Mangroves are enormously valuable coastal ecosystems. Healthy mangrove ecosystems not only buffer shorelines against rising sea levels, but they also provide valuable protection against erosion, abundant carbon sinks, shelter for animals, nursery habitat, and food for marine life.
In the summer of 2015–2016, some 40 million mangroves shrivelled up and died across the wild Gulf of Carpentaria in northern Australia, after extremely dry weather from a severe El Niño event saw coastal water plunge 40 centimetres.
The low water level lasted about six months, and the mangroves died of thirst. Seven years later, they have yet to recover.
This event, I discovered, is the world’s worst incidence of climate-related mangrove tree deaths in recorded history. Over 76 square kilometres of mangroves were killed, releasing nearly one million tons of carbon into the atmosphere.
But this event, while unprecedented in scale, is not unique. My research also discovered evidence of another mass die-back of mangroves in the region in 1982—the same year the Great Barrier Reef suffered its first mass bleaching event.
The mangroves took 15 years to recover. This time, we won’t be so lucky.
Our research reveals the presence of a previously unrecognized “collapse-recovery cycle” of mangroves along Gulf shorelines. The mangroves, damaged in 1982, are now attempting to recover again after the mass-death event in 2015.
But, at least three factors have changed since 1982, leaving recovery less likely –
- Sea levels have risen dramatically due to climate change, causing erosion. Younger trees are essential for future mangrove habitat. But upland, environmental conditions for newly established seedlings can be deadly by landward pressures of bushfires, feral pigs and weed infestations.
- Localized storms, such as tropical cyclones, have become increasingly severe.
- The threat of future Taimasa low sea level events appear imminent, as evidence points to a link between climate change and severe El Niño and La Niña events. In Samoa, El Niño-driven sea level drops are called “Taimasa” because of the putrid smell of decaying marine life from long-exposed corals, when sea levels remained low for months on end. In northern Australia, Taimasa conditions in 2015 left mangroves at higher elevations exposed for at least six months. Without regular flushing and wetting of tides, shoreline mangroves don’t stand a chance.
Under these circumstances, the potential for the mangroves to recover are understandably low.