Experimental studies regarding impacts of high concentration of CO2, as a modification of CO2 ocean sequestration, on marine organisms were carried out. As representatives of the marine organisms bacteria and nematodes were investigated. The former is not only the major decomposer but also the most important potential genetic resource, and the latter the most abundant in number and the highest in species diversity in the benthic ecosystem. Both nematodes and bacteria were so resistant to the high concentration of CO2 that drastic impacts were observed only under the condition of pH 5.5 similar to 6 or less. In addition to the experiment using a monospecific material, however, further studies are needed taking interactions of variety of marine species into account.