Mangroves protect coastlines, provide wildlife habitat and are a huge carbon sink. For Bermuda to lose what is left would be an environmental disaster. In spite of being a protected species, mangroves are threatened by rising sea levels, hurricanes and human pollution. We examine why they are so crucial and look at what we can do to help them thrive.
When an undersea earthquake sent 100-foot-high waves barrelling to the coastlines of countries bordering the Indian Ocean on December 26, 2004, it left an appalling human tragedy in its wake.
In the years leading up to this tragedy, many of the hardest hit areas had cleared away their mangroves to make way for shrimp farms and coastal development. In the aftermath, a World Wildlife Fund study published in Science Daily, found that “areas buffered by coastal forests, like mangroves, were strikingly less damaged by the 2004 tsunami than areas without tree vegetation.”
Mangroves don’t just provide a buffer from tidal waves. They also provide protection to coastlines from the wind and surge that comes with hurricanes—something Bermudians are all too familiar with, and one of many reasons why our island’s environmentalists, concerned citizens and community groups are taking action to protect and restore these humble trees.
- Bermuda’s Mangroves
- Bermuda is home to two species of mangrove, red and black, both of which are found in sheltered areas such as Hungry Bay, Walsingham Pond, Foot of the Lane and Paget Marsh. Ironically, for a tree that protects land from wind and waves, mangroves need calm, protected water in order to thrive. They live in the “intertidal” zone between land and sea, with the red mangroves growing in front, at the seaward edge of the forest, and the black mangroves behind. They are the only trees in the world that grow in salt water and they survive by extracting freshwater and then excreting the salt through their leaves.
The red mangroves are recognisable by their long, strong “prop roots,” which are particularly visible when the tide is out. In contrast, the black mangroves have more shallow roots, from which grow hundreds of pneumatophores, which act like, and don’t look dissimilar to, snorkels sticking out above the surface of the water. These absorb oxygen from the air.
- Natural Solution to Natural Disasters
- As our climate changes, Bermuda is most at threat from rising sea levels and stronger storms, and the island’s mangroves can provide us with some level of protection from both.
“They can help dissipate waves and to some extent wind energy as well,” explains Dr Annie Glasspool, vice president at Bermuda Environmental Consulting. “They can also prevent erosion because they’re encouraging deposition of soils.”
While this is all well and good, where mangroves really earn their keep is by capturing and storing huge amounts of carbon. “Estimates suggest they can capture and store four to five times more than typical tropical forests,” she says. Given that one of the primary causes for sea level rise is rising temperatures due to rising carbon dioxide levels and other gases in the atmosphere, this carbon capture, or “blue carbon,” is vital. Blue carbon is a term for any carbon captured by the ocean or coastal ecosystems. “What they do is basically build up peat soil and that’s where a lot of the carbon is stored,” continues Dr Glasspool. This can remain stored for centuries. Peat soil is built using fallen leaves and other “breakdown materials.” As the peat builds up, so do the mangroves, giving them protection from slow sea level rise.
Mangroves don’t just protect coastlines. They also help the surrounding marine habitat by “cleaning” the water and it is for this reason that mangroves were planted around the perimeter of the pond in front of the new airport. “You may have run off from the land, and to some extent, they will filter that water before it goes out to the ocean,” says Dr Glasspool. “It might go out to the seagrasses and to the corals.”
- Wildlife Habitat
- Mangroves help the coral reefs thrive in another way too. “A lot of our reef fish will use them as a nursery area,” says Dr Glasspool. “That may be parrot fish, or snappers, even small groupers, so there’s lots of nutrition in them. Lots of things grow on the roots. They’re an important nursery area for juvenile fish.”
As well as juvenile fish, Bermuda’s mangroves provide food and protection for a mass of other sea and bird life including giant land crabs, land hermit crabs, mangrove oysters, young lobsters, upside-down jellyfish, yellow-crowned night herons, green herons and a number of migratory birds.
- Mangrove Decline
- Up until relatively recently, the number of mangrove forests around the world, including in Bermuda, had been in decline. Dr Glasspool estimates that Bermuda had around 62 acres of mangrove forests before human development began and by the year 2000, that was down to around 45 acres. Both human and natural factors are to blame for this reduction.
Human factors include boats and ocean trash as well as clearance to develop coastline before mangroves became protected. People have been known to tie up their boats among the mangroves to protect them during a hurricane, for example, but that boat will turn into a battering ram against the trees. Ocean trash also collects in the mangrove forests. “The really big ships’ ropes will come into Hungry Bay,” says Dr Glasspool. “I’ve seen them also in Blue Hole Park. That’s hugely destructive. It’s pounding against them.”
