Egg density and sinking rate of a planktonic copepod Calanus sinicus (Copepoda: Calanoida)

Calanus sinicus is regarded as one of the key secondary producers, linking phytoplankton and higher trophic levels, in the China-GLOBEC Project. The density and sinking rate of Calanus sinicus eggs were studied in order to understand the depositional dynamics of eggs. The egg density of C. sinicus was determined by the density-gradient centrifugation with sucrose solution. The mean density of C. sinicus eggs was 1.0733 g cm^-3 with a SD of 0.0087 g cm^-3 in Xiamen Bay from December 2002 to May 2003. Based on Stokes' Law, the values of sinking rate for Calanus sinicus eggs were estimated, ranging from 43.9 to 67.5 m d^-1. The comparison of the egg deposition time and egg hatching time suggested that in most cases virtually all eggs of C. sinicus would settle to the bottom before their hatching in Xiamen Bay even though the eggs have high potential to hatch. The ecological significance of fast settlement of C. sinicus eggs was discussed.