Deep-Sea Research II 50 (2003) 1311–1325 Planktonic community respiration in the East China Sea: importance of microbial consumption of organic carbon Chung-Chi Chen a,1 , Fuh-Kwo Shiah b, *, Gwo-Ching Gong c , Kuo-Ping Chiang d a National Center for Ocean Research, National Science Council, P.O. Box 23-13, Taipei, Taiwan 10617, ROC b Institute of Oceanography, National Taiwan University, P.O. Box 23-13, Taipei, Taiwan 10617, ROC c Department of Oceanography, National Taiwan Ocean University, Keelung 202-24, Taiwan, ROC d Department of Fishery Science, National Taiwan Ocean University, Keelung 202-24, Taiwan, ROC Accepted 18 December 2002 Abstract Planktonic community respiration (PCR) rates were measured using the oxygen method in autumn 1998 in order to evaluatetherespectiverolesplayedbymicrobes(heterotrophicbacteriaandciliates)inorganiccarbonconsumptionon the continental shelf of the East China Sea (ECS). For comparative purposes, the ECS shelf was divided into mesotrophic ([NO 3  ]>0.3 mM) and oligotrophic ([NO 3  ]p0.3 mM) systems. Bacterial biomass (23.4728.4mgCm 3 ) and production (4.976.8mgCm 3 d 1 ) as well as particulate organic carbon concentrations (129.3740.4mgCm 3 ) were significantly higher in the mesotrophic system, while protozoa (95.6774.9mgCm 3 ) were more abundant in the oligotrophicsystem.PCRratesrangedfrom127.6to4728.6mgCm 2 d 1 , and the rates were either linearly related to protozoan biomass or multiply regressed with both bacterial and protozoan biomass. Further analysis showed that PCR were dominated by distinct microbial components in different trophic systems, with bacteria and protozoa contributing 72% and 85% of PCR in meso- and oligotrophic systems, respectively. The low primary production to PCRratio(0.3370.30)suggeststhattheECSwasnetheterotrophicduringthestudyperiod.Allochthonoussuppliesof organic carbon, in addition to in situ production, are required to support these high respiration rates. Riverine inputs and/or resuspension from superficial sediments are potential sources of this allochthonous organic carbon. r 2003 Elsevier Science Ltd. All rights reserved. 1. Introduction The continental shelf is a boundary zone between the land-ocean margins. Although the continental shelf represents less than 20% of the world’s oceanic area, it’s high nutrient input from riverine run-off has made it one of the most productive areas in the world (Liu et al., 2000a). Continental shelf primary production total could be as important as that in the ocean interior (Walsh, 1991). Even though there is a debate as to whether the continental shelf is primarily a carbon source or sink, the carbon flow in this area to global carbon flux is important. (Liu et al., 2000a). Understanding the carbon fluxes and cyclingprocessesintheshelfecosystemistherefore a key step toward estimating the global carbon *Corresponding author. Fax: +011-886-2-369-5746. E-mail address: fkshiah@ccms.ntu.edu.tw (F.-K. Shiah). 1 Now at: Deparment of Biology, National Taiwan Normal University,88,Sec.4,Ting-ChouRd.Taipei116,Taiwan,ROC 0967-0645/03/$-see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0967-0645(03)00025-0