Red List of Mangrove Ecosystems

The world’s mangrove ecosystems cover about 150 thousand km² along mainly tropical, sub-tropical and some warm temperate coasts of the world. About 15% of the world’s coastlines are covered by mangroves.  

Mangrove ecosystems are important for biodiversity conservation, provision of essential goods and services to local communities, and reducing the impact of climate change. For this reason, understanding risk of ecosystem collapse has serious socioeconomic implications. 

Threats menacing mangroves are evolving rapidly: in the past we saw degradation from wood exploitation, deforestation for agriculture and shrimp farming, and indirect imparts from dam construction altering freshwater and sediment fluxes. Today, mangroves face additional challenges due to climate change, including sea-level rise and an increased frequency and severity of cyclonic storms.  

Overview of Results

Fifty percent of Mangrove Ecosystems units are at risk of collapse (in the IUCN threat categories of Vulnerable (VU), Endangered (EN), or Critically Endangered (CR); equally they represent 50% of the world’s mangrove area. And one out of five are at severe risk of collapse (either Endangered or Critically Endangered). The other units are Near Threatened (NT), Least Concern (LC) or Not Evaluated (NE).  

Figure 1: The Risk category for each mangrove ecosystem unit.

Main Threats Affecting Mangroves

Climate change is a recent and growing threat to mangrove ecosystems, especially their exposure to more frequent and severe weather events, and sea-level rise. Increased frequency and intensity of cyclones/typhoons/hurricanes and tropical storms impact mangroves on some coastlines. While sea-level rise is a global process, certain regions will be only mildly affected (these include mangroves that can occupy more elevated shore levels, or which receive sufficient sediment flows to keep pace with sea-level rise). 

Mangrove flourish in tropical, humid areas of the planet. Climate change will affect the distribution of mangroves, and changes at the limits of their distribution are already observable. For example, there is expansion of mangrove patches into temperate areas, such as in parts of the Pacific, where they were not previously present. Conversely, in some arid countries, climate change and the widespread practice of diverting freshwater for agricultural irrigation have led to insufficient freshwater and sediment supplies reaching coastal areas, to support mangrove survival and growth.  

Sea-level rise is the main threat affecting mangrove ecosystems. According to the models used, under business as usual, 25% of the global mangrove area is predicted to be submerged in the next 50 Years. One third of the world’s mangrove ecosystem provinces will be severely affected by sea-level rise. However, the impact of sea-level rise on mangrove ecosystems will differ regionally: the Northwest Atlantic, North Indian Ocean, Red Sea, South China Sea, and Gulf of Aden coasts are expected to be particularly severely affected. 

Additionally, while the rate of loss of mangrove area caused by direct human activities has slowed in many ecoregions e.g. Sunda Shelf, the rate of loss remains alarmingly for mangroves in other ecoregions, e.g. Gulf of Guinea South. About 28% of the mangrove ecosystems are affected by this past decline in mangrove surface.

Economic and Social Importance of Mangroves 

Mangrove ecosystems are exceptional in their ability to provide essential ecosystem services to people, including coastal disaster risk reduction, carbon sequestration and long-term storage, and ecological support for fisheries and biodiversity. As of today, global mangroves: 

• Store almost 11 billion tons of carbon, which is almost three times the amount of carbon stored by tropical forests of the same size.  

• Protect 15.4 million people and USD 65 billion worth of property per year from coastal disasters. In 2050, this could rise to 15.5 million and USD 118 billion because of population growth and rise in property values. 

• Support 126 million fishing days per year, providing a key source of food for human populations living near coasts and beyond, along with valuable employment provided by millions of fisheries-related jobs.  

This global assessment shows that more than 50% of mangrove ecosystems are at risk of collapse. In the absence of additional conservation efforts, by 2050, about -~7,065 km² (- 5%) more mangroves will be lost and ~23,672 km² (-16%) will be submerged. If we let this happen, the world is at risk of losing: 

• ~1.8 billion tonnes of carbon stored (16% of the total current carbon stored in mangroves), currently valued at least $13 billion at market prices in voluntary carbon markets and representing a cost to society equal to $336 billion based on the social cost of carbon. 

• Protection for 2.1 million lives exposed to coastal flooding (14.5% of current lives exposed) and $36 billion worth in protection value to properties (35.7% of current property values protected).  

• 17 million days of fishing effort per year (14% of current fishing effort supported by mangroves).

The Methods: ecosystem units and Collaborators

To undertake a comprehensive global assessment of Mangrove Ecosystems, it is essential to establish a manageable number of assessment units that are both meaningful and reflective of the variation in the geographical, abiotic and biotic diversity associated with mangrove ecosystems around the world.  

Level 4 of the IUCN Global Ecosystem Typology subdivides mangroves into different ecoregional expressions of these ecosystems, each representing compositionally distinct geographic variants that occupy different areas. The Marine Ecoregions and Provinces of the World (MEOW) defined by Spalding et al. (2008) provided a useful starting point to define these Level 4 units for mangroves. Developed to represent biogeographic patterns in all coastal marine biota (not only mangrove systems). The MEOW was used alongside the Global Mangrove Watch dataset (GMW) to start delineating Level 4 units. 

Through consultation with mangrove experts between August and December 2021, the MEOW ecoregions and provinces were adjusted to a total of 39 units to serve as biogeographic proxies for compositionally different mangrove ecosystems and to be more suitable for Red List of Ecosystems assessment. These units were later refined to a final list of 36 ecosystem units through a broad consultation with regional mangrove experts in 2022 and 2023. 

Mangroves in Hawaii, and Southeast Polynesia were not assessed because they are not natural to these provinces but have invaded into other habitats.  

This work has been led by IUCN, but the results are being possible thank to collaboration and reviewed by more than 250 experts worldwide from 44 countries where mangroves occur.  

The Red List of Ecosystems: Disaggregated results by Criteria 

The table below summarises the results of the Red List of Ecosystem assessment in each of the units. The columns represent the criteria triggering the risk status (A- Changes in Geographic Distribution, B- Restricted Geographic distribution, C- Changes in Abiotic components and D- Changes in Biotic components of ecosystems). No ecosystem was assessed using criterion E, that which quantitative analysis of collapse risk provability.  

Conclusions and Next steps

Now a headline indicator for the Kunming Montreal Global Biodiversity Framework, The Red List of Ecosystems is a useful tool. By reviewing the status of mangroves, it has been possible to identify the main threats to mangrove degradation and loss that apply most widely across countries on the planet. This is a valuable approach because many of the key mangrove ecological functions, as well as their valuable goods and services, are transboundary and regional in nature. The assessment has identified both widespread and more site-specific threats to mangroves, as well as the underlying drivers causing these threats.

We hope that this global study can help guide future national assessments and actions to mitigate further mangrove loss through informed decision-making. However, it is recommended that countries should always use national, sub-national or other lower scale assessment results whenever these are available.

Maintaining Ecosystem integrity is key for coping with climate change impacts. Ensuring maintenance of old growth mangrove forest, for example, will increase the resilience of the system and the capacity of other mangrove areas to recover and adapt to the effects of climate change.

 The Red List of Mangrove Ecosystems study is a contribution towards achieving the global goals for mangroves. Global commitments like the Mangrove Breakthrough , which aims to secure the future of 150,000 km² of mangroves, should take into account the identified risks of ecosystem collapse, including from climate change impacts, in the development of efficient conservation management strategies.