Distribution of the Sea Urchin Strongylocentrotus nudus in Relation to Marine Algal Zonation in the Rocky Coastal Area of the Oshika Peninsula, Northern Japan

Abstract

The spatial variability of the density of sea urchins (Strongylocentrotus nudus) soon after settling and metamorphosis and after having grown to at least 1 cm was analyzed in relation to offshore marine algal zonation. Newly settled sea urchins occurred throughout, from the shoreward cobblestone area to the offshore area dominated by crustose coralline red algae, where the highest density was observed. Individuals smaller than 2 cm diameter occurred mainly in the crustose corallines-dominated area. Sea urchins 2-4 cm in diameter occurred with a high density in the crustose corallines-dominated area and with a low density in a narrow zone in the Eisenia bicyclis-dominated area close to the crustose corallines-dominated area. These results suggest that they had settled in the crustose corallines-dominated area, survived and later dispersed during growth toward the E. bicyclis-dominated area.