How do mangroves respond to climate oscillations?

A team of researchers from Tulane University, Xiamen University and the National University of Singapore has studied how mangrove forests in various locations around the world respond to short-term climate change, particularly that caused by the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) phenomena. The results of the pioneering study were published in May 2025 in the journal Nature Geoscience.

Scope of the study

Mangroves are a key coastal ecosystem because they counteract coastal erosion, and additionally serve as stores of so-called blue carbon. To assess their condition, the researchers used satellite data from 2001-2020. The main parameter analyzed was the leaf area of mangrove trees growing around the world, considered a basic indicator of vegetation growth. The resulting data were linked to information on climate and ocean conditions, including air temperature, wind strength, precipitation, sea surface temperature and salinity, and sea level. The focus was specifically on three episodes: El Niño of 2015-2016, La Niña of 2010-2012 and the positive phase of the 2019 IOD.

Mangroves vs. climate

The study found that more than half of the world’s mangroves are clearly responding to El Niño and La Niña climate phenomena, as evident in changes in their leaf area. The scientists noticed a characteristic swing-like pattern: when El Niño occurs, mangroves in the western Pacific, i.e. Australia and Southeast Asia, lose their leaves and weaken, while those growing on the other side of the ocean, along the American coast, gain strength and thrive.

During La Niña, the situation reverses – it is the mangroves in the western Pacific that recover, while those on the U.S. side weaken somewhat. A good example of this relationship is the events of 2015 and 2016. At that time in the Gulf of Carpentaria, in the north of Australia there was a massive die-off of mangroves, while the plants growing along the coast of Central and South America experienced a period of intense growth.

Similar changes were also observed during the positive phase of a climate phenomenon called the Indian Ocean Dipole in 2019. At that time, much of the mangroves in Southeast Asia, Australia and North America began to decline rapidly, while in eastern Africa they greened noticeably. This observation, according to Asian researchers, confirms the fact that different regions can respond differently to the same climate change.

Sea level and humidity – two key factors

Sea level has proven to be the main factor affecting changes in the condition of mangroves. During El Niño in some regions, the water recedes, exposing the roots and leading to their drying out, which in turn causes massive leaf loss and, in extreme cases, even the death of entire trees. Such a situation has been observed in northern Australia.

In other regions with higher rainfall, however, the same drop in sea level did not lead to such dramatic effects, as plants were able to draw water from other sources.

In contrast, humidity proved to be the most important factor during the Indian Ocean Dipole phenomenon. In Western Australia, where there was a prolonged drought, the mangroves began to die. At the same time, in eastern Africa, thanks to more rainfall, vegetation thrived.

Other factors, such as air temperature, wind strength and water salinity, also played a role in mangrove health, but their impact was smaller and usually limited to specific locations. For example, strong winds during El Niño may have contributed to the weakening of mangroves in the Amazon basin, but on a global scale their impact was negligible.

What is the significance of this to the world?

The study’s authors note that the increase in the frequency of El Niño and Indian Ocean Dipole phenomena predicted due to climate change could particularly threaten mangrove forests in Australia and Southeast Asia. These regions concentrate more than half of the world’s mangrove area and are also the most vulnerable to extreme weather events. Reducing the green mass of these ecosystems not only means weakening them locally, but could also negatively affect their ability to absorb carbon from the atmosphere.

On the other hand, the researchers note that during La Niña periods, when sea levels and water availability rise, mangroves generally recover and show strong growth. If such phenomena begin to occur more frequently or last longer, they could offset the effects of droughts and the associated drop in water levels.

Recommendations of the study’s authors

The study’s authors recommend incorporating short-term sea level fluctuations and drought frequency into monitoring and modeling changes in coastal ecosystems. They also suggest taking local environmental factors into account when predicting the effects of ENSO/IOD phenomena. However, extrapolating local results to a global scale for mangroves should be approached with caution.

MAIN PHOTO: Timothy K/Unsplash

Source: Zhang, Z., Luo, X., Friess, D.A. et al. Global mangrove growth variability driven by climatic oscillation-induced sea-level fluctuations. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01701-8