Distribution and abundance of mud crabs (Crustacea: Portunidae) in Pacific and Indian Ocean coasts of Thailand

Scylla olivacea is a commercially important species in the Indo-Pacific region, currently facing growing pressures from anthropogenic stressors. This study compares populations from the Indian Ocean (Andaman Sea) and the Pacific Ocean (Gulf of Thailand) to assess how different oceanic region and seasonal conditions influence key reproductive traits. By examining parameters such as sex ratio, size at first maturity, fecundity, and gonadosomatic index (GSI), the study aims to identify the differences that can inform targeted and sustainable management strategies. Crab samples were collected monthly from five sampling sites along the coast of the Indian Ocean (Ranong, Satun and Trang provinces) and the Pacific Ocean (Pattani and Surat Thani provinces) using traditional crab traps by local fishermen from April 2022 to May 2023 and subsequently analyzed in the laboratory. Results indicated that crabs from Ranong province, the Indian Ocean, exhibited smaller body sizes and values of most reproductive parameters (p < 0.01). The fecundities were 1.03 × 106 and 1.49 × 106 for crabs from Ranong and Pattani provinces, respectively. Positive relationships were found between internal carapace width (ICW), carapace length (CL), abdomen width (AW), and body weight (BW) with ovary weight (OW). Mature females, based on gonad development stages III and IV, were present year-round at both oceanic coasts. Peak abundances were found in November at both sites. High GSI levels were recorded in April and June for Ranong province (3.05 ± 1.97 to 10.97 ± 1.96) and February and June for Pattani province (3.19 ± 1.72 to 10.52 ± 1.71). The estimated sizes at maturity (M50) for female/male of S. olivacea varied across locations with smaller sizes observed from the Indian Ocean viz., 78.0/83.1 mm, 64.0/79.2 mm and 81.9/80.6 mm in the provinces of Ranong, Satun and Trang, respectively and 92.3/93.2 mm and 96.9/96.8 mm in Pattani and Suratthani, respectively. The sex ratio also indicated variations across region, with male:female ratios of 1:0.92, 1:0.78, 1:0.77 and 1:1 in the provinces of Pattani, Ranong, Satun and Trang. It is thus concluded that the oceanic region affects reproductive characteristics of S. olivacea and these findings can be applied to highlight the importance of localized management strategy for a sustainable use of mud crab resources.

A 225-year pine (Pinus latteri) tree-ring record of pre-monsoon relative humidity variation in Nan province of northern Thailand and the linkage with large-scale ocean-atmospheric circulations

The time-space evolution of the El Niño-Southern Oscillation in sea surface temperature (SST) and heat storage of the upper 400 m (HS400) for the Pacific, Indian, and Atlantic Oceans is investigated for 13 years (1979–1991). EOF and rotated EOF (Varimax or VRX) analyses are performed using the time series of normalized anomalies for each ocean separately and then for the global ocean. In the Pacific and Indian Oceans, the two dominant EOF modes for both SST and H5400 are associated with ENSO. For SST they account for 49% of the total variance in each mean, while for H5400 they account for over 35% of the total variance in each ocean. In the Pacific Ocean, the first EOF modes for SST and HS400 display peak values during spring-summer of 1983 and 1987. They are characterized by maximum positive loadings (or warmer temperature) in the eastern and central Pacific Ocean straddling the equator. These modes represent the peak phase of El Niño off the west coast of South America. The second modes for SST and HS400 are precursor modes with maximum positive loadings in the western and central Pacific Ocean both on and off the equator. The peak values in HS400 second mode lead peak values in HS400 first mode by 6–9 months. Taken together, SST and HS400 first two modes are associated with slow equatorial and eastward propagation of ENSO signals, more clearly though in HS400 than in the SST. In the Indian Ocean, the dominant EOF modes for SST display peak values in summer-fall of 1983 and summer of 1987, while peak values for HS400 are found during fall of 1982 and summer of 1987. Corresponding positive SST loadings are found in the central Indian Ocean while positive HS400 loadings are found in the western Indian Ocean. Maximum values are both straddling the equator. As in the Pacific Ocean, the second EOF modes for SST and HS400 in the Indian Ocean are precursor modes to the first modes. They occur 9–15 months earlier, with warmer SST in the Arabian Sea, colder SST northwest of Australia, and colder H5400 in the vicinity of the boreal winter ITCZ. Taken together, thew two modes suggest a slow equatorial and eastward propagation of ENSO signals in SST and HS400, very similar to those in the Pacific Ocean. This propagation can he seen extending eastward south of Indonesia and on into the Timor Sea. There the anomalies have the same sign as the anomalies found in the Philippine and Coral Seas in the western tropical Pacific Ocean during the peak phase of El Niño. In the Atlantic Ocean, ENSO is represented by the third SST VRX mode but not at all in HS400. As such, the Atlantic ENSO signal at the equator is a passive response to a globally perturbed atmosphere. It lags by approximately 18 months the dominant Pacific ENSO mode.

