Short-term variation in abundance of four Acartia species (Copepoda, Calanoida) in a eutrophic bay

The short-term variation in the abundance of Acartia copepods in the eutrophic Gamak Bay of South Korea was investigated with weekly measurements from October 2007 to September 2008. During this period, four Acartia species (A. erythraea, A. ohtsukai, A. omorii, and A. sinjiensis) were recorded as showing seasonally different peak abundance. The abundance of A. erythraea and A. sinjiensis was high in autumn, whereas that of A. omorii was high from winter to spring. In summer, A. erythraea, A. ohtsukai, and A. sinjiensis coexisted at peak abundance significantly related to water temperature and salinity. Results from the response curves of the four Acartia species to water temperature and salinity suggest that A. erythraea and A. sinjiensis increased in abundance at water temperatures >18 °C, whereas A. ohtsukai increased in abundance at water temperatures >27 °C. The occurrence of A. erythraea, A. ohtsukai, and A. sinjiensis decreased with increasing salinity, but chlorophyll-a concentration showed no effect on occurrence. Despite these findings, the coexistence of the three ecologically similar species may be due to prey abundance in summer and autumn (chlorophyll-a concentration >10 µg L-1). Notably, the wide range of the response curve of A. omorii indicates its occurrence at higher salinity levels than other species.