Laura Geselbracht’s home backs onto a small canal just off the Middle River, not far from George English Park. It’s not exactly the swampy wilds of backcountry Florida, but from her backyard, she can see all sorts of wildlife in the air and in the water. Herons swoop and dive, attracted by the many kinds of fish that hang out at the end of the canal. That marine rush hour, Geselbracht says, is no accident.
“I have mangroves in my backyard, and we don’t have a seawall,” she says. “That’s one of the reasons we picked this property.”
It makes for a fun meetup with nature, but for Geselbracht, it’s also an at-home example of the work she does. As a senior marine scientist for the Florida chapter of the Nature Conservancy, she has researched the benefits offered by the plant life that flourishes where the ocean meets the Florida land. Mangroves provide habitats for a diverse collection of marine life, including just-hatched fish that will eventually move into open water and become some of the most sought-after by fishermen and diners. But they offer benefits for humans that go beyond our ability to order a grouper sandwich. They and other natural barriers such as dunes and salt marshes help protect coastal areas from hurricane storm surges as well as the creeping threat of sea-level rise. When it comes to hurricanes, Geselbracht and her colleagues can even put a number on it.
In 2019 the Nature Conservancy teamed with the University of California-Santa Cruz and Risk Management Solutions, a private company that works closely with the insurance industry, to study the risk of a Hurricane Irma-type storm.
“When mangroves are not present, we would have had $1.5b more in damages to our urban infrastructure,” Geselbracht says. “In Irma, most of the storm surge damages occurred in Collier County and Miami-Dade County. Both of those areas have some pretty substantial mangrove forests. The more extensive the width of the mangrove forest, the more protective it is.”
In other words, mangroves slow the penetration of water, stopping it from reaching as far inland. Using their sophisticated modeling program, Risk Management Solutions estimated mangroves’ value at $7,500 per hectare. And as an added bonus, Geselbracht notes, they’re cheap. Planting mangroves is a lot easier and less costly than surrounding everything in taller and taller seawalls.
“They do multiple duties,” she says. “They provide dozens of services to us. The very modest amount of money we put into management delivers dividends well in excess of any cost associated with them.”
Preservation, Eventually
University of Miami biology professor Kathleen Sullivan Sealey has done similar research and in 2018 co-authored the book Will Miami Survive? The Dynamic Interplay between Floods and Finance. For her, mangroves are an economic no-brainer.
“It’s civically responsible,” she says. “It’s the biggest bang for our buck; it’s a win-win situation.”
That said, she cautions against congratulating ourselves for preserving and planting the number of mangroves we have in developed areas.
“I’m not saying (planting and preservation is) bad; I’m glad to see it,” she says. “But let’s not delude ourselves. We need hectares of mangroves if we’re going to stabilize the shoreline.”
In recent decades, the state of Florida has made it harder to significantly lessen the number of mangroves. According to the Florida Department of Environmental Protection, Florida now has 469,000 acres of mangrove forest, down from 555,000 in 1996, the year the Florida legislature passed the Mangrove Trimming and Preservation Act. That piece of legislation set out fairly strict guidelines for when and how property owners may trim or remove mangroves – but of course, by the mid-1990s, the trend of replacing mangroves with seawalls already had more than a half-century head start.
While removing mangroves in Florida is hard, actively adding more has been a hit-and-miss affair. Sealey notes that some mangroves were planted after another piece of 1990s legislation, 1994’s Everglades Forever Act. Miami-Dade County, for example, had to show that it was improving the nutrient quality of northern Biscayne Bay. Mangroves are natural filters of nutrients.
“Those mangroves went in – they took all the fill islands,” Sealey says. “This happened to keep the county from a lawsuit.”
Nobody claims mangroves fix everything. The existential threat South Florida faces from both hurricanes and sea-level rise is bigger than any one magic bullet; any potential remedy must be big, broad and multifaceted. But in any potential solution, bringing more of the land back to nature and adding natural barriers like mangroves will undoubtedly play a role. And again, when you look at the money that goes into maintaining and rebuilding seawalls, a solution that gets planted once and grows on its own might start to sound better.
“When you think of something like a green infrastructure, they are repairing themselves naturally,” says Ashley Marranzino, a research assistant at Nova Southeastern University, where she will soon start PhD work. “You don’t have to do anything, and they’re going to (give you) all these benefits. They’re going to suck out all this carbon for us; they’re going to create all this glorious habitat.”
Fish & Friends
“Mangrove” can conjure up different images depending on where in the world you are, but for Floridians, there’s one big one. As many as 50 species of mangrove exist worldwide, and three live in Florida. “You talk about mangroves and everybody thinks of the red mangrove and then there’s the black mangrove and the white mangrove,” naturalist and author Roger Hammer says.
Of those, the red mangrove, which grows at the water’s edge with a large exposed root system, is the one most Floridians probably think of.
“That’s the one that’s most important,” Hammer says. “It holds the unstable land – helps support the tree by those prop roots in a low-oxygen habitat that other trees just can’t deal with.”
