Researchers investigate massive mangrove dieback in Northern Australia

One of the largest mangrove dieback events in living history occurred this year in northern Australia along approximately 700 km of coastline.

While the causes of this dieback are unknown, a team of Southern Cross University scientists and students have just undertaken some of the first ‘on the ground’ assessments of how this dieback event is affecting the coastal zone.

“The scale of this event is phenomenal, and there may be significant implications for fisheries and water quality in the area,” said James Sippo, a PhD candidate with the University’s School of Environment, Science and Engineering at the National Marine Science Centre.

“There are no clear answers at the moment, but something has caused mass mortality of the mangroves along an extensive length of the coast. Hopefully our research will help solve the mystery.”

The mangrove dieback follows a widespread coral reef bleaching event in the Great Barrier Reef. Both events may be related to climate change.

“Low rainfall and high seawater temperatures may be related to these events. The mean sea level was also very low in the Gulf leading up to the dieback event due to the prevailing climatic conditions,” said James.

The team of students and scientists, which also includes Dr Damien Maher, Mitchell Call, Ash McMahon, Dylan Brown, Stephen Conrad, Professor Isaac Santos and Dr Christian Sanders, is looking at changes in carbon cycling in the affected area, including how the event is changing the chemistry of the adjacent coastal waters.

Team members have spent two weeks in the field, working in and around Karumba in the Gulf of Carpentaria, one of the most impacted areas.

“The Gulf of Carpentaria has a massive fisheries industry including a large commercial prawn fishery. The area is also a popular destination for recreational fishers. Considering the importance of mangroves as fisheries habitat this event may have significant economic implications,” James said.

The team is also hoping to see if events like this have occurred in the past and how much carbon is at risk of being returned to the atmosphere as carbon dioxide as a result of this event.

“By looking at the chemical composition of the soils, we can assess whether the area has suffered similar dieback events in the past,” said Dr Damien Maher, a senior lecturer and project leader at the University.

“By linking this information with historic climate, we can also gain insights into how climate change might be leading to events such as this.

“Mangrove soils sequester large amounts of carbon dioxide from the atmosphere and act as natural sinks by accumulating carbon in the soils. One concern is that this mangrove dieback may release large amounts of carbon dioxide back to the atmosphere.”

The team is looking at the issue from a number of angles.

“We are taking a multidisciplinary approach. Looking at the effects on a local and regional scale, both on the land and water will help us understand how wide-ranging the consequences are. It is clear that there will be flow-on effects from this event on the nearby ocean, but we have no clear idea how large these might be.

“There is a genuine concern this might be a sign of things to come, with climate change marching on at an unprecedented pace.”

Dr Maher said large scale events like the mangrove dieback in the Gulf of Carpentaria could impact other iconic tropical ecosystems, such as coral reefs.

“If there was to be a similar dieback along the coastline adjacent to the Great Barrier Reef, the consequences could be catastrophic. Mangroves act as the kidneys of the landscape, filtering the water as it transitions from land to the ocean, so without them the already stressed reef would suffer a major blow.”

The research involves collaboration with colleagues from the Queensland Government and the University of New South Wales, James Cook University, the University of Queensland, and Griffith University.