Arimatéa C. Ximenes, Marília Cunha-Lignon, Mário Luiz Gomes Soares, Armando S. Reis-Neto, Luis Américo Conti, Monica M. P. Tognella, Ena Suarez

Mangroves of the Warm Temperate Southwestern Atlantic is a regional ecosystem subgroup (level 4 unit of the IUCN Global Ecosystem Typology). It includes the marine ecoregions of Rio Grande and Southeastern Brazil. The mapped extent of mangroves in 2020 was 709.5 km2, representing 0.5% of the global mangrove area. The biota is characterized by three species of true mangroves, Rhizophora mangle, Laguncularia racemosa and Avicennia schaueriana. The mangroves are associated with estuaries, coastal lagoons and bays, and the lagoons of barrier islands. This province marks the southernmost latitude for mangroves in South America. Seasonal factors may interact to limit the poleward dispersal of mangrove species. Primary influences include the year-round, northward-directed longshore drift and the high frequency of cold fronts and chilling events during winter. Additionally, seasonal upwelling of cold waters in spring and summer may impact the viability of propagules.
The Warm Temperate Southwestern Atlantic province includes the most populated coastal region of Brazil and includes major cities each with almost 7 million inhabitants. Mangrove forests in this province are subjected to severe degradation and loss due to urban expansion, changes in land use and occupation patterns, and various other factors, including over-harvesting and pollution from domestic, industrial, and agricultural sources. However, the southern part of this province contains important remnants of preserved mangroves.
As of 2020, the net area of Warm Temperate Southwestern Atlantic mangroves has decreased by 0.9% since 1996. If this trend continues an overall change of -0.8% is projected over the next 50 years. Furthermore, under a high sea level rise scenario (IPCC RCP8.5) ≈-13.6% of the Warm Temperate Southwestern Atlantic mangroves would be submerged by 2060. Moreover, 1.4% of the province’s mangrove ecosystem is undergoing degradation, with the potential to increase to 4% within a 50-year period, based on a vegetation index decay analysis. Overall, the Warm Temperate Southwestern Atlantic mangrove ecosystem is assessed as Least Concern (LC).