Using sea surface salinity (SSS) observation from the soil moisture active passive (SMAP) mission, we analyzed the spatial distribution and seasonal variation of SSS around Changjiang River (Yangtze River) Estuary for the period of September 2015 to August 2018. First, we found that the SSS from SMAP is more accurate than soil moisture and ocean salinity (SMOS) mission observation when comparing with the in situ observations. Then, the SSS signature of the Changjiang River freshwater was analyzed using SMAP data and the river discharge data from the Datong hydrological station. The results show that the SSS around the Changjiang River Estuary is significantly lower than that of the open ocean, and shows significant seasonal variation. The minimum value of SSS appears in July and maximum SSS in December. The root mean square difference of daily SSS between SMAP observation and in situ observation is around 3 in both summer and winter, which is much lower than the annual range of SSS variation. In summer, the diffusion direction of the Changjiang River freshwater depicted by SSS from SMAP is consistent with the path of freshwater from in situ observation, suggesting that SMAP observation may be used in coastal seas in monitoring the diffusion and advection of freshwater discharge.

Ciliates are important components in planktonic food webs, but our understanding of their community structures in different oceanic water masses is limited. We report pelagic ciliate community characteristics in three seas: the tropical West Pacific, the Bering Sea and the Arctic Ocean. Planktonic ciliate abundance had “bimodal-peak”, “surface-peak” and “DCM (deep chlorophyll a maximum layer)-peak” vertical distribution patterns in the tropical West Pacific, the Bering Sea and the Arctic Ocean, respectively. The abundance proportion of tintinnid to total ciliate in the Bering Sea (42.6%) was higher than both the tropical West Pacific (7.8%) and the Arctic Ocean (2.0%). The abundance proportion of small aloricate ciliates (10–20 μm size-fraction) in the tropical West Pacific was highest in these three seas. The Arctic Ocean had higher abundance proportion of tintinnids in larger LOD (lorica oral diameter) size-class. Proportion of redundant species increased from the Arctic Ocean to the tropical West Pacific. Our result provided useful data to further understand ecology roles of planktonic ciliates in different marine habitats.

Transitional ecosystems, estuaries and the coastal seas, are distinctively affected by natural and anthropogenic factors. Organic matter (OM) originating from terrestrial sources is exported by rivers and forms a key component of the global biogeochemical cycles. Most previous studies focused on the bulk biochemical and anthropogenic aspects affecting these ecosystems. In the present study, we examined the sources and fate of OM entrained within suspended particulate matter (SPM) of the Zuari River and its estuary, west coast of India. Besides using amino acid (AA) enantiomers (L- and D-forms) as biomarkers, other bulk biochemical parameters viz. particulate organic carbon (POC), δ¹³C, particulate nitrogen (PN), δ¹⁵N and chlorophyll a were analyzed. Surprisingly no significant temporal variations were observed in the parameters analyzed; nonetheless, salinity, POC, δ¹³C, PN, δ¹⁵N, glutamic acid, serine, alanine, tyrosine, leucine and D-aspartic acid exhibited significant spatial variability suggesting source differentiation. The POC content displayed weak temporal variability with low values observed during the post-monsoon season attributed to inputs from mixed sources. Estuarine samples were less depleted than the riverine samples suggesting contributions from marine plankton in addition to contributions from river plankton and terrestrial C₃ plants detritus. Labile OM was observed during the monsoon and post-monsoon seasons in the estuarine region. More degraded OM was noticed during the pre-monsoon season. Principal component analysis was used to ascertain the sources and factors influencing OM. Principally five factors were extracted explaining 84.52% of the total variance. The first component accounted for 27.10% of the variance suggesting the dominance of tidal influence whereas, the second component accounted for heterotrophic bacteria and their remnants associated with the particulate matter, contributing primarily to the AA pool. Based on this study we ascertained the role of the estuarine turbidity maximum (ETM) controlling the sources of POM and its implications to small tropical rivers. Thus, changes in temporal and regional settings are more likely to affect the natural biogeochemical cycles of small tropical rivers.

The Lake Tian E Zhou (TEZ, an oxbow lake) was formed during the rerouting of the Changjiang River in 1972, with strong influences from the main river channel and flood events. Herein, a sediment core was collected from the Lake TEZ for the measurements of carbon isotopes and biomarkers, including stable carbon isotopes (δ¹³C), radiocarbon composition (∆¹⁴C), and lignin phenols, as well as lead-210 to reconstruct recent heavy flood events over the past 70 years. At the 24–26 cm interval, the sediment contained the highest OC%, TN%, and lignin phenols content, as well as significantly depleted ¹³C but enriched ¹⁴C, corresponding to the extreme flood event in 1998. In addition, statistics from t-test showed that lignin phenols normalized to OC (Λ8), the concentration of 3, 5-dihydroxy benzoic acid (3, 5-BD), and the ratio of p-hydroxy benzophenone to total hydroxyl phenols (PHB/HP) were all significantly different between the layers containing flood deposits and the layers deposited under normal non-flood conditions (p<0.05). These results indicate that the later three parameters are highly related to flood events and can be used as compelling proxies, along with sediment chronology, for hydrological changes and storm/flood events in the river basin and coastal marine environments.

