Jeffrey McNeill, Karin Bryan, Joanne Ellis, Julia C. Mullarney, Ena Suarez

Mangroves of New Zealand is a regional ecosystem subgroup (level 4 unit of the IUCN Global Ecosystem Typology). It includes the marine ecoregions of Central New Zealand, Northeastern New Zealand and Three Kings-North Cape. Their mapped extent in 2018 was 281.7 to 296.2 km2, representing 0.2% of the global mangrove area. The biota is characterized by a single species: Avicennia marina subsp. australasica. New Zealand's mangroves represent the southernmost global limit of mangroves and are classified as temperate formations. Typically, they thrive in monostands on estuarine mudflats and the lower reaches of rivers in the northern part of North Island. New Zealand's mangrove ecosystems differ significantly from tropical ones in terms of their lower biodiversity. Unique pressures and drivers of change are leading to mangrove range expansion rather contraction. Thus, research and management are geared towards addressing mangrove expansion: there is a need for comprehensive catchment management to reduce the influx of silt into estuaries; and management efforts to prevent loss of nearby salt-marsh ecosystems and the resulting impacts of mangrove colonisation on the amenity and recreation values of sandy-beach areas. Today, New Zealand’s mangroves cover at least 23% more than our broad estimation for 1970. However, the mangrove net area change was -3.0% between 1996 and 2018. If this trend continues, an overall change of +6.2% is projected over the next 50 years. Under a high sea-level rise scenario (IPCC RCP8.5) ≈-16.5% of the area currently covered by mangroves would be submerged by 2060. Moreover, 0.48% of the province’s mangrove ecosystem is undergoing degradation. This may increase to 1.4% within a 50-year period, based on a vegetation index decay analysis. Possible changes to land use and sediment fluxes in catchments draining into estuaries represent further uncertainties in predictions. Overall, the New Zealand mangrove ecosystem is assessed as Least Concern (LC).