Life Strategy Of Calanus Sinicus In The Southern Yellow Sea In Summer

Calanus sinicus is the dominant planktonic copepod in the Yellow Sea and the East China Sea. The population abundance is high in spring and decreases in summer . But are latively higher density of C.sinicus occurs in the Yellow SeaBottom Cold Water (YSBCW ) during summer , with the fifth cope podite stage (CV) making up a high proportion in the population. What is the life strategy of C.sinicus in the southern Yellow Sea in summer? Are the CVs in a state of diapause? And what are the environmental factors that control the population dynam ics? These questions are some of the China-GLOBEC program . s key questions that have to be resolved for achieving a better understanding of the ecology of C.sinicus . The population features of C.sinicus in the southern Yellow Sea during summer were investigated in this work. Results of our study on the effects of temperature and food supply on the survival, development, prosom elengths, dry weight, carbon and nitrogen content and vertical migration clarified the life strategy of C.sinicus in the southern Yellow Sea in summer . According to the environm ental conditions and population features, the investigated area maybe divided to three parts: the shallow water in the northwest, the central part with the YSBCW and the warmer water in thesoutheast. The fifth copepodite stage (CV) dom inated the population in the central part . CVs from the YSBCW were in cubated at different temperatures andfood concentrations. 82% of the individuals died in three days when exposed to 27 ℃ whether food was supplied or not. The survival time at 18 ℃ depended on the food supply . More than 80% of the population survived the 27-dayincubation. The development rate of CV was higher at 18 ℃ than at 9 ℃ , and washigher at higher food concentr ations than that at lower food concentrations at 9℃ . Longer prosome lengths were associated with lower temperature and higherfood concentration. The dry weight, condition, carbon and nitrogen content were mainly affected by food supply .The CVs at St .5-7 have longer prosome lengths, higher dry weights,conditions , carbon and nitrogen contents than those at other sites; but adultfemales at St .5-7 have low condition factors. CVs with prosomele ngths more than 2.1 mm do not migrate into the therm ocline while some smaller ones do.The duration time was much longer for CVs in the YSBCW than for CV reared in high food concentrations in lab so that CVs are in a state of diapause in the YSBCW , with the degree of diapause varing over a wide range. Since the environmental condition is not good for adult C.sinicus to reprodu ceat the center area where the YSBCW locates, the prolonged duration in CV stage is helpful for the population to survive and be ready to reproduce upon improvement of the environm ent. The filtration rates and feeding selectivity of CV , adultfemale and male C.sinicus were investigated with food removal methods. When fed with Thalassiosira pseudonana 3H and Thalassiosira rotula at 13 ± 1 ℃ , the filtrationrates were 3.47 , 0.53 and 3.33 mlindhrfor CV , adult female and maleC.sinicus , respectively , . The feeding abilities were similar for CV and adult female, but the feeding rate for adult male was only 15% of that of CV and adult female . C.sinicus has higher filtration rates for larger food particles. Phytoplankton abundance and Chla concentration is low in the YSBCW , where the volume of phytoplankton cells is only 8.18% of the volume of total particles. The feeding effect on the phyt oplankton biomass is not significant for CV and adult female C.sinicus . This result im plies that C.sinicus is not actively feeding due to the low food concentration.