Mangrove

Mangroves are shrubs or trees adapted to live in saline or brackish coastal waters, forming distinctive intertidal forests known as mangals. They dominate sheltered shorelines, estuaries and tidal rivers in tropical and subtropical regions, with the greatest concentrations occurring within a few degrees of the equator. Their unique structural and physiological adaptations enable survival in environments characterised by fluctuating tides, variable salinity, low oxygen availability and unstable sediments.

Geographical distribution and evolutionary origins

Mangrove species occur mainly between latitudes 30° N and 30° S, although some extend marginally into warmer temperate zones. Modern remote-sensing data estimate that mangroves inhabit more than one hundred countries and territories. Southeast Asia, particularly the Indonesian archipelago, hosts the greatest species diversity and the largest contiguous mangrove areas.
The evolutionary origins of mangroves trace back to the Late Cretaceous and Paleocene, when early mangrove plant families began adapting to coastal saline conditions. Fossil evidence of Nypa fruticans suggests the presence of mangrove-like vegetation as early as 75 million years ago. The subsequent spread of mangrove taxa was influenced heavily by plate-tectonic movements that created extensive tropical coastlines.

Ecological characteristics and biome features

Mangroves occupy depositional environments where fine, organic-rich sediments accumulate in areas protected from strong wave action. These forested wetlands serve as vital habitats for a wide range of aquatic and terrestrial species, including fish, crustaceans, molluscs, birds and insects. The complex network of roots provides shelter, nursery grounds and feeding sites, while stabilising sediments and reducing coastal erosion.
Saline tolerance among mangrove species spans brackish waters to seawater and even hypersaline lagoons produced by evaporation. Many species thrive in the upper sections of the intertidal zone, where tidal inundation is less frequent and oxygen availability is slightly greater.

Diversity and taxonomic composition

Mangroves demonstrate significant taxonomic diversity due to convergent evolution across numerous plant families. Approximately seventy species across twenty genera and sixteen families are considered true mangroves—those restricted almost exclusively to mangrove habitats. Despite this diversity, species richness within any given mangrove stand is relatively low compared with other tropical ecosystems.
Mangrove terminology varies: the term can denote the entire ecosystem (mangal), the collective assemblage of trees and shrubs, or narrowly the species of the genus Rhizophora. Etymologically, the English word “mangrove” has multiple proposed origins, potentially relating to Portuguese, Spanish, Malay or Caribbean languages and influenced by folk etymology.

Adaptations to environmental stress

Mangroves exhibit numerous morphological and physiological traits enabling survival in saline, waterlogged and nutrient-poor conditions.
Adaptations to low oxygenWaterlogged mud lacks free oxygen, prompting the development of specialised root structures.

• Rhizophora mangle (red mangrove) produces stilt or prop roots that elevate the trunk above the water, allowing gas exchange through bark lenticels.
• Avicennia germinans (black mangrove) forms pneumatophores—vertical aerial roots protruding from the soil that function like breathing tubes. These can reach substantial heights and contain aerenchyma tissue to facilitate internal gas movement.

Nutrient uptakeAnaerobic sediments generate compounds such as methane, sulphides and soluble iron, which reduce nutrient availability. Mangrove roots absorb essential gases and nutrients directly from the air or from highly reduced soils, storing gases internally to maintain metabolic processes even during high tides.
Salt exclusion and regulationMangrove species employ several mechanisms to limit salt intake:

• Red mangroves use highly suberised roots that act as ultrafiltration systems, excluding most sodium ions before water enters the plant.
• Species such as Avicennia officinalis exclude 90–95 per cent of salt at the root cortex, aided by suberin production and salt-regulating enzymes.
• Some species exhibit salt management through leaf shedding, often referred to as the “sacrificial leaf” concept, although research shows this mechanism varies among species.

Water conservationTo reduce water loss in arid saline conditions, mangroves may close stomata during peak sunlight and orient leaves to avoid excessive exposure. Cultivated specimens often require frequent misting with fresh water to mimic natural rainfall.
Filtration processesStudies of Rhizophora stylosa show that mangrove roots possess multilayered pore structures that filter salt through surface-charge interactions and macroporous barriers. This biophysical filtration maintains internal salt levels while allowing the uptake of necessary ions for osmotic balance.

Environmental significance and ecosystem services

Mangrove forests provide essential ecosystem services. They buffer coastlines from storms, tsunamis and erosion, trapping sediments and stabilising shorelines. Their intricate root networks attenuate wave energy and protect inland areas. As highly efficient carbon sinks, mangroves store large quantities of carbon in both biomass and soil, contributing substantially to climate-change mitigation.
Mangroves support fisheries, sustain biodiversity and contribute to the livelihoods of coastal communities. Their ecological importance has prompted extensive global interest in conservation and restoration.

Threats, loss and restoration efforts

Despite their value, mangroves face continuing degradation. Remote-sensing analyses show steady global decline due to land conversion, aquaculture, coastal development and pollution. Although the global deforestation rate is modest on average, some countries experience much higher rates of loss. Degradation of remaining forests also reduces ecological quality and functional integrity.
Restoration initiatives highlight the need for careful planning, species-specific suitability assessments and community participation. Successful restoration integrates ecological knowledge with local cultural and economic considerations. The International Day for the Conservation of the Mangrove Ecosystem, observed annually on 26 July, underscores global commitment to mangrove protection.