Half of the world’s mangrove ecosystems — a natural defense against coastal flooding — are in danger of collapsing in the coming decades, reports a first-of-its-kind global assessment from the International Union for Conservation of Nature (IUCN; Gland, Switzerland). This landmark study marks the first time an ecosystem group has been assessed comprehensively on a global scale using the IUCN Red List of Ecosystems, a standard for measuring the health of ecosystems worldwide.

The findings, resulting from IUCN-led collaboration between conservationists in more than 44 countries containing mangroves, also show that nearly 20% of the assessed mangroves are classified as “Endangered” or “Critically Endangered,” indicating severe risk of collapse.

“The first global assessment of mangrove ecosystems highlights the urgent need for coordinated conservation of mangroves — crucial habitats for millions in vulnerable communities worldwide,” said Grethel Aguilar, IUCN Director General.

Providing Flood Control

Mangroves cover about 15% of the world’s coastlines, spanning roughly 150,000 km2 (57,915 mi2), and provide a variety of ecological benefits, especially with regards to flood control. Mangroves reduce the intensity of waves and storm surges in many tropical and subtropical regions and serve as a first line of defense against flooding and erosion, according to a 2020 study in Scientific Reports. These benefits are provided through bottom friction, the cross-shore width of forests, as well as tree shape and density. The mangroves’ aerial roots retain sediments, stabilizing the soil against erosion.

As a result, conservationists estimate that mangroves reduce property damage by more than USD $65 billion and protect more than 15 million people each year globally. If current mangrove ecosystems disappeared, 29% more land, 28% more people, and 9% more property would sustain flooding damage each year, research suggests.

“Mangrove ecosystems are exceptional in their ability to provide essential services to people, including coastal disaster risk reduction, carbon storage and sequestration, and support for fisheries. Their loss stands to be disastrous for nature and people across the globe,” said Angela Andrade, Chair of IUCN Commission on Ecosystem Management.

Threats to Mangrove Ecosystems

Climate change is the primary threat to mangrove ecosystems in the form of sea-level rise as well as increasing frequency and intensity of droughts and coastal storms.

The mangrove forest’s aerial root system is key to its ability to stabilize soil and reduce erosion. Image courtesy of Nandhu Kumar/Pixabay.

Under current IUCN projections, 25% of the current global mangrove area is expected to be submerged underwater in the next 50 years, with coastal regions in the Northwest Atlantic Ocean, North Indian Ocean, Red Sea, South China Sea, and Gulf of Aden identified as particularly vulnerable. While sea-level rise is a global issue, mangroves in certain regions may face lower submersion risks. These include mangroves that can occupy higher shore levels or receive enough sediment to keep pace with rising sea levels.

Additionally, communities facing drought conditions often divert freshwater away from natural ecosystems for agriculture, reducing the amount of freshwater and sediment supplies available for mangrove growth. Mangroves also face an array of human threats including deforestation, development, pollution, and dam construction.

Rehabilitating Mangroves

Restoring and maintaining mangrove ecosystems is crucial for mitigating climate change impacts, as healthy mangroves can better cope with sea level rise and provide inland protection from hurricanes, typhoons, and cyclones. Despite numerous efforts, some regions still experience high failure rates largely due to limited knowledge of best practices, according to a report by the Global Mangrove Alliance (GMA; Washington, D.C.).

Current restoration initiatives often focus on the number of trees planted, neglecting key aspects such as project design, long-term maintenance, and community support. Without these elements, the success rate of mangrove restoration projects is significantly lower.

The unique position of mangroves directly on the coast also adds complexity, as environmental conditions can vary even over small areas. In some cases, planting mangroves even can cause environmental damage, such as when other valuable habitats like mudflats and seagrass beds are converted into mangrove forests.

To address these issues, scientists and local stakeholders should consider larger ecological restoration projects of which mangroves are a part as opposed to mass tree-planting efforts alone, according to GMA.

In addition to ecological considerations, mangrove restoration projects also should engage local communities. Public discussions on project implementation and benefits such as ecotourism monetization and flood control can help ensure continued maintenance and support.

Learn more about IUCN’s mangrove assessment at its website.

Top image courtesy of Pixabay

Michelle Kuester is a staff member of the Water Environment Federation, where she serves as Associate Editor of Stormwater Report and Water Environment & Technology magazine. She can be reached at mkuester@wef.org.