于2008年和2009年夏季分别对南海东北部和东海陆架区浮游植物生物量和群落结构的昼夜变化进行了24 h时间序列连续观测和研究。通过高效液相色谱法分析浮游植物特征光合色素可以看出3个测站的叶绿素a浓度均呈现出明显的昼夜变化，最高值出现在夜间，而在中午至午后达到最低值，而这种昼夜变化主要是由于光照和潮汐作用所导致。各站均以硅藻为最主要的优势类群，受上升流影响的S702站硅藻生物量超过80％，S305和D H04站硅藻也占据了35％～50％，且3个测站硅藻生物量昼夜变化与叶绿素a一致，但所占生物量百分比却在叶绿素 a高值的时间段较低，表明高生物量对应着更为丰富的浮游植物类群组成多样性。除硅藻外，S305站青绿藻也表现出与叶绿素a同步的昼夜变化规律。而在东海DH04站，由于存在明显层化特征，聚球藻是上混合层的主要优势类群，且表现出与叶绿素a一致的变化。黎明前后，甲藻出现了暴发式的生物量升高，所占生物量超过30％，由于其昼夜变化并不明显，分析可能由于水团的侧向输送所致。%Three time-series stations were assigned to the survey of the diurnal variations of phytoplankton biomass and community by the means of photosynthetic pigments at two stations in the northeastern South China Sea ,sum-mer 2008 and one station in the East China Sea in summer 2009 ,respectively .Remarkable diurnal variations of Chl a biomass (fluctuation between 34% ~81% ) ,with the maximum in the nighttime and minimum under daylight was the generality at the three stations under the effects of the tidal mixing and light .Diatoms were more preponderant at Sta .S702 (> 80% ) than Sta .S305 and DH04 (35% ~50% ) ,at which the former was influenced by the coast-al upwelling .The biomass of diatoms varied with total Chl a biomass synchronously ,but the percentage of diatoms changed inversely .It implied the diversity of phytoplankton composition were also improved during the nighttime under the effect of tidal mixing .Prasinophytes was the second dominate group at Sta .S305 ,and also exhibited the same diurnal variation as total Chl a biomass .And the similar response of Synechococcus at Sta .DH04 ,the stratifi-cation status at the East China Sea ,dominated at the upper mixed layer ,also had the diurnal variation pattern with the total Chl a .But the dinoflagellates had a outburst at 03:30 as no indication of any diurnal variation .So the dis-tribution might be the results of lateral transport of other water mass .
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