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.

To determine if water-sediment regulation has affected macrobenthic community structure in the Huanghe River Estuary, China, macrobenthic samples were collected following regulation events from 2012 to 2016. We identify seven phyla and 138 macrobenthic species from within samples throughout the survey area, over time. Species richness and abundance in 2012 were significantly higher than in 2016. Biomass did not differ significantly during 2012–2016. Dominant species were mostly small polychaetes, with mollusks, arthropods, and echinoderms all being relatively rare. In 2016, dominant species were small polychaetes. MDS reveals macrobenthic communities at all surveyed distances from the estuary to have become the same community structure over time. Shannon-Wiener diversity and Margalef richness indexes trended down over time. CCA reveals the most dominant sediment-dwelling species to prefer lower dissolved oxygen, sulfides, and pH, and sediments with high D₅₀ and low clay content. We speculate that water-sediment regulation has affected seabed communities, particularly Region A in our survey area.

The Huanghe River (Yellow River) is known by its high suspended sediment concentration (SSC) in its river mouth tidal flat. However, the factors controlling the high SSC over there are not well understood. Therefore, we conducted 7-d hydrodynamic observations (water depth, wave height, and current velocity) and SSC measurements on the tidal flat off the Huanghe River Mouth. The data shows that in most of time, under the calm sea condition, the SSC ranges 0.1–3.5 g/L, and sediment discharge from the river is the main source. However, when hydrodynamics are enhanced in a tidal cycle and large-scale erosion occurs on the seafloor, resuspended sediment becomes the main source, and the SSC in the water column reaches 17.3 g/L. We find the suspended sediment flux is mainly controlled by the tidal current and Stokes drift, while the wave-induced shear stress could also affect the variation of suspended sediment flux. During the observation period, when sea under calm-rippled conditions, the current-induced resuspended sediment concentration (RSC) was greater than the wave-induced RSC. In contrast, in smooth-wavelet sea conditions, the wave-induced RSC was greater than the current-induced RSC, for instance, a single wave event was found to cause 11.8 cm seabed erosion within 6 h. This study reveals different controlling factors for the high SSC near a river-influenced tidal flat, and helps us get a better understanding of a delta's depositional and erosional mechanisms.

The data of field surveys during 2009 to 2018 was analyzed to understand the seasonality and inter-annual variability of the floating Ulva and Sargassum in the Subei Shoal, the southwestern Yellow Sea of China on decadal scale. The floating Ulva biomass was consistently originated from the central region of the Subei Shoal in middle to late April, increased rapidly, drifted and extended into the offshore water in May and June. The average floating Ulva biomass in the shoal generally increased over the years with evident inter-annual fluctuations. In contrast, pelagic Sargassum was accumulated in the Subei Shoal and formed the spring bloom only in 2013, 2017 and 2018, and the biomass was higher than the co-occurring Ulva during the survey in these three years. Compared to the raft-origin floating Ulva, genesis and development of the pelagic Sargassum was distinct. Based on the current research, the Sargassum biomass was exotic and often initiated in the offshore water in March, and intruded into the shoal in April and May. The analysis on the environmental parameters was inconclusive since multiple anthropogenic and non-indigenous factors could influence the green tides in this region. Further research covering both the East China Sea and the Yellow Sea is needed to trace the origin of the floating Sargassum and to understand the interactions between these two co-occurring seaweeds.

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.

Subseasonal Arctic sea ice prediction is highly needed for practical services including icebreakers and commercial ships, while limited by the capability of climate models. A bias correction methodology in this study was proposed and performed on raw products from two climate models, the First Institute Oceanography Earth System Model (FIOESM) and the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS), to improve 60 days predictions for Arctic sea ice. Both models were initialized on July 1, August 1, and September 1 in 2018. A 60-day forecast was conducted as a part of the official sea ice service, especially for the ninth Chinese National Arctic Research Expedition (CHINARE) and the China Ocean Shipping (Group) Company (COSCO) Northeast Passage voyages during the summer of 2018. The results indicated that raw products from FIOESM underestimated sea ice concentration (SIC) overall, with a mean bias of SIC up to 30%. Bias correction resulted in a 27% improvement in the Root Mean Square Error (RMSE) of SIC and a 10% improvement in the Integrated Ice Edge Error (IIEE) of sea ice edge (SIE). For the CFS, the SIE overestimation in the marginal ice zone was the dominant features of raw products. Bias correction provided a 7% reduction in the RMSE of SIC and a 17% reduction in the IIEE of SIE. In terms of sea ice extent, FIOESM projected a reasonable minimum time and amount in mid-September; however, CFS failed to project both. Additional comparison with subseasonal to seasonal (S2S) models suggested that the bias correction methodology used in this study was more effective when predictions had larger biases.

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%.

Clay minerals deposited at the southern Mendeleev Ridge in the Arctic Ocean have a unique provenance, which can be used to reconstruct changes in the local sedimentary environment. We show that sediments in core ARC7-E23 record high-frequency changes in clay minerals since the penultimate interglacial. The clay minerals, grain size, and ice-rafted debris indicate the extent of the East Siberia Ice Sheet (ESIS). During the glacial periods of Marine Isotope Stage 2 (MIS2) and MIS4, the southern Mendeleev Ridge was likely covered by an ESIS-extended ice shelf, blocking almost all sediment input from the Canadian Arctic and Laptev Sea, but allowing transport of fine-grained sediments from the East Siberian and Chukchi Sea shelves. After ESIS retreat, the Beaufort Gyre and Transpolar Drift became the primary transport mechanism for the distally sourced sediments. Climate conditions in MIS3 enhanced both the oceanic circulation and sediment transport.

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.

We analyzed the biogenic silica (BSi) content and produced a diatom-based summer sea-surface temperature (SST) reconstruction for sediment core GC4 from the Holsteinsborg Dyb, West Greenland. Our aim was to reconstruct marine productivity and climatic fluctuations during the last millennium. Increased BSi content and diatom abundance suggest relatively high marine productively during the interval of AD 1000–1400, corresponding in time to the Medieval Warm Period (MWP). The summer SST reconstruction indicates relatively warm conditions during AD 900–1100, followed by cooling after AD 1100. An extended cooling period during AD 1400–1900 is characterized by prolonged low in reconstructed SST and high sea-ice concentration. The BSi values fluctuated during this period, suggesting varying marine productivity during the Little Ice Age (LIA). There is no significant correlation between the BSi content and SST during the last millennium, suggesting that the summer SST has little influence on marine productively in the Holsteinsborg Dyb. A good correspondence between the BSi content and the element Ti counts in core GC4 suggests that silicate-rich meltwater from the Greenland ice sheet was likely responsible for changes in marine productively in the Holsteinsborg Dyb.