Institutional Repository of South China Sea Institute of Oceanology, CAS
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Spawning, larval development and juvenile growth of the tropical sea cucumber Holothuria leucospilota
No full textThe tropical sea cucumber Holothuria leucospilota (Echinodermata: Holothuroidea) is one of the most widespread sea cucumber species with high economic value. To develop the artificial breeding methods of H. leucospilota, we conducted the first detailed study on the processes of spawning, embryonic and larval development, and juvenile growth of the species. The results showed that the suitable breeding season of H. leucospilota in the Daya Bay might be from June to October and that at least 30 days were needed for embryos to develop into juveniles at a temperature of 29-33 degrees C, a salinity of 27-30 parts per thousand, and a pH of 7.9-8.2. The survival rate of the juveniles were approximately 8.5%, the average growth rate during days 31-49 of culture was 0.11mm per day and increased to 0.72mm per day during days 73-120. The body color of the juveniles was transparent yellow at approximately 55 days of culture, and it began to darken at 79 days later. These results indicated that an artificial culture method of H. leucospilota was realized. Our research might contribute a feasible way to the artificial breeding, natural resource restoration, and sustainable use of tropical sea cucumbers
Aerosol concentrations and atmospheric dry deposition fluxes of nutrients over Daya Bay, South China Sea
No full textBased on one and a half years of observations (September 2015 to March 2017) in Daya Bay, we analysed the nutrient concentrations in aerosols and calculated dry deposition fluxes of nutrients. DON was the dominant species of TDN in aerosol particles, accounting for 63.3%. The mean values of DIP, DOP and DSi were 0.78, 0.61 and 2.6 nmol.m(-3), respectively. The mean fluxes of nutrients (TDN, TDP and DSi) from dry deposition during the field observation were 2150, 7.4 and 28.2 mu mol.m(-2).month(-1), respectively. The fluxes of nitrogen species show a seasonal pattern with higher input in spring and winter. The dry deposition of nutrients accounted for approximately 20% of the total deposition budget. The molar ratios of DIN/DIP in the dry deposition (mean value 167) suggest that atmospheric dry deposition of nutrients may increase the risk of the unbalanced nutrient condition in the seawater column of Daya Bay
Contamination level, chemical fraction and ecological risk of heavy metals in sediments from Daya Bay, South China Sea
No full textContamination level, chemical fraction and ecological risk of heavy metals in sediments from Daya Bay (DYB) were conducted in this study. The results revealed that the concentration of Cr, Cu, Zn, As, Cd and Pb in sediments were in the range of 36.38-90.33, 9.54-61.32, 33.54-207.33, 7.80-18.43, 0.13-0.43 and 15.89-30.01 mg kg(-1), respectively, with bioavailable fractions of 13.29, 54.16, 47.60, 32.74, 68.14, 26.59%, respectively. A modified potential ecological risk index (MRI) was used for the ecological risk assessment, with ecological risk contribution ratios of 75.73, 14.29, 5.47, 1.74, 1.57 and 1.21% for Cd, As, Cu, Cr, Pb and Zn, respectively. The main contaminants were Cd and As, with their ecological risks "High" and "Moderate" levels, and their enrichment degrees "Moderately Severe" and "Moderate", respectively. The multivariate statistical analysis suggested that the various anthropogenic activities along the bay might contribute mainly to the heavy metals contamination in DYB
The complete mitochondrial genome sequence of Photopectoralis bindus (Perciformes: Leiognathidae)
No full textThe complete mitochondrial genome of Photopectoralis bindus was sequenced by high throughput sequencing method in this study. Length of this genome is 16,517 bp, containing 13 protein-coding genes, 22 tRNA genes, two rRNA genes and one large non-coding region. ND6 and eight tRNA genes are encoded by L-strand, and others are encoded by H-strand, which is similar to those in most vertebrates. The nucleotide composition of the whole mitogenome is 29.9% A, 30.1% C, 15.1% G, and 25.0% T, with a slight bias of A +T content (54.9%). Phylogenetic tree based on the first and second codon sequences of 12 protein coding genes (except ND6) shows that the Glade of P. bindus is closely clustered with that of Gazza minuta, and families Rachycentridae and Carangidae have the closest relationship to Leiognathidae
High temperature stress might hamper the success of sexual reproduction in Hizikia fusiformis from Shantou, China: a photosynthetic perspective
