Daniel M. Alongi, Norman C. Duke, Joanna C. Ellison, Mary Tahu, Ena Suarez

Mangroves of the Eastern Coral Triangle are a regional ecosystem subgroup (level 4 unit of the IUCN Global Ecosystem Typology). It includes the marine ecoregions of the Bismarck Sea, Solomon Archipelago, Solomon Sea, and Southeast Papua New Guinea. The mapped extent of mangroves in this province in 2020 was 2128.9 km2, representing 1.4% of the global mangrove area. The Eastern Coral Triangle is home to 46 true mangrove species and seven mangrove plant associates. Three mangrove species are on the IUCN Red List of Threatened Species: Avicennia rumphiana (VU = vulnerable), Sonneratia ovata (NT = near threatened), and Bruguiera hainesii (CR = critically endangered). Of 242 animal species associated with mangroves, five species are near threatened, four are endangered, and three are critically endangered.
The province’s mangroves inhabit a variety of sediment types, including carbonate deposits, with many fringing mangrove patches on the many hundreds of islands in the Eastern Coral Triangle. Mangroves are threatened by illegal logging, conversion for agriculture and aquaculture, various types of urban development, including land reclamation, and mining. Climate change, especially sea-level rise, is a potent threat as is increasingly more frequent and stronger cyclones and tropical storms.
Today, the Eastern Coral Triangle mangroves cover approximately 15% less than our estimate for 1970 based on national studies. However, the mangrove net area change has been –0.36% since 1996. If this trend continues, an overall change of –1.0% is projected over the next 50 years. However, under a high sea-level rise scenario (IPCC RCP8.5), roughly –61.5% of the Eastern Coral Sea mangroves will be submerged by 2060. Moreover, 1.3% of the province’s mangrove ecosystems are undergoing degradation, with the potential to increase to 4% within a 50-year period, based on a vegetation index decay analysis. Overall, the mangrove ecosystems in the Eastern Coral Triangle are assessed as Endangered (EN).