EFFECT OF THE HIGH CO2 ON GROWTH OF PHYTOPLANKTON SPECIES: LABORATORY STUDY

Abstract

Cultured phytoplankton, Cylindrotheca closterium, Melosira nummuloides, Nitzschia sp., Phaeodictylum triconutum, Prorocentrum minimum were subjected to test the growth rates under the different conditions of CO2 concentration. Two different CO2 concentrations were defined as 'normal condition' (pCO2: 200ppm) and 'high condition' (pCO2: 980ppm). The experiment was performed under the nutrient enriched-condition. The temperature was maintained 25±1 ℃ under the equally lit light cycle (12 hr. light : 12 hr. dark). Nitzschia sp. and M. nummuloides showed higher chlorophyll-a concentration under the high condition than under the normal condition. However, higher chlorophyll-a concentration was measured for P. minimum under the normal condition than under the high condition. These results may reflect that the highly concentrated CO2 environment increased the growth rate of Nitzschia sp. and M. nummuloides, while the growth rate of P. minimum was retarded under the high condition. There was no a clear difference of growth rate between high and normal conditions in the case of C. closterium and P. triconutum. The researches are in progress and will argue on the matter of the rapid variations of phytoplankton community structure and primary productivity which is induced by the increase of global CO2 level.