SIZE STRUCTURES OF MICROPLANKTON BIOMASS AND PRODUCTION IN JIAOZHOU BAY, CHINA

Seasonal investigations of size-fractionated biomass and production we re carried out from February 1992 to May 1993 in Jiaozhou Bay, China. Microplankton assemblages were separated into three fractions: pico-(0 .7-2 mu m), nano- (2-20 mu m) and netplankton (20-200 mu m). The bioma ss was measured as chlorophyll a (Chl a), particulate organic carbon ( POC) and particulate organic nitrogen (PON). The production was determ ined by C-14 and N-15 tracer techniques. The seasonal patterns in biom ass, though variable, were characterized by higher values in spring an d lower values in autumn and summer (for Chl a only). The seasonal pat terns in production, on the other hand, were more clear with higher va lues occurring in summer and spring, and lower values occurring in aut umn and winter. Averaged over the whole study period, the respective p roportions of total biomass accounted for by net-, nano- and picoplank ton were 26, 45 and 29% for Chl a, 32, 33 and 35% for POC, and 26, 32 and 42% for PON. The contributions to total primary production by net- , nano- and picoplankton were 31, 35 and 34%, respectively. The respec tive proportions of total NH4+-N uptake accounted for by net-, nano- a nd picoplankton were 28, 33 and 39% in the daytime, and 10, 29 and 61% at night. The respective contributions to total NO3--N uptake by net- , nano- and picoplankton were 37, 40 and 23% in the daytime, and 13, 2 3 and 64% at night. Some comprehensive ratios, including C/N biomass r atio, Chl a/C ratio, C uptake/Chl a ratio, C:N uptake ratio and the f- ratio, were also calculated size separately, and their biological and ecological meanings are discussed.