MANGROVES ARE ‘GREEN LUNGS’ THAT BREATHE LIFE INTO CITIES AND SHORES
▶ Natural ‘ecosystem engineers’ support wildlife, act as erosion breakwaters and clean up our air, Louise Burke writes
Mangroves are estimated to cover more than 60 hectares of the UAE’s coastline, acting as “green lungs” for big cities such as Abu Dhabi and Dubai, while also providing a habitat for wildlife and recreation grounds for people.
Most of us would regard mangroves as a beautiful element of our landscape – a natural fringe to our developed urban environment, where flamingos gather and fish and crustaceans proliferate.
But how much do we really know about the complexity of our mangrove ecosystems?
Two biologists from New York University Abu Dhabi, Shady Amin, assistant professor of biology, and Guillermo Friis, an evolutionary biologist, help us understand the incredible ecosystems on our doorstep.
Mangroves are woody plants that inhabit the intertidal zones of tropical and subtropical coasts.
They are highly recognisable from their visible root systems which can give them the strange impression of being planted upside-down.
This is the result of adaptations developed to survive in harsh environments, including high temperatures, high salinity and intense UV exposure.
Mangroves can accumulate salt in their roots and excrete it through their leaves. Their seeds germinate before they fall from the parent tree, which increases their chances of successful rooting in tidal environments.
Dr Friis says the salinity and temperature variability that mangroves thrive in are particularly extreme in the Arabian Gulf.
“Mangroves are the only evergreen forest in the Gulf and their unique ability to survive in this habitat makes them what we know as an ‘ecosystem engineer’, providing shelter and foraging for many marine and terrestrial species,” he says. “In addition, different biological, chemical and physical processes connect mangroves to adjacent ecosystems including coral reefs or seagrass meadows.”
Mangroves are photosynthetic organisms that can convert sunlight into energy. This is used to transform the carbon from carbon dioxide gas produced by burning fossil fuels, into organic carbon. This feeds the plants themselves and the entire ecosystem they exist in.
They also provide a habitat for many organisms including
oysters, phytoplankton, sponges and crabs.
This relationship is symbiotic, with mangroves depending upon the organisms they support to help them in return.
“For example, mangroves cannot survive without microbes living around their roots, just like we cannot survive without microbes in our gut that help us digest food,” Dr Amin says.
“One of the main things microbes provide for mangroves is nitrogen, a required element to make DNA and proteins.
“For example, some microbes are symbiotic with mangroves and are able to convert nitrogen gas into ammonia, the main constituent of agricultural fertilisers. This ammonia then allows mangroves to grow just like they do with trees.”
Other types of microbes in the mangrove ecosystem include sulphate-reducing bacteria that thrive in the oxygen-deprived environment, and organisms that produce methane.
“No organism on Earth lives in isolation and all these microbes, the mangrove and other higher organisms like algae and crabs, are interacting with each other,” Dr Amin says. “It is these interactions that truly form a healthy ecosystem”.
Mangrove forests support a high level of biodiversity and the mangroves in the UAE are no exception.
“To name a few of the species we can find, in the UAE there are reports of six different families of crabs, 49 mollusc species including clams and marine snails, examples of both resident and migratory birds such as the Western Reef Heron or the Greater Flamingo and numerous roving fish populations,” Dr Friis said.
“If we are lucky, we can also find ray fishes hiding under the sand, or even blacktip sharks that occasionally enter mangrove swamps.
“There are also large communities of fungi, algae and bacteria associated with the mangrove ecosystems.”
However, Dr Friis said there were relatively few studies documenting UAE mangrove wildlife and further research was needed.
Mangroves also protect coastal areas from erosion by creating a buffer zone, filtering and pacifying tidal flows. They can even reduce the damage and loss of life caused by tsunamis.
“For the UAE and with increasing sea-level rise, mangroves are essential because I expect they will play an important role in protecting our shorelines from erosion,” Dr Amin says.
Historically, mangroves also provided fodder for livestock and served as an important building material in pre-oil times.
On top of all of these benefits, mangroves provide recreational grounds, such as the Mangrove National Park in Abu Dhabi.
“They are part of the heritage of the country, and one to be protected,” Dr Friis says.
A lesser-known potential benefit of mangroves lies in the microbes they coexist with. At NYUAD, scientists are working to isolate and identify unique molecules produced by the microbes in mangroves that could have the potential to tackle cancer and pathogenic bacteria.
Estimates of mangrove coverage in the UAE vary, with the Environment Agency Abu Dhabi – which uses high-resolution satellites to map the emirate’s mangroves – putting their area at about 15,500ha.
That figure is thought to have nearly doubled over the past 20 to 30 years because of plantation and rehabilitation projects first began by UAE Founding Father Sheikh Zayed.
There are several threats to mangroves, including urban expansion, limited freshwater resources, pollution and physical damage by humans.
“Coastal development is an important objective of human civilisation but if not done properly it could severely harm these ecosystems, which in turn harm us on the longer time scale,” Dr Amin says.
“Although we can remove mangrove forests and replant them elsewhere, the fact that we are only planting mangrove trees without all the other microbes and higher organisms that are essential for mangroves means we are basically creating ‘zombie’ trees that can never flourish.”
Dr Friis says sustainability is gaining importance in Gulf policymaking.
“Favouring the plantation of mangroves as soft defence structures to dissipate wave energy instead of breakwaters and seawalls would be an excellent way of preserving them while meeting urban development needs,” he said.
The best thing people can do is remember that our habits always have an impact on the natural environment.
“More efficient use of water and energy in our daily lives, and, of course, being respectful when visiting the mangrove forests, can help to protect this ecosystem,” Dr Friis says.
Both scientists agree that ecotourism activities such as kayaking are good ways to enjoy mangroves while having minimal impact on the forests. But visitors should be careful not to stand on roots, the surrounding sediments or disturb its animal residents.
“The diversity of wildlife in mangroves is amazing and is worth exploring, but we must be careful not to tread too heavily as to destroy it,” Dr Amin says.