Many Records of Hermatypic Scleractinian Corals that Grew on Molluscan Shells

Abstract

Forty cases of hermatypic scleractinian corals colonizing molluscan shells were recorded. Forty-five colonies of the corals belonging to eight genera in six families grew on 40 shells belonging to 15 genera in 12 families. Forty colonies were found in Tanabe Bay and its vicinity, southwestern Kii Peninsula, Japan, and 10 colonies in coral reef regions in Okinawa, Palau and probably the Banda Sea and/or the Arafura Sea. Usually one colony, rarely two to four colonies of at least two species of corals, grew on a shell of three families of gastropods and nine families of bivalves. Although the shell surface is a suitable substratum for planula larvae to settle down, coral colonies can not grow to large sizes on the shells. In most cases, shells may not be stable and sufficient substrata for continuous growth of corals. However, the corals on the shells may conduct the sexual reproduction to some extent. Unstability of molluscan shells as footholds may be one of the reasons why the association is not remarkable on the reefs.