Based on Bayesian network (BN) and information flow (IF), a new machine learning-based model named IFBN is put forward to interpolate missing time series of multiple ocean variables. An improved BN structural learning algorithm with IF is designed to mine causal relationships among ocean variables to build network structure. Nondirectional inference mechanism of BN is applied to achieve the synchronous interpolation of multiple missing time series. With the IFBN, all ocean variables are placed in a causal network visually, making full use of information about related variables to fill missing data. More importantly, the synchronous interpolation of multiple variables can avoid model retraining when interpolative objects change. Interpolation experiments show that IFBN has even better interpolation accuracy, effectiveness and stability than existing methods.

Quantifying the gross and net production is an essential component of carbon cycling and marine ecosystem studies. Triple oxygen isotope measurements and the O₂/Ar ratio are powerful indices in quantifying the gross primary production and net community production of the mixed layer zone, respectively. Although there is a substantial advantage in refining the gas exchange term and water column vertical mixing calibration, application of mixed layer depth history to the gas exchange term and its contribution to reducing indices error are unclear. Therefore, two cruises were conducted in the slope regions of the northern South China Sea in October 2014 (autumn) and June 2015 (spring). Discrete water samples at Station L07 in the upper 150 m depth were collected for the determination of δ¹⁷O, δ¹⁸O, and the O₂/Ar ratio of dissolved gases. Gross oxygen production (GOP) was estimated using the triple oxygen isotopes of the dissolved O₂, and net oxygen production (NOP) was calculated using O₂/Ar ratio and O₂ concentration. The vertical mixing effect in NOP was calibrated via a N₂O based approach. GOP for autumn and spring was (169±23) mmol/(m²·d) (by O₂) and (189±26) mmol/(m²·d) (by O₂), respectively. While NOP was 1.5 mmol/(m²·d) (by O₂) in autumn and 8.2 mmol/(m²·d) (by O₂) in spring. Application of mixed layer depth history in the gas flux parametrization reduced up to 9.5% error in the GOP and NOP estimations. A comparison with an independent O₂ budget calculation in the diel observation indicated a 26% overestimation in the current GOP, likely due to the vertical mixing effect. Both GOP and NOP in June were higher than those in October. Potential explanations for this include the occurrence of an eddy process in June, which may have exerted a submesoscale upwelling at the sampling station, and also the markedly higher terrestrial impact in June.

Metal-enriched minerals have been widely observed near hydrothermal vent fields. However, the dynamics of particulate metals influenced by hydrothermal activities is poorly constrained. Here, radioactive ²³⁴Th in both dissolved and particulate phases were used to examine the kinetics of particle-reactive metal adsorption, removal, and residence in a newly found hydrothermal plume over the Southwest Indian Ridge. The results showed a relatively low value on ²³⁴Th/²³⁸U ratios (i.e., 0.73–0.88) compared to the deep oceans, indicating an enhanced adsorption of particle-reactive metals onto particulate matter in the plume. Based on the ²³⁴Th-²³⁸U disequilibria, the adsorption and sinking rate constants of ²³⁴Th averaged (0.009±0.001) d^–1 and (0.113±0.024) d^–1 in the hydrothermal plume, corresponding to the residence times of (115±19) d and (16±5) d for dissolved and particulate ²³⁴Th, respectively. This timescale allows vent-discharged particle-reactive metals to disperse hundreds to thousands of miles away. Thus, hydrothermal activities might influence the metal distribution in deep ocean over a very large scope. Also, a high sinking flux of (36.2±5.4) Bq/(m²·d) for ²³⁴Th was observed for the plume, suggesting an enrichment of metal in particles deposited close to the vent. The enhancement of particle sinking could also benefit the transport of organic carbon and nitrogen and fuel the benthic ecosystems under the plume regimes. Thus, hydrothermal plumes may have an impact on both the elemental geochemistry and/or ecosystem to the deep oceans interior than previous expectation.

