As an economically important marine fish, the large yellow croaker Larimichthys crocea suffered from marine white spot disease caused by the ectoparasite Cryptocaryon irritans in recent years. This disease not only could result in physiological damage, but also lead to secondary bacterial invasion. Reports indicated some AMPs (antimicrobial peptides) were of antiparasitic activity to C. irritans. Hepcidin-like (Lc-HepL) was one of the significant differential expression genes excavated from the transcriptome following a challenge with C. irritans. In this study, we characterized this AMP’s bioactivity based on the levels of mRNA and protein. After challenged by C. irritans, qRT-PCR showed Lc-HepL was significantly upregulated in six tissues, including gill, muscle, liver, head kidney and spleen during theront infection, trophont falling off, and secondary bacterial invasion stages, which implicated a role Lc-HepL played in the immune defense against C. irritans and secondary bacterial infection. Recombinant Lc-HepL (rLc-HepL) was induced and purified successfully. rLc-HepL exhibited antibacterial activity to certain bacteria in a dose- and time-dependent manners. Anti-C. irritans activity was explored for the first time and found it could cause the theronts membrane rupture and contents leakage. These results provided the first evidence that Lc-HepL had strong antiparasitic activity against marine fish ectoparasites C. irritans theronts. Together, data indicated that Lc-HepL might be an important component in the innate immune system against C. irritans and has the potential to be employed in future drug development.

Rapid and accurate identification of Vibrio species has been problematic because phenotypic characteristics are variable within species and biochemical identification requires two or more days to complete. Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) has become a powerful tool for rapidly distinguishing between related bacterial species. However, its accuracy depends on the number of strains in a database. In the current study, we extend and apply the Vibrio database based on MALDI-TOF MS. A total of 74 strains of Vibrio representing 28 species were identified and included in new database. A phylogenetic tree based on rpoB sequence and dendrograms were constructed. We analyzed 30 clinical Vibrio of three species to evaluate the new database and carried out PCA dendrogram analyses for differences of strains. We created a new database that offered fast and accurate Vibrio identification. MSP and PCA dendrogram analyses provided technical support to track sources and incidences of Vibrio infection. In addition, the discovery of characteristic and differential peaks is useful for the future identification of Vibrio. This represents a powerful tool for the rapid and accurate classification and identification of Vibrio and closely related species.

Cadmium (Cd) is a common heavy metal pollutant in the aquatic environment, generally toxic to plant growth and leading to growth inhibition and biomass reduction. To study the oxidation resistance in Sargassum fusiforme seedlings in response to inorganic Cd stress, we cultured the seedlings under two different Cd levels: natural seawater and high Cd stress. High Cd stress significantly inhibited the seedlings growth, and darkened the thalli color. Additionally, the pigment contents, growth rate, peroxidase (POD) activity, dehydroascorbic acid (DHA) content, and glutathione reductase (GR) activity in S. fusiforme were significantly reduced by high Cd treatment. Contrarily, the Cd accumulation, Cd²⁺ absorption rate, dark respiration/net photosynthetic rate (R_d/P_n), ascorbic acid (Vc) content, soluble protein (SP) content, glutathione (GSH), and the activities of superoxide dismutase (SOD) and catalase (CAT) of S. fusiforme under Cd treatment significantly increased compared to the control group. The decrease of malondialdehyde (MDA) was not significant. Although S. fusiforme seedlings increased the antioxidant activities of POD, SOD, Vc, and the AsA-GSH cycle to disseminate H₂O₂ and maintain healthy metabolism, high Cd stress caused Cd accumulation in the stem and leaves of S. fusiforme seedlings. The excessive Cd significantly restricted photosynthesis and reduced photosynthetic pigments in the seedlings, resulting in growth inhibition and deep morphological color, especially of the stems. High levels of Cd in seawater had toxic effects on commercial S. fusiforme seedlings, and risked this edible seaweed for human food.

As the largest genus of Halymeniaceae, Grateloupia has been widely reported. Here, we observed the life history and early development of Grateloupia constricata Li et Ding and investigated the effects of temperature, irradiance, and photoperiod on the discoid crust and sporeling development of G. constricata under laboratory conditions. We observed that the type of carpospore development was “mediate discal type”. The life history included homotypic gametophyte (haploid), carposporophyte (diploid), and tetrasporophyte (diploid), with typical isomorphic alternation of generations. The results of double factorial analysis showed that both single factorial effects and interaction among temperature, photoperiod, and irradiance were obviously significant on the discoid crust and sporeling development. Furthermore, we found that the optimum combination of condition for the early growth and development of G. constricata was temperature 20°C, irradiance 80 μmol photons/(m²·s) and photoperiod 16L:8D. This study provides the theoretical basis and technical support for the conservation of the Grateloupia germplasm, artificial breeding, large-scale cultivation and sustainable development.

Due to extensive morphological plasticity, the taxonomy of Cladophora species remains unclear. As one of the widely distributed species, C. gracilis was reported to hold many varieties, which make it difficult to identify the species. This study explored the morphology diversity of nine C. gracilis samples collected along the coast of western Yellow Sea. Some samples showed extremely varied characteristics, by which one cannot classify them correctly. Hence, 18S rDNA and nuclear ribosomal DNA internal transcribed spacer regions (ITS) sequences were employed to delimit species. For 18S rDNA, sequence similarity ranged from 99.6% to 100%. For ITS region, the similarity ranged from 98.7% to 100%. Molecular data strongly suggested that the morphologically heterogeneous samples were actually the same species. Characteristics comparison of the samples revealed that the taxonomy criteria including branching pattern and density, thallus color, height and texture varied widely, influenced by environmental conditions and age of alga. Besides, cell dimensions, as the relatively stable criterion, also exhibited intraspecific variance. Successful application of 18S rDNA and ITS sequences indicated that molecular method can be a powerful assistant as DNA barcodes to traditional morphology taxonomy.

