Establishment and maintenance of coral communities on sandy-muddy bottom: Studies based on "Inhabitation-chain hypothesis"

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We studied mechanisms of establishment and maintenance of coral communities on sandy-muddy bottoms, in Amitori Bay of Iriomote Island, Oura Bay and Kin Bay of Okinawa island.In Amitori Bay, coral communities changed along the environmental gradient from bay mouth to bay bottom. On the mudy bottom, branching Acropora, Anacropora and Millepora were abundant. In and around patches of these corals, there were many fragments. The larger fragments survived better than smaller ones. Fragmentation seems important for extension of the patch and colonization of new site. On the skeletal debries of these corals, we found many attaching coral species. Provision of attachment substrate and settlement of planulae of various corals seem important for establishment and maintenance of coral communities and multi-species coexistence in such habitat.In Oura Bay of Okinawa Island, Oulastrea crispata expanded its distribution range to muddy bottom by colonizing shells of adult Strombus snail. On the sandy bottom in Kin Bay, solitary corals Heterocyathus and Heteropsammia established high density populations by inhabitation-symbiosis with a sipunculan Aspidosiphon.