Assessing mangrove dieback in the Gulf Go Back

The dieback event has caused concern amongst local communities and industry bodies such as commercial and recreational fishing groups that rely on many ecosystem services provided by mangroves. The wider national and international community are also concerned about the dieback event due to its scale, diverse impacts and possible link to climate change.

Biodiversity is likely to have been significantly impacted by the dieback. For example, epibiont communities – the small plants and animals that live on mangrove trunks and aerial roots – have been shed, and leaf litter supplies, an important part of aquatic food chains, have almost ceased.

Of the affected mangroves, approximately 200 km are shoreline mangroves whose death would expose the coast to erosion and storm surge effects causing extensive geomorphic and ecological disturbance.

This project will:

• provide a survey, description and analysis of the extent and condition of dieback
• examine the extent, patterns, condition, trend and likely cause of dieback
• train local Indigenous ranger groups in mangrove assessment and monitoring methods
• provide recommendations for recovery, potential intervention, future monitoring and further studies

Project activities

• Initial Rapid Assessment of dieback recovery using the Shoreline Video Assessment Method and LiDAR – an airborne technology which takes precise, three-dimensional measurements of the shape of the mangrove forest and forest floor.
• Field verification and detailed monitoring including building the capacity of local Indigenous ranger teams to help monitor mangroves
• Formal assessment of the condition of affected forests and what proportion are recovering
• Analysis of the patterns of impact across the extent of dieback – in some areas, all mangrove species in all tidal elevations have been affected but it can be different in other areas

Anticipated outcomes

• A best practice standard baseline assessment of the affected shoreline to underpin future assessments of mangrove forests and/or associated environmental changes
• More informed management options in response to mangrove dieback events, i.e. deciding on whether to intervene in the recovery process, and if so, where and how
• Better informed management policies for fishery species and biodiversity that depend on mangrove habitats (e.g. catch quotas, seasonal closures), for carbon accounting, and for water resource planning where freshwater flows influence mangrove health
• Increased coastal monitoring and reporting capability in the Gulf, including increased capacity of local Indigenous ranger groups (e.g. extension of MangroveWatch training courses and joint fieldwork) to continue coastal monitoring after the project has ceased.
• Improved understanding of the effects of the dieback on shoreline erosion and geomorphology
• Improved understanding of the values and ecological services provided by mangroves and associated coastal ecosystems

Anticipated outputs

• A map and report assessing the extent of the dieback, its condition, the patterns of processes across the full range of the dieback in detail
• Contributions to an online, interactive portal for displaying the dieback imagery collected by rangers, scientists and others, including a baseline dataset and associated condition metrics for each assessment location for monitoring change and recovery into the future
• An evaluation of risks to shorelines and recommendations for the on-going standardised monitoring of tidal wetland vegetation bordering Gulf dieback areas
• An assessment of the amount of carbon lost from dead and rotting trees, and the likely consequences
• A review of mangrove habitat recovery and whether mitigation interventions might facilitate shoreline restoration
• Fact sheets, peer-reviewed scientific publications and other products

Project update June 2019.

Field work is covering the entire dieback zone along southern Gulf shorelines from Weipa in the east to the Gove Peninsula in the west with more detailed ongoing monitoring near Karumba, Burketown, Borroloola and Numbulwar townships. The fieldwork discovered major dieback areas between Pormpuraaw to Numbulwar.