A mangrove is a shrub or tree that grows mainly in coastal areas with salty or brackish water. Mangroves grow in warm, tropical climates, usually near coastlines and tidal rivers. They have special features that help them take in extra oxygen and remove salt, allowing them to survive in conditions that harm most plants. The term also refers to the tropical coastal plants that grow in these areas. Mangroves are found in many different plant families because of similar traits that developed 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 the movement of Earth’s tectonic plates. The oldest known mangrove fossils are about 75 million years old.
Mangroves are salt-tolerant plants that live in harsh coastal environments. They have special systems to filter salt and complex root systems to handle saltwater and strong waves. They grow in areas with little oxygen in waterlogged soil but usually thrive in the upper part of the intertidal zone.
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 collect in places protected from strong waves. Mangrove plants can survive in water with varying salt levels, from brackish water to seawater with up to 9% salinity.
Since 2010, scientists have used satellite technology and global data to study mangrove areas, their health, and deforestation rates. In 2018, a global study estimated that there were about 137,600 square kilometers of mangrove forests worldwide in 2010, covering 118 countries and territories. A 2022 study found that mangrove areas decreased by about 3,700 square kilometers between 1999 and 2019. Mangroves continue to be lost due to human activities, with an estimated annual deforestation rate of 0.16% globally. Some countries have deforestation rates as high as 0.70%. The quality of remaining mangroves is also declining.
Mangrove restoration is important because these plants support coastal and marine ecosystems. They help protect nearby areas from tsunamis and extreme weather. Mangrove forests also store large amounts of carbon. Successful restoration depends on working with local communities and ensuring the environment is suitable for the mangrove species chosen.
In 2025, the total global mangrove area is estimated at 15.9 million hectares. Asia has the largest area, with 6.10 million hectares, while Europe has no mangrove areas. Indonesia has the most mangroves globally, 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 not certain and people disagree about where it came from. It may have been borrowed from the Portuguese word "mangue" or the Spanish word "mangle." Earlier, the word might have come from languages spoken in South America, such as Taíno. Another possibility is that it came from the Malay language word "manggi-manggi." The English word may have changed over time through a process called folk etymology, combining "mangrow" and "grove."
The word "mangrove" is used in three different ways:
- Most generally, it refers to the area where mangroves grow and all the plants found there, also called a mangrove forest biome or mangrove swamp;
- It can also describe all the trees and large shrubs found in a mangrove swamp; and
- It is sometimes used narrowly to describe only 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 considered "true mangroves." These species live almost only in mangrove habitats. Many of these species have developed similar ways to survive in tropical conditions with changing salt levels, high tides, soil without oxygen, 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 takes in 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, over 3 m (9.8 ft). The roots also have aerenchyma, which helps move gases and nutrients through the plant.
Because the soil is always wet, there is little oxygen available. Bacteria that live without oxygen release nitrogen gas, 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, even when the roots are underwater during high tide.
Red mangroves keep salt out by having roots that are very hard to pass through. These roots are filled with a waxy substance called suberin, which acts like a filter to stop salt from moving into the rest of the plant. A study found that the roots of the Indian mangrove Avicennia officinalis keep 90% to 95% of salt out of the water it takes in, leaving the salt in the root’s outer layer. When the water becomes saltier, the plant produces more suberin and activates a gene that helps control salt. In a well-known idea called the "sacrificial leaf," salt that builds up in the plant’s stem is stored in old leaves, which the plant then drops. 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
Because there is little fresh water in salty intertidal soils, mangroves reduce the amount of water they lose through their leaves. They can close their stomata (pores on leaves that let in carbon dioxide and release water vapor) and change the way their leaves are positioned to avoid the strong midday sun, which helps reduce water loss. A red mangrove in captivity needs to be misted with fresh water several times a week to grow, as if it were experiencing frequent tropical rainstorms.
A 2016 study by Kim et al. examined how the roots of the mangrove Rhizophora stylosa filter seawater. R. stylosa can grow in salty water, and its roots keep salt levels within a safe range by filtering it out. The roots have layers of tiny pores, and most sodium ions are blocked at the outermost layer. The high salt-blocking ability is due to a property of the first layer. The second layer, made of large pores, also helps filter sodium ions. The study explains how mangrove roots filter water and could inspire new methods for desalination.
Taking in sodium ions helps halophytes (salt-tolerant plants) absorb water and maintain pressure inside their cells. However, too much sodium can be harmful. Therefore, halophytes carefully balance salt levels to survive and grow. A new, sustainable way to desalinate water could be inspired by halophytes, which filter salt through their roots, release it through their leaves, and store it in old leaves or bark. Mangroves are halophytes, and Bruguiera has a special system that filters about 90% of sodium ions from seawater through its roots. Mangroves have been studied for decades because their roots filter water in ways that help them survive harsh conditions.
