A mangrove is a shrub or tree that grows mainly in coastal areas with salty or brackish water. They are found in equatorial climates along coastlines and tidal rivers. Mangroves have special traits that allow them to take in extra oxygen and remove salt, helping them survive in conditions that harm most plants. The term "mangrove" also refers to tropical coastal plants that include these species. Mangroves come from many different plant families because similar traits developed in different families over time. They grow worldwide in tropical and subtropical coastal areas, mainly between 30° N and 30° S latitude, with the most mangrove areas near the equator. Mangrove plants first appeared during the Late Cretaceous to Paleocene periods and spread widely due to movement of tectonic plates. The oldest known mangrove fossils are about 75 million years old.

Mangroves are salt-tolerant and adapted to live in harsh coastal conditions. They have systems to filter salt and complex root systems to handle saltwater and wave action. They survive in waterlogged soil with low oxygen but grow best in the upper part of the intertidal zone, where water levels rise and fall.

The mangrove biome, also called a mangrove forest or mangal, is a saline woodland or shrubland habitat found in coastal areas where fine sediments collect in places protected from strong waves. Mangroves can live in water with varying salt levels, from brackish water to seawater with up to 9% salinity.

Starting in 2010, satellite technology and global data have been used to study mangrove areas, conditions, and deforestation rates. In 2018, the Global Mangrove Watch Initiative estimated the world’s mangrove forest area in 2010 as 137,600 square kilometers, covering 118 countries. A 2022 study found a net loss of 3,700 square kilometers of mangroves globally 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% yearly. The quality of remaining mangroves is also declining.

Mangrove restoration is important because they support coastal and marine ecosystems, protect areas from tsunamis and extreme weather, and store large amounts of carbon. Success in restoring mangroves depends on working with local communities and ensuring suitable growing conditions for chosen species.

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 at 3.40 million hectares, followed by Brazil (1.39 million), Australia (1.11 million), Nigeria (976,000), and Mexico (947,000). These five countries together hold nearly half of the world’s mangrove area.

The International Day for the Conservation of the Mangrove Ecosystem is celebrated 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 by groups like the Taíno people in South America. Another possibility is the Malay word "manggi-manggi." The English word may have changed over time through misunderstandings, combining "mangrow" and "grove."

The word "mangrove" is used in three ways:

• Most broadly, it refers to the habitat and all the plants that live there, also called a mangal. Other terms for this include "mangrove forest biome" and "mangrove swamp."
• It can refer to all the trees and large shrubs found in a mangrove swamp.
• It can also be used more narrowly to describe only the mangrove trees in the Rhizophora genus, which belongs to the Rhizophoraceae family.

Biology

According to Hogarth (2015), there are about 70 species of true mangroves in 20 genera from 16 families. These species live mostly in mangrove habitats. Many of these plants have developed similar ways to survive in tropical conditions with changing salt levels, high tides, waterlogged soil, and strong sunlight. Mangrove areas usually have few plant species, but the most diverse mangrove regions are 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 takes in air through small openings in its bark called lenticels. The black mangrove (Avicennia germinans) grows on higher ground and has special 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 inches) tall in some species. The roots also have air-filled spaces called aerenchyma to help move water and nutrients inside the plant.

Mangrove soil is always wet, so there is little oxygen. Bacteria that live without oxygen release gases like nitrogen, iron, phosphates, sulfides, and methane, which make the soil less rich in nutrients. 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 hard to pass through. These roots are filled with a substance called suberin, which acts like a filter to stop salt from entering the rest of the plant. One study found that the roots of the Indian mangrove Avicennia officinalis can block 90% to 95% of salt in water. When salt builds up in the plant’s stems, it is stored in old leaves, which the plant then sheds. However, recent research on red mangroves suggests that older leaves may not have more salt than younger ones.

Examples of mangrove adaptations include:
– Pneumatophores (aerial roots) of the grey mangrove (Avicennia marina)
– Vivipary in Rhizophora mangle seeds, where seeds begin to grow while still attached to the parent tree

Mangroves reduce water loss from their leaves because fresh water is scarce in salty intertidal soils. They can close their stomata (tiny pores on leaves used for gas exchange) and change the way their leaves are positioned to avoid the sun and reduce evaporation. A red mangrove in captivity needs fresh water misted on its leaves several times a week to survive, like during tropical rainstorms.

A 2016 study by Kim et al. examined how the mangrove Rhizophora stylosa filters saltwater through its roots. This plant can grow in salty water, and its roots control salt levels within a safe range. The roots have a layered structure with tiny pores that filter out salt. The first layer of the root stops most salt ions, and the second layer helps move salt out. This discovery could inspire new methods for desalination (removing salt from water).

Mangroves need to balance salt intake to survive. Too much salt can harm the plant, but some salt helps them absorb water. Mangroves and other salt-tolerant plants (halophytes) remove salt through their roots, release it through their leaves, or store it in old leaves or bark. Bruguiera mangroves have a special system that filters about 90% of salt from seawater through their roots. Scientists have studied mangrove roots for decades to understand how plants survive in salty environments.

