## 3 Results
### Change Detection Analysis
#### 3.5.2 Spatio-Temporal Mangrove Distribution in Menai Bay  
The 1973 to 2020 period shows that the mangrove cover reduced from 1694.6 ha to 819.2 ha, i.e., a 51.7% decrease. This is equivalent to a deforestation rate of 1.1% per annum. During the 1973-1990 period, there was a 3.4% decrease of the mangrove forest cover, i.e., from 1694.6.0 ha to 1637.2 ha, equivalent to a degradation rate of 3.4 ha per annum. In the  
Figure 8: The dynamics of mangrove forests along the coast of Chwaka Bay in Unguja, Zanzibar from 1973 to 2020.  
Figure 7: Mangrove forest loss/gain (ha) from 1973 to 2020, Chwaka Bay in Unguja, Zanzibar.  
17-year period, 34.2 ha of mangroves were covered by sea water, 164.3 ha were degraded to bare land, 404.3 ha were converted into agricultural land use, and 266.4 ha into other forests. In the same period, the mangrove forest cover gained an area equivalent to 95.7 ha originally covered by sea water, 194.8 ha from bare land, 247.1 ha from agricultural land use, and 274.2 ha from other forests. Between 1990 and 1995, the mangrove forest cover reduced from 1637.2 ha to 1561.9 ha, i.e., a 4.4% loss. The mangrove forest cover gained 15.4 ha of land earlier occupied by sea water, 135.2 ha by bare land, 332.4 ha by agricultural activities, and 277.6 ha by other forests. About 37.7 ha of mangroves were covered by sea water, 184.3 ha were converted into bare land, 321.2 ha into agricultural land, and 292.7 ha into other forests. The 1995-2000 period saw mangroves decrease from 1561.9 ha to 1358.9 ha, i.e., a reduction equivalent to 12.0%. About 3.9 ha of mangrove were covered in water, 179.7 ha turned into bare land, 169.9 ha into agricultural land use, and 550.3 ha into other forests. In this period, mangrove gained 261.2 ha from an area initially covered by water, 107.8 ha from bare land, 192.8 ha from agricultural land, and 139.0 ha from other forests. In the 2000-2009 period, mangrove forest cover fell by 125.6 ha (7.4%), i.e., from the initial 1358.9 ha to 1233.4 ha. The fall is equivalent to a mangrove degradation rate of 14.0 ha per annum. About 341.3 ha of mangroves were occupied by sea water, 146.8 ha transformed into bare land, 94.6 ha into agricultural land, and 108.3 ha into other forests. The mangrove forest cover gained 6.8 ha originally occupied by sea water, 113.8 ha by bare land, 141.0 ha by agricultural activities, and 303.9 ha by other forests. From 2009 to 2020, the area covered by mangroves declined by 414.2 ha (24.4%), i.e., from 1233.4 ha to 819.2). The mangrove degradation rate was 37.7 ha per year. In this period, mangrove forest cover increased by 12.0 ha, an area initially covered in water, 92.3 ha from bare land, 128.7 ha from agricultural land, and 62.1 ha from other forests. About 76.2 ha of mangrove forest cover was covered by sea water, 240.3 ha turned into bare land, 349.3 ha lost to agricultural land use, and 43.4 ha to other forests.  
Mangrove forest gain and loss (in ha) from 1973 to 2020 is shown in Figure 9. Generally, mangroves gained, c., 295 ha from the other LULC classes, but lost 709 ha to water, bare land, agriculture, and other forests. In the period from 1973 up to 1990, about 57.4 ha of mangrove forest cover was destroyed, while between 1990 and 1995, about 75.4 ha were cleared. The next three periods recorded massive destruction of mangroves. The highest change in the area covered by mangroves was between 2009 and 2020. The overall destruction of mangrove forests was, c., 875 ha.  
Figure 10 shows the spatio-temporal mangrove distribution in Menai Bay, Unguja, Zanzibar, Tanzania between 1973 and 2020.  
Figure 9: Mangrove forest loss and gain (ha) from 1973 to 2020, Menai Bay in Unguja, Zanzibar.