Abstract
Phytoplankton community composition and dynamics with physicochemical factors were investigated monthly on the western coast of Jeju Island, Republic of Korea. A total of 291 phytoplankton species were identified, cell abundance varied between 2.95-34.39 and 2.81-26.66 x10(4) cells L-1, chlorophyll a between 0.19-1.56 and 0.07-1.51 mu g L-1 at bottom and surface, respectively. A phytoplankton bloom was observed in spring which was associated with low temperature and high salinity, NH4+ and NO3. Diatoms were 89 and 91% of total cell abundance at surface and bottom, respectively, in which Chaetoceros socialis, C. costatus, C. lorenzianus, C. pseudocrinitus and Skeletonema costatum each contributed over 10% to the total phytoplankton. In autumn, dinoflagellates contributed 49.87 and 51.57% to total phytoplankton at surface and bottom, respectively. Prorocentrum micans, P. triestinum and Gymnodinium conicum were predominant species. Such predominance of dinoflagellates is alarming for sustainable aquaculture in this area.