In this tough environment, mangroves have evolved ways to help their young survive. Mangrove seeds float, making them good for spreading through water. Unlike most plants, which grow seeds in soil, many mangroves (like red mangroves) are viviparous, meaning their seeds grow while still attached to the parent tree. Once the seed grows, it may develop inside the fruit (like in Aegialitis, Avicennia, and Aegiceras) or push through the fruit (like in Rhizophora, Ceriops, Bruguiera, and Nypa) to form a propagule (a seedling ready to grow).
The mature propagule falls into the water, where it can travel long distances. Some propagules, like those of red mangroves, can survive dry conditions and stay afloat 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 instead of sideways. 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 lists, based on Tomlinson, 2016, show 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 mangroves in the New World. Differences in genes between mangroves 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 types has grown steadily, with few species disappearing globally. However, the earliest mangroves were marine plants that adapted to coastal, brackish environments. These early mangroves are recorded as far back as the Pennsylvanian period, with other examples from the early Cisuralian period. It is likely that mangroves are even older, as life began in the oceans, and many areas once thought to be freshwater show signs of marine influence.
Species distribution
Mangroves are plants found in tropical areas, but some also grow in subtropical regions, such as South Florida, southern Japan, South Africa, New Zealand, and Victoria, Australia. These mangroves grow where there are long coastlines or islands, or where seeds float on warm ocean currents from areas with many mangroves.
At the edges of where mangroves can grow, the plants are usually small and sparse, often made up mostly of one type of Avicennia. For example, in Westonport Bay and Corner Inlet, Victoria, Australia, the highest latitude (38° 45'S) where mangroves naturally grow is found. In New Zealand, mangroves extend as far south as 37°, and they form low forests in the northern part of the North Island but become low, sparse plants near their southern limit. The species in both places is called Avicennia marina var. australis, though more genetic research is needed. In Western Australia, A. marina grows as far south as Bunbury (33° 19'S).
In the northern hemisphere, small, sparse Avicennia germinans plants in Florida grow 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 carried there by the Gulf Stream. In southern Japan, Kandelia obovata grows up to about 31°N (Tagawa, as noted by Hosakawa et al., 1977, though initially called K. candel).
Mangrove forests
Mangrove forests, also known as mangrove swamps or mangals, are found in tropical and subtropical areas where the land meets the sea. These forests grow in places like estuaries and along the edges of oceans.
The environment where mangroves live is challenging for plants. At high tide, saltwater covers the soil. When the tide goes out, the sun evaporates the water, making the soil even saltier. When the tide returns, it washes away the salt, bringing the soil’s salt level back to that of seawater.
During low tide, the area is exposed to higher temperatures and less water. When the tide returns, it cools the area and adds water again. To survive in this environment, mangrove plants must handle changes in salt, temperature, and moisture, as well as other conditions. Because of these challenges, only a few plant species live in mangrove forests.
About 110 species of plants are considered mangroves because they grow in salty swamps. However, most of these are not from the mangrove plant group called Rhizophora. A typical mangrove forest usually 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 support many other living things, such as up to 174 types of large marine animals.
Mangrove plants have special traits to survive in their environment. They must deal with low oxygen in the soil, high salt levels, and frequent flooding from tides. Each species has its own way of solving these problems, which is why different mangrove species often grow in separate areas of a mangrove forest. Small differences in the environment can lead to different ways plants survive, so the mix of species depends on how well each plant can handle conditions like flooding and salt.
Once mangrove trees are established, their roots provide homes for oysters and slow down water movement, which helps build up soil. The soil under mangroves can trap heavy metals from the water. If mangroves are removed, these metals can pollute the water and harm animals in the area.
Mangrove forests protect coasts from erosion, storm surges, and tsunamis. Their strong root systems reduce the power of waves during storms and help deposit sediment, which builds up the land. Because of their importance for ecosystems and protection against erosion, mangroves are often protected through conservation efforts.
The tangled roots of mangroves create a quiet, safe habitat for young marine animals. In areas where roots are always underwater, animals like algae, barnacles, oysters, and sponges live there because they need hard surfaces to attach to. Other animals, like shrimps and crabs, live in the muddy areas. Crabs eat mangrove leaves, which adds nutrients to the soil for other animals. Mangroves also help support food chains in coastal areas.
Larger animals, like lemon sharks, use mangrove forests as nurseries for their young. The dense roots provide cover, reducing the risk of predators for baby sharks as they learn to hunt.
In countries like Vietnam, Thailand, the Philippines, and India, mangrove forests support many fish and crustacean species that are important for fishing.
Mangrove forests can turn into peat deposits over time due to the work of fungi, bacteria, and termites. The type of peat depends on the environment and the species of mangroves. In Puerto Rico, red, white, and black mangroves grow in different areas and have different chemical compositions, so the amount of carbon stored in their tissues varies.
