The morphology of seven specimens of Chrysaora chinensis (Scyphomedusae, Semaestomae) obtained from four sites off the coast of Peninsular Malaysia was examined. Morphological characteristics of C. chinensis that encompasses structures such as the bell, tentacles, oral arms, stomach, manubrium, radial canals and gonads were described in detail. A total of 107 specimens that represented C. chinensis populations of four coastal areas of Peninsular Malaysia (East-Central, East-North, West-Central, and West-North) were also analysed for shape variation using geometric morphometric analysis. Procrustes superimposition, Principal Component Analysis (PCA) and Canonical Variate Analysis (CVA) were applied to the images of gastrovascular pouches of C. chinensis to extract the shape information. Independent contrasts were used for comparisons between shapes. There were no significant differences in shape variation between all the specimens based on the PCA results. However, CVA results showed shape variations between specimens taken from the four areas of Peninsular Malaysia, especially with higher magnitudes of Mahalanobis distances between the east and west coast areas, including between East-Central and East-North, but lower magnitudes were detected between the West-Central and West-North.

Generally one dimensional (1-D) empirical salinity intrusion model is limited to natural alluvial estuary. However, this study attempts to investigate its ability to model a sheltered alluvial estuary of the Terengganu River in Malaysia. The constructed breakwater at the mouth of the river shelters the estuary from direct influence of the open sea. The salinity density along the estuary was collected during the wet and dry seasons for scenarios before and after the constructed breakwater. Moreover, the freshwater discharges, tidal elevations and bathymetry data were also measured as model inputs. A good fit was demonstrated between simulated and observed variables, namely salinity distribution and intrusion length for both scenarios. Thus, the results show that 1-D empirical salinity model can be utilized for sheltered estuarine condition at the Terengganu Estuary, but with an appropriate determination of an initial point. Furthermore, it was observed that the salinity intrusion in the study area is largely dependent on the freshwater discharge rather than tidal elevation fluctuations. The scale of the salinity intrusion length in the study area is proportional to the river discharge of the -1/2 power. It was appeared that the two lines of the 1-D empirical salinity model and discharge power based equation fitted well to each other, with the average predicted minimum freshwater discharge of 150 m³/s is going to be required to maintain acceptable salinity levels during high water slack (HWS) near the water intake station, which is located at 10.63 km from river mouth.

The effects of tidal currents (i.e., barotropic and internal tides) are important in the biogeochemistry of a coastal shelf sea. The high-frequency of currents and near-bottom temperatures collected in three consecutive southwest monsoon seasons (May, June, July and August of 2013 until 2015) is presented to reveal the role of the tidal currents to the temperature variability in the coastal shelf sea of the east coast of Peninsular Malaysia (ECPM), south of the South China Sea (SCS). The results of a spectral density and harmonic analysis demonstrate that the near-bottom temperature variability and the tidal currents are influenced by diurnal (O₁ and K₁) and semidiurnal (M₂) tidal currents. The spectral density of residual currents (detided data) at 5, 10 and 16 m depth also shows significant peaks at the diurnal tidal frequency (K₁) and small peaks at the semidiurnal tidal frequency (M₂) indicating the existence of internal tides. The result of the horizontal kinetic energy (HKE) shows a strong intermittent energy of internal tides in the ECPM with the strongest energy is found at 16 m depth during a sporadic cooling event in June and July. A high horizontal cross-shore heat flux (16 m) also indicates strong intrusions of cooler water into the ECPM in June and July. During the short duration of cold pulse water observed in June and July, a cross-wavelet analysis also reveals the strong relationship between the near-bottom temperatures and the internal tidal currents at the diurnal tidal frequency. The intrusion of this cooler water is probably related to the monsoon-induced upwelling in June. It is loosely interpreted that the interaction between the strong barotropic tides and the steep slope in the central basin of the SCS under the stratified condition in southwest monsoon has generated these internal tides. The dissipation of internal tides from the slope area probably has driven the cold-upwelled water into the ECPM coastal shelf sea when the upwelling intensity is the highest in June and July.

The El Niño Southern Oscillation (ENSO) is a natural phenomenon that relates to the fluctuation of temperatures over the Pacific Ocean. The ENSO significantly affects the ocean dynamics including upwelling event and coastal front. A recent study discovered the seasonal upwelling in the east coast of Peninsular Malaysia (ECPM), which is significant to the fishery industry in this region. Thus, it is vital to have a better understanding of the influence of ENSO towards the coastal upwelling and thermal front in the ECPM. The sea surface temperature (SST) data achieved from moderate resolution imaging spectroradiometer (MODIS) aboard Aqua satellite are used in this study to observe the SST changes from 2005 to 2015. However, due to cloud cover issue, a reconstruction of data set is applied to MODIS data using the data interpolating empirical orthogonal function (DINEOF) to fill in the missing gap in the dataset based on spatial and temporal available data. Besides, a wavelet transformation analysis is done to determine the temperature fluctuation throughout the time series. The DINEOF results show the coastal upwelling in the ECPM develops in July and reaches its peak in August with a clear cold water patch off the coast. There is also a significant change of SST distribution during the El Niño years which weaken the coastal upwelling event along the ECPM. The wavelet transformation analysis shows the highest temperature fluctuation is in 2009-2010 which indicates the strongest El Niño throughout the time period. It is suggested that the El Niño is favourable for the stratification in water column thus it is weakening the upwelling and thermal frontal zone formation in ECPM waters.

The population parameters of blood cockles, Tegillarca granosa in the intertidal zone of Marudu Bay, Sabah, Malaysia were investigated based on monthly length-weight frequency data (July 2017 to June 2018). A total of 279 cockle individuals with shell length and weight ranging from 27.7 mm to 82.2 mm and 13.11 g to 192.7 g were subjected to analysis. T. granosa in Marudu Bay showed a consistent moderately high condition index 4.98±0.86 throughout the year. The exponent b of the length-weight relationship was 2.6 demonstrating negative allometric growth. The estimated asymptotic length (L_∞), growth coefficient (K) and growth performance (ϕ) of the T. granosa population in Marudu Bay were estimated at 86.68 mm, 0.98 a^–1 and 3.87, respectively. The observed maximum shell length was 82.55 mm and the predicted maximum shell length was 84.44 mm with estimated maximum life span (t_max) of 3.06 years. The estimated mean lengths at the end of 2, 4, 6, 8, 10 and 12 months of age were 21.31 mm, 31.16 mm, 39.53 mm, 46.63 mm, 52.67 mm and 57.79 mm. Total, natural, and fishing mortalities were estimated at 2.39 a^–1, 1.32 a^–1 and 1.07 a^–1. The exploitation level (E) was 0.45. Results of the current study also demonstrated that T. granosa in the Marudu Bay has two major recruitment peaks; one in March and another in October. The exploitation level revealed that natural stock of T. granosa in the Marudu Bay was approaching the maximum exploitation level. If such trend continues or demand for T. granosa is increasing, coupled with no effective fisheries management in place, possibility of the T. granosa population in the Marudu Bay to collapse is likely to elevate.

Assessments of phytoplankton diversity in Sabah waters, North Borneo, have primarily relied on morphology-based identification, which has inherent biases and can be time-consuming. Next-Generation Sequencing (NGS) technology has been shown to be capable of overcoming several limitations of morphology-based methods. Samples were collected from the Sepanggar Bay over the course of the year 2018 in different monsoon seasons. Morphology-based identification and NGS sequencing of the V8–V9 region of the 18S LSU rDNA were used to investigate the diversity of the phytoplankton community. Microscopy and NGS showed complementary results with more diatom taxa detected by microscopy whereas NGS detected smaller and rarer taxa. The harmful algal genera in the study site comprised of Skeletonema, Margalefidinium, Pyrodinium, Takayama, and Alexandrium as detected by NGS. This study showed that that an integrative approach of both morphological and molecular techniques could provide more comprehensive information about the phytoplankton community as the approach captured quantitative variability as well as the diversity of phytoplankton species.

The southwest Lahad Datu felsic rocks were previously thought to have formed in the late Triassic as part of the microcontinental crystalline basement. Based on U-Pb ages, geochemistry, and the Hf isotopes of zircon from the southeastern Sabah gabbro and granite, in this study, the tectonic properties of the Sabah area during the Triassic were investigated. The weighted average U-Pb zircon ages of the gabbro and granite samples were determined to be (230.9 ± 2.5)Ma and (207.1 ± 3.3)Ma, respectively. The granite had SiO₂ contents of 66.54%–79.47%, low TiO₂ contents of 0.08%–0.3%, Al₂O₃ contents of 10.97%–16.22%, Na₂O contents of 5.91%–6.39%, and low K₂O contents of 0.15%–0.65%. The chondrite-normalized rare earth element (REE) patterns exhibit light REE enrichment, with right-sloping curves. The primitive mantle-normalized trace element spider diagrams exhibit Th, U, La, Sr, and Zr enrichment and Nb, Ta, P and Ti depletions, i.e., the geochemical characteristics of typical island arc igneous rocks. The tectonic discriminant diagram indicates that the granite is a volcanic arc granite. The Hf isotopic analysis of gabbro zircon revealed that the zircons have ε_Hf(t) values of 12.08–16.24 (mean of 14.32) and two-stage model ages (t_DM2) of 223–491 Ma (mean of 347 Ma). This indicates that the diagenetic magma of the gabbro was mainly derived from melting of newly formed crustal materials. The ophiolite in southeast Sabah has existed since the early Late Triassic. The crystalline basement granite in southeastern Sabah was emplaced lasted from late Triassic to early Cretaceous. Based on previous studies and global plate reconstruction models, it is speculated that the southeastern Sabah granite may have been formed in an island arc setting, i.e., where the oceanic crust of the Paleo-Tethys Ocean collided with the oceanic crust of the Panthalassa Ocean.

The clay minearals are composed of illite, chlorite, kaolinite, montmorillonite and mixed-layer minerals in the submarine sediments of the northern South China Sea. Three types of clay mineral zone can be recognized on the basis of the distributive regularity of clay minerals, submarine relief, hydrodynamic conditions and depositional characteristics in this region. Apart from the northern mainland source, kaolinites carried from the Philippines volcanic arc in the east and Malaysia in the south are also assumed to be one of the sources of the clay minerals in the deep sea. The increase of chlorites to the abyssal direction in the west of 116°E might be associated with the residual chlorites carried from the ancient Zhujiang River during the glacial period and the conversion of kaolinite into chlorite submarine volcanoes appear to be one of the sources of the increment of montmorillonite and chlorite around the Huangyan Island. From the distribution pattern of clay minerals in the whole area, it is known that the types of clay mineral assemblage in the study area are mainly controlled by climate and rock types of the source area.

Genetic diversity of two wild Penaeus monodon populations sampled from the coastal waters of Qinglan (Hainan Province of China, HN) and Malaysia (KD), and the F1 generation of a Thailand broodstock population (CP) were examined by vertical polyacrylamide gel electrophoresis. Of 21 loci encoded by ten enzymes, 11 were polymorphic. The mean proportions of polymorphic loci of HN, KD and CP were 36.36%, 45.45% and 50.00%, with the average heterozygosities of 0.135, 0.181 and 0.191, and the effective numbers of alleles per loci were 1.300, 1.330 and 1.329, respectively. The divergent indexes of HN, KD and CP were 0.023, 0.124, and 0.117, respectively. The genetic distance between the two wild populations was 0.005, and the gene differentiation coefficient was also very low (0.014). The results indicated that the F1 generation population had a higher genetic diversity than the two wild populations, and that the HN population had the lowest one. There was no significant differentiation between HN and KD populations and all populations existed with a slight heterozygote excess.

Pampus minor is an important commercial fish. Due to the similarity of external morphological characteristics among the genus Pampus species, P. minor has often been identified as the juvenile group of both P. cinereus and P. argenteus. While little genetic background on this species is known, this study was based on control region sequences and provided the first evaluation of the genetic signature of 264 individuals of P. minor from 11 populations along the coasts of China and Malaysia. The results indicate high genetic haplotype diversity and low nucleotide diversity in this species. Additionally, two differentiated haplotype lineages were identified in the P. minor populations. However, phylogenetic structures corresponding to the geographical locations were unable to be established. Analysis of molecular variance identified a vast majority of the genetic variation occurring within populations. F-statistic test value (F_ST) of pairwise indicated that great differences existed between the Chinese and Malaysian P. minor populations. For the Chinese populations, the genetic differences were insignificant with the exception of the Xiamen population, which is a marginal population. During the late Pleistocene, a population expansion of P. minor occurred. These expanded populations originated from the glacial refugium in the South China Sea and then rapidly occupied and adapted to their new habitat. The results of this study provide genetic information for ensuring the protection and management of P. minor resources.