Institutional Repository of South China Sea Institute of Oceanology, CAS
Not a member yet
6199 research outputs found
Sort by
Studies of the cryopreservation condition of Gymnocypris przewalskii spermatozoa
No full textThe endemic naked carp (Gymnocypris przewalskii Kessler, 1876) plays an important role in the maintenance of the distinctive ecological system of Lake Qinghai at 3.2 km altitude on the Qinghai-Tibet Plateau in China. This study aimed to develop a cryopreservation protocol for Gymnocypris przewalskii spermatozoa. Semen was collected from mature individuals during migration and frozen using the liquid nitrogen vapor method. The influence of different cryoprotectants and three extenders on the post-thaw quality of the sperm was analyzed. The highest sperm motility rate and longest motility time after cryopreservation were achieved by combining Ringer's solution with 15% ethylene glycol (P < 0.05). The fertilization rate of this cryopreserved semen was 15.26 +/- 4.54%. This study thus provides a valuable method for the cryopreservation of the sperm of this important endangered fish species
Impact of diurnal temperature fluctuations on larval settlement and growth of the reef coral Pocillopora damicornis
No full textDiurnal fluctuations in seawater temperature are ubiquitous on tropical reef flats. However, the effects of such dynamic temperature variations on the early stages of corals are poorly understood. In this study, we investigated the responses of larvae and new recruits of Pocillopora damicornis to two constant temperature treatments (29 and 31 degrees C) and two diurnally fluctuating treatments (28-31 and 30-33 degrees C with daily means of 29 and 31 degrees C, respectively) simulating the 3 degrees C diel oscillations at 3m depth on the Luhuitou fringing reef (Sanya, China). Results showed that the thermal stress on settlement at 31 degrees C was almost negated by the fluctuating treatment. Further, neither elevated temperature nor temperature fluctuations caused bleaching responses in recruits, while the maximum excitation pressure over photosystem II (PSII) was reduced under fluctuating temperatures. Although early growth and development were highly stimulated at 31 degrees C, oscillations of 3 degrees C had little effects on budding and lateral growth at either mean temperature. Nevertheless, daytime encounters with the maximum temperature of 33 degrees C in fluctuating 31 degrees C elicited a notable reduction in calcification compared to constant 31 degrees C. These results underscore the complexity of the effects caused by diel temperature fluctuations on early stages of corals and suggest that ecologically relevant temperature variability could buffer warming stress on larval settlement and dampen the positive effects of increased temperatures on coral growth
Microplastics and polycyclic aromatic hydrocarbons (PAHs) in Xiamen coastal areas: Implications for anthropogenic impacts
No full textMicroplastics and polycyclic aromatic hydrocarbons (PAHs) were investigated to study the influence of human activities and to find their possible relationship on the coastal environments, where the coastal areas around Xiamen are undergoing intensive processes of industrialization and urbanization in the southeast China. The abundance of microplastics in Xiamen coastal areas was 103 to 2017 particles/m(3) in surface seawater and 76 to 333 particles/kg in sediments. Concentrations of dissolved PAHs varied from 18.1 to 248 ng/L in surface seawater. The abundances of microplastics from the Western Harbor in surface seawater and sediments were higher than those from other areas. Foams were dominated in surface seawater samples, however, no foams were found in sediments samples. The microscope selection and FTIR analysis suggested that polyethylene (PE) and polypropylene (PP) were dominant microplastics. The cluster analysis results demonstrated that fibers and granules had the similar sources, and films had considerably correlation with all types of PAHs (3 or 4-ring PAHs and alkylated PAHs). Plastic film mulch from agriculture practice might be a potential source of microplastics in study areas. Results of our study support that river runoff, watershed area, population and urbanization rate influence the distribution of microplastics in estuarine surface water, and the prevalence of microplastic pollution calls for monitoring microplastics at a national scale. (C) 2018 Elsevier B.V. All rights reserved
Artificial reefs for sea cucumber aquaculture confirmed as settlement substrates of the moon jellyfish Aurelia coerulea
