Dead mangroves shut down carbon cycle

Mangroves help fight climate change but they’re at serious risk from its effects. That’s one of the findings from a study of a massive mangrove dieback that occurred in late 2015.

Local fishermen reported mangroves were dying along hundreds of kilometres along the Gulf of Carpentaria coastline, in northern Australia, an area known for its barramundi fishing and high-value commercial fisheries.

This caught the attention of Damien Maher of Southern Cross University in Melbourne, who is interested in the chemistry of mangroves – how they store carbon in their soils, remove planet-warming nitrous oxides from the atmosphere, and neutralise ocean acidification by releasing alkaline chemicals into nearby waters.

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Maher and his colleagues studied the dead zones, as well as adjacent areas that survived.

“The dead areas were emitting carbon dioxide to the atmosphere straight from the soils,” he says. 

“The carbon cycle had shut down because the trees weren’t locking up carbon anymore.”

And the dead areas were no longer exporting alkalinity, which meant a loss of the buffering benefits for nearby marine life such as coral and shellfish that are vulnerable to ocean acidification.

Maher says this event is a warning of how increasing climate-linked stressors might affect these important ecosystems in coastal zones worldwide.

“Mangroves are valuable habitat that supports fisheries, and provide a natural defence against storm damage during tropical cyclones,” he explains.

“We think a perfect storm of factors led to this dieback: monsoon seasons with very low rainfall, record high temperatures, and a strong El Niño event with lower sea levels, which prevented toxicity being flushed from soils.”

The research was published in the journal Scientific Reports.

Used with the permission of Science in Public.