The rate of loss of mangrove ecosystems has declined in the past decade, to about 2 percent per year, although the rate is much higher in some countries, notably in Asia.[4] This average global rate of loss remains alarming, although important gains have been made in some countries through restoration.

Mangroves are being destroyed principally for shrimp farming (“aquaculture”), or in-filled to provide space for human settlements, agriculture and infrastructure such as airports. Mangroves are being converted to aquaculture at only a slightly slower rate today than they were a decade ago – even though there is now strong evidence that the long-term financial viability of this land use is mostly low. Proposals for the further conversion of mangroves for any purpose should be scrutinized carefully, and illegal clearing should be prevented and properly penalized. Abandoned aquaculture ponds, which are common in many places in the tropics, are often available for restoration, but restoration efforts may be thwarted because soils have become degraded and water flows blocked. Avoiding the clearing of mangrove forests for any purpose is preferable to expensive rehabilitation later. Mangroves are also being degraded by resource overexploitation; the extent of such degradation is less well measured but likely to be substantial.

[4] Bankespoor, Dasgupt and Lange (2016).

Diverse people live in coastal areas, ranging from impoverished and geographically isolated communities to wealthy urbanites, and the values attributed to mangrove ecosystems and their seascapes and landscapes are accordingly wide-ranging. Although wood harvests are important for both subsistence and cash income, most mangrove-dependent people derive their incomes mainly from fishing and related activities. Some fish species important for commercial, subsistence and sport fisheries complete most of their life cycles in mangroves, and many others use mangroves during the larval or juvenile stages.

Local people harvest various crustaceans and molluscs living in mangrove soils for subsistence and sale. Even fisheries seemingly remote from mangroves (e.g. those based on species characteristic of coral reefs and seagrass beds) benefit from the improved water quality provided by the sediment-trapping services of healthy mangrove ecosystems. There is abundant evidence that integrated forestry–fishery–aquaculture systems provide more economically viable and ecologically sound alternatives than clearcutting mangrove forests for aquaculture. The justification of efforts to protect and restore mangroves and use them sustainably should include consideration of the full range of ecosystem goods and services they provide beneficiaries, who range from subsistence users to ecotourists. 

Given that about one-third of the world’s human population lives in coastal zones, the protection afforded by mangroves from storm surges, tsunamis and high winds is crucial – and will be even more so given projected increased storm intensities due to climate change, coupled with rising sea levels. The bioshield benefits of mangroves can be substantial; they vary with the width of the forest as well as its tree density and tree height and according to topography, bathymetry and wave and wind characteristics. Compared with commonly employed hard-engineering approaches to coastal community protection, such as the installation of subtidal breakwaters and seawalls, maintaining and restoring mangroves is generally more cost-effective and longer-lasting; moreover, healthy mangroves provide many other ecosystem goods and services that such hard-engineering approaches do not.

The cost of restoring mangroves to serve as bioshields against waves is 2–6 times lower than the cost of installing submerged breakwaters, a common alternative.[5] Protecting intact mangroves from deforestation and degradation is an even more cost-effective approach to the protection of low-lying coastal areas – where human settlements are often growing rapidly. The coastal zone protection function of mangroves is increasing with rising sea levels, but about one-quarter of all mangroves are threatened by such rises.[6] Some mangrove ecosystems could be starved of sediments due to sea-level rise, and some may be prevented from “migrating” to suitable terrain by local topography or human infrastructure.

[5] Narayan et al. (2016)

[6] Alongi (2008)

Mangrove ecosystems are among the most productive in the world, and they contain massive amounts of carbon in their biomass and soils – estimated at 1 028 MgCO_2-e per hectare (to a depth of 1 m in the soil). This carbon storage, as well as the rapid rate of carbon uptake by mangrove trees, should be considered in decisions on mangrove protection, exploitation and management. The carbon emissions due to the high rate at which mangroves are being destroyed are estimated at 0.25 PgCO₂ per year, which is more than the total annual emissions of Spain. The global marginal economic cost of environmental damage has been estimated at US$41 per MgCO₂ emitted to the atmosphere; thus, stopping mangrove destruction would save an estimated US$9.8 billion per year worldwide. 

The ability of mangroves to trap sediments and absorb nutrients makes them suitable for organic wastewater treatment, but they also bio-accumulate heavy metals, which can cause tissue damage and may lead to disruptions higher up in the food chain. Effluent from intensively managed shrimp ponds can be treated effectively by mangrove ecosystems; it is estimated, however, that 2–22 hectares of mangrove forest are required to biofilter the wastes generated by 1 hectare of shrimp pond.[7]

[7] Walters et al. (2008)

The many uses of mangroves – ranging from tourism and sport fishing, to protection against coastal erosion and storm damage, to commercial harvests of wood and fish – suggest that zoning may be an effective approach to landscape-level ecosystem management. The success of a zoning approach requires the participation of the full range of stakeholders and adherence to the principle of free, prior and informed consent to ensure that management does not disadvantage marginalized people. Another benefit of an inclusive approach is that mangrove users have much local and traditional knowledge which, combined with scientific research, can help in restoring and managing mangrove ecosystems. Buffer zones of protected forest are especially important along watercourses and in areas likely to be affected by storms, erosion and drought. Mangroves near heavily populated areas should be reserved for recreational and educational purposes (and to provide ecosystem services and perform protective functions), as should mangroves in relatively pristine condition. 

