Mangroves under stress

Mangroves provide vital ecosystem services that protect coastal communities and contribute to environmental resilience. But these environments face a range of human- and climate-driven stressors that threaten to reduce habitat quality, biodiversity, and the ability of mangrove environments to mitigate climate change.

Understanding the changing conditions of and threats to mangroves is critical to effectively manage these ecosystems. However, the vast spatial coverage of mangroves presents a challenge for collecting data on their health. Coupled with satellite assessments, aerial surveys offer a practical solution to evaluate environmental health and shoreline condition over large spatial scales.

Aerial surveys to understand mangrove health

Our team has developed a method to capture high-resolution, overlapping images of shoreline vegetation from small helicopters. These images have been paired with notes on the condition of mangroves and coastal habitats, including any noticeable changes taking place such as mangrove dieback or shoreline erosion.

By recording the condition of shoreline ecosystems as well as any changes taking place, we can recognise current and emerging threats and quantify the dominant drivers of change throughout the region.

Gulf of Carpentaria and mass mangrove dieback

This project initially evaluated the impact of the 2015-16 mangrove mass dieback event in the Gulf of Carpentaria, with surveys in 2017 and 2019. These surveys recorded the condition of shorelines and health of mangroves along approximately 2,000km of the southern shoreline of the Gulf.

The team found over 80 km2 (around 6%) of mangrove forests in the Gulf of Carpentaria had been lost in the 2015-16 mass dieback event. Moderate to severe damage was observed along around 171.1km (22.5%) of shorelines mostly fringed by mangroves.

The team also identified other indicators of poor shoreline condition throughout the region, including human impacts such as weeds, vehicle tracks, grassland fires and feral pigs, along with climate-related impacts such as bank erosion, storm damage and terrestrial retreat.

The team will conduct further surveys in 2025 to evaluate recovery over the last decade and develop strategies to reduce the impact of potential mass diebacks from future extreme climate-related events.

Northern Great Barrier Reef

This project investigated the condition of shorelines and mangroves and the health of tidal wetlands bordering eastern Cape York Peninsula, surveying from Cape York to Cairns in 2017.

The team surveyed nearly 1,500km of coastline alongside the northern Great Barrier Reef and generated a library of 52,187 geotagged images covering every metre of shoreline.

A key outcome of this project was the development of a robust classification system for identifying and quantifying current and emerging environmental issues impacting Australian mangroves and tidal wetlands. This produced a set of around 24 environmental indicators that represent the dominant drivers of change, allowing the team to record the status and condition of 28 major estuarine sites along the coast. A notable finding was a link between shoreline retreat and rates of sea level rise.

Southern Great Barrier Reef

This project assessed the condition of the mangroves and tidal saltmarshes of the southern Great Barrier Reef region between Cairns and Gladstone in 2023. The goal was to identify key threats and the dominant drivers of change, as well as locating potential sites for remediation.

The team found that mangroves and saltmarshes along the southern Great Barrier Reef coastline were significantly affected by human- and climate-related stressors. Human impacts were most obvious near major population centres such as Cairns, Townsville, Mackay, Rockhampton, and Gladstone. Climate stressors were dominant with shoreline erosion present throughout the region, likely driven by steadily rising sea levels.

Southern Torres Strait

This project surveyed the complete shorelines of five Torres Strait Islands – Horn, Thursday, Hammond, Friday, and Goods – and the northwest shoreline of Prince of Wales Island, in 2024. This provided a regional-scale assessment of the condition of shoreline mangroves and saltmarshes in south-central Torres Strait, identifying key threats and drivers of change.

Human threats were noticeable as reclamation works, coastal development, access tracks, fire scorch damage and altered hydrology. Climate-related indicators were associated with rising sea levels.

Data from this project will contribute to an online database of environmental and geophysical information for coastal resource managers in Torres Strait.

Each of these projects have provided valuable baseline data on the health and condition of shoreline ecosystems and insights into drivers of change specific to different regions of northern Australia. These findings support tracking of future trends and other critical observations required for more effective local and national management of coastal ecosystems, especially for mangroves and tidal saltmarshes.

Project details

These projects were led by Professor Norm Duke, Jock Mackenzie, and Dr Adam Canning. Work in the Gulf of Carpentaria was funded by the Northern Australia Environmental Resources Hub and Tropical Water Quality Hub. Work in the northern Great Barrier Reef was funded by the Australian Government, for the southern Great Barrier Reef by Greening Australia, and for Torres Strait by SmartState.