SUMMER DISTRIBUTION OF PICOPHYTOPLANKTON IN THE NORTH YELLOW SEA

Aims The North Yellow Sea is a typical model for marine ecologic systems of the North Temperate Zone. Over the past decade, much non-biological research had been done in multidisciplinary projects. Our aims were to provide basic biological information for marine picoplanktonic study. Methods Water samples were collected from 80 stations in the North Yellow Sea in August 2006 and immediately fixed in situ with paraformaldehyde (final concentration: 1%). After treatment for 15 to 20 min, samples were transferred into liquid nitrogen for deep freezing and then stored in –80 oC for laboratory analysis. Picophytoplankton was examined using epifluorescence microscopy, and the components, distribution and diurnal variations of picophytoplankton in the sea were analyzed. Important findings Two groups of picophytoplankton were found, Synechococcus (Syn) and picoeukaryotes (Euk). Phycoerythrin-rich Synechococcus (PE cells) dominated Syn in abundance (1.76×105 cells&;#8729;ml–1 on average) and phycocyanin-rich Synechococcus (PC cells) were less abundant (only contributed 5.48% of Syn abundance). Syn and Euk were more abundant in northern Rongcheng Bay than other areas. There was extremely low Syn abundance in the Cold Water Mass of the North Yellow Sea at 30-m depth and 2-m depth above the bottom, whereas no low Euk abundance in the Cold Water Mass. In vertical distribution, Syn abundances at surface and 10-m depth were higher than at 30-m depth and 2-m depth above the bottom; however, no significant vertical changes in Euk concentration were found. There were no significant variations in both the Syn and Euk abundances at different depths in daytime and nighttime.