VOICES Voices Icon Ideas and Insight From Explorers


Taking stock of mangroves, thin frontlines of diversity

Mark Spalding, a marine scientist with The Nature Conservancy, has spent decades researching mangroves, the rare and critically important forests that grow at the intersection of land and sea. He is also lead author of the World Atlas of Mangroves, the first in-depth look in over a decade of mangroves. (‘Atlas of Mangroves’ highlights global loss of tidal forests)


According to the Atlas, which was released today, about one fifth of all mangroves are thought to have been lost since 1980. Mangroves are lost at a rate three to four times higher than land-based global forests, despite positive restoration efforts by some countries, Spalding and the other Atlas authors note. “Any further destruction due to unsustainable activities such as, shrimp farming and coastal development, will cause significant economic and ecological decline,” they warn.

“While mangroves are rare compared to other forest types, the waters all around them foster some of the greatest productivity of fish and shellfish in any coastal waters. Mangrove forests help prevent erosion and mitigate natural hazards–they are natural coastal defenses whose importance will only grow as sea level rise becomes a reality around the world,” the authors noted in a news release.

David Braun interviewed Mark Spalding about the new atlas:

While the rate of loss of mangroves may be slowing, some species of mangroves are disappearing much more rapidly than others. What are the hottest spots for loss of mangroves and associated biodiversity on the planet?

The most dramatic, rapid losses at large scales almost always link to conversion to aquaculture. It is incredible to zoom in on satellite imagery and suddenly find mile after mile of rectangular “fields” of water, separated by embankments, where once there were mangroves–in Ecuador, Honduras, Thailand, China, the Philippines and elsewhere.

But this front line of destruction is constantly moving. China has lost most of its mangroves, but Indonesia is still the largest mangrove country in the world (and with the greatest diversity of species). Here the front line of is moving eastwards–the densely populated island of Java barely has any mangroves left. Southern Borneo has also lost vast areas, but here the pressure remains for more conversion. Further east some of the most extensive mangroves in the world are threatened by logging and by oil and gas extraction.

Another front line, which of course doesn’t do much to the statistics, is the loss of small patches in countries where mangroves were never abundant. Coastal development, including tourism, has decimated mangroves in many small island nations, particularly in the Caribbean. Here mangrove forests are precious packets of diversity, rich in fish and crabs, sheltering resident and migratory birds. But to some eyes they are prime development land, quickly replaced by hotels or golf courses.

But loss is just the extreme end of degradation. Look at the mangroves of the Niger Delta, one of the world’s largest mangrove forests. Still standing, these forests have been choked by oil pollution on a scale close to that of the Deepwater oil spill in the Gulf of Mexico for some 50 years.

Or take the mangroves in the deltas of great rivers such as the Zambezi in Mozambique or the Indus in Pakistan. Upstream water use has shrunk these mighty rivers to mere trickles, barely reaching the sea for parts of the year. Without the enriching waters of the deltas, and the resupply of sediments, erosion sets in, and the rich diversity is lost as only the hardiest species can survive.

Some countries are making big efforts to restore mangrove forests. Which examples are the most encouraging in terms of showing others the right path?

The Philippines is a fascinating place–we don’t have a good handle on how many mangroves there were originally, but it seems likely that they have lost half, perhaps more of the original cover. This was largely to aquaculture, aided by some large-scale government policies and subsidies.

Recently, however the value of mangroves has risen right to the fore and there have been massive efforts to restore mangroves in many areas. And these efforts give us the whole spectrum–good news and bad.

Some of the least successful efforts have come from big money, top-down approaches: remarkable failures involving planting the wrong species in the wrong places.

But wonderful successes too. Of course some of these were also the big schemes, but many of the more successful efforts came from local initiatives. Here there was perhaps a greater effort to get around the problems of land ownership, so the mangroves were planted in the right place (a little above the mid-tide line, all the way to the high tide).

And of course local leadership gives a sense of ownership, and a sense of pride. And in the Philippines has also led to some very healthy copycat restoration as neighboring towns and villages see the benefits–fisheries, timber and coastal protection–set against the unproductive dead no-man’s land of abandoned or unproductive aquaculture–and want the same.