Vertical variability in the bio-optical properties of seawater in the northern South China Sea (NSCS) including inherent optical properties (IOPs) and chlorophyll a concentration (Chl) were studied on the basis of in situ data collected in summer 2008 using an absorption/attenuation spectrophotometer. An empirical model was developed to estimate Chl profiles based on the absorption line height at long wavelengths, with a relative root mean square error of 37.03%. Bio-optical properties exhibited large horizontal and vertical spatial variability. As influenced by coastal upwelling and the Zhujiang River (Pearl River) discharge, both IOPs and Chl exhibited high values in the surface waters of the inner shelf, which tended to decrease with distance offshore. Subsurface maximum layers of IOPs and Chl were observed in the middle and outer shelf regions, along with significantly higher values of attenuation coefficients beneath this layer that rapidly increased towards the bottom. In the open ocean, both IOPs and Chl exhibited consistent variability, with the subsurface maximum layer typically located at 34–84 m. Phytoplankton were found to be one of the major components in determining the vertical variability of bio-optical properties, with their vertical dynamics influenced by both physical forcing and light attenuation effects. The depth of the subsurface maximum layer was found to be closely related to the fluctuation of the oceanic thermocline and the depth of the euphotic zone, which also affected the total integrated biomass of the upper ocean. Typically high values of attenuation coefficients observed in the bottom waters of the continental shelf reflected the transport of particulate matter over the bottom boundary layer. Our results reveal large spatial differences in bio-optical profiles in response to complex marine ecodynamics in the NSCS. From the perspective of marine research, high-resolution optical measurements are clearly advantageous over conventional bottle sampling.

The ridgetail white prawn Exopalaemon carinicauda is a euryhaline shrimp species in the estuarine and coastal areas of China. In this study, survival rates, transcription levels of two prophenoloxidase system-related genes (EcLGBP and EcproPO) and PO activity were determined quantitatively in juvenile and adult E. carinicauda under different salinity levels. The results showed that E. carinicauda juveniles could survive in a wider range of salinity conditions than adults. For juvenile E. carinicauda, the expression levels of EcLGBP and EcProPO were up-regulated in low salinities and showed no significant difference at 20–40, while PO activities in low salinities were higher compared to those in high salinities. For adult E. carinicauda, the expression profiles of EcLGBP and EcproPO had a different trend of up-regulation in salinity stress treatments and no obvious difference was observed in the gene expression levels and PO activity between 30 and 40. The salinity tolerance range of immunity for juvenile and adult E. carinicauda is 20–40 and 30–40, respectively.

Food differentiation among coexistent species in the field is important strategy for copepods to acquire materials and maintain population stabilization. In situ diet analysis of co-occurring six copepod species in coral waters of the Sanya Bay was conducted using a PCR protocol based on 18S ribosomal gene. Various prey organisms were uncovered, including dinoflagellate, diatom, green algae and plant, protozoa and metazoan. All these spatially co-existing six species showed different dietary diversity, with the food niche breadth (B) ranging from 1.00 (Temora turbinate in morning) to 10.68 (Calanopia elliptica in night). While food overlap between all these copepods were low, with the average value of the diet niche overlap index being approximately 0.09. Even temporally co-existing species sampled from the same time point fed on different groups of prey items with the food overlap index of 0.04 to 0.07 in midday and night but 0 in morning. As the most important dominant copepod in the Sanya Bay, Subeucalanus subcrassus seems to be capable to regulate its feeding, by exhibiting a rhythm of herbivorous feeding in midday and carnivorous feeding in morning and night, to better coordinate with other competitors for utilization of food resources. For most copepods, none of the prey items belonged to the dominant phytoplankton in the ambient water, indicating that copepod can better their survival by widening the choice of potential food resources in food limited environment. The dietary separation observed here might be important strategy for copepod to maintain population stabilization and thriving in the Sanya coastal waters.

Halocyprid ostracods are appreciable part of ostracods floating through virtually everywhere in marine environment. In this study, we describe a new species of genus Polyconchoecia Xiang, Chen and Du, 2018, tribe Conchoeciini Chavtur and Angel, 2011, family Halocyprididae Dana, 1853 from the middle of the South China Sea. Polyconchoecia chenii sp. nov. is very close to P. commixtus Xiang, Chen and Du, 2018. But it differs from P. commixtus by the distinctions of locations of major glands of carapace and the characteristics of appendages: more posteriorly situated left asymmetric gland of carapace, no right asymmetric gland; segmented frontal organ; the endopod 2 of the first antenna with a very small seta; a- and c-setae of the first antenna with long end joint have long end joint, the b- and d-setae have no end joint, spinose e-seta without end joint; the e-seta of the second antenna is present; teeth side is distinctive; the setal counts of the mandible, maxilla, fifth limb, and sixth limb are individual. The locations of the major glands on carapace and the characteristics of the first antenna can be the key of the new species. This work is the second discovery of the genus Polyconchoecia from the world.

The samples of Anthomedusae were collected from the Guangdong coastal water, China. Three new species of Anthomedusae, i.e. Zhangiella condensum Huang, Zhang et Sun, sp. nov., Hydractinia leizhouensis Huang, Zhang et Yang, sp. nov., and Cladosarsia simplex Huang, Zhang et Ke, sp. nov. are described. All type specimens are deposited in College of Ocean and Earth Sciences, Xiamen University.