Mangrove planting on dredged material: three decades of nature-based coastal defence along a causeway in the Arabian Gulf

Nature-based coastal defence approaches are increasingly being explored to protect shorelines from erosion and climate change-related threats such as sea level rise, storms and coastal flooding. At Mubarraz, near Abu Dhabi in the Arabian Gulf, mass plantings of >500 000 nursery-reared seedlings of the mangrove Avicennia marina were conducted over 30 years in response to erosion of an artificially created, 17-km-long causeway of dredged material. Planting efforts resulted in successfully established mangrove vegetation along 6.7 km of shoreline, covering an area of 16.5 ha. Survival rates of planted mangrove seedlings to healthy saplings or trees were in the order of 26% averaged over all years, with best results obtained at planting sites established in artificial tidal channels excavated parallel to the causeway, ensuring appropriate tidal hydrological conditions. The mangroves and causeway have attracted a high diversity of birds (48 species), some of which breed on the island, and there are significant densities of crabs and gastropod snails in the mangroves. These results demonstrate that planting mangroves on dredged material is feasible (even under extreme climatic conditions) and may offer a cost-effective alternative for shoreline protection, with added benefits for biodiversity through the creation of new habitats.