Population dynamics of four dominant copepods in Prydz Bay, Antarctica, during austral summer from 1999 to 2006

Abstract

Population dynamics of four dominant Antarctic copepods, Calanoides acutus, Calanus propinquus, Metridia gerlachei and Rhincalanus gigas were studied based on zooplankton samples collected in the Prydz Bay during austral summer from 1999 to 2006. We found that C. acutus was the most abundant species among these four copepods, followed by C. propinquus, M. gerlachei and R. gigas. R. gigas occurred mainly in the warmer oceanic regions and showed distribution patterns discrete from the other three species, whose distribution in the whole survey area overlapped. By December 15(th) (about one month before our sampling) of the years 1999, 2003 and 2006, sea ice retreated earlier and polynyas existed in the neritic region one month before sampling. These periods were characterized by numerical dominance of C. acutus, C. propinquus and M. gerlachei, elevated proportions of Copepodite I and Copepodite II stages especially in the neritic region. While for the years 2000, 2002, and 2005, the ice edge located more northerly and polynyas did not exist in the neritic region, the copepods abundance was lower, indicating poor recruitment. Population structure of R. gigas was mainly composed of advanced stages Copepodite V and female during all cruises. Log(10) (x+1) transformed densities of C. acutus, C. propinquus and M. gerlachei showed positive correlation with temperature and chlorophyll a concentration, while mean population stages of these copopods were negatively correlated with these environmental variables. Younger copepodite stages of C. acutus, C. propinquus and M. gerlachei appeared more often in neritic regions. We confirmed that the polynyas had a great contribution to phytoplankton blooms, which promote copepods reproduction and recruitment success. The study suggested that population dynamics of the four copepods have good correspondence with sea ice and polynya variations during all cruises of the Prydz Bay.