I don’t know how many of my readers have waded through a mangrove swamp before – if you have, you’ll know it’s no ‘walk in the park’. They are generally mosquito-infested with waist-deep mud, have more creepy-crawlies than you can poke a stick at, and in some places (such as my former stomping ground, the Northern Territory of Australia) are down-right dangerous due to lovelies such as saltwater crocodiles.
But, most people probably don’t know just how important mangroves are. Just like the maggot who can sicken the hardiest of individual, under-appreciated mangroves provide major ecosystem services.
For example, did you know that mangroves:
- Protect inland human communities from damage caused by coastal erosion and storms?
- Provide critical habitat for a variety of terrestrial, estuarine and marine species? Indeed, it has been estimated that ~80 % of fish catches globally depend directly or indirectly on mangroves.
- Are a source and sink for nutrients and sediments for other inshore marine habitats including seagrass beds and coral reefs?
- Protect coasts from floods?
- Process nutrient and organic matter?
- Control sediment?
- Provide at least US$1.6 billion per year in ecosystem services worldwide?
- Sequester up to 25.5 million tonnes of carbon per year?
- Provide more than 10% of essential organic carbon to the global oceans?
- Occupy only 0.12% of the world’s total land area?
Pretty staggering, no?
So, even if you don’t like them, it’s difficult to deny that they’re important.
But, like almost every other habitats worldwide, mangroves are on the big downward slide. In a new paper in PLoS One by Polidoro & colleagues entitled The loss of species: mangrove extinction risk and geographic areas of global concern, the authors not only highlight the above benefits, they quantify just how badly the 70 mangrove species around the world are faring.
Although highly variable, between 20 and 25 % of mangroves have been lost since 1980, with many more severely degraded – meaning that we’re losing about 1 % per year, and in places the rate of loss is as high as 8 % per year.
This means that 11 (16 %) of the 70 mangrove species are Red-Listed, and two are Critically Endangered. But it’s not just the number of threatened species that are of principal concern; because mangroves are considered ‘foundational’ species and provide so many essential ecosystem services, even the reduction in common species is worrying. This is one case where threatened species status doesn’t do the taxon’s conservation status justice.
Where are the ‘hotspots’ of loss (and corresponding endemism – to keep consistent with Myers’ and colleagues’ definition)? The Indo-Malay Philippine Archipelago is probably of most concern considering the high number of unique species and the rates of mangrove clearing, with the Atlantic and Pacific coasts of Central America and the Caribbean following closely behind.
How do we fix the problem? Polidoro and colleagues have some suggestions. First, none of the 11 international treaties that afford some protection to mangroves (e.g., RAMSAR Convention, Convention on the Prevention of Marine Pollution, CITES, International Tropical Timber Agreement, Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region, Convention on Biological Diversity) have any binding legal power – something that should be addressed at an international level. Also, more mangroves should be explicitly incorporated into protected areas.
Thanks to yet another paper spelling out the dire straits of a particular taxon (in this case, a pretty important one), maybe we have the chance to protect and restore these vital habitats.
Polidoro, B., Carpenter, K., Collins, L., Duke, N., Ellison, A., Ellison, J., Farnsworth, E., Fernando, E., Kathiresan, K., Koedam, N., Livingstone, S., Miyagi, T., Moore, G., Ngoc Nam, V., Ong, J., Primavera, J., Salmo, S., Sanciangco, J., Sukardjo, S., Wang, Y., & Yong, J. (2010). The Loss of Species: Mangrove Extinction Risk and Geographic Areas of Global Concern PLoS ONE, 5 (4) DOI: 10.1371/journal.pone.0010095