Based on a coupled ocean-sea ice model, this study investigates how changes in the mean state of the atmosphere in different CO₂ emission scenarios (RCP 8.5, 6.0, 4.5 and 2.6) may affect the sea ice in the Bohai Sea, China, especially in the Liaodong Bay, the largest bay in the Bohai Sea. In the RCP 8.5 scenario, an abrupt change of the atmospheric state happens around 2070. Due to the abrupt change, wintertime sea ice of the Liaodong Bay can be divided into 3 periods: a mild decreasing period (2021–2060), in which the sea ice severity weakens at a near-constant rate; a rapid decreasing period (2061–2080), in which the sea ice severity drops dramatically; and a stabilized period (2081–2100). During 2021–2060, the dates of first ice are approximately unchanged, suggesting that the onset of sea ice is probably determined by a cold-air event and is not sensitive to the mean state of the atmosphere. The mean and maximum sea ice thickness in the Liaodong Bay is relatively stable before 2060, and then drops rapidly in the following decade. Different from the RCP 8.5 scenario, atmospheric state changes smoothly in the RCP 6.0, 4.5 and 2.6 scenarios. In the RCP 6.0 scenario, the sea ice severity in the Bohai Sea weakens with time to the end of the twenty-first century. In the RCP 4.5 scenario, the sea ice severity weakens with time until reaching a stable state around the 2070s. In the RCP 2.6 scenario, the sea ice severity weakens until the 2040s, stabilizes from then, and starts intensifying after the 2080s. The sea ice condition in the other bays of the Bohai Sea is also discussed under the four CO₂ emissions scenarios. Among atmospheric factors, air temperature is the leading one for the decline of the sea ice extent. Specific humidity also plays an important role in the four scenarios. The surface downward shortwave/longwave radiation and meridional wind only matter in certain scenarios, while effects from the zonal wind and precipitation are negligible.

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 waters near the Antarctic Peninsula have always been a study hot spot because of their variable and unique oceanographic conditions. To determine the distribution and possible influencing factors on phytoplankton size and abundance near the Antarctic Peninsula, a large-scale survey was conducted during the austral summer of 2018. Samples were collected in 27 stations located in the Drake Passage (DP), South Shetland Islands (SSI), and South Orkney Islands (SOI). Phytoplankton communities were described using chlorophyll a (Chl a), flow cytometry and light microscopy to cover a size range from pico- to microphytoplankton. Nanophytoplankton, especially small nanophytoplankton (2−6 μm) with abundance ranging from 0.66 ×10³ cells/mL to 8.46 ×10³ cells/mL, was predominant throughout the study area. Among different regions, there was an obvious size shift. The proportion of picophytoplankton near the Elephant Island (EI) and DP was higher than other regions, and larger cells were found mainly in east of SOI. The distribution of phytoplankton abundance detected by flow cytometry was not completely consistent with Chl a concentrations due to the contribution of larger cells to Chl a. Possible influencing factors on the phytoplankton size distribution were discussed. The properties of water masses such as temperature and salinity can influence the phytoplankton size distribution. Correlation analysis revealed that only picophytoplankton is significantly correlated with salinity. Light and Fe availability might affect phytoplankton abundance and size distribution especially near the waters of SSI and EI in this study. It was also speculated that the abundance of cryptophytes is possibly related to ice melting.

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.

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.

Phytoplankton communities can response immediately and directly to environmental changes, and thus have been applied as reliable biotic indicators in aquatic systems. This study provided insights into the relationships concerning ecological thresholds of phytoplankton communities and individual taxon in response to environmental changes in coastal waters of northern Zhejiang Province, East China Sea. Results demonstrated that there existed seasonal variations of phytoplankton community ecological thresholds of which spring being higher than those in summer. As for individual species, Prorocentrum donghaiense and Noctiluca scintillans were identified as the most tolerant and sensitive indicator species in spring and summer, respectively. They exhibited strong indications in response to environmental changes. These findings highlighted that phytoplankton community structure in this region was stable when environmental gradients were below the thresholds of sensitive species, whereas potential harmful algal blooms may occur when environmental gradients exceeded the thresholds of tolerant species.

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.

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.

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.