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The main objective of this study is to improve the retrieval of phytoplankton absorption coefficients using ocean and land color instrument (OLCI) bands (413, 443, 490, 510, 560, and 665 nm). In this study, the Raman-scattering correction was considered in an analytical forward model, and the corresponding Raman excitation OLCI band centers were calculated. The coefficients and exponents for the power law model of phytoplankton absorption were determined by a neural network classifier using a combination of sun elevation, photosynthetically active radiation, and remote sensing reflectance at OLCI bands (413, 443, 490, 510, 560, 620, 665, and 683 nm). Two optimizations were executed. The shape of the colored detrital matter (CDM) spectrum was allowed to change during the second optimization. Based on comparisons of the phytoplankton absorption coefficients at 443 nm (a Φ[443]) predicted by the improved inversion with field measurements taken from cruise surveys of the Pearl River estuary and Daya Bay and the SeaWiFS Bio-optical Archive and Storage System dataset and NASA bio-Optical Marine Algorithm Dataset, the modified inversion procedure could provide a good performance (r 2 = 0.86). The results showed that the contribution of Raman scattering to the remote sensing reflectance at 665 nm exceeded 22% in the open ocean. Moreover, the residual from the first optimization was compared with that from the second optimization, demonstrating that the variable CDM spectral slope in the analytical forward model could improve the accuracy of the forward model.

A coastal front was detected in the eastern Guangdong (EGD) coastal waters during a downwelling-favorable wind period by using the diffuse attenuation coefficient at 490 nm (Kd(490)). Long-term satellite data, meteorological data and hydrographic data collected from 2003 to 2017 were jointly utilized to analyze the environmental factors affecting coastal fronts. The intensities of the coastal fronts were found to be associated with the downwelling intensity. The monthly mean Kd(490) anomalies in shallow coastal waters less than 25 m deep along the EGD coast and the monthly mean Ekman pumping velocities retrieved by the ERA5 dataset were negatively correlated, with a Pearson correlation of − 0.71. The fronts started in October, became weaker and gradually disappeared after January, extending southwestward from the southeastern coast of Guangdong Province to the Wanshan Archipelago in the South China Sea (SCS). The cross-frontal differences in the mean Kd(490) values could reach 3.7 m−1. Noticeable peaks were found in the meridional distribution of the mean Kd(490) values at 22.5°N and 22.2°N and in the zonal distribution of the mean Kd(490) values at 114.7°E and 114.4°E. The peaks tended to narrow as the latitude increased. The average coastal surface currents obtained from the global Hybrid Coordinate Ocean Model (HYCOM) showed that waters with high nutrient and sediment contents in the Fujian and Zhejiang coastal areas in the southern part of the East China Sea could flow into the SCS. The directions and lengths of the fronts were found to be associated with the flow advection.

The hepatopancreatic disease in shrimp has caused great economic losses in recent years, and it is necessary to identify the responsible pathogen and establish control methods. The present study aimed to identify the primary pathogenic bacteria in diseased Litopenaeus vannamei hepatopancreas (HP) and to explore the protective effects of functional bacteria on shrimp. Four pathogenic Vibrio spp. were isolated and identified from shrimp with hepatopancreatic disease, of which Vibrio harveyi HAH could be the primary pathogen causing higher rates of mortality (~ 73%) with observed symptoms. In addition, HAH had five virulence-related genes: luxR, flaB, toxR, vhhA, and vhhB. Anti-Vibrio bacterium M146 and quorum quenching (QQ) bacterium W1B were screened and used as a feed supplement. The results showed that M146 and W1B (dosed at 1.0 × 107 CFU/g) decreased the mortality of shrimp after challenge with HAH. Supplementation with M146 significantly increased the activities of alkaline phosphatase (AKP) and lysozyme (LZM), whereas supplementation with W1B had no significant effect. AKP and acid phosphatase (ACP) activities of shrimp supplemented with W1B showed a significant increase after infection with HAH, whereas a decrease in the activities of AKP and superoxide dismutase (SOD) was observed in the negative control (NC). Supplementation with M146 and W1B significantly decreased the relative messenger RNA expression of Relish and TRAF6. However, after infection with HAH, the M146 and W1B groups exhibited a different pattern of gene expression regulation compared with that in the NC group, which might suggest weakening of the virulence of the pathogen. The results suggest that these two bacteria can protect L. vannamei and that M146 not only inhibited the growth of HAH but also had an immunostimulatory effect on shrimp. On contrast, W1B did not improve the immunity of shrimp, so it is speculated that it may protect the host by affecting the quorum sensing (QS) system of pathogenic bacteria.

