Dynamics Of Virioplankton, Picophytoplankton, Heterotrophic Bacteria And Correlation With Environmental Factors In The Coastal Waters Of Qingdao

In this paper,four seasons samples were collected during four cruises in August 2006(summer),December2006(winter),April2007(spring) and October2007(autumn) in the coastal waters of Qingdao.Virioplankton,picophytoplankton and heterotrophic bacteria are determined by flow cytometry,and the correlation of the abundance between virioplankton,picophytoplankton,heterotrophic bacteria and environmental factors were analyzed.It is identified that two types of virioplankton (â…¤-â… virioplankton andâ…¤-â…¡virioplankton),three types of heterotrophic bacteria(B-â… bacteria,B-â…¡bacteria and B-â…¢bacteria) and two types of picophytoplankons (Syneckococcus and Eukaryote) in the Coastal waters of Qingdao,but Procklorococcus is not found in all samples.In the Coastal waters of Qingdao,the average value of virus abundance is 1.22×10⁷ mL^-1 in summer,3.28×10⁶ mL^-1 in winter,2.47×10⁷ mL^-1 in spring,and 1.25×10⁷ mL^-1 in fall.The abundance of virus shows obvious difference among four seasons(P＜0.01),and decreases with seasons in sequence of spring,summer,summer, fall.In horizontal direction,the distribution of virus is extremely similar with that of heterotrophic bacteria.The virus abundance at the surface water layer is higher than that of 10 m layer only in summer.No obvious difference exists among water layers in winter,spring and fall.Diel patterns of vius abundance variation is stable at all water layers and the variation is little in spring and fall,but the situation is reversed in summer and winter.The variation of virus abundance at bottom layer is larger than others.The average value of Syn abundance is 2.24×10⁴ mL^-1 in summer,8.83×10³ mL^-1 in winter,5.43×10³ mL^-1 in spring,and 1.96×10⁴ mL^-1 in fall.Syn abundance shows obvious difference among seasons(P＜0.01),and decreases with seasons in sequence of summer,fall,winter,spring.In horizontal distribution,high Syn abundance locates mostly in southern and far off-coastal waters.In vertical distribution,Syn abundance at 10 m layer of water is lower than that of bottom layer only in winter,and varies little in the other three seasons.Diel patterns of of Syn abundance change is much the same at surface and 10m layer(including 5 m layer in spring and winter) of water.A rising trend appears in all layers in afternoons.Syn abundance shows similar diel variation in fall and winter.The average value of Euk abundance is 1.86×10³ mL^-1 in summer,4.20×10³ mL^-1 in winter,2.93×10⁴ mL^-1 in spring,and 8.34×10³ mL^-1 in fall.Euk abundance shows obvious difference among seasons(P＜0.01),and decreases with seasons in sequence of spring,fall,winter,summer.Distribution of high Euk abundance shows in the coastal waters in summer,spring and fall,while shows in the southern area in winter.In vertical distribution,Euk abundance at surface,5m and 10m layer of water is higher than that of bottom layer only in spring,and shows no distinct variation in the other three seasons.The diel trend of Euk abundance change is much the same at surface and 10m layer(including 5 m layer in spring and winter) of water.A rising trend appears in all layers in afternoons.The same diel pattern of Euk abundance is decreases a little and increases then and repeats again,which resembles in all seasons except summer.The average value of heterotrophic bacteria abundance is 2.08×10⁶ in summer, 3.74×10⁵ mL^-1 in winter,1.41×10⁶ mL^-1 in spring,and 1.08×10⁶ mL^-1 in fall. Heterotrophic bacteria abundance shows obvious differences among seasons(P＜0.01), and decreases with seasons in sequence of summer,spring,fall,winter.There is no obvious difference in all the seasons in vertical distribution of heterotrophic bacteria. The diel patterns of heterotrophic bacteria abundance stay stable at all water layers and the variation is little in spring and fall,but the situation is reversed in summer and winter.In the coastal waters of Qingdao,virioplankton abundance has major positive correlation with heterotrophic bacteria and VBR,while heterotrophic abundance has evident negative correlation with VBR.Syn abundance has obvious positive correlation with Euk abundance in summer and winter.In spring,heterotrophic abundance has distinct positive correlation with Euk abundance,as is negative with Syn abundance.In summer and winter of the coastal waters of Qingdao,the relation between nutrient salt and Syn as well as Euk is closer than that for virioplankton and heterotrophic bacteria.Syn abundance shows obvious positive correlation with ammonium,active phosphate,nitrate and nitrite in summer.In winter,Syn and Euk show obvious negative correlation with total nitrogen,total phosphorus,nitrate,active phosphate and silicate as well as soluble nitrogen and phosphorus.Virioplankton, heterotrophic bacteria abundance and VBR relate with the concentration of silicate in winter and summer.Chlorophyll a is negatively correlated with viral abundance and VBR,as is positive correlated with bacterium and Euk.