With 213,000 ha of remaining mangroves in 2016, Madagascar has about 4260 ha of mangrove on its Eastern coast. The purpose of this article is to provide essential data on the spatial distribution of this ecosystem of Eastern Madagascar, its ecological potentials and the pressures on its resources. Five Eastern Mangrove sites were selected, from South to North, because of their accessibility and their spatial position: Foulpointe, Sainte Marie, Manompana, Mananara Nord and Rigny. Eastern mangroves regenerate quite well, with a regeneration rate of over 500%. Their height and basal area range respectively between 1.7 - 12 m and 7 - 42 m 2 ·ha-1. The aboveground biomass perfacies can go up to 47 t·ha-1, or even more, at the level of the large homogeneous mangrove of Mananara and Rigny (>70 t·ha-1), whereas this one does not exceed 10 - 20 t·ha-1 in the sporadic mangroves of Foulpointe and Manompana. The carbon sequestration capacity of the aboveground biomass is estimated at more than 5 - 20 t·ha-1, along a South-North gradient, equivalent to a minimum sequestration potential of 21,300 to 85,200 t for the whole East. Despite these ecological potentials and the low annual clearance rates observed for some sites, this ecosystem is subject to anthropogenic pressures linked to urbanization, timber harvesting and irrational exploitation of fishery resources.
With 213,000 ha of remaining mangroves in 2016 [
Comprising a rich, varied and complex ecosystem [
Five main mangrove sites on the Eastern coast of Madagascar were chosen from South to North because of their accessibility and spatial position: Foulpointe, Sainte Marie, Manompana, Mananara Nord and Rigny (
From June 2017 to September 2017, floristic and forest inventory work was carried out at these sites to know their floristic biodiversity, their forest potential in terms of aboveground biomass and regeneration capacity. Transects of 50 - 100 m, perpendicular to the coast line and/or water courses, including 10 m × 10 m plots [
35 - 55 trees per site were randomly selected, slashed to the ground and weighed on site using a precision scale at 0.001. Samples of boles, aerial roots, leaves, flowers, seeds and branches were taken and brought back to the laboratory
for drying in an oven at 105˚C for 48 hours. This operation allowed calculating the dry weight of tree samples taken from fields. Knowledge of the dry weight of the aboveground biomass B was used to calculate the carbon stock C content in their above-ground portion, according to the formula C = B/2 [
The diachronic satellite image analysis Landsat 8 OLI and Google Earth 2016, combined with interviews of residents living on the mangrove lots, allowed to understand the magnitude of the anthropogenic pressures experienced by each site. From June 2017 to September 2017, 33 people living near mangrove sites were surveyed in Foulpointe, 158 in Sainte Marie, 33 in Manompana and 78 in Rigny. In other words, 10% to 17% of the residents and/or direct users of the mangrove lots studied were surveyed. It should be noted that the interviews had been focused on the qualitative and quantitative anthropogenic use of Mangrove resources.
The spatial distribution of mangroves in Eastern Madagascar is sporadic, with the exception of the few homogeneous mangrove sites in the Sainte Marie, Mananara Nord and Manompana complex (Analanjirôfo Region, ~371 ha) on one hand, and that of the Ambodivahibe, Rigny and Irodo complex (Diana Region, ~3831 ha), on the other hand. The latter gathers nearly 90% of the mangroves of the East. That means, from South to North, from Fort Dauphin to Farafangana (<100 ha), through Foulpointe (<2 ha) and Tampolo (<0.5 ha), small lots of scattered and heterogeneous mangroves stretch along the littoral.