Biological information and population features of mud crab, genus Scylla from mangrove areas of Sarawak, Malaysia

The Indo-Pacific Ocean is a biodiversity hotspot for marine organisms. In this area, most of the research has focused on marine animals, such as reef fish, molluscs and other associated coral fauna, but very little has been done on macroalgae. The Thai-Malay Peninsula is an important north–south barrier in this area, which faces two different oceans – the Indian Ocean and the Pacific Ocean. This study aims to investigate genetic distribution patterns of Padina boryana Thivy around the Thai-Malay Peninsula, where it is common. Three DNA marker regions, the mitochondrion-encoded cytochrome c oxidase subunit 3 gene (cox3); the plastid rbcL, and the nuclear internal transcribed spacer 2 (ITS2) were used to evaluate genetic diversity and the relationships within and between populations. Samples were collected from both the Andaman Sea and Gulf of Thailand sides of the peninsula. Parsimony networks and maximum likelihood and Bayesian analyses showed clearly that there are two separated P. boryana lineages, one restricted to the Gulf of Thailand and the other to the Andaman Sea and other areas of the Indo-Pacific. The effect of different ocean currents along the Andaman Sea and Gulf of Thailand may have shaped these populations of P. boryana. This phylogeographic separation, based on persistent currents in the area, may affect other marine organisms along the Thai peninsula.

Background: The Lethrinidae (emperors) include many important food fish species. Accurate determination of species and stocks is important for fisheries management. The taxonomy of the genus Lethrinus is problematic, for example with regards to the identification of the thumbprint emperor Lethrinus harak. Little research has been done on L. harak diversity in the Pacific and Indian Oceans. This study aimed to evaluate the morphometric and genetic characters of the thumbprint emperor, L. harak (Forsskål, 1775) in the Pacific and Indian Oceans. Methods: This research was conducted in the Marine Biology Laboratory, Faculty of Marine Science and Fisheries, Hasanuddin University, and Division of Fisheries Science, University of Miyazaki. Morphometric character measurements were based on holotype character data, while genetic analysis was performed on cytochrome oxidase subunit I (COI) sequence data. Morphometric data were analysed using principal component analysis (PCA) statistical tests in MINITAB, and genetic data were analysed in MEGA 6. Results: Statistical test results based on morphometric characters revealed groupings largely representative of the Indian and Pacific Oceans. The Seychelles was separated from other Indian Ocean sites and Australian populations were closer to the Pacific than the Indian Ocean group. The genetic distance between the groups was in the low category (0.000 - 0.042). The phylogenetic topology reconstruction accorded well with the morphometric character analysis, with two main L. harak clades representing Indian and Pacific Ocean, and Australia in the Pacific Ocean clade. Conclusions: These results indicate that the morphological character size of L. harak from Makassar and the holotype from Saudi Arabia have changed. Genetic distance and phylogeny reconstruction are closely related to low genetic distance.

On the influence of the Norwegian-Greenland and Weddell seas upon the bottom waters of the Indian and Pacific oceans

Background: The Lethrinidae (emperors) include many important food fish species. Accurate determination of species and stocks is important for fisheries management. The taxonomy of the genus Lethrinus is problematic, for example with regards to the identification of the thumbprint emperor Lethrinus harak. Little research has been done on L. harak diversity in the Pacific and Indian Oceans. This study aimed to evaluate the morphometric and genetic characters of the thumbprint emperor, L. harak (Forsskål, 1775) in the Pacific and Indian Oceans. Methods: This research was conducted in the Marine Biology Laboratory, Faculty of Marine Science and Fisheries, Hasanuddin University, and Division of Fisheries Science, University of Miyazaki. Morphometric character measurements were based on holotype character data, while genetic analysis was performed on cytochrome oxidase subunit I (COI) sequence data. Morphometric data were analysed using principal component analysis (PCA) statistical tests in MINITAB, and genetic data were analysed in MEGA 6. Results: Statistical test results based on morphometric characters revealed groupings largely representative of the Indian and Pacific Oceans. The Seychelles was separated from other Indian Ocean sites and Australian populations were closer to the Pacific than the Indian Ocean group. The genetic distance between the groups was in the low category (0.000 - 0.042). The phylogenetic topology reconstruction accorded well with the morphometric character analysis, with two main L. harak clades representing Indian and Pacific Ocean, and Australia in the Pacific Ocean clade. Conclusions: These results indicate that the morphological character size of L. harak from Makassar and the holotype from Saudi Arabia have changed. Genetic distance and phylogeny reconstruction are closely related to low genetic distance.

