Five Red List assessments (RLE) of Mangrove Ecosystems at the ecoregion level have been successfully completed. These assessments covered: The Bay of Bengal, Andaman, Sunda Shelf, South China Sea and  the Western Coral Triangle ecoregions (map below), which together represent 32% of the world’s mangrove area. The results from these RLE assessments highlight the crucial importance of these ecosystems in preserving global mangrove biodiversity, hosting two-thirds of the approximately 70 species of true mangrove plant species worldwide, including the Critically Endangered Bruguiera hainesii and Sonneratia griffithii. These assessments mark the initial results of the global mangrove Red List of Ecosystems, an ongoing collaborative effort between IUCN and mangrove experts from around the world.

Each assessment consists of two parts: a comprehensive ecosystem description and identification of the main regional threats to mangrove degradation, followed by an evaluation of the risk of ecosystem collapse using the RLE criteria. Building on this knowledge, a set of conclusions and recommendations have been drawn to provide guidance for conservation efforts and mitigate the risk of ecosystem collapse.

 

Threats to Mangroves 

Fig 1. Risk assessment of five Asian Mangrove Ecosystems

Mangrove ecosystems, major blue carbon sinks and providers of key ecosystem services,  face multiple threats across the five Asian Ecoregions assessed. These threats, which often occur in combination, pose a significant risk of ecosystem degradation or loss. While there may be specific exceptions, the main threats to mangroves in these ecoregions are  often similar, although they may vary in scale and impact at the national to sub-national levels. 

Key identified threats include:

• Over-harvesting of mangrove products.

• Sea level rise.

• Illegal encroachment and degradation of mangroves, including within protected areas. 

• Conversion for agriculture or aquaculture production.

• Diversion of freshwater for agricultural irrigation. 

• Coastal land reclamation and development activities.

• Pollution from sewage, oil spills or garbage accumulation in  adjacent mangroves areas. 

 

Mangrove ecoregions’ risk of collapse 

Due to significant habitat loss in the 1970's and projected submergence of mangroves under sea level rise, the South China Sea mangrove ecosystem is categorized as Endangered (EN) and the Sunda Shelf and Western Coral Triangle mangrove ecosystems as  Vulnerable (VU). In contrast, in the Bay of Bengal and Andaman ecoregions, the reduction of mangrove area has been below 30% over the last 50 years, plus the ecosystems appear to be more resilient to sea-level rise facilitated by sufficient sediment supply, and were therefore classified as Least Concern (LC) based on the available data.

Fig 2. RLE assessment for each ecoregion. Criterion A assesses the reduction in geographic distribution, which in this case was evaluated through national studies and the GMW dataset. Criterion B corresponds to the evaluation of restricted geographic distribution, for which the extent of occurrence (EOO) and the area of occupancy (AOO) were calculated; the 2020 GMW spatial layer was also used for this criterion. Criterion C assesses environmental degradation, and in this case, a model of future mangrove vulnerability, sea level rise, and sediment supply was used. Criterion D evaluates the disruption of biotic processes or interactions, which was evaluated through a mangrove degradation map.

 

Results dissemination 

The completion of these five RLE assessments and their key findings was presented at the IUCN Asia Nature Forum on March 27th 2023 : YouTube recording available.  Following the public presentation of the results, several countries have expressed requests to extend the RLE Assessment  to the National Level (GET Level 5 and 6). It is of critical importance to utilize this information to generate interest in national RLE assessments, particularly considering the RLE’s selection as a Headline indicator for the Global Biodiversity Framework. RLE assessment results can be instrumental in taking concrete actions to influence national planning policy as well as mangrove protection and conservation. 

These results make part of the Global Mangrove Red List of Ecosystems, which will be the first functional group assessed atLevel 4 of the IUCN Global Ecosystem Typology. The IUCN, in close collaboration with mangrove experts from around the world, expects to share the results of the global assessment in the first half of 2024.

 

Written by Susana Barreto and Ena Suárez