To help their offspring survive, mangroves have evolved special ways to spread their seeds. Mangrove seeds are buoyant and can float in water. Unlike most plants, which grow seeds in soil, many mangroves (like red mangroves) are viviparous, meaning their seeds start growing while still attached to the parent tree. Some seeds grow inside the fruit (like in Aegialitis, Avicennia, and Aegiceras), while others grow out of the fruit (like in Rhizophora, Ceriops, Bruguiera, and Nypa) to form a propagule (a seedling ready to grow).

Once mature, the propagule drops into the water and can travel far. Some propagules, like those of red mangroves, can survive dry conditions and stay buoyant and alive for up to a year. When they reach a suitable, low-salt environment, air-filled spaces in the propagule fill with water, causing it to float upright. This position helps the propagule lodge in 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 mangrove areas 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 living in marine environments. Over time, the number of mangrove plant groups has grown steadily during the Tertiary period, with little loss of species globally. 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 possible that mangroves are even older, as life began in the seas, and many environments once thought to be freshwater show signs of past 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 occurrences happen because of long, unbroken coastlines and island chains, or because seeds from dense mangrove areas travel on warm ocean currents.

At the edges of where mangroves grow, the plants are usually small and mostly made up of one type of Avicennia species. For example, in Westonport Bay and Corner Inlet, Victoria, Australia, this type of vegetation grows. Corner Inlet is the northernmost place where mangroves naturally grow in the Southern Hemisphere, located at 38° 45'S. In New Zealand, mangroves grow as far south as 37°, and they are the same type of plant. They form small forests in the northern part of the North Island but become low, scrubby plants near the southern edge. In both places, the species is called Avicennia marina var. australis, though more research is needed to confirm their genetic differences.

In Western Australia, A. marina grows as far south as Bunbury (33° 19'S). In the Northern Hemisphere, scrubby Avicennia germinans in Florida grows as far north as St. Augustine on the east coast and Cedar Point on the west. There are reports of A. germinans and Rhizophora mangle in Bermuda, likely brought there by the Gulf Stream. In southern Japan, Kandelia obovata grows around 31°N (Tagawa in Hosakawa et al., 1977), though it was initially called K. candel.

Mangrove forests

Mangrove forests, also called mangrove swamps or mangals, are found in tropical and subtropical areas where the water level changes with the tides. These areas include places like estuaries and the edges of oceans.

The area between high and low tide where mangroves grow is a major reason why only certain species can live there. When the tide rises, saltwater flows into the soil. When the tide goes out, the sun evaporates the water, 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 the ocean.

At low tide, living things in the area face higher temperatures and less moisture. When the tide returns, they are cooled and covered with water again. For a plant to survive here, it must handle changes in salt, temperature, and moisture, as well as other environmental conditions. Because of this, only a few species of trees live in mangrove forests.

About 110 species of plants are considered mangroves because they grow in salty swamps, even though only a few belong to the mangrove plant group called Rhizophora. A typical mangrove forest usually has only a few types of trees. For example, a mangrove forest in the Caribbean might have only three or four tree species. In comparison, tropical rainforests have thousands of tree species. However, mangrove forests still support many other living things. The trees themselves are few in number, but the ecosystem they create is home to many species, including up to 174 types of large marine animals.

Mangrove plants have special features that help them survive in their environment. These features help them deal with low oxygen levels, high salt, and frequent flooding from the tides. Each species has its own way of solving these problems, which is why different mangrove tree species often grow in separate areas along shorelines. Small changes in the environment can lead to different ways of surviving. The mix of species in a mangrove forest depends on how well each species can handle conditions like flooding and salt levels, but other factors, like crabs eating young plants, can also affect this.

Once mangrove trees grow, their roots provide homes for oysters and slow down water flow, which helps more sediment settle in the area. The fine, oxygen-poor sediments under mangroves trap heavy metals that have been collected from the water by tiny particles. Removing mangroves can disturb these sediments, causing heavy metals to pollute the water and harm nearby living things.

Mangrove swamps protect coasts from erosion, storm surges (especially during tropical storms), and tsunamis. Their large root systems help reduce the energy of waves during events like storm surges and tsunamis. They also slow down the movement of water during the tide, allowing sediment to settle and build up the land. Because of their importance in protecting coasts and their unique ecosystems, mangrove forests are often protected through conservation programs.

The complex network of mangrove roots creates a quiet, underwater habitat for young marine 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 while they filter food from the water. Shrimps and mud lobsters live in the muddy areas. Mangrove crabs eat leaves and add nutrients to the mud, helping other bottom-dwelling animals. In some cases, the carbon stored in mangroves is important for food chains in coastal areas.

Larger animals use mangrove areas as nurseries for their young. For example, lemon sharks give birth to their young in mangrove creeks. These areas have little competition and fewer dangers, allowing young sharks to learn to hunt before moving into the open ocean.

In countries like Vietnam, Thailand, the Philippines, and India, mangrove forests support many types of fish and crustaceans that are important for trade.

Mangrove forests can turn into peat deposits because of the work of fungi, bacteria, and termites. This happens under certain conditions in the soil and environment. In Puerto Rico, red, white, and black mangroves grow in different areas and have slightly different chemical compositions, so the amount of carbon stored in each type of tree varies.

