Impact Test Size and Type of Echinometra mathaei as Agent ofBioerosion on Reef Flat

Bioerosion is an activity of various organisms such as erosion and destruction of coral calcium carbonate and become a major factor influencing coral reefs morphology. Bioerosion is influenced by three variables: type of species, size of species and abundance. Seventyfive percent of bioerosion caused by sea urchin. Differences on size and type of sea urchin gave a significant impact to the bioerosion area. This study aimed to examine the influence of the size and the type of sea urchin E. mathaei (type A and type B) on the composition of CaCO3 in the gut content and feces as bioersion agent on the reef flat in Minatogawa Coast, Okinawa-Japan. The organisms used were E. mathaei type A and type B with each type distinguished by size ≥ 30 mm and 30 mm with three replications. The maintenance was carried out at laboratory for 3 days by observing analysis of the composition of CaCO3 on feces and gut content. It indicates that the composition of CaCO3 as daily bioerosion was caused by E. mathaei. The results showed E. mathaei with diameter ≥ 30 mm was more active than those with diameter of 30mm and type B was more active than type A in each of the same size. Percentage of CaCO3 in the gut during maintenance in the laboratory was 73% and the other 27% consist of organic and inorganic materials. Daily bierosion E. mathaei type A ≥ 30 mm 166.70 mg.day^-1 , type A 30 mm 77.78 mg.day^-1 , type B ≥ 30 mm 126.30 mg.day^-1 , type B 30 mm 116.17 mg.day^-1. Daily bioerosion rate E. mathaei was influenced by the type, species, speed of grind, and the size of the sea urchin.