Abstract
Acropora species richness was studied on the reefs surrounding Siladen Island in North Sulawesi, where a marine park was established in 1991. Direct observation was done at 8 stations, where each station comprised the three topographic reef zones: reef flat, reef crest and reef slope. 46 Acropora species were identified. Among all these species, only Acropora indonesia is endemic to Indonesia, while most of the other Acropora species have widespread Indo-Pacific distribution and a few (Acropora hoeksemai and A. brueggemanni) are limited to the central Indo-Pacific. Acropora palifera was the most wide distributed species, occurring at all the stations observed. 11 species were found on the reef slope that do not occur in the other zones. On the reef crest, the unique species are A. aspera, A. specifera and A. divaricata, while A. palmerae was the only unique representative of the reef flat. Although the composition of Acropora species in each reef zone was not statistically different, we found 38 Acropora species on the reef slope, 27 on the reef crest and 22 on the reef flat. The 46 Acropora species found in 3000 m2 of habitat area corresponds to predicted data based on the relationship between Acropora species richness and habitat area. Several Acropora species were only found at a typical side of Siladen Island and were not found at other sides during this study.
