Marine heatwave-driven mortality of bleached colonies of the massive coral Goniopora is exacerbated by a black band disease epizootic

Abstract

During the recent fourth global mass coral bleaching event, the Great Barrier Reef (GBR) experienced the highest temperatures for centuries and widespread bleaching. For massive, long-lived Goniopora, bleaching coincided with a black band disease (BBD) epizootic at One Tree Reef (OTR). This necrotic wasting disease, typically rare on the GBR, appeared along the edge of bleached polyps. We tracked 112 Goniopora colonies from bleaching onset through winter to summer in seven surveys. In February 2024, 75% of colonies were bleached, and 4% of these had BBD. By April, 61% of bleached colonies had an aggressive black band invading the tissue. For heat stressed and diseased Goniopora, winter cooling did not promote substantial recovery with 75% of tagged colonies dead by October. Only 24% of tagged colonies recovered, albeit with partial mortality. Population surveys at two sites showed a similar bleaching-disease pattern with high mortality by October (46% and 66%). Repeated health assessments revealed a link between bleaching, disease and heat in the demise of these normally resilient massive colonies, many of which have been lost at OTR. Understanding the connection between the ‘evil twins’ of bleaching and disease is important as corals are faced with unprecedented thermal anomalies.