Coral community responses to Pleistocene sea-level and environmental change on the Great Barrier Reef

This study investigates the long-term responses of coral reef communities on the Great Barrier Reef across glacial–interglacial cycles, using data from offshore and onshore drill cores. It compares coral assemblages from submerged glacial and deglacial reefs (IODP Expedition 325, Ribbon Reef, Noggin Pass, and Hydrographers Passage) with interglacial highstand reefs (Ribbon Reef 5 and Boulder Reef). Results show that coral community composition is strongly influenced by sea-level fluctuations, shelf morphology, and environmental conditions such as turbidity and/or temperature. Deglacial and highstand barrier reefs are dominated by fast-growing Acropora and Isopora , which sustain vertical reef growth during rapid sea-level rise. In contrast, glacial and early deglacial fringing reefs feature encrusting to massive Isopora , fine-branching Acropora and Seriatopora , and to a lesser extent merulinids and Tubipora . Boulder Reef's persistent dominance of massive Porites highlights the resilience of turbid inner shelf reefs. The study identifies coral successions during reef initiation and drowning, with sediment-resistant taxa, i.e., massive Porites and merulinids, colonizing newly inundated substrates while laminar to submassive Porites and Montipora mark deepening prior to reef demise. Key reef-building taxa persisted during glacial periods, enabling reef recovery and growth. These findings underscore the importance of external environmental drivers in shaping coral community structure and provide insights into reef resilience under future climate change scenarios.