There are different kinds of sand in the eulittoral zones: sand that easily absorbs water, fine sand, sticky sand, etc. Crab species have clear preferences. "Soldier crabs live in relatively wet sandy areas, and fiddler crabs dig their holes in relatively dryer mud, whereas ghost crabs live above the high tide line," says Liu Hung-chang, as if he is listing his family treasures.
潮間帶的沙土，質地是易積水，或顆粒較細，還是黏性高，螃蟹分的可清楚，「兵蟹棲息在較潮濕的沙質地裡，招潮蟹在較乾燥的泥地上挖洞，幽靈蟹則在高潮線以上活動」，劉烘昌如數家珍說，螃蟹領域分明。