Institutional Repository of South China Sea Institute of Oceanology, CAS
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Effects of intensive mariculture on the sediment environment as revealed by phytoplankton pigments in a semi-enclosed bay, South China Sea
No full textPhytoplankton pigment concentrations in the sur-face sediments of a fish and oyster farm in Dapeng Cove, South China Sea, were measured monthly to investigate the effects of mariculture on the envi-ronment from December 2011 to December 2012. The highest contents of the identified phytopig-ments, sulphides and total organic carbon in the surface sediments were all found at the fish farm, followed by the oyster farm; the lowest contents were detected at the control site. Fucoxanthin in the surface sediments was the most abundant car-otenoid and was significantly correlated with chlorophyll a (Chl a; r = 0.922, P < 0.01). This finding suggested that the deposited diatoms could be the main source of the Chl a concentration. Besides a differential sedimentation of phytoplank-ton (i. e. higher downflux at fish and oyster site than that at control site), we assume that the extent of pigment diminution from the fish site to control site was also controlled by the chemical conditions of the surface sediments. The fish farm provided the most optimum preservation condi-tions for the phytopigments and was a good sink for phytodetritus among the three sites because of its anoxic and reductive characteristics. Phyto-plankton pigments could be useful biomarkers to evaluate the influence of mariculture on sediment environment
A comparative study of the survival, growth and gonad development of the diploid and triploid Hong Kong oyster, Crassostrea hongkongensis (Lam & Morton 2003)
No full textThe Hong Kong oyster, Crassostrea hongkongensis is an economically important and widely cultivated oyster species in southern China. Aiming to improve the aquaculture potentials of C.hongkongensis, a triploid organism was generated by inhibiting the second polar body formation in the fertilized eggs, using 0.5mgL(-1) cytochalasin B. Triploids exhibited significantly higher growth and were larger than the diploids throughout the life cycle. Much of the triploid growth advantage can be attributed to resource reallocation to structural development due to gonadal sterility. Most of the triploid oysters exhibited polymorphic sterility with atrophic gonads and abnormal gametogenesis. Only few dysfunctional' sperms were produced by the triploid males, thus ruling out reproductive and genetic contamination of natural oyster populations from triploid cultivations. This advantage in addition to the superior growth of triploids makes it a potent alternative in Hong Kong oyster aquaculture industry. Triploid survival was mostly found to be similar to that of diploids except for day 360, when a significant triploid advantage in terms of survival was noted. Furthermore, we found that growth and survival of Hong Kong oyster is significantly higher at the Zhuhai site in comparison to the Beihai site. Our results indicate a strong environmental effect in Hong Kong oyster cultivation and points to the fact that Zhuhai site was more suitable for oyster farming than the Beihai site. Overall, this study provides valuable information to the aquaculture industry of southern China
Metagenomic Insights into Effects of Chemical Pollutants on Microbial Community Composition and Function in Estuarine Sediments Receiving Polluted River Water