With 5 to 8 species, the floristic biodiversity of the whole of eastern Madagascar resembles that of the west coast. The 6 western typical families, namely Avicenniacea, Rizhophoraceae, Meliaceae, Combretaceae, Sonneratiaceae and Sterculeaceae are all present in the East. In Rigny bay, at least 6 species can be found, compared to 8 in Mananara Nord and Sainte Marie, 7 in Manompana and 5 in Foulpointe (
Globally, Eastern mangroves regenerate well, with a regeneration rate greater than 300%, according to [
Administrative Region | Main sites | Area (ha) | % of all Eastern mangroves of Madagascar |
---|---|---|---|
Diana | Irodo | 1160 | 27.23 |
Ambodivahibe | 600 | 14.08 | |
Rigny | 2071 | 48.62 | |
Analanjirôfo | Sainte Marie | 173 | 4.06 |
Manompana | 98 | 2.30 | |
Mananara Nord | 100 | 2.35 | |
Tampolo | <0.5 | <0.01 | |
Atsinanana | Foulpointe | <2 | <0.05 |
AtsimoAtsinanana | Farafangana | <50 | <1.17 |
Anosy | Fort Dauphin | <50 | <1.17 |
Mangrove tree species | Rigny | Mananara Nord | Manompana | Sainte Marie | Foulpointe |
---|---|---|---|---|---|
Rhizophora mucronata | X | X | X | X | X |
Ceriops tagal | X | X | X | ||
Bruguiera gymnorrhiza | X | X | X | X | X |
Avicennia marina | X | X | X | X | X |
Xylocarpus granatum | X | X | X | X | |
Sonneratia alba | X | X | X | X | X |
Lumnitzera racemosa | X | X | X | X | |
Heritiera littoralis | X | X | X |
to ten times higher than that of mature seed trees. However, the rates vary according to the sites studied, according to the type of mangrove and following a North-South gradient (
Respectively, the height and the basal area of the trees range between 1 - 12 m and 2.5 - 42 m2・ha−1, depending on the site and, generally, according to a South-North gradient (
The aboveground biomass perfacies can go up to 47 t・ha−1, or even more, at the level of the large homogeneous mangrove of Mananara and Rigny (>70 t・ha−1), whereas this one does not exceed 10 - 20 t・ha−1 in the sporadic mangroves of Foulpointe and Manompana. The carbon sequestration capacity at the level of the aboveground biomass is estimated at more than 5 - 20 t・ha−1, along a
Sites | Mangrove | Regenerated species in order of dominance | |
---|---|---|---|
Littoral | Lagoon/bay | ||
Rigny Bemanevika Ampanohara Antsaharavo Antsabemoko Ampasira Abigodra | <100% <100% | >300% >720% >400% >350% >170% >1000% | Rhizophora m., Avicennia m. Rhizophora m., Avicennia m. Avicennia m. Rhizophora m., Avicennia m. Rhizophora m., Avicennia m., Ceriops t. Rhizophora m., Avicennia m., Ceriops t. Rhizophra m., Bruguiera g., Ceriops t. |
Mananara Nord | >200% | Bruguiea g., Avicenia m., Rhizophora m. | |
Manompana Apombe Analapenja Mahela | <300% <300% | >500% >75% >900% | Sonneratia a., Bruguiera g., Rhizophora m. Bruguiera g., Rhizophora m. Sonneratia a., Avicennia m. Sonneratia a., Bruguiera g. |
Sainte Marie Ampanihy ForbansIkoa Marorano Ambodiforaha Saint Joseph La Pointe | <100% <100% | >300% >500% >300% <100% >300% >300% | Rhizophora m., Bruguiera g., Ceriops t. Rhizophora m., Ceriops t., Avicennia m. Rhizophora m., Bruguiera g., Ceriops t. Rhizophora m., Bruguiera g. Rhizophora m., Bruguiera g. Rhizophora m., Lumnitzera r. Sonneratia a., Rhizophora m., Avicennia m. |
Tampolo | <100% | Ceriops t. | |
Foulpointe | >900% | Avicennia m., Sonneratia a., Bruguiera g. |
Mangrove sites | Height (m) | Density (mature tree ha−1) | Diameter at breast height (cm) | Basal area (m2・ha−1) | Aboveground biomass (t・ha−1) |
---|---|---|---|---|---|
Rigny | 3.5 - 12 | 1000 - 7960 | 3.8 - 22 | 11 - 42 | >70 |
Mananara Nord | 3.6 - 8 | 1600 - 3400 | 3 - 18 | 8 - 32 | >45 |
Manompana | 3 - 6 | 1000 - 4000 | 4 - 19.1 | 6 - 34 | >40 |
Sainte Marie | 2.7 - 8 | 1500 - 5400 | 3 - 17 | 5.1 - 22 | >46 |
Tampolo | 1 - 1.3 | <150 | 1.5 - 4 | 2.5 - 8 | <10 |
Foulpointe | 1.3 - 5 | 300 - 3000 | 3 - 14 | 3.5 - 15 | <20 |
South-North gradient, equivalent to a minimum sequestration potential of 21,300 to 85,200 t for the whole Eastern coast (
