Mangroves are systematically destroyed when the ecosystem is close to urban areas. Here a plan to construct a development-- never built-- destroyed this small ecosystem in La Paz, Mexico. Remnants of a black mangrove grove along the old channel still can be seen in front of a hotel.
Worldwide, the mangrove ecosystems are dramatically shrinking as a result of logging, aquaculture (mainly shrimp cultivation), charcoal production, and unregulated deposition of pollutants into the wetlands (Chansang et al. 1983; Hatcher et al. 1989). Some illustrative examples:
- In Ecuador, large mangrove forests were clearcut to make room for shrimp cultivation. In some areas, the damage exceeded 90% of the total mangrove area, as in Bahía de Caraquez (Twilley et al. 1997).
- Aquaculture in the Far East Asia severely threatened all mangrove ecosystems in the area (Honculada-Primavera 1993).
- In Panama, about half of the mangrove ecosystem have disappeared in the last 30 years.
- In French Guyana, mangroves are systematically destroyed for rice cultivation (Lacerda et al. 1992).
- In Vietnam, use of defoliators in the Mekong delta during the Vietnam war eliminated large stands of mangroves that have never recovered completely.
- In all Latin American countries, mangrove wood is used as domestic firewood. In Nicaragua, 80% of the households use wood for cooking and most of it come from mangrove forests.
- In Honduras, up to 120,000 m3 of wood is cut annually for firewood.
- In El Salvador, having only 350 km2 of mangrove ecosystems, 30,000 m3 of wood is cut annually.
- Panama, a major producer of tannins in Latin America extracts 400 t/year of these substances from mangrove trees (Lacerda et al. 1992).
- In Pakistan, the mangrove forests of the Indus river, which are the world sixth largest, shrank drastically over the last several decades. The trees that remain are mainly small Avicennia marina restricted to the banks of the better-flushed tidal channels (Harrison et al. 1994).
- In Rio de Janeiro, Brazil, construction of a dam diverting the flow of fresh water from a mangrove forest caused degradation of the entire ecosystem (Lacerda et al. 1992).
Housing project from 1997 was constructed in a small mangrove ecosystem in La Paz, Mexico
Other destructive forces threatening the mangrove ecosystems are:
- Coastal engineering projects like a major highway in Santa Marta in the north of Colombia blocking mangrove channels required for sea water exchange.
- Construction of tourist resorts and governmental housing projects such as this one in in Baja California, Mexico, and Hong Kong, a practice that eliminated almost the entire wetlands from the urban environment (Tam et al. 1997).
- Oil spills, occurring frequently in Panama and southern Mexico, are particularly damaging for the ecosystems, blocking the diffusion of gases in plants and in the soil (Lacerda et al. 1992).
- A particular threatening practice for the future well-being of mangroves is the use of these wetlands as natural wastewater treatment facilities for domestic sewage and industrial wastewater (Wong et al. 1995, 1997). In addition to the disruption of the detritus food web and the organisms feeding on it, mangrove sediments tend to adsorb heavy-metal residues (Tam and Wong 1995, 1996, 1997).