The condition of the coral reef ecosystem in Natuna Island

Abstract Three groups of marine biotas in the coral reef ecosystem were analyzed to determine the overall condition coral reef ecosystem in Natuna Island (coral, reef fish, and megabenthos). Nineteen sampling sites are distributed completely in Natuna Island, including Natuna Besar Island, Tiga Island, and Sedanau Island. The coral reef monitoring refers to the Underwater Photo Transect (UPT), and data processing used the Coral Point Count for excel (CPCe). The reef fish observation using the Underwater Visual Census (UVC) and megabenthos observations using the Benthos Belt Transect (BBT). The percentage of the benthic cover was analyzed for several benthic categories. The analysis for reef fish consisted of diversity and abundance for the three fish groups, including the corallivore, herbivore, and carnivore. The megabenthos community’s analysis consisted of diversity and density from eight groups, including giant clams, lobster, Drupella sp., Linckia laevigata, sea urchin, sea cucumber, trochus, and Acanthaster planci. The Coral Reef Health Index (CRHI) analysis was used to determines the coral reef condition in Natuna. Nine sites were categorized as the fair condition of live coral cover with 26.53–36.87%. The largest composition of coral reef fish groups from herbivorous groups and the highest density megabenthos was sea urchins.