In Puerto Rico, red mangroves are most common near the coast, while white mangroves grow farther inland. Mangrove forests are important for storing and moving carbon in coastal ecosystems. Scientists study sediment layers to learn about past environments and changes in coastal areas. However, organic matter from the ocean can also mix with mangrove deposits. Termites help form peat by breaking down mangrove leaves, roots, and wood. Their nests 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, 2% of this carbon was lost, which could have released up to 0.317 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 productivity of mangroves. Scientists have used what they learned about plant microbiomes to create special mixtures of microbes that help protect crops. These mixtures can help plants grow by releasing plant hormones and improving how plants take in nutrients like phosphorus and nitrogen. However, most studies on plant microbiomes have focused on plants like Arabidopsis thaliana and crops such as rice, barley, wheat, maize, and soybean. There is less information about the microbiomes of tree species. The types of microbes found on and inside plants depend on factors related to the plant, such as its type, health, and genetic makeup, as well as environmental factors like climate, soil use, and nutrient availability. The type of plant and its genetic makeup are especially important in shaping the microbes that live in the soil around roots and inside plants. Different parts of the plant, such as roots, stems, and leaves, also have unique groups of microbes based on factors like the plant's genetic makeup, available nutrients, and conditions in the environment.
Mangrove roots are home to many types of microbes that help perform important functions in mangrove ecosystems. Like other plants, mangroves rely on helpful relationships with microbes. Microbes living in mangrove roots help change nutrients into forms that the plant can use. These microbes also produce plant hormones that help mangroves fight off diseases or survive in salty and hot conditions. In return, the microbes receive carbon-based nutrients from the plant through root secretions, creating a mutual benefit between the plant and microbes.
At the taxonomic class level, most Proteobacteria found in mangroves belong to the Gammaproteobacteria group, 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 involved in sulfur-related processes, such as those carried out by Desulfobacterales and Desulfuromonadales. Mangrove roots are home to a wide variety of microbes, including bacteria and fungi. For example, certain bacteria near mangrove roots can fix nitrogen, providing 40–60% of the nitrogen needed by mangroves. The soil attached to mangrove roots has little oxygen but is rich in organic matter, making it a good environment for sulfate-reducing bacteria and methanogens. Fungi that break down complex materials like lignin, cellulose, and starch are also common in mangrove root areas. Rhizosphere fungi help mangroves survive in waterlogged and nutrient-poor environments. These studies show how important root-associated bacteria and fungi are for mangrove growth and health.
Recent research has studied the detailed structure of microbial communities in plant roots by dividing the root into four parts: the inside of the root (endosphere), the outer surface of the root (episphere), the soil directly around the root (rhizosphere), and the soil far from the root (bulk soil). Each of these areas has unique microbial communities. Root secretions help attract specific microbes, but these secretions have little effect on microbes in the bulk soil outside the rhizosphere. It was also found that the episphere, not the rhizosphere, is mainly responsible for controlling which microbes enter the root, leading to a higher presence of Proteobacteria inside the root. These findings help scientists understand how microbes in different root areas are specialized. However, methods that analyze microbial communities based on genetic markers may not fully explain how these microbes function in plant growth or nutrient cycles. Understanding how these microbes work in each root area could help improve knowledge of how they support mangrove ecosystems.
Studies show that disturbed mangroves have more diverse bacterial communities than undisturbed mangroves. Comparing mangroves in different conservation states reveals that disturbed mangrove sediments change their 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, more work is needed to understand how bacteria and other microbes affect nutrient cycles in mangrove sediments and how this influences mangrove growth, structure, and their role 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 key environmental indicators 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 believed to play a major role in local and global nutrient cycles, but as of 2019, little was known about the types of viruses, their genetic diversity, or their roles in mangrove ecosystems.
Viruses are the most common living organisms on Earth, found in nearly all environments. By breaking open their host cells, viruses control how many hosts exist and influence the structure of host communities. Viruses also affect host diversity and evolution by transferring genes between hosts, encouraging resistance to infection, and altering bacterial metabolism. Marine viruses help local and global nutrient cycles by releasing large amounts of organic carbon and nutrients from their hosts and by helping microbes carry out nutrient cycles using special genes called auxiliary metabolic genes (AMGs).
It is thought that AMGs help infected hosts produce more energy and support the creation of new viruses. These genes have been studied in marine viruses that infect algae and include genes involved in photosynthesis, carbon use, phosphate absorption, and stress responses. Studies of viral communities without growing the microbes have identified more AMGs involved in movement, energy production, photosynthesis, iron-sulfur clusters, anti-oxidation, and sulfur and nitrogen cycles. A recent study of viruses in the Pacific Ocean found AMGs that help microbes adapt to different depths in the ocean. Since microbes drive global nutrient cycles and viruses infect many microbes at any time, the genes viruses carry must play important roles 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.