The red band signal of the color spectrum is of significant interest because its remote sensing reflectance yields valuable information on phytoplankton. In this study, we combined a fluorescence model with a modified version of the Garver-Siegel-Maritorena (GSM) algorithm to retrieve the chlorophyll a concentration (Chla) and the magnitude of fluorescence in coastal waters. An analytical inverse optimization procedure was performed using the measured reflectance over the whole visible spectrum with a focus on the Ocean and Land Color Instrument (OLCI) sensor (from 413 to 709 nm). The coupled visible-infrared model (GSM&Fluo) was validated by a comparison with Chla that was measured in situ in a wide variety of productive coastal water conditions in the South China Sea. The coefficients of determination (r2) were 0.79 and 0.88 for the GSM and our algorithm, respectively. The combined approach produced more accurate results in our study location. The coupled GSM&Fluo model was able to avoid being trapped in a local optimum by adding an estimation of the fluorescence signal. The results also showed that the suspended particulate matter (SPM) played a major role in the magnitude of the reflectance peak in the chlorophyll fluorescence emission band, and the Fluorescence Line Height (FLH) calculated with a simple baseline approach tended to overestimate the true magnitude of the fluorescence emission as SPM increased.

The abundance of phytoplankton is generally estimated by measuring the chlorophyll-a concentration (Cchla), which is an important factor in photosynthesis and can be used to analyze the density and biomass of phytoplankton in the ecosystem. The band-ratio-based empirical or semi-analytical algorithms are operationally applied to retrieve Cchla in global oceans, which generally experience difficulties from the diversity of optical properties and the complexity of the radiative transfer equations in analytical analyses, respectively. With an attempt to develop an accurate Cchla retrieval model for the optically complex coastal and estuarine waters, this study aimed to explore the deep learning (DL) methods in satellite retrieval of Cchla. A two-stage convolutional neural network (CNN), named Cchla-Net, was proposed, which utilized the spectral information of remote sensing reflectances at MODIS/Aqua’s visible bands. In the first-stage phase, the Cchla-Net was pretrained by a set of remote sensing patches, in which the Cchla was generated from an existing model (OC3M). The pretrained results were than used as the initial values to refine the network with the synthetic oversampled in-situ dataset in the second-stage training phase. Using in-situ samples for training with the new initial values has a higher probability to reach the global optimum. The quantitative analyses showed that the two-stage training was more likely to achieve a global optimum in the optimization than the one-stage training. Matchups of the in-situ Cchla measurements were used to evaluate the retrieval models. Results showed that the proposed Cchla-Net produced obvious better performance than the empirical and semi-analytical algorithms, implying the DL method was more effective for optically complex waters with extremely high Cchla. This study provided an applicable method for remote sensing retrieval of Cchla, which should be helpful for studying the spatial distribution and temporal variability in the productive Pearl River estuary (PRE) waters.

This study investigates the acute responses of pacific white shrimp Litopenaeus vannamei to an abrupt reduction of salinity in osmosis-, metabolism-, and immune-related enzyme activities in the hemolymph of L. vannamei previously reared at 56‰ salinity. Three salinity reductions (56 to 54‰, 56 to 52‰, and 56 to 48‰) were used, and L. vannamei was directly transferred from the salinity of 56 to 54‰, 52‰, and 48‰, respectively. The hemolymph was collected from five shrimp in each group at 1 h, 6 h, 12 h, 18 h, 24 h, 36 h, and 48 h to detect the change of ATPase (including Na+/K+-ATPase and T-ATPase), alkaline phosphatase (AKP), acidic phosphatase (ACP), and superoxide dismutase (SOD) activities. Our results showed that no shrimp death occurred after an abrupt reduction of salinity. However, ATPase, SOD, ACP, and AKP enzyme activities in three salinity reductions all changed significantly, and the activities of T-ATPase and Na+/K+-ATPase showed a single peak trend during the process of experiment. The SOD activity peaked at 24 h after the salinity was decreased. ACP activities remained an increasing trend within 48 h after salinity was decreased in the three salinity treatments. A single peak trend was found in AKP activity and peaked at 18 h and then decreased significantly. The results indicate that an abrupt decrease in salinity significantly affected ATPase, SOD, ACP, and AKP activities. Osmotic, metabolism, and immune-related enzyme activities of L. vannamei are sensitive parameters to respond to an abrupt drop of salinity.

