It has been observed by divers who were engaged in maintenance and management of marine structures that their surface coating was damaged by sea urchins. There are no reports with regard to such damages in the past. Therefore, survey was performed for sea urchins to survive on marine structures and for the damage of surface coating. As a result, 4 kinds of sea urchins such as ‘tawashi-uni’ (
E. molaris) and ‘murasaki-uni’ (
A. crassispina) were observed and the coating damage was observed at the location where 3 sorts of sea urchins such as ‘tawasi-uni’ (
E. molaris) were living. Pieces of coating as well as feed creatures were detected in their digestive canals. The ‘tawasi-uni’ (
E. molaris) more frequently observed on the damaged coating surface are usually said that they stay, in almost all cases, in holes dug in rock beds at a sea coast and eat pieces of sea weeds which flow into the holes. Because they cannot dig holes in metal of ocean structures, it is considered that they move on the surface of marine structures, biting sea weeds and barnacles on those as feeds. At the time, their hard teeth may damage the coating. The survey showed that high frequency of coating damage was observed at the points of ‘tawasi-uni’ (
E. molaris) existence. But teeth of ‘murasaki-uni’ (
A. crassispina) are as hard as those of ‘tawasi-uni’ (
E. molaris), and it is not clear why ‘murasai-uni’ (
A. crassispina) has more influence on it.
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