The coral reefs of Bali Barat National Park, one of Indonesia’s oldest marine protected areas, are known for their high biodiversity and excellent sport diving; however, stressors such as destructive fishing practices, elevated water temperatures, damage from anchors and careless visitors have been observed on these reefs for decades. The purpose of this study was to document and quantify changes in the fish and stony coral community structure of reefs within and outside the boundaries of Bali Barat National Park from 2011 to 2016, including its most popular dive site, Menjangan Island. The results provide further knowledge about the reefs of NW Bali and the efficacy of current management practices, and they will inform management decisions for locally managed reef stewardship programs.
Between 2011 and 2016 the reefs of NW Bali lost 44.4% of their living coral cover, declining from 36% to 20% overall cover. Mortality was principally attributed to thermal bleaching caused by persistently high sea temperatures, which peaked in January 2016 at 32.2°C, coinciding with the third documented global bleaching event. Approximately one third of all stony corals were found to be bleached or recently dead. Despite the decline in coral cover, stony coral genus richness remained unchanged, with 56 genera recorded in both years, representing a combined total of 59 distinct genera. Mean fish biomass at Menjangan Island increased, with herbivorous fish biomass quadrupling, presumably due to decreased fishing effort at the island. The abundance of fish at all sites—both inside and outside the park—more than doubled, indicating a predominance of small fish at sites where fish biomass did not correspondingly rise. Crown-of-thorns starfish (Acanthaster planci), not observed on transects in 2011, were found in 2016 in areas of relatively high disturbance from marine recreation and possible eutrophication from shrimp farm effluent and mainland runoff. Patterns of coral cover and damage, fish abundance and biomass, and lost fishing gear suggest that management activities inside and outside the park have reduced ecological damage. Local community conservation groups are practicing one or more of the following at Menjangan Island and in some of the locally managed conservation areas: installing moorings, removing coral predators (crown-of-thorns starfish and Drupella snails), reducing fishing pressure, securing live coral fragments back onto the reef and planting mangroves. These nature groups are raising community awareness about the importance of NW Bali’s marine ecology to their economic and cultural wellbeing.