Here, we sequenced the complete mitogenome of Parasesarma eumolpe (Brachyura: Grapsoidea: Sesarmidae) for the first time. The characteristics of this newly sequenced mitogenome were described and compared with other Sesarmidae species. The 15 646-bp mitogenome contains 13 protein-coding genes (PCGs), two ribosomal RNA genes (rRNAs), 22 transfer RNA genes (tRNAs), and an A-T rich region. All of the PCGs are initiated by the start codon ATN and terminated by the standard TAN codon or an incomplete T. The pairwise Ka/Ks ratio analysis shows that all 13 PCGs are under purifying selection, whereas the ATP8 gene is an outlier, with pairwise comparison values ranging from neutral selection (0.000) to positive selection (1.039). The gene arrangement of P. eumolpe compared with ancestral Decapoda shows the translocation of two tRNAs (tRNA-His and tRNA-Gln), which is identical to other Sesarmidae species. Phylogenetic analyses show that all Sesarmidae species are placed into one group, and the polyphyly of Eriphioidea, Ocypodoidea, and Grapsoidea is well supported. The relationship between gaps in the QIM region and the phylogeny of Sesarmidae is analyzed. It is obvious that both the G5 (the gap between Q and I) and G6 (the gap between I and M) decrease progressively with the evolution process. These results will help to better understand the genomic evolution within Sesarmidae and provide insights into the phylogeny of Brachyura.

A thorough understanding of the biogeochemical cycling of trace metals in the ocean is crucial because of the important role these elements play in regulating metabolism in marine biotas and thus, the climate. However, a precise and accurate analysis of trace metals in seawater is difficult because they are present at extremely low concentrations in a high salt matrix. In this study, we report an analytical method for the preconcentration and separation of six trace metals, Fe, Ni, Cu, Zn, Cd and Pb, in seawater using a seaFAST automatic solid-phase extraction device, analysis by a triple quadrupole collision/reaction technique with inductively coupled plasma mass spectrometry (ICP-MS), and quantification by the isotope dilution technique. A small volume (10 mL) of seawater sample was mixed with a multi-element isotope spike and subjected to seaFAST procedures. The preconcentrate solution was then analyzed using the optimized collision/reaction cell mode of ICP-MS, with NH₃ gas for Fe and Cd with a flow rate of 0.22 mL/min and He for Ni, Cu, Zn and Pb with a flow rate of 4.0 mL/min. The procedure blanks were 130 pmol/L, 3.0 pmol/L, 6.8 pmol/L, 37 pmol/L, 0.29 pmol/L and 0.42 pmol/L, for Fe, Ni, Cu, Zn, Cd and Pb, respectively. The method was validated using five reference materials (SLRs-6, SLEW-3, CASS-6, NASS-7 and GEOTRACE-GSC), and our results were consistent with the consensus values. The method was further validated by measuring full-water-column seawater samples from the subtropical Northwest Pacific Ocean, and our results demonstrated good oceanic consistency.

Planktonic metabolism plays an important role in affecting the energy transportation and carbon cycle of the marine ecosystem. However, its regulation mechanism remains unclear under the continuously exogenous nutrient inputs in nearshore waters. In this study, a mesocosm experiment was conducted in a semi-enclosed bay, the Daya Bay, to explore the responses of plankton metabolic balance and community structure to a concentration gradient of daily nitrogen and phosphorus inputs. The results showed that nutrient enrichments promoted phytoplankton biomass, total primary production, and community respiration, and the promoting effect enhanced alongwith the increase of nutrient concentration. However, the net community production fluctuated more violently between autotrophic and heterotrophic with the increase of nutrient inputs and tended to be more heterotrophic from the 5th day to the 10th day of the experiment. In addition, the daily flux of nitrogen and phosphorus, 2 μmol/(L·d) and 0.066 μmol/(L·d), respectively, could be regarded as a potential threshold for ecosystem stability and health, since most of the ecological characteristics related to plankton structure and function have undergone significant changes when the nutrient level is higher than that. In the nearshore enclosed or semi-enclosed waters, nutrient from continuous terrigenous input is likely to be concentrated and exceed this level, indicating the ecological risks due to the metabolic unbalance and the deterioration of plankton community structure.