That support network also provides a stable home for many young fish and other marine life.
“Animals really like to have something to hide under, to stick themselves onto,” Marranzino says. “They like structure.” The nooks and crannies of mangrove prop roots are perfect for that. “You’re going to see a lot of species popping up.”
Oysters, snails and other smaller animals are attracted to mangroves. And where they are smaller animals, there are hungry larger animals. Among them are young versions of some of Florida’s tastiest and most commercially important fish such as snapper, grouper and snook.
“All of the fish that you like to fish for start their life cycle in the mangroves,” Sealey says. Mangroves are places that allow those fish to both be predators and hide from predators.
“Because the support structure is there,” Marranzino says, “everything else can live there.”
That structure even holds soils and sediment in place, which means it doesn’t wash out into the ocean. “The first place all that sediment goes is to the corals, and it smothers the corals.
“I like to think of it almost like the human body. Maybe you’re overweight and you have high blood pressure. You can’t just take a pill and get everything in your body back to normal right away.”
You might have to take medicine, change your diet, exercise and make lots of different changes. “The same thing happens for our ecosystem. If you do one good thing for our ecosystem, it can have cascading effects that are beneficial.”
Geselbracht, the scientist who can see the world of mangroves at work from her Fort Lauderdale backyard, notes that you see this even in spaces like hers – urban areas where nature has retaken a small space.
“There are those pockets,” she says. “If we put more attention to re-creating the conditions so that some of our natural habitats could take hold … the species move right in. We still have some of those species in our somewhat degraded water systems. Nature is very persistent.”
She cites Palm Beach County, where in wider areas of the Intracoastal they’ve added mangrove islands.
“Over just a few short years the mangroves have grown tremendously, and they’ve seen bird life that they haven’t seen for 20 years,” she says. “With a little attention, we could see some big changes in the amount of fish, the amount of bird life and a healthier ecosystem.
“The benefits of keeping our natural systems intact and healthy is that they sequester carbon. The other thing they do is, with each one-foot rise in sea level, storm surge can penetrate another 100 feet inland… (With mangroves) you can help reduce the amount surge penetrates inland.”
When the Water Comes
As with most conversations about South Florida ecosystems and development, talk about mangroves must inevitably get around to that. The big topic. The rising seas.
Sealey has spent much of her career studying this – and a career spent studying sea-level rise does not necessarily beget a cheerful outlook on it. In the long term, she says, “we have to have strategies in which we can keep coastal areas financially viable until they’re not, and then you have to strategically retreat.”
This is personal for Sealey; more than 20 years ago, she sold the Key Largo house she inherited from her grandparents, who had owned it since 1948. A bidding war broke out for the house but even as others wanted it, Sealey wasn’t dissuaded from selling it. Even in 1998, she knew the science.
“Three feet, eight inches – that’s why I sold it. It was three feet, eight inches from high tide. People in the Keys live in the land of denial.”
The medium-range strategy needs to revolve around preventing extreme property loss in time to do the planned retreat, she says. “Anybody that’s not accepting that is trying to sell you a condo on Miami Beach.”
Natural barriers such as mangroves can make up a big part of that plan.
“I think it’s a good intermediate timeframe solution,” she says.
And it’s not a solution that necessarily requires massive, wholesale giving back of oceanfront lands to their natural state – although in the longer term, that’s exactly what could happen. Sealey says hectares of mangroves will be needed to fully stabilize the shoreline, but more gradual improvements are possible with less.
“You’re going to start getting some of those effects as soon as you start letting nature back into an area,” Marranzino, the NSU research assistant, says. “Obviously a larger area would be the best, but I don’t by any means think it’s an all-or-nothing benefit.”
If lots of waterfront homeowners sacrificed a bit of property on land and water, it could make for better overall outcomes. (In addition to mangroves instead of seawall, it would also require taking four or five meters of yard running up to the water and putting in a berm and swale.)
“There are ways where you would have to A) give up some of your lawn and B) give up some of your dock access,” Sealey says. “If you got everybody to do that, you could A) improve water quality, B) improve wildlife quality and diversity, and C) begin to stabilize a little bit of the impacts of the floodwater in the canals.
“It may be something that if a bunch of people did it, it could be a mechanism (by which) you could get insurance for a group of houses.”
Still though, mangroves and other natural barriers aren’t always welcomed by all. “Everybody wants that ocean view,” Roger Hammer says, “and that’s why people want mangroves pruned.”
That’s why some of the people who study them are trying to get the word out about the benefits they offer – including the cold hard cash benefits.
“I think attitudes are changing,” Geselbracht says. “We’ve done a lot of work to quantify and value the benefit that nature gives to promote the protection of our natural resources.”
Perhaps sober analysis of risks and costs will change more minds. Although in Florida, focus-sharpening weather conditions are never far away, either.
“Maybe,” Sealey says, “we’ll shift after another disaster.”
