NEW ASPECTS ON THE BIOLOGY OF THE ENCRUSTING EXCAVATING SPONGES CLIONA APRICA, CLIONA CARIBBAEA AND CLIONA SP.

Abstract

In order to understand the mechanisms of interaction with corals in three species of encrusting and excavating sponges (Cliona aprica; Cliona caribbaea=Cliona langae; Cliona sp.) that actively undermine live coral tissue, detailed observations and follow-up of marked individuals were carried out in reefs of two coralline areas of the Colombian Caribbean. A not previously described final growth stage was found, in which tissue of older individuals thickens and becomes infested by epibiotic zoanthids. An agglutinating stage occurred in one species when growing on rubble. Maximum rates of lateral advance against live coral in 13 months were 19.7 cm Cliona sp., 8.3 cm for C. aprica, and 6.5 cm for C. caribbaea. By sending excavating tissue threads underneath live coral tissue, these sponges weaken the skeletal support of the polyps, resulting in their retraction or detachment. Fish bites and growth of turf algae and accumulation of sediment at the boundary produce further coral death. The sponge then advances, excavating and encrusting the freed substratum. This undermining mechanism is thus a highly effective competitive strategy that explains partly the ability of these sponges to gain and monopolize reef space.