAM to assess the variables comprehensively. The reveals a significant upward trend in SSH, increasing from ∼0.79 m in 1993–1998 to ∼0.89 m in 2017–2021, highlighting the impacts of climate change. SST analysis revealed fluctuations, with a maximum reaching ∼30.6 °C in 2019–2020, correlating with climatic events such as El Niño. Our study results at station 1 (near Bangkok) showed that the average SSH in 1998 during strong El Niño years was equal to 0.82 m, while the maximum SST was equal to 29.89 °C. Seasonal patterns indicated SSH peaks in DJF and SON at ∼0.92 m, while SST peaked in spring MAM and summer JJA at ∼30.7 °C. Volume transport analysis showed significant variability, with 0.3634 Sv (0–55 m) at longitude 99°E-107° E and latitude 6° N, indicating complex circulation patterns influenced by bathymetry and wind. Time series analysis revealed an average SSH increase of 0.0038 m/year, with a high pseudo-R-squared of 0.99. Our findings underscore the critical influence of climate variability on oceanographic conditions in the GoT, emphasizing the need for ongoing monitoring to address the implications of rising sea levels and temperature fluctuations. In conjunction with increased SSH, the rising SST heightens the risk of flooding in low-lying areas, exacerbating vulnerabilities for local populations and necessitating adaptive management strategies to mitigate these impacts.
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Resolving Species Identification and Distribution Patterns of Neotrygon spp. in Thai Waters: Inefficiency of Morphometric Analysis and the Power of COI Gene Barcoding and Phylogenetics
(2025-01-01)
Panithanarak, Thadsin
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Karuwanjaroen, Ratima
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Utama, Chanapa
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Laongmanee, Penchan
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Meejan, Titirat
Three species of maskrays in the genus Neotrygon have previously been reported in Thai waters. However, the high morphological similarity among species within the blue-spotted maskray complex (Neotrygon spp.) makes accurate identification challenging. This study aimed to confirm species identification in Neotrygon spp. using morphometric and genetic data and to further examine their phylogenetic relationships in Thai waters by analyzing mitochondrial COI (cytochrome c oxidase subunit I) sequences. Multivariate analysis (PCA) of 37 morphometric characters from 55 specimens proved insufficient for species-level discrimination. However, molecular phylogenetic analysis of 14 unique COI sequences from Thai waters, combined with 61 reference sequences from previously documented related species and closely related species, identified two monophyletic clades. These clades corresponded to two species: N. varidens, found exclusively in the Gulf of Thailand, and N. malaccensis, recorded for the first time in Thailand, occurring in both the Gulf of Thailand and the Andaman Sea. This DNA-based identification provides clear evidence for species boundaries within Thai Neotrygon species and highlights the importance of molecular tools for distinguishing morphologically similar marine species in the Indo-Pacific region.
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Optimal Prediction of Effectiveness of Mangrove Forest Against Coastal Erosion: Case Study of Coastal Area along the Gulf of Thailand
(2024-01-01)
Rattanarama, Puangpet
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U-Tapao, Chalida
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Yamamoto, Yoshimichi
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Nopmuang, Arj Ong
Coastal erosion in Thailand is severe due to the deforestation of mangrove forests, which naturally dissipate waves, making it necessary to establish how to reproduce mangrove forests of a suitable size. First, a survey of mangrove forests was performed in 2012-2013 along the coast of the Gulf of Thailand, where mangrove vegetation has been affected by human activities. The survey showed that tentacle-root mangroves (Rhizophora mucronata) accounted for the largest proportion of the mangrove trees in the area. The distribution characteristics of the root number per mangrove tree and the diameters of root systems and main trunks were also clarified. The parametric results were used to make replicas of mangrove vegetation. Hydraulic experiments were carried out in a wave tank in 2014, and a calculation diagram for obtaining the wave transmission ratio was constructed, which was improved over 2015-2018. Moreover, experimental data of eight existing papers were used to increase the value and reliability of this diagram. As a result, a wave transmission ratio can be obtained as a function of the density of mangrove vegetation and the ratio of the incident wavelength to the offing direction width of a mangrove forest. Next, the wave transmission ratio of existing detached breakwaters made of geotextile sandbags was evaluated by simulation using the numerical model [V. T. Ca: VNU J. Sci., Earth Sci. 23 (2007) 160], then the required width of a mangrove forest for it to have the same effect as an existing detached breakwater was estimated. The wave transmission ratio of this breakwater was 0.33, and the offing direction width of the tentacle-root mangrove forest was 250 m with a tree density of 0.8 (the number of trees/m2). By performing verification simulations using experimental data, the high reproduction accuracy of the topographical changes obtained by the numerical model of Ca et al. was confirmed.
