High-resolution hydrodynamics of coral reefs and tracing of pollutants from hotel areas along the west coast of Unguja Island, Zanzibar

A rapid increase in population size along with expansion in hotel investment have been identified as key drivers of marine pollution in Zanzibar coastal waters. A validated high-resolution hydrodynamic tracer model was used to estimate the dispersal and impact range of pollutants from the main hotel areas along the western coastline of Unguja Island. The model showed the highest impact of pollutants from land during the northeast monsoon season due to the weakening of the main current. Marine protected areas with short distances to hotel areas and weak tidal currents were more likely to be impacted by pollutants from land than the more remote areas with higher flushing in agreement with water quality and seagrass health measurements. Cumulative effects of pollutants instead of single sources are important to consider for integrated wastewater treatment plans and management strategies to reduce pollution for the protection of biodiversity and guide future monitoring. •Sensitive benthic habitats around Zanzibar are exposed to pollutants from hotel areas.•High-resolution hydrodynamic tracer modeling was developed to track the pollutants.•Tracer distributions were in accordance with water quality and seagrass measurements.•Main sources and impact range of pollutants were estimated in rugged coral reefs.