A mangrove is a shrub or tree that grows mainly in coastal areas with salty or brackish water. These plants are found in equatorial climates, usually along coastlines and in tidal rivers. Mangroves have special features that help them take in extra oxygen and remove salt, allowing them to survive in conditions that would harm most other plants. The term "mangrove" also refers to tropical coastal plants that include these species. Mangroves belong to many different plant families because several groups of plants evolved similar traits over time. They are found worldwide in tropical and subtropical coastal regions, mostly between 30° N and 30° S latitude, with the largest areas near the equator. Mangrove plants first appeared during the Late Cretaceous to Paleocene periods and spread widely due to movements of Earth’s tectonic plates. The oldest known mangrove fossils are about 75 million years old.
Mangroves are salt-tolerant plants that grow in difficult coastal environments. They have systems to filter salt and root structures that help them survive in salty water and strong waves. They are adapted to low-oxygen conditions in waterlogged soil but usually grow best in the upper part of the intertidal zone, where water covers the area only during high tide.
The mangrove biome, also called a mangrove forest or mangal, is a unique habitat with salty woodlands or shrublands. It forms in coastal areas where fine sediments (often rich in organic material) collect in places protected from strong wave action. Mangrove species can live in water with varying salt levels, from brackish water to seawater with salinity as high as 9%.
Starting in 2010, scientists used satellite technology and global data to study mangrove areas, their health, and deforestation rates. In 2018, the Global Mangrove Watch Initiative estimated that the world had about 137,600 km² of mangrove forests in 2010, covering 118 countries. A 2022 study found that global mangrove areas decreased by 3,700 km² between 1999 and 2019. Mangrove loss continues due to human activities, with an estimated annual deforestation rate of 0.16% globally, and some countries losing up to 0.70% per year. The quality of remaining mangroves is also declining.
Mangrove restoration is important for several reasons. Mangroves support ecosystems that help sustain life in coastal and ocean areas. They protect nearby regions from tsunamis and severe weather. Mangrove forests also store large amounts of carbon. Successful restoration depends on working with local communities and carefully choosing species that can grow in the area.
In 2025, the global mangrove area was estimated at 15.9 million hectares. Asia has the largest area, with 6.10 million hectares, while Europe has no mangroves. Indonesia has the most mangroves, with 3.40 million hectares, followed by Brazil (1.39 million hectares), Australia (1.11 million hectares), Nigeria (976,000 hectares), and Mexico (947,000 hectares). These five countries together hold nearly half (49%) of the world’s mangrove areas.
The International Day for the Conservation of the Mangrove Ecosystem is observed annually on July 26.
Etymology
The origin of the English word "mangrove" is uncertain and not agreed upon. It may have come from the Portuguese word "mangue" or the Spanish word "mangle." Earlier, it might have come from languages spoken in South America and the Caribbean, such as Taíno. Another possibility is the Malay word "manggi-manggi." The English word may also result from a mistaken or simplified version of the words "mangrow" and "grove."
The word "mangrove" can mean three different things:
- Most generally, it refers to the habitat and all the plants that live there, called a mangal. This habitat is also called a mangrove forest or mangrove swamp.
- It can refer to all the trees and large shrubs found in a mangrove swamp.
- It can specifically refer only to the trees in the Rhizophora genus, which belongs to the Rhizophoraceae family.
Biology
According to Hogarth (2015), there are about 70 species of mangroves in 20 genera from 16 families that are called "true mangroves." These species mostly live in mangrove habitats. Many of these species have developed similar ways to survive in tropical conditions with changing salt levels, high tides, waterlogged soil, and strong sunlight. Mangrove areas usually have low plant diversity. The highest diversity of mangroves is found in Southeast Asia, especially in the Indonesian archipelago.
The red mangrove (Rhizophora mangle) grows in areas that are often flooded. It uses stilt or prop roots to stay above water and absorbs air through small openings in its bark called lenticels. The black mangrove (Avicennia germinans) grows on higher ground and has root-like structures called pneumatophores that stick out of the soil like straws to help the plant breathe. These "breathing tubes" can be up to 30 cm (12 in) tall, and in some species, they grow over 3 m (9.8 ft). The roots also have wide spaces called aerenchyma to help move nutrients inside the plant.
Because the soil is always wet, there is little oxygen. Bacteria in the soil release gases like nitrogen, iron, phosphates, sulfides, and methane, making the soil less nutritious. Pneumatophores allow mangroves to take in gases directly from the air and absorb nutrients like iron from the soil. Mangroves can store gases inside their roots and process them even when the roots are underwater during high tides.
