Summary
A novel circovirus called porcine circovirus type 3 (PCV3) was recently reported to exist in the USA. This circovirus is associated with porcine dermatitis, nephropathy syndrome and ...reproductive failure. This study reports on the first identification, widely epidemic, different phylogenetic clusters, potential role in sow reproductive failure and possible origins of PCV3 in China.
Microplastics are widely present in the marine environment, but their pollution and potential risk assessment in the seabed sediments have not been well addressed in remote sea areas. In this study, ...microplastics in 50 surface sediment samples from the Xuande Atolls at the Xisha of the South China Sea were studied. There were 20 samples with detectable microplastics of 5–20 items kg−1. They were all fibers in shapes and blue/transparent in colors with the dominant chemical component of polyester and the typical size of 0.02-3 mm. We found a large spatial variability of microplastic abundance in the surface sediment with generally low or undetectable levels in the lagoon deposits and the offshore deep-sea sediments but elevated abundances in the slope sediments of the Xuande Atolls. Correlation analyses suggested that microplastic variability in the Xisha sediment was less affected by local environmental parameters such as water depth, sediment particle size, organic carbon content, and sediment types. We also found that elevated microplastics in the seabed sediments on various sides of the Xuande Atolls could be related to the seasonal change in monsoon-driven currents. Finally, a low risk of microplastic pollution in the surface sediment of the Xisha is concluded based on the assessments of the polymer hazard index and the pollution load index. These findings provide not only a baseline understanding of microplastics but also their dynamics in the surface sediment of the remote Xisha area of the South China Sea.
•Large spatial variability of microplastics in the seabed sediment of the relatively uninhabited northeast Xisha Islands•An elevated microplastic abundance in the slope sediments on the northeastern and the southern parts of the Xuande Atolls.•Sediment microplastic patchiness at Xisha could be related to varying wind-driven currents during different monsoon periods•A low risk of sediment microplastics at the Xisha was supported by the Pollution Hazard Index and the Pollution Load Index
Diatom-bacteria interactions and the associated bloom dynamics have not been fully understood in the coastal oceans. Here, we focus on the polyunsaturated aldehydes (PUAs) produced by diatoms in the ...post-bloom phase and look into their roles in microbial phosphorus (P) recycling outside of a P-limited estuary. The phytoplankton community in the bloom was dominated by PUAs-producing diatoms (Skeletonema costatum, Thalassiosira spp., and Pesudonitzschia delicates) with elevated concentrations of biogenic particulate PUAs. In addition, there were micromolar levels of particle-adsorbed PUAs hotspots with distinct compositions in and out of the bloom determined by a combining large-volume filtration and on-site derivation method. Field experiments were conducted to further assess the responses of particle-attached bacteria (PAB) to different PUAs amendments. We found no differences in the alkaline phosphatase (APase) activity and the abundance of PAB between inside and outside the bloom at a low PUAs dosage (<30 μM). However, for a high PUAs dosage (300 μM), APase activity and PAB growth were reduced significantly outside the bloom but no influences within the bloom. Our findings indicate that the hotspot-level oxylipins may play essential roles in bacterial P-remineralization in P-limited coastal areas. PAB can adapt to the high level of PUAs released by diatoms (or their resulting detritus) and potentially maintain a high rate of organic P recycling during the late stages of diatom blooms. Consequently, the interaction between oxylipin-rich diatoms and bacteria may affect phytoplankton blooms and carbon sequestration in the coastal oceans.
Display omitted
•Coastal diatom blooms dominated by PUAs-producing species with elevated levels of particulate PUAs•A micromolar level of particle-adsorbed PUAs hotspots with distinct compositions in and out of the patch•PAB can adapt to the high PUAs levels to maintain a high POP recycling rate in the late stages of blooms.•Hotspot-level of oxylipins may play essential roles in bacterial P-remineralization in P-limited coastal areas.
