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The population explosion of jellyfish Aurelia coerulea occurred in Jiaozhou Bay, China in 2009. The potential predation impact of A. coerulea on zooplankton was investigated. Population clearance potential and residence time (t1/2) for copepods were calculated from laboratory clearance rates and measurements of jellyfish size and abundance from May to August 2009 in Jiaozhou Bay. Clearance rates varied widely with prey organisms, but they were not significantly different among various prey concentrations. Medusae captured rotifers, fish larvae and hydromedusae more efficiently than fish eggs, copepods and chaetognaths. Ephyrae captured rotifers and hydromedusae more efficiently than fish larvae and copepods. Clearance rate linearly increased with the cross sectional area of A. coerulea (size from 0.3 to 7.1 cm). Water temperature also had a marked effect on clearance rate and this was related to the increased beat frequency as water temperature increased. In early May 2009, A. coerulea potentially cleared the volume of water in the Bay less than 0.001 times a day, but this value was estimated to be more than 0.3 times a day in July. The t1/2 for copepods was less than 6 d in June and July. Abundances of copepods, hydromedusae and chaetognaths were extremely low in 2009 compared to 2008 and 2010 (jellyfish non-bloom years). Large predation pressure by the A. coerulea population occurred to control zooplankton communities in Jiaozhou Bay. A. coerulea, when present at a high population level, can be a keystone species in Jiaozhou Bay and control the trophic structure here. [ABSTRACT FROM AUTHOR]

Zooplankton abundance, biovolume and taxonomic composition in Jiaozhou Bay and the adjacent coastal Yellow Sea were evaluated using ZooScan measurement of samples collected by net towing every August from 2005 to 2012. Zooplankton abundance and biovolume ranged from 1 938.5 to 24 800 ind./ m3 and 70.8 to 1 480.1 mm3 /m3 in Jiaozhou Bay and 73.1 to 16 814.3 ind./m3 and 19.6 to 640.7 mm3 /m3 in the coastal Yellow Sea. Copepods were the most abundant group in both regions, followed by Noctiluca scintillans and appendicularians in Jiaohzou Bay, and chaetognaths and Noctiluca scintillans in adjacent coastal Yellow Sea. Over the study period, the most conspicuous hydrographic change was an increase in water temperature. Meanwhile, a general decrease in zooplankton abundance was observed, particularly in copepod populations. Based on redundancy analysis (RDA), the warming trend was the key environmental factor influencing to decrease of copepod abundance. The proportion of small-sized copepods increased while the mean size of all copepods decreased, in significant correlation with water temperature. Our results indicate that zooplankton, particularly copepods, are highly sensitive to change in water temperature, which is consistent with predicted impacts of warming on aquatic ectotherms. Due to their dominance in the zooplankton, the decline in copepod size and abundance could lead to an unfavourable decrease in energy availability for predators, particularly planktivorous fish. [ABSTRACT FROM AUTHOR]

Seasonal variations in numerical abundance, cell diameter and population carbon biomass of the heterotrophic dinoflagellate Noctiluca scintillans were studied for 10 years from 2004 to 2013 in Jiaozhou Bay and adjacent coastal Yellow Sea, China, and their ecological functions were evaluated. In both areas, N. scintillans occurred throughout the year and demonstrated an essentially similar seasonality; the cell abundance increased rapidly from the winter minimum to an annual peak in late spring and early summer, and decreased gradually toward the autumn-winter minimum. The peak abundance differed by years, and there was no consistent trend in long-term numerical variations. The cell diameter also showed a seasonal fluctuation, being larger in spring and early summer than the other seasons. Estimated carbon biomass of N. scintillans population reached to a peak as high as 90.3 mg C/m3, and occasionally exceed over phytoplankton and copepod biomass. Our results demonstrate that N. scintillans in northwestern Yellow Sea displays the seasonal phenology almost identical to the populations in other temperate regions, and play important trophic roles as a heterotroph to interact with sympatric phytoplankton and copepods. [ABSTRACT FROM AUTHOR]