Continental Shelf Research 22 (2002) 3–13 Spatial and temporal variation of the Synechococcus population in the East China Sea and its contribution to phytoplankton biomass Kuo-Ping Chiang a, *, Min-Chieh Kuo a , Jeng Chang b , Ru-Huey Wang a , Gwo-Ching Gong c a Institute of Fishery Science, National Taiwan Ocean University, Keelung 202-204, Taiwan, ROC b Institute of Marine Biology, National Taiwan Ocean University, Keelung 202-204, Taiwan, ROC c Department of Oceanography, National Taiwan Ocean University, Keelung 202-204, Taiwan, ROC Received 13 April 2000; received in revised form 6 September 2000; accepted 19 July 2001 Abstract Variations in the spatial and temporal distribution of the Synechococcus population in the East China Sea were investigatedinfivecruisesofthe R/V Ocean Research I betweenMay1996andOctober1998.Onthecontinentalshelf, a two-phased (warm >201C; and cold o201C) seasonal cycle with 10-fold variation was found in the Synechococcus population. In the cold season (winter to late spring), when temperature is probably a limiting factor, a low density Synechococcus population was homogeneously distributed over the entire continental shelf. A dome-type spatial distributionpatternappearedinsummer,thatis,populationdensitieswerehightowardthemiddleofthesea.Thisarea ofhigherdensitymovedtowardtheoutershelfinfall.NoseasonalvariationwasfoundintheCoastalWater,probably becauseinsummerthelowtransmissionmeansthatlightislimitedbelowthesurface.Theaveragecarbonbiomassof Synechococcus intheEastChinaSearangedfrom0.09(earlyspring)to0.90gCm 2 (fall). Based on carbon biomass, Synechococcus accountedforlessthan25%ofthetotalphotosyntheticplanktonincoldseasonandabout50%inthe warm season. Our results suggest that the cyanobacterium Synechococcus is a major contributor to the seasonal variation of phytoplankton in the East China Sea. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Synechococcus; East China Sea; Phytoplankton; Seasonal variation 1. Introduction Over the last 20 years, several photosynthetic picoplanktons have been discovered in marine ecosystems. These include the cyanobacterium Synechococcus (Waterbury et al., 1979; Johnson and Sieburth, 1979), Prochlorococcus (Chisholm et al., 1988) and small eukaryotes. It is now also recognized that picophytoplankton make a sig- nificant contribution to phytoplankton biomass and productivity in marine ecosystems (Stockner and Antia, 1986; Shiomoto et al., 1997). Among these small size autotrophic picoplankton, the most important primary producers are Synecho- coccus and Prochlorococcus (Olson et al., 1990; *Corresponding author. Fax: +886 2 2462-1016. E-mail address: kpchiang@mail.ntou.edu.tw (K.-P. Chiang). 0278-4343/02/$-see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0278-4343(01)00067-X