Possible effects of gold mining on coral reef health

Indonesia, being the core of the Coral Triangle, is supposed to hosts the most healthy and diverse coral reefs on the Planet Earth. However, the combination of global and local stressors has led to a decline in coral reef communities around the world. Anthropic activities of particular interest in North Sulawesi are industrial and artisanal gold mining (ASGMs). Industrial mining activities generally used the alkaline cyanidation method while ASGMs still employ mercury amalgamation to extract gold from ores. The extraction and processing of gold produces mine tailings that contain heavy metals, which may be dispersed in the catchment basin due to rain and flooding events and could alter the natural defences of the corals and favour the onset of diseases. The objective of this study was to assess the possible impacts of gold mines in North Sulawesi on coral reef health by comparing prevalence of coral diseases and aggressive species interactions between putatively affected and control sites. As putatively impacted sites, coral reefs downstream to four mining sites were selected: one long-time and one recently established ASGM, a modern industrial mine and a new site in preparation. Among the 21 possible diseases and other signs of compromised health investigated, gastropod corallivory, aggressive overgrowth, skeletal deformations caused by pyrgomatid barnacle and bleaching, were significantly more abundant at some sites affected by mining activities, compared to controls. A significant increasing of coral bleaching appeared as a result of the pollution generated by ASGMs, which release mercury in the aquatic environment. Detected alterations indicate that long term mining activities can affect the health of coral reefs. Mining in the area is expected to increase due to the large availability of resources, but well environment-based policies are needed to ensure that this development does not compromise biodiversity and marine resources.