Zooplankton community structure, abundance and biovolume in Jiaozhou Bay and the adjacent coastal Yellow Sea during summers of 2005–2012: relationships with increasing water temperature

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.