Satellite imagery reveals a severe die-off of mangroves along Australia’s northern coast. More than 7,000 hectares (27 square miles) of mangroves have dried up, research indicates. The tree deaths come amid high temperatures that have also been linked to massive coral bleaching and kelp forest deaths in the region.
These natural-color images were acquired on July 15, 2014, and July 20, 2016, by the Operational Land Imager (OLI) on Landsat 8. They capture the extent of mangrove die-offs on a strip of beach along the Gulf of Carpentaria.
Notable tree loss occurred between November and December 2015, said Norman Duke, leader of the Mangrove Research Hub at Australia’s James Cook University. Between 5 and 25 percent of trees have died along more than 1000 kilometers (620 miles) of shoreline and fringing inlets.
There are few direct human pressures in this isolated region, said Duke. However, the die-off correlates with record-high daytime and nighttime temperatures in the region, according to the Australian Government Bureau of Meteorology. From January through April, rainfall measured 41 percent less than average for that period—the lowest it’s been since 1961, the Bureau reported. The heat arrived on the heels of an unusually long dry season and a 20-centimeter drop in local sea levels that lasted for a month, said Duke.
“These factors coincided in the critical months...when habitat tolerances were at their limit,” Duke wrote in an email. He pointed to man-made climate change as a main cause.
Mangrove trees and shrubs grow at tropical and subtropical latitudes. A dense network of stilt-like roots allows them to thrive in shallow waters. It also provides shelter to many species of fish and turtles. And it helps shelter the dugong, a threatened species that is a relative of the manatee.
Mangrove forests fortify the coast, providing a buffer against storm surges by holding sand together with their roots and causing sediment to build up around them. Scientists like Duke worry that without the mangroves, Australia’s shores could become highly vulnerable to erosion, especially if tropical cyclones hit the region over the next decade.
NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Caption by Pola Lem.