Biosphere Solutions & Challenges

Living Sea Walls: Mangrove forests’ importance and potential for smart cities

Salt is a death sentence for many plants, but not for the mangrove. Mangrove trees are at home in the shallow, slow moving waters of tropical and sub-tropical coasts. The leaves and roots excrete or exclude salt, allowing this large group of over 50 species to survive in the intertidal regions of 118 countries. Fine sediments accumulate among their roots and the soil of mangrove forests is rich in organic matter. Prop roots help stabilize the mangroves in the soft, oxygen-poor soils. Once thought of as wasted space and mosquito breeding grounds, the mangrove’s ecosystem services and ecological importance is now understood and can provide a win-win solution for sustainable development.

Mangrove forests are complex, biodiverse ecosystems. Juvenile fish hide amongst the tangle of roots, seeking refuge from predators as they feed and grow rapidly in the warm, calm waters. Mangrove roots are coated with sponges, shrimp, anemones, barnacles, oysters and other molluscs. Crabs scurry along the under and above water roots and up into the leaves above. Resident and migrating birds sing from the trees, feeding, roosting and nesting in the canopy. Snakes and lizards move up the trunks and through the branches. Frogs croak at night. Monkeys, bats, deer, tigers, crocodiles and other mammals, amphibians and reptiles occupy different mangrove forests around the world.

World map mangrove distribution.jpg

“World map mangrove distribution” by ChandraGiri – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

Mangroves are among the most carbon dense forests in the world. Leaves and branches fall into the water, accumulate and slowly decay. Bacteria break down some of the detritus and release nutrients to marine food webs. Much of the material is buried and amasses in deep, carbon-rich soils. Recent research has suggested that mangroves sequester approximately 1.5 metric tons of carbon per hectare every year, or 3.7 pounds per acre every day. The majority if this carbon, 50-98% depending on the location, is stored in the soils. This storage makes mangroves important players for longer-term removal of carbon from the atmosphere. If mangroves are removed, the stored carbon can be released back into the atmosphere.

Bali Barat mangroves.jpg

“Bali Barat mangroves” by Ron from Nieuwegein / South Moreton Oxfordshire, Netherlands / UK – flickr: Taman Nasional Bali Barat (West Bali National Park). Licensed under CC BY-SA 2.0 via Wikimedia Commons.

Carbon sequestration and biodiversity are all very nice, some people say, but what do these forests have to do with my daily life? Leaving mangrove forests intact can protect cities and other inland areas from extreme weather. The dense roots trap sediments, building coastline and making it more stable and resistant to erosion (as well as preventing sediments from clouding coral reefs). Like other wetlands, mangroves act as horizontal barriers that can absorb and disperse tidal surges, wave and storm impacts. Research found that mangroves can reduce wave height by 66% and the destructive forces of a tsunami by up to 90%. These living barriers are more effective and less expensive than man-made structures built to protect coastlines. This protection saves money on rebuilding costs and could save lives.

Mangroves are constantly being threatened by deforestation, aquaculture, pollution, rising sea level and coastal development. Mangrove forests have declined worldwide ~50% in the last 50 years and deforestation continues as you are reading this. Some studies estimate that with current practices mangroves may functionally disappear in as little as 100 years. This loss is a death sentence to many of the endangered species that call mangrove forests home.

ShrimpFarming Honduras L7 1987-99.jpg

Mangroves lost to development, “ShrimpFarming Honduras L7 1987-99,” Jesse Allen, NASA Earth Observatory, data: University of Maryland’s Global Land Cover Facility.

Deforestation also impacts humans—threatening fisheries, coastal buildings and increasing carbon emissions in a world struggling to get control over climate change. Deforestation of mangroves contributes to roughly 10% of the carbon emissions from deforestation and only occupies 0.7% of the tropical forest area. Sea walls and other man-made barriers are expensive and fail. Thousands of people rely on mangroves for their food and income. Mangroves provide sources of food, natural resources and income. The wood is harvested and sold. Local people harvest shellfish, crab, shrimp and fish from mangroves to feed their families. Most commercially important fish in the tropics spend part of their life cycle (often as juveniles) living in mangroves. If mangroves are lost, the fisheries will suffer causing job losses and food shortages.

Shielding coastal areas from ocean and storm damage is a crucial component of developing coastal cities. Protecting and restoring mangroves is a promising eco-friendly solution. Increased education and political will is needed to stop mangrove destruction and capitalize on the inherent ecosystem services that mangroves offer.

 

The Ecocity World Summit 2017 will take place in Abu Dhabi, UAE. Abu Dhabi is a coastal city home to expansive mangrove forests. As they seek to safeguard their city from rising ocean levels and protect the natural resources of their mangroves. EWS 2017 will be sure to include many necessary discussions and workshops on preserving these “living sea walls”. Find out more about the Summit.

About the author

Sierra Stevens McGeever

Sierra Stevens McGeever

Sierra Joy Stevens-McGeever received her master’s degree from Scripps Institution of Oceanography, UC San Diego in marine biology. Sierra is passionate about environmental conservation and is pursuing a career in science education, communication and science based travel writing. To read more of her work and get information about her upcoming book, visit SierraStevensMcGeever.com.

Leave a Comment