Chen^{1, 2}, Shang, Mingyuan Zhu¹, Ruihua Nu¹, Ruixiang Li¹, Baohua Li¹ and Zilin Liu³

¹Key Lab for Science and Engineering of Marine Ecology and Environment, SOA, First Institute of Oceanography, SOA, 6 Xianxialing Road, Qingdao, 266061, China, Tel: 86-532-8897476, Fax: 86-532-8895544, Email: qdcs@163.com and ²College of Marine Life, Ocean University of Qingdao, China and ³Second Institute of Oceanography, SOA, 9 Xixihexia Road, Hangzhou, 310012, China

Carbon flux into marine pelagic food web in Yangtze River Estuary: Mesocosm experiments

To understand the carbon flux into the marine pelagic food web in the Yangtze River Estuary, two in situ mesocosm experiments with adding phosphate were conducted in Oct 1997 and May 1998 respectively. Adding phosphate increased the carbon flux into both classical food chain (diatom -> copepod) and microbial food chain (bacteria -> protozoan -> copepod). For the phosphate-enrichment mesocosm (PE), the carbon flux into classical food chain averaged 7.75 gC.d^-1 while the carbon flux into microbial food chain averaged 13.3 gC.d^-1 in Oct 1997. They were 3.14 and 1.86 gC.d^-1 respectively in control. In May 1998, the carbon flux into classical food chain averaged 3.87 gC.d^-1, while the carbon flux into microbial food chain averaged 7.29 gC.d^-1 in PE. They were 0.91 and 6.64 gC.d^-1 respectively in control. Compared to the PE in Oct, the carbon fluxes into the two food chains were lower in May. In Oct and May the carbon flux into microbial food chain was higher than the carbon flux into classical food chain during the decaying period of HAB. When algal boom occur the carbon into classical food chain is blocked at the link of phytoplankton then much carbon (in form of DOC and detritus) from phytoplankton into microbial food chain. Our experiments show eutrophication of phosphorous not only increases the ecosystem productivity but also speeds the material cycling and energy flow of coastal ecosystem, which usually makes the balance mechanism of ecosystem out of order. For one healthy ecosystem, the ratio of carbon load into the classical and microbial food chains should be kept at a certain range. Its abnormal change may indicate the ecosystem is destroyed.