Large scale study of benthic communities in Eastern Indonesia’s reef systems

Abstract Broad-scale studies and regional comparisons of Indonesia’s coral reefs are critical given the relative lack of information about these large, diverse, and threatened ecosystems. Most studies on reef benthic composition and distribution have largely focused on rather short transects spanning relatively small areas. Here, we quantify the shallow large-scale spatial distribution of benthic communities in four locations in Eastern Indonesia, i.e. the Spermonde Archipelago in South Sulawesi, and Ambon, Halmahera and Lucipara in Maluku Islands. Shallow coral reef ecosystems (0.5-2 m depth) were assessed using a georeferenced photoquadrat survey method that can cover larger proportions of reefs, as well as benthic assemblages in deeper reefs ( ∼ 8 m depth) recorded with photoquadrats. A total of 27.8 km of shallow and 4.8 km of deeper reef ecosystem transects were surveyed in this study. We found that reef benthic communities at the study locations were mainly characterized by low to moderate cover of live hard corals and relatively high cover of dead corals or abiotic components. Ninety percent of the surveyed reefs at both depths exhibited 25% dead corals or abiotic components. A combination of georeferenced photoquadrats and CoralNet machine learning rapidly identified benthic composition across a large area, which is useful for mapping or other large-scale applications. This information can support decision-makers for better management of resources and marine spatial planning, crucial for an archipelagic state with tens of thousands of islands such as Indonesia. Our broad-scale reef surveying, focusing on under-studied areas of Indonesia, can contribute to this effort, as well as others seeking to better map coral reef habitats, as an important foundation for their conservation amidst growing threats.