One answer to human cravings for living at the shore has always been “filling the swamps.” In many areas of the world, shoreline wetlands of mangroves thrive. These plants live in a world of high salinity, tidal inundation and storms, and oxygen depletion—conditions fatal to most other vegetable species. Because people perceive swampy ecosystems as smelly, often a bit dangerous, obstructive of views, and relatively easy to convert to “productive” land uses, we have not historically given much thought to the consequences of meddling with the lowly mangrove.
We’ve been wiping out mangroves for a long time. Early agricultural societies across the world drained and filled the coastal margins to increase their holdings of arable land. That practice continues, along with industrial and residential destruction of coastal habitat in the name of “reclamation.” For instance, the development of Miami Beach, once a mangrove island off the coast of Florida, turned it into a fabulous coastal resort. We’re only beginning to find out that in the long run, indiscriminate decimation of coastal forests has a hand in shifting the very climate that created them.
Land plants that live in the shallow tidal seawater of the world’s coasts, mangroves create unique ecosystems in tropical and subtropical regions of the world. Their densest populations grow between 5° N and 5° S latitude. Over 118 countries and territories harbor mangrove forests (see map). Asia has 40%, followed by Africa (21%), North and Central America (15%), the islands of Oceania (12%), and South America (11%).
With roots submerged in water, mangrove shrubs and trees thrive in hot, muddy, salty conditions that would quickly kill most other plants. Although mangrove forests feature at most three or four of the tree species, they comprise one of the world’s most threatened biomes. Like tropical rainforests (which contain thousands of different tree species), the simple mangroves create a habitat that results in one of the the most productive and biologically complex ecosystems on Earth. A stunning variety of codependent organisms, including many that are unique, call mangroves home.
Mangrove areas represent less than 2% of the ocean’s surface—but they generate about 20% of global marine production. Their ecosystems supply humans with seafood, fruits, medicines, fiber, and wood. Says the Ocean Portal of the Smithsonian Institution:
“Dive underwater, and a mangrove’s smooth brown roots suddenly take on the textures and hues of the multitude of marine organisms clinging to its bark. Anchored in mud, the roots are literally coated with creatures—barnacles, oysters, crabs, sponges, anemones, and much, much more. The dense, intertwining roots serve as nurseries for many colorful coral reef fishes and for fishes valued by fishermen. Juvenile fish find shelter there during their first vulnerable weeks of life, before swimming off to deeper, more dangerous waters.”
The filtration systems of the mangroves isolate and concentrate marine salt. Their complex roots stabilize the soil, slow currents, and hold the plants upright in the shifting sediments where land and water meet. The mangroves build new land. In this lifestyle begins their doom.
The greatest threat to mangrove forests is development by humans. Since 1980, at least 35% of the world’s mangrove ecosystems have disappeared. In countries like India, the Philippines, and Vietnam, the number is more like 50%. The rate of loss in the 21st century is higher for mangroves than for the tropical rainforests.
Looking at the fate of mangroves in the United States, we should consider Florida first because of estimates that people have slain up to 90% of the forest population there. A publication from the Florida Bar Association states:
“Mangroves in Florida have been degraded by poorly conceived development that failed to consider losses of natural productivity. The greatest threat comes from construction activities.”
During the late 1800s and in the first half of the 1900s, Florida’s public policy favored the development of coastal areas. Pioneers drained cypress swamps, mangrove areas, and marshlands, filled in low-lying and submerged lands, channelized the rivers and streams, and began to regulate lakes, rivers, and other water bodies. As well as development itself, associated activities like dredging, using herbicides, increasing wastewater runoff, and spreading pollution are fatal to shoreline ecosystems.
Development has killed off about 90% of the state’s rich mangrove habitat, according to some estimates. Not only wiped out for residential use and tourism (hotels and associated facilities, eco-adventure, water sports), the resource has diminished because of aquaculture (tilapia), and associated channel changes work to destroy nearby coral reefs.
Heading into the 21st century, the state’s public policy has shifted, with more regulation and limits in environmentally sensitive areas. But continued urban development threatens even the remaining mangrove habitat along Florida’s coasts. Millions of tourists visit each year. Large numbers of people move south every day: the state is fourth in number of relocations, behind only California, New York, and Texas in numbers.
(Part Two of this story, which describes how mangroves protect us—even against the impersonal forces of climate change—will follow shortly.)