In the present study, four new species of the genus Reticunassa Iredale, 1936 collected from Chinese waters are described and illustrated. Reticunassa hugokooli sp. nov., Reticunassa jungi sp. nov. and Reticunassa aureolineata sp. nov. were collected from the northeastern coast of Taiwan Island, whereas Reticunassa fuscofasciata sp. nov. was collected from the northeastern coast of Taiwan Island and the South China Sea. The four new species can be distinguished conchologically from other congeners mainly in protoconch, shell shape, sculpture, and coloration. These findings demonstrate that the biodiversity of this group in China might be largely underestimated.

²¹⁰Po, ²¹⁰Pb, and ²³⁴Th were determined in water columns of the East China Sea (ECS) to investigate their biogeochemical behaviors during a severe red tide event. Dissolved ²¹⁰Po, ²¹⁰Pb, and ²³⁴Th accounted for large fractions of the total phases. The abnormally high concentrations of dissolved ²¹⁰Pb were observed. Partition behaviors of these radionuclides were influenced by particle content effect and particle composition based on distribution coefficient (K_d) vs. total suspended matter (TSM) content and K_d vs. ratios of particulate organic carbon and total suspended matter contents (POC/TSM content ratios). The peaks of mass specific activities of ²¹⁰Po, ²¹⁰Pb, and ²³⁴Th indicated that degraded particles could have an intensified enrichment ability for radionuclides compared with the surficial suspended matters. Fractionation factor of ²¹⁰Po and ²¹⁰Pb (F_Po/Pb) (>1) and fractionation factor of ²¹⁰Po and ²³⁴Th (F_Po/Th) (>1) were much higher at algal blooming regions than that at non-blooming stations, indicating that algal blooms promoted the fractionation of ²¹⁰Po against ²¹⁰Pb and ²³⁴Th, and proving that ²¹⁰Po exhibited a stronger affinity for biogenic particles than ²¹⁰Pb and ²³⁴Th when POC content increased in the sea. POC/²¹⁰Po, POC/²¹⁰Pb and POC/²³⁴Th ratios (content/activity ratios) sharply decreased with depth in both algal bloom and non-bloom stations. The outbreak of algal bloom promoted the complexity of suspended particles and increased the variability of POC/tracer ratios (content/activity ratios) in the different depth of the shallow seas. More considerations should be taken to the difficulty of the selection of export interface and the suitable tracers when algal blooming occurs.

Quantitative identification of long-term changes in the abundance of Japanese anchovy (Engraulis japonicus) in the Yellow Sea is particularly important for understanding evolutionary processes of the Yellow Sea ecosystem. Unfortunately, the driving mechanisms of climate variability on the anchovy are still unclear due to the lack of long-term observational data. In this study, we used the fish scale deposition rate in the central Yellow Sea to reconstruct the time series of the anchovy stock over the past 400 a. On this basis, we further explored the impacts of the Pacific Decadal Oscillation (PDO) on the anchovy. Our results show that the anchovy stock is positively correlated with the PDO on a decadal time scale. In addition, anchovy abundance was relatively high during 1620–1860 AD (the Little Ice Age, LIA), though in a state of constant fluctuation; anchovy abundance maintained at a relatively low level after ~1860 AD. In particular, followed by overfishing since the 1980s, the anchovy stock has declined sharply. Based on these findings, we infer that fluctuations of the anchovy stock may be regulated by basin-scale “atmosphere–ocean” interactions. Nevertheless, the role of overfishing should not be ignored.

Long-chain n-alkanols and n-alkanes in core sediments from the northern South China Sea (SCS) were measured to make a comparison during terrestrial vegetation reconstruction from ~42 ka to ~7 ka. The results showed that terrestrial vegetation record from long-chain n-alkanes matched well with previous studies in nearby cores, showing that more C₄ plants developed during the Last Glacial Maximum (LGM) and C₃ plants dominated in the interglacial period. However, these scenarios were not revealed by terrestrial vegetation reconstruction using long-chain n-alkanols, which showed C₃ plant expansion during the LGM. The discrepancy during the interglacial period could be attributed to the aerobic degradation of functionalized long-chain n-alkanols in the oxygen-rich bottom water, resulting in poor preservation of terrestrial vegetation signals. On the other hand, the different advantages of functionalized n-alkanols and non-functional n-alkanes to record local and distal vegetation signals, respectively, may offer a potential explanation for the contradiction during the LGM when the SCS was characterized by low-oxygen deep water. Nevertheless, large variations on n-alkyl lipid compositions in C₃/C₄ plants could play a part in modulating sedimentary long-chain n-alkanols and n-alkanes toward different vegetation signals, thereby suggesting that caution must be taken in respect to the terrestrial vegetation reconstruction using long-chain n-alkanes and long-chain n-alkanols.

