1 Proccedings of the 11th International Coral Reef Symposium, Ft. Lauderdale, Florida, 7-11 July 2008 Session number 18 Organisms associated with live scleractinian corals as indicators of coral reefs status in the Wakatobi Marine National Park (SE Sulawesi, Indonesia) P. SCAPS 1* , V. DENIS 1 and J. HAAPKYLÄ 2 1) Laboratoire de Biologie Animale, USTL, 59 655 Villeneuve d’Ascq Cédex, France. 2) Coral Reef Research Unit, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK. Abstract. Organisms associated with live scleractinian corals were studied on four sites located around Hoga and Kaledupa islands in the Wakatobi Marine National Park. The number of coral colonies infested by coral associates was estimated along 20 m long line intercept transects and the number of coral associates found on each coral colony was recorded. A 0.5 m point intercept transect method was used to describe the benthic cover. A total of 2815 associates were recorded infesting 376 coral colonies. The most conspicuous coral associates were lithophagid bivalves making up for 73% of total coral infestations. The highest number of infested colonies was found for the genera Montipora, Pavona and Porites. They represented 33%, 23% and 18% of the total number of colonies infested respectively. The number of infested coral colonies and the density of Lithophaga spp. were high in the most impacted site (Sampela) and one of the intermediately impacted site (Pak Kasim’s) whereas they were low in the most pristine site (Kaledupa). Despite the high biotic cover of Pak Kasim’s, this site suffers from a similar level of infestation as Sampela suggesting process of reef degradation previously experienced by the most impacted site. Our results suggest that coral associates can be used as indicators of coral reef status. Key words: Coral, Macrobioeroders, Coral predators, Reef health, Indonesia Introduction Coral reefs are critically important for the ecosystem goods and services they provide to maritime and subtropical nations (Moberg & Folke 1999). Reefs are currently in serious decline (Bellwood et al. 2004) due primarily to over-harvesting (Jackson et al. 2001), pollution (McCulloch et al. 2003), disease (Harvell et al. 2002), and climate change (Wilkinson 2004; Hughes et al. 2003). Already 20% of the coral reefs have been destroyed (Wilkinson 2004) and show no immediate prospects of recovery, 24% are under imminent risk of collapse through human pressures and a further 26% are under a long-term threat of collapse. The worst scenarios, prospected by Woolridge et al. (2005), suggest that reefs will become devoid of significant coral cover and associated biodiversity by 2050. The managing and a strong focus of key functional groups have become today a priority as part of insurance for sustainability (Hughes et al. 2003). Coral associates (bioeroder and coral predator organisms) represent one of these key groups. Bioerosion and predation on scleractinian corals are indeed an important part of coral reefs dynamics. Scleractinian corals provide microhabitats and are used by a large number of parasites and other associated organisms, which use the tissue and skeleton of the coral colonies as food or substrata (Frank et al. 1995; Floros et al. 2005). Many taxa are involved and most of these coral associates stress the coral to some degree. Any natural or anthropogenic disturbances that lead to the loss of live coral tissue will ultimately increase the chances of bioeroder invasion. The bioerosion process can lead to important coral damage and even, depending on the intensity, can lead to mortality of coral colonies (Kleemann 2001). Bioerosion plays an important part in the degradation of the reefs and affects coral reef health. Nevertheless, although very important, the community structure of organisms involved in this process is relatively poorly documented. The aim of this study was therefore to link the different assemblages of coral associates on reefs around Hoga and Kaledupa islands in Indonesia with the health of these reefs. Study sites and methods This study was conducted on the reefs around the islands of Hoga and Kaledupa in the Tukang Besi Archipelago of the south-eastern coast of Sulawesi in the Banda Sea, in Indonesia and took place in July and August 2005. Four sites were studied (Fig. 1) and 810