Despite the ecological potential and low annual clearing rates observed for some sites (Sainte Marie: 0.47%, Foulpointe: 0.15%, Rigny: 0.006%, Mananara: <0.47%), this ecosystem is subject to anthropogenic pressures linked to urbanization (Sainte Marie, Foulpointe), timber harvesting (all sites) and the irrational exploitation of fishery resources (Sainte Marie, Manompana) (
Compared with the mangroves of the West Malagasy coast where the tidal range can reach 4.75 m [
All the mangroves of the East and West of Madagascar belong to the Indo-Pacific region [
Mangrove sites | Aboveground biomass (t・ha−1) | Carbon stock | |
---|---|---|---|
(t・ha−1) | total site (t) | ||
Rigny (2071 ha) | >70 | >35 | >72,485 |
Mananara Nord (100 ha) | >45 | >22.5 | >2250 |
Manompana (98 ha) | >40 | >20 | >1960 |
Sainte Marie (173 ha) | >46 | >23 | >3979 |
Tampolo (<0.5 ha) | <10 | <5 | <2.5 |
Foulpointe (<2 ha) | <20 | <10 | <20 |
Total mangroves of the East of Madagascar (4260 ha) | 10 - 40 | 5 - 20 | 21,300 - 85,200 |
Mangrove sites | The 8 main uses of mangrove resources | |||||||
---|---|---|---|---|---|---|---|---|
Fishing (sale) | Fishing (feeding) | Construction Wood | Energy Wood | Phyto-medecine | Crafts | Phyto-chemistry | Others* | |
Rigny | 20 | 0 | 0 | 0 | 0 | 0 | 0 | 80 |
Mananara N. | 20 | 20 | 10 | 0 | 0 | 0 | 0 | 50 |
Manompana | 18 | 25 | 20 | 30 | 2 | 0 | 0 | 5 |
Sainte Marie | 28 | 36 | 3 | 0.5 | 8 | 0.5 | 4 | 20 |
Tampolo | 0 | 20 | 0 | 0 | 0 | 0 | 0 | 80 |
Foulpointe | 30 | 0.2 | 20 | 2 | 0 | 0 | 0 | 47.8 |
*: human dwelling, conservation, tourism, etc.
The presence of Heritiera littoralis Ait (Sterculiaceae) and Lumnitzera racemosa Willd (Combretaceae) on the Eastern coast of Madagascar shows that the following ecological conditions of installation of those two species also exist in the East: a site located in back mangrove where water is less salty and banks of fresh water subject to tides. It means it would be possible to find micro-habitats similar to those recorded in the West of the big island, in the East of Madagascar.
The abundance of natural regenerations in a mangrove ecosystem is common, if one refers to the study conducted by [
Referring respectively to the trees of the Mangoky Delta (southwestern Madagascar), Tsiribihina and Sahamalaza (West Madagascar) where the total height of the trees is between 3.66 and 7.14 m [
In terms of aboveground biomass, those of Sainte Marie, Manompana, Mananara Nord and Rigny are comparable with the figures obtained by [
The amount of carbon sequestered at the level of the aboveground part of the mangroves of East Madagascar is not negligible if one refers to ecosystem services that derive from it. Indeed, with a hypothetical price of 9 USD the ton1, an annual carbon income of around 191,700 to 766,800 USD could be generated, just at the aboveground part of this ecosystem. It should be noted that according to [
In addition to the possible spatial advances related to the fattening mechanism and the abundance of regeneration [
The mangroves of Madagascar eastern coast have a certain number of ecological potentials, especially at homogenous mangrove sites such as Irodo, Ambodivahibe, Rigny and Sainte Marie, where the horizontal and vertical structures of the trees are comparable to those of the Malagasy West. They are dynamic ecosystems subject to generally weak but more significant pressures in urbanized areas such as Sainte Marie and Foulpointe. Their natural regeneration capacity is an asset for their recovery, as is their capacity for carbon sequestration, a promising aspect in terms of mangrove economic valuation.
The authors declare no conflicts of interest regarding the publication of this paper.
Rakotomavo, A. (2018) The Mangroves of the East of Madagascar: Ecological Potentials and Pressures. Open Journal of Ecology, 8, 447-458. https://doi.org/10.4236/oje.2018.88027