Earth's Secret Weapon

Why mangroves matter – and what we can do to help conserve them.

- Melinda Murphy

There might not be much of them, and you might not see them often, but Hong Kong’s mangroves constitute one of our most important ecological habitats. Unfortunately, this miracle plant is under threat, not just here but all around the world – and that spells bad news for our fight against climate change.

“Blue carbon” ecosystems such as mangroves, tidal marshes and seagrasses sequester and store large quantities of carbon. This is in both the biomass of the plants themselves, as well as in the sediments they secure below water.

“The root systems of coastal mangroves secure large quantities of rich sediment,” says ROBERT BAIGRIE, who is the senior director of partnerships and conservation finance at Conservation International (CI). “Some of these ecosystems can hold up to ten times more carbon than a terrestrial forest. Ten times!”

When we lose mangroves to coastal development, the carbon they’ve stored for centuries is released into the air and becomes a source of large quantities of greenhouse gases. Experts estimate that as much as 1.02 billion tons of carbon dioxide are being released annually from degraded coastal ecosystems. That’s equivalent to almost a fifth of all emissions from tropical deforestation globally! Wow.

So, where are the mangroves going? Urban development, along with agriculture and aquaculture (shrimp ponds, for example) are primarily to blame for the loss of these ecosystems. And it’s a widespread problem – more than 100 countries have mangrove forests along their coastlines. Hong Kong is among them, with 350 hectares of mangroves dotted across 40 forests – a modest amount, yet still the largest within the Pearl River Delta. The biggest mangrove coverage in the world can be found in Indonesia, where the trees cover some 23,000 square kilometres – that’s more 20 times the size of Hong Kong.