Aude Carro’s research while affiliated with Blue Ventures Conservation and other places

Although the importance of regulating and provisioning services provided by mangroves is widely recognised, our understanding of their role in the maintenance of terrestrial biodiversity is patchy globally and largely lacking for many regions, including conservation priorities such as Madagascar. We carried out the first multi-site bird inventory of mangroves in Madagascar and complemented our data with assessments of local knowledge, in order to broaden our knowledge of which species use this habitat. We directly observed 73 species across three sites in Ambanja and Ambaro Bays, while local respondents indicated the presence of 18 additional species: four observed species are globally threatened, while 37 are endemic to Madagascar or the Malagasy region. Over half the species observed are typically terrestrial, of which 22 have not previously been recorded in mangrove habitats in Madagascar. Local knowledge provided a useful complement to our observed data but we are likely to have underestimated total richness; nevertheless, our findings greatly increased our knowledge of mangrove use by Madagascar’s birds. However, further research is required to investigate the functional role of mangroves in the ecology of the observed species and provide insights into the factors influencing mangrove use.

Madagascar contains Africa’s fourth largest extent of mangroves, representing approximately 2% of the global distribution. Since 1990, more than 20% of Madagascar’s mangrove ecosystems have been heavily degraded or deforested due primarily to increased harvest for charcoal and timber and the expansion of agriculture and aquaculture. Anthropogenic-driven loss is particularly prominent in the north-western Ambanja and Ambaro Bays (AAB). At over 24,000 ha, AAB is one of Madagascar’s largest mangrove ecosystems, including prominent estuaries fed by rivers and streams originating in the country’s highest mountain range. Similar to the national rate, AAB has experienced approximately 20% loss since 1990, driven primarily by over-harvesting for charcoal and timber. Continued loss threatens the livelihoods and wellbeing of thousands of residents who rely on the many goods and services provided by a healthy, relatively intact mangrove ecosystem. To combat this loss, Blue Ventures (BV), in partnership with local communities and the University of Antananarivo, is working to protect, restore and encourage the sustainable use of mangroves. BVs’ Blue Forests project aims to help maintain and diversify local livelihoods and to sustainably manage mangroves and their associated biodiversity in AAB, as well as throughout western Madagascar. This chapter provides an overview of the biophysical characteristics, historic dynamics and current status of the AAB mangrove ecosystem, and mitigation strategies being implemented through BVs’ Blue Forests project.

Mangrove ecosystems help mitigate climate change, are highly biodiverse, and provide critical goods and services to coastal communities. Despite their importance, anthropogenic activities are rapidly degrading and deforesting mangroves world-wide. Madagascar contains 2% of the world’s mangroves, many of which have undergone or are starting to exhibit signs of widespread degradation and deforestation. Remotely sensed data can be used to quantify mangrove loss and characterize remaining distributions, providing detailed, accurate, timely and updateable information. We use USGS maps produced from Landsat data to calculate nation-wide dynamics for Madagascar’s mangroves from 1990 to 2010, and examine change more closely by partitioning the national distribution in to primary (i.e., >1000 ha) ecosystems; with focus on four Areas of Interest (AOIs): Ambaro-Ambanja Bays (AAB), Mahajamba Bay (MHJ), Tsiribihina Manombolo Delta (TMD) and Bay des Assassins (BdA). Results indicate a nation–wide net-loss of 21% (i.e., 57,359 ha) from 1990 to 2010, with dynamics varying considerably among primary mangrove ecosystems. Given the limitations of national-level maps for certain localized applications (e.g., carbon stock inventories), building on two previous studies for AAB and MHJ, we employ Landsat data to produce detailed, contemporary mangrove maps for TMD and BdA. These contemporary, AOI-specific maps provide improved detail and accuracy over the USGS national-level maps, and are being applied to conservation and restoration initiatives through the Blue Ventures’ Blue Forests programme and WWF Madagascar West Indian Ocean Programme Office’s work in the region.

Mangroves are found throughout the tropics, providing critical ecosystem goods and services to coastal communities and supporting rich biodiversity. Globally, mangroves are being rapidly degraded and deforested at rates exceeding loss in many tropical inland forests. Madagascar contains around 2% of the global distribution, >20% of which has been deforested since 1990, primarily from over-harvest for forest products and conversion for agriculture and aquaculture. While historically not prominent, mangrove loss in Madagascar’s Mahajamba Bay is increasing. Here, we focus on Mahajamba Bay, presenting long-term dynamics calculated using United States Geological Survey (USGS) national-level mangrove maps contextualized with socio-economic research and ground observations, and the results of contemporary (circa 2011) mapping of dominant mangrove types. The analysis of the USGS data indicated 1050 hectares (3.8%) lost from 2000 to 2010, which socio-economic research suggests is increasingly driven by commercial timber extraction. Contemporary mapping results permitted stratified sampling based on spectrally distinct and ecologically meaningful mangrove types, allowing for the first-ever vegetation carbon stock estimates for Mahajamba Bay. The overall mean carbon stock across all mangrove classes was estimated to be 100.97 ± 10.49 Mg C ha⁻¹. High stature closed-canopy mangroves had the highest average carbon stock estimate (i.e., 166.82 ± 15.28 Mg C ha⁻¹). These estimates are comparable to other published values in Madagascar and elsewhere in the Western Indian Ocean and demonstrate the ecological variability of Mahajamba Bay’s mangroves and their value towards climate change mitigation.