Red mangroves keep salt out by having roots that are very thick and waxy, which act like a filter to stop salt from entering the rest of the plant. A study found that the roots of the Indian mangrove Avicennia officinalis can keep out 90% to 95% of salt from water. When the water becomes saltier, the plant produces more waxy material and activates a gene that helps control salt levels. In the "sacrificial leaf" concept, salt that builds up in the plant’s stems is stored in older leaves, which the plant then sheds. However, recent research on red mangroves suggests that older leaves do not have more salt than younger ones.
- Pneumatophores (aerial roots) of the grey mangrove (Avicennia marina)
- Vivipary in Rhizophora mangle seeds
Mangroves reduce water loss from their leaves because fresh water is limited in salty, tidal areas. They can close the tiny pores on their leaves (called stomata) to limit water loss. They also change the way their leaves face the sun to avoid overheating and reduce evaporation. A red mangrove in captivity needs to be misted with fresh water several times a week to grow, as if it were experiencing tropical rainstorms.
A 2016 study by Kim et al. examined how the roots of Rhizophora stylosa filter seawater. This mangrove can grow in salty water, and its roots control salt levels through a special filtering system. The roots have a layered structure with tiny pores that trap sodium ions. The first layer of the root has a strong electrical charge that blocks sodium ions. The second layer, with larger pores, also helps filter sodium. This research explains how mangrove roots filter water and could inspire new methods for desalination.
Mangroves take in sodium ions to help them absorb water and maintain pressure inside their cells. However, too much sodium can be harmful. Mangroves balance salt levels carefully to survive. Scientists have studied how mangroves filter salt through their roots and how they secrete excess salt through their leaves or bark. Some mangroves, like Bruguiera, can filter about 90% of sodium from seawater through their roots. The way mangrove roots filter water has been studied for many years, as their structures have evolved to survive harsh conditions.
Mangroves have special ways to help their young survive. Their seeds float and can travel long distances in water. Unlike most plants, which grow seeds in soil, many mangroves (like the red mangrove) are viviparous, meaning their seeds begin to grow while still attached to the parent tree. The seedling grows inside the fruit (as in Aegialitis, Avicennia, and Aegiceras) or pushes out of the fruit (as in Rhizophora, Ceriops, Bruguiera, and Nypa) to form a propagule, which is a seedling that can make its own food through photosynthesis.
Once the propagule is ready, it falls into the water and can float for long distances. Some propagules, like those of the red mangrove, can survive dry conditions and stay buoyant and alive for up to a year. When they reach a suitable area with low salt levels, water fills the air spaces inside the propagule, causing it to float upright. This position helps the propagule sink into the mud and grow roots. If it does not root, it can float again to find better conditions.
Taxonomy and evolution
The following list, based on Tomlinson, 2016, shows the mangrove species found in each plant genus and family. Mangrove areas in the Eastern Hemisphere have six times more tree and shrub species than those in the New World. Differences in genes between mangrove plants and their land relatives, along with fossil evidence, suggest that the variety of mangrove species is limited by the challenges of adapting to the marine environment. Over time, the number of mangrove lineages has grown steadily during the Tertiary period, with little global extinction. However, the first mangroves were marine plants that adapted to coastal, brackish environments. These early mangroves are recorded from the Pennsylvanian period, and other examples are found from the early Cisuralian period. It is likely that mangroves are even older, as life began in the seas, and many environments once thought to be freshwater show signs of marine influence.
Species distribution
Mangroves are a type of tropical plant that sometimes grow in subtropical areas, such as South Florida, southern Japan, South Africa, New Zealand, and Victoria, Australia. These areas occur because of long coastlines and island chains or because of tiny seeds that float on warm ocean currents from regions where mangroves are common.
At the edges of where mangroves grow, the plants are often small and dominated by a single type of tree called Avicennia. This is seen in places like Westonport Bay and Corner Inlet in Victoria, Australia, where mangroves grow naturally at the farthest southern point (38° 45'S). In New Zealand, mangroves extend as far south as 37°, and they grow as small forests in the northern part of the North Island but become low, scrubby plants near their southern limit. In both regions, the plant is called Avicennia marina var. australis, though more genetic studies are needed to confirm this. In Western Australia, Avicennia marina grows as far south as Bunbury (33° 19'S).
