The coupling of bacterial production and hydrography in the southern East China Sea: Spatial patterns in spring and fall

Heterotrophic bacterial biomass, production and turnover rates were investigated in a transect across the continental shelf of the southern East China Sea during spring and fall. The sampling area covered different water types including nutrient-rich coastal and upwelling waters as well as oligotrophic Kuroshio waters. On area basis, bacterial biomass (IBB; 350–1200 mgC m−2), production (IBP; 28–329 mgC m−2 d−1) and averaged turnover rates (μ=IBP/IBB; 0.09–0.22 d−1) in the coastal and upwelling areas were at least 2-fold of those in the Kuroshio waters. IBB, IBP and μ were positively correlated with primary production (IPP; 90–2133 mgC m−2 d−1) and particulate organic carbon (IPOC; 1415–4682 mgC m−2) but showed a negative trend with temperature in the outer shelf area. While in the inner shelf (<20°C), IBP and μ were positively correlated with temperature; the Q10 value for bacterial μ was 3.12. These indicated that the spatial patterns of IBB, IBP and μ were more likely to be controlled by substrate supply and temperature interactively. Values of IBP : IPP ratio ranged 6–42% with an average of 22±10%. Under the assumption of a growth efficiency of 20%, shelf bacteria might consume carbon equivalent to almost 100% of the in situ daily particulate IPP. Dissolved organic carbon from non-phytoplankton and allochothonous sources might play a significant role in supporting bacterial carbon demand in the shelf area of the East China Sea.