Abstract
To define nanoflagellate-bacteria interactions and potential trophic levels within the microbial food web in the oligotrophic South China Sea, we conducted fourteen size-fractionation experiments in which seawater was filtered through 1, 2, 5, 10, 20, 60, and 200 μm membranes or meshes and the growth of four groups of picoplankton, Prochlorococcus, Synechococcus, high DNA heterotrophic bacteria, and low DNA heterotrophic bacteria were monitored in each filtrate after 24 hours of incubation. Removing grazers by filtration would relieve the grazing pressure on lower trophic levels which finally influenced the net growth rates of picoplankton. The growth patterns of Prochlorococcus and Synechococcus were similar, with higher growth rates in the < 1 μm or < 2 μm treatments, a second peak in the < 10 μm treatments and often a third peak in the < 200 μm treatments. The net growth rates of low DNA heterotrophic bacteria were little influenced by size-fractionation. Due to a subgroup of high DNA heterotrophic bacteria with larger size and higher DNA content which appeared to resist the grazing by < 5 μm nanoflagellates, the net growth rates of high DNA heterotrophic bacteria were higher in the < 2 μm or < 5 μm treatments with a second peak in the < 60 μm treatments. A general pattern of five potential trophic levels (< 2 μm, 2-5 μm, 5-10 μm, 10-60 μm, 60-200 μm) was revealed combining all the experiments, confirming the existence of multiple trophic levels within the microbial food web in the oligotrophic South China Sea.
Original language | English |
---|---|
Pages (from-to) | 59-66 |
Number of pages | 8 |
Journal | Journal of Experimental Marine Biology and Ecology |
Volume | 368 |
Issue number | 1 |
Early online date | 17 Nov 2008 |
DOIs | |
Publication status | Published - 15 Jan 2009 |
Funding
We thank Prof. D. Wang in the South China Sea Institute of Oceanology and Prof. M. Dai in Xiamen University, P. R. China, for providing the cruise opportunities and data of temperature and salinity. We also thank Y. K. Tam and L. He for logistical help. This study was supported by the Hong Kong RGC research grant HKUST6414/06M provided to H. L and a HKUST postgraduate scholarship provided to B. C. Additional support was provided by the State Key Lab of Marine Environmental Science (Xiamen University), China. [SS]
Keywords
- grazing
- microbial food web
- picoplankton
- size-fractionation