Distribution Of Picoplankton Abandance And Their Relationship With Environmental Parameters In Three Ocean Waters

Picoplankton plays an important role in marine ecostystem. Over the past decades,much effort has been devoted to understand picoplankton abundance and their spatialdistribution in Pacific Ocean, India Ocean and the encycling southern Ocean.However，distribution of picophytoplankton, heterotrophic bacteria and viruses onlarge-scale pelagic investigations is practically rare. The correlation amongpicophytoplankton, heterotrophic bacteria and viruses and their relationships withenvironmental factors in different marine environmental conditions, especially thecorrelation between viruses and their host cells are rarer. Therefore, Flow cytometrywas used to study the spatial distribution pattern of Prochlorococcus （Pro）,Synechococcus （Syn）, Picoeukaryotes （Euk）, heterotrophic bacteria and virioplanktonin Pacific Ocean, India Ocean, the encircling southern Ocean and Antarctic waters.PCA （Principal component analysis） and Pearson correlation coefficient analysiswere also used to analyze the relationships between picoplankton and watertemperature, salinity, nutrients （phosphate, nitrate+nitrite and silicate）, dissolvedoxygen in different marine environmental conditions and study the relationshipsbetween viruses and their host cells. RFLP （Restriction Fragment LengthPolymorphism） method was also applied to analyze genetic diversity of Eukaryoticpicoplankton in the Great Wall Bay, Antarctica. It hopes to investigate thedistribution characteristics of picoplankton and their relationship with environmentalfactors, in order to provide the basic data for monitoring, early warning and repairingthe marine environment.（1） In this paper, spatial distribution of Pro, Syn, Euk, heterotrophic bacteria and virioplankton were detected in the waters （30°N–69°S,155°E–69°W）. Euk, heterotrophic bacteria and virioplankton are distributedwidespreadly in the surveyed area, while pico-photosynthetic prokaryotes are not.The latitudinal distribution of pico-photosynthetic prokaryotes was limited by watertemperature. Pro in the western Pacific and the Indian Ocean was distributed to50°Sand46°S from the north, respectively. The minimum temperature limiting theirgrowth was9.7°C and11.8°C, respectively. Pro abundance was the highest in theequatorial regions, it decreased gradually as the latitude increases and finally itdisappears. The range of Pro abundance in the western Pacific and the Indian Oceanwere5.4×10³-4.20×10⁵cells mL^-1and1.45×10⁴-3.73×10⁵cells mL^-1,respectively. The Biomasses in the western Pacific and the Indian Ocean were0.16-15.64mg m^-3and0.20-11.6mg m^-3, respectively. Pro made up55.2%of theestimated phytoplankton biomass in the equatorial regions and accounted for themain contributor to phytoplankton biomass in the Western Pacific, In the WesternPacific, the major factors affecting the distribution of Pro were temperature andnutrients. Pro biomass correlated positively with temperature and low phosphate（p<0.01）, and negatively with high silicate concentration （p<0.01）; Due to highlevels of nutrient waters in the Indian Ocean, Pro was mainly affected by temperatureand Pro biomass were significantly positively correlated with temperature （p <0.01）.（2） Syn in the western Pacific and Indian Ocean distribution was extended to55°S and54.1°S, respectively. The minimum temperatures limiting their growth were4.1°C and6.4°C, respectively. Syn abundance in Mid-latitude waters was higherthan that in the low-latitude waters. Syn in the western Pacific and Indian Oceanwaters abundance were1.10×10³–2.29×10⁵cells mL^-1and1.54×10³–2.79×10⁵cells mL^-1, respectively. The Biomasses were0.26–17.74mg m^-3and0.35–12.93mg m^-3, respectively. In the Western Pacific, Syn was significantly and negativelycorrelated with temperature （p <0.01）, and significantly and positively with nitrate+nitrite and silicate （p <0.01）. In the Indian Ocean, Syn was mainly affected bytemperature, and syn biomass were significantly and positively correlated withtemperature （p <0.01）. 3) Euk abundance in mid-latitude waters was higher than that of low-latitude watersand the lowest in the high-latitude Antarctic waters. Euk abundance in the continentalshelf waters was lower than that of the open waters. Euk abundance in the westernPacific, Indian Ocean, Central Southern Ocean and Antarctic waters were5.2×102–4.68×10⁴cells mL^-1,4.9×102–1.73×10⁴cells mL^-1,7.6×10²–1.04×10⁴cells mL^-1and1.42×10²–4.00×10³cells mL^-1, respectively. Their biomasses were0.26–17.74mg m^-3，0.36–29.8mg m^-3，0.99–14.1mg m^-3and0.06–3.21mg m^-3,respectively. Spatial distribution of Euk was effected by different environmentalfactors in different oceans. In the Western Pacific, the distribution of Euk wasprimarily affected by nutrients and Euk biomass showed a significant and positivecorrelation with nitrate+nitrite and silicate （p <0.01）. In the Indian Ocean, Euk ismainly influenced by temperature and Euk biomass was significantly and positivelycorrelated with temperature （p <0.01）; in the encircling Southern Ocean, Euk biomassshowed a significant and positive correlation with phosphate （p <0.01）, and asignificant and negative correlation with temperature （p <0.01）. In Antarctic waters,eukaryotic phytoplankton abundance showed significant and negative correlationswith water depth, salinity, nitrate+nitrite, phosphate and silicate concentrations （p<0.01）.