World's mangrove forests under threat from climate swings

The climate patterns associated with El Niño and La Niña affect nearly half of the world’s mangrove forests, new international research has found, underscoring the vulnerability of these vital coastal ecosystems to climatic shifts.

Mangroves are shrubs or trees that grow in dense thickets mainly in coastal saline or brackish water. They are also, according to scientists, some of the most valuable ecosystems on the planet – existing in a delicate balance with their environment.

The study has been led by researchers at Tulane University and published this week in Nature Geoscience. It’s based on nearly two decades of satellite data from 2001 to 2020 and is the first study to demonstrate global-scale patterns in how El Niño-Southern Oscillation influences mangrove growth and degradation.

Previously, impacts had only been documented at individual sites, such as a dramatic die-off in northern Australia in 2015, when more than 40 million mangrove trees perished along a 1,200-mile stretch of coastline.

“We wanted to know whether these events were isolated or part of a broader pattern,’ said lead author, Zheng Zhang, a postdoctoral scholar at Tulane School of Science and Engineering. “Our findings confirm that ENSO has large-scale recurring effects on mangrove ecosystems around the world.”

El Niño is a climate pattern of Pacific Ocean temperature and wind shifts that affect global weather. It brings warm weather to the eastern Pacific; La Niña brings cool waters there. It’s these changes that disrupt rainfall, storms, and temperatures worldwide – causing floods, droughts, and shifts in hurricane activity.

El Niño is known, meanwhile, for triggering coral bleaching, droughts, wildfires, and now – researchers have confirmed – it also plays a major role in mangrove health.