Abstract: With dilution method,this paper studied the microzooplankton grazing on phytoplankton inside,outside and in a harbor area of the Jiaozhou Bay during June and July 2002.The dominant phytoplankton species outside and inside the bay were Cylindrotheca closterium and Skeletonema costatum,while the samples in the harbor had Skeletonema costatum,Eucampia zodiacus,and Chaetoceros curvisetus as the dominant species.The dominant microzooplankton species outside and inside the Jiaozhou Bay were Tintinnopsis beroidea and unidentified Strombidium sp.,while in the harbor,Strombidium sp.was the predominant microzooplankton species coexisted with few T.beroidea.The grazing rate of microzooplankton was 0.96 and 1.20 d^-1 outside the bay,1.33 d^-1 inside the bay,and 0.36 d^-1 in the harbor.The grazing rates of microzooplankton and the consumption percentages of potential primary production increased in turn from harbor area,outside the bay,to inside the bay.They were 74% and 84% outside the bay,93% inside the bay,and 53% in the harbor.The ingestion rate of phytoplankton carbon by microzooplankton was the highest in the harbor,with a value of 281 mgC穖^-3穌^-1,the next was inside the bay,with a value of 102 mgC穖^-3穌^-1,and the lowest was outside the bay,ranged from 31 to 49 mgC穖^-3穌^-1.It seems that the phytoplankton community size structure and grazing behaviors of dominant microzooplankton species are the causes for these grazing differences.Compared with the similar studies in other bays around the world,the grazing pressure of microzooplankton in the Jiaozhou Bay is at the middle levels.

Key words: Microzooplankton, Phytoplankton, Carbon-to-chlorophyll a ratio, Grazing rate, Grazing pressure, Jiaozhou Bay