Effect of coral-inhabiting barnacle (Cantellius pallidus) on planula production in a scleractinian coral Alveopora japonica

Although many species of scleractinian corals are known to be infested by barnacles, there is a paucity of detailed ecological information on coral-barnacle relationships. In high latitude waters of western Kyushu, Japan, a scleractinian Alveopora japónicawas found to be infested by a barnacle Cantellius pallidus. The present study reports for the first time the effects of barnacle infestation on the reproduction of the host coral. Cabtellius pallidusattached themselves to the surface skeleton of A. japónicaand, as they grew, covered a polyp underneath, while the barnacles were in turn covered by the coral's skeletal growth, leaving only the barnacles' aperture visible in the end. Planula production was depressed in polyps immediately adjacent to an attached barnacle. Fecundity (number of planulae per polyp) declined with an increasing infestation load of barnacles. Thus, the relationship between C. pallidusand its coral host should be termed parasitism, rather than commensal-ism or symbiosis which were used to describe the relationship between barnacles and their sessile hosts in some previous studies.