Distribution pattern of zooplankton functional groups in the Yellow Sea in June: a possible cause for geographical separation of giant jellyfish species

Because jellyfish are sensitive to the availability of prey, their distribution likely is linked to the distribution pattern of zooplankton functional groups. We studied the regional and interannual variations of zooplankton functional groups in the Yellow Sea using data from six cruises conducted in June between 2000 and 2009. We compared these data to previously collected data on giant jellyfish distri- bution and biomass. Our results indicate that different zooplankton functional groups have their own rela- tively fixed distribution patterns and that the distribu- tion of zooplankton can affect the distribution of the jellyfish community. Giant crustaceans and large copepods were found to be mainly distributed off- shore, small copepods and small jellyfish tended to be located in the coastal region, and chaetognaths were mainly sampled along the 50 m isobath. Sea bottom temperature and salinity, determined by the Yellow Sea Cold Water Mass, are shown to have been major factors affecting the distribution of zooplankton functional groups. Among zooplankton functional groups, small copepods and giant jellyfish show similar distribution patterns, suggesting that the abundance of small copepods is feeding that of giant jellyfish. The observed interannual biomass of small copepod was positively related to temperature, and we suggest that this relationship may explain the rarity of giant jellyfish outbreaks in cold years.