ANNUAL CHANGES IN CLYTIA HEMISPHAERICA ABUNDANCE AND ITS GRAZING PRESSURE ON ZOOPLANKTON POPULATION IN THE JIAOZHOU BAY
胶州湾半球美螅水母(Clytia hemisphaerica)数量周年变动及对浮游动物摄食压力估算

Annual changes in Clytia hemisphaerica abundance was analyzed,according to the monthly zooplankton samples collected using 50cm diameter net(mesh size 500μm) in 2009—2010.The grazing pressure on zooplankton population in the Jiaozhou Bay was also calculated via the feeding rates of C.hemisphaerica.As far as seasonal variation of abundance and the grazing pressure on zooplankton were concerned,C.hemisphaerica became one of the dominant species that peaked once a year,i.e.,in May and June,2009 and June,2010.Its abundance values were 34.5,41.3,45.3ind/m3 during these three periods,accounting for 74.0%,95.2%,48.9% of the total medusa population,respectively.In May and June,2009,the daily grazing pressure values on zooplankton were 0—28.08%,0—74.99%,respectively;while the grazing pressure was 0—105.96% in June,2010.In May and June,2009,C.hemisphaerica was mainly distributed near the Bay mouth,outside and center.The daily grazing pressure on zooplankton in D6 station was up to 74.99% in June,2009.In June,2010,C.hemisphaerica was mainly distributed in western of Jiaozhou Bay,in which the daily grazing pressure on zooplankton of C1 station reached 105.96%.The outbreak of C.hemisphaerica seriously impacts the zooplankton community structure.However,in other months of 2009 and 2010,C.hemisphaerica significantly diminished,exerting minimal impact on the zooplankon population.