Effect of river plume on phytoplankton community structure in Zhujiang River estuary

To examine the phytoplankton assemblages and the effect of diluted waters on them,a research cruise was conducted from July 19 to August 7,2015 in the Zhujiang(Pearl)River estuary in the northern South China Sea(21°N–23.5°N,111°E–117°E).Samples were collected from 65 stations including one for time-series sampling.A total of 212 phytoplankton taxa were identified from 61 genera belonging to 4 phyla.Among them,122 species identified from 42 genera of Bacillariophyta and 83 species from 15 genera of Pyrrophyta.Chain-forming diatoms dominated the phytoplankton community where Pseudonitzschia delicatissima,Guinardia striata,Thalassionema nitzschioides,and P.pungens comprised about 52%of the total abundance.However,higher cell abundances concentrated on both sides of the estuary,because of low salinity and high nutrients brought by diluted water.In addition,Canonical Correspondence Analysis revealed that salinity and dissolved inorganic nitrogen shaped the species composition in the study area.Furthermore,the Jaccard similarity index showed prevailing high similarity in the distribution of species in low-salinity diluted waters,and the Bray-Curtis similarity depicted distinguished grouping for phytoplankton assemblages along the salinity gradient.However,phytoplankton diel vertical cycles showed maximum abundance occurred at 2:00 am,which was mainly contributed by benthic phytoplankton species Pseudo-nitzschia spp.and T.nitzschioides.

Distribution and environmental impact factors of picophytoplankton in the East China Sea during spring

Marine picophytoplankton(Pico)as a major contributor to primary productivity in oligotrophic waters,play a very important role in marine material cycle and energy conversion,and their key role in the carbon cycle and global climate change is increasingly emphasized.To study the factors aff ecting the dynamic distribution of Synechococcus,Prochlorococcus,and picoeukaryotes in the East China Sea(ECS),a marginal sea of the Northwest Pacific,we investigated 27 stations in May 2017,and collected 148 samples of Pico and nutrients from the surface to the bottom.By means of flow cytometry,the abundance of Pico was measured,and then we estimated the carbon biomass and analyzed the distribution of Pico.Finally,combined with the ECS unique geographical situation and hydrological regime,we evaluated various factors aff ecting the Pico in the ECS.In Pico community,the picoeukaryotes cell abundance was between 0.49×10^(2)-1.44×10^(4) cells/mL.Prochlorococcus ranged from 1.36×10^(3)-3.47×10^(4) cells/mL and Synechococcus ranged from 0.69×10^(3)-1.15×105 cells/mL.Synechococcus was the most,both in abundance and in carbon biomass.Picoeukaryotes were the least in abundance,but has larger contribution to carbon biomass than Prochlorococcus.Water temperature,salinity,and stability of water column influenced Pico distribution.Picoeukaryotes were abundant in the shelf sea,whereas Synechococcus and Prochlorococcus were detected in the northeast of Taiwan,China.This study provided basic information for the study of Pico communities in the ECS and its adjacent marine ecosystem.

The profound influence of Kuroshio intrusion on microphytoplankton community in the northeastern South China Sea

To further understand the effect of Kuroshio intrusion on phytoplankton community structure in the northeastern South China Sea(NSCS,14°–23°N,114°–124°E),one targeted cruise was carried out from July to August,2017.A total of 79 genera and 287 species were identified,mainly including Bacillariophyta(129 species),Pyrrophyta(150 species),Cyanophyta(4 species),Chrysophyta(3 species)and Haptophyta(1 species).The average abundance of phytoplankton was 2.14×10~3 cells/L,and Cyanobacterium was dominant species accounting for 86.84%of total phytoplankton abundance.The abundance and distribution of dominant Cyanobacterium were obviously various along the flow of the Kuroshio,indicating the Cyanobacterium was profoundly influenced by the physical process of the Kuroshio.Therefore,Cyanobacterium could be used to indicate the influence of Kuroshio intrusion.In addition,the key controlling factors of the phytoplankton community were nitrogen,silicate,phosphate and temperature,according to Canonical Correspondence Analysis.However,the variability of these chemical parameters in the study water was similarly induced by the physical process of circulations.Based on the cluster analysis,the similarity of phytoplankton community is surprisingly divided by the regional influence of the Kuroshio intrusion,which indicated Kuroshio intrusion regulates phytoplankton community in the NSCS.

Living coccolithophores in the western Pacific Ocean with mesoscale eddies

Living coccolithophores(LCs)are regarded as a group of calcifiers and play important roles in global carbon cycle.This study used microscopic observations of LCs in the western Pacific Ocean to investigate their community structure and biodiversity,especially to test whether local physical traits(mesoscale eddies)could explain their biogeographic distributions during autumn of 2017.The coccolithophore calcite inventory based on carbon-volume transformation was estimated in this study.A total of 28 taxa of coccospheres and 19 types of coccoliths were identified from 161 samples.Gephyrocapsa oceanica was the most predominant species in all the coccolithophore community,followed by Florisphaera profunda,Emiliania huxleyi,Umbilicosphaera sibogae,Gladiolithusflabellatus and Umbellosphaera tenuis.The abundance of coccospheres and coccoliths ranged from 0 to 26.8×10^(3)cells/L and from 0 to 138.5×10^(3)coccoliths/L,averaged at 4.2×10^(3)cells/L and 10.9×10^(3)coccoliths/L,respectively.This study indicated that coccolithophore community in the survey area can be clustered into four groups.Three ecological niches of coccolithophores were characterized by their vertical profiles and multivariate statistical analysis.Coccolithophore abundance and species composition were remarkably different among warm-eddy region,G.oceanica dominated warm-eddy region,while F.profunda dominated warm-eddy and none-eddy region.The average values of estimated particulate inorganic carbon,particulate organic carbon were0.197μg/L and 0.140μg/L,respectively.The current field study widened the dataset of coccolithophores in western Pacific Ocean.

Effects of typhoon Roke and Haitang on phytoplankton community structure in northeastern South China sea

The influence of typhoon and Kuroshio intrusion process on the natural phytoplankton assemblages in the northeastern South China Sea(neSCS)was examined during a cruise in summer 2017.One hundred ninety-six seawater samples were collected and analyzed in the neSCS.In total,299 species were identified belonging to 82 genera,mostly dominated by Bacillariophyta(159),followed by Dinophyta(132),Cyanophyta(4)and Chrysophyta(4).Among all,Thalassionema nitzschioides,Thalassionema frauenfeldii,Thalassiosira minima,in Bacillariophyta,Prorocentrum lenticulatum,Prorocentrum compressum in Dinophyta,and Trichodesmium thiebautii,in the Cyanophyta were the most dominated species,respectively.Correlation analysis shows compared with other groups Bacillariophyta was mostly influenced by silicate,whereas,Dinophyta and Cyanophyta showed significant correlation with temperature,salinity,phosphate,and nitrate.After the typhoon,the higher abundance of Dinophyta was observed,whereas it was lower in case of Bacillariophyta and Cyanophyta,shows typhoon“Roke“and”Haitang”had a significant influence on the phytoplankton assemblages,which could be manifested by the variations of total phytoplankton abundance in the surface water of neSCS.Overall,our present study provides the latest in-depth information about how the environmental factors influencing the phytoplankton density and diversity in the neSCS during summer.