Zoological Studies

Unexpected Dominance of the Subtropical Copepod Temora turbinata in the Temperate Changjiang River Estuary and Its Possible Causes

Guang-Tao Zhang, Song Sun, Zhao-Li Xu, and Qi-Long Zhang (2010) The zooplankton community in the Changjiang (Yangtze) River estuary (CRE) was sampled quarterly in 2004, the 1st yr after the Three Gorges Reservoir was impounded to a water level of 135 m, in order to investigate possible changes in the community structure after freshwater control upstream at the dam.  Zooplankton assemblages were consistent with previous studies in all seasons except summer.  A tropical-subtropical copepod species, Temora turbinata, was found to be the most abundant zooplankton species in this area for the 1st time in Aug. 2004, while previously dominant species, such as Calanus sinicus, Euchaeta concinna, and Labidocera euchaeta, decreased in abundance and appearance frequency.  From historical data, T. turbinata was never dominant in this area before 2003.  It was present only in summer, in accordance with the northerly invasion of the Taiwan Warm Current (TWC).  In this study, the range of the Changjiang River Diluted Water was found to have shrunk in summer, and the TWC occupied a larger area of both the bottom and surface layers, compared to the long-term average.  Our results indicate that T. turbinata in the CRE area was recruited from the southern part of the East China Sea by the TWC.  Its unexpected dominance suggests a northward extension of warm-water species resulting from global warming, although it appeared immediately following water control at the Three Gorges Reservoir.