Annual Occurrence of Calanus sinicus Carcasses in the Jiaozhou Bay and the Adjacent Waters

The dead proportion of a calanoid copepod Calanus sinicus population was investigated monthly with neutral red staining method at 12 stations in the Jiaozhou Bay and the adjacent waters from December 2008 to November 2009. C. sinicus could be observed through the whole year, with an evident numerical peak from February to April and an extremely low abundance in summer. Annual variation of the dead proportion differed greatly between adult females and copepodites. Dead females were observed only in the southern part and outside the bay sporadically in five months, when the egg production was the most active. Dead proportion of females was usually less than 5%. Dead copepodites could be observed in all but three months in summer in the whole study area, and the proportion varied between 3.8%–18.2%. Death percentage of copepodites increased significantly in the northern part in January and June, when water temperature exceeded it’s favorable limits; however, the fluctuated salinity had no significant effect on the survival of both females and copepodites. Thus the dead proportion of C. sinicus was relatively low in the Jiaozhou Bay, while difference could be observed between females and copepodites. Dead copepodites were common in all samples, but dead females were presented mainly as ‘reproduction cost’ during generation alternation.