Current trends of space occupation by encrusting excavating sponges on Colombian coral reefs

Sponges are a significant component of coral reefs, their bottom cover and density often being similar to or higher than those of stony corals (Rützler 1978; Zea 1993). Among the various morpho-functional types of reef sponges, those that excavate the calcium carbonate reef framework play a key role in the balance between reef accretion and erosion (reviews in Wilkinson 1983; Glynn 1997). Additionally, excavating sponges that encrust the substratum are also strong reef space competitors, aggressively undermining and displacing live coral tissue (Rützler 1975, 2002; LópezVictoria et al. 2003). Indeed, during the last three decades, the cover of these sponges has increased considerably, especially at zones suffering massive coral tissue die-off from disease, bleaching and other causes (Cortés et al. 1984; Glynn 1997; Williams et al. 1999; Rützler 2002). This has led some authors to catalog them as a contemporary threat to coral reefs (Antonius & Ballesteros 1998; Williams et al. 1999). The increase of these and other excavating sponges has also been related to other factors which are detrimental to reef corals but are favorable to sponges, such as organic pollution or temperature increase (Rose & Risk 1985; Holmes 1997, 2000; Rützler 2002). Cliona aprica Pang, 1973, C. caribbaea Carter, 1882 (1⁄4 C. langae Pang, 1973) and C. tenuis Zea & Weil, 2003,