Coral skeletal destruction – boring sponges on the Great Barrier Reef

Little is presently known about the role of sponges in bioerosion on the Australian Great Barrier Reef. Porites colonies from three reefs on the Great Barrier Reef (inner-shelf Pandora, mid-shelf Rib and outer-shelf Myrmidon Reef) were examined for evidence of bioerosion with emphasis on sponges. Patterns were found despite relatively low replication. Myrmidon Reef showed least evidence of bioerosion. On Pandora Reef, mollusc and especially Lithophaga bioerosion dominated. On Rib and Myrmidon Reefs, sponges were the main cause of bioerosion. We divided the sponges into two groups according to the appearance of borings. Chamberlike excavations were predominantly found in Myrmidon Reef Porites, whereas porous boring was by far the main sponge boring encountered at the other sites. This suggests a change in the species composition along the gradient of changing environmental conditions from nearshore to offshore. Bioerosion by other organism groups was sparse and only of minor importance on Rib and Myrmidon Reefs. These results are basis for ongoing studies of implications for sponge bioerosion in context of environmental conditions and its management on the Great Barrier Reef.