Community And Bacterial Respiration In The South China Sea And Fujian Coastal Waters

We measured gross primary production and community respiration using the light and dark bottle method during2cruises in the summer of2012and2013, respectively, to investigate the metabolic states of the plankton community in the northern and the western South China Sea.We also studied the temperature sensitivity of plankton metabolism at one fixed site in Xiamen coastal waters. The main results were:1. Metabolism of marine plankton in the northern South China Sea in summerGPP averaged106.6mmol O2m-2d-1with a standard error of7.51mmol O2m-2d-1. CR averaged131.1mmol O2m-2d-1with a standard error of5.95mmol O2m-2d-1. Net community productivity varied from-179.0to377.6mmol O2m-2d-1with a median value of-40.4mmol O2m-2d-1. Our results showed that the area affected by Qiongdong upwelling was autotrophic. In the areas affected by the Pearl River discharge, the plankton community was also autotrophic. In contrast, other areas including the Taiwan Strait inshore waters and the South China Sea open waters were heterotrophic. Therefore, community respiration was not entirely determined by the local primary productivity in the sampled areas. Our results suggested that the spatial transport of organic carbon could play an important role in affecting the metabolic state of the plankton community.2. Metabolism of marine plankton in the western South China Sea in summerGPP averaged1.844μmoL O2L-1d-1with a standard error of0.242μmoL O2L-1d-1.CR averaged1.624μmoL O2L-1d-1with a standard error of0.182μmoL O2L-1d-1. Net community productivity varied from-7.089to3.079μmoL O2L-1d-1, averaged0.22μmoL O2L-1d-1with a standard error of0.312μmoL O2L-1d-1. The coastal waters in Qiongdong and the western South China Sea were affected by upwelling and coastal current, leading to NCP greater than zero. Therefore, the plankton community in these areas were autotrophic. In contrast, the plankton communities in other areas were heterotrophic.3. Temperature sensitivity of plankton metabolism in Xiamen BayThis study showed that temperature affected community productivity and respiration rate. Q10of GPP averaged2.22, while Q10of CR averaged2.23, which showed that the temperature effects on GPP and CR were similar, in contrast with previous studies showing that CR would respond more sharply to temperature that GPP.BP and BR were two invese processes of bacterial metabolism. They responded differently to temperature. Q10of BR and BP averaged1.04and2.08, respectively. BP was more sensitive to temperature than BR, leading to the pattern that the temperature sensitivity of BGE was mainly controlled by that of BP.