Mangrove assessment in Manamoc Island for coastal retreat mitigation

Abstract

Manamoc Island is experiencing coastline retreat and is in urgent need of economical 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. Time series analysis of sand and mangrove cover change was carried out 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 followed that of typical mangrove zonation landward, middleward, and seaward although with a relatively short width. Canonical correspondence analysis (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 mangrove were responsible for the accumulation of sand in the entrance of the studied lagoon. In areas with less sediments and the very strong water currents, mangroves were not able to colonize. The authors are thankful for the assistance and support of the following: University of the Philippines Los Baños (UPLB) Graduate School; DOST-ASTHRDP; UPLB–School of Environmental Science and Management (SESAM); Plant Systematics Laboratory (Plant Biodiversity Laboratory), Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños; The Andres Soriano Foundation, Inc. (ASF); and Western Philippines University (WPU).