Abstract: An investigation was made on the chlorophyll-a (Chla) concentration and phytoplankton size-fractionated composition in Jiaozhou Bay and its adjacent waters in February, May, August, and November 2008. The average annual Chla concentrations inside and outside the Bay was 4.90 mg·m^-3 and 2.03 mg·m^-3, respectively. The Chla concentration presented a decreasing trend from the northeast and near-shore to the central, south, and outside of the Bay, and had an obvious double-peak seasonal variation, being higher in summer and winter. The phytoplankton in the Bay was dominated by nanophytoplankton, accounting for 60.9% of the total Chla concentration, followed by microphytoplankton, and picophytoplankton, which was consistent with the phytoplankton size-fractionated composition in coastal waters of China. Comparing with historical data, the proportion of nanophytoplankton in the Bay had some increase, while that of picophytoplankton decreased to some extent.

Key words: Chla, phytoplankton, size-fractionated composition, Jiaozhou Bay, peanut, salinity stress, salinity tolerance index, membership function, cluster analysis.