No full textIn coastal areas with a high intensity of human activities, expansion of artificial structures may enhance Aurelia spp. blooms because these constructions may provide additional substrates for the settlement and proliferation of the polyps. In the present study, the possible occurrence and distribution of Aurelia coerulea ephyrae and polyps were investigated in sea cucumber (Apostichopus japonicus) culture ponds that contain huge amounts of artificial structures. Our results showed that A. coerulea ephyrae were widely distributed in the A. japonicus culture ponds along the Bohai and Yellow Seas. Furthermore, underwater photography revealed that polyps of A. coerulea mainly occurred on the undersides of the artificial reefs made by plastic sunshade nets, tiles and substrate cages. The artificial reefs may decrease the time A. coerulea planulae spend settling, provide more hidden, calm and shady places for the settlement and proliferation of A. coerulea planulae, and thus were suitable substrates for the moon jellyfish A. coerulea. Our study suggests that the A. japonicus culture ponds may act as nursery grounds for the jellyfish A. coerulea and may potentially enhance the blooms of this species in the coastal waters along the Bohai and Yellow Seas
Progress on shelf and slope circulation in the northern South China Sea
No full textInfluenced by the seasonally reversed monsoons, water exchange through straits, and topography, the shelf and slope circulation in the northern South China Sea (NSCS) is complex and changeable. The typical current system in the NSCS consists of the slope current, South China Sea warm current (SCSWC), coastal current, and associated upwelling (in summer) and downwelling (in winter). This paper reviews recent advances in the study of NSCS shelf and slope circulation since the 1990s, and summarizes the roles of Kuroshio intrusion, the monsoons, topography, and the buoyancy effect of the Pearl River plume in the shelf and slope current system of the NSCS. We also point out some potential scientific issues that require further study, such as the dynamic connection between the internal basin and shelf areas of the NSCS, the persistence of the SCSWC in winter, the temporo-spatial characteristics of downwelling during winter in the NSCS, and its material and energy transport
Change in Coherence of Interannual Variability of Summer Rainfall over the Western Pacific around the Early 2000s: Role of Indo-Pacific Ocean Forcing
No full textThe observations show that the covariability between the western North Pacific (WNP) and the South China Sea (SCS) summer rainfall has experienced an obvious weakening since the early 2000s. During the period 1982-2003, the combined north Indian Ocean (NIO), central North Pacific (CNP), and central equatorial Pacific (CEP) sea surface temperature (SST) forcing results in a high coherence between the WNP and SCS summer rainfall variations via a zonally elongated anomalous lower-level cyclone over the western Pacific. During the period 2004-16, the Indian Ocean SST contribution is largely weakened, and the WNP rainfall variability is dominated by the enhanced Pacific SST forcing with an eastward retreated lower-level wind and rainfall anomalies, whereas the SCS rainfall variability is mainly associated with local air-sea interaction processes. The results obtained from observational analysis are supported by numerical experiments with atmospheric and coupled general circulation models. The change in the coherence of interannual summer rainfall variability over the WNP and SCS has important implications for regional climate prediction in South and East Asia
Deep water characteristics and circulation in the South China Sea
No full textThis study investigates the deep circulation in the South China Sea (SCS) using oceanographic observations combined with results from a bottom layer reduced gravity model. The SCS water, 2000 m below the surface, is quite different from that in the adjacent Pacific Ocean, and it is characterized by its low dissolved oxygen (DO), high temperature and low salinity. The horizontal distribution of deep water properties indicates a basin-scale cyclonic circulation driven by the Luzon overflow. The results of the bottom layer reduced gravity model are consistent with the existence of the cyclonic circulation in the deep SCS. The circulation is stronger at the northern/western boundary. After overflowing the sill of the Luzon Strait, the deep water moves broadly southwestward, constrained by the 3500 m isobath. The broadening of the southward flow is induced by the downwelling velocity in the interior of the deep basin. The main deep circulation bifurcates into two branches after the Zhongsha Islands. The southward branch continues flowing along the 3500 m isobath, and the eastward branch forms the sub-basin scale cyclonic circulation around the seamounts in the central deep SCS. The returning flow along the east boundary is fairly weak. The numerical experiments of the bottom layer reduced gravity model reveal the important roles of topography, bottom friction, and the upwelling/downwelling pattern in controlling the spatial structure, particularly the strong, deep western boundary current
Influence of the South Pacific decadal variability on Southeast China rainfall during boreal autumn
