Impact of Holocene relative sea-level changes on patch reef-island development in the Spermonde Archipelago, South Sulawesi, Indonesia

Reef cores that have been radiometrically dated are increasingly used to examine Holocene reef geomorphology, accretion rates, and community changes. Further, these accretion rates can be compared to sea level change regimes to see if, and how coral reefs have been keeping up with sea level. As Sea level rise is expected to accelerate over the next 100 years, it is important to examine whether these reef complexes are able to “keep up” and avoid “drowning.” Coring has been conducted in many highly studied areas such as the Great Barrier Reef and the Caribbean. However, in the Indo-Pacific region, an area of the highest coral diversity, there have been only a handful of reef cores collected. Here, we present data of 16 cores from two islands of different reef zones from the Spermonde Archipelago, South Sulawesi, Indonesia. Cores were taken from the reef flat and slope, with recovered length varying from 0.41 to 3.53 m, providing a history of each reef after radiocarbon dating. From 7200 to 5500 YBP, sea level rise rapidly increased and these reef complexes accreted at rates able to match this. This is in part driven by a higher occurrence of massive and foliose corals. After this point and toward the present day, sea level declined, causing sub-aerial exposure of these sand cays and the slope now sustaining the growth. This shows that these reef complexes (some of which contain heavily populated islands) are able to keep growing in the face of sea level rise regimes.