On an expedition in the Amazon River Delta, researchers found mangroves growing in water with little to no salinity and overlapping with freshwater forested wetlands — a phenomenon never before documented in deltas or coastal mangroves anywhere else in the world.
Mangroves are hardy trees and shrubs that have adapted to live primarily in saltwater in the changing intertidal zones along marine coasts. National Geographic explorers Angelo Bernardino and Thiago Silva found these unique freshwater mangroves in April 2022 during a two-week expedition that was part of the larger, two-year National Geographic and Rolex Perpetual Planet Amazon Expedition.
The mangroves had been overlooked by previous satellite mapping efforts. Their identification increases the known area of mangroves in the region by 20%, or an additional 180 square kilometers (70 square miles). The findings were published July 20 in the journal Current Biology.
“It was phenomenal to see this type of freshwater flooded forests in this environment,” Bernardino, a marine ecologist, said in a press release. “This discovery is critical to further understanding the intricacies of mangrove forests and how they are crucial to local communities that surround them.”
This area of unique freshwater mangroves was found in the Amazon Delta, the region where the world’s largest river meets the ocean. Here, the plume of water spilling out from the river’s mouth, combined with the area’s high rainfall, releases an enormous volume of freshwater northwest along the coast of Brazil. Scientists say the freshwater mangroves growing here are strong evidence of the ecosystem’s adaptability to the Amazon River’s flow.
“Discovering a large area of mixed mangrove and freshwater forest trees along the upper estuarine reaches of the Amazon Basin is significant given that most tidal wetland overlap is restricted in area,” Ken Krauss, a research ecologist with the U.S. Geological Survey, who was not involved in the study, told Mongabay.