Remote Sensing-Based Mapping and Change Detection of Mangrove Ecosystems in the Bight of Benin, Lagos State

Mangrove ecosystems along the Bight of Benin coast in Lagos State are among the most ecologically significant but most threatened coastal habitats in West Africa, and quantitative assessment of their spatial extent and change dynamics requires a rigorous remote sensing approach. This study mapped the spatial extent, composition zones, and temporal change of mangrove ecosystems along the Lagos State coastline using multi-temporal satellite imagery: Landsat 5 TM (2000), Landsat 8 OLI (2013), and Sentinel-2A MSI (2022). Object-based image analysis (OBIA) was employed for classification of mangrove zones (Rhizophora, Avicennia, Nypa, and mixed zones), tidal flats, open water, and upland land cover. Accuracy assessments were conducted using stratified random sampling with GPS-verified ground truth points. Change detection matrices and transition probability analysis were performed for 2000 to 2013 and 2013 to 2022 periods. Classification overall accuracy exceeded 87% across all three time periods. Total mangrove area declined from 22,140 ha (2000) to 14,870 ha (2022), a net loss of 32.8% over 22 years. Nypa fruticans monoculture expanded by 41% in area, replacing native Rhizophora stands in the inner delta and creek zones. Urban expansion and aquaculture pond conversion were the dominant drivers of loss in the outer delta. Rhizophora-dominated mangrove declined fastest (-38% area). The study fills a quantitative evidence gap for Lagos State mangrove management, and recommends integrating the change detection map into the Lagos State Environmental Monitoring and Management Programme.

Keywords: mangrove mapping, remote sensing, change detection, Bight of Benin, Lagos State