No full textPyrosequencing and metagenomic profiling were used to assess the phylogenetic and functional characteristics of microbial communities residing in sediments collected from the estuaries of Rivers Oujiang (OS) and Jiaojiang (JS) in the western region of the East China Sea. Another sediment sample was obtained from near the shore far from estuaries, used for contrast (CS). Characterization of estuary sediment bacterial communities showed that toxic chemicals potentially reduced the natural variability in microbial communities, while they increased the microbial metabolic enzymes and pathways. Polycyclic aromatic hydrocarbons (PAHs) and nitrobenzene were negatively correlated with the bacterial community variation. The dominant class in the sediments was Gammaproteobacteria. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) enzyme profiles, dominant enzymes were found in estuarine sediments, which increased greatly, such as 2-oxoglutarate synthase, acetolactate synthase, inorganic diphosphatase, and aconitate hydratase. In KEGG pathway profiles, most of the pathways were also dominated by specific metabolism in these sediments and showed a marked increase, for instance alanine, aspartate, and glutamate metabolism, carbon fixation pathways in prokaryotes, and aminoacyl-tRNA biosynthesis. The estuarine sediment bacterial diversity varied with the polluted river water inputs. In the estuary receiving river water from the more seriously polluted River Oujiang, the sediment bacterial community function was more severely affected
Benthic habitat health assessment using macrofauna communities of a sub-tropical semi-enclosed bay under excess nutrients
No full textThis research was conducted to assess the ecosystem health of Daya Bay benthic habitat, investigate the effects of anthropogenic nutrients, and evaluate the application of ecological indicators for benthic health assessment. Environmental indicators and macrobenthic communities, were investigated during summer and winter 2015. Results indicated a strong seasonality in biotope of intertidal and subtidal zones. Lower macrobenthic diversity were calculated from subtidal inner bay, reflecting the effects of anthropogenic nutrients. However, intertidal sites in that part were indicated to be in a relatively healthier ecological status. Seasonal effects of excess nutrients on benthic habitat were reflected in ecological indicators. It is concluded that the excess nutrients at spatiotemporal scales, influences on the health of benthic habitat. Eventually, it is recommended by this research that, with considering the natural/anthropogenic circumstances, the taxonomic and phylogenetic ecological indicators would be helpful tools to evaluate the benthic health of a typical sub-tropical semi-enclosed bay. (C) 2017 Elsevier Ltd. All rights reserved
Characterization of the flavoenzyme XiaK as an N-hydroxylase and implications in indolosesquiterpene diversification
No full textFlavoenzymes are ubiquitous in biological systems and catalyze a diverse range of chemical transformations. The flavoenzyme XiaK from the biosynthetic pathway of the indolosesquiterpene xiamycin A is demonstrated to mediate the in vivo biotransformation of xiamycin A into multiple products, including a chlorinated adduct as well as dimers characterized by C-N and N-N linkages that are hypothesized to form via radical-based mechanisms. Isolation and characterization of XiaK in vitro shows that it acts as a flavin-dependent N-hydroxylase that catalyzes the hydroxylation of xiamycin A at the carbazole nitrogen to form N-hydroxyxiamycin, a product which was overlooked in earlier in vivo experiments because its chemical and chromatographic properties are similar to those of oxiamycin. N-Hydroxyxiamycin is shown to be unstable under aerobic conditions, and characterization by electron paramagnetic resonance spectroscopy demonstrates formation of an N-hydroxycarbazole radical adduct. This radical species is proposed to serve as a key intermediate leading to the formation of the multiple xiamycin A adducts. This study suggests that non-enzyme catalyzed reactions may play a greater role in the biosynthesis of natural products than has been previously recognized
Comparative study of Rhodamine B degradation by the systems pyrite/H2O2 and pyrite/persulfate: Reactivity, stability, products and mechanism