No full textComparative studies of photosynthetic physiology were carried out to evaluate high light and temperature stresses in reproductive (receptacles) and vegetative (blades) tissues of fertile thalli of Hizikia fusiformis from Nanao Island, China. Receptacles had much higher rates of photosynthesis than blades, and temperature sensitivity was much higher for photosynthesis than for respiration. Both receptacles and blades survived extended exposure to 1500 mu mol photons m(-2) S-1; however, above 30 degrees C, photosynthetic activity declined rapidly. Prolonged exposure to high temperature sharply depressed photosynthesis, and extended exposure to 40 degrees C was more detrimental to photosynthesis than exposure to 30 degrees C. Moreover, photosynthesis of receptacles was more susceptible to heat than photosynthesis in blades. Following 15 min at 40 degrees C, receptacle photosynthesis declined to 28% of initial value and recovered to only 60% of initial value within 1 h in recovery conditions. However, after 30 min at 40 degrees C, receptacle photosynthesis did not recover within 4 h, suggesting that the photosynthetic apparatus had suffered irreversible injury. Respiration was not affected by high temperature. Our study shows that high temperature but not high light stress might hamper sexual reproduction in H. fusiformis
Subsurface low dissolved oxygen occurred at fresh- and saline-water intersection of the Pearl River estuary during the summer period
No full textEstuarine oxygen depletion is one of the worldwide problems, which is caused by the freshwater-input-derived severe stratification and high nutrients loading. In this study we presented the horizontal and vertical distributions of dissolved oxygen (DO) in the Pearl River estuary, together with temperature, salinity, chlorophyll a concentration and heterotrophic bacteria abundance obtained from two cruises during the summer (wet) and winter (dry) periods of 2015. In surface water, the DO level in the summer period was lower and varied greater, as compared to the winter period. The DO remained unsaturated in the summer period if salinity is < 12 and saturated if salinity is > 12; while in the winter period it remained saturated throughout the estuary. In subsurface ( > 5 m) water, the DO level varied from 0.71 to 6.65 mg L-1 and from 6.58 to 8.20 mg L-1 in the summer and winter periods, respectively. Particularly, we observed an area of similar to 1500 km(2) low DO zone in the subsurface water with a threshold of 4 mg DO L-1 during this summer period, that located at the fresh- and saline-water intersection where is characterized with severe stratification and high heterotrophic bacteria abundance. In addition, our results indicate that spatial DO variability in surface water was contributed differently by biological and physio-chemical variables in the summer and winter periods, respectively
Occurrence of four species of algae in the marine water of Hong Kong
No full textHarmful algal blooms (HABs) have broken out frequently throughout the world in recent decades; they are caused by the rapid multiplication of algal cells in near-coastal waters polluted with nitrogen and phosphorus and greatly affect the quality of marine water and human health. Over the past several decades, climate change and increasing environmental degradation have provided favourable growth conditions for certain phytoplankton species. Therefore, it is essential to rapidly identify and enumerate harmful marine algae to control these species. In this study, quantitative PCR (qPCR) was used to detect four representative species of HABs that are widespread in the marine water of Hong Kong, namely, Alexandrium catenella, Pseudo-nitzschia spp., Karenia mikimotoi and Heterosigma akashiwo. We applied qPCR with the dye SYBR Green to detect Alexandrium spp. and Pseudo-nitzschia spp. and used TaqMan probe for the enumeration of Karenia mikimotoi and Heterosigma akashiwo. The total genomic DNA of these algae from Hong Kong marine water was extracted successfully using the CTAB method, and for each kind of alga, we constructed a ten-fold series of recombinant plasmid solutions containing certain gene fragments of 18S rDNA and ITS1-5.8S-ITS2 as standard samples. Ten-fold dilutions of the DNA of known numbers of the extracted algal cells were also used to create an additional standard curve. In this way, the relationship between the cell number and the related plasmid copy number was established. The qPCR assay displayed high sensitivity in monitoring marine water samples in which the low concentrations of harmful algae were not detected accurately by traditional methods. The results showed that the cell numbers of the four species were all in low abundance. For Alexandrium catenella, the cell abundances at 12 sites ranged from 3.8 x 10(2) to 4.3 x 10(3) cells L-1, while H. akashiwo, K. mikimotoi and Pseudo-nitzschia ranged from 1.1 x 10(2) to 13 x 10(3), from 23 to 6.5 x 10(2) and from 45 to 3.3 x 10(2) cells L-1, respectively. The concentrations of these algae were much lower than those observed during outbreaks of HABs in Hong Kong. These results may be useful for local aquaculture development and may provide effective suggestions and a theoretical basis for HAB monitoring and management. (C) 2017 Elsevier Ltd. All rights reserved
