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.

Ulvophytes are attractive model systems for understanding the evolution of growth, development, and environmental stress responses. They are untapped resources for food, fuel, and high-value compounds. The rapid and abundant growth of Ulva species makes them key contributors to coastal biogeochemical cycles, which can cause significant environmental problems in the form of green tides and biofouling. Until now, the Ulva mutabilis genome is the only Ulva genome to have been sequenced. To obtain further insights into the evolutionary forces driving divergence in Ulva species, we analyzed 3 905 single copy ortholog family from U. mutabilis, Chlamydomonas reinhardtii and Volvox carteri to identify genes under positive selection (GUPS) in U. mutabilis. We detected 63 orthologs in U. mutabilis that were considered to be under positive selection. Functional analyses revealed that several adaptive modifications in photosynthesis, amino acid and protein synthesis, signal transduction and stress-related processes might explain why this alga has evolved the ability to grow very rapidly and cope with the variable coastal ecosystem environments.

Investigating the spatiotemporal variability of biogeochemical processes and ecological responses under multiple physical controls in shelf seas is of great importance for obtaining an in-depth understanding of marine ecosystem. Based on a compiled data set of historical observations and remote sensing data, the spatiotemporal variability and heterogeneity of physical-biogeochemical processes in the semi-enclosed South Yellow Sea (SYS) are investigated, and the intrinsic connectivity among different subregions and the associated mechanisms are examined. The results show that the seasonal alternation between southward transport in cold seasons and upwelling-induced vertical delivery in warm seasons is the primary physical control of the biogeochemical processes and primary production off Shidao and in the area adjacent to the Haizhou Bay. The northeastward expansion of coastal waters in the Subei Shoal constitutes an important physical driver for the offshore transport of Ulva prolifera in summer. Stratification significantly affects the biogeochemical processes in the Yellow Sea Cold Water Mass (YSCWM)-dominated area during warm seasons, and nutrients can accumulate in bottom waters from spring to autumn, making the Yellow Sea Cold Water Mass (YSCWM) be an important nutrient pool. Upwelling around the YSCWM boundary in the stratified season leads to consistency among the high chlorophyll a (Chl a) area, high primary productivity region and low-temperature upwelling zone. During cold seasons, the interactions of the southward cold waters in the western nearshore area and the northward warm waters in the central region lead to an “S”-shaped front in the SYS. In summer, upwelling can extract nutrients from the YSCWM; thus, the biogeochemical-ecological processes inside the cold-water mass and in the frontal zone are well connected via upwelling, and three typical physical-biogeochemical coupling regions are generated, namely, the Shidao coast, the area beyond the Haizhou Bay and the area off the Subei Shoal. This work refines and integrates studies on regional oceanography in the SYS and provides a comprehensive and systematic framework of physical-biogeochemical-ecological processes.

The Nankai Trough subduction zone is a typical subduction system characterized by subduction of multiple geological units of the Philippine Sea Plate (the Kyushu-Palau Ridge, the Shikoku Basin, the Kinan Seamount Chain, and the Izu-Bonin Arc) beneath the Eurasian Plate in the southwest of Japan. This study presents a geophysical and geochemical analysis of the Nankai Trough subduction zone in order to determine the features and subduction effects of each geological unit. The results show that the Nankai Trough is characterized by low-gravity anomalies (–20 mGal to –40 mGal) and high heat flow (60–200 mW/m²) in the middle part and low heat flow (20–80 mW/m²) in the western and eastern parts. The crust of the subducting plate is 5–20 km thick. The mantle composition of the subducting plate is progressively depleted from west to east. Subduction of aseismic ridges (e.g., the Kyushu-Palau Ridge, the Kinan Seamount Chain, and the Zenisu Ridge) is a common process that leads to a series of subduction effects at the Nankai Trough. Firstly, aseismic ridge or seamount chain subduction may deform the overriding plate, resulting in irregular concave topography along the front edge of the accretionary wedge. Secondly, it may have served as a seismic barrier inhibiting rupture propagation in the 1944 M_w 8.1 and 1946 M_w 8.3 earthquakes. In addition, subduction of the Kyushu-Palau Ridge and hot and young Shikoku Basin lithosphere may induce slab melting, resulting in adakitic magmatism and the provision of ore-forming metals for the formation of porphyry copper and gold deposits in the overriding Japan Arc. Based on comparisons of their geophysical and geochemical characteristics, we suggest that, although the Izu-Bonin Arc has already collided with the Japan Arc, the Kyushu-Palau Ridge, which represents a remnant arc of the Izu-Bonin Arc, is still at the subduction stage characterized by a single-vergence system and a topographic boundary with the Japan Arc.

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.

Triacylglycerols (triglycerides, TAGs) are the major carbon and energy storage forms in various organisms, and important components of cellular membranes and signaling molecules; they have essential functions in multiple physiological processes and stress regulation. Acyl-CoA: diacylglycerol acyltransferase (DGAT) catalyzes the final and only committed acylation step in the synthesis of TAGs in eukaryotes. The present work identified and isolated a novel gene, UpDGAT1, from the green tide alga Ulva prolifera. The activity of UpDGAT1 was confirmed by heterologous expression in a Saccharomyces cerevisiae TAG-deficient quadruple mutant. Results of thin-layer chromatography and BODIPY staining indicated that UpDGAT1 was able to restore TAG synthesis and lipid body formation in the yeast. Lipid analysis of yeast cells revealed that UpDGAT1 showed broad substrate specificity, accepting saturated as well as mono- and polyunsaturated acyl-CoAs as substrates. High salinity and high temperature stresses increased UpDGAT1 expression and TAG accumulation in U. prolifera. The present study provides clues to the functions of UpDGAT1 in TAG accumulation in, and stress adaptation of, U. prolifera.

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.

Ulva prolifera is a green alga that plays an important role in green tides. Carotenoid biosynthesis is a basic terpenoid metabolism that is very important for maintaining normal life activities in algae. In this study, we first reported the complete sequences of all genes in the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, which is the only carotenoid synthesis pathway in U. prolifera. Then, we compared these genes with those of other species. Additionally, by detecting the carotenoid contents and expression levels of key genes participating in carotenoid biosynthesis in U. prolifera under three different light (1 000 lx, 5 000 lx and 12 000 lx) and salinity (12, 24 and 40) regimes, we found that carotenoid synthesis could be influenced by light and salinity, such that low light and high salinity could promote the synthesis of carotenoids. The results showed that the expression levels of genes involved in the MEP and the downstream pathway could affect the biosynthesis of carotenoids at the molecular level. This study contributes to a better understanding of the roles of genes participating in carotenoid biosynthesis in U. prolifera and the environmental regulation of these genes.

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.

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.