In Puerto Rico, red mangroves are most common in low-lying areas, while white mangroves are more common farther inland. Mangrove forests are important for storing and moving carbon in tropical coastal areas. Scientists study sediment layers to learn about past environments and changes in coastal ecosystems. However, marine material brought in by tides can also mix with mangrove deposits, making the process more complex. Termites help turn mangrove materials into peat by breaking down leaves, roots, and wood. This peat helps store carbon, which is later buried in the soil and continues to cycle through the environment.

Mangroves are a major source of blue carbon, which is carbon stored in coastal ecosystems. In 2012, mangroves worldwide stored 4.19 gigatons of carbon. 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.

Mangroves also 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 that help protect crops. These mixtures can help plants grow by releasing certain hormones and improving the uptake of nutrients like phosphorus and nitrogen. However, most studies on 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. The types of microbes found in plants depend on factors related to the plant, such as its genetic makeup, type of plant part, species, and health, as well as environmental factors like land use, climate, and nutrient availability. Two plant-related factors, the type of plant and its genetic makeup, have been shown to strongly influence the microbes in the rhizosphere and inside the plant. Different parts of the plant also have unique microbial communities based on factors like the plant’s genetic makeup, available nutrients, and the physical and chemical conditions of the plant part, as well as environmental conditions like those on the plant’s surface and disturbances.

Mangrove roots are home to a variety of microorganisms that help with important functions in mangrove ecosystems. Like other plants, mangroves rely on helpful interactions with microbes. Microbes in the roots can change nutrients into forms that mangroves can use. These microbes also provide hormones that help mangroves resist diseases, heat, and salt. In return, the microbes receive carbon from the plant through root exudates, creating a mutual relationship between the plant and microbes.

At the taxonomic class level, most Proteobacteria found in mangroves belong to Gammaproteobacteria, followed by Deltaproteobacteria and Alphaproteobacteria. Gammaproteobacteria, which includes groups like Alteromonadales and Vibrionales, are common in marine and coastal areas and are abundant in mangrove sediments, where they help recycle nutrients. Deltaproteobacteria in mangrove soil are mostly related to sulfur and include groups like Desulfobacterales, Desulfuromonadales, Desulfovibrionales, and Desulfarculales. A wide range of microbes, mainly bacteria and fungi, live in mangrove roots. For example, nitrogen-fixing bacteria near mangrove roots provide 40–60% of the nitrogen mangroves need. The soil attached to mangrove roots lacks oxygen but has plenty of organic matter, making it a good environment for sulfate-reducing bacteria and methanogens. Fungi that break down lignin, cellulose, and starch are common in mangrove roots, and rhizosphere fungi help mangroves survive in waterlogged and nutrient-poor conditions. These studies show the importance of root-associated bacteria and fungi for mangrove growth and health.

Recent research has studied the detailed structure of root-associated microbes in other plants by dividing the root into four parts: endosphere, episphere, rhizosphere, and nonrhizosphere or bulk soil. Each part has unique microbial communities. Root exudates help select certain microbes, but they have little effect on microbes outside the rhizosphere. 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 are distributed in different root areas. However, methods that analyze microbial communities may not fully show their functions in plant growth and nutrient cycles. Understanding the roles of microbes in these four root areas 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 sediments change their microbial structure, leading to a balance in chemical processes that reshape the microbial community.

Although there have been many advances in studying the diversity of bacteria in mangrove sediments under different conditions, more research is needed to understand how these microbes, mainly bacteria, interact with nutrient cycles in mangrove sediments and how they affect mangrove growth, structure, and their role as coastal barriers and other ecological services. Based on a review by Lai et al., improvements in sampling methods and a basic environmental index are suggested for future studies.

Mangrove forests are among the most carbon-rich ecosystems, storing 11% of the total carbon from land that enters the ocean. Viruses are thought to greatly influence 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 ecosystems. By breaking open their host cells, viruses control how many hosts there are and shape host communities. Viruses also influence host diversity and evolution through gene sharing, resistance to infection, and changes in bacterial metabolism. Marine viruses affect nutrient cycles by releasing large amounts of organic carbon and nutrients from hosts and help microbes drive nutrient cycles using special genes called auxiliary metabolic genes (AMGs).

It is believed that AMGs help infected hosts produce more viruses and support their metabolism. AMGs have been studied in marine viruses that infect algae and include genes related to photosynthesis, carbon use, phosphate absorption, and stress responses. Studies of viral communities without growing the viruses have found more AMGs involved in movement, carbon metabolism, photosynthesis, energy use, iron-sulfur clusters, anti-oxidation, and sulfur and nitrogen cycles. A recent study of viruses in the Pacific Ocean found AMGs that help hosts adapt to different depths. Since microbes drive global nutrient cycles and viruses infect many microbes, viral AMGs must play a key role in global nutrient cycles and the evolution of microbial metabolism.

Mangrove forests are the only woody plants that grow in saltwater along tropical and subtropical coastlines. Mangroves are among the most productive and ecologically important ecosystems on Earth.