No full textThis study makes a comparison between the pyrite/H2O2 and pyrite/persulfate (PS) Fenton systems to investigate the degradation of Rhodamine B (RhB). The most relevant findings revealed that a significantly negative effect of carbonate and a narrow pH range of 2-4 were found in the pyrite/H2O2 system, whereas a relatively less negative effect of carbonate and a broad pH range of 2-11 were observed in the pyrite/PS system. It was demonstrated that the pyrite catalyst in the pyrite/PS system exhibited better structural stability and showed a relatively limited loss in performance upon reuse as compared to pyrite in the pyrite/H2O2 system. Experiments with different scavengers indicated that HO center dot radicals were the major reactive species responsible for RhB degradation by pyrite/H2O2. In this case the contribution of radical was in the order of HOHO center dot > O-2(center dot-) whereas the SO4 center dot- radicals prevailed over HO center dot in the pyrite/PS system. The role of O-2(center dot-) in the recycling of Fe(III) to Fe(II) was very important. The possible mechanism for RhB degradation by pyrite/H2O2 mainly involves the reaction of the dissolved Fe2+ released by the surface of the pyrite with added H2O2, whereas the reaction of the dissolved Fe2+ formed in the pyrite with PS triggers degradation in the pyrite/PS system. The degradation of RhB is initiated in both cases by N-deethylation, chromophore cleavage and ring opening processes, which leads to the production of a series of oxidation products with smaller molecular sizes. The pyrite/PS system is here proven to be a superior heterogeneous Fenton-like oxidant process for the removal of dyes from wastewater. (C) 2017 Elsevier B.V. All rights reserved
Analyzing the influences of two types of El Nino on Tropical Cyclone Genesis with a modified genesis potential index
No full textTo understand the impacts of large-scale circulation during the evolution of El Nino cycle on tropical cyclones (TC) is important and useful for TC forecast. Based on best-track data from the Joint Typhoon Warning Center and reanalysis data from National Centers for Environmental Prediction for the period 1975-2014, we investigated the influences of two types of El Nino, the eastern Pacific El Nino (EP-El Nino) and central Pacific El Nino (CP-El Nino), on global TC genesis. We also examined how various environmental factors contribute to these influences using a modified genesis potential index (MGPI). The composites reproduced for two types of El Nino, from their developing to decaying phases, were able to qualitatively replicate observed cyclogenesis in several basins except for the Arabian Sea. Certain factors of MGPI with more influence than others in various regions are identified. Over the western North Pacific, five variables were all important in the two El Nino types during developing summer (July-August-September) and fall (OctoberNovember-December), and decaying spring (April-May-June) and summer. In the eastern Pacific, vertical shear and relative vorticity are the crucial factors for the two types of El Nino during developing and decaying summers. In the Atlantic, vertical shear, potential intensity and relative humidity are important for the opposite variation of EP- and CP-El Ninos during decaying summers. In the Southern Hemisphere, the five variables have varying contributions to TC genesis variation during peak season (January-February-March) for the two types of El Nino. In the Bay of Bengal, relative vorticity, humidity and omega may be responsible for clearly reduced TC genesis during developing fall for the two types and slightly suppressed TC cyclogenesis during EP-El Nino decaying spring. In the Arabian Sea, the EP-El Nino generates a slightly positive anomaly of TC genesis during developing falls and decaying springs, but the MGPI failed to capture this variation
