Grazing on the Crustose Coralline Alga Lithophyllum yessoense by the Sea Urchin Styongylocentrotus nudus and the Limpet Acmaea pallida

Abstract

Lithophyllum yessoense, a dominant crustose coralline alga on lsoyake (urchin-dominated barren) ground in southwestern Hokkaido, was experimentally fed to the sea urchin Strongylocentrotus nudus (3cm in test diameter) and the limpet Acmaea pallida (2cm in shell length) in the laboratory. Grazing marks of the urchin were composed of pentagonally-arranged five strips, and scattered on the crust surface. The wound was 0.01mm deep within sacrificial epithallium, and crust surface of 0.20mm² was removed by one biting. The limpet grazed more densely and deeply (0.04mm) enough to remove distal columnar cells as well as epithallial cells. Crust surface of 0.43mm² was removed by one biting. The urchin-grazing marks (shallow wounds) became vague by the usual production of epithallial cells in 5 days. On the contrary, the limpet-grazing marks (deep wounds) recovered by regeneration of the intact columnar cells in 10 days. The production of epithallial cells and the regeneration from columnar cells must be the important nature to elucidate the vigorous coverage of this species under high urchin-grazing pressure in the Isoyake ground.