Assessing the Gulf of Carpentaria mangrove dieback

Norman Duke
Led by: Dr Norman Duke, JCU

 

Project Summary

In early 2016, extensive dieback of mangrove forests was recorded along the southern and western Gulf of Carpentaria coastline. Landsat analysis suggests that 7,400 hectares of mangrove forest suffered dieback over a relatively short and synchronous time period around November 2015, along a >1,000km wide front from Karumba in the east to Limmen River in the west.   Recent field visits to a limited range of affected sites suggest that a relatively low percentage of trees have recovered and most are dying/dead.  This is the largest event of natural dieback of mangroves ever recorded in the world.  This project will provide a survey, description and analysis of the extent of the dieback across its range, as well as examining patterns of dieback.  The assessment will include training and participation of local Indigenous ranger groups in mangrove assessment and monitoring methods, as well as providing recommendations for recovery, potential intervention, future monitoring and further studies.  A synthesis workshop will also be held to present the findings of the assessment to a wide audience.

 

Project Statements

Problem

An estimated 7,400 hectares of mangrove forests along a >1,000km long stretch of shoreline of the southern and western Gulf of Carpentaria, have suffered dieback.  Recent field visits to a limited range of affected sites suggest that a relatively low percentage of trees have recovered and most are dying/dead.  Across the whole dieback area, there is not for any location, a current formal assessment of the condition of affected forests and what proportion are recovering.  Thus, though there is clear evidence that extensive stands of mangrove trees have died, the actual condition status of these extensive forests is unknown.

Of the >1,000km front of affected forests, an estimated 200km are shoreline mangroves, whose death would leave the coastal shoreline exposed to erosion and storm surge effects which may cause even greater and more serious geomorphic and ecological disturbance to this coastline.

Biodiversity is likely to have been significantly impacted.  For example, recent field observations have revealed that the epibiont communities that reside upon the trunks and aerial roots of the mangroves have been shed as these structures die and decay, and leaf litter supplies, an important source of food that drive benthic productivity important for fisheries production, has almost ceased.

Whilst photographic and video evidence of extensive dead forests demonstrates the scale of the dieback event, there is currently little to no understanding of the patterns of dieback across the geographic range of the event.  In some areas, all mangrove species in all tidal elevations have been affected but in other areas, only some species in specific locations have been affected.  There is considerable variability in the patterns of impact across the whole extent of this dieback event.  A proper understanding of the causes of, and management responses to, this dieback, will require that the patterns of its manifestation across the whole area is understood.

This dieback event has caused considerable angst amongst local communities in the Gulf and industry groups such as commercial and recreational fishing, that rely upon the ecosystem services provided by mangroves.  The wider national and international community are also especially interested in this dieback event for its scale and for the possibility of a link to climate as the driver.  This event has also attracted significant media attention but to date, there has been no scientific assessment of the status of the affected mangroves.

Given that the dieback was not reported to authorities for nearly 5 months after it occurred, this demonstrates shortcomings in coastal monitoring capability.  Government agencies were unaware the dieback had occurred.  Some local community and industry members were aware of dieback in their local areas but did not recognise the scale of the dieback occurring or report their observations to authorities.

 

How Research Addresses Problem

This is the largest event of natural dieback of mangroves ever recorded in the world.  This project will provide a survey, description and analysis of the dieback across its range, as well as examining patterns of dieback.  Examination of the patterns of dieback will provide significant insights into the causes of the dieback, what species in what locations and in what tidal elevations were most impacted by the dieback, where the dieback was most pronounced etc.  In addition, a full assessment will assist with identification of the causes and enable a basis for deciding on whether to intervene in the recovery process, and if so, where and how.  It will also provide the necessary baseline dataset that will underpin assessment of future recovery of the mangrove forests and associated negative impacts and environmental changes that occur.  Despite the time since the dieback began, these patterns will still be evident as will evidence of successful recovery.

The assessment will include training and participation of local Indigenous ranger groups in mangrove assessment and monitoring methods, as well as providing recommendations for recovery, potential intervention, future monitoring and further studies.  Project findings will be presented to government, industry and community audiences at a local and national level.  A synthesis workshop will also be held to present the findings of the assessment to a wide audience.

 

NESP 2017 Research Priority Alignment

THEME 1. Ensuring that the development of northern Australia minimizes the risks to the region’s environmental resources

1.1 Identify critical knowledge gaps in the understanding of environmental resources in northern Australia to better prioritise government investment.

This project will provide considerable information on the dynamics of coastal mangrove forests across a large part of the Gulf of Capentaria coastline.

1.2 Develop and trial spatially explicit tools to guide planning and management decisions that support a mix of multiple uses and protected areas while maintaining environmental values.

This project will use the Shoreline Video Assessment Method (SVAM) to assess the mangrove dieback, in conjunction with Indigenous rangers.  This output will enable better planning and management of coastal habitats.

THEME 2. Improving management of threats to environmental resources in northern Australia

2.1 Determine the impacts of natural stressors and current management regimes on biodiversity loss and landscape degradation to underpin on-ground management actions.

This project will assess the impacts of natural stressors on a major mangrove dieback event and provide a baseline for recovery planning and management interventions.

THEME 4. (cross-cutting). Developing approaches for monitoring environmental resources in the northern Australia

4.1 Demonstrate how to better measure environmental drivers, pressures, stressors and responses in northern Australia, taking into account remoteness and limited specialist skills base within the region, including approaches to environmental accounting.

This project will demonstrate a rapid mangrove assessment method that is suitable for community use and will be trialled with Indigenous rangers.

THEME 5 (cross-cutting). Supporting Indigenous natural resource management in northern Australia

5.1 Participation of Indigenous people in environmental management across northern Australia, including Indigenous Protected Areas.

This project involves training Indigenous rangers in mangrove assessment methods and working together with internationally-recognised scientists.

 

Project Keywords

Mangrove dieback; Gulf of Carpentaria; Climate; Sea level; Indigenous rangers; Coastal monitoring.

 

Project Funding

This project is jointly funded through JCU and the Australian Government’s National Environmental Science Programme.

 

Project Publications

 

 

 

 

 

Project Map

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