THE RELATIONSHIP BETWEEN QUANTITATIVE CHANGES OF MICROPLANKTON AND POPULATION DYNAMICS OF SMALL MEDUSA IN THE JIULONG RIVER ESTUARY IN SPRING OF 2011
九龙江口春季微型浮游生物数量变动及其与小型水母消长的关系

The abundances and compositions of phytoplankton,microzooplankton and small medusa were investigated in the Jiulong River Estuary in spring of 2011,meanwhile environmental factors such as nutrients,temperature,and salinity were measured.Totally 45 species of phytoplankton were recorded,and Skeletonema costatum,Melosira granulate,Synedra spp,Scenedesmus obliquus,Alexandrium minutum,and Merismopedia elegans showed high detection rate.Microzooplankton contained four classes,in which Mesodinium rubrum was the most common species,accounting for 55.5%—79.8% of the total population,aloricate ciliates were second;and loricate ciliates and nauplius were less than 10%.The total abundances of Blackfordia virginica,Pleurobrachia globosa,Eirene xiamenensis,and Hydroidomedusae larvae dominated 85% of small medusa species.There was a peak value of small medusa abundances in late April and early May,up to(69.49±29.4)ind/L,and the quantity of microzooplankton decreased from(1085±574.66)ind/L to(526±152.93)ind/L,while the percentage of micro-chlorophyll a in bulk chlorophyll a was(42.26±12.94)%.Then,the abundances of microzooplankton increased alone with the decreasing numbers of small medusa.The abundances of phytoplankton,microzooplankton,and small medusa were in a dynamic equilibrium during the spring period in this estuary.