Human impact on mangrove habitats maintenance against sea-level change : case study of tongatapu island, the kingdom of tonga, south pacific

Mangrove forests and their habitats have been formed and maintained under changing conditions in sea-level over the past few thousands of years. The human impact generated by use of mangrove environments is analyzed in respect to habitats maintenance against sea-level change with a case study dealing with sedimentary structure under mangrove forests on Tongatapu Island and socio-economic environments of the island. First, the application of island classification based on topography and subsurface geology to evaluate mangrove habitats maintenance was examined. It reveals that habitats located on the low islands consisting of reef limestone are most sensitive to sea-level rise. Second, the use of mangrove environments on Tongatapu was described with reference to socio-economic background: the human impact was little within traditional use of mangrove plants because of usage in the consideration of regeneration. But change of usage of mangrove plants and rise of exploitation of mangrove habitats have occurred corresponding to a shift of socio-economic background. These changes have a strong impact on mangrove ecosystems resulting in the decrease of biological productivity of mangrove plants, which is important for habitats maintenance on Tongatapu as a "low island"