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Red Sea mangroves fight back in the face of global decline

Hanan Almahasheer, Author provided

Red Sea mangroves fight back in the face of global decline

Hanan Almahasheer, Author provided

Mangroves are the only woody plants that connect land and sea. They act as a protective bridge: from one side, they protect coasts from storms and sea-level rise, from the other they have a huge root system that stabilises sediment protecting both offshore seagrass and coral reefs from being smothered.

Mangroves act as nurseries to terrestrial as well as marine plants, algae, invertebrates and vertebrates, and as carbon sinks.

Their role in climate change mitigation and adaptation is increasingly acknowledged – mangroves are the ecosystems with the highest capacity to absorb and bury CO2 from the atmosphere into the sediment via photosynthesis. Mangroves also play a key role in protecting coastal communities in the face of natural disasters, such as hurricanes and tsunamis.

It’s no surprise, then, that the worldwide ecosystem services provided by tidal marshes and mangroves are valued at US$ 194,000 per hectare each year.

Global threats

Sadly, mangroves are one of the most threatened ecosystems on earth. The lack of knowledge about their ecological benefit meant that worldwide, mangroves have been destroyed for many years. The land they had protected and fed so well has been increasingly converted and used for agriculture and aquaculture.

A third of the global mangrove cover has been lost since the second world war, with an annual loss rate of around 2%.

Australia recently experienced a massive die-back of around 7,000 hectares of mangroves, which coincided with the world’s worst global coral bleaching event.

Evidence of mangrove dieback in Australia’s Northern Territory. Google Timeline

Of small comfort is the fact that a recent paper found the deforestation rate to be decreasing by between 0.3% and 0.7% per year from 2000 to 2012.

But there is one place in the world where mangroves are not just surviving – they’re multiplying.

Red sea mangroves

Our research shows that there has been no decline in mangrove stands in the Red Sea – the body of water that runs between Africa and the Arabian peninsula. Red Sea mangrove coverage has actually increased by 12% since 1972. We used remote sensing to analyse satellite images and map the temporal and spatial prevalence of mangroves around the coasts of the Red Sea over the past four decades.

The Red Sea is one of the world’s saltiest and warmest seas. It is an extremely harsh environment, surrounded by desert and subject to very high temperatures. No rivers empty into the sea, which, along with the warm conditions, give it its high salt content. The mangroves found along the Red Sea coasts are some of the northernmost in the world.

The extreme conditions mean that the mangroves of the Red Sea have been subjected to much lower levels of human activity than elsewhere.

Mangrove cover in the Red Sea, from 1972 to 2013. Hanan Almahasheer

This does not mean there have been no human threats to mangroves in the region, nor any losses: stands remain at risk of coastal development and pollution along the Saudi Arabian coast. Along the coasts of Yemen and Africa, overgrazing by camels and logging have affected mangrove cover.

These losses have been partially compensated for with large-scale plantation projects. A rehabilitation project in Yanbu, Saudi Arabia saw mangrove cover increase by around 50-fold from 1975 to 2013. I have also had the pleasure to lead a small school mangrove replantation project in the Saudi Arabian fishing town of Thuwal as part of my PhD.

Planting mangroves in Thuwal. Hanan Almahasheer

A reforestation project conducted in the mid 1990s in Hirgigo, Eritrea has improved coverage along the east coast of the Red Sea. The project has also helped alleviate hunger among local people by providing high-nutrient feed to livestock and vital habitats for fish.

Increasing coverage is vital

Now we know the importance of mangroves in fending off ecological collapse and capturing carbon, it’s vital we do all we can to preserve them, and even increase coverage. That’s why the results of our research are so significant.

But there is much we still don’t know. The knowledge gap about Red Sea mangroves in scientific literature is even greater when we consider that these plants exist in extreme conditions that are unique to mangrove ecosystems.

The very reason our Red Sea mangroves are thriving makes it difficult to extrapolate conservation findings from other regions.

But in the face of massive diebacks and worlwide deforestation, at least we know there’s one place on earth where the mangrove is allowed to play its full role as the superhero of the marine world.