IUCN Red List of Ecosystems, Mangroves of The Tropical Northwestern Pacific

Joanna C. Ellison, Zachary B. Williams, Richard A. MacKenzie, Hannah E. Joss, Cara Lin, David Adema, Ena Suarez

Mangroves of the Tropical Northwestern Pacific is a regional ecosystem subgroup (level 4 unit of the IUCN Global Ecosystem Typology). It includes the marine ecoregions of the East Caroline Islands, Mariana Islands and West Caroline Islands. The Tropical Northwestern Pacific mangrove province mapped extent in 2020 was 144.8 km2, representing 0.1% of the global mangrove area. The biota is characterized by 10-18 species of true mangroves species and 211 species listed as mangrove associates in the IUCN Red List. These include many threatened species occupying relatively small and disconnected habitats between islands.
The diversity of species across a wide range of taxa - including birds, mammals, fishes, sharks, reptiles and invertebrates - underscores the conservation significance of mangrove ecosystems in the Tropical Northwestern Pacific. It highlights the urgency of protecting these ecosystems not only for their ecological functions, but also for the survival of numerous species.
Pacific Island mangroves are largely represented by fringing coastal mangroves, although estuarine mangroves also occur on the larger islands. The greatest threats to mangroves include loss of habitats owing to coastal development, consequences of upland erosion, and increasingly relative sea-level rise (SLR). Rates of SLR for the province are far higher than global rates owing to island subsidence.
The mangrove net area change has been stable at -1.8% since 1996 according to global models and as indicated by a high-resolution spatial change study of Pohnpei. Under a globally modelled high SLR scenario (IPCC RCP 8.5) ≈-22.0% of the Tropical Northwestern Pacific mangroves would be submerged by 2060. Additionally, the area of occupancy (AOO) is restricted and is threatened by land-based pollution, road construction, other coastal development and damage from severe cyclones. Therefore, the Tropical Northwestern Pacific mangrove province is assessed as Vulnerable (VU) for subcriterion B2.
Moreover, 1.2% of the province’s mangrove ecosystem is undergoing degradation, with the potential to increase to 3.4% within a 50-year period, based on a vegetation index decay analysis. Overall, the Tropical Northwestern Pacific mangrove ecosystem is assessed as Vulnerable (VU).