The correlation of ambient noise with wind speed, and the depth dependence of ambient noise are both investigated, where the ocean noise data were recorded by a vertical line array in the northern South China Sea. It is shown that the correlation coefficients increase with increasing hydrophone depth during typhoon periods when the frequency ≥ 250 Hz, which opposes the generally accepted knowledge that the correlation coefficients of noise level and wind speed decrease with increasing depth during non-typhoon periods. Particularly at frequencies of 250 Hz, 315 Hz and 400 Hz, the correlation coefficients increase by more than 0.05 at depths ranging from 155 m to 875 m. At the three frequencies, the average noise levels also increase with increasing depth during typhoon periods. It is suggested that these differences are attributed to the wind-generated noise in shallow waters and the effect of “downslope enhancement” to sound propagation. During typhoon periods, the surf breaking and surf beat upon the shores and reefs are strengthened, and the source levels are increased. The wind-generated noise in shallow waters interacts with the downslope sea floor, with the noise-depth distribution changed by a “downslope enhancement” effect promoting noise propagation.

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.

Seasonal fishing closures are often used in fisheries management to conserve overfished stocks. As one of the unintended consequences, fishermen often contend for maximizing catches immediately after reopening fisheries. The resultant large catch landings in a short time period (i.e., pulse fishing) may undermine the benefit of closure. We implemented an end-to-end model OSMOSE-JZB (Object-oriented Simulator of Marine ecOSystem Exploitation OSMOSE) modelling ecosystem in the Jiaozhou Bay located in China to evaluate the impact of pulse fishing on the effectiveness of seasonal closure at levels of fish community, population, and individual. Our study demonstrated that the three-month closure was successful in conserving fish stocks. There were small variations on ecological indicators (i.e., total biomass of the community, mean trophic level of the community, mean trophic level of the catch, and Shannon-Wiener biodiversity index) when pulse fishing occurred. Pulse fishing seemed not to result in a great shift in community structure. Compared to other species, the biomass of two large predatory fishes were more susceptible to pulse fishing. Pulse fishing could change the pressure of predators to fish stocks via food webs, especially for young individuals. Our simulations indicate that we can improve the effectiveness of seasonal closure by managing pulse fishing. Although the results derived in this study may be specific to the target ecosystem, the general approach is applicable to other ecosystems when evaluating fishing impacts.

Most of reported harmful algal blooms (HABs) of microalgae (75%) have been caused by dinoflagellates. Studies on the negative effects of HABs have generally focused on animals, valuable organisms in particular, and environmental factors such as dissolved oxygen and nutrients, but relatively fewer on community level, particularly that using metagenomic approach. In this study, we reported an investigation on the effects of a HAB caused by the dinoflagellate Prorocentrum donghaiense on the species diversity and community structure of the dinoflagellate sub-community via a pyrosequencing approach for the samples taken before, during, and after the bloom season of P. donghaiense in the East China Sea. We sequenced partial 28S rRNA gene of dinoflagellates for the field samples and evaluated the species richness and diversity indices of the dinoflagellate community, as a sub-community of the total phytoplankton. We obtained 800 185 valid sequences (categorized into 560 operational taxonomic units, OTUs) of dinoflagellates from 50 samples and found that the biodiversity of dinoflagellate community was significantly reduced during the blooming period in comparison to that in pre- and after-blooming periods, as reflected in the four diversity indices: the species richness expressed as the number of OTUs, Chao1 index, Shannon index (evenness), and Gini-Simpson index. These four indices were all found to be negatively correlated to the cell density of the bloom species P. donghaiense. Correlation analyses also revealed that the P. donghaiense cell abundance was correlated negatively with ${\rm{NO}}_3^- $-N, and ${\rm{NO}}_2^- $-N, but positively with total nitrogen (TN) and total phosphorus (TP). Principal coordinates analysis (PCoA) showed that the community structure of dinoflagellates was markedly different among the different sampling periods, while the redundancy analysis (RDA) revealed P. donghaiense abundance, salinity, ${\rm{NO}}_3^- $-N, and ${\rm{SiO}}_3^{2-} $ were the most four significant factors shaping the dinoflagellate community structure. Our results together demonstrated that HABs caused by the dinoflagellate P. donghaiense could strongly impact the aquatic ecosystem on the sub-community level which the blooming species belongs to.

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.

Epizoic diatoms on marine copepods are common in nature and may have a special ecological relationship with their hosts. However, this special ecological group is not well known, and it has only rarely been studied in the China seas. To address this knowledge gap, the species diversity and classification of epizoic diatoms on planktonic copepods were studied with samples collected from the East China Sea. In the present study, a marine araphid diatom genus Protoraphis and its type species, Pr. hustedtiana, were observed and identified by light and electron microscopy, thus representing the first record of this genus and its type species in China. This genus is characterized by a median sternum strongly bent to opposite sides and terminate in two transapical grooves at the valve ends. Protoraphis hustedtiana was found to be epizoic on the posterior body appendages and segments of the marine calanoid copepod Candacia bradyi. An internal view shows a complex, ear-shaped process that is close to the apical slit field. The ecological habitats and geographical distributions of Protoraphis were also discussed, and, together with complementary morphological studies, our results have increased the number of records for marine epizoic diatoms to three genera with three species in China, including Pseudohimantidium and Pseudofalcula.

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.

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.

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.