Latitudinal changes (6°S-20°N) of summer ciliate abundance and species compositions in surface waters from the Java Sea to the South China Sea

Ciliates play a curial role in energy transfer from pico- and nano-phytoplankton to mesozooplankton in marine ecosystems. In order to visualize their geographical distributions from the Java Sea to the South China Sea (6°S to 20°N), the authors investigated the ciliate abundance and species composition in surface waters during May 18 to 27 of 2010. The ciliate abundance decreased latitudinally from 3 080 ind./L (～6°S) to 40 ind./L (～3°N), and then increased to 1 180 ind./L (～16°N) at the end of the survey. A total of 22 ciliates belonging to 15 genera were identified with the tintinnids accounted for 50% (11 species); and the species number showed a same spatial change as the ciliate abundance. Moreover, the Strombidium occupied over 50% of total ciliate abundance in most stations and Mesodinium and Tintinnopsis contributed to about 18.7% and 11.4%, respectively. In particular, our results indicate that the geographical changes in ciliate abundance were positively regulated by larger nano- and micro-phytoplankton biomass, rather than smaller pico-phytoplankton in the investigated waters.