Pemuteran study finds uneven coral disease at five shallow-reef sites

Pemuteran — A 2018 field study of Pemuteran’s shallow reefs found that coral health conditions varied markedly between five survey sites, with the lowest proportion of live coral recorded at site 2 and the highest prevalence of coral disease at site 4, according to conference proceedings on coral health in North Bali waters.

The research, presented in the IOP Conference Series: Earth and Environmental Science, investigated coral diseases and what the authors termed compromised health syndromes on shallow reefs in Pemuteran, Buleleng regency. Fieldwork was carried out in March 2018, using modified belt transects measuring 2 by 20 metres, with three replicated transects at each of five sites.

According to the conference paper abstract, results showed that site 2 had the lowest percentage of live coral cover among the five locations, while site 4 recorded the highest disease prevalence. Other publications on Bali coral conservation cite the same Pemuteran study in summarising reef-health pressures in the area.

Survey methods and recorded conditions

The Pemuteran study identified three coral diseases on the shallow reefs: ulcerative white spots, white syndromes and trematodiasis. The authors also classified several observations as compromised health syndromes rather than diseases, focusing on visible stressors affecting coral colonies.

Stress indicators recorded in the abstract included aggressive overgrowth by algae, predation by Drupella snails and crown-of-thorns starfish, and sedimentation on the reef. These factors were described as dominant agents of compromised coral health at the survey sites, alongside the identified diseases.

The study reported extremely high nitrate concentrations at sites 4 and 5, which it described as popular snorkeling and diving spots. Organic-matter concentrations were significantly high at all five sites compared with levels reported from other reef areas, according to the same abstract. Later literature reviews on coral-reef conservation in Bali reference the Pemuteran findings as evidence of nutrient and pollution pressures on tourist-exposed reefs.

Key data points from the Pemuteran study

• Survey period: March 2018 in Pemuteran waters, Buleleng regency, North Bali.
• Coverage: five shallow-reef sites, with three replicated 2 × 20 metre belt transects per site.
• Site-level extremes: lowest live-coral percentage at site 2; highest disease prevalence at site 4.
• Identified diseases: ulcerative white spots, white syndromes and trematodiasis.
• Other stress indicators: aggressive algal overgrowth, Drupella and crown-of-thorns predation, and sedimentation.
• Water-quality findings: extremely high nitrate at sites 4 and 5; significantly high organic matter at all sites compared with other reported reef areas.

What the results do and do not show

The March 2018 survey provides a site-specific snapshot of coral health and water quality on Pemuteran’s shallow reefs, highlighting that conditions at one location cannot be assumed to represent the entire area. The abstract summarises relative differences in live coral cover and disease prevalence between sites but does not list numerical percentages for each location.

The published abstract also reports high nitrate and organic-matter levels alongside coral-health indicators, but it does not test or claim a direct causal link between these parameters and the observed disease patterns. Subsequent scientific reviews on coral-reef conservation in Bali discuss nutrient enrichment and pollution as key pressures on coral health but treat the Pemuteran study as one data point within a broader body of evidence.

The 2018 findings therefore serve as a baseline for monitoring shallow-reef conditions in Pemuteran, particularly at tourism-exposed sites, rather than a current assessment of reef health. To evaluate trends since 2018, follow-up surveys would need to repeat measurements at the same sites, use clearly stated field criteria for diagnosing coral diseases and compromised syndromes, and distinguish disease from physical damage, predation and other stress forms.

Context

Pemuteran’s reefs are a focus of ecological and socio-economic interest in North Bali, where coral ecosystems sit adjacent to a growing coastal tourism sector. The 2018 Pemuteran study, as cited in later conservation literature, links reef-health assessment to both ecological integrity and human activity, including tourism-related pressures and land-based inputs that can affect water quality.

Sources

• IOPscience – Status of coral diseases and compromised health syndromes on Pemuteran shallow reefs, North Bali island
• Coral reef conservation in Bali in light of international best practice, a literature review (Bournemouth University e-print)
• Coral reef conservation in Bali in light of international best practice, a literature review (Undiknas repository copy)