It is likely that dynamics of a population is under control of the seasonally different density-dependent and density-independent processes operating at different spatial scales. To test this hypothesis, we observed coverage of intertidal barnacle Chthamalus challengeri over eight years by using hierarchical sampling design. We then analyzed the data by fitting a population model that incorporated both a density-dependent process (strength of density dependence) and density-independent processes (intrinsic growth rate and stochastic fluctuation at different spatial scales). The coverage tended to decrease in summer, when the population growth were characterized by a relatively lower intrinsic growth rate, weaker density dependence, and stronger stochastic fluctuation. In contrast, the coverage tended to increase in winter, reflecting a higher intrinsic growth rate, strong density dependence, and weak stochastic fluctuation. In summer the population growth rate was strongly affected by regional-scale stochastic fluctuation, whereas in winter it was more affected by rock-scale stochastic fluctuation. These results indicate that seasonally variable density-dependent and density-independent processes determine the population dynamics of C. challengeri.