Norfolk Island Lagoonal Reef Ecosystem Health 2025

This report is part of ongoing reef health monitoring of Emily and Slaughter bays, Norfolk Marine Park. This report details survey findings for the period between December 2024 and August 2025, and includes management recommendations. 

Summary

The 2024/25 reporting period for Norfolk Marine Park’s (NMP) inshore coral reef ecosystems presents a mixed picture of reef condition and resilience. 

Key findings are mixed and highlight both encouraging signs of ecological recovery from the 2023/24 coral bleaching event and ongoing stressors that can limit future reef health and recruitment and if continued may result in rapid decline of reef health. 

Sea surface temperature and coral bleaching 

During the austral summer of 2024/25, sea surface temperatures remained below the long-term average. This period of cooler conditions was significant in that no bleaching responses were observed across monitored inshore coral reef habitats. 

The absence of thermal stress has allowed for a minimum two-year recovery window following the widespread bleaching event of 2023/24. Continued low-stress summers will be critical to maintaining this recovery trajectory. 

Algal cover and reef substrate availability 

Despite the reprieve from heat stress, and conditions of low stress to corals, algal cover continues to increase across all surveyed inshore bays. 

This increased algal covered has resulted in a decline in the amount of free space on the reef surface, reducing the availability of suitable substrate for coral larval settlement. This trend represents a long-term risk to reef resilience, as high algal dominance and low substrate availability may suppress coral recruitment and hinder the replenishment of coral populations in coming years. 

Flooding, run-off and sedimentation 

From April 2025 onwards, the inshore reef environment has been significantly affected by severe rain events leading to prolonged flooding, catchment run-off, and sedimentation. Elevated sediment loads in nearshore waters reduce light availability for corals and smother benthic organisms, compounding pressures from algal growth. 

The persistence of these conditions is of concern, as it has the potential to drive further declines in coral cover and ecosystem function. 

Outlook 

Overall, Norfolk Marine Park’s inshore coral reefs have benefitted from the absence of thermal stress in the 2024/25 summer, enabling ongoing recovery from the prior bleaching event. However, rising algal cover, declining free space, and intensified sedimentation represent escalating challenges for the health of the inshore coral reef ecosystems. These pressures have the potential to severely constrain coral recruitment and slow ecosystem recovery from marine heatwave and coral bleaching events. 

Targeted management of catchment inputs, coupled with ongoing monitoring of reef condition, is essential to support the resilience of inshore coral reef ecosystems in Norfolk Marine Park.