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Gordonia aquimaris sp. nov., a novel marine actinobacterium isolated from seawater in the upper gulf of Thailand
(2023-03-01)
Pansomsuay, Rawirat
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Duangupama, Thitikorn
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Pittayakhajonwut, Pattama
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Intaraudom, Chakapong
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Suriyachadkun, Chanwit
An actinobacterium strain, SW21T, was isolated from seawater collected in the upper Gulf of Thailand. Cells were Gram-stain-positive, aerobic and rod-shaped. Growth was observed from 15 to 37 °C and at pH 6–8. Maximum NaCl for growth was 14% (w/v). meso-Diaminopimelic acid, arabinose, galactose, glucose, rhamnose and ribose were detected in the whole-cell hydro-lysate. Diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositol mannoside were detected as the phospholipids in the cells. The major menaquinones were MK-9(H<inf>2</inf> ) and MK-7(H<inf>2</inf> ). The major cellular fatty acids were C<inf>16:0</inf>, C<inf>18:1</inf> ω9c, C<inf>18:0</inf> and C<inf>18:0</inf> 10-methyl (TBSA). The 16S rRNA gene sequence data supported the assignment of strain SW21T to the genus Gordonia and showed that Gordonia mangrovi KCTC 49383T (98.7%) was the closest relative. Moreover, the average nucleotide identity-blast (85.5%) and digital DNA–DNA hybridization (30.7%) values between strain SW21T and its closest neighbour were below the threshold values for delineation of a novel species. The combination of genotypic and phenotypic data indicated that strain SW21T is representative of novel species of the genus Gordonia. The name Gordonia aquimaris sp. nov. is proposed for strain SW21T. The type strain is SW21T (=TBRC 15691T=NBRC 115558T).
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Spatial Changes of Ocean Circulation Along the Coast of Gulf of Thailand Using Tide Gauge Measurements
(2022-01-01)
Ansari, Kutubuddin
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De Oliveira-Junior, Jose Francisco
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Jamjareegulgarn, Punyawi
The study presents linear and nonlinear (smoothing spline) modeling of sea-level measurements on the basis of 50-year (1971-2020 A.D.) permanent service for mean sea-level (PSMSL) tide gauge data at the coastal area of the Gulf of Thailand. These tide gauge measurements are compared with the ORAS5 data extracted from the latest ECMWF atmospheric reanalysis-ERA5. The comparative analyses showed that both kinds of data are correlated with a correlation coefficient of more than 0.94. Moreover, to examine the performance and the complexity of tide gauge measurements at each site, the multitaper spectral analysis is carried out and the spectral estimates are also estimated. Our spectral analyses showed that the sea-level measurements at each site have different levels of fluctuation because of individual local influence. The proposed multitaper spectral analysis can be considered as an appropriate method for tide gauge analysis and can be applied to attain the fluctuation of sea-level at the global level.
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Effect of coastal prevention by beach and serious problems in some coasts of the Gulf of Thailand
(2011-09-19)
Charusrojthanadech, Nunthawath
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Yamamoto, Yoshimichi
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Sirikaew, Uba
Beach erosion in most of Thailand became significant in some many years ago. The causes of this change are considered to be the combination of human induced development and big waves. Though people tried to respond to it mainly by building seawall, there are many inappropriate elements in design and materials. In this research, the authors assessed the mangrove presence and beach change in coastal areas and analyzed the effective prevention to coastal disaster by beach using a lot of beach information gotten by the authors' field surveys, aerial photographs, wave and tidal data gotten from government organization. The authors introduce two serious problems on coastal disaster in the Gulf of Thailand, and propose countermeasures for those. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

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