Productivity and abundance of bacteria and phytoplankton in Incheon Dock, western coast of Korea.

The monthly variations of abundance and productivity of bacteria and phytoplankton were investigated in 2002 at Incheon Dock in Korea, almost closed marine ecosystem. Incheon Dock has unique marine environment with scarcely a current and waves such as in a lake. The bacterial abundance was 0.4-6.3 x 10(6) cells x ml(-1), while the bacterial productivity showed in the range of 0.7-26.3 mgC m(-3) hr(-1). The phytoplankton chlorophyll-a concentrations fell between 2.1 and 18.1 microg x l(-1), where nanoplankton fractions contributed in 32.5-96.78% (average: 73.2%). The algal bloom occurred in March and August, and primary productivity measured by using 14C method, showed a fluctuation ranging from 49.4 to 4,359.4 mgC m(-2) day(-1). The primary productivity of nanotoplankton accounted for 79% of total phytoplankton. Meanwhile, the ratio of bacterial productivity over primary productivity was between 2.0 and 7.7. This study showed that the abundance and productivity of bacteria and phytoplankton were higher at Incheon Dock than those at other coastal areas in Korea. Especially the assimilation number was higher at Incheon Dock than that at lake Shihwa which is a severely eutrophicated area. This result indicates that Incheon Dock has unique ecosystem oceanographically and topographically and it differs from other coastal areas in terms of the low trophic level organisms being abundant and highly productive.