Spatial distribution of juvenile corals (Scleractinia) in the coastal and small islands of Sumatra, Indonesia

Abstract

Coral community structure exhibits variation at each stage of its life cycle, but the spatial distribution of corals in early life stages, including from juvenile to adult stages, is not well understood, especially at a larger scale. Spatially, our study compared the genera richness and abundance of juvenile and sub/adult corals at 9 locations and 83 sites along the coast and small islands of western and eastern Sumatra, Indonesia. Field surveys were conducted by recording juvenile corals measuring ≤5 cm in diameter in 1 ×1 m quadrat transects with 6 times randomly at each site, while those with diameters greater than 5–10 cm were categorized as transitional to sub/adult corals. A total of 52 genera from 16 juvenile coral families were recorded and identified, which is higher than the sub/adult level, where a total of 40 genera from 14 families were found. The most common genera came from the Acroporidae (23.0 %), Merulinidae (18.7 %), and Agariciidae (12.7 %) families. The genera richness at the juvenile stage showed variation between locations and regions in western and eastern Sumatra, except between locations in the eastern region, while at the sub/adult stage there was no variation between the western and eastern regions. Abundance at the juvenile stage also showed variation between locations, but did not differ between the western and eastern regions and at locations in the eastern region. In contrast, coral abundance at the sub/adult stage showed differences between locations and regions, but did not show variation at locations in the eastern region. The abundance of juvenile corals was influenced by live coral cover, the presence of herbivorous and corallivorous reef fish, and hard substrates of dead coral, limited to sandy or muddy bottoms and coral rubble. Genera richness was also influenced by live coral cover, but limited by sandy and rubble reef habitats, the cover of other biota such as soft corals, and the presence of herbivorous fish. Variations in water conditions and geomorphological forms between locations on the west and east sides of Sumatra impacted the diversity and abundance of corals in the early stages of life, affecting their success in becoming adult colonies. The transition from juvenile to sub/adult corals emerged as a critical phase in the early life stages of coral for population maintenance and sustainability.