Rare mangroves discovered

National Geographic
Structurally unique freshwater mangrove forests have been discovered in Brasil's Amazon Delta for the very first time.

What was really unique for me was seeing freshwater trees growing side by side with mangrove species, all thriving equally.

Freshwater mangroves have been discovered in the Amazon Delta for the first time - suggesting ecosystem adaptability to the river flow.

This study is the first scientific finding published as part of the National Geographic and Rolex Perpetual Planet Amazon Expedition, a two-year exploration of the Amazon River Basin from the Andes to the Atlantic.

Angelo Bernardino and Thiago Silva, both National Geographic Explorers, conducted the first exploration of 11 mangrove forests along the Amazon Delta in April this year (2022).

Coexist 

The Explorers analysed data from the soil pore water, salinity, composition and tree density and volume using 3-D laser scanning from the ground and from drones. Their findings have been published in the journal, Current Biology

Bernardino, a marine ecologist, told The Ecologist: "It was fascinating. At first, I was confused because we were not seeing the same forests we are used to seeing all over Brazil. In the Amazon Delta, the forests have this unique mixture of freshwater plants. 

"These forests, in this location, prove that the nature around us is extremely diverse - they are growing, mixing, and adapting to their environment so they can weather the storm, so to speak. "

The study shows that the Amazon river plume and high rainfall conditions allow a unique set of mangroves to coexist. These mangrove structures, which yield little to no salinity, have never been documented on deltas or coastal fringing mangroves anywhere in the world.

Thrive 

Bernardino and Silva also found that the sampled mangrove forests exhibited a one-of-a-kind structure in comparison to other mangroves that have been studied worldwide.

Silva told The Ecologist: "I am beyond happy to have captured this one-of-a-kind environment in full detail using 3-D laser scanning. This will allow us to keep revisiting the forest for the months to come and really start to understand it."

What was really unique for me was seeing freshwater trees growing side by side with mangrove species, all thriving equally.

Globally, very few mangroves have been found to thrive in such low-saline environments, and only one other site has reported estuarine mangroves growing in freshwater conditions.

As a result of their unique structure, these mangrove forests will likely provide distinct ecosystem functioning, carbon stocks, and support for related animal and plant species over their large expanse.

The lower salinity may influence soil functions including pollutant retention, carbon sequestration, and greenhouse gas emissions.

Jurassic 

Additionally, the distinct soil properties of this coastal region further set the stage for the diverse plant species found in this atypical mangrove setting, which has not yet been observed in any other region of the world.

Thiago said: "What was really unique for me was seeing freshwater trees growing side by side with mangrove species, all thriving equally.

Bernardino added: "This mysterious combination, together with the abundance of the giant Aninga herbs and Acrostichum ferns gave the forest this unique, kind of an eerie feeling that we ended up nicknaming the 'Jurassic Park feel'."

Findings from Bernardino and Silva’s research also signify the expansion of the existing mapped mangroves of the Amazon delta by nearly 20 per cent with an additional 180 square kilometres.

Aerial 

This research reveals the importance of field explorations of the Earth’s natural habitats, as existing satellite imagery had not detected mangroves in a significant area of the Amazon Delta. 

“Ecologically, mangroves provide a habitat for a diverse array of organisms. They are a natural laboratory for how we understand plants,” said Silva.

“The findings from the 3-D terrestrial laser scanning allow us to see from aerial root density to tree height and volume, develop new methods to estimate carbon stocks, follow where the individual trees are, and even see underground channels of vegetation. It’s fascinating.”

Communities 

The second phase of this research is currently underway in Pará, Brazil, where Bernardino and National Geographic Explorer Margaret Owuor will survey and document the economic and social value mangrove forests provide to Amazonian communities.

Angelo added: "We also expect that these mangroves will be key for food supply and carbon burial in this part of the Brazilian coast. There are many communities that rely entirely on local fishing for their subsistence and depend on fresh and clean water from the Amazon River.

"These freshwater mangrove forests are key to all these services in some way, but we need a deeper understanding of these links in these newly discovered ecosystems."

Protection

These ecosystems are some of the most productive systems on the planet, and also some of the most biologically complex.

Over the past 50 years, "aquaculture and commercial fish farming has destroyed a third of the world's mangrove forests. In some regions of the world such as the Philippines, the loss has been up to 80 per cent." according to Endangered Species International.

Nicole Alexiev, the vice president of science and innovation at National Geographic Society, concluded: “The expedition into the Brazilian mangrove forest and subsequent discovery of freshwater mangroves is critical to painting the full picture of the vast Amazon river basin.”

“Through the multi-year expedition... we will continue to gather new information about these critical ecosystems and how we can support solutions to ensure their protection."

This Author 

Yasmin Dahnoun is the assistant editor of The Ecologist.

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