Institutional Repository of South China Sea Institute of Oceanology, CAS
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Grouper MAVS functions as a crucial antiviral molecule against nervous necrosis virus infection
No full textMitochondrial antiviral signaling protein (MAVS), also known as IPS-1, VISA, and Cardif, has been well studied for its crucial roles in the mammalian interferon immune response. To better understand the actions of MAVS in fish immune response, a MAVS homolog from orange spotted grouper (Epinephehts coioides) (EcMAVS) was cloned and characterized in this study. EcMAVS encoded a 563-amino acid peptide which showed 64% and 20% identity to rock bream (Opiegnathus fasciatus) and human (Homo sapiens), respectively. Sequence alignment analysis showed that EcMAVS shared a conserved CARD domain at N terminal, a central proline-rich region and a TM domain at C terminal. Phylogenetic analysis indicated that EcMAVS showed the nearest relationship to rock bream, followed by other fishes, birds and mammals. In healthy grouper, the transcript of EcMAVS was predominantly detected in gill, intestine and skin. In vitro, the expression level of EcMAVS was significantly increased during red-spotted grouper nervous necrosis virus (RGNNV) infection, but only slightly increased at the late stage of Singapore grouper iridovirus (SGIV) infection, suggested the EcMAVS might exert various roles in response to different viruses. Subcellular localization analysis showed that the fluorescence in EcMAVS transfected cells primarily co-localized with mitochondria. Overexpression of EcMAVS in grouper cells significantly inhibited the replication of RGNNV, demonstrated by the delay of CPE progression and the decrease of viral gene transcription. Differently, the replication of SGIV was almost not affected by the ectopic expression of EcMAVS. Furthermore, our results also showed that EcMAVS overexpression significantly increased the expression of interferon related cytokines, and activated both IRF3- and IRF7-mediated interferon promoter activities. Taken together, our results demonstrated that grouper MAVS exerted antiviral function against nodavirus infection via up-regulating the interferon immune response
Size-dependent phytoplankton growth and grazing in the northern South China Sea
No full textField 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 sizespecific dilution experiments for 3 phytoplankton size classes, including micro-(20 to 200 mu m), nano-(2 to 20 mu m), and picophytoplankton (< 2 mu m). 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 picocells 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
Features of the Equatorial Intermediate Current Associated with Basin Resonance in the Indian Ocean
No full textThis paper investigates the features of the Equatorial Intermediate Current (EIC) in the Indian Ocean and its relationship with basin resonance at the semiannual time scale by using in situ observations, reanalysis output, and a continuously stratified linear ocean model (LOM). The observational results show that the EIC is characterized by prominent semiannual variations with velocity reversals and westward phase propagation and that it is strongly influenced by the pronounced second baroclinic mode structure but with identifiable vertical phase propagation. Similar behavior is found in the reanalysis data and LOM results. The simulation of wind-driven equatorial wave dynamics in the LOM reveals that the observed variability of the EIC can be largely explained by the equatorial basin resonance at the semiannual period, when the second baroclinic Rossby wave reflected from the eastern boundary intensifies the directly forced equatorial Kelvin and Rossby waves in the basin interior. The sum of the first 10 modes can reproduce the main features of the EIC. Among these modes, the resonant second baroclinic mode makes the largest contribution, which dominates the vertical structure, semiannual cycle, and westward phase propagation of the EIC. The other 9 modes, however, are also important, and the superposition of the first 10 modes produces downward energy propagation in the equatorial Indian Ocean
A new index for identifying different types of El Nino Modoki events
