Temperature versus substrate limitation of heterotrophic bacterioplankton production across trophic and temperature gradients in the East China Sea

Abstract

A survey of heterotrophic bacterioplankton biomass (BB; 4 to 64 mg C m-3), production (BP; 0.3 to 14.7 mg C m-3 d-1) and specific growth rates (μ; 0.07 to 0.38 d-1) as well as concentrations of nitrate (NO3-; <0.1 to 15.6 μM), particulate organic carbon (POC; 1 to 60 μM) and chlorophyll a (chl; 0.1 to 4.0 mg chl m-3) in the euphotic zone was conducted over the continental shelf of the East China Sea during the spring seasons of 1996 and 1997. Concentrations of NO3- were high in the coastal areas and decreased offshore. In contrast, temperature (12.2 to 24.5°C) showed the opposite trend, with cool (<20°C) and warm (>20°C) waters distributed inside and outside the shelf edge, respectively. Inside the shelf edge, bacterial rate parameters (BP and μ) were positively correlated with temperature but showed no correlation with POC; values of Q10 for BP and μ were 2.7 and 3.3 respectively. From the shelf edge to the adjacent open ocean, bacterial rate parameters were positively correlated with POC only. These results imply that during the spring season, mechanisms controlling the spatial patterns of bacterial rate parameters over the shelf area are system-dependent. It is concluded here that temperature plays a more dominant role than substrate supply inside the shelf edge; however, from the shelf edge to the open ocean, the situation is reversed.