No full textUsing observational data and numerical experiments, the decadal relationship between South Pacific and rainfall over southeastern China during boreal autumn is examined. In the observational analyses, it is found that the boreal autumn South Pacific shows significant decadal variability with a significant periodicity of 11-21years from 1960 to 2000, which is an independent phenomenon in the whole Pacific. This South Pacific decadal variability can induce significant decadal variability of boreal autumn rainfall over southeastern China. When the boreal autumn South Pacific decadal variability is in its positive phase, less rainfall appears over the southeastern China, and vice versa. The possible physical mechanisms are further investigated. It is suggested that the negative sea surface temperature anomalies (SSTA) in the extratropical South Pacific associated with positive phase of South Pacific decadal variability could result in an anomalous anticyclone to the east of Australia. The cross-equatorial flow over the Maritime Continent and tropical western Pacific is enhanced under the influence of this anomalous anticyclone, favouring the location of western Pacific subtropical high moving more eastwards and then leading to the formation of anomalous cyclone over western North Pacific. To the west flank of this anomalous cyclone is the significantly anomalous northerly, which is favourable for less rainfall over southeastern China. On the other hand, significant negative SSTA appears in the Maritime Continent and tropical western Pacific could cause anomalous sinking motion here, which can further induce anomalous sinking motion over southeastern China through two meridional cells extending from Maritime Continent to southeastern China with a common rising branch over the southern South China Sea, thus resulting in less rainfall over southeastern China. Numerical experiments confirm our observational results
Variability in the empirical leucine-to-carbon conversion factors along an environmental gradient
No full textBacterial production is one of the key parameters to evaluate bacterial role in ocean carbon fluxes. Estimation of bacterial production requires the leucine-to-carbon conversion factors that change widely across environments. However, empirical leucine-to-carbon conversion factors (eCFs) are seldom determined in situ because of time consuming and little is known on regulating factors for the eCFs. During May 2015 to January 2016, fourteen dilution experiments were conducted, from the Zhujiang (Pearl River) Estuary to the coast of the northern South China Sea, to determine spatiotemporal variability in the eCFs and its potential controlling factors along an environmental gradient. The eCFs showed clear spatial variations with the highest (1.27-1.69 (kg C)/(mol Leu)) in low salinity waters (salinity < 15), intermediate (1.03-1.25 (kg C)/(mol Leu)) in moderate salinity (salinity of 15-25), and the lowest (0.48-0.85 (kg C)/(mol Leu)) in high salinity waters (salinity > 25). Substrate availability was responsible for spatial variability in the eCFs. In the pristine coastal waters, low eCFs was related to substrate limitation and leucine incorporated was respired to maximize the survival rather than bacterial production. Hence, the eCFs measurement was needed for estimating bacterial production accurately in various marine environments
High-Frequency Monitoring of Suspended Sediment Variations for Water Quality Evaluation at Deep Bay, Pearl River Estuary, China: Influence Factors and Implications for Sampling Strategy
No full textSuspended sediment (SS) is an important water quality indicator of coastal and estuarine ecosystems. Field measurement and satellite remote sensing are the most common approaches for water quality monitoring. However, the efficiency and precision of both methods are typically affected by their sampling strategy (time and interval), especially in highly dynamic coastal and estuarine waters, because only limited measurements are available to analyze the short-term variations or the long-term trends of SS. Dramatic variations of SS were observed, with standard deviation coefficients of 48.9% and 54.1%, at two fixed stations in Deep Bay, China. Therefore, it is crucial to resolve the temporal variations of SS and its main influencing factors, and thus to develop an improved sampling strategy for estuarine ecosystems. Based on two years of continuous high-frequency measurements of SS and concurrent tidal and meteorological data, we demonstrated that the tide is the dominant factor influencing the SS variation among tide, wind (speed and direction), and rainfall in Deep Bay, China. For the monitoring of maximum suspended sediment concentration (SSC), the recommended optimum sampling time coincides with the occurrence of the ebb tides, whereas multiple sampling times are recommended for monitoring of minimum SSC. Although variations of SS are also affected by other factors, the recommended sampling strategy could capture the maximum and minimum SSC variations exactly more than 85% days in a year on average in Deep Bay. This study provides a baseline of SS variation and direct sampling strategy guidance for future SS monitoring and could be extended to other coastal or estuarine waters with similar climatological/tidal exposures