| Budget Amount *help |
¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1987: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1986: ¥700,000 (Direct Cost: ¥700,000)
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| Research Abstract |
Echinometra mathaei is the most abundant sea urchin species along the coasts of Okinawa Island and is divided into 4 types (A-D) according to the characters of spine color, spicule and chromosome. Type A urchins inhabit moats and rock pools, and show a gregarious distribution. On the other hand, Types B, C and D urchins inhabit burrows, which may be excavated by themselves, on the reef crest and no typical differences in the distribution area among them are recognized. Urchins inhabiting in burrows expell the intruders and Type C urchins are more aggressive than Types A and B urchins (Type D urchins were not studied). E. mathaei makes environmental heterogeneity on the rocky substratum by its bioerosive activity. The heterogeneity and its activity affects the organization process of the lower intertidal and shallow subtidal communities. The burrows, From which the urchins had been removed or in which they had died, were not re-colonized fully within 1 yr. In the emptied burrows, sands and coral rubbles were accumulated and infaunal animals could invade. Some sessile organisms were also seen on the walls of the burrows, but these organisms were not seen in the burrows occupied by the urchins. Outside the burrows, small algae were growing abundantly and some animals including crustaceans, polychaetes and mulluscs lived among them or in small holes. Species diversity is higher outside the burrows than inside, because the urchin seems to live only in burrows and burrow walls may receive strong grazing effect by the urchin.
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