Spatial modelling of cumulative human pressure in the tropical coastscape of Zanzibar, Tanzania

Coastal landscapes and seascapes ('coastscapes') are under immense anthropogenic pressures emanating from multiple human activities. We applied spatial modelling to characterise the cumulative pressures in the coastscape of Zanzibar's main island Unguja (hereafter Zanzibar), in the western Indian Ocean. We modified the European Union's list of the human pressures in this context, conjointly covering Zanzibar's marine and terrestrial environments. We applied a widely accepted algorithm for modelling cumulative human pressure. Spatial data were gathered from various sources and, where primary data were absent, model results were used as proxies. We used a hexagon lattice with a resolution of 0.5 km2 to map the anthropogenic pressures within the coastscape. Five typologies of coastscape were identified. A total of 283.55 km (68.86%) of the island's coastscape is under moderate to high anthropogenic pressure, while the remaining 128.06 km (31.14%) is under low to moderate pressure. Cumulative human pressures are highest in the urbanised coastal areas, especially Zanzibar City, and in the growth zones. Principal components analysis was used to further explore the coexistence of separate human pressures and their contributions to the cumulative human pressure. Predominant pressures within the coastscape were litter, noise, the introduction of synthetic compounds, and inputs of organic matter. We recommend the use of these results for coastal-zone management in Zanzibar and for prioritisation of the management efforts.