When I first got to Florida in March of 2021, to scope out the area, my husband and I took our first paddleboard tour at Lido Keys. The moment we started venturing into the mangrove tunnels, I felt like I was entering one of Disneyland’s magical boat rides. A combination of Pirates of the Caribbean and Jungle Cruise.
This time, though, we had a private tour with a marine biologist who loved that we were actually interested in learning on this tour despite me warning him that I would be asking a lot of questions because, at the time, I was in the middle of my marine biology diploma with the Centre of Excellence in the UK. He didn’t disappoint and neither did the mangroves. Of course, as soon as we got back to the place we were staying for the month, we bought two inflatables SUP boards so that we could now explore at our leisure, and we surely did…a few times…in several locations, which helped us determine where we actually wanted to live.
WHERE THEY GROW
There are approximately 50 to 110 different species of mangroves found all over the world, though many would agree to settle on there being about 80 species, all of which grow in low-oxygen soil that is made up of fine sediments that are built up by slow-moving water.
Mangroves are considered trees and shrubs that grow in the intertidal zone, which is the area where the ocean meets the land between high and low tides. This area will be underwater during high tide and will be exposed during low tide. They grow only at the tropical and subtropical latitudes, or between 25 degrees north and 25 degrees south of the equator and can’t survive in freezing climates. Yet, with rising temperatures and sea levels, mangroves are expanding farther in either direction of the equator and are moving into the wetlands. They are also the only species of trees that can tolerate saltwater because of their ability to prevent the absorption of salt or are capable of excreting salt through their leaves or special pores, depending on the species. The conditions that Mangroves can live in would quickly kill most plants, making mangroves, extra special.
You can find three types of mangroves in Florida, the Red Mangrove, the Black Mangrove, and the White Mangrove. Identifiable by subtle differences. One way is where you will find them growing. In total, Florida has approximately 470,000 acres of mangroves. Florida has a coastline of 1350 miles, not including the milage of barrier islands, and you can find mangroves mainly growing all along the coast from just above Tampa on the Gulf side and starting just below Jacksonville on the Atlantic side, and growing continuously down to the keys. Just within the Florida Keys National Sanctuary, mangroves cover more than 1800 miles of its shorelines.
ANATOMY OF A MANGROVE
You can tell the difference between the red, black, and white mangroves by their leaf structure, their root system, and their propagules. Mangroves range in height from 6.5′ to 80′ (2-10 meters). The red mangrove can grow up to 6′ (2 meters) within two years and depending on the nutrients available and up to 60′ to 80′ when fully grown. Black mangroves can grow to about 50′ in Florida but can grow up to 65′ in other locations around the world. White mangroves can also grow to heights of 50′.
LEAVES
RED MANGROVES Rhizophora
The leaves on the red mangroves are approximately 5″ inches in length, oblong or oval-shaped, and pointy. The color of their leaves is dark green on top and lighter green on the backside and waxy in texture. The leaves of the Red Mangrove are known as a non-secretor, creating a barrier that can almost completely exclude over 90 percent of salt from seawater from entering their vascular system, allowing the water to move from areas low in salt concentration to areas of high salt concentration through a process known as osmosis. This ability prevents the ocean water from sucking a mangrove dry.
BLACK MANGROVES Avicennia
The leaves on the black mangroves are 3-5′ inches in length, oblong or oval-shaped, and pointy just like the red mangrove. The difference is in the color and function of the leaves. The color of the black mangrove leaves is green and waxy on one side and grayish on the backside. They are known as secretors and can push the salt from the ocean water out through special pores on their leaves, also known as salt glands found within their leaves. When the water evaporates, you can observe salt crystals forming on the leaves’ surface. Some leaves actually store unwanted salt to help balance the salt concentration within their large cells, which hold a large amount of water. This hoarding creates thick and fleshy leaves, also known as succulence.
