This study attempted to compare the performance of local polynomial interpolation, inverse distance weighted interpolation, and ordinary kriging in studying distribution patterns of swimming crabs. Cross-validation was used to select the optimum method to get distribution results, and kriging was used for making spatial variability analysis. Data were collected from 87 sampling stations in November of 2015 (autumn) and February (winter), May (spring) and August (summer) of 2016. Results indicate that swimming crabs widely distributed in autumn and summer: in the summer, they were more spatially independent, and resources in each sampling station varied a lot; in the winter and spring, the abundance of crabs was much lower, but the individual crab size was bigger, and they showed the patchy and more concentrative distribution pattern, which means they were more spatially dependent. Distribution patterns were in accordance with ecological migration features of swimming crabs, which were affected by the changing marine environment. This study could infer that it is applicable to study crab fishery or even other crustacean species using geostatistical analysis. It not only helps practitioners have a better understanding of how swimming crabs migrate from season to season, but also assists researchers in carrying out a more comprehensive assessment of the fishery. Therefore, it may facilitate advancing the implementation in the pilot quota management program of swimming crabs in northern Zhejiang fishing grounds.

Hepcidins are small cysteine-rich antimicrobial peptides that play a vital role in immunity against pathogen invasion. Here, a hepcidin (Cshep) from Centropristis striata was described, which is considered as a valuable aquaculture marine species in China. The open reading frame consisted of 273 bp. Eight conserved cysteine residues were identified. Phylogenetic analysis showed that Cshep had a relatively close relationship with the hepcidin from Epinephelus moara. Quantitative real-time PCR analysis demonstrated that Cshep was highly expressed in liver and significantly up-regulated when challenged with Vibrio harveyi. In addition, the synthetic Cshep peptide had a high antimicrobial activity against V. harveyi, but low against other pathogenic bacteria tested in this study. The killing kinetics analysis revealed that Cshep had a fast bactericidal effect on V. harveyi. These results suggested that Cshep may be involved in the immune response of C. striata against V. harveyi infection.

Larimichthys crocea is a marine fish species cultured in China. Short-term starvation is often applied to improve the quality of cultured L. crocea, and the expression of ghrelin in tissues of stomach, muscle, brain, intestines, liver, and kidney, involved in starvation response, under starvation conditions were studied to understand the effect of starvation on the expression of ghrelin in L. crocea juveniles. The ghrelin expression was tissue-specific, and expression was significantly higher in the stomach compared to other tissues (P<0.01). Additionally, ghrelin expression in different tissues changed along with prolongation of fasting. In the stomach, ghrelin expression levels increased gradually at the beginning of the fast, and then declined after eight days of fasting. Gene expression in the brain and intestines increased at the beginning of the fast, and then decreased with longer fasting time. Interestingly, ghrelin expression declined at the beginning of the fast, then increased with longer fasting in the kidneys and muscles. These results suggest that ghrelin is involved in starvation response in L. crocea juveniles. This study provids insights into ghrelin function and an important reference for the development of reasonable feeding strategies for L. crocea juveniles.

Chinese black sleeper (Bostrychus sinensis) is a fish that lives both in seawater and freshwater, feeds on crustaceans, aquatic insects and occasionally shellfish. The existence of digestive enzyme in viscera to act on chitinous exoskeleton of the prey is of interest. In this study, a chitinase was purified to homogeneity using ammonium sulfate precipitation, DEAE-Sephacel ion exchange, Sephacryl S-200 HR and Superdex 200 gel filtration columns. The purified protein presents a molecular mass of 58 kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and results in a single band on native PAGE. According to peptide mass fingerprinting, two peptides containing a total of 20 amino acid residues, were 95% identical to a chitinase from yellow perch (Perca flavescens) and 100% identical to the chitinase from greater amberjack (Seriola dumerili). The purified chitinase showed optimum activity at pH 6.0, and was stable at acidic conditions and temperature below 55°C. The enzymatic activity was quite stable in the presence of NaCl, even at 1 mol/L . The chitinase was capable of degrading chitosan into low molecular mass chitooligosaccharides (COS) with sizes in a range of 200–700 Da, and the circular dichroism profile of the COS greatly differed from native chitosan. Full-length cDNA encoding the present chitinase was cloned and the transcript levels of chitinase in various tissues were determined by quantitative real-time PCR. The results showed that the transcript level of chitinase was highest in esophagus and hepatopancreas.

The methane bubble plume attracts interest because it offers direct evidence of seafloor gas leakage and plays an indirect role in the exploration and identification of natural gas hydrate. In this study, based on established plume models and their migration sections, three amplitude-class attributes were extracted from three formations for the migration sections of five plumes, and the correlation between the gas content and seismic attribute was obtained. As the gas content increases, the amplitude attribute correspondingly increases, and the linear correlation is relatively good. Moreover, correlation coefficients between gas content and amplitude attributes are close to 1.0. By using linear fitting, the relation model between the gas content of the plume and the seismic attribute was obtained. The relation model was subsequently used to invert the gas content from a real data-bearing plume. Comparison of the gas content section of the plume with the attribute section and real seismic section reveals common distribution characteristics, namely, the color of the section in the lower right corner is dark. If the amplitude value is large in the seismic section of the real plume, the amplitude attribute value is also large in the corresponding attribute section, and the inverted value of the gas content is also large (because gas content and amplitude are linearly correlated), which indicates that the plume bubbles of the section in the lower right corner is intensively distributed. Finally, the obtained gas content section of the plume can reflect the distribution of the plume bubble content more simply and intuitively, from which the distribution law of seafloor bubbles can be deduced, and this lays a foundation for the further estimation of the gas content of the plume and hydrate reserves.

