Distribution and drivers of coral disease at Ningaloo reef, Indian Ocean

We investigated the prevalence and potential drivers of coral disease across Ningaloo Reef on the Western Australian coast. Coral disease assessment surveys were undertaken at 2 spatial scales, the first over a small area of reef (Bill’s Bay, 2.5 × 5.0 km), where human use is high and where several anoxic events have caused significant coral mortality, and the second over a broader area (spanning ~200 km of the Ningaloo coast). Throughout Ningaloo, 2.3% of coral colonies showed signs of disease, although disease prevalence varied at both broad and local scales, ranging from 1.1 to 7% along the coast, and from 0.1 to 3.1% locally—all within the range of values recorded in other Indo-Pacific regions. Seven diseases were identified, the most common being ‘skeletal eroding band’ (which affected ~1% of colonies). At a broad spatial scale, prevalence of skeletal eroding band was positively related to the number of coral colonies exhibiting Drupella spp. feeding scars, whilst blackband disease (BBD) was positively associated with density of coral colonies. At the local scale, severity of anoxic events and occurrence of Drupella spp. feeding scars were positively related to prevalence of BBD, whilst other cyanobacterial bands were associated only with Drupella spp. scars. We saw no strong indication that human activities, measured as density of people or vessels in the water, were related to disease prevalence. Positive relationships amongst disease, anoxic events and Drupella spp. feeding suggest that natural stressors are potential drivers of disease at Ningaloo.