Mangrove forests are vulnerably threatened by sea level rise (SLR). Vegetation organic carbon (OC) stocks are important for mangrove ecosystem carbon cycle. It is critical to understand how SLR affects vegetation OC stocks for evaluating mangrove blue carbon budget and global climate change. In this study, biomass accumulation and OC stocks of mangrove vegetation were compared among three 10 year-old Kandelia obovata (a common species in China) mangrove forests under three intertidal elevations through species-specific allometric equations. This study simulated mangrove forests with SLR values of 0 cm, 40 cm and 80 cm, respectively, representing for the current, future ~100 a and future ~200 a SLR of mangrove forests along the Jiulong River Estuary, China. SLR directly decreased mangrove individual density and inhibited the growth of mangrove vegetation. The total vegetation biomasses were (12.86±0.95) kg/m², (7.97±0.90) kg/m² and (3.89±0.63) kg/m² at Sites SLR 0 cm, SLR 40 cm and SLR 80 cm, respectively. The total vegetation OC stock decreased by approximately 3.85 kg/m² (in terms of C) from Site SLR 0 cm to Site SLR 80 cm. Significantly lower vegetation biomass and OC stock of various components (stem, branch, leaf and root) were found at Site SLR 80 cm. Annual increments of vegetation biomass and OC stock also decreased with SLR increase. Moreover, significant lower sedimentation rate was found at Site SLR 80 cm. These indicated that SLR will decrease mangrove vegetation biomass and OC stock, which may reduce global blue carbon sink by mangroves, exacerbate global warming and give positive feedback to SLR.

The prokaryotic microbial communities in the sediments play crucial roles in the ecological functions of mangrove ecosystems. Therefore, the environmental factors that affect the structures of these prokaryotic microbial communities could indirectly participate in the regulation of mangrove functions, which is of great value for mangrove studies. The particle size (PS) of soils is recently demonstrated as a key environmental factor for shaping the microbial communities; however, this hypothesis has rarely been tested for mangrove environments. A case study of three tropical mangroves from Sanya, China was performed in this work to assess the influence of PS on the prokaryotic microbial community structures of bacteria, archaea, diazotrophs, and denitrifiers in the sediments. Results showed the variability in the spatial scale and the stability in the temporal scale for the prokaryotic communities, indicating that the tropical mangrove sediments could be a versatile but stable environment. Among the collected environmental factors, PS, salinity, and humidity had the greatest impacts, and PS mostly affected the structures of these prokaryotic communities based on its highest R² values of canonical correspondence analysis, Mental test, and linear fitting (p≤0.05). Furthermore, PS was positively correlated with the diversity and abundance of diazotrophic communities and negatively correlated with the abundances of methanogenic communities including Methanobacteriaceae, Methanospirillaceae, Methanoregulaceae, and Methanosaetaceae. Former studies show the increasing trend of PS caused by the rise of sea level and the intensification of human activities. Therefore, our findings indicate that PS could be a potential intermediate that links climate change and human activities with the possible ecological function migration of mangroves; meanwhile, the increase of PS could in turn release the stress of these environmental changes by increasing the abundance and diversity of the diazotrophic community and decreasing the abundances of methanogens.

The circadian clock is a fundamental endogenous mechanism of adaptation that coordinates the physiology and behavior of most organisms with diel variations in the external environment to maintain temporal homeostasis. Diatoms are the major primary producers in the ocean. However, little is known about the circadian clock in marine diatoms compared with other organisms. Here, we investigated circadian clock genes, their expression patterns, and responses to environmental stimuli such as light, nitrogen and phosphorus in two marine diatoms, Skeletonema costatum and Phaeodactylum tricornutum, using a combination of qRT-PCR and bioinformatic analysis. We identified 17 and 18 circadian clock genes in P. tricornutum and S. costatum, respectively. Despite significant evolutionary differences, these genes were similar to those of the higher plant Arabidopsis. We also established a molecular model for the marine diatom circadian clock comprising an input pathway, core oscillator, output pathway, and valve effector. Notably, the expression patterns of core clock genes (circadian clock associated 1 (CCA1), late elongated hypocotyl (LHY) and timing of cab 1 (TOC1)) in both species differed from those of terrestrial plants. Furthermore, the expression of these genes was influenced by variations in ambient light, nitrogen and phosphorus availability. Although marine diatoms and higher plants share common circadian clock components, their clock genes have diverged throughout evolution, likely as a result of adapting to contrasting environments.