Abundance pattern of heterotrophic nanoflagellates in the southern Taiwan Strait

The analysis of 103 samples collected quantitatively from the southern Taiwan Strait (22°4'~24°3'N, 117°5'~119°9'E), China, in August 1997 indicates that the abundance of heterotrophic nanoflagellates (HNF) ranges from 391 to 1 846×10³ cell/dm³, with an average of 949×10³ cell/dm³,and 96.2% of cells are in size of 2~22 μm in all HNF met in the samples. The HNF cells are 9.83~45.79 μg/dm³ after conversion from cell number to carbon content, with an average of 22.82 μg/dm³.The HNF abundance is relatively low in comparison with other areas. The nitrogen and phosphorus nutrients of the water are lower than previous investigations, which may be caused by the El Nino. The biormass of HNF is higher in southern waters, where cell concentration is 3~5 folds higher than that in other waters, and nearly 2-fold as high as the average of the investigated areas. The HNF is mainly habitat in 0~30 m water layer. Both horizontal and vertical HNF distribution must be influenced by hydrographical dynamic process to a great extent. Continuous in situ observations of HNF indicate the 24 h diurnal rhythm, with two peaks, one in night at one station (Station 9701) and one during the period of 12:00~24:00 at another (Station 9704). The factors controlling the diurnal variation of HNF are unclear, although vertical migration of HNF is obviously.