울산항에 정박중인 해외상선 선박평형수 기인 식물플랑크톤의 생존 가능성

Abstract

Despite recognition of the risks of marine invasion, the viability of foreign phytoplankton transferred via ballast water has not been studied previously in Korea. Through culture experiments, we investigated the viability of phytoplankton collected from the ballast water of international commercial ships berthed at the ports of Ulsan and Onsan. The incubation conditions used were temperatures of 13°C to represent ambient water and 20°C to represent the thermal optimum, as well as nutrients in ballast water, shipside water, and F/2 medium simulating coastal eutrophication.Phytoplankton in new (~7 days) and old (20 and 23 days) ballast water survived when incubated under the nutrients typical of shipside water and eutrophic environments at 13°C and 20°C. When hydrographic conditions (temperature and salinity) were matched between ballast tank water and receiving water, foreign phytoplankton showed normal growth curves in shipside water&#8211;based medium and F/2 medium at both temperatures. Conversely, normal growth was not observed under large saline differentials. In thermal optimum temperature (20°C) and eutrophic conditions, compared to shipside water, there was shortening of lag time and maximal fluorescence of foreign phytoplankton. Most species observed in the inoculated phytoplankton did not occur during the doubling phase or the last phase of growth. Colonization by foreign phytoplankton was mostly dominated by Skeletonema costatum, Chaetoceros debilis, and Cylindrotheca closterium. S. costatum and C. closterium were persistent throughout the incubation period, whereas pennate diatoms (<10 μm in diameter) dominated in the three types of media from the doubling phase to the last phase of growth. This study did not prove that foreign phytoplankton will be established as result of international shipping but did show the potential for their colonization.