Numerical Simulations to Project Argo Float Positions in the Middepth and Deep Southwest Pacific
No full textArgo float trajectories are simulated in the southwest Pacific basin (25 degrees-45 degrees S, 170 degrees E-165 degrees W) using velocity fields from a 1/12 degrees Southern Ocean model and a Lagrangian particle tracking model programmed to represent the vertical motions of profiling Argo floats. The system is applied to simulate both core Argo floats (typically parked at 1000-m depth and profiling to 2000-m depth) and Deep Argo floats (parked 500 m above the seafloor). The goal is to estimate probability density functions (PDFs) predicting future float positions. Differences are expected in the trajectory statistics, largely because of limitations in the temporal and spatial resolution of the model fields and uncertainties associated with a random walk component included in the particle advection scheme to represent this unresolved variability. Nonetheless, the core Argo float displacements over similar to 100-day time intervals are mostly consistent with the derived PDFs, particularly in regions with stable midlayer flows. For the Deep Argo floats, which are released into the open ocean and parked near the bottom, the simulations predict an average total displacement of less than 50 km within 100 days, in good agreement with the Deep Argo floats deployed as part of a pilot study. The study explores both the representativeness and the predictability of float displacements, with an aim to contribute to planning for the float observing system
Influence of the Interaction Between Typhoons and Oceanic Mesoscale Eddies on Phytoplankton Blooms
No full textPhytoplankton blooms induced by the interaction between typhoons and oceanic mesoscale eddies in the South China Sea were investigated using the composite averaging method based on cyclone-centric coordinates from nine years (2002-2010) of satellite observations. Increases in the chlorophyll (Chl) concentration following the passage of a typhoon differed greatly among the pre-existing cyclonic eddy (PCE), pre-existing anticyclonic eddy (PACE) and non-eddy (NE) ocean conditions (with Chl increases of approximately 35%, 6% and 12%, respectively), but the magnitude of sea surface temperature (SST) cooling was similar under the three conditions (approximate to 1 degrees C). Under the same level of SST decreases, the greater increase in the Chl concentration in the PCE condition was attributed to the longer persistence of both SST cooling and nutrient input caused by the typhoon-strengthened PCE (associated with upwelling), which stopped the re-warming of the typhoon-induced cold water
Role of wind forcing and eddy activity in the intraseasonal variability of the barrier layer in the South China Sea
No full textIn addition to widely discussed seasonal variability, the barrier layer (BL) of the South China Sea (SCS) also exhibits significant intraseasonal variability (ISV) and plays an important role in the upper heat and salt balances. The characteristics and mechanisms of spatiotemporal variations in the BL are investigated using an eddy-resolving ocean model OFES (OGCM For the Earth Simulator) ouput and related atmospheric and oceanic processes. The active intraseasonal BL variability in the SCS occurs mainly during the late summer/autumn and winter and exhibits remarkable differences between these two periods. The BL ISV in late summer/autumn occurs in the southern basin, while in winter, it is limited to the northwestern basin. To further discuss the evolution and driving thermodynamic mechanisms, we quantify the processes that control the variability of intraseasonal BL. Different mechanisms for the intraseasonal BL variability for these two active periods are investigated based on the case study and composite analysis. During late summer/autumn, the active BL in the southern basin is generated by advected and local freshwater, and then decays rapidly with the enhanced wind. In winter, anticyclonic eddy activity is associated with the evolution of the BL by affecting the thermocline and halocline variations, while wind stress and wind stress curl have no obvious influence on BL