Ping-Ping Shen

Latitudinal variability (6 degrees S-20 degrees N) of early summer phytoplankton species compositions and size-fractioned productivity from Java Sea to South China Sea

Abstract In order to study the effects of latitudinal change in physical and chemical environments on phytoplankton cells, we investigated the early summer phytoplankton biomass, species composition and size-fractioned productivity in surface water from the Java Sea to the South China Sea (from 6°S to 20°N) from 18 May to 27 May 2010. Chlorophyll a (Chl a) concentration decreased latitudinally from 0.18 (∼6°S) to 0.05 µg l–1 (∼10°N). The dominant species, the cyanobacteria Trichodesmium erythraeum, dinoflagellates (e.g. Gyrodinium dominans, Amphidinium carterae and Gonyaulax spp.) and diatoms (e.g. Thalassionema nitzschioides, Rhizosolenia spp. and Chaetoceros spp.) changed to only the dinoflagellate species. Also, the Chl a biomass increased to 0.14 µg l–1 towards the end of the survey (∼20°N) with the dinoflagellates as the most abundant group. Productivity of phytoplankton assemblages coincided with Chl a concentration, and decreased accordingly from 9.24 ± 0.71 to 2.87 ± 0.41 µg C l–1 day–1, then increased to 5.45±1.1 µg C l–1 day–1. Chl a concentration and productivity were significantly correlated (P<0.05) with microplankton cell abundance, as well as nutrient concentrations, which appeared to exert a strong influence over latitudinal variation in primary production.

Occurrence of brackish water phytoplankton species at a closed coral reef in Nansha Islands, South China Sea.

The phytoplankton assemblage of Zhubi Reef, a closed coral reef in Nansha Islands (South China Sea, SCS) was studied in June 2007. A total of 92 species belonging to 53 genera and four phyla have been identified. The dominant taxa in the lagoon were the diatom Chaetoceros and cyanobacteria Nostoc and Microcystis, while in reef flats were cyanobacteria Trichodesmium erythraeum, dinoflagellates Gymnodinium and Prorocentrum. The species richness and diversity were consistently lower in the lagoon than in reef flats. Classification and nMDS ordination also revealed significant dissimilarity in phytoplankton community structure between the reef flat and lagoon, with statistical difference in species composition and abundance between them (ANOSIM, p=0.025). Nutrient concentrations also spatially varied, with ammonium-enrichment in the lagoon, while high Si-concentration existed in reef flat areas. Both nutrient levels and currents in SCS may play important roles in determining the composition and distribution of microalgae in Zhubi Reef and SCS.

Evaluation of sampling sizes on the intertidal macroinfauna assessment in a subtropical mudflat of Hong Kong

In this study, two types of sediment cores with different diameters were used to collect sediment samples from an intertidal mudflat in Hong Kong to investigate the influence of sampling unit on the quantitative assessment of benthic macroinfaunal communities. Both univariate and multivariate analyses were employed to detect differences in sampling efficiencies by the two samplers through total abundance and biomass, species richness and diversity, community structure, relative abundance of major taxa of the infaunal community. The species-area curves were further compared to find out the influence of the sampling units. Results showed that the two sampling devices provided similar information on the estimates of species diversity, density and species composition of the benthos in main part of the mudflat where the sediment was fine and homogenous; but at the station which contained coarse sand and gravels, the significant differences were detected between the quantitative assessments of macrobenthic infauna by the two samplers. Most importantly, the species-area curves indicated that more and smaller samples were better in capturing more species than less large ones when comparing an equal sampling area. Therefore, the efficiency of the sampler largely depended on the sediment properties, and sampling devices must be chosen based on the physical conditions and desired levels of precision on the organisms of the sampling program.

