4. Heritage values

Contained within the structures of its reef formations and diverse ecosystems, the modern Great Barrier Reef holds outstanding examples of the Earth’s evolutionary history.¹⁰⁷⁹ Geological coring has revealed a complex history of reef growth and regression as sea levels rose and fell through a sequence of ice ages during the Pleistocene epoch.¹⁰⁸⁰ Between coral reefs, the lagoon floor (Section 2.3.6) preserves records of ancient shorelines and river courses. ^205,1081 The diversity of reef islands (Section 2.3.1) reflects the varied geometries and relative sea level histories of the reefs on which they formed.⁹⁷ This evolutionary history not only has intrinsic value but represents a vital repository of data that can inform evidence-based responses to environmental challenges, such as climate change.^775,1082

Since 2019, important advancements have extended our scientific understanding of the Reef’s evolution. These include insights into the origin of the Reef itself. One study links the formation of K’gari (formerly Fraser Island) around 800,000 years ago, and its consequential interruption of longshore drift, to the preconditions for coral formation in the Region.¹⁰⁸³ Recent studies have considered sea temperatures,¹⁰⁸⁴ turbidity,^775,1085 tectonically driven subsidence of central parts of the continental shelf ^1086,1087 and other environmental factors affecting the geomorphology and growth history of the Reef since the last ice age.¹⁰⁸⁸ 

Other studies have explored the influence of reef platforms on the development and evolution of seafloor features ¹⁰⁸⁹ and of reef growth patterns ¹⁰⁹⁰ during periods of low sea level, such as the last glacial maximum. Halimeda bioherms (Section 2.3.8), recognised for their contribution to the Reef’s outstanding universal value,¹⁰⁷⁹ have also been a focus of study.^234,1091 More recent geomorphological changes have also been documented, such as the development and growth of low wooded islands.^100,123 Taken together, these findings underscore the importance of the Reef as a living archive of key chapters in the Earth’s evolutionary history. 

The Reef is considered resilient with respect to the geological and geomorphological processes that have shaped and link the Region’s habitats across the continental shelf to the continental slope and abyssal plains.^97,186 However, the effects from climate change, such as ocean acidification (very high risk), sea-temperature increase (very high risk) and sea-level rise (very high risk) present a threat to this world heritage criterion. 

The combined impacts on key organisms ¹⁰⁹² are likely to affect not only ecosystems (Section 6.3.2) but also reef structures.¹⁰⁹³ For example, if not effectively mitigated, climate change will lead to reduced growth and diminished structural integrity of some reefs. Persistent rubble beds will become more widespread, reducing the structural complexity of reef habitat.¹⁰⁹⁴

The Reef’s ability to change and adapt to shifting environmental conditions over millennia has made it a living document of major stages in the Earth’s evolutionary history. However, if current trajectories of climate change continue unabated, declining ecosystem condition and damage to key features, especially coral reefs, will erode the Region’s outstanding universal value.