While Australia burns under a changing climate, our mangroves die-off

By PhD student Yota Harada

Climate driven mass die-back is causing significant changes in mangrove ecosystems.

Numerous marine species, including crabs, prawns and fish, rely on mangroves for nurseries, refuges and food. Mangrove forests support global fisheries and the livelihood’s of people, but large-scale mortality of mangroves is anticipated due to climate change and associated extreme climatic conditions.

Dead mangrove forest. Photo: Larissa D, Shutterstock.

In the Australian summer of 2015-16, over 7000 hectares of mangroves along 1000 km’s of coastline in the Gulf of Carpentaria, Australia, died as a result of low rainfalls, extreme heat and low sea levels. This was one of the worst mangrove die-back events ever recorded, it also coincided with the mass bleaching event of corals on the Great Barrier Reef.

We found that the dead site was dominated by one group of animals, Fiddler Crabs, whereas the healthy area displayed a more diverse community of animals.

Fiddler Crabs, that dominated the dead mangrove site. Photo: Kim Taylor, Getty Images.

Our team traveled to the Gulf of Carpentaria in 2017, to conduct a field survey that compared an area consisting of dead mangroves and an area consisting of healthy mangroves, about 2km away. We found that the dead site was dominated by one group of animals, Fiddler Crabs, whereas the healthy site displayed a more diverse community of animals. Our stable isotope analysis, a method that analyses animal’s diets, shows animals at the impacted site predominantly consume benthic algae, whereas animals from the healthy site consume a variety of food, including mangrove leaf litter.

Collecting samples. Photo: Luke Jeffrey.

The die-back not only changed the community of mangrove animals and their food, but also the habitat structure. The dead mangrove site lost tree canopy cover and complex root structures, these typically provide important nurseries and refuges for numerous marine species. These findings show a major loss in mangrove ecosystem services for varying species, these include, provisions of nurseries, refuges and food sources.

Dead mangrove forest. Photo: Yota Harada.

Our research, published in the scientific journal, Limnology and Oceanography, will help expand the understanding of the effects of extreme weather events on mangroves. It can also help inform policy management plans for these important ecosystems that support unique biodiversity and fisheries.

Unfortunately, we still do not know much about how mangrove forests will recover from extreme weather die-backs. However, our upcoming new research focuses on longer-term monitoring of the post die-back recovery and knowing how things develop over time.

While doing field work there are always a few surprises. Photo: Jeff Balland.

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