The Loss of Species: Mangrove Extinction Risk and Geographic Areas of Global Concern

Study Number:

15

Author:

B. A. Polidoro, K. E. Carpenter, L. Collins, N. C. Duke, A. M. Ellison, J. C. Ellison, E. J. Farnsworth, E. S. Fernando, K. Kathiresan, N. E. Koedam, S. R. Livingstone, T. Miyagi, G. E. Moore, V. N. Nam, J. E Ong, J. H. Primavera, S. G. Salmo III, J. C. Sanciangco, S. Sukardjo, Y. Wang & J. W. H. Yong

Abstract:

Mangrove species are uniquely adapted to tropical and subtropical coasts, and although relatively low in number of species, mangrove forests provide at least US $1.6 billion each year in ecosystem services and support coastal livelihoods worldwide. Globally, mangrove areas are declining rapidly as they are cleared for coastal development and aquaculture and logged for timber and fuel production (deforestation). Little is known about the effects of mangrove area loss on individual mangrove species and local or regional populations. To address this gap, species-specific information on global distribution, population status, life history traits, and major threats were compiled for each of the 70 known species of mangroves. Each species’ probability of extinction was assessed under the Categories and Criteria of the IUCN Red List of Threatened Species. Eleven of the 70 mangrove species (16%) are at elevated threat of extinction. Particular areas of geographical concern include the Atlantic and Pacific coasts of Central America, where as many as 40% of mangroves species present are threatened with extinction. Across the globe, mangrove species found primarily in the high intertidal and upstream estuarine zones, which often have specific freshwater requirements and patchy distributions, are the most threatened because they are often the first cleared for development of aquaculture and agriculture. The loss of mangrove species will have devastating economic and environmental consequences for coastal communities, especially in those areas with low mangrove diversity and high mangrove area or species loss. Several species at high risk of extinction may disappear well before the next decade if existing protective measures are not enforced.

Main Results and Conclusions:

• A classification of mangrove species and their level of endangerment has been created by the IUNC: “The IUCN Red List Categories and Criteria were applied to 70 species of mangroves, representing 17 families”(2)…Of the 70 species of true mangrove species, 11 (16%) qualified for one of the three Red List categories of threat: Critically Endangered, Endangered, or Vulnerable (see Table 1)”(3).
• There are a number of different threats to mangrove forests, each of which vary in severity and their expected/observed consequences: “The primary threats to all mangrove species are habitat destruction and removal of mangrove areas for conversion to aquaculture, agriculture, urban and coastal development, an overexploitation. Of these, clear-felling, aquaculture and overexploitation of fisheries in mangroves are expected to be the greatest threats to mangrove species over the next 10–15 years (Alongi, 2002). Climate change is also considered a threat to all mangrove species, particularly at the edges of a species range where sea temperature and other environmental changes may be greatest. With a rise in sea level, the habitat requirements of each species will be disrupted, and species zones will suffer mortality in their present tidal zones and attempt to re-establish at higher elevations in areas that were previously landward zones (Ellison, 2005). Mangrove species with a habitat on the landward margin are particularly vulnerable to sea-level rise if, owing to coastal development, their movement inland is blocked”(6).
• Certain mangrove species have greater threats than others mainly due to the species’ abiotic environmental requirements: “Many mangrove forests exhibit distinct zones of species that are controlled by the elevation of the substrate relative to mean sea level and the associated variation in frequency of elevation, salinity and wave action (Duke, Ball MC, and Ellison JC, 1998). Such zonation is not always apparent (Ellison, Mukherjee BB, and Karim A, 2000) and may be disrupted by anthropogenic disturbance”(6).
• There are many regions around the world where mangrove forests threatened:
• “Although less than 15% of species present in this region are in threatened categories (Figure 2), the Indo-Malay Philippine Archipelago has one of the highest rates of mangrove area loss globally, with an estimated 30% reduction in mangrove area since 1980 (FAO, 2007)”(6).
• “Geographic areas with high numbers of mangrove species at elevated risk of extinction are likely to exhibit loss of ecosystem function, especially in areas of low mangrove diversity. Globally, the highest proportion of threatened mangrove species is found along the Atlantic and Pacific coasts of Central America (Figure 2)”(7).
• “The Caribbean region has the second highest mangrove area loss relative to other global regions, with approximately 24% of mangrove area lost over the past quarter-century (FAO, 2007)”(7).
• “In the Gulf of California, for example, where there are only 4 mangrove species present (Avicennia germinans, Rhizophora samoensis, Laguncularia racemosa, Conocarpus erectus), it is estimated that one linear kilometer of the species R. samoensis, listed as Near Threatened, provides up to 1 ha of essential marine habitat and provides a median annual value of US$37,000 in the fish and blue crab fisheries (Aburto-Oropez et al., 2008)”(8).
• Recommendations: “In addition to legislative actions, initiatives are needed on the part of governments, NGOs, and private individuals to acquire and protect privately-owned parcels of coastal land, especially those that contain viable populations of threatened mangrove species”(8).

Works Cited:

Aburto-Oropez O, Ezcurra E, Danemann G, Valdez V, Murria J, et al. (2008) Mangroves in the Gulf of California increase fishery yields. PNAS 105: 10456–10459.

Alongi DM (2002) Present state and future of the world’s mangrove forests. Environ Conserv 29: 331–349.

Duke NC, Ball MC, Ellison JC (1998) Factors influencing biodiversity and distributional gradients in mangroves. Global Ecol Biogeog Let 7: 27–47.

Ellison AM, Mukherjee BB, Karim A (2000) Testing patterns of zonation in mangroves: scale-dependence and environmental correlates in the Sundarbans of Bangladesh. J Ecol 88: 813–824.

Ellison J (2005) Holocene palynology and sea-level change in two estuaries in Southern Irian Jaya. Palaeogeog Palaeoclim Palaeoecol 220: 291–309.

FAO (2007) The World’s Mangroves 1980-2005, FAO Forestry Paper 153. Rome: Forest Resources Division, FAO. 77 p.