Studies On Phytoplankton And Microzooplankton Grazing In The Jiaozhou Bay

The herbivorous activities of microzooplankton were estimated by dilution technique from August 2002 to January 2004 in three typical stations A, B, C in the Jiaozhou Bay. Based on these experiments, the phytoplankton species succession, the grazing rates on phytoplankton of microzooplankton, the intrinsic growth of phytoplankton, the grazing pressure on phytoplankton standing stocks, and the gazing pressure on potential primary productivity were measured.There were 74 phytoplankton species found at the station A, which mainly were composed of diatom. The cell abundance of phytoplankton changed dramatically in different month and the maximum value was 568.4 106cells m-3 which appeared in July, while the minimum was 9.7 106cells m-3 which took place in December. Microzooplankton dominant species were Strombidium sp., Tintinnopsis beroidea and so on. The abundance was lowest and averaged 160 ind L-1 for microzooplankton in February, while there was a maximum value (7720ind L-1) in July. The intrinsic growth rate of phytoplankton and the grazing rate of microzooplankton were 0.18-1.29d-1 and 0.13-1.47d-1 respectively. Microzooplankton ingested 19.12-177.39% phytoplankton standing stocks and 33.64-467.48% daily potential primary productivity. The phytoplankton carbon consumed by microzooplankton ranged from 6.02 to 80.07gCL-1d-1.There were 86 phytoplankton species found at the station B, which were mainly composed of diatom too. The cell abundance cf phytoplankton changed greatly in different month at this station and the maximum value was 1362.4 l06cells m-3 which appeared in January, the sub-maximum value in July (305.2 l06 /m3), while the minimum was 17.0xl06cells m-3 which took place in November and the sub-minimum value in November (16.0 l06 /m3). Microzooplankton dominant species were Strombidium sp., Stenodemella parvicollis, Tin'innopsis beroidea and so on. The abundance was lowest and averaged 760 ind L-1 for microzooplankton in April, whilethere was a maximum value (6680 ind L-1) in March. The intrinsic growth rate of phytoplankton and the grazing rate of microzooplankton were 0-1.12d"' and 0.10-0.15d"' respectively. Microzooplankton ingested 12.47-209.44% phytoplankton standing stocks and 22.57-309.07% daily potential primary productivity. The phytoplankton carbon consumed by microzooplankton ranged from 5.22 tol39.28(igCL"'d"1.There were 76 phytoplankton species found in the station C, which shared the same trend of the two former stations: phytoplankton community was mainly composed of diatom. The cell abundance of phytoplankton changed dramatically in different month at this station and the maximum value was 3693.2* 106 cells m"3 which appeared in June, while the minimum was 17.0xl06cells m"3 which took place in November. Microzooplankton dominant species were Strombidium sp., Tintinnopsis beroidea, Copepod nauplii and so on. The abundance was lowest and averaged 920 ind L"1 for microzooplankton in November, while there was a maximum value (54440 ind L"1) in June. The intrinsic growth rate of phytoplankton and the grazing rate of micrpzooplankton were 0-0.85d'' and 0.02-0.49d~' respectively. Microzooplankton ingested 2.84-48.95% phytoplankton standing stocks and 6.55-419.36% daily potential productivity. The phytoplankton carbon consumed by microzooplankton ranged from 6.60tol51.50ugCL-'d-'.Besides biological factors, sea water temperature, microzooplankton dominant species and phytoplankton cell abundance can effect microzooplankton grazing rate, especially in some special period.Grazing studies on different-size phytoplankton show that microzooplankton prefer ingesting <20p.ni phytoplankton in May inside the Bay and harbor area, while it prefer ingesting >20um phytoplankton outside the Bay. But it seemly prefer ingesting >2um phytoplankton in August in the three stations.Compared with the similar studies in other waters around the world, the grazing pressure of microzooplankton in the Jiaozhou Bay is at the middle levels.