Evidence of iron cyanides as supplementary nitrogen source to rice seedlings

The effect of iron cyanides on activities of nitrate reductase (NR) and glutamine synthetase (GS) of plants was investigated. Young rice seedlings (Oryza sativa L. cv. XZX 45) were grown in the nutrient solutions containing KNO3 or NH4Cl and treated with ferro-cyanide [K4Fe(CN)6] or ferri-cyanide [K3Fe(CN)6]. Total cyanide and free cyanide in solutions and in plant materials were analyzed. Activities of NR and GS in different parts of plants were assayed in vivo. Results indicated that all rice seedlings exposed to either ferro- or ferri-cyanide showed positive growth. The phyto-assimilation rates of both iron cyanide species by rice seedlings were positively correlated to the doses supplied. Seedlings grown on NO3− showed significantly higher assimilatory potential for both ferro- and ferri-cyanide than those on NH4+. Rice seedlings grown on NH4+-containing nutrient solution accumulated more cyanide in plant materials, majority being in roots rather than shoots, than these grown on NO3−-containing nutrient solution, suggesting that the presence of ammonium (NH4+) in the nutrient solution caused a negative impact on botanical assimilation of both iron cyanides. Sensitivity of NR and GS in rice seedlings exposed to ferro- and ferri-cyanide was identical, where conspicuous effects were only observed at the highest concentration supplied. The evidence offered here suggests that both iron cyanides can be a supplementary source of nitrogen to plant nutrition.

Vertical Patterns of Early Summer Chlorophyll a Concentration in the Indian Ocean with Special Reference to the Variation of Deep Chlorophyll Maximum

Vertical patterns of early summer chlorophyll a (Chl a) concentration from the Indian Ocean are presented, as well as the variations of depth and size-fractioned Chl a in the deep chlorophyll maximum (DCM). A total of 38 stations were investigated from 12 April to 5 May 2011, with 8 discrete-depth samples (7 fixed and 1 variable at real DCM) measured at each station. Depth-integrated Chl a concentration (∑Chl𝑎) varied from 11.5 to 26.8 mg m−2, whereas Chl a content at DCM ranged from 0.17 to 0.57 μg L−1 with picophytoplankton (l3 μm) accounting for 82% to 93%. The DCM depth varied from 55.6 to 91 m and shoaled latitudinally to northward. Moreover, our results indicated that the ∑Chl𝑎 could be underestimated by up to 9.3% with a routine sampling protocol of collecting samples only at 7 fixed depths as the real DCM was missed. The underestimation was negatively correlated to the DCM depth when it varied from 55.6 to 71.3 m (𝑟=−0.63, 𝑃l0.05) but positively correlated when it ranged from 75.8 to 91 m (𝑟=0.68, 𝑃l0.01). This indicates that in the Indian Ocean the greater the departure of the DCM from 75 m depth, the greater the underestimation of integrated Chl a concentration that could occur if the real DCM is missed.

Longitudinal patterns of spring-intermonsoon phytoplankton biomass, species compositions and size structure in the Bay of Bengal

Vertical distributions of phytoplankton biomass, compositions and size structure were investigated during the spring-intermonsoon (April 22 to 30) of 2010 along transact 10°N of the Bay of Bengal, northern Indian Ocean. Surface phytoplankton biomass (Chl a) was (0.065±0.009) µg/L, being greater than 80% of which was contributed by pico-phytoplankton (<3 µm). The Chl a concentration vertically increased to the maximal values at deep chlorophyll maximum (DCM) layer that shoaled eastwards from 75 to 40 m. The Chl a biomass at DCM layer generally varied between 0.2 and 0.4 µg/L, reaching the maximum of 0.56 µg/L with micro-phytoplankton cells (>20 µm) accounting for 58% and nano- (3–20 µm) or pico-cells for 15% and 27%, respectively. In particular, the cells concentration coupling well with phosphate level was observed at middle layer (75–100 m) of 87° to 89°E, dominated by micro-cells diatoms (e.g., Chaetoceros atlanticus v. neapolitana, Chaetoceros femur and Pseudonitzschia sp.) and cyanobacteria (i.e., Trichodesmium hildebrandtii), with the cells concentration reached as high as 4.0×104 and 4.3×104 cells/L. At the rest of the transact however, dinoflagellates (e.g., Amphisdinium carterae and Prorocentrum sp.) were the dominant species, with the cells concentration varying from 0.3×103 to 6.8×103 cells/L. Our results also indicate that the regulation of large cells (micro-, nano-) on phytoplankton biomass merely occurred at DCM layer of the Bay.

