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What if mangroves could float on top of the oceans?

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The tropical and subtropical habitat of mangroves makes them especially important in the majority of the world’s low and middle-income countries where they provide a range of ecosystem services and livelihood support. UNESCO

What if mangroves could float on top of the oceans?

UNESCO is deeply engaged in the monitoring, scientific research and sustainable utilisation of mangroves. The inclusion of mangroves in UNESCO-designated sites, such as Biosphere Reserves, World Heritage sites and Global Geoparks contributes to improving the knowledge, management and conservation of mangrove ecosystems throughout the world. The tropical and subtropical habitat of mangroves makes them especially important in the majority of the world’s low and middle-income countries where they provide a range of ecosystem services and livelihood support.

The International Day for the Conservation of the Mangrove Ecosystems, celebrated each year on 26 July, aims to raise awareness of the importance of mangrove forests for humanity. This year, UNESCO releases a new global poster series on the mangrove ecosystems in the world, a first of its kind. https://www.unesco.org/en/articles/unesco-publishes-125-posters-mangrove...

Today, these unique, extraordinary and vulnerable ecosystems are under serious threat. It is estimated that more than half of all mangrove forests globally have been lost to coastal aquaculture, agriculture, deforestation, tourism development and climate change. Half of mangrove losses in the last decade occurred in Asia alone. This trend needs to be redressed, because of the important services that mangrove forests provide. Not only do they function as a natural nursery for fisheries, and for the protection against coastal erosion, mangroves also have very high primary productivity rates at the beginning of the marine food-web. In other words: the more mangroves there are, the more seafood there will be. Moreover, mangroves are classified as blue carbon ecosystems, with superior and long-lasting carbon sequestration capacities in comparison with terrestrial forests.

It is therefore very clear that mangrove forests need to be conserved and restored, and more scientific and development work is required, also as a contribution to achieve the Sustainable Development Goal 14 (Life below Water).

Naturally, mangroves occur mostly in the tropics and sub-tropics, along coastal shores that are well protected from high wave activities, as well as in deltas, lagoons, and estuaries. Mangrove forests make up less than 1 per cent of all tropical forests, and coastal areas of South Asia, Southeast Asia, Middle East, Oceania and the Pacific account for almost half of all mangroves on earth. They are restricted to grow in the inter-tidal zone, where they are exposed to oxygen at low tide, and provided with moisture at high tide. They do not occur on land, and they do not occur in the oceans. These restrictions leave just a narrow fringe of suitable geomorphology where mangroves can naturally grow.

But what if mangroves could float? If they could indeed float, the narrow range of space that is suitable for mangroves could be significantly widened in scope to include the surface of vast stretches of the world’s oceans.

UNESCO, with Mourjan Marinas and Lusail City carried out a successful experiment in Qatar some years ago, and the results were quite remarkable. Planting seeds of Avicennia marina mangroves in sand-filled containers with a semi-permeable membrane at the bottom of the containers allowed seawater to penetrate the containers, and provide the necessary moisture to the roots, whereas the plants itself were exposed to the air, allowing for enough oxygen supply to the aerial roots and leaves. The system was simply supported with air-filled containers for buoyancy to adjust the exact depth to which the containers were inserted into the ocean surface.

The system is simple, replicable, and does not need any energy for pumping.

Further tests have been carried out by the Water Research Laboratory and Global Water Institute at the University of New South Wales (UNSW) in Australia on pontoon design and stability for floating mangrove plantations. A new discussion building on the ecological and engineering experiments to date has been initiated between UNESCO, the Asian Institute of Technology (AIT), in Thailand, and UNSW.

UNESCO, AIT and UNSW agree that further tests are necessary, together with some basic scientific research, to develop this promising new technology in order to obtain science-based data and knowledge for wider and possibly profitable applicability, that can be useful for the production of biofuel (wood-chips, wood-pellets; charcoal), which in turn would reduce the transport of diesel fuel, for example to the Maldives and many other Small Island Development States, that depend on the import of fuel. Importantly, floating mangrove plantations do not place any pressure on freshwater resources which is especially important for small islands. Efforts to advance environmental, social and economical targets of the UN Development Goals without creating a competing need for freshwater to capture carbon are beneficial indeed.

To be sure, a whole new system of forestry on the ocean’s surface could be developed, for the production of fuel, biomass, honey, carbon sequestration and other products. But it is not only for producing useful commodities without the need of precious freshwater or land. The carbon-sequestration capacity of these systems needs to be demonstrated, as well as the capacity to take up land-based marine pollutants, in particular nitrogen, phosphates and potassium. Importantly, floating mangrove plantations are not seen as a replacement of shoreline forests but as a way to reduce resource pressures on the latter. Coastal management that integrates floating plantations with shore-based mangroves would strengthen ecosystem services. Further, design and location of the pontoons would offer additional wave attenuation and coastal protection measures.

UNESCO, AIT and UNSW are in discussion on how best to advance this innovative technology and to demonstrate to the general public and investors this new system for the production of seawater-based trees, that can function as a new and clean source of energy, improve ecosystems services and livelihoods for coastal communities, as well as for the sequestration of atmospheric carbon.

Benno Boer is the Natural Sciences Specialist of the UNESCO New Delhi Office, which covers Bangladesh, Bhutan, India, Nepal, the Maldives and Sri Lanka.

Shawn Kelly is the Director of International Affairs at the Asian Institute of Technology in Bangkok, Thailand.

Andrew Dansie is the Academic Lead, Humanitarian Engineering at the University of New South Wales in Sydney, Australia.

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