Mangrove ecosystem restoration interventions range in intensity. At the lower end of the spectrum, the cessation of logging or other pressures in a mangrove forest may allow it to regenerate naturally; at the more intense end, restoration efforts may involve hydrological reconfiguration for water flow and sediment deposition, followed by the hand-planting of nursery-reared seedlings. The cost of interventions varies accordingly, from about US$200 per hectare to more than US$200 000 per hectare.

The main reason for the failure of mangrove restoration projects is the improper matching of tree species with hydrological conditions (e.g. tidal flooding frequencies and depths). It is crucial that potential restoration interventions are fully assessed before implementation; this may include consideration of floral elements (e.g. tree stocking and species selection), faunal recruitment, ecosystem function (e.g. carbon sequestration), and potential for sustainable use. Herbivorous crabs and molluscs are generally sensitive to ecosystem degradation and thus are good indicators of restoration success. Many problems can be avoided by engaging the services of local people in all phases of mangrove management: their knowledge and experience can contribute substantially to the success of interventions.

In the past, the goals of mangrove restoration have typically been wood production and coastal stabilization, but more holistic approaches that favour multiple uses for multiple constituencies are now being advocated and piloted. A great deal is known about how to plant and tend mangrove forests, but costly mistakes still happen when managers fail to learn from previous experiences. Moreover, an excessive focus on tree-growing may produce tree plantations rather than functional mangrove ecosystems capable of providing habitats for crabs, molluscs, fish and other organisms, on which many local people may depend. Fortunately, even planted tree monocultures ultimately develop into relatively diverse ecosystems if clearfelling or other high-intensity forms of logging are avoided.

The clearcutting of mangrove forests for charcoal and other forest products continues, often with government approval, because it is more financially remunerative for harvesters than selective harvesting or shelterwood systems. The environmental impacts of clearcutting can be reduced by leaving buffer strips along watercourses, restricting clearcuts to small patches, and replanting areas where natural regeneration fails. Even in the best-managed areas, however, yields – of timber and edible molluscs and crustaceans – diminish with each successive clearcut and biodiversity declines. Moreover, the channels often dug to facilitate wood extraction can have long-term hydrological impacts. Before approving clearcuts, authorities should consider other silvicultural options and the wide range of ecosystem services that mangroves provide. 

If a mangrove ecosystem is unlikely to regenerate naturally after logging due to a lack of local seeds or other propagules, interventions may be required to re-establish the forest. Several options are available, which vary in their cost and likelihood of success. If the focal species are from the Rhizophoraceae family, which produce elongated, buoyant propagules, an approach is to collect such propagules in adjacent areas and insert them into the sediment; this is often a successful technique if the hydrological conditions (e.g. tidal flooding depth and water flow rates) are conducive and the seedlings are not damaged by logging debris, which can move around with the tide. Where the season of propagule availability is shorter than the planting season, propagules can be planted in bags or tubes, tended in nurseries, and transplanted at the appropriate time. Nursery stock is often used in mangrove restoration, especially for species with small, crypto-viviparous seedlings (e.g. Avicennia spp.) and species propagated from seed (e.g. Sonneratia spp.). When properly out-planted, well-tended nursery stock can have high survival rates and grow well; the cost of this approach can be high, however, because nursery operations can be expensive and workers cannot carry more than a few seedlings at a time. 

In some places, mangrove management and restoration efforts are thwarted by the presence of native weeds or invasive exotic species, which may be introduced accidentally or deliberately for aquaculture or forestry purposes. Giant mangrove ferns (Acrostichum spp.), for example, can proliferate in cleared areas and outcompete planted or naturally regenerated mangrove trees. The mangrove palm, Nypa fruticans, a native of Southeast Asia, where it is much used by local people, is an aggressive invader in West Africa, where its uses are less appreciated. Similarly, the introduction of alien fish species such as the African tilapia has caused problems in mangrove ecosystems in Asia and South America. 

Mangroves are often subject to jurisdictional ambiguity because mangroves grow in the margins of both land and sea and produce both terrestrial and marine resources. Overlapping responsibilities for mangrove ecosystems can lead to mismanagement, management conflicts, and disregard for ecosystem functions and the needs of certain stakeholders. The historical tendency to place mangroves within the jurisdiction of forestry departments (which are likely to unduly favour wood production) is changing, and there is now greater interagency collaboration and efforts to include local stakeholders in decision-making processes. In the past, many mangrove development projects have proceeded despite the protests of traditional owners, whose customary claims were not recognized by the state. Many countries are now taking steps to address these customary claims. 

Access to information about mangrove ecology and management is increasing as a result of services such as the Global Mangrove Database and Information System (GLOMIS), created and maintained by the secretariat of the International Society of Mangrove Ecosystems (ISME) in Japan with support from regional centres in Brazil, Fiji, Ghana and India. The Mangroves for the Future initiative also acts as a clearinghouse for information on mangroves. The Tropical Coastal Ecosystems Portal is an excellent source of mangrove maps and species lists and descriptions. The increasing availability of high-resolution satellite images (e.g. Landsat and SPOT), synthetic aperture radar, and canopy-penetrating laser-based information (e.g. airborne LiDAR) is facilitating the monitoring of mangrove restoration and protection.