（4） The abundance of heterotrophic bacteria was the lowest in Antarctic waters, Theanalysis on vertical profile of bacterial abundance indicated that there was nosignificant decrease （p>0.05） in the IS Transect, which depth is shallow. Theirabundance in the bottom layer was lower than in the upper layers in those deeptransects, which the viral vertical distribution was similar to in Antarctic waters. Theabundance in the Western Pacific, the Indian Ocean, Southern Ocean and Antarcticwaters were2.27×10⁵–3.80×10⁶cells mL^-1,2.65×10⁵–1.27×10⁶cells mL^-1,8.4×10⁵–1.32×10⁶个mL^-1and1.05×10⁵–3.69×10⁶cells mL^-1, respectively. The biomasseswere4.54–79.55mg m^-3,5.31–25.4mg m^-3,1.68–26.4mg m^-3and2.10–73.8mgm^-3, respectively. In the Western Pacific, spatial distribution of heterotrophic bacteriais mainly affected by nutrients and bacteria biomass was significantly and positivelycorrelated with nitrate+nitrite and silicate （p <0.01）. In the Indian Ocean, heterotrophic bacteria biomass was significantly and negetively correlated withnitrate+nitrite concentration （p <0.01）. In Antarctic waters, heterotrophic bacteriaabundance showed a significant and negative correlation with water depth, salinity,phosphate and silicate （p <0.01）.（5） Viral abundance in the western Pacific, Indian Ocean, encircling Southern Oceanand Antarctic waters were2.17×10⁶–2.49×10⁷particles mL^-1,3.80×10⁶–2.41×10⁷particles mL^-1,1.46×10⁶–2.98×10⁷particles mL^-1and1.49×10⁶–4.39×10⁷particlesmL^-1, respectively. The biomasses were0.42–4.95mg m^-3,0.76–4.82mg m^-3,0.11–13.3mg m^-3and0.25–8.78mg m^-3, respectively. The spatial distribution ofvirus was mainly affected by the distribution of the host cells. In the western Pacific,viral distribution is affected by host cells and environmental factors. Viral biomasscorrelated positively with the Syn, Euk, heterotrophic bacteria biomass, nitrate+nitrite and silicate （p<0.01）, and negatively with temperature （p<0.01）. In the IndianOcean and Southern Ocean, the distribution of viruses were only affected byheterotrophic bacterial and viral biomass showed a significant and positivecorrelation with heterotrophic bacteria biomass （p <0.01）. In Antarctic waters, viralabundance was significantly and positively correlated with chlorophyll a, eukabundance and bacteria abundance （p <0.01）, and significantly and negativelycorrelated with water depth, salinity, phosphate and silicate were （p <0.01）.（6） According to analyze the biomass of each group of picoplankton in the westernPacific, Indian Ocean and encircling Southern Ocean （including the three partitions ofthe Pacific, Indian Ocean and the Atlantic）, it was found that heterotrophic bacteriaaccounted for the vast majority of the estimated picoplankton biomass in the Pacificand Atlantic, while the contribution of Euk to total picoplankton biomass dominatedin the Indian Ocean. Our results also suggested that antagonistic and synergisticeffects existed among the groups of picoplankton. In one hand, Pro showed asignificant and negative correlation with Syn, Euk and heterotrophic bacteria （p<0.01）, which suggested that pro showed the antagonistic effects with Syn and Euk.In the low-latitude waters, Pro abundance was higher than that of Syn and Eukbecause of high temperature and low nutrients. In the mid-latitude waters, it benifited for the growth of the bigger algae cells with the nutrients increased, then Euk and Synabundance increased while pro growth was limited and its abundance decreased. Onthe other hand, bacteria showed a significant and positive correlation with Syn andEuk （p <0.01）, which which suggested that bacteria showed the synergistic effectswith Syn and Euk. In the mid-latitude waters, Syn and Euk utilized inorganicnutrients for the purpose of growth and thereby changed them into organic nutrients,this then leaded to an increase in the level of organic material. This increased level oforganic nutrients was then utilized to the benefit of heterotrophic bacteria, wherebacterial growth turned organic into inorganic matter. Conversely, the producedinorganic nutrients of bacterial origin could further sustain the growth of Syn andEuk.（7） In the present study, molecular tools were used to investigate the marineeukaryotic communities of Great Wall Bay, Antarctica.18s rDNA genetic library wasconstructed, and then the library of eukaryotic ribosomal DNA were screened byrestriction fragment length polymorphism analysis. The phylogenetic diversity in thelibrary was rather great,430positive clones and38OTUs have been isolated, whichindicates that hat the microeukaryotes in this area are diverse. The38OTUs arefound to distribute in Fungi, Dinophyceae, Cercozoa Ciliates, and Uncultured marineeukaryote clones. The microeukaryotic groups are arranged from the most diverse tothe least diverse as: uncultured Dinophyceae, Fungi, Cercozoa, Ciliates and marinemicroeukaryotes. And the number of OTU of these groups is:2,16,5,2and13,respectively. And the uncultured marine microeukaryotes amounts33.4%of the totalnumbers.