Despite their ability to provide some protection again storms, mangroves themselves have also fallen victim to hurricane damage. Hurricane Fabian damaged the natural rock barrier protecting Hungry Bay’s mangroves and took out most of the Blue Hole mangrove forest as well. Even though their peat system raises mangroves up, they are still vulnerable to sea level rise because of the way they absorb oxygen through their roots. If sea level rises too high, too quickly, the roots will be “drowned.”
Should mangrove forests recede or disappear completely, it’s not just the coastline that’s vulnerable. It’s all the blue carbon as well. Destruction of mangrove ecosystems releases the stored carbon back into the atmosphere, further exacerbating climate change.
- Restoration and Protection
- The good news, however, is that as more people, communities and governments accept the indisputable value of mangroves, more worldwide initiatives are underway to protect existing forests and, where possible, restore them to their former glory. In Bermuda, no initiative embodies this determination more than the formation of the Hungry Bay Restoration Committee, a group of area residents and interested people including engineers, architects, environmental consultants, such as Dr Glasspool, marine scientists and contractors who have come together to give their time and expertise to restore the Hungry Bay mangroves, which have been in decline since Fabian breached the aforementioned rock barrier in 2003. Together they have raised the money and received planning permission to restore the barrier and have already planted hundreds of mangrove propagules.
In addition to Hungry Bay, mangrove restoration projects are also underway at Lagoon Park in Sandys and on Trunk Island. These have received financial support from Rotary International and locally based international business respectively. One of those involved in these restoration initiatives is Dr Robbie Smith, curator of the Natural History Museum at the Aquarium. He explained that up until now, mangrove restoration had been on an ad hoc basis, with the Department for Environment and Natural Resources (DENR) providing licensing and some oversight to community initiatives, but work has now begun on a more formal restoration plan. Mangroves also have a place in the Bermuda Ocean Prosperity Programme’s Draft Marine Spatial Plan. “It’s a peculiar set of circumstances that brought all these issues together,” he explains. “Now we have to think more carefully about, if we have all this enthusiasm from groups like Rotary or citizens that live around Hungry Bay, how do we go forward with that. How do we coordinate it?”
In Bermuda, mangroves are a protected species, making it illegal to damage or disturb them or their propagules; however, should people wish to be part of a planting group, they can apply for a licence from DENR. “The restoration plan has to look at, ‘how do we be supportive of people propagating mangroves,’” adds Dr Smith. Restoring mangroves isn’t as simple as planting the propagules and leaving them to grow. They must be in a suitable area, and they need to be nurtured until mature enough to withstand their natural environment. In Lagoon Park, for example, the area had to be cleared of invasive species first. “Brazil peppers specifically were going to be limiting for the mangroves to continue growing in that space,” he explains. You must also take rising sea level into account. “We have to look ahead and pick sites where, as sea level rises, mangroves are going to be able to survive or flourish. And that was one of the reasons we picked Lagoon Park, because we can see where sea levels are going to go and it’s going to get wetter in some places, but it’s not going to compromise the adjacent areas.”
The Trunk Island mangrove planting was a different scenario. Dr Smith doesn’t know if mangroves ever existed there; however, they provided a natural solution to an erosion problem with the added bonus of enhancing this “living classroom.” “We looked at that site and said, ‘if we didn’t want to have that erosion, we have to stabilise it in some way. We came up with this idea of creating a slightly larger sea wall that allowed us to think about taking that site, adding soil and sand to it, so we could plant mangroves that would stabilise that coast line and provide an opportunity for kids to see what a mangrove is supposed to look like.
“We don’t have clear records that there were mangroves there, but we saw one problem and created an opportunity to add mangroves because, at a broad level, we’ve lost most of our mangroves through coastal development over the last 400 years, so every little piece is beneficial.”
- What can we do to help restore Bermuda’s mangroves?
- Not tying up our boats near them and helping to clean up beach and ocean trash is a great start, but also just talking about it. “Just spreading awareness,” says Dr Smith. “We all have to work together and whether you do it next week, next month, next decade, start teaching your kids to think about the environment.”
Dr Glasspool agrees that working together is a positive way to help. “I think we’re all struggling with ‘what can I do about climate change?’ This feels like something we can do that is positive. I think we’re going to see more community driven initiatives. We don’t feel quite so helpless when we can actually do something.”