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.