Mighty Mangroves: Coastal Protectors
Mangroves are critically important ecosystems for both marine life and people around the world—but they are rapidly disappearing.
Aquarium of the Pacific
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Mangroves reflecting off a waterway in Palm Beach County Image ID: corp2270, NOAA's America's Coastlines Collection
A dense forest of shrubs, many as big as trees, standing on a tangled net of stiltlike roots lines the coast in the tropics. These are mangroves. Here in Southern California people may not be as familiar with mangrove forests because to see them, you would have to travel south of the Mexican border into Baja or across the country to Florida’s coast.
Mangroves in Monroe County reflecting off the water. Image ID: corp2271, NOAA's America's Coastlines Collection
What are Mangroves?
Mangrove forests are made up of shrubs or trees that grow in the intertidal zone along shorelines in tropical and subtropical areas. The term mangrove can apply to both the individual shrub or tree and the ecosystem as a whole.
Their branch-like roots, also called prop roots, grow in a dense network that is submerged at high tide. The roots break the force of tides and waves, allowing sediment to settle, and provide shelter for fish and other marine life that make their homes among the mangroves.
There are seventy to eighty species of mangrove trees, and they can tolerate varying levels of salinity. Mangrove trees have adapted to survive in saltwater with special mechanisms to remove salt from their tissues. Some expel salt through their leaves, while others avoid taking up salt through their roots.
They grow in waterlogged soil that lacks oxygen, instead absorbing oxygen through their exposed roots.
Mangrove prop roots (Rhizophora rts. sp.), Halimeda, turtle grass (Thalassia testudinum), and Caulerpa spp. Image ID: reef2649, NOAA's Coral Kingdom Collection
Many mangrove species have an interesting method of reproduction. Instead of dropping seeds that grow in soil, mangrove seedlings sprout while they are still attached to the parent plant. The seedlings sprout roots and leaves, then fall into the water below where they float until they reach a spot shallow enough for their roots to take hold.
Where are Mangroves Found?
Mangroves are found along coastlines in most tropical and subtropical areas, including Central America, the Caribbean, the northern coasts of South America, the coasts of central Africa, Southeast Asia, Australia, and the Indo-Pacific.
In the United States, mangroves are found along the coast of Florida and in U.S. territories Puerto Rico and Guam. The largest single tract of mangroves in the world is the Sundurbans, a group of low-lying islands, mudflats, and tidal waterways in the Bay of Bengal straddling the border of India and Bangladesh.
A very large alligator in a mangrove swamp area. Florida. Photographer: Dr. Igor Smolyar, NOAA/NESDIS/NODC.
Why Are Mangroves Important?
Mangroves are like dense cities. Animals like the endangered Bengal tiger native to the Sundurbans can stealthily hunt for prey in the mangrove forest. Reptiles, amphibians, and a few small mammals like rats live in the mangrove forest. Animals like crocodiles, sea turtles, crabs, fish, and shrimp live in the water among the mangrove root systems.
Manatees forage for food in the warm, shallow water near mangroves. Insects populate the mangroves above water and at its surface. Algae, oysters, mussels, sea anemones, brittle stars, barnacles, and sponges grow on mangrove roots and help filter the water. Snails and worms inhabit the muddy soil.
Species of orchids and bromeliads also grow among mangrove branches. Birds, particularly migratory birds, rely on mangroves for nesting, roosting, foraging, and wintering sites along their migratory routes.
Great egret using mangrove trees as roosting site. Florida Keys National Marine Sanctuary.
In addition to providing habitat, foraging grounds, and protective nurseries for many types of animals, mangroves protect coral reefs from being covered by sand and sediment. Their ability to slow tidal and wave action and allow sediment to settle protects the reefs and also acts as a water filtration system.
Grunt (Haemulon sp.), French grunt (Haemulon flavolineatum), herring (Jenkinsia sp.), sponge (Porifera sp.), and mangrove prop roots (Rhizophora rts. sp.). Image ID: reef2647, NOAA's Coral Kingdom Collection
While mangroves do not take up a very large portion of our planet’s surface, they play a key role in protecting coastlines and providing economic value. Many fish and shellfish species that are sold commercially rely on mangroves as juveniles while they grow to adult size, then as adults for foraging.
In addition to seafood, people also use mangroves as a resource for timber and a place to gather honey, firewood, and medicines. During storms, mangroves serve as a buffer on the coastline, breaking the impact of high tides, strong waves, and storm surges. Areas that have mangroves suffer less damage from hurricanes and cyclones. The mangroves’ sturdy roots also stabilize soil, preventing erosion.
Mangroves are also considered key “blue carbon” habitats, because they are especially efficient at absorbing and storing atmospheric carbon—an important function as increasing amounts of carbon emissions enter our atmosphere leading to climate change.
Brown pelicans in mangrove trees. Photo credit: USFWS/Steve Hillebrand
They are natural “carbon scrubbers,” pulling carbon dioxide from the air and storing it in the soil for thousands of years. With all these factors taken together, it is estimated that mangroves provide an economic value of about $8,100 per acre.
At The Aquarium
Aquarium visitors can see examples of mangrove forest habitats at the mudskipper and archerfish exhibits outdoors on Harbor Terrace. Mudskippers live among the mangroves, digging burrows into the muddy soil between mangrove roots. This exhibit even features a simulated tide, with water levels rising and falling twice per day.
The archerfish exhibit shows how fish live among mangrove root systems protected from predators and foraging for prey. Upside-down jellies were recently added to this exhibit. Kids can also experience what it’s like to crawl through mangroves in the play area next to Shark Lagoon. Learn more about mangrove conservation when you visit these exhibits at the Aquarium, and read more here about how sustainable seafood can help mangroves.
View of Ashton Lagoon. Frigate Island, and failed marina infrastructure with naturally recruited mangroves and other vegetation growing are visible in the distance; mangroves and salt pond are in the foreground. Greg Moore
Threats to Mangroves
Despite providing many benefits to both humans and marine life, mangrove forests are disappearing at a rate of 1 to 2 percent per year. The primary threats to mangroves include deforestation, pollution, water diversion, and rising sea levels.
Sea Level Rise Rising sea levels, a result of climate change, could force mangroves to grow further inland, but they will only survive if there is available open space.
Deforestation Mangrove forests are cut down and removed to make space for seafood cultivation, primarily shrimp farms, and other development, like coastal resorts and harbors. Mangroves are also unsustainably harvested for timber and animal fodder.
Pollution Human activity on land causes pollutants like agricultural pesticides to wash into mangrove habitats. Mangroves help filter these pollutants from the water, but in excess these can damage mangrove forests and the plants and animals that make up the mangrove ecosystem.
Water Diversion Dams and irrigation that alter tidal flow or the paths of rivers can starve mangroves of the sediments they need to grow or increase the salinity of their ecosystem beyond the normal range.
In a study published in 2011, researchers estimate that 30 to 50 percent of mangrove areas have been lost in the past fifty years.