Chen1, Chung-Chi, Fuh-Kwo Shiah2, Gwo-Ching Gong3 and Kuo-Ping Chiang4

Chen¹, Chung-Chi, Fuh-Kwo Shiah², Gwo-Ching Gong³ and Kuo-Ping Chiang⁴

¹Department of Biology, National Taiwan Normal University, 88, Sec. 4, Ting-Chou Rd., Taipei 116, Taiwan, ROC, Tel: 011-886-2-2933-3149, Fax: 011-886-2-2931-2904, E-mail: ccchen@cc.ntnu.edu.tw, ²Institute of Oceanography, National Taiwan University, P.O. Box 23-13, Taipei, Taiwan 10617, ROC, ³Department of Oceanography, National Taiwan Ocean University, Keelung 202-24, Taiwan, ROC and ⁴Department of Fishery Science, National Taiwan Ocean University, Keelung 202-24, Taiwan, ROC

Planktonic community respiration in the East China Sea

Planktonic community respiration (PCR) rates were measured in autumn 1998, in order to evaluate the respective roles played by microbes (heterotrophic bacteria and ciliates) in organic carbon consumption of the East China Sea (ECS). For comparative purposes, the ECS shelf was divided into mesotrophic ([NO₃^-] > 0.3µM) and oligotrophic ([NO₃^-]£ 0.3µM) systems. Bacterial biomass (23.4 ± 28.4 mg C m^-3) and production (4.9 ± 6.8 mg C m^-3 d^-1) as well as particulate organic carbon concentrations (129.3 ± 40.4 mg C m^-3) were significantly higher in the mesotrophic system, while protozoa (95.6 ± 74.9 mg C m^-3) were more abundant in the oligotrophic system. PCR rates ranged from 127.6 to 4728.6 mg C m^-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 PCR ratio (0.33 ± 0.30) suggests that the ECS was net heterotrophic during the study period. Allochthonous supplies of 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 discussed as the potential sources of this allochthonous organic carbon.