Seasonal reproduction of marine sessile organisms may be an adaptation of seasonal variation in suitable substratum availability. This research is focused on how to quantfy the suitable substratum of marine sessile organisms. Then the potential seasonal change of suitable substrate availability can be assessed. We tested 1-1.5 meters scale is a population closed spatial scale. At this scale we try to find ¡§intensification phenomenon¡¨ using different-size panels. If intensification phenomenon dose exist at 1-1.5 meter scale, then the amount of the suitable substratum can be estimated. We also compared three different current environments at Tiaoshi area in Nan-wan-Bay, the 3rd Nuclear Power Plant Inlet and the Hobihu Yacht Wharf to find out if the intensification phenomenon exists at this different situations. Lastly, sand and reef area were compared. Since reef areas has more suitable natural substratum than sand areas. The intensification phenomenon at 1-meter scale was not found. The larval density in water column might be highly heterogeneous even in very small scale. On the other hand, we consistently found higher settlement density in sand areas than in reef areas. This phenomenon may well have been caused by the intensification phenomenon.