Until about 2 years ago, I didn’t even know what a mangrove tree was. Then I took a course in Marine Ecology and was introduced to this slightly odd but fascinating species of tree. At first glance they might not look overly impressive with their gnarled branches and an aerial root system that allows them to draw oxygen from the surrounding air. However, the vital role that mangrove forests play in maintaining healthy coastal ecosystems and mitigating climate change through carbon sequestration can’t be overstated. Unfortunately, though, mangrove forests have been deforested at an alarming rate in the past few decades. Despite this, there is growing optimism that through science, education, outreach, and restoration projects, these species will reestablish their former habitat and thus be able to provide the surfeit of positive ecosystem services that they offer to both aquatic and terrestrial organisms.
MANGROVES: WHAT ARE THEY
Mangroves aren’t actually the biggest fans of salt water, but yet they have brilliantly adapted themselves to live in it. For instance, according to Newfound Harbor Marine Institute mangroves are facultative halophytes and this means salt water is not a physical requirement for growth. In fact, it is actually tidal fluctuation that indirectly gives them a great advantage over their competitors. Most species can’t cope with the alternating periods of wet and dry caused by the daily incoming and outgoing tides, in addition to the waterlogged, anaerobic soils they live in. Yet through some brilliant adaptations, mangroves thrive in these seemingly inhospitable conditions. For example, mangroves need freshwater to survive and so they either exclude salt from entering their system or expel it through their leaves, roots, or branches. According to Mangrove Action Project, mangroves that exclude salt do it so effectively that a human could safely drink the water from a cut root, even though the tree itself rests in saline soil! Furthermore, depending on the species, they produce either prop roots or pneumatophores, which let oxygen diffuse into the plant and then into their underground plant roots. The lengths this species has gone to in order to survive and thrive in these unique living environments is quite remarkable.
THE ECOSYSTEM SERVICES THEY PROVIDE
The list of beneficial ecosystem services that mangroves offer is lengthy. Arguably the most notable service is the critical habitat these forests provide to a plethora of organisms. According to the U.S. Fish and Wildlife Service, approximately 55 species of mangrove exist worldwide and these forests are home to both aquatic and terrestrial organisms. For example, depending on the location one could find manatees, sea turtles, fishing cats, and monitor lizards amongst many other species. They are also nursery grounds for juvenile fish, crabs, mollusks, and other invertebrates, and their root systems shelter these organisms from predators. Conversely, this biodiverse habitat draws in numerous bird species, which feed on these smaller organisms. Additionally, mangroves filter and trap sediment from run-off and river water before it enters adjacent ecosystems. This lessens the turbidity of the water, which lets more sunlight in, and it promotes soil accretion, which stabilizes and strengthens coastal environments making them more resistant to extreme storm events like hurricanes. This is good news for coastal communities, since the mangrove forests help mitigate the wave action of storms, reduce flooding, and thus lessen the destructive impact of storms. Furthermore, research shows that mangroves are one of the most efficient and effective trees at sequestering carbon. The article Carbon Sequestration in Mangrove Forests details that although mangroves only account for approximately 1% of carbon sequestration by the world’s forests, in terms of coastal habitats they account for 14% of carbon sequestration by the global ocean. Lastly, the aforementioned vast abundance of biodiversity that mangroves support provides a boon for the fishing industry, which can boost local economies and also be used as a means to highlight why the preservation and sustainable management of mangrove forests is also crucial for humans.
Despite the numerous benefits of mangroves, they have suffered intense deforestation in the past few decades. They have been cleared to make room for agriculture, aquaculture, urban expansion, and the palm oil industry amongst others. Sadly, this anthropogenic pressure has led to the removal of 32 million hectares of mangrove forests, which is approximately half of the worldwide total according to the International Union for Conservation. As with most unsustainable practices, the driving force of mangrove deforestation has been money, convenience, and the underestimation of the short, and more importantly, long term value of them. Not to make an excuse for their decimation, but before research highlighted their ecological importance, one could understand in some cases why people looked at these mucky places as nuisance areas that could be put to better use. For instance, Robin Lewis, an ichthyologist-turned-wetland scientist who now restores mangroves around the world says that, “Mangroves prior to 1970 were generally considered to be mosquito-infested swamps that nobody needed really to worry about, and if you wanted to destroy them, that was okay.” However, as knowledge on them has increased, there has been a concerted effort by scientists like Robin as well as activists across the globe to protect current mangrove forests and restore former ones.
MANGROVE RESTORATION EFFORTS
It is surprisingly a bit more complicated to successfully restore decimated mangrove areas than one might think. It is not as simple as planting a monoculture of mangroves in a deforested area and the rest will work itself out. In fact, there is a significant amount of thorough planning that needs to be undertaken prior to any restoration project. For example, the hydrology of an area plays a paramount role in determining whether or not mangroves can and likely will successfully establish there. The aforementioned Robin Lewis has spent many decades studying and working with mangroves, and it was during this time that he deduced that mangroves should be planted in areas that are conducive to their very narrow wet/dry ratio of which the tides control. For instance, during one of his studies in Tampa Bay he concluded that a ratio of 30% of the time wet and 70% of the time dry was the almost perfect for mangroves to thrive. Even more astounding is that in one of his successful studies, they planted 0 mangrove trees. The only thing they altered was the slope of the intertidal area so that it would create what he thought to be the perfect wet/dry ratio for mangroves. In turn, mangrove seeds took hold, produced seedlings, and created a new and far more diverse mangrove ecosystem! This research has guided a multitude of restoration projects in the United States and 25 other countries as well, and I personally am fascinated by the profound effect that any one passionate individual can have on the environment. However, this is not to say that all restoration projects should let mangroves recolonize on their own. Each site is different, and what is certainly known is that hydrology and even the types of species are the two most important factors to be considered before commencing any project. There are many people like Robin Lewis and organizations like Mangrove Ghana and Mangrove Action Project that dedicate their time to restoring our environment, and I would highly recommend looking further into their work. Hopefully through their efforts, in addition to countless others throughout the globe, mangrove ecosystems will begin to regain their former coastal strongholds.
What steps can you take to raise awareness of the importance of degraded coastal ecosystems like that of the mangrove?
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