In the northern hemisphere, small Avicennia germinans trees grow as far north as St. Augustine on Florida’s east coast and Cedar Point on its west coast. There are also records of Avicennia germinans and Rhizophora mangle in Bermuda, likely carried there by the Gulf Stream. In southern Japan, Kandelia obovata grows as far north as about 31°N (Tagawa, as noted by Hosakawa et al., 1977, though initially called K. candel).
Mangrove forests
Mangrove forests, sometimes called mangrove swamps or mangals, grow in tropical and subtropical areas where tides come and go. These areas include places like estuaries and the edges of oceans.
The way these trees live between high and low tides is a big challenge. This makes it hard for many species to survive there. When the tide comes in, saltwater enters the soil. When the tide goes out, the sun evaporates the seawater, making the soil even saltier. When the tide returns, it washes away some of the salt, bringing the soil’s salt level back to that of seawater.
At low tide, living things in the area face higher temperatures and less water. When the tide returns, they are cooled and flooded again. To survive in this environment, plants must handle wide changes in salt levels, temperature, and water. Because of this, only a few species live in mangrove forests.
About 110 types of plants are considered mangroves because they grow in salty swamps. However, most of these are not from the mangrove plant group called Rhizophora. Usually, a mangrove forest has only a few tree species. For example, a mangrove forest in the Caribbean might have only three or four types of trees. While tropical rainforests have thousands of tree species, mangrove forests still support many other living things. These trees create homes for up to 174 types of large sea animals.
Mangrove plants have special ways to survive problems like low oxygen, high salt, and frequent flooding. Each species has its own way of dealing with these challenges. This is why, on some shorelines, different mangrove species grow in separate areas. Small changes in the environment can lead to different survival methods. The mix of species depends on how well each plant can handle conditions like flooding and salt, but other factors, like crabs eating young plants, also play a role.
Once mangroves grow, their roots help oysters live and slow down water movement. This makes more sediment settle in the area. The soft, oxygen-poor soil under mangroves holds heavy metals that are pulled from water by tiny particles. Removing mangroves can cause these metals to pollute seawater and harm local life.
Mangrove swamps protect coasts from erosion, storm surges (especially during tropical storms), and tsunamis. Their strong root systems reduce wave energy and slow water, letting sediment settle. This helps build the environment. Because of their importance and the protection they offer, mangroves are often protected through conservation programs.
The tangled roots of mangroves create a quiet home for young sea life. In areas where roots are always underwater, animals like algae, barnacles, oysters, sponges, and bryozoans live there because they need hard surfaces to attach to. Shrimps and mud lobsters live in the muddy areas. Crabs eat mangrove leaves, adding nutrients to the mud for other animals. In some cases, the carbon from mangroves supports food chains in coastal areas.
Larger sea animals use mangroves as nurseries for their young. Lemon sharks, for example, give birth in mangrove areas. The ecosystem provides a safe place for baby sharks to learn to hunt before joining the ocean’s food web.
In countries like Vietnam, Thailand, the Philippines, and India, mangrove forests are home to many fish and crustaceans that are important for trade.
Mangrove forests can turn into peat deposits through the work of fungi, bacteria, and termites. This happens in certain conditions. The type of peat depends on the environment and the mangrove species. In Puerto Rico, red, white, and black mangroves grow in different areas and have slightly different chemical makeup. Red mangroves are more common near the coast, while white mangroves grow farther inland. Mangroves play a key role in storing and moving carbon in coastal ecosystems. Scientists study sediment layers to learn about past environments and changes in coastal areas. However, marine matter brought in by tides also mixes with peat. Termites help create peat by breaking down mangrove leaves, roots, and wood. Their nests store carbon, which is later buried in sediment and continues the carbon cycle.
Mangroves are a major source of blue carbon. In 2012, mangroves stored 4.19 gigatons of carbon worldwide. Between 2000 and 2012, about 2% of this carbon was lost, which could have released up to 0.316996250 gigatons of carbon dioxide into the atmosphere.
Globally, mangroves help protect coastal communities from economic losses caused by tropical storms.
Mangrove microbiome
Plant microbiomes are important for the health and growth of mangroves. Scientists have used knowledge about plant microbiomes to create special mixtures of microbes that help protect crops. These mixtures can help plants grow by releasing plant growth hormones and improving the absorption of nutrients like phosphorus and nitrogen. However, most studies about plant microbiomes have focused on model plants like Arabidopsis thaliana and important crops such as rice, barley, wheat, maize, and soybean. There is less information about the microbiomes of tree species. Plant microbiomes are influenced by factors related to the plant (such as its type, part of the plant, and health) and environmental factors (like land use, climate, and available nutrients). Two plant-related factors, the type of plant and its genetic makeup, are important in shaping the microbes around the roots and inside the plant. Different parts of the plant also have unique microbial communities based on factors like the plant’s genetics, available nutrients, and the physical and chemical conditions of the part, as well as environmental conditions like those on the plant’s surface and disturbances.
