## 1 Introduction  
Mangrove forests are among the most valuable ecosystems on Earth [1]. In 2002, mangroves were estimated to cover, c., 20,100,000 ha of the world's coastline [1], but they have suffered large-scale deforestation and degradation. According to [PERSON] et al. and [PERSON], mangroves covered c. 13,776,000 ha by 2010 [2] and 8,349,500 ha in 2016 [3], respectively. Mangroves, which occur at the land-ocean interface in the tropics and subtropics, have significant ecological, economic, and social benefits [4, 5]. Mangroves and related marine resources support tourism, fishing, and agriculture in Zanzibar [6, 7, 8]. Mangroves are crucial in protecting coastlines from storm surges and are also able to regulate local climate [6, 7, 8]. Mangrove habitats offer coastal and marine organisms a place to feed, breed, and flourish [9, 10]. Mangroves act as bio-filters by trapping sediment and inorganic substances [6, 11, 12, 13]. Mangrove forests store more carbon per unit area than any other forest on Earth, i.e., mangroves store, c., 3-5 times as much organic carbon as tropical upland forests [11]. Mangroves supply essential ingredients to the chemical, pharmaceutical, and cosmetic industries [12]. However, mangroves are vulnerable to human activities [11, 13, 14] and environmental changes [15, 16]. Mangrove establishment, restoration, and conservation have all received increased attention in Zanzibar [17]. However, national- and regional-scale strategies and solutions for mangrove management and rehabilitation have been significantly hampered by the lack of up-to-date, reliable, and consistent cost-effective and high-resolution spatial data on mangrove forests [18; 19]. A multi-spatiotemporal analysis of changes in mangrove forests in Zanzibar is vital in advising on their management and conservation and their sustainable use thereof [14]. The assessment of Zanzibar's mangrove cover using ground-based methods is difficult because of the expertise required and the expenses involved [20]. In many cases, areas covered by these surveys are small and not spatially contiguous [21]. Therefore, ground-based approaches are unreliable to estimate mangrove cover/degradation. The satellite remote sensing technique has been used to track mangrove changes [22; 23; 24] and is essential for managing natural resources and preserving the environment [25; 26]. Landsat imagery has been extensively utilized to track historical changes in mangrove distribution and extent at the local [24; 25; 26; 27], regional [28], national [29], and global [2] scales. This is made possible by the free and open-source Landsat imagery archive, dating as far back as 1972, with consistent revisit periods and global coverage [30]. Mangroves in Zanzibar have been studied since the 1990s. However, these studies were themed around calculating the total mangrove volume [31], the mapping of mangrove flora and fauna [32], the inventorying of wood biomass [33], the impact of the deforestation of mangroves on the nutrition, ecology, and genetic diversity of _Uca anunilpes_[34], a review of the status of mangrove ecosystems [35], the exploitation and regeneration of mangroves [36], and a management strategy for mangrove habitats [37]. Global mangrove forest losses exceed those of tropical rain forests and coral reefs; therefore, global mangrove distribution maps, e.g., the World Atlas of Mangroves-1 (WAM-1), the World Atlas of Mangroves-2 (WAM-2), the Global Distribution of Mangroves (GDM), and the Global Mangrove Watch (GMW), were initiated to monitor mangroves [38; 39]. The global mangrove maps may be most useful for mapping the national and regional coverage of mangroves [39]. Therefore, they may be of limited use for those managing relatively small/protected areas containing mangrove forests. Effective protection of mangroves would be attained if losses are recognized as soon as feasible after the loss event and were made available to users in a form they can easily access and use.