Mesoscale eddies play an important role in modulating the ocean circulation. Many previous studies on the three-dimensional structure of mesoscale eddies were mainly based on composite analysis, and there are few targeted observations for individual eddies. A cyclonic eddy surveyed during an oceanographic cruise in the Northwest Pacific Ocean is investigated in this study. The three-dimensional structure of this cyclonic eddy is revealed by observations and simulated by the four-dimensional variational data assimilation (4DVAR) system combined with the Regional Ocean Modeling System. The observation and assimilation results together present the characteristics of the cyclonic eddy. The cold eddy has an obvious dual-core structure of temperature anomaly. One core is at 50–150 m and another is at 300–550 m, which both have the average temperature anomaly of approximately −3.5°C. The salinity anomaly core is between 250 m and 500 m, which is approximately −0.3. The horizontal velocity structure is axis-asymmetric and it is enhanced on the eastern side of the cold eddy. In the assimilation experiment, sea level anomaly, sea surface temperature, and in situ measurements are assimilated into the system, and the results of assimilation are close to the observations. Based on the high-resolution assimilation output results, the study also diagnoses the vertical velocity in the mesoscale eddy, which reaches the maximum of approximately 10 m/d. The larger vertical velocity is found to be distributed in the range of 0.5 to 1 time of the normalized radius of the eddy. The validation of the simulation result shows that the 4DVAR method is effective to reconstruct the three-dimensional structure of mesoscale eddy and the research is an application to study the mesoscale eddy in the Northwest Pacific by combining observation and assimilation methods.

The orthogonal supersegment of the ultraslow-spreading Southwest Indian Ridge at 16°–25°E is characterized by significant along-axis variations of mantle potential temperature. A detailed analysis of multibeam bathymetry, gravity, and magnetic data were performed to investigate its variations in magma supply and crustal accretion process. The results revealed distinct across-axis variations of magma supply. Specifically, the regionally averaged crustal thickness reduced systematically from around 7 Ma to the present, indicating a regionally decreasing magma supply. The crustal structure is asymmetric in regional scale between the conjugate ridge flanks, with the faster-spreading southern flank showing thinner crust and greater degree of tectonic extension. Geodynamic models of mantle melting suggested that the observed variations in axial crustal thickness and major element geochemistry can be adequately explained by an eastward decrease in mantle potential temperature of about 40°C beneath the ridge axis. In this work, a synthesized model was proposed to explain the axial variations of magma supply and ridge segmentation stabilities. The existence of large ridge-axis offsets may play important roles in controlling melt supply. Several large ridge-axis offsets in the eastern section (21°–25°E) caused sustained along-axis focusing of magma supply at the centers of eastern ridge segments, enabling quasi-stable segmentation. In contrast, the western section (16°–21°E), which lacks large ridge-axis offsets, is associated with unstable segmentation patterns.

An internal gravity wave model was employed to simulate the generation of internal solitary waves (ISWs) over a sill by tidal flows. A westward shoaling pycnocline parameterization scheme derived from a three-parameter model was adopted, and then 14 numerical experiments were designed to investigate the influence of the pycnocline thickness, density difference across the pycnocline, westward shoaling isopycnal slope angle and pycnocline depth on the ISWs. When the pycnocline thickness on both sides of the sill increases, the total barotropic kinetic energy, total baroclinic energy and ratio of baroclinic kinetic energy (KE) to available potential energy (APE) decrease, whilst the depth of isopycnal undergoing maximum displacement and ratio of baroclinic energy to barotropic energy increase. When the density difference on both sides of the sill decreases synchronously, the total barotropic kinetic energy, ratio of baroclinic energy to barotropic energy and total baroclinic energy decrease, whilst the depth of isopycnal undergoing maximum displacement increases. When the westward shoaling isopycnal slope angle increases, the total baroclinic energy increases whilst the depth of turning point almost remains unchanged. When the depth of westward shoaling pycnocline on both sides of the sill reduces, the ratio of baroclinic energy to barotropic energy and total baroclinic energy decrease, whilst the total barotropic kinetic energy and ratio of KE to APE increase. When one of the above four different influencing factors was increased by 10% while the other factors keep unchanged, the amplitude of the leading soliton in ISW Packet A was decreased by 2.80%, 7.47%, 3.21% and 6.42% respectively. The density difference across the pycnocline and the pycnocline depth are the two most important factors in affecting the characteristics and energetics of ISWs.

The El Niño-Southern Oscillation (ENSO) has great impacts on the Indian Ocean sea surface temperature (SST). In fact, two major modes of the Indian Ocean SST namely the Indian Ocean Basin (IOB) and the Indian Ocean Dipole (IOD) modes, exerting strong influences on the Indian Ocean rim countries, are both influenced by the ENSO. Based on a combined linear regression method, this study quantifies the ENSO impacts on the IOB and the IOD during ENSO concurrent, developing, and decaying stages. After removing the ENSO impacts, the spring peak of the IOB disappears along with significant decrease in number of events, while the number of events is only slightly reduced and the autumn peak remains for the IOD. By isolating the ENSO impacts during each stage, this study reveals that the leading impacts of ENSO contribute to the IOD development, while the delayed impacts facilitate the IOD phase switch and prompt the IOB development. Besides, the decadal variations of ENSO impacts are various during each stage and over different regions. These imply that merely removing the concurrent ENSO impacts would not be sufficient to investigate intrinsic climate variability of the Indian Ocean, and the present method may be useful to study climate variabilities independent of ENSO.