Storm-mediated coral colonization by an excavating Caribbean sponge

The broken, dead stands of the Caribbean elkhorn coral Acropora palmata, which suffered massive mortalities from disease and bleaching during the early 1980s, are now widely covered by Cliona tenuis, an encrusting and excavating brown sponge (Hadromerida, Clionaidae). This sponge displaces live coral tissue by undermining the polypal skeletal support. On the windward fringing reef of Islas del Rosario (Colombian Caribbean), 26% of C. tenuis individuals currently dwelling on live corals had colonized their host from sponge-carrying branches of A. palmata thrown against the corals during storms. Times of initial colonization were traced back from sponge growth rates in a few marked massive coral colonies and found to coincide approximately with hurricanes that had affected the area. Transplantation experiments confirmed that C. tenuis is able to spread to new coral hosts from attached fragments. The extent of C. tenuis dispersion via branching coral fragments and further massive coral colonization is now evident and, given that C. tenuis-encrusted A. palmata fragments are becoming progressively smaller, the phenomenon is likely to increase. C. tenuis was also found undermining encrusting and foliose corals settled on dead A. palmata branches, thus also retarding the process of reef recovery to an unknown degree.