Coastal development may be the primary threat to mangroves. Not only are the forests lost when a coast is developed, but a man-made structure almost always replaces them. That structure (e.g., a hotel, desalination plant, coal-fired power plant, nuclear plant, port facility, marina, cruise ship dock) inevitably brings with it associated issues of altered hydrology, erosion, and pollution. Rivers that once traveled through the mangroves before emptying into the sea are blocked or re-routed, causing changes in filtration, sedimentation, temperature, and salinity. These changes in turn can affect the aquatic species, including commercial or subsistence fish species for coastal communities. The developments are often associated with increased levels of pollution as well, including solid waste, pesticides, thermal, biological (invasive species), brine, and oil. In Panama, for example:

“In recent years the biggest regional threats to mangroves are the ever-increasing development of the tourism industry, pollution from runoff of fertilizers and pesticides, and improper disposal of wastes. Oil pollution is not a widespread problem for the region as a whole, but it is a serious threat in Panama owing to the extremely high maritime traffic in the Panama Canal (Spalding et al. 1997, FAO 2007, p. 34).

There are approximately 70 species of mangroves around the world (Polidoro et al. 2010). When activities such as logging, shrimp farming, coastal agriculture, hotel development, and other activities are valued over the ecosystem services the intact mangroves provide, genetic diversity is among the first—but least considered—casualty. The trees and associated species (e.g., birds, snakes, crabs) are visibly lost, but so too are the specific genotypes and phenotypes that have evolved in microhabitats around the world to withstand insects, tidal fluctuations, precipitation patterns and salinity regimes. Mangroves are not species-rich to begin with, especially in comparison with other tropical forests (Alongi 2002). And in the areas where replanting is attempted, it is often done with seeds from elsewhere, and often done with one species, rather than the mix of species that originally existed. As Polidoro et al. (2010) have stated:

The close proximity of mangroves to the ocean makes them ideal locations for shrimp farming and other kinds of mariculture. Further, they are areas rich in nutrients, and part of larger wetland systems, making them attractive as agricultural areas. Finally, these areas near the sea are prized for salt production. As a result, hundreds of thousands of hectares of mangrove forests have been cleared, and the hydrology has been altered, in order to intensify commercial production of shrimp and other species, cultivate agricultural crops, and create salt ponds. The delicate tidal regimes are interrupted and the balance between fresh and salt water is lost. The intensive mariculture operations are most often constructed for export. The shrimp and other species that are raised and harvested from the artificial ponds are fed specific diets that often include chemicals. Extra nutrients from the concentration of food and animals cause eutrophication, which harms the surrounding marine habitats by lowering oxygen levels and changing species distributions. The chemicals enter the food chain and can harm nearby species. Shrimp farm activity alone has been responsible for the loss of 38 percent of the world’s healthy mangroves; the percent climbs to 52 if all agricultural activities are counted (Ellison 2008).

Climate change is causing two important impacts along the world’s coastlines. Sea levels are rising and the chemistry of the oceans is shifting (IPCC 2007 and NRC 2011). The rates at which these impacts are occurring is likely to exceed the ability of mangrove forests and the species that live within them to adapt (Gilman et al. 2008).

Most destructive uses of mangrove forests require their removal. The motivations behind deforestation include direct use of the mangrove wood and leaf products, use of the wetland habitat, or complete fill and conversion for coastal developments.

Deforestation for fuel & timber accounts for the ongoing loss of approximately 26 percent of existing mangroves (Valiela et al. 2001). Mangrove reforestation has had very low success, although new hydrology-based methods may be more promising (Lewis & Gilmore 2007). Even so, we cannot rely on reforestation to prevent mangrove loss. These fragile and rare ecosystems are being lost at such a tremendous rate that mangrove experts predict that without changes to current practices, mangroves will be functionally extinct in less than a century (Duke et al. 2007). A world without mangroves means a world without most fisheries, without bioshields from storms, and without many bird and other species. The loss of mangroves as a unique habitat would directly jeopardize more than a billion of the world’s human population.