How is technology, such as satellite-monitoring, helping mangrove restoration and conservation?

Mangroves have often lost out in large-scale satellite mapping. Even where they are extensive there are challenges for expert mappers to determine what’s what due to the complex reflections from a habitat that is sometimes waterlogged, sometimes just wet, and sometimes hyper arid.

Meanwhile in many areas this problem is compounded by the fact that mangroves are narrow strips tracing the shore, with bright reflective water on one side and often completely different land use on the other. From a satellite that makes them very difficult to make out.

But with good resolution data, and with expert interpretation and verification we can make them out very well indeed. That’s what this new atlas has done for the first time at a global scale. We’ve used mapping expertise from the Food and Agriculture Organization of the United Nations and from the UNEP World Conservation Monitoring Centre, but such maps have benefitted immensely from expert review, verification, and quite often correction. We had a network of over 100 experts feeding into this project and that has made a huge difference.

And its only when you’ve got the images that you can start to measure extent and change. All too often its numbers and statistics that start to turn heads and change policies, so we need reliable mapping in the first instance to make the case for management. And with that we can also start to use the same imagery for other purposes–for the design of protected areas systems, for planning for restoration, and, importantly now, planning for the proposed changes arising from sea level rise.

How does this atlas help land developers make more sensible decisions about land use? How can conservation groups use it to assist their efforts in shoring up protection of habitats?

The Atlas is a very high altitude overflight–you wouldn’t use it for navigation on the ground, but it’s a critical stock-take at a global and a regional scale.

Some of the most fascinating stories come from comparisons. The contrasts between countries can be shocking, with different government policies showing up quite clearly on the maps. Some countries such as Malaysia and Tanzania have state ownership of mangroves and have attempted to manage them sustainably. Others, such as the Philippines effectively privatized their mangroves, selling or leasing vast areas to aquaculture development.

The detailed descriptions which fill this Atlas give a wealth of examples, not just stand-alone, one-off stories. Such facts, backed up by repetition, and by good solid numbers and reliable science, should lie at the heart of coastal development decisions–do you want to make money fast, for a few years, from aquaculture, or have a regular good income, with employment for hundreds of people, from sustainable use? Can aquaculture be done differently? (Yes!).

And of course the conservationists need these lessons too. We need to learn from experiences round the world.

Mangroves can be restored, quite easily in fact. Mangrove plantations, using native species, can be good for wildlife as well as for timber production. How can ecotourism be developed in mangroves?

Does the atlas show any global connectivity between the last patches of mangrove forests? I was thinking specifically if certain animal species (birds, fish) need mangroves for way stations or as crucial places for their life cycles?

Mangroves are disappearing relatively fast, and some authors have talked about the end of mangroves, but I think this book shows that we’re not yet dealing with “the last mangroves”–we don’t know how much we’ve lost, but there are still many. And about a quarter are in protected areas, which is higher than for most other habitat types. That said the connectivity story is a great story to tell.

First off we need to think about how mangroves connect with adjacent areas. The big, obvious connection is fish and shellfish. Many, many offshore fisheries rely on mangroves which are critical spawning and nursery areas.

Quite a few governments and fishers don’t even realize this connection. Australia benefits tens of millions of dollars annually from its prawn capture fisheries in northern waters which are almost entirely mangrove dependent–and the same can be said for Malaysia, the Guianas and many other areas.

Many coral reef fish too, utilize mangroves and adjacent salt marshes moving between the three like a connected whole. But in this case mangroves are also functionally critical–holding back sediments and stripping nutrients from the waters, enabling reefs to flourish in adjacent waters.

But there are global connections too. The most striking of course are the migratory birds–the Coppename Monding Nature Reserve in Suriname extends along just 50 km [35 miles] of coast, but is host to 1.2 million migratory shorebirds each year. These are the same birds familiar as summer arrivals in temperate countries to the north and south of the equator–that nest in vast numbers in the coasts and marshes of northern Europe, the USA, Canada and Russia.