Plankton respiration in the northern South China Sea during summer and winter

Plankton respiration is an important part of the carbon cycle and significantly affects the balance of autotrophic assimilation and heterotrophic production in oceanic ecosystems. In the present study, respiration rates of the euphotic zone plankton community (CReu), size fractionated chlorophyll a concentration (Chl a), bacterial abundance (BAC), and dissolved oxygen concentration (DO) were investigated during winter and summer in the northern South China Sea (nSCS). The results show that there were obvious spatial and temporal variations in CReu in the nSCS (ranging from 0.03 to 1.10 mu mol/(1,11)), CR, in winter ((0.53 +/- 0.27) mu mol/(L.h)) was two times higher than that in summer ((0.26 +/- 0.20) mu mol/(1,11)), and decreased gradually from the coastal zone to the open sea. The distribution of CReu was affected by coupled physical-chemical-biological processes, driven by monsoon events. The results also show that CReu was positively correlated with Chl a, BAC, and DO, and that BAC contributed the highest CReu variability. Furthermore, the results of the stepwise multiple linear regression suggest that bacteria and phytoplankton were the dominant factors in determining CReu (R-2 = 0.82, p<0.05) in the nSCS. Based on this relationship, we estimated the integrated water column respiration rate (CRint) within 100 m of the investigated area, and found that the relationship between the biomass of the plankton community and respiration may be nonlinear in the water column.