No full textEl Nio Modoki events can be further classified into El Nio Modoki I and II in terms of their opposite impacts on southern China rainfall (Wang and Wang, J Clim 26:1322-1338, 2013) and the Indian Ocean dipole mode (Wang and Wang, Clim Dyn 42:991-1005, 2014). The present paper develops an index to identify the types of El Nio events. The El Nio Modoki II (MII) index is defined as the leading principle component of multivariate empirical orthogonal function analysis of the normalized El Nio Modoki index, Nio4 index and 850 hPa relative vorticity anomalies averaged near the Philippine Sea during autumn. The MII index exhibits dominant variations on interannual (2-3 and 4-5 years) and decadal (10-20 years) timescales. El Nio Modoki II events can be well identified by using the MII index value being larger than 1 standard deviation. Further analyses and numerical model experiments confirm that the MII index can portray the major oceanic and atmospheric features of El Nio Modoki II events. The constructed MII index along with previous ENSO indices can be used for classifying and identifying all types of El Nio events. Because of distinct impacts induced by different types of El Nio events, the implication of the present study is that climate prediction and future climate projection under global warming can be improved by using the MII index and other indices to identify the types of El Nio events
Using Satellite Sensors and In Situ Observations to Monitor Phytoplankton Blooms in the Pearl River Estuary
No full textEutrophication in the Pearl River Estuary (PRE) has become severe with the rapid urbanization of the Pearl River Delta in recent years. As a result, large-scale phytoplankton blooms occur frequently because of eutrophication. This study investigated a massive Cochlodinium geminatum bloom near the mouth of the Pearl River in August 2011 based on data from both in situ measurements and satellites. Both methods provided a useful approach for monitoring phytoplankton blooms. The in situ measurements illustrated a high concentration of algal cells (1.5 x 10(7) cells L-1) in the study area, and the bloom reached dimensions of approximately 10 to 15 km in length, 8 to 10 km in width, and 100 km(2) in area based on continuous field measurements. A chlorophyll algorithm for satellite sensors was developed based on in situ chlorophyll concentrations and remote sensing reflectance data collected during six cruises from August 2009 to July 2010. The algorithm was applied to Medium Resolution Imaging Spectrometer full-resolution data at the daily scale (300 m at nadir) and obtained details regarding the spatial distribution and temporal variations of the phytoplankton bloom that were consistent with the in situ measurements. An abrupt shift in wind direction and an extreme drought increased the residence time of nutrients and led to the phytoplankton bloom
Interannual variability of significant wave height in the northern South China Sea
No full textBased on the hindcast data from third-generation wave model WAVEWATCH III, this study presents a notable interannual variability of significant wave height in the northern South China Sea. As indicated by the empirical orthogonal function analysis result of the significant wave height during 1976-2005, the first mode of this analysis captures a monopole structure with maximum amplitude in the southwestern Luzon Strait. Power spectrum analysis of the first empirical orthogonal function time series indicates that the significant wave height peaks at 2.67 and 8 year periods in the northern South China Sea. The first-time series had good correlation with El Nino events, with a correlation coefficient of -0.58. By comparing frequency and total duration of the intense tropical cyclones with the significant wave height in the northern South China Sea, it is revealed that the two were associated during 1978-1998 and that the recent increase of the significant wave height is due to the increase in total duration of intense tropical cyclones during 1999-2005. The sea level pressures also support the interannual variability of significant wave height in the northern South China Sea
A curvelet-based method to determine wave directions from nautical X-band radar images
No full textA new method to determine wave directions from nautical X-band images is proposed. The signatures of ocean waves show obvious scale and directional characteristics in nautical X-band radar images. Curvelet transform (CT) possesses very high scale and directional sensitivities. Therefore, it has good capability to analyze ocean wave fields. The radar images are decomposed at different scales, in different directions, and at different positions by CT, and curvelet coefficients are obtained. Given to the scale and directional characteristics of surface waves, the information of ocean waves is centralized in the curvelet coefficients of certain directions and at certain scales. Therefore, the wave orientations can be determined. The 180 ambiguity is removed by calculating crosscorrelation coefficients (CCCs) between continuous collected images. The proposed method is verified by the dataset collected on the Northwest coast of the Zhangzi Island in the Yellow Sea of China from March to April 2009
Spatial and seasonal distributions of bacterioplankton in the Pearl River Estuary: The combined effects of riverine inputs, temperature, and phytoplankton
No full textIn this study, we used flow cytometry and 16S rRNA gene pyrosequencing to investigate bacterioplankton (heterotrophic bacteria and picocyanobacteria) abundance and community structure in surface waters along the Pearl River Estuary. The results showed significant differences in bacterioplankton dynamics between fresh- and saltwater sites and between wet and dry season. Synechococcus constituted the majority of picocyanobacteria in both seasons. During the wet season, Synechococcus reached extremely high abundance at the mouth of the estuary, and heterotrophic bacteria were highly abundant (> 10(6) cells ml(-1)) throughout the studied region. At the same time, bacterioplankton decreased dramatically during the dry season. Pyrosequencing data indicated that salinity was a key parameter in shaping microbial community structure during both seasons. Phytoplankton was also an important factor; the proportion of Synechococcus and Rhodobacteriales was elevated at the frontal zone with higher chlorophyll a during the wet season, whereas Synechococcus were markedly reduced during the dry season
Acoustic impedance properties of seafloor sediments off the coast of Southeastern Hainan, South China Sea
No full textGeoacoustic parameters are essential inputs to sediment wave propagation theories and are vital to underwater acoustic environment and explorations of the sea bottom. In this study, 21 seafloor sediment samples were collected off the coast of southeastern Hainan in the South China Sea. The sound speed was measured using a portable WSD-3 digital sonic instrument and the coaxial differential distance measurement method. Based on the measured sound speed and physical properties, the acoustic impedance and the pore-water-independent index of impedance (IOI) were calculated in this study. Similar to the sound speed, the IOI values are closely related to the sediment physical properties and change gradually from the northwest to the southeast. The relations between IOI and physical properties were studied and compared to the relations between the sound speed and physical properties. IOI is better correlated to physical properties than sound speed. This study also uses an error norm method to analyze the sensitivity of IOI to the physical parameters in the double-parameter equations and finds that the most influential physical parameters are as follows: wet bulk density > porosity > clay content > mean particle size
Modern shallow water radiolarians with photosynthetic microbiota in the western North Pacific
No full textTo study the photosynthetic associations of modern radiolarians, we analyzed plankton samples from waters shallower than 200 m at 30 stations in the western North Pacific. A total of 328 taxa, including morphotypes, were identified from 2091 specimens. The fluorescence patterns under an epifluorescence microscope were mainly classified into five groups: 1) R & D; 2) R-G; 3) Y-B; 4) Periph-R; and 5) Pale-R. There were 37 species/morphotypes with the R&D pattern in the orders Collodaria, Entactinaria, Nassellaria, and Spumellaria. The R-G and Y-B patterns were confirmed in only four species (Dictyocoryne profunda, D. truncata, Spongaster tetras tetras, S. tetras irregularis) of our identified 328 taxa, suggesting a strong species-specific effect on the presence of PE-containing Synechococcus-type cyanobacteria. In the Periph-R pattern, red fluorescence is emitted from the peripheral part inside flat spumellarians, suggesting that the source of this pale red fluorescence is photosynthetic organisms digested by radiolarians. In particular, taxa with the R&D pattern can be classified into three groups: 1) obligate associations; 2) facultative associations; and 3) non-associations. Many taxa belonging to Acanthodesmiidae and Lophospyris have a great number of symbiotic dinoflagellates outside the central capsule. However, the Acanthodesmiidae includes non-photosynthetic holobionts (Amphispyris and Ceratobotrys borealis), suggesting different environmental adaptability in some acanthodesmiid species. In contrast with the obligate symbiosis tendency in Acanthodesmiidae, the Lophophaenidae tends to have non-photosynthetic holobionts. In Spumellaria, one significant tendency was recognized in Tetrapyle and Phorticium as obligate dinoflagellate holobionts. Thus, Tetrapyle and Phorticium are useful for tracing oceanographic conditions in the euphotic zone. Dictyocoryne truncata and D. profunda are classified into the R-G pattern, whereas D. muelleri was grouped into the R&D pattern, indicating that the difference in the photosynthetic association may be closely related to the dwelling depth. The Q-mode cluster analysis showed that the 30 stations were classified into four clusters: A1, A2, B, and C. The geographical distributions of the four cluster groups are consistent with the climate zone and water masses, suggesting that the species composition of these shallow taxa is influenced by the distribution of water masses. In particular, the Kuroshio Current may play an important role in the migration of shallow living radiolarian species from the subtropical climatic zone to the subarctic climatic zone