A groundbreaking international study led by researchers at Tulane University reveals how the El Niño-Southern Oscillation (ENSO) climate phenomenon exerts a profound influence on nearly half of the world’s mangrove ecosystems. These vital coastal forests, which thrive in saline and brackish waters, provide essential environmental services such as carbon sequestration, storm protection, and fisheries support. However, their delicate balance and ecological sensitivity leave them vulnerable to the shifting climate patterns driven by ENSO events. This comprehensive investigation sheds new light on the global-scale dynamics linking climatic oscillations to mangrove growth and degradation, marking a significant advancement in ecosystem and climate science.
Published in the esteemed journal Nature Geoscience, the study is grounded in nearly twenty years of satellite data spanning from 2001 to 2020. Leveraging satellite-derived Leaf Area Index (LAI) measurements—which quantify plant productivity through leaf density—the research team conducted a meticulous temporal analysis to capture trends in mangrove vitality worldwide. This innovative approach allowed the identification of systematic and large-scale responses within mangrove populations to the alternating phases of ENSO: El Niño and La Niña. Prior to this study, such impacts of ENSO on mangroves were understood only through localized observations, lacking a coherent global perspective.
One of the most remarkable findings is the discovery of a “seesaw” effect in mangrove ecosystems along the Pacific Rim. During El Niño episodes, mangroves spread across the Western Pacific show widespread degradation, a response attributed primarily to temporary drops in sea level that increase soil salinity and stress. In stark contrast, mangrove forests in the Eastern Pacific experience enhanced growth under the same conditions. This polarity in response reverses during La Niña events, where the Western Pacific sees recovery and expansion in mangrove health, while the Eastern Pacific exhibits decline. Such spatial heterogeneity suggests complex, region-specific pathways through which ENSO modulates environmental drivers critical to mