Induced colonization of corals by a clionid bioeroding sponge

Colonization abilities of the bioeroding sponge Cliona orientalis were studied in a field experiment conducted at Orpheus Island, on the central Great Barrier Reef. Live grafts of sponge tissue were fixed onto nine coral species: Porites australiensis, Porites cylindrica, Porites rus, Acropora formosa, Astreaopora myriophtalma, Favites abdita and Monastrea curta. No sponge tissue was observed in Lobophyllia hemprichii and Pachyseris speciosa. While colonization of dead substrates can take place within a few weeks, invasion through live coral tissue occurred after 2-3 months. The frequency and area of sponge tissue in coral tissue were statistically independent of host coral species. The coral species affected sponge survival and health, presumably due to coral chemical defence. We ranked coral defence abilities against the sponge in the order: L. hemprichii > P. cylindrica = P. rus = F.abdita > A. formosa = M. curta (= P. speciosa) > A. myriophtalma = massive Porites. Overall, sponge fragments had a considerable capacity to survive on live coral and to recover from injury, handling and the initial stress caused by contact with corals (96% survived for 3 months). The ability of the sponge to resist coral defence on direct contact may offer it an alternative to sexual reproduction - by propagation through fragments - and may enable the sponge to invade various coral species laterally.