Mangrove Ecosystems of Southwest Madagascar: An Ecological, Human Impact, and Subsistence Value Assessment

The importance of mangrove forests in maintaining crucial ecosystem functions such as nutrient filtering, supporting coral reef fisheries, and providing storm buffers has become more evident after the tsunami that ravaged parts of Asia in December 2004 (Alongi 2002; Mumby et al. 2003; UNEP-WCMC 2006). However, these vital tropical ecosystems in the coastal inter-tidal zones, covering about 181,000 km2 (Spalding et al. 1997), continue to be under immense threat from a variety of human actions. Over the last twenty years, approximately 35% of the world’s mangrove forest area has been lost (Valiela et al. 2001). Nevertheless, activities that contribute to this depletion continue. These activities include timber and fuel wood extraction, urban development, and the expansion of shrimp aquaculture, which is by far the greatest cause of mangrove loss (Valiela et al. 2001). Mangrove ecosystems in many countries face a combination of these pressures. This is true for the island nation of Madagascar as well. Along with some of the most remote and biodiverse coral reefs, 3,270 km2 of mangrove forest lie within Madagascar, supporting numerous coastal communities and the nation’s economy (Cooke et al. 2003). There is limited documentation of these forests in Madagascar, particularly in southwest Madagascar, which is home to the nomadic Vezo fishing communities. My summer research focused on the mangrove ecosystems of Baie des Assassins, a small bay harboring about 25 km2 of mangrove forest, approximately 185 km north of the port city of Toliara. I aimed to explore the dynamics of the forest structure, to obtain a measure of the human impact on the forest, and to understand the subsistence value of mangroves to the local community. The indigenous Vezo populations that reside in fishing villages around and north of the Baie des Assassins use these mangroves for timber, fuel wood, and fishing. However, the intensity and periodicity of use and level of dependence on the mangrove forest is undocumented. The region around the Baie des Assassins may potentially form part of a multiple-use conservation site, thus necessitating a clear understanding of the forest structure and its significance to local communities.