WHITE MANGROVES Laguncularia
The white mangrove is the smallest of the three species. The leaves on the white mangroves are smaller and round at the ends and approximately 3″ in length. The color is similar to the red mangrove as well. The white mangrove has two glands located at the base of each leaf that can expel salt.
ROOTS
RED MANGROVES Rhizophora
Mangroves are easy to identify by their densely tangled prop root system. Their roots give the visual of trees that are standing in water but there is a reason for this. This prop root system allows the Mangrove to adapt to the rise and fall of tides in addition to slowing the movement of tidal waters, allowing the sand or sediments to settle and build up. The bark of a red mangrove is easy to identify as its coloring has a reddish tone to them. They produce prop roots called knee or arching roots that derive from the trunk, growing vertically and taking a drop downward, giving the appearance that the tree is walking. They also produce drop roots that hang vertically down from their branches. These roots add stability to the tree while allowing the looping or exposed portions to have increased access to air.
BLACK MANGROVES Avicennia
Because the soil that mangroves grow in is lacking in oxygen, unlike most plants that can take oxygen from trapped gasses within the soil, mangroves need to access air. As some of the roots are underground, the mangrove can gain access to oxygen for those roots through cone roots known as pneumatophores or vertical roots, allowing the mangrove to gain access to oxygen, much like a snorkel even when the roots are partially submerged underwater. These pneumatophores have small pores on their surface called lenticels that allow oxygen to be exchanged. These lenticels contain a substance that is hydrophobic or repels water so that when they are submerged during a higher tide, water will not be able to flood the roots. The pneumatophores of certain species can reach up to 10 feet (3 meters) tall, whereas most grow between 8-20″ (20-50 cm).
WHITE MANGROVES Laguncularia
The white mangrove develops peg roots that are similar to the black mangroves’ pneumatophores, except shorter and thicker.
REPRODUCTION
Mangroves reprodouce in a unique way. they are considered viviparous, which means they produce live young, similar to most mammals. So instead of producing seed, like most flowering plants, mangroves produce and release propagules that float away in the water. While the propagule is floating along, it continues to develop for a set period. For red mangroves is an additional 40 days, black mangroves, 14 days, and white mangroves, five days. Once they finish their embryonic development, they hopefully find the right place to take root and spend another period referred to as “stranding”, where the propagule hangs out in the soil before the primary roots emerge and take root. The longest period is 15 days and that is for the red mangrove, the black and white mangrove spend less time in the stranding period.
RED MANGROVES Rhizophora
The propagules that a red mangrove produces are approximately 6″ in length and shaped like a cigar. Mangroves are easy to identify by their densely tangled prop root system. These propagules can be found hanging from the trees all year round.
BLACK MANGROVES Avicennia
The propagules that black mangroves produce are approximately 1″ in size and are shaped similar to a lima bean, slightly long and bean-shaped. The propagule from black mangroves is produced after the flowers come during late summer and early fall.
WHITE MANGROVES Laguncularia
The propagules that a white mangrove produces are very small, measuring less than half an inch. The propagule from the white mangroves produces a month after the flowers are produced.
WHY THEY ARE IMPORTANT
Aside from them being the only trees or shrubs that can survive in saltwater and low-oxygen soil, Mangroves serve several roles that benefit not only other wildlife but us and the planet as well.
Protectors
They are a natural rampart for our shorelines. With increasing storm surges and rising sea levels, mangroves act as natural protection by slowing down the flow and force of winds, water currents, waves, and tides with their tangled root system and winds. These roots also help to hold the soil in place, preventing erosion and the degradation of our coastlines. According to a report by Wetlands International and The Nature Conservancy (UK), every 330 feet (100 meters) of mangrove forest can help to reduce wave height by 66 percent. If you would like to read the report, you can find it here.