A reproducible stationary high-confinement regime with small "edge-localized modes" (ELMs) has been achieved recently in the Experimental Advanced Superconducting Tokamak, which has a metal wall and ...low plasma rotation as projected for a fusion reactor. We have uncovered that this small ELM regime is enabled by a wide edge transport barrier (pedestal) with a low density gradient and a high density ratio between the pedestal foot and top. Nonlinear simulations reveal, for the first time, that the underlying mechanism for the observed small ELM crashes is the upper movement of the peeling boundary induced by an initial radially localized collapse in the pedestal, which stops the growth of instabilities and further collapse of the pedestal, thus providing a physics basis for mitigating ELMs in future steady-state fusion reactors.
Microplastics are recognized as a newly emerging threat to marine organisms as they can be ingested and accumulated through multiple trophic levels. However, microplastic contamination and its ...potential risk assessment in coral reef fishes have been less addressed, particularly in remote ocean regions. In this study, microplastics in 167 samples of coral reef fish (a total of eighteen species) from the Xisha areas of the South China Sea were studied. There were fifteen species of coral reef fish contaminated by microplastics with an average occurrence rate of 29.3 %. The shape of microplastics in the fishes was mostly fibrous with small sizes (400–900 μm) and light colors (transparent and blue). The dominant types of microplastic polymers are polyamide and polyethylene terephthalate, accounting for 77 % and 11 % of microplastics in the fish body. There were generally more microplastics in the herbivorous fishes than the carnivorous ones. The highest microplastic abundance and occurrence was found in parrotfish due to its direct feeding on the microplastics-contaminated corals. In addition, there were much more microplastics in the gastrointestinal tracts than in the gills of the Xisha fishes. Microplastic abundance was found negatively correlated with the trophic level of the Xisha fishes supporting a stronger microplastic impact at lower levels of marine animals. Finally, a risk assessment using the polymer hazard index (PHI) revealed that microplastic contamination in the Xisha fishes was lower than those in the eutrophic coast. Our study provides new evidence for the widespread presence of microplastic contamination in the fishes of the remote Xisha coral reefs.
Display omitted
•Microplastic characteristics in the fish of the remote Xisha reefs are identified.•Microplastic abundance negatively correlates with the trophic level of the Xisha fish.•Risk of microplastic contamination in Xisha fish is lower than the eutrophic coast.
Transparent exopolymer particles (TEPs) have drawn extensive attention in recent decades due to their crucial role in the biogeochemical and ecological processes of the ocean. However, TEP ...distribution and fluxes are relatively less addressed in the shelf-seas, where its variability can be affected by not only biology but also complex physical dynamics. Here, we present a comprehensive study of TEP from the coast to the basin (12 sampling sites) of the northern South China Sea (NSCS). We found a large TEP variability from 0.6 to 78.6 μg Xeq. L−1 with higher levels in the coastal waters than the offshore epipelagic waters and the deep waters. In addition, the spatial distribution of TEP was significantly correlated to the cross-shelf change of temperature, salinity, and chlorophyll-a, revealing the complex physical-biogeochemical controls on TEP variability. We found the TEP dynamics nearshore largely influenced by the sedimentation and transportation of TEP-rich aggregates from the river plume. The contribution of TEP to particulate organic carbon (POC) increased gradually when approaching the shore from the sea, suggesting an elevated role of TEP in the coastal carbon cycle. Finally, a good correlation of particle-attached bacteria (PAB) with TEP but not POC revealed a preferential utilization of TEP by PAB. Thus, TEP may play an essential role in the recycling of carbon and nitrogen in the shelf-sea. These findings are crucial for understanding of the TEP dynamics under a changing environment and the associated impacts on the oceanic carbon cycle.
Display omitted
•TEP dynamics were affected by production, degradation, and sedimentation/ transportation.•TEP played a more important role in the carbon cycle nearshore than offshore of the NSCS.•TEP-C was preferably utilized by particle-attached bacteria relative to non-TEP POC.
