The Distribution Of Picoplankton Communities In The Southern Yellow Sea

The distribution of the picoplankton community in the south Yellow Sea,including Synechococcus, picoeukaryotes and heterotrophic bacteria was studiedbased on samples collected during eight cruises in August2006, January2007, April2007, November2007, February2008, August2008, August2010and August2011.Plankton abundance was acquired and analyzed using flow cytometry method. Thecorrelation between the distribution of plankton abundance and enviromental factorswas also discussed in this paper. The major objective of this paper is to reveal theinfluence factors on seasonal and interannual variation of picoplankton in southernYellow Sea. This research can provide fundamental data and basic information for thefurther study on large marine ecosysterm of Yellow Sea.The main results of this study are as follows:1. The abundance and distribution of picoplankton in the south Yellow Sea.Picoplankton abundance has obvious seasonal change. The average abundance ofSynechococcus in each season has a rule with: summer> autumn> spring> winter.The rule of average picoeukayotes abundance is: summer> spring> autumn=winter.And the rule of the average abundance of heterotrophic bacteria is summer> autumn>spring> winter.As the data shows, the highest abundance of Synchococcus is91.3×104cells/mLin summer2006, the highest abundance of picoplankton is6.4×104cells/mL in spring2007, and the highest abundance of heterotrophic bacteria is946.1×104cells/mL inautumn2007, respectively. The picoplankton distribution has different rules in eachseason, but in most case the distribution of surface and10m is similar. Thedistribution of vertical section reflects the feature as hydrological features changing.In summer and autumn, they are limited above the thermocline. While in spring and winter, the abundance mixed well in upper and lower layers with the seawaterstratification becoming waker. The distribution of heterotrophic bacteria is relativelyless influenced by the seawater stratification. In addition, there are also some tracksinfluenced by ocean currents in spring.2. The effects of environmental factors on distribution of picoplankton.Temperature is one of the main factors which can affect the abundance ofpicoplankton. With the effect of low temperature, the Prochlorococcus could not befound in the south Yellow Sea. At the same time, temperature could determine theregional distribution characteristics of picoplankton. In summer and autumn, theseawater vertical stratification was forming as the increase of surface temperature.Picoplankton was isolated above the thermocline by vertical stratification. Thisphenomen was disappeared as the seawater stratification fading away.Salinity did not have obvious influence on picoplankton, but it could reflect theinvasion of diluted water and ocean currents. Combining with temperature data, theocean currence water with high temperature and high salinity could be found invadingfrom northwest, in spring2007. Along its diffusion path, the abundance ofpicopankton was relatively high. And in August2008, picoplankton distributed alongthe diffusion direction of diluted water, and their abundance was also relatively high.The concentration of nutrients from terrestrial injection was so high that thelimitation of nutrients only emerged in some local scope. In July2006and April2007,there were some obvious areas with limitation of phosphate in the vertical directionand the spread of phytoplankton was blocked by the low concentration of phosphate.Light and turbidity could also affect the distribution of phytoplankton.Phytoplankton had the similar mechanism of light adaptation to make up for the shortof light in deeper layer, and the pigment content increased for photosynthesisradiation as the light became weaker. In addition, the effects of other environmentalfactors, such as dissolved oxygen, were also discussed in this study.3. The relationship between picoplankton and chlorophyll a classification.The distribution of chlorophyll a in different layer had similar rules. Theseasonal distribution of chlorophyll a was as follows: the high concentration of it was in the northeast area and coastal area, which was similar with the distributioncharacteristics of picoplankton in spring. In summer, high concentration appeared inthe southern part of the research area influenced by the Changjiang River and inautumn and winter the high concentrations mainly distributed at the south ofShandong peninsula. The seasonal variation of chlorophyll a was summer (1.4mg/m3)> autumn (1.3mg/m3)> spring (0.99mg/m3)> winter (0.98mg/m3).Size-fractionated chlorophyll a reflected the contributon of plankton inparticle-size spectra. The contribution of picoplankton to total chlorophyll a was33%in spring,35%in summer,31%in autumn and25%in winter. While in the centralmass of Yellow Sea, the contribution was48%in spring,58%in summer,40%inautumn and73%in winter.