Variations in silicate concentration affecting photosynthetic carbon fixation by spring phytoplankton assemblages in surface water of the Strait of Malacca

The Strait of Malacca (SoM), the world’s busiest sea-route, is increasingly polluted as the rapid development of world trades, affecting phytoplankton primary productivity therein. The variations of surface phytoplankton biomass, size-structure and carbon fixation were investigated across the SoM during the spring period (May 4 to 9, 2011). Chlorophyll a concentration increased from 0.12 µg/L at the northwest entrance of the SoM to a maximal 0.63 µg/L at narrowest section, and decreased to 0.10 µg/L at the southeast entrance. Photosynthetic carbon fixation by phytoplankton coincided well with Chl a biomass, and increased from 10.8 to 22.3 µg C/(L·d), then decreased to 9.21 µg C/(L·d); while the carbon fixation rate showed an inverse pattern to the changes of Chl a, and decreased from 87.1 to 35.5 µgC/(µgChla·d) and increased thereafter to 95.3 µg C/(µg Chl a·d). Picophytoplankton cells (<3 µm) contributed to more than 60% and 50% of the total Chl a and carbon fixation at both the entry waters; while the contributions of pico-cells decreased sharply to the minimum of 18.3% and 27.5% at the narrowest part of the SoM. In particular, our results showed that the silicate concentration positively regulated Chl a biomass and carbon fixation, reflecting that the higher silicate favoured the growth of phytoplankton and thus led to higher primary production in this strait.

Novel polymorphism of internal transcribed spacers (ITS) and their utilization in phylogenetic analysis of Neanthes glandicincta (Annelida: Polychaeta: Nereididae).

Sequences of internal transcribed spacers (ITS1 and ITS2) are increasingly being used to infer phylogenetic relationships at or below species levels. Here we report a novel case of ITS polymorphism within Neanthes glandicincta (Annelida: Polychaeta: Nereididae). Two types of ITS sequence (Type I and Type II) were cloned and sequenced, which showed significant differences both in nucleotide composition and length. Variations of these two types sequences also differed from each other with Type I was highly divergent while Type II was highly conserved. Phylogenetic trees inferred from ITS1 and ITS2 sequences showed striking discrepancy in N. glandicincta. Non-concerted evolution of multi-gene is suggested to be responsible for the high degree of polymorphism in ITS regions. Due to the two divergent types of ITS presented within a single N. glandicincta individual, the utilization of ITS regions for delineation of population or closely related species cannot be substantiated. The finding of different types of ITS in a single individual also stresses the need for analyzing a large number of clones whenever ITS sequences obtained by PCR amplification and cloning are being used in phylogenetic reconstruction.

Subsurface low dissolved oxygen occurred at fresh- and saline-water intersection of the Pearl River estuary during the summer period

Estuarine 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 (>5m) water, the DO level varied from 0.71 to 6.65mgL-1 and from 6.58 to 8.20mgL-1 in the summer and winter periods, respectively. Particularly, we observed an area of ~1500km2 low DO zone in the subsurface water with a threshold of 4mgDOL-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.

Composition and Distribution of Planktonic Ciliates in the Southern South China Sea During Late Summer： Comparison Between Surface and 75 m Deep Layer

Ciliates are very important components in most marine ecosystem. They are trophic link between the microbial food web and grazing food chain. In this study, ciliates were collected from 11 sites in the southern South China Sea (SCS) during August 25 to September 28, 2011. Their composition and distribution at the surface and 75 m deep depth of the ocean were studied. A total of 30 species belonging to 22 genera were identified, and 22 species of 15 genera were Tintinnids. Eutintinnus fraknoii and E. stramentus were the most common species. The other dominants were strombidiids ciliates including Strombidium conicum and S. globosaneum, which were followed by the tide form, Mesodinium pulex. Ciliates abundance ranged from 46 ind L-1 to 368 ind L-1 in the open sites, 46–368 ind L-1 at surface and 73–198 ind L-1 at 75 m deep layer. In the Yongshu reef, ciliates abundance ranged from 167 ind L-1 to 365 ind L-1 in the water column, similar to that in Sanya coral reef waters. Ciliates composition showed obvious difference between surface and 75 m deep layer at station S2 (P < 0.05), while no similar result was observed at other sites. At 75 m deep layer, salinity was negatively related to mixed layer depth (P < 0.05), but positively to chlorophyll a concentration (P < 0.05), indicating that the change of vertical mixing in water column influenced vertical distribution of ciliates in the southern SCS.