Background: The Lethrinidae (emperors) include many important food fish species. Accurate determination of species and stocks is important for fisheries management. The taxonomy of the genus Lethrinus is problematic, for example with regards to the identification of the thumbprint emperor Lethrinus harak. Little research has been done on L. harak diversity in the Pacific and Indian Oceans. This study aimed to evaluate the morphometric and genetic characters of the thumbprint emperor, L. harak (Forsskål, 1775) in the Pacific and Indian Oceans. Methods: This research was conducted in the Marine Biology Laboratory, Faculty of Marine Science and Fisheries, Hasanuddin University, and Division of Fisheries Science, University of Miyazaki. Morphometric character measurements were based on holotype character data, while genetic analysis was performed on cytochrome oxidase subunit I (COI) sequence data. Morphometric data were analysed using principal component analysis (PCA) statistical tests in MINITAB, and genetic data were analysed in MEGA 6. Results: Statistical test results based on morphometric characters revealed groupings largely representative of the Indian and Pacific Oceans. The Seychelles was separated from other Indian Ocean sites and Australian populations were closer to the Pacific than the Indian Ocean group. The genetic distance between the groups was in the low category (0.000 - 0.042). The phylogenetic topology reconstruction accorded well with the morphometric character analysis, with two main L. harak clades representing Indian and Pacific Ocean, and Australia in the Pacific Ocean clade. Conclusions: These results indicate that geographical and environmental factors can affect the morphometric and genetic characteristics of L. harak.

The semidiurnal tides of the Pacific and Indian Oceans penetrate deeply into the Southeast Asian waters. The tides of the Pacific Ocean govern the whole of the China Sea, the Philippines waters and the Sulawesi Sea while the tides of the Indian Ocean govern the Timor Sea, the Banda Sea, the Andaman Sea and the Malacca Strait. The Maluku Sea, the Makassar Strait and the Java Sea are the boundary region between tides from the Indian and Pacific Oceans. In the Java Sea the semidiurnal tide is produced mainly by the tide from the Indian Ocean. At the boundary region, the amplitudes are generally very small. As an example of a boundary region, the tides of the Sunda Strait are considered in some detail. An analytical solution of two overlapping standing waves, one wave resulting from open mouth reflection of a wave incident from the Indian Ocean and the other standing wave from open mouth reflection of a wave incident from the Java Sea, adequately describe the M2 tide in the Sunda Strait.

The semidiurnal tides of the Pacific and Indian Oceans penetrate deeply into the Southeast Asian waters. The tides of the Pacific Ocean govern the whole of the China Sea, the Philippines waters and the Sulawesi Sea while the tides of the Indian Ocean govern the Timor Sea, the Banda Sea, the Andaman Sea and the Malacca Strait. The Maluku Sea, the Makassar Strait and the Java Sea are the boundary region between tides from the Indian and Pacific Oceans. In the Java Sea the semidiurnal tide is produced mainly by the tide from the Indian Ocean. At the boundary region, the amplitudes are generally very small. As an example of a boundary region, the tides of the Sunda Strait are considered in some detail. An analytical solution of two overlapping standing waves, one wave resulting from open mouth reflection of a wave incident from the Indian Ocean and the other standing wave from open mouth reflection of a wave incident from the Java Sea, adequately describe the M2 tide in the Sunda Strait.

In the last decade, a great deal of attention has been paid to the irregular interannual oscillation, known to the acronym writers as ENSO, or El Niño–Southern Oscillation. Algorithms have been developed which model the interaction between the ocean and the atmosphere, and because of the dependency of such modelling on the state of the oceans, various attempts have been made to predict the sea‐surface temperature (SST) anomalies and, further, to understand the relationship between the oceans and their role in the global propagation of the ENSO signal. To this end, a statistical study, using singular value decomposition (SVD), has been made of the relationship between the SSTs of the Pacific and Indian Oceans in the last 4 decades and, in particular, the changes which have taken place, especially in the Indian Ocean. The point of using SVD is that it enables the user to compare the Pacific and Indian Oceans as two separate entities with different dimensions, not one as an adjunct of the other. For the purpose of this analysis, it is assumed that the two oceans are distinct and have separate characteristics. A simple EOF analysis treating the two oceans as one tropical system, for example, would not accomplish this objective. While SVD analyses in meteorology and climatology have mainly been applied to two different meteorological parameters, for example SST and sea level pressure, in the same area, there is no valid reason why SVD should not be applied to the same (or different) parameter(s) in different regions. Although the Indian and Pacific Oceans are of different dimensions, SVD does not weight the result in favour of either the smaller or the larger of the two. SVD is a statistical tool which gives results comparable with canonical correlation analysis, though several authors warn against its indiscriminate use. It is found that the Indian Ocean SSTs have a strong association with Pacific Ocean SSTs, particularly when the Indian Ocean lags the Pacific Ocean by one season in mid‐summer. It is also found that there is a distinct change in the SST patterns in the equatorial Indian Ocean in the second half (1977–1996) of the period under study. Copyright © 2001 Royal Meteorological Society