Additionally, mangroves can store more than 28 million tons of carbon every year worldwide and just one acre can store 1450 lbs of carbon each year, which is equivalent to driving your car across the united states, three times (9,000 miles). Here in Florida, that means that our 470,000 acres can store approximately 340,750 tons of carbon, each year. Even their fallen leaves contribute to the ecosystem by decomposing when eaten by primary consumers or when colonized by bacteria and protozoans who break it down into organic compounds, minerals, carbon dioxide, and nitrogenous waste.
The Wildlife Within
Mangroves are considered nurseries for many of the world’s shrimp, fish, shellfish, crustaceans, and jellies (jellyfish). Several of Florida’s fish, such as tarpon and snook, find shelter within the mangrove roots as juveniles, providing them a safe place to grow while they head out to forage in the seagrass nearby, heading out to the open water when they become adults. It is estimated that 75 percent of fish that are commercially caught will spend some portion of their lives in mangroves. You can also find baby lemon sharks, spending their first year within the mangrove community.
You can find many species of insects, spiders, snails, snakes, oysters, and barnacles that live within the mangrove community. Around the world, you will also find Bengal tigers, other cats, lizards, and even monkeys who call mangroves home.
Move up from the root system and you will find that mangroves are also rookeries and home to kingfishers, herons, egrets, ibises, cormorants, and many more. Mangroves provide safety for birds who are nesting and serve as a resting place for migratory birds who have set routes.
Threats to their existence
The mangroves here in Florida face habitat loss and changes in freshwater that flows into estuaries. Since the 80s, we have lost 20-30 percent of the mangroves here in Florida, with the potential to lose an additional 1-8 percent each year moving forward. The biggest issues mangroves face are habitat loss due to human practices such as overfishing, land-use changes, coastal development, and agriculture. The rising sea levels and reduced freshwater flow are causing mangroves to move inward toward land, seeking safety. Unfortunately, the rising sea levels, saltwater intrusion, and reduced and poor freshwater flow due to poor water management are causing the peat to collapse. If the peat collapses before the mangroves can take root and become established, the area will transform into open water, changing our coastline, shrinking our estuaries, and displacing all the species that live within the mangrove system. This is currently happening in the everglades.
Each year, approximately 1 percent of the world’s mangroves are lost due to human practices such as overfishing, land-use changes, coastal development, and agriculture. The United Nations Environmental Program estimates that nearly 25 percent of the loss is due to shrimp farming around the world.
Bringing It All Together
As you can see, mangroves aren’t just trees you get the joy of floating past on your kayak or paddleboard trip, it is a wonderland that, if you look closely, you can see is the beginning of a food web and home to 100s of species. So, now when you enter the arched entrance, remember to stop and truly examine the connection between the filtering oysters attached to the mangrove roots, the great white egret hiding in the canopy, or the fish swimming amongst the tangled roots, and think about all you learned here today and just enjoy the working system you are witnessing amongst the enchanting mangroves.
The Greatest question is, what can you do to help protect mangroves? Know the rules about trimming your mangrove. Know when and how much you can trim without causing damage by referring to the FDEP, and keep in mind that the ecosystem is more important than your view. According to conservation.org, the ways you can help is by looking for sustainable alternatives to eating farmed shrimp from mangrove areas and finding local conservation and government organizations near you, that you can support in their efforts to conserve your local mangrove forests. In the end, find ways to coexist with all that makes this planet the home you love. Allowing mangrove forests to disappear doesn’t just affect the mangroves themselves, it affects 100s of lives, theirs and our ecosystem, and potentially lives if our shores can no longer be protected from storms.
If you by chance have more knowledge or insight, please reach out. My goal is accurate information and complete understanding and I will always have questions that I would love clarity on.
Stay Salty and Stay Connected,
Kelley
RESOURCES
- NOAA
- Florida Keys National Marine Sanctuary NOAA
- Ocean Conservancy
- Mangroves and the Plants and Animals that Live There
- Everything You Need to Know About mangroves
- One Tree Planted
- Florida Department of Environmental Protection
- Conservation.org
- South Florida Aquatic Environments
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