2.3.1 Islands

The Great Barrier Reef World Heritage Area includes approximately 1050 islands, consisting of continental islands (617), reef islands or coral cays (more than 300), and mangrove islands.65 There are 70 Commonwealth islands in the Region, and the remainder are under Queensland Government jurisdiction or a range of other tenures.66 About 470 of the Reef’s islands are protected as Commonwealth islands or National Parks. This assessment considers all these islands because of their connection to, and influence on, the values of the Region. 

The Reef’s islands support unique flora and fauna and are critical to the life cycles of many species, for example, by providing internationally significant nesting sites for 4 species of marine turtle (Section 2.4.10) and supporting breeding colonies for 21 seabird species (Section 2.4.12).66 They function as important refuges because islands are often isolated from impacts present on the mainland and serve as key links connecting coastal and offshore ecosystems.66,67 Ongoing regional ecosystem mapping and fauna surveys since 2019 68,69,70,71,72 are adding to a rich baseline understanding of island ecosystems.66,73 There is growing evidence that islands with nesting seabirds support more-resilient coral reefs, with improved coral growth and recovery rates linked to supply of seabird-derived nutrients.74

Islands serve as key links connecting coastal and offshore ecosystems

The Reefs’ islands hold a deep history of stewardship by Traditional Owners, as evidenced by numerous cultural and archaeological sites,75 and continue to be a critical component of the living cultural landscape for many groups.76,77,78 For example, Jessie Island and Sisters Island, offshore from Cowley Beach, are important story places for the Mandubarra people. These sites are increasingly being documented and mapped to preserve and share this heritage.76 

Since 2019, 146 islands, or parts thereof, amounting to 1508 hectares (15.08 square kilometres), have been added to Queensland’s protected area estate, and more are on the way.79,80,81,82,83 While these islands are not technically part of the Region, they have important influence on condition and connectivity for its habitats and species. Active efforts to acquire and bring more island area into Queensland’s protected area estate and rehabilitation of degraded areas are reducing legacy impacts and providing additional protection for vulnerable species.72,84,85,86,87 

Threats to island habitats include legacy impacts of historical guano mining; invasive plants and animal pests, such as goats, pigs and rats (Section 3.6.3); wildfires; impacts from direct use such as vegetation clearing; the degradation of cultural heritage (Indigenous and European); and plastic pollution transported from local and distant sources (Section 6.5.1).72,88 Between January 2019 and October 2023,55 of the more than 1000 islands within the Region were affected by fire including prescribed burns and wildfires.89,90 During the same period, 26 wildfires burned within protected areas and forests on islands.90 Preventing and eradicating highly invasive species (Section 3.6.3), such as yellow crazy ants,91,92,93 contribute to improved biodiversity outcomes for island-dependent species in the Region.

Aerial photograph showing Cockermouth Island surrounded by fringing coral reef.
Cockermouth Island near Mackay. © Mark Fitz 2023

Climate change is an important persistent threat. Rising sea and air temperatures, changes in cyclonic activity and otherwise amplified disturbance regimes, sea-level rise, and inhibition of reef-building processes, all present threats to island species and ecosystems.94,95 Low-lying reef islands can be particularly vulnerable to rising sea levels and increased storm intensity, through impacts on water tables, island over-wash and erosion, and sand supply,96,95 with consequential effects on vegetation 97 and species such as marine turtles.65 Reef islands are dynamic landforms subject to the interplay between the living and non-living forces that shape them. Responses to climate change are likely to be complex and vary between islands (Section 6.3.2).96,98 Efforts to document the detailed responses of reef islands to sea-level rise are underway using new data sources including drone technology, but detailed trend analysis is not yet available. Analysis of satellite images shows that island coastlines within the Region have been less stable in the past few years (2019 to 2022), compared to long-term average values (1988 to 2022): the proportion of island coastlines that are eroding has increased (Figure 2.3).99 The significance of this in the context of natural long-term change is not yet clear.

Use of continuously evolving technologies (Section 6.2.3), such as acoustics and drones for seabird and marine turtle monitoring, is improving data collection and enhancing understanding of island resources.66,100 

The condition of islands varies considerably across the Region and between island types. Some islands have experienced localised damage from severe weather and the accumulation of plastic pollution. Improvements have occurred on others due, for example, to pest eradication. Monitoring of island condition is increasing, and work is underway to assess the response of coral cays to sea-level rise.

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