Abstract:

During the austral summer of 1989/1990 and 1990/1991 net sampling survey was carried out on the distribution,abundance,age-composition,development and reproductive ecology of Thysanoessa macrura G.O.Sars in the prydz Bay region.Larvae occurred throughout the research areas with comparatively high abundance. The average density of larvae was 744 ind./1000m 3 in Jan.1990 and 1155 ind./1000m 3 in Jan.1991.They were more abundant in open ocean area than in slop and shelf areas.In 1990, the larval developmental stages from C1 to F2 were found in early Jan.with the mean stage index (MSI) equal to 2 78. In late Feb.they were substituted by C2-F5 (MSI=4.89),and in early March C3-F6(MSI=5.00).More advanced developmental larval stages were found in 1991,C1-F3(MSI=3 75) in early Jan.and F1-F6(MSI=8.70) in early March. Latitudinal difference in larval developmental stage composition or in MSI could be clearly found,i.e.the closer to the shelf the younger of the larvae.The mean developmental time from stage to stage by field data was 13-19 days in 1989/1990 and 11 days in 1990/1991.The main breeding season of T.macrura in Prydz Bay area seemed to start in early October and end in early January.Adults and Juveniles were widely dispersed,but swarms were found mainly close to the Antarctic Divergency.Inter-annual variations in timing of breeding ,survival of larvae and abundance of adults were evident.More advanced larval stages,which means an earlier breeding season,shorter developmental time for larval stages,and more abundant adults and juveniles were observed in 1990/1991.These might be attributed to the warmer water temperature compared with 1989/1990.