In the northern South China Sea of western Pacific Ocean during winter, clouds, sun glint, and other factors block optic sensors, leading to a high missing rate and hence a major concern in ocean ...color products such as the chlorophyll-a (CHL) data. These constraints inhibit the understanding of CHL variabilities at short (< seasonal) scales. Here, we introduce a new gap-filling method to reconstruct data gaps in a daily CHL remote sensing product. We applied discrete cosine transform with penalized least square (DCT-PLS) approach in the adjacent Luzon Strait, yielding a 15-year full-coverage daily 4-km CHL product. Against the cross-validation set and an independent observational data set collected from 34 cruises, evaluations suggest that DCT-PLS has outperformed the widely applied classical data-interpolating empirical orthogonal function (DINEOF) method. Besides, the DCT-PLS method is characterized by more efficient computation. The complete CHL product was analyzed with a particular focus on the intraseasonal (~30-60 days) control on the winter bloom by the Madden-Julian Oscillation (MJO). The MJO's local signature on the CHL presents asymmetry. The CHL peaks at the late phases of MJO events, which could be explained by the relaxation after the MJO-induced wind strengthening. This gap-filling approach can be promisingly applied in other remote sensing gap-filling problems, which could shed light on the short-term variability of biological and physical dynamics in the ocean.
Field surveys of the northern South China Sea (NSCS) were conducted during the summer of 2015 and 2016 with size-fractionated chlorophyll a (chl a) measurements and size-specific dilution experiments ...for 3 phytoplankton size classes, including micro- (20 to 200 μm), nano- (2 to 20 μm), and picophytoplankton (<2 μm). Our results suggest that phytoplankton size structure and size-specific rates of growth and grazing mortality could vary substantially along the coastal, transition, and oceanic zones of the NSCS. There was an elevated microphytoplankton concentration in the inner shelf, in contrast to the dominance of nanophytoplankton over the middle and outer shelves. However, the phytoplankton community was mostly dominated by pico-cells in the oligotrophic oceanic regions. We found a nonlinear relationship between nanophytoplankton and total chl a, which is different from both pico-cells (a linear decrease) and micro-cells (a linear increase). By assessing the functional responses of the size-specific growth rates to nitrate concentrations, we found a higher nitrate-saturated maximal growth rate and a larger half-saturation constant for microphytoplankton, whereas nano- and picophytoplankton showed similar lower maximal rates and smaller half-saturation constants. There was also much higher grazing mortality of microphytoplankton in response to the increase in total chl a. These findings are important for understanding plankton dynamics and the associated biogeochemical fluxes in contrasting marine ecosystems, as well as for future size-structure modeling of the NSCS.
Episodic eddy-driven upwelling may supply a significant fraction of the nutrients required to sustain primary productivity of the subtropical ocean. New observations in the northwest Atlantic reveal ...that, although plankton blooms occur in both cyclones and mode-water eddies, the biological responses differ. Mode-water eddies can generate extraordinary diatom biomass and primary production at depth, relative to the time series near Bermuda. These blooms are sustained by eddy/wind interactions, which amplify the eddy-induced upwelling. In contrast, eddy/wind interactions dampen eddy-induced upwelling in cyclones. Carbon export inferred from oxygen anomalies in eddy cores is one to three times as much as annual new production for the region.
Surface ocean phosphate is commonly below the standard analytical detection limits, leading to an incomplete picture of the global variation and biogeochemical role of phosphate. A global compilation ...of phosphate measured using high-sensitivity methods revealed several previously unrecognized low-phosphate areas and clear regional differences. Both observational climatologies and Earth system models (ESMs) systematically overestimated surface phosphate. Furthermore, ESMs misrepresented the relationships between phosphate, phytoplankton biomass, and primary productivity. Atmospheric iron input and nitrogen fixation are known important controls on surface phosphate, but model simulations showed that differences in the iron-to-macronutrient ratio in the vertical nutrient supply and surface lateral transport are additional drivers of phosphate concentrations. Our study demonstrates the importance of accurately quantifying nutrients for understanding the regulation of ocean ecosystems and biogeochemistry now and under future climate conditions.
PDF