To characterize environmental factors controlling decadal-scale variations in the buried flux of marine organic carbon (${\rm{BF}}_{\rm{C_m}} $) in the eastern shelf sea areas of China (ECSS), four well preserved sediment cores collected from the central Yellow Sea mud (CYSM) area, the Yellow Sea Coastal Current (YSCC) area and the Changjiang River Estuary (CRE) were investigated in this study. In the CYSM, variations in ${\rm{BF}}_{\rm{C_m}} $ were found to be dependent on variations in primary productivity and to exhibit a cyclical trend possibly related to fluctuations in the Pacific Decadal Oscillation (PDO) and the East Asian winter monsoon index (EAWM). In the YSCC, ${\rm{BF}}_{\rm{C_m}} $ likewise depends on primary productivity. Prior to the 1950s, variations in ${\rm{BF}}_{\rm{C_m}} $ were similar to that of the EAWM. After the 1950s, ${\rm{BF}}_{\rm{C_m}} $ increased rapidly and exhibited maximum values in the surface layer, consistent with an increase in primary productivity caused by the input of terrestrial nutrients associated with China’s economic development. In the CRE, variations in ${\rm{BF}}_{\rm{C_m}} $ were affected by several competing factors making it difficult to identify clear relationships between variations in ${\rm{BF}}_{\rm{C_m}} $ and primary productivity. In contrast, long-term variability in ${\rm{BF}}_{\rm{C_m}} $ is more similar to changes in the Changjiang River sediment load. Thus, it is speculated that the construction of dams along the Changjiang River may be the main cause of variations in ${\rm{BF}}_{\rm{C_m}} $ in this area. Given the disproportionate effects of human activities on marine environments and decadal variations in ${\rm{BF}}_{\rm{C_m}} $ in the ECSS, careful attention should be paid to regional differences in organic carbon preservation and environmental changes lest estimates of these values be made imprecise or inaccurate.

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.

The stock enhancement programs for black sea bream Acanthopagrus schlegelii have been conducted in China for a few years. However, little information has been reported concerning the effectiveness and genetic effect of black sea bream stock enhancement. In order to detect the contribution of released individuals in Zhujiang River Estuary (ZRE) and Daya Bay (DB), six microsatellite markers were used to identify the hatchery-released individuals. In addition, this pedigree of hatchery populations (broodfish and hatchery-released offspring) was traced to detect the number of effective parents (N_e), the inbreeding coefficient and the decrease of genetic variability in the reproduction. The pedigree reconstruction showed that at least 69 (out of 93) broodfish had offspring. The estimated N_e was 54.8, consequently the inbreeding coefficient was 0.91%. The genetic diversity of hatchery-released offspring was lower than that in that of broodfish (heterozygosity alleles, 0.727–0.774), some alleles (number of alleles, 61–69) and genetic variance were lost during reproduction. It was observed that wild samples had higher levels of genetic diversity compared with hatchery populations as well as recaptured samples in releasing area. A total of 128 hatchery-released black sea bream were identified among 487 recaptured samples in ZRE, while a total of 15 samples were identified among 96 samples in DB. In summary, there was a high survival of released fish. Nevertheless, the results provided evidence to consider a loss of genetic variation in hatchery-released stock and a negative genetic effect of the stock enhancement.

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.

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.

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.

A laboratory-based microcosm experiment was carried out to examine both the behavioral and antioxidant response of the clam Gomphina veneriformis under the conditions of 3 types of burial material (sand, silt, silt-sand mixture) with 3 burial depths (5 cm, 15 cm, 30 cm). The concentration of dissolved oxygen decreased significantly after 3 d of burial in all experimental groups. In silt and sand-silt mixture groups, the interstitial water quality became worsened with lower pH, and higher $ {\rm {NH}}_4^+$-N concentration, where clam mortality occurred simultaneously. However, clam samples in all sand groups and 5 cm, 15 cm sand-silt mixture groups survived well for 8 d. Obviously fewer individuals left in the bottom sand in the 15 cm, 30 cm silt groups and 30 cm sand-silt mixture groups than in the 5 cm groups. Therefore, it suggests that adding silt and increasing burial depth could stimulate the vertical movement of organisms and cause lethal effects. It was found that the burial depth was the key factor that influenced the activities of antioxidant enzymes, such as superoxide dismutase (SOD) and catalase (CAT). The SOD and CAT activities in the gills and hepatopancreases of organisms both showed significant up-regulation in 30 cm burial depth after buried for 8 d. Higher enzyme activities were found in gills than in hepatopancreases, which indicated that the gills of the bivalve G. veneriformis were more susceptible to burial effects than hepatopancreases. Overall, this study shows that sediment burial could cause effects on the biological behavior and antioxidant enzyme activities.