Mangrove roots are home to many types of microbes that help perform important functions in mangrove ecosystems. Like other land plants, mangroves rely on helpful relationships with microbial communities. Microbes living in the roots can help convert nutrients into forms the plant can use. These microbes also provide plant growth hormones that help mangroves resist diseases, heat, and salt. In return, microbes receive carbon-based molecules from the plant through root exudates, creating a mutual benefit between the plant and microbes.
At the taxonomic class level, most Proteobacteria in mangroves are from the Gammaproteobacteria group, followed by Deltaproteobacteria and Alphaproteobacteria. Gammaproteobacteria, which includes groups like Alteromonadales and Vibrionales, are found in marine and coastal areas and are common in mangrove sediments, where they help recycle nutrients. Deltaproteobacteria in mangrove soil are often involved in sulfur-related processes and include groups like Desulfobacterales and Desulfuromonadales. Diverse communities of bacteria and fungi live in mangrove roots. For example, nitrogen-fixing bacteria near mangrove roots can provide 40–60% of the nitrogen needed by mangroves. The soil attached to mangrove roots has little oxygen but is rich in organic matter, creating a good environment for sulfate-reducing bacteria and methanogens. Fungi that break down lignin, cellulose, and starch are also common in mangrove roots. Rhizosphere fungi help mangroves survive in waterlogged and nutrient-poor conditions. These studies show that bacteria and fungi associated with roots are important for mangrove growth and health.
Recent studies have examined the structure of root-associated microbial communities in detail by dividing the root into four parts: the inside of the root (endosphere), the surface of the root (episphere), the area around the root (rhizosphere), and the soil outside the root (bulk soil). Each part has unique microbial communities. Root exudates help attract specific microbes but have little effect on microbes in the bulk soil. The episphere, not the rhizosphere, is mainly responsible for controlling which microbes enter the root, leading to the presence of Proteobacteria in the endosphere. These findings help explain how microbes in different root areas differ in their roles. However, methods that study microbial communities based on genetic markers may not show their functions in plant growth or nutrient cycles. Understanding how microbes function in each root area could improve knowledge of how they support mangrove ecosystems.
Studies show that disturbed mangroves have more diverse bacteria than well-preserved mangroves. Comparisons of mangroves in different conservation states reveal that disturbed mangrove soil changes its microbial structure, leading to a balance in chemical processes that reshape the microbial community.
Although research on bacterial diversity in mangrove sediments has advanced in recent years, gaps remain in understanding how microbes, mainly bacteria, interact with nutrient cycles in mangrove sediments and how they affect mangrove growth, structure, and their roles as coastal barriers and providers of other ecological services. Based on a review by Lai et al., improvements in sampling methods and the use of basic environmental indicators are suggested for future studies.
Mangrove forests are among the most carbon-rich ecosystems, contributing 11% of the total carbon from land to oceans. Viruses are thought to play a major role in local and global nutrient cycles, but as of 2019, little was known about the structure, genetic diversity, and roles of viruses in mangrove ecosystems.
Viruses are the most common living things on Earth, found in nearly all environments. By breaking open their host cells, viruses control the number of hosts and influence the structure of host communities. Viruses also affect host diversity and evolution by transferring genes between organisms, selecting for resistance, and altering bacterial metabolism. Marine viruses impact nutrient cycles by releasing large amounts of organic carbon and nutrients from hosts and help microbes drive nutrient cycles through genes that assist in metabolism.
Scientists think that these genes, called auxiliary metabolic genes (AMGs), help infected hosts produce more viruses. AMGs have been studied in marine viruses that infect algae and include genes involved in photosynthesis, carbon use, phosphate uptake, and stress responses. Studies of viral communities without growing the microbes have found more AMGs involved in movement, energy use, photosynthesis, and nutrient cycling. A recent study of ocean viruses found AMGs that help microbes adapt to different water depths. Since microbes drive global nutrient cycles and viruses infect many microbes, the genes viruses carry must be important for global nutrient cycles and the evolution of microbial metabolism.
Mangrove forests are the only woody plants that grow in saltwater along tropical and subtropical coasts. Mangroves are among the most productive and ecologically important ecosystems on Earth.