Mangrove assessment in Manamoc Island for coastal retreat mitigation

Abstract

Manamoc Island has been experiencing coastline retreat and was in urgent need of efficient and least costly mitigating measures. This study explored the role of mangroves in the mitigation of coastal retreat in Manamoc Island. Assessment of mangroves through standard vegetation analysis was done in relation to the topography and coastal dynamics prevalent in Manamoc Island. Finally, time series analysis of sand and mangrove cover change was done to determine the role of mangroves in coastal retreat mitigation. Cluster analysis revealed five clusters named after the dominant species: Cluster I – Avicennia marina (Forsk.) Vierh.; Cluster II – Bruguiera sexangula (Lour.) Poir.; Cluster III – Rhizophora apiculata Blume and Rhizophora mucronata Lam.; Cluster IV – Rhizophora mucronata Lam.; and Cluster V – Sonneratia alba J. Smith. The clustering pattern follows that of the typical mangrove zonation: landward, middleward, and seaward although with a relatively short width. CCA indicated that environmental factors like soil texture, pH, N, and P influenced mangrove distribution in Manamoc Island. Time series analysis of sand and mangrove cover change revealed that mangroves were responsible for the accumulation of sand in both upper and lower section of the mouth of the lagoon. Likewise, in areas with less sediments and the water current was very strong, mangroves were not able to colonize.