The Hong Kong-Zhuhai-Macau Bridge crosses the Pearl River Estuary and is the largest bridge and tunnel project in the world. During the construction period of this project, the excessive suspended sediment was found in the construction region. The suspended sediment generated by sand excavation in the upstream was assumed to have a significant impact on the suspended sediment in the tunnel region. In this study, we assessed the impact of upstream sand excavation on the suspended sediment in the Hong Kong-Zhuhai-Macau Bridge construction area using Landsat OLI, ETM+, and TM data. Regional suspended sediment algorithms were developed for Landsat using a symbolic regression method based on data from in situ measurements in the study area from 2003 to 2014. A band shift was conducted on the remote sensing reflectance data from Landsat ETM+ and OLI to produce a time series of the suspended sediment concentrations that was internally consistent with that of the Landsat TM data. The suspended sediment distribution was extracted and used to compare under two different conditions, with and without sand excavation. The correlations of the time series of the suspended sediment concentrations in different regions in the surrounding waters, including the correlations between the construction regions and the sand excavation regions, were calculated. Our results indicated that the sand excavation north of the Pearl River Estuary had a limited impact on the surface suspended sediment concentrations in the Hong Kong-Zhuhai-Macau Bridge tunnel area.

We evaluated six empirical and semianalytical models of the diffuse attenuation coefficient at 490 nm (Kd(490)) using an in situ dataset collected in the Pearl River estuary (PRE). A combined model with the most accurate performance (correlation coefficient, R2 = 0.92) was selected and applied for long-term estimation from 2003 to 2017. Physical and biological processes in the PRE over the 14-year period were investigated by applying satellite observations (MODIS/Aqua data) and season-reliant empirical orthogonal function analysis (S-EOF). In winter, the average Kd(490) was significantly higher than in the other three seasons. A slight increasing trend was observed in spring and summer, whereas a decreasing trend was observed in winter. In summer, a tongue with a relatively high Kd(490) was found in southeastern Lingdingyang Bay. In Eastern Guangdong province (GDP), the relatively higher Kd(490) value was found in autumn and winter. Based on the second mode of S-EOF, we found that the higher values in the eastern GDP extended westward and formed a distinguishable tongue in winter. The grey relational analysis revealed that chlorophyll-a concentration (Cchla) and total suspended sediment concentration (Ctsm) were two dominant contributors determining the magnitude of Kd(490) values. The Ctsm-dominated waters were generally located in coastal and estuarine turbid waters; the Cchla-dominated waters were observed in open clear ocean. The distribution of constituents-dominated area was different in the four seasons, which was affected by physical forces, including wind field, river runoff, and sea surface temperature.

