From August 10 to August 28, 2008, four surveys of phytoplankton were conducted in the coastal waters of Rushan, Shandong Province. The results showed that the red tide was caused by the bloom of Chattonella marina, the area was about 100 km^2 with an average cell concentration of 1.46×10^6 cells/L, accounting for 91.32% of the total phytoplankton in the surveyed waters. From August 19, the abundance of C. marina began to decline, and the abundance of Skele- tonema costatum and Pseudo-nitzschia pungens began to increase. The red tide attenuated completely on August 28. Eutrophication, low salinity, low light and favorable hydrometeorological conditions provided a good physical and chemical environment for the occurrence of red tide. The abundance of C. marina was positively correlated to dinoflagellate abundances, pH, COD, nitrates, inorganic nitrogen and chlorophyll a （r = 0.933, 0.546, 0.706, 0.645, 0.649, 0.568, P〈0.01）, but negatively correlated to salinity （r =-0.707, P〈0.01）.%于2008年8月10—28日，在山东乳山近海赤潮发生海域采用直接采水计数法对浮游植物种类组成进行了4次跟踪监测。结果表明，此次赤潮主要由海洋卡盾藻引起，面积约100km^2，平均密度1．46×10^6cells／L，占浮游植物总数的91．32％。从8月19日开始，海洋卡盾藻赤潮开始消退，同时中肋骨条藻和尖刺拟菱形藻密度增高，到8月28日本次赤潮完全消失。研究发现，该海域富营养化、低盐度的理化环境和低光照、低气压的气象条件是此次赤潮发生的关键因子。海洋卡盾藻丰度与甲藻丰度、pH、化学需氧量、硝酸盐、无机氮和叶绿素a等呈显著正相关（P〈0．01），相关系数分别为0．933、0．546、0．706、0．645、0．649和0．568，而与盐度呈显著负相关（r=-0．707，P〈0．01）。
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