Coral reefs in the Gulf of Thailand have experienced severe coral bleaching events and anthropogenic disturbances during the last two decades. This study assessed the resilience potential of coral communities at Ko Losin offshore reef sites and Mu Ko Chumphon nearshore coral reefs, in the south of Thailand, by conducting field surveys on the live coral cover, hard substratum composition and diversity and density of juvenile corals. Most study sites had higher percentages of live coral cover compared to dead coral cover. Some inshore and offshore reef sites showed low resilience to coral bleaching events. The total densities of juvenile corals at the study sites were in the range of 0.89–3.73 colonies/m². The density of the juvenile corals at most reef sites was not dependent on the live coral cover of adult colonies in a reef, particularly for the Acropora communities. We suggest that Ko Losin should be established as a marine protected area, and Mu Ko Chumphon National Park should implement its management plans properly to enhance coral recovery and promote marine ecotourism. Other measures, such as shading, should be also applied at some coral reefs during bleaching periods.

Two new marine actinobacteria, designated as J2-1^T and J2-2^T, were isolated from a coral, Favites pentagona, collected from Rayong Province, Thailand. The taxonomic positions of the two strains were identified based on polyphasic taxonomy. Based on morphological characteristics and chemotaxonomy, strains J2-1^T and J2-2^T were identified as members of the genus Streptomyces and Kineosporia , respectively. Strains J2-1^T and J2-2^T showed the highest 16S rRNA gene sequence similarity to Streptomyces broussonetiae T44^T (98.62 %) and Kineosporia babensis VN05A0415^T (98.08 %), respectively. Strain J2-1^T had chemotaxonomic properties resembling members of the genus Streptomyces . ll-Diaminopimelic acid, glucose and ribose were detected in the whole-cell hydrolysate. Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositolmannoside, unidentified aminolipid and five unidentified phospholipids were detected as the polar lipids. The major cellular fatty acids were C_16 : 0 iso, C_15 : 0 anteiso, C_15 : 0 iso, C_16 : 0, C_17 : 0 anteiso, C_14 : 0 iso and C_17 : 0 iso. Strain J2-2^T a showed similar cell composition to members of the genus Kineosporia . Both isomers of ll- and meso-diaminopimelic acid were detected in the peptidoglycan. Arabinose, galactose, madurose and xylose were observed in the whole-cell hydrolysate. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, phosphatidylcholine, an unidentified phospholipid and an unidentified glycolipid. The major cellular fatty acids were C_16 : 0, C_18 : 1 ω9c, C_18 : 0 10-methyl, tuberculostearic acid, C_18 : 0 and C_17 : 0. Both strains could be distinguished from their closely related type strains according to their phenotypic characteristics. Comparative genome analysis indicated the delineation of two novel species based on digital DNA–DNA hybridization and average nucleotide identity values, which were below 70 and 95 %, respectively. The names proposed are Streptomyces corallincola sp. nov. (J2-1^T=TBRC 13503^T=NBRC 115066^T) and Kineosporia corallincola sp. nov. (J2-2^T=TBRC 13504^T=NBRC 114885^T).

The brown macroalgal genus Lobophora plays important ecological roles in many marine ecosystems. This group has received much attention over the past decade, and a considerable number of new species have been identified globally. However, our knowledge of the genus diversity and ecology along south-east Asian coasts are still limited. Given the growing body of research that uses a combination of molecular and morphological data to identify cryptic species, this study investigates the diversity of Lobophora in the western Gulf of Thailand using morphological and molecular data, as well as their interactions with scleractinian corals. A total of 36 Lobophora specimens were collected from 15 sites in the western Gulf of Thailand and used for molecular and morphological analyses. One mitochondrial (cox3) and two chloroplast (psbA and rbcL) genes were amplified and sequenced for molecular phylogenetic analyses. Based primarily on phylogenetic evidence, two new species were formally described, L. chumphonensis sp. nov. and L. thailandensis sp. nov. Additionally, L. lamourouxii was newly recorded from Thailand. Two new lineages of Lobophora obscura were identified, L. obscura12 and L. obscura13. Among the Lobophora species identified, three were found in interaction with corals, the most notable of which was the massive coral Porites. Lobophora chumphonensis sp. nov. only interacted with Porites by growing on bare coral skeleton between Porites colonies. Furthermore, L. obscura13 was observed under the branching coral Pocillopora. Our findings revealed that Lobophora presented both effects and absence of effects on coral. A thorough understanding of Lobophora diversity and ecology is essential for ongoing and future research on coral–macroalgal ecological relationships.

This study investigates the occurrence, abundance, and characteristics of microplastics (MPs) in coral reef ecosystems at two reef sites, Ko Khang Khao and Ko Ngam Yai, in the Gulf of Thailand. Coral, seawater, and sediment samples were analyzed to evaluate the spatial variability of microplastics in terms of their abundance, size distribution, shape, polymer composition, and color. MPs were detected in all coral samples, with concentrations ranging from 0.24 to 2.60 particles g ^- ¹ w.w. Ko Khang Khao exhibited higher MP concentrations across coral species, with Pavona decussata , Pocillopora acuta , and Galaxea fascicularis showing the greatest accumulation. Statistically significant inter-site differences in MP abundance were observed in four coral species ( p < 0.05). Coral surface was the dominant compartment for MP accumulation (63.05% at Ko Khang Khao and 61.82% at Ko Ngam Yai), followed by skeleton and tissue. MP size distribution varied by coral compartment, with coral skeletons retaining larger particles (>3000 µm) and tissues favoring smaller MPs (25–1500 µm). Fiber-shaped MPs were predominant across all sites and compartments. Polymer analysis revealed polyethylene terephthalate (PET) and polyethylene (PE) as the most common polymers, while notable amounts of polypropylene (PP), nylon, and polystyrene (PS) were also identified, indicating diverse anthropogenic sources. Color analysis showed blue MPs as the most abundant, followed by black, white/yellow, red, and green particles. Green MPs were notably absent at Ko Ngam Yai. In seawater, MP concentrations ranged from 0.88 to 1.61 particles m ^- ³, with higher levels at Ko Khang Khao. Fiber was again the dominant shape, and PE and PET were the most common polymers. Sediment samples exhibited MP abundances ranging from 164.80 to 295.20 particles kg ^- ¹, with Ko Khang Khao having a greater prevalence of smaller particles (<600 µm) and more diverse polymer types. Across all matrices, Ko Khang Khao consistently showed higher MP concentrations and greater diversity in MP characteristics compared to Ko Ngam Yai, likely reflecting greater anthropogenic influence. These findings emphasize the spatial heterogeneity of microplastic pollution in coral reef systems and underscore the need for localized management strategies to mitigate microplastic inputs in nearshore marine environments.