Daily variations of red-tide organisms and factors controlling their abundance in Jangmok Bay during summer 2003

Abstract

To estimate the abundance of red-tide organisms and understand factors controlling the abundance in the planktonic ecosystem of Jangmok Bay, the study was conducted daily during summer (n=47). The abundance of phytoplankton was in the range of 0.06 – 12.23x106 cells/l (mean 2.63±3.04x106 cells/l). Twenty-four high concentrations of phytoplankton abundance (n=6: >5 x106 cells/l, n=18: 1-5 x106 cells/l) occurred mainly by the 4 dominant species, accounting for over 5% of the total phytoplankton abundance; Chaetoceros sp1, Chaetoceros sp6, Skeletonema costatum, Thalassionema nitzschioides. The contribution of the 4 dominant species to the total phytoplankton abundance was in the range of 16.6-88.9% (mean 59.8±21.5 %). We found that during the summer the abundance of phytoplankton and 4 dominant species had negative relationships with inorganic nutrients, temperature and salinity, and no relationship with zooplankton. This study suggests that the phytoplankton abundance might be controlled by resource limitation (bottom-up) such as concentrations of inorganic nutrients, that predation effects of zooplankton (top-down) might not be significant, and red-tides occurred in Jangmok Bay might be caused by increasing inorganic nutrients due to rainfalls.