Finding alternative measures to antibiotics for shrimp bacterial disease management is a current need. The application of quorum quenching (QQ) bacteria to prevent bacterial diseases in aquaculture is a current research hotspot, but the effect and mechanism of QQ bacteria in the practical application of shrimp farming requires further exploration. In the present study, in vitro and in vivo tests were conducted to comprehensively analyze the effect and mechanism of the QQ bacteria W1B (Cobetia sp.) in preventing shrimp vibriosis caused by Vibrio harveyi HAH. Cocultivation of strains W1B and HAH was used to conduct an in vitro test. Strain W1B and its intracellular and extracellular proteins could significantly reduce the concentration of quorum sensing (QS) signaling molecules (AHLs) of V. harveyi HAH without affecting its growth. The intracellular proteins of strain W1B could significantly reduce the expression of the QS regulatory gene luxR and virulence genes of strain HAH. An in vivo test was performed by adding strain W1B to shrimp culture water. Shrimp were cultured for 35 days, and then a challenge test was performed by injecting strain HAH into the shrimp. The results showed that strain W1B at low concentrations (1 × 104 CFU·mL−1) reduced the expression of shrimp immune genes and that high concentrations (1 × 106 CFU·mL−1) increased the expression of SOD, LZM, and IMD. In the challenge test, strain W1B could significantly reduce the mortality and protect the hepatopancreas epithelial cells of shrimp. Additionally, strain W1B could change the expression patterns of shrimp immune-related genes. The relative expression levels of the QS regulatory gene and virulence genes of strain HAH in the shrimp hepatopancreas were significantly downregulated by strain W1B. Additionally, strain W1B significantly reduced the relative expression of shrimp apoptosis-related genes. The above results indicated that QQ strain W1B could inhibit the transcriptional expression of V. harveyi luxR and induce the downregulation of virulence gene expression, thereby reducing V. harveyi pathogenicity. Ultimately, strain W1B could reduce shrimp mortality. These findings can provide new methods and basic data for the prevention and treatment of shrimp bacterial diseases.

A support vector machine (SVM) regression algorithm was developed for estimating the chlorophyll-a concentration (Cchla) in the turbid estuarine waters of the Pearl River estuary (PRE) based on visible infrared imaging radiometer suite (VIIRS) ocean color data. The proposed SVM algorithm outperformed the OC3 algorithm in the turbid waters. The temporal variation and spatial distribution of SVM-based monthly Cchla products were determined during 2012 and 2018. By analyzing the monthly average Cchla products and ancillary data, the underlying mechanisms of the Cchla coastal summer plume jet and winter bloom were revealed. The Cchla coastal plume jet was often observed in June, when the zonal wind direction changed from westward to eastward and the river runoff reached its maximum value of the year. The winter bloom in the ocean area was attributed to strong mixing in the upper layer, which resulted from cooling-induced buoyancy changes.

Remote-sensing of ocean colour has an advantage over any other biological data source for monitoring long-term global changes in phytoplankton biomass, due to its spatial and temporal sampling capabilities. Chlorophyll-a concentration (Chl-a) provide a proxy for phytoplankton biomass. The Operational Land Imager (OLI) is a multispectral radiometer hosted on the recently launched Landsat8 satellite, which is a potential tool for ocean color radiometry because it includes narrow band, high signal-to-noise ratios (SNRs) and the addition of a band centered at 443 nm, has competitive advantage in phytoplankton pigment Chl-a estimation compare with previous Landsat instruments. The aim of this work was to evaluate the performance of the standard NASA algorithm OC3 type for Landsat-8 OLI in determining Chl-a concentrations in both turbid estuary and clear open sea waters of the north South China Sea, in which the empirical coefficients were tuned by using field data and used 443-, 561-, and 655nm bands instead of 443-, 482 and 561nm bands. The standard OC3-based algorithm for OLI performed well in the Southeast continental shelf of Hainan Island (HNI). While empirical algorithm should be developed in the Pearl River estuary (PRE), and the comparisons between estimated and in situ measured Chl-a produced R2 reaching 0.88 and APD

An empirical algorithm is proposed to estimate suspended particulate matter (SPM) ranging from 0.675 to 25.7 mg L-1 in the turbid Pearl River estuary (PRE). Comparisons between model predicted and in situ measured SPM resulted in R2s of 0.97 and 0.88 and mean absolute percentage errors (MAPEs) of 23.96% and 29.69% by using the calibration and validation data sets, respectively. The developed algorithm demonstrated the highest accuracy when compared with existing ones for turbid coastal waters. The diurnal dynamics of SPM was revealed by applying the proposed algorithm to reflectance data collected by a moored buoy in the PRE. The established algorithm was implemented to Hyperspectral Imager for the Coastal Ocean (HICO) data and the distribution pattern of SPM in the PRE was elucidated. Validation of HICO-derived reflectance data by using concurrent MODIS/Aqua data as a benchmark indicated their reliability. Factors influencing variability of SPM in the PRE were analyzed, which implicated the combined effects of wind, tide, rainfall, and circulation as the cause.

