Jianqiang Yin

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.

Seasonal Community Structure of Mesozooplankton in the Daya Bay, South China Sea

Mesozooplankton are key components of coastal ecosystems, linking the microbial food web to the classic food chain. In this study, species composition and abundance of mesozooplankton is studied for the Daya Bay in April (spring) and October (fall), 2006. A total of 27 species of mesozooplankton were identified in spring and 58 species in fall. Dominant species were Oithona tenuis, Flaccisagitta enflata, Penilia avirostris and Centropages tenuiremis in spring, shifting to Microsetella norvegica, Oithona tenuis and Parvocalanus crassirostris in fall. Higher mesozooplankton abundance was found at Aotou Cove and Dapeng’ao Cove compared to other stations, indicating the influence of eutrophication on mesozooplankton community in the Daya Bay. The outbreak of Noctiluca scintillans bloom in spring reduced the species diversity and abundance of mesozooplankton.

Spatio-temporal variations in the siphonophore community of the northern South China Sea

To understand how hydrological and biological factors affect near- to off-shore variations in the siphonophore community, we sampled zooplankton at 82 stations in the northern South China Sea during summer, winter, and spring. Forty-one species of siphonophore were collected by vertical trawling. The species richness of siphonophores increased from the nearshore to offshore regions in all three seasons of investigation, with maximum richness in summer and minimum richness in winter. The abundance of siphonophores was also higher in summer than in spring and winter, concentrated in the nearshore region in the warm season and scattered in the offshore region in the cold season. Four siphonophore groups were classified according to the frequency of occurrence: nearshore, near-offshore, offshore, and tropical pelagic. Among them, the nearshore group had higher abundance nearshore compared with the offshore. The tropical pelagic group had higher species number offshore than nearshore. Spatial and temporal fluctuations in taxonomic composition and abundance of siphonophores were due to the influence of the coastal upwelling and surface ocean currents of the South China Sea, driven by the East Asia monsoonal system.

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.

Bathyconchoecia liui n. sp., a new species of ostracod (Myodocopa, Halocyprididae) from the South China Sea

A new species of halocyprid ostracod, Bathyconchoecia liui, from the bathypelagic zone of the Nansha Trough (North-West Borneo Trough, southern South China Sea) is described and illustrated. It is compared with the closely similar species B. angeli George, 1977. The present species is easily distinguished from B. angeli by the structures of the toothed edges of the mandibular basis and coxa, and by the segmentation of the fifth limb.

Distribution patterns of appendicularians and copepods and their relationship on the northwest continental shelf of South China Sea during summer

The potential suppression of copepods on appendicularians was found in field and experimental conditions. The abundance and distribution of appendicularians and planktonic copepods were studied with reference to their correlations during summer on the northwest continental shelf of the South China Sea (SCS). Based on the topography and water mass of the surveyed region, it was divided into three sub-regions: Region I (inshore waters of the east Leizhou Peninsula) with low temperature, salinity and high chlorophyll a (Chl a) concentration, Region II (inshore waters of the east and southeast Hainan Island) with low temperature, high salinity and moderate Chl a concentration and Region III (offshore waters from the Leizhou Peninsula to Hainan Island) with high temperature, high salinity and low Chl a concentration. The species richness of appendicularians and copepods increased from the inshore to offshore waters, and high values were observed in Region III. The distribution of appendicularian and copepod abundance decreased generally from the inshore to offshore waters, with the highest values at Region I. Our results suggest that the distribution patterns of appendicularians and copepods differed significantly, as a result of the influence of physical and biological factors. The negative impact of pelagic copepods on appendicularians was not found based on in situ data in the northwest continental shelf of SCS.

Seasonal variations in diversity and abundance of surface ichthyoplankton in the northern South China Sea

The objective of this study was to investigate the seasonal variations of ichthyoplankton diversity and abundance in the northern South China Sea based on the data collected during summer, winter and spring. In total, 95 taxa of larval fishes were identified. The greatest number of species was recorded in spring, followed by summer and winter. The number of species was distributed mainly in the coastal waters from the east of Leizhou Peninsula to the southeast of Hainan Island during the surveyed periods of summer and spring, but in the offshore waters during winter. The abundance of larval fish was lowest in winter, increased in spring, and reached the maximum in summer. High abundance of larval fish was generally restricted to coastal waters with the isobaths less than 50 m. Seasonal variations of larval fish richness, abundance and diversity index were significant (P<0.001). Carangidae was the most common and abundant taxon in summer and winter, while Sardinella sp., Thrissa mystax and Leiognathus sp. were dominant in spring. High diversity and abundance of larval fish might be attributed to increased temperature and coastal upwelling in spring and summer.

BATHYCONCHOECIA INCISA SP NOV (MYODOCOPA, HALOCYPRIDIDAE), A NEW SPECIES OF OSTRACOD FROM THE NERITIC ZONE OF THE SOUTH CHINA SEA

Specimens previously identified as Bathyconchoecia paulula sensu Yin & Chen, 1991 and Bathyconchoecia galerita sensu Yin & Chen, 1991, together with two similar specimens, are reclassified as a new species, Bathyconchoecia incisa sp. nov., which we describe and illustrate in detail here. The present species is similar to Bathyconchoecia sagittarius and Bathyconchoecia kornickeri in having a shallow notch on the posterodorsal corner of the carapace, but can be easily distinguished from these species by the structure of the posterior margin of the carapace and the striated sculpturing on the surface of the valves. The specimens on which this new classification was based were collected at shallow depths (<125 m) off the east coast of Hainan Island, in the northern South China Sea and in the Zengmu (James) Shoal and adjacent areas in the southern South China Sea. B. incisa is likely to be a shallow-water species or has a wide bathymetric range.

SEASONAL AND SPATIAL VARIATIONS OF CLADOCERANS ON THE NORTHWEST CONTINENTAL SHELF OF THE SOUTH CHINA SEA

The seasonal and spatial variations of cladocerans were studied based on samples collected with 169 mu m mesh plankton nets from July to August 2006 (summer), December 2006 to January 2007 (winter), and in April 2007 (spring) on the northwestern continental shelf of the South China Sea. Three species of cladocerans (Pseudevadne tergestina, Penilia avirostris, and Podon schmackeri) were observed. Cladocerans occur in spring and summer, but not in winter. They showed an average abundance of 12.82 (+/- 48.44) inds m(-3) in spring and 64.66 (+/- 188.82) inds m(-3) in summer. P. avirostris occurred in the inshore waters of the Leizhou Peninsula during spring, but in summer they were found in large number along the inshore waters from Leizhou Peninsula to the southeast of Hainan Island, with the highest abundance (1121.50 inds m(-3)). P. tergestina was the most dominant species both in spring and summer, being widely distributed throughout the whole surveyed area. P. schmackeri was distributed mainly along the inshore waters of the Leizhou Peninsula during spring, and mainly along the inshore waters of Hainan Island during the summer (with low density). Our results suggest that the unstable water environment resulting from the strong northeastern monsoon in winter may explain the absence of cladocerans in a large area of the northwest continental shelf of the South China Sea. High chlorophyll a concentration owing to physical factors (e.g., cold eddy, coastal upwelling and mixing) may be the main reason for the difference in the spatial distribution of cladocerans in the subtropical and tropical areas of our survey.