What are Mangroves?
Mangroves are groups of trees and shrubs that inhabit coastal intertidal zones in the tropics. There a more than 80 extant species, some growing as high as 200 feet. The slow moving waters in mangrove forests allow for the accumulation of fine sediments, creating a muddy benthic area. Some mangroves have dense tangles of prop roots or buttresses that enable the trees to cope with rising and falling tides; others have snorkel-life roots called pnuematophores that stick out of the mud to help them take in air.
Where are They Found?
Mangroves only grow at tropical and subtropical latitudes near the equator. Mangroves also require an environment containing low-oxygen soil to grow. Most of the world's mangroves are found in Southeast Asia, with many also being found in Florida.
What Benefits Do They Offer?
Mangroves stabilize the coastline, reducing erosion from storm surges, currents, waves, and tides. This means that mangroves act as a great buffer against hurricanes and tropical storms. Their intricate root system is attractive to fish and other organisms seeking food and shelter. They also serve as habitats for many juvenile fish, oysters, crabs, shrimp, and birds. Mangroves help decrease the effects of global warming through carbon sequestration and storage. Mangrove growth helps to intercept pollutants and land derived nutrients before they contaminate deeper water. This is important because nutrient transport from land to estuaries is one of the main agents of ecological change in coastal areas.
What are the Stressors of Deforestation?
It is estimated that at least half of the world’s mangroves have been lost and continue to be destroyed at a rate of about one percent per year The main stressors of mangrove deforestation are:
- Coastal development driven by tourism and growing populations
- Aquaculture, particularly shrimp farming
- Mariculture has been reported as responsible for 50% loss of mangroves in the Philippines and 50-80% in Southeast Asia
- These ponds often have short life spans due to toxin accumulation and sulfide acidification, causing these pond owners to move to a new section of mangrove, furthering the destruction of mangrove forests
- Agriculture run-off carrying pesticides and herbicides
- Man-made changes in tidal or river flow that starve the system of sediment input
- Sea level rise
What are the Side Effects of Deforestation?
Loss of mangroves reduces the amount of carbon sequestration possible and releases carbon stored in the soils, worsening the greenhouse effect. Coastal communities are left vulnerable to tropical storms and hurricanes with less mangrove buffering. Deforested shorelines are subject to greater rates of erosion and are unable to keep pace with sea level rise. Mangroves are one of the world's most threatened tropical ecosystems with global loss exceeding 35%. There is a pattern of reduced mangrove forest area for all countries containing them, especially countries with large mangrove areas. In the Americas, mangrove deforestation is 2,251 km squared per year, which is a higher rate than tropical rainforest deforestation.
What lives in the Mangroves?
Many species of birds roost in the canopy. Shellfish and organisms such as barnacles, oysters, crabs, sponges, and anemones attach themselves to the roots. Species of snakes and crocodiles hunt in mangroves for food. Mangroves provide a nectar sources for bats and honeybees. Juvenile fish find shelter during their vulnerable first weeks.
What are the Common Types of Mangroves?
Red Mangrove Red mangroves grow along the edge of the shoreline where conditions are harshest. They have tangled, reddish prop roots and a gray bark over a dark red wood. Red mangroves grow to heights of up to 80 feet. They have clusters of white flowers that will bloom during the spring months.
Black Mangrove Black mangroves have long horizontal roots with pneumatophores. They have bark that is dark and scaly. They can grow up toheights of 65 feet. Black mangroves also have white flowers that blossom in the spring.
White Mangrove White mangroves occupy higher altitude land than the Red and Black Mangroves. They don't have any visible aerial roots. White mangroves are the least cold tolerant. They grow up to heights of 50 feet. They produce greenish-white flowers in spikes during the spring.
Buttonwood Mangrove Buttonwood mangroves are found in the upland transitional zone. They are sensitive to frost and have flower heads that have button-like appearance that grow in branched clusters, forming a cone-like fruit.
How Are They Linked to Coral Reefs?
Mangroves are important to coral reefs because they balance nutrients for neighboring ecosystems such as coral reefs and sea grass beds. Studies show that nearby coral reefs suffer from greater sedimentation when mangroves are removed and can no longer filter the water. In the Caribbean, mangroves have a strong influence on local fish populations. For example, the largest herbivorous fish in the Atlantic, Scarus guacamaia (rainbow parrotfish), is dependent on mangroves and has become locally extinct when they are gone. A lower amount of herbivores in a reef system will cause reefs to become less resilient to algal overgrowth. In a study in Belize comparing mangrove-scarce reefs to mangrove-rich reefs, the biomass of nearly every fish studied was much greater in the mangrove-rich areas. The biomass of the blue striped grunt on patch reefs in the mangrove-rich area increased by 2667%. The biomass of all 6 species studied in the patch reefs increased from 191% to 2667% in mangrove-rich areas. Mangroves act as intermediate nursery between seagrass beds and patch reefs.
- Valiela . Mangrove forests: One of the world's threatened major tropical environments. Bioscience. 2001;51:807-815.
- Mumby P. Mangroves enhance the biomass of coral reef fish communities in the Caribbean. Nature (London). 2004-02-05;427:533.