The Malacca Strait permits salt exchange between the western Pacific Ocean and the Andaman Sea in the northern Indian Ocean. Here, we show a joint inter-basin mechanism that modulates the freshwater exchange through the Malacca Strait using reanalysis and remote sensing datasets. The salinity variation within the Malacca Strait and the southern Andaman Sea is related to both the volume transport and the properties of the source water to the Malacca Strait that all experience interannual variability due to the climate modes from the Indian and Pacific Oceans. On interannual time scales, the Indian Ocean Dipole (IOD)-related anomalous wind pattern prevails in the boreal summer and autumn, acting to modulate the seasonal volume transport of the Malacca Strait such that there is a strengthened (weakened) transport in boreal summer-autumn during positive (negative) IOD events. An atmospheric moisture budget analysis shows that the moisture divergence term governs the source water through the Malacca Strait, with a saltier (fresher) transport during El Niño (La Niña). Taken together, the joint modulation reveals separate contributions from the Pacific and Indian Oceans through interbasin dynamics in governing salinity transport on interannual time scales, suggesting substantial impacts on water properties and exchange through the Malacca Strait.

Hybrid zones are natural laboratories for investigating the dynamics of gene flow, reproductive isolation, and speciation. A predominant marine hybrid (or suture) zone encompasses Christmas Island (CHR) and Cocos (Keeling) Islands (CKE), where 15 different instances of interbreeding between closely related species from Indian and Pacific Oceans have been documented. Here, we report a case of hybridization between genetically differentiated Pacific and Indian Ocean lineages of the three‐spot dascyllus, Dascyllus trimaculatus (Rüppell, 1829). Field observations indicate there are subtle color differences between Pacific and Indian Ocean lineages. Most importantly, population densities of color morphs and genetic analyses (mitochondrial DNA and SNPs obtained via RADSeq) suggest that the pattern of hybridization within the suture zone is not homogeneous. At CHR, both color morphs were present, mitochondrial haplotypes of both lineages were observed, and SNP analyses revealed both pure and hybrid genotypes. Meanwhile, in CKE, the Indian Ocean color morphs were prevalent, only Indian Ocean mitochondrial haplotypes were observed, and SNP analysis showed hybrid individuals with a large proportion (~80%) of their genotypes assigning to the Indian Ocean lineage. We conclude that CHR populations are currently receiving an influx of individuals from both ocean basins, with a greater influence from the Pacific Ocean. In contrast, geographically isolated CKE populations appear to be self‐recruiting and with more influx of individuals from the Indian Ocean. Our research highlights how patterns of hybridization can be different at scales of hundreds of kilometers, due to geographic isolation and the history of interbreeding between lineages.

The present study investigated the phylogeography of the intertidal barnacle Tetraclita in the Gulf of Thailand ecoregion (Sunda Shelf Province in the Pacific) and the Andaman Sea Coral Coast ecoregion (Andaman Province in the Indian Ocean) in Thailand’s waters. Tetraclita species were identified by a combined morphological and molecular approach using mitochondrial gene fragments (CO1 and 12S rRNA). Tetraclita singaporensis is a major occupiers on the Andaman coast but is sparse in the western Gulf of Thailand. Tetraclita squamosa inhabits almost all of our collection sites in the Gulf of Thailand but has a very low abundance in the Andaman Sea. Tetraclita kuroshioensis has two genetically distinct populations, one in the Andaman Sea and the other in the West Pacific region. S-DIVA analysis showed that the most recent common ancestor (MRCA) of T. kuroshioensis was distributed in both the Andaman Sea and West Pacific region, with a relative probability of 63%; the analysis further identified two molecular subclades, one on each side of the Sunda Shelf by vicariance about 0.53 million years ago, far before the Last Glacial Maximum (LGM). The MRCA of T. squamosa was based in the West Pacific region (relative probability: 90%), and dispersed into the Andaman Sea after the LGM. The MRCA of T. singaporensis was in the Andaman Sea (relative probability: 89.5%) and dispersed into the Gulf of Thailand via monsoonal currents through the Malacca Strait after the LGM. Presently, T. singaporensis is absent from the West Pacific region, further supporting its origin in the Andaman Sea. The distribution of intertidal barnacles in the Sunda Shelf and Andaman provinces is a result of the interplay between geological events and present day oceanographic currents.