IUCN Red List of Ecosystems Assessment of Tropical Saccostrea Oyster Reef Ecosystems in Queensland, Australia

ABSTRACT Tropical oyster reefs are ecologically important ecosystems that support significant ecosystem services across coastal seascapes. Yet their current distribution and conservation needs remain poorly understood, limiting the effectiveness of management. In tropical Queensland, Australia, historical oyster reef declines and current threats have not been evaluated within a standardised risk‐assessment framework. Here, we apply the IUCN Red List of Ecosystems (RLE) criteria to assess the conservation status of tropical eastern Australian Saccostrea (TEAS) reef ecosystems. We synthesised historical records, contemporary satellite imagery and field surveys to delineate TEAS reef ecosystem characteristics, define functional and collapsed states and quantify changes in distribution. Our analysis reveals a reduction in reef ecosystem occurrences since 1750, restricted contemporary distributions, pervasive environmental degradation driven by increased catchment modification and sediment loads and identifies ongoing climate change and declining water quality as continuing and persistent risks to their conservation. We conclude that TEAS reef ecosystems are Vulnerable to extinction under three of five criteria (A: reduction in geographic distribution, B: restricted geographic range and C: environmental degradation). Criterion D (disruption of biotic processes and interactions) and Criterion E (quantitative risk analysis) were Data Deficient and not assessed. Formal recognition of TEAS reefs within state and federal conservation frameworks, alongside integrated catchment management, climate‐adaptive restoration approaches and improved species‐level taxonomic resolution, is essential for safeguarding these ecosystems. This assessment establishes the first baseline conservation evaluation for tropical oyster reefs in the world and provides a foundation for future regional and international assessments.