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This article demonstrates the urban anthropogenic threats and their impacts on Sainte Marie (Eastern Madagascar) mangrove ecosystem. In addition to conducting interview with 158 residents, floristic inventories were carried out in order to compare the mangrove structure between a control site and another one that was impacted by Belle Vue dyke (south of the District downtown) rehabilitation. From 2003 to 2014, the island of Sainte Marie lost 0.47% per year of its mangrove area. 87% of the harvested resources from this ecosystem are fish products and are related to human nutrition. The mangrove is used as a dumping ground for liquid and solid waste in the lots of Saint Joseph and La Pointe. Defecation in the open air is topical under the island's mangrove forest. A very weak resilience of the mangrove impacted by the rehabilitation of Belle Vue dyke was noted. Indeed, regenerations of Bruguiera gymnorrhiza and Ceriops tagal have struggled to rebuild. The total height and diameter of impacted trees decreased by 37.2% and 44.3%, respectively. The development of an updated urban master plan, including mangroves in the related zoning process is an imperative measurement for the conservation and/or valuation of existing lots.

Located about fifty kilometers North of Toamasina (East Madagascar), the Commune of Mahavelona Foulpointe has a mangrove relic of about 2 hectares. Despite the ecological and socioeconomic roles played by this ecosystem, it remains so far an orphan site, both in terms of official management and development. The purpose of this article is to take stock of the situation with a view to proposing methods for the sustainable development of this small mangrove via valuation of its natural dynamics. Systematic floristic inventory work was carried out, following a linear ABC transect of 50-100 m, from the sea (zone C) to the rear mangrove (zone A). Five mangrove species exist at Foulpointe: Avicennia marina, Sonneratia alba, Bruguiera gymnorrhiza, Rhizophora mucronata, Lumnitzera racemosa. With anthropogenic harvesting and tourism activities in the area, this ecosystem suffers an annual spatial loss of about 0.14 ha between 2009 and 2016. With a natural regeneration rate of about 966% the small mangrove has a strong capacity for regeneration. Taking into account the pace of current clearing, it would disappear in 10-15 years. The valorization of regenerated young plants, followed by intensive preservation and restoration actions, constitutes a sustainable development path.

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.

Forty-three trees (23 Rhizophora mucronata and 20 Avicennia marina) were studied for the establishment of allometric relationships between the aboveground biomass "y" and the following dendrometric variables "x": diameter at breast height DBH, ( that is the best correlated for the estimation of less woody compartments (R 2 = 0.826 to 0.847). As for R. mucronata, these are much more related to DBH.For trees of 8 -10 m height, the aboveground biomass of the delta is higher (171 t·ha −1 for R. mucronata) than that of Puerto Rico, but quite comparable to that of Australia (110 t·ha −1 for A. marina). The first tools for estimating aboveground biomass are given for these two characteristic species of the Indo-Pacific Region and East Africa. Because of the low values of the regression coefficients for some allometric relationships obtained, precautions should be taken in case of extrapolation.