Distribution and abundance of the sea-star Archaster typicus in Kabira Cove, Ishigaki Island, Okinawa

The tropical sea-star Archaster typicus has a high population density on protected sandy flats in the Yaeyama Islands, Okinawa. Intensive studies of horizontal and vertical distribution patterns show that within small areas the young sea-stars show a random dispersal. With growth they shift their distribution pattern to a contagious one with patches of about 2 m × 2 m size. In the middle-scale spatial distribution, they change their center of distribution from deep to shallow intertidal bottoms with growth. Although factors responsible for the macro-spatial distribution remained obscure, aspects of the shore in relation to wind direction and life-size topography were thought to be important.