Based on an ice concentration threshold of 90%, it has been identified that two polynya events occurred in the region north of Greenland during the 2017/2018 ice season. The winter event lasted from February 20 to March 3, 2018 and the summer event persisted from August 2 to September 5, 2018. The minimum ice concentration derived from Advanced Microwave Scanning Radiometer 2 (AMSR2) observations was 72% and 65% during the winter and summer events, respectively. The occurrence of both events can be related to strengthened southerly winds associated with an increased east-west zonal surface level air pressure gradient across the north Greenland due to perturbation of mid-troposphere polar vortex. The relatively warm air temperature during the 2017/2018 freezing season in comparison with previous years, together with the occurrence of the winter polynya, formed favourable pre-conditions for ice field fracturing in summer, which promoted the formation of the summer polynya. Diminished southerly winds and increased cover of new ice over the open water were the dominant factors for the disappearance of the winter polynya, whereas increased ice inflow from the north was the primary factor behind the closure of the summer polynya. Sentinel-1 Synthetic Aperture Radar (SAR) images were found better suited than AMSR2 observations for quantification of a new ice product during the polynya event because the SAR images have high potential for mapping of different sea ice regimes with finely spatial resolution. The unprecedented polynya events north of Greenland in 2017/2018 are important from the perspective of Arctic sea ice loss because they occurred in a region that could potentially be the last “Arctic sea ice refuge” in future summers.

Ship-borne infrared radiometric measurements conducted during the Chinese National Arctic Research Expedition (CHINARE) in 2008, 2010, 2012, 2014, 2016 and 2017 were used for in situ validation studies of the Moderate Resolution Imaging Spectroradiometer (MODIS) sea ice surface temperature (IST) product. Observations of sea ice were made using a KT19.85 radiometer mounted on the Chinese icebreaker Xuelong between July and September over six years. The MODIS-derived ISTs from the satellites, Terra and Aqua, both show close correspondence with ISTs derived from radiometer spot measurements averaged over areas of 4 km×4 km, spanning the temperature range of 262–280 K with a ±1.7 K (Aqua) and ±1.6 K (Terra) variation. The consistency of the results over each year indicates that MODIS provides a suitable platform for remotely deriving surface temperature data when the sky is clear. Investigation into factors that cause the MODIS IST bias (defined as the difference between MODIS and KT19.85 ISTs) shows that large positive bias is caused by increased coverage of leads and melt ponds, while large negative bias mostly arises from undetected clouds. Thin vapor fog forming over Arctic sea ice may explain the cold bias when cloud cover is below 20%.

The reduction in Arctic sea ice in summer has been reported to have a significant impact on the global climate. In this study, Arctic sea ice/snow at the end of the melting season in 2018 was investigated during CHINARE-2018, in terms of its temperature, salinity, density and textural structure, the snow density, water content and albedo, as well as morphology and albedo of the refreezing melt pond. The interior melting of sea ice caused a strong stratification of temperature, salinity and density. The temperature of sea ice ranged from –0.8°C to 0°C, and exhibited linear cooling with depth. The average salinity and density of sea ice were approximately 1.3 psu and 825 kg/m³, respectively, and increased slightly with depth. The first-year sea ice was dominated by columnar grained ice. Snow cover over all the investigated floes was in the melt phase, and the average water content and density were 0.74% and 241 kg/m³, respectively. The thickness of the thin ice lid ranged from 2.2 cm to 7.0 cm, and the depth of the pond ranged from 1.8 cm to 26.8 cm. The integrated albedo of the refreezing melt pond was in the range of 0.28–0.57. Because of the thin ice lid, the albedo of the melt pond improved to twice as high as that of the mature melt pond. These results provide a reference for the current state of Arctic sea ice and the mechanism of its reduction.

In order to apply satellite data to guiding navigation in the Arctic more effectively, the sea ice concentrations (SIC) derived from passive microwave (PM) products were compared with ship-based visual observations (OBS) collected during the Chinese National Arctic Research Expeditions (CHINARE). A total of 3 667 observations were collected in the Arctic summers of 2010, 2012, 2014, 2016, and 2018. PM SIC were derived from the NASA-Team (NT), Bootstrap (BT) and Climate Data Record (CDR) algorithms based on the SSMIS sensor, as well as the BT, enhanced NASA-Team (NT2) and ARTIST Sea Ice (ASI) algorithms based on AMSR-E/AMSR-2 sensors. The daily arithmetic average of PM SIC values and the daily weighted average of OBS SIC values were used for the comparisons. The correlation coefficients (CC), biases and root mean square deviations (RMSD) between PM SIC and OBS SIC were compared in terms of the overall trend, and under mild/normal/severe ice conditions. Using the OBS data, the influences of floe size and ice thickness on the SIC retrieval of different PM products were evaluated by calculating the daily weighted average of floe size code and ice thickness. Our results show that CC values range from 0.89 (AMSR-E/AMSR-2 NT2) to 0.95 (SSMIS NT), biases range from −3.96% (SSMIS NT) to 12.05% (AMSR-E/AMSR-2 NT2), and RMSD values range from 10.81% (SSMIS NT) to 20.15% (AMSR-E/AMSR-2 NT2). Floe size has a significant influence on the SIC retrievals of the PM products, and most of the PM products tend to underestimate SIC under smaller floe size conditions and overestimate SIC under larger floe size conditions. Ice thickness thicker than 30 cm does not have a significant influence on the SIC retrieval of PM products. Overall, the best (worst) agreement occurs between OBS SIC and SSMIS NT (AMSR-E/AMSR-2 NT2) SIC in the Arctic summer.