Factors affecting the habitat of Haliotis discus discus on the coast of Sado Island, Niigata, Japan

: Between 2011 and 2017, we studied the effects of habitat characteristics on the abundance of the Japanese abalone （ Haliotis discus discus ） on the coast of Sado Island, Niigata, Japan. Subtidal areas （ depth, 1–7 m ） along the island were evaluated using quadrat surveys performed by scuba divers. The habitat characteristics （ water depth, percent macroalgal cover, number of macroalgal species, and percent boulder cover ） were recorded within each quadrat, along with the number and size of the abalones. Nonlinear models of the habitat characteristic data revealed differences in the habitat characteristics that affected the abundance of large （ ≥90 mm ） and small （＜ 90 mm ） abalones. The large abalones were more prevalent between 3 and 5 m, and their abundance increased as the macroalgal cover decreased. Alternatively, most small abalones inhab-ited areas covered up to 40 ％ by macroalgae. These results suggest that Japanese abalones ontogenetically shift their habitat requirement and thereby contribute to the restoration of their habitats in coastal areas.