A MODIS-based algorithm was developed to investigate the impact of Typhoon Vicente on the total suspended solid concentration in the Pearl River Estuary. This algorithm used two high resolution bands at 645 nm and 555 nm to map the concentrations. Regression between the remote sensing reflectance and in situ total suspended solid concentration showed good correlation (R2 = 0.91), indicating that the algorithm was valid for the high turbid waters in the Pearl River Estuary. MODIS-derived maps showed different total suspended solid concentration anomalies in different sub-regions of the estuary during the passage of Typhoon Vicente. In western inlets, the increase of total suspended solids (maximum values of 22.20 g m−3 before and 55.71 g m−3 after the typhoon) was possibly related to the larger rainfall discharge from the Pearl River. In Lingdingyang, the increase of total suspended solids (maximum values of 19.60 g m−3 before and 44.59 g m−3 after the typhoon) might be the result of typhoon-induced resuspension. In the southeastern portion of the Estuary, due to the typhoon-induced current, a significant decrease of total suspended solid area (decreased by 10 g m−3) was observed. Different changes were observed in different sub-regions under the influence of the typhoon, implying the complicated hydrological environment is an important feature in the Pearl River Estuary.

Based on a modified Vertically Generalized Production Model (VGPM), the primary productivity in the Pearl River Estuary, China, was estimated using the Moderate Resolution Imaging Spectroradiometer (MODIS) data. A regional parameterization of euphotic depth from diffuse attenuation coefficient at 490 nm was developed in order to improve the accuracy of VGPM. An empirical algorithm using the fluorescence line height to retrieve chlorophyll-a concentration was also employed for the estuarine waters. The modified VGPM was applied to MODIS data for primary productivity estimation. The results indicated a higher productivity in summer and autumn. The average values of the primary productivity in summer and autumn were over 300 mg m−2 day−1 while in spring and winter, the values were about 250 mg m−2 day−1.

Understanding the optical properties of polluted sea ice is important for analyzing remote sensing data, and studying energy balance. Liaodong Bay in China provides a kind of representative of "dirty" sea ice for there are many industrial and residential areas surrounding it. Optical properties of sea ice were observed. Albedos for different types of sea ice surface were obtained, and their peaks would tend to shift to longer wavelengths for the high concentrations of PM and CDOM in sea ice. Upwelling (K-u) and downwelling (K-d) irradiance extinction coefficients profiles were obtained in situ with a self-made instrument. At 586 nm, the maximum K-u reached 13.68 m(-1) in a layer close to ice bottom, while the maximum K-d reached 15.52 m(-1) in surface layer. Because understanding the energy distribution in sea ice is important to research mass budget in air-ice-sea, solar radiance distribution in sea ice was observed in a series of bored holes in situ. From 4 cm to ice bottom, the logarithms of radiance profiles almost decrease linearly with increasing the path length of light transfer. Because sea ice is a highly scattering medium and the effects of scattering become stronger with increasing depth, the dependence of scattering light on scattering angle (theta) becomes weaker with increasing depth. An optical model was brought forward to describe the solar radiance distribution at a random depth and theta. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Internal waves can bring nutrients to the upper level of water bodies and facilitate phytoplankton photosynthesis. Internal waves occur frequently in the northern portion of the South China Sea and inflict an important effect on chlorophyll a distribution. In this study, in-situ observation and satellite remote sensing data were used to study the effects of internal waves on chlorophyll a distribution. Based on the in-situ observations, lower chlorophyll a concentrations were present in the middle and bottom level in areas in which internal waves occur frequently, while the surface chlorophyll a distribution increased irregularly, and a small area with relatively higher chlorophyll a concentrations was observed in the area around the Dongsha Island. Satellite remote sensing showed that the chlorophyll a concentration increased in the area near Dongsha Island, where internal waves frequently occurred. The results of the increased chlorophyll a concentration in the surface water near Dongsha Island in the northern portion of the South China Sea indicated that internal waves could uplift phytoplankton and facilitate phytoplankton growth.