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.
To understand the influence of Kuroshio intrusion on the phytoplankton community,a field investigation was conducted in spring 2017 in the East China Sea(ECS),and 130 seawater samples were collected and analyzed.Trichodesmium comprised the highest cell abundance contributing about 66%of the total phytoplankton followed by diatoms(17%)and dinoflagellates(16%).The dominance of the Kuroshio Waters(KW)and the Taiwan Warm Currents(TWC)were higher than the Coastal Waters(CW).The vertical distribution of physicochemical parameters depicted the intrusion of KW at the bottom layer,but it failed to reach the surface as strong upwelling was not initiated.Therefore,the dissolved inorganic phosphate(DIP)concentrations and P/N ratios were the lowest in the CW and the upper water layers,which limited the diatom growth in this area.Besides,the dinoflagellates cell abundance was also lower except in the surface and CW,though they comprised the maximum richness of species among the phytoplankton community.However,the unique characteristics such as diazotrophy and gas vacuoles of Trichodesmium made the situation advantageous,and they comprised the maximum cell abundance in this area especially in KW and the TWC.Temperature,DIP and P/N ratios appeared to be the major environmental drivers for Trichodesmium proliferation in the ECS during the study period.
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.
Qi ZHONGBing XUEMd Abu NOMANYuqiu WEIHaijiao LIUHongbin LIULiping ZHENGHongmei JINGJun SUN
