This report introduces influences of physical environments on living things on tidal flats and on reef areas. Bottom change and ground temperature on emerging tidal flats understood to be severe conditions to post-larvae of short-necked clams. Next, it was explained that feeding of sea urchinsare controlled by wave motion. From the result to apply them to a site, it understood it to be an important factor that a physical environment decides a distribution of a predator and a prey.