Deep seismic structure of the northeastern South China Sea: Origin of a high-velocity layer in the lower crust
No full textWe present a 2-D seismic tomographic image of the crustal structure along the OBS2012 profile, which delineates the Moho morphology and magmatic features of the northeastern South China Sea margin. The image was created by forward modeling (RayInvr) and traveltime tomographic inversion (Tomo2D). Overall, the continental crust thins seaward from similar to 27 km to similar to 21 km within the continental shelf across the Zhu I Depression and Dongsha Rise, with slight local thickening beneath the Dongsha Rise accompanying the increase in the Moho depth. The Dongsha Rise is also characterized by similar to 4-7 km thick high-velocity layer (HVL) (similar to 7.0-7.6 km/s) in the lower crust and exhibits a relatively high velocity (similar to 5.5-6.4 km/s) in the upper crust with a velocity gradient lower than those of the Zhu I Depression and Tainan Basin. Across the continental slope and continent-ocean transition (COT), which contain the Tainan Basin, the crust sharply thins from 20km to 10km seaward and a similar to 2-3 km thick HVL is imaged in the lower crust. We observed that volcanoes are located only within the COT, but none exist in the continental shelf; the Dongsha Rise exhibits a high magnetic anomaly zone and different geochemical characteristics from the COT. Based on those observations, we conclude that the HVL underlying the COT is probably extension related resulting from the decompression melting in the Cenozoic, whereas the HVL beneath the Dongsha Rise is probably arc related and associated with the subduction of the paleo-Pacific plate. These findings are inconsistent with those of some previous studies. Plain Language Summary We show a seaward thinning trending of the crustal structure across the continental shelf and continent-ocean transition (COT), whereas the crust was slightly and unconventionally thickened beneath the Dongsha Rise accompanying the increase in the Moho depth. The Dongsha Rise is also characterized by similar to 4-7 km thick high-velocity layer (HVL) in the lower crust underlying the thick crust. In the COT, the crust sharply thinned seaward and a similar to 2-3 km thick HVL was imaged underlying the hype-extended crust. We discuss the nature of the HVL in the northeastern South China Sea (SCS) by integrating the volcanic activity, magnetic anomaly, Moho morphology, and geochemistry of the region. We observed that the HVL underlying the COT is probably extension related resulting from the decompression melting in the Cenozoic, whereas that beneath the Dongsha Rise is probably arc related and associated with the subduction of the paleo-Pacific plate. These findings are inconsistent with those of some previous studies. We believe that our viewpoint is first put forward through the detailed demonstration and provides new insights into the rifting processes of the northeastern SCS margin. It will be of great interest to the broad marine geosciences community, particularly those interested in the formation and evolution of the marginal seas
Upper Devonian reefs and microbialite at Maoying, South China-implications for paleoenvironmental changes
No full textReefal carbonate deposits in South China preserve a record of community structure and environmental change across the Frasnian-Famennian boundary and through the Late Devonian, detailing a regional response to one of the largest mass extinction events in Earth history. The Upper Devonian (Frasnian to Famennian) limestone outcrops in the Maoying area of northern Ziyun County, South China, record a carbonate platform depositional setting with some patch reef development. The Upper Devonian carbonate deposits in Maoying area are distinctive from those in correlative sections in Dushan County with rare argillaceous limestone and dolomitic limestone as well as less dolostone. Exposures to the south in the Guilin area of northeastern Guangxi Province are similar to those seen in the study area. Upper Devonian carbonates in the Maoying area are divided into two lithologic groups, reef limestones or dolostone beds, composed of five lithologically distinctive intervals. The Upper Devonian strata have a cumulative thickness of 530 m. The Upper Devonian reefs in the Maoying area were developed on a shell pavement of brachiopod- and bivalve-shell shoal packstones and evolved into patch reefs in the interior of the carbonate platform. Patch-reef development was limited to early Frasnian time. Reef building organisms are dominated by massive and tabular stromatoporoids, Amphipora sp., Stachyodes sp., and coral Thamnopora sp., while brachiopods and algae accumulated between stromatoporoid skeletal frameworks. Three evolutionary stages of the Frasnian patch reefs, including an initial development stage, maturity stage and demise stage, can be recognized according to sedimentary structures and fossil assemblage characteristics. The Frasnian strata overlying the patch reefs represent a well-bedded back-reef depositional setting and are mainly composed of Amphipora floatstone and packstone containing a few bulbous stromatoporoids and small fasciculate corals. Famennian strata are characterized by laminated limestone and fenestrate limestone that are interbedded with infrequent mudstone and argillaceous limestone horizons. A prominent microbialite bed developed in the laminated limestone of the Famennian carbonate platform consists of stromatolite and thrombolite framestone. This bed can be correlated, in horizon and age, with microbial reefs and mounds in the Famennian offshore carbonate platform in the Huanan Epeiric Sea (such as Famennian microbial reefs and mounds in Guilin). This represents a biogenic carbonate formation characterized by microbial fabrics that accumulated in a nearshore carbonate platform setting after the global Frasnian/Famennian biotic extinction event, which promoted the growth of microbialites during the latest Devonian in South China. (C) 2016 Elsevier B.V. All rights reserved
西北太平洋及其边缘海的放射虫生物地理特征
No full text北太平洋具有独特的环流系统及边缘海特征。浮游性放射虫生活于某些特定性质的水团中，也可随海流或大洋环流而迁移，成为追溯海洋环境变化的重要证据。本论文通过分析西北太平洋的南海、东海、日本海、鄂霍次克海、白令海、菲律宾海盆以及西北太平洋边界流等典型区域的代表性海底表层样品，首次揭示了西北太平洋各边缘海的放射虫生物地理特征，以及探讨了其与海洋环境、北太平洋环流之间的关联。获得主要认识有：
（1）首次阐明了西北太平洋边缘海表层沉积物中放射虫的生物地理特征：西北太平洋高—低纬度不同边缘海表层沉积物中主要放射虫属种类型总体上呈现出亚北极、温带—亚热带和热带气候的放射虫组合特征；西北太平洋各边缘海沉积物中放射虫丰度和分异度的分布具有明显的纬向性和水深变化。纬向上，低纬度各边缘海区中放射虫的数量和种类远比高纬度边缘海区丰富，水深变化则在水深较深的大洋海盆区分布最高；西北太平洋各海区沉积物中的放射虫可以划分为类群A和类群B两个大的生物地理区系，其中，类群A主要分布在热带—亚热带海区，其放射虫丰度与分异度较高，群落组成以暖水种为主。而类群B主要分布于亚北极海区，放射虫丰度与分异度较低，群落组成中冷水种含量较高。此外，类群A可分为A1至A5五个亚类，分别对应于东海、菲律宾海、南海、日本海以及黑潮区，类群B分为B1至B3三个亚类，分别与鄂霍次克海、白令海和亚北极环流区有着较好的对应关系。
（2）揭示了西北太平洋边缘海表层沉积物中放射虫特征种的分布特征：运用Q—型因子分析将西北太平洋边缘海放射虫优势种划分出3个放射虫组合并分别代表不同的水团，同时这些因子的放射虫特征种与开放大洋有一定相似性。亚北极因子放射虫特征种主要有：Ceratospyris borealis，Siphocampe arachnea，Stylochlamydium venustum，Botryopyle setosa，Botryocyrtis quinaria和Cycladophora davisiana。其主要分布在日本海的北部、鄂霍次克海、白令海和少部分楚科奇海；温带—亚热带因子放射虫特征种主要有：Monozonium pachystylum，Stylodictya validispina，Arachnocorallium calvata，Lithelius spiralis，Lithocarpium polyacantha，Lithomelissa thoracites，Stylodictya sp.和Lithomelissa setosa。该组合主要分布在日本海的南部、东海和菲律宾海的西北部；热带因子放射虫特征种主要有：Pterocorys campanula，Euchitonia cf. E. trianglulum，Tholospyris sp.，Giraffospyris angulata，Tetrapyle octacantha，Ommatartus tetrathalamus tetrathalamus，Euchitonia furcata，Tetrapyle quadrilobah和Streblacantha circumtexta。该组合主要分布在西北太平洋赤道海区与亚热带边缘海（南海和菲律宾海西南部）之间。这些组合的分布与海水表层温度密切相关，并且特征种的分布还可用来指示亚北极锋或者亚热带锋。
（3）比较分析了西北太平洋边缘海表层沉积物的放射虫分布与海洋环境的关系：CCA环境分析结果表明，放射虫的分布与海水表层温度的相关性最大，同时，与夏季海水表层温度相关性最大的放射虫组合主要受黑潮的影响；而高纬度边缘海区的放射虫分布还受含氧量以及营养物质的控制。结合不同海区放射虫的沉积分布特征可知，西北太平洋边缘海区海水表层温度、含氧量以及营养物质的分布是沉积放射虫具有明显纬向性分布规律和特殊现象的主导因素，而水深变化是同一海区不同区域放射虫沉积分布存在差异特征的重要原因。
（4）划分出了能够指示北太平洋环流的放射虫指示种：受西北太平洋环流的影响，不同生物地理区的放射虫组合存在一定的关联与共性。依据不同海区放射虫共有属种的含量与分布特征，划分出了八组放射虫指示种，它们分别较好地指示着阿拉斯加流、勘察加流、亲潮、对马暖流、黑潮—东海分支、黑潮主流和赤道逆流。另外，还归纳总结出了一些深水体放射虫属种