A report on a Moon Jellyfish Aurelia aurita bloom in Sishili Bay, Northern Yellow Sea of China in 2009

In recent years, an increasing number of reports on blooms of Moon Jellyfish (Aurelia aurita) have occurred in the northern coast of China. Throughout the summer of 2009, we studied the occurrence of an A. aurita bloom in relation to environmental variables in the Yantai Sishili Bay of the Northern Yellow Sea. The mean abundance of A. aurita was 0.62 no m^-3 in summer 2009 with a highest density of 2.28 n m^-3, while the mean biomass of A. aurita was 163.7 mg C m^-3. Highest biomass peaked at 673.6 mg C m^-3. The present study showed that the spatial distribution of A. aurita seemed unrelated to the environmental variables: sea surface temperature, salinity, dissolved oxygen and nutrients. Chlorophyll a concentration was positively correlated to the occurrence of A. aurita in summer 2009, suggesting a cascading effect resulting from the jellyfish grazing on zooplankton that in turn reduced grazing of zooplankton on phytoplankton. Increased suitable settlement and reduced currents in the Bay by intense building of coastal construction and aquaculture rafts were discussed as possibly being the main drivers for the proliferation of Moon Jellyfish A. aurita. Further investigations on A. aurita polyps in situ should be conducted to address this hypothesis and relate these to current management policies.