Ocean Science Journal

The new puffer fish species Chelonodontops bengalensis (Pisces: Tetraodontidae) is described from two specimens collected on the southwest coast of the Bay of Bengal, Bangladesh. C. bengalensis is closely related to C. patoca (Hamilton, 1822), both species being large puffers with a peculiar, disc-shaped exposed nasal organ. The new species however differs from C. patoca with respect to dorsal rays (12 vs 10), anal rays (10 vs 8), pectoral rays (19 vs 15–16) and gill rakers (8 vs 7). C. bengalensis has spinules on its lateral sides but not on the caudal peduncle (vs. a patch of spinules on the back from behind the interorbital nearly to the dorsal fin and another on the throat and abdomen but absent on the lateral sides in C. patoca). Both the DNA barcode region of the mitochondrial COI gene and 16S rRNA gene region of C. bengalensis showed a clear monophyletic clade that distinguishes it as a separate species in the phylogenetic tree from other closely related puffer fish species. The COI barcode region shows a genetic divergence of 6 to 7.6% between C. bengalensis and C. patoca reported in GenBank from different parts of Asia.

We investigated the distributional pattern of mesozooplankton and the related environmental characteristics across the frontal zone in the South Sea of Korea during spring and autumn 2016. The frontal zone (FZ) was formed by Korean Southern Coastal Waters and Tsushima Warm Current, and the physical structure of front was more distinct during autumn than spring. The peaks of mesozooplankton abundance were not coincident (p > 0.05) with peaks of integrated chlorophyll-a (chl-a) concentrations (spring: chl-a = 44.5 mg m−2 at FZ, mesozooplankton = 8,198 inds.m−3 at coastal zone (CZ); autumn: chl-a=141.2 mg m−2 at CZ, mesozooplankton = 5,412 inds.m−3 at FZ). Cluster analysis divided the mesozooplankton community into FZ, CZ and offshore zone (OZ) mainly by the dominant copepods (adult and immature) during both seasons that was associated with chl-a based on principal component analysis. All the zones were characterized by temporal difference in occurrence of copepods, which can be explained by the cyclopoid-to-calanoid (Cy:Ca) ratio. Cy:Ca ratio was dependent mainly on the co-occurrence of higher concentrations of chl-a and cyclopoids at each zone between spring and autumn. Paracalanus copepodites dominated at all stations across the FZ during both periods. Cy:Ca ratio at FZ in spring showed a distinctively higher value than that of CZ and OZ, whereas the pattern was the opposite in autumn. These results indicated that the temporal distribution of mesozooplankton across the frontal zone in the South Sea was mainly characterized by the zonal characteristics of FZ, unlike CZ and OZ, and was the result of temporal differences in chl-a concentrations and the associated increase of cyclopoid copepods (Oithona spp.).

The objectives of this study were to distinguish fossil specimens of Meretrix (Bivalvia, Veneridae) using discriminant score and multivariate analysis, and to examine temporal changes in the geographical distributions of M. lusoria and M. petechialis in Japan and South Korea. Fossil shells of Meretrix were collected from Miyagi, Fukui, Aichi and Kumamoto in Japan, and Gimhae, Seosan, Siheung and Ganghwa-do in South Korea. The outside of the right valve was photographed with a digital camera, and ten characteristics of the shell morphology, such as shell height and shell length, were measured using image analysis software and a digital slide caliper. The discriminant score and multivariate analysis of the shell morphology identified all of the examined fossils as M. lusoria, while living individuals collected from the western coast of South Korea were identified as M. petechialis. These results suggest that the fossil shells excavated from the western coast of South Korea are a different species from the living individuals collected from the same areas. Radioactive carbon isotopic results revealed that the ages of the four fossil shells collected from tidal flats in Ganghwa-do ranged between 3,270 ± 30 and 1,830 ± 30 Cal BP. These results suggest that M. lusoria inhabited the western coast of South Korea until at least 2,000 years ago, but was replaced by M. petechialis during the last 2,000 years. Therefore, we propose that either M. petechialis spats were introduced artificially, or planktonic larvae migrated naturally from China to the western coast of South Korea during the last 2,000 years.

The variability in the tidal current in the Jeju Strait was investigated based on sea surface current fields observed by a high-frequency (HF) radar and vertical current profiles observed by three bottom-moored acoustic Doppler current profilers (ADCPs). The monthly M2 tidal current, the most dominant constituent in the study area, had significant temporal variability, and there were spatial changes in the temporal variation trend. While the semi-major axis of the M2 tidal current in winter was stronger than that in summer in some parts of the HF radar observation range, the summertime semi-major axis was stronger than that in wintertime in other parts of the observation range. Both opposite trend areas coexisted within the HF radar coverage area of several tens of kilometers. The vertical structure of the tidal currents in winter was similar to the theoretical structure in which Ekman dynamics was applied under depth-independent vertical eddy viscosity, and the year-to-year change was weak. In contrast, the vertical structure of the tidal currents in summer significantly varies over depth and years. Furthermore, the seasonal variation patterns at the three ADCP stations differed spatially. The temporal and spatial variability of tidal currents could be explained as a result of the strengthening stratification and, consequently, semidiurnal internal tides in summer. In summer, an internal tide with a wavelength of tens of kilometers could be generated in the vicinity of and propagate into the study area. The overlapping and offsetting of the barotropic and internal tidal components within the HF radar observation range caused complex spatial variations.

Argo drifters provide information of the vertical structure in the water column and have a potential for the improvement of understanding phytoplankton primary production and biogeochemical cycles in combination with ocean color satellite data, which can obtain the horizontal distribution of phytoplankton biomass in the surface layer. Our examples show that using Argo drifters with satellite-measured horizontal distribution of phytoplankton biomass at the sea surface allow an improved understanding of the development of the spring bloom. The other possible uses of Argo drifter are discussed.