Differential coupling of bacterial and primary production in mesotrophic and oligotrophic systems of the East China Sea

Spatial patterns of integrated bacterial production (IBP; 9 to 179 mg C m^-2 d^-1), bacterial biomass (IBB; 125 to 658 mg C m^-2), bacterial turnover rates (Bμ = IBP/IBB; 0.03 to 0.37 d^-1), primary production (IPP; 18 to 2079 mg C m^-2 d^-1) and hydrographical variables were measured in the continental shelf of the East China Sea (25.4 to 31.6°N, 120.5 to 127.0°E) during summer and autumn 1998. Sea surface temperatures were >21°C in both seasons. The slopes for Log₁₀IBP vs Log₁₀IPP (summer 0.44 ± 0.09, autumn 0.52±0.06) and Log₁₀Bμ vs Log₁₀IPP (summer 0.52 ± 0.06, autumn 0.50 ± 0.06) were significant with no seasonal difference. IBB showed no trend with IPP. When data were analyzed by separating the study area into the inner- (surface NO₃ >0.25 μM; mesotrophic) and outer- (surface NO₃ <0.25 μM; oligotrophic) shelf systems, the slope values of Log₁₀IBP vs Log₁₀IPP derived from the inner-shelf (summer 0.48 ± 0.25, 12 stations; autumn 0.52 ± 0.09, 16 stations) data sets were significantly higher than those of the outer-shelf (summer 0.27 ± 0.13, 20 stations; autumn 0.36 ± 0.11, 26 stations); there was no difference for the slopes between seasons within each system. Mechanisms causing such differential coupling are not clear since this issue has seldom been addressed before. The results implied that care should be taken when analyzing cross-system or large spatial scale data sets. Our study also revealed that the IBP:IPP ratios (4 to 57%) of both seasons showed negative relationships with IPP. Phytoplankton effects on these ratios were dominated concomitantly by algal turnover rate and biomass on the inner-shelf in summer and then shifted to algal biomass dominated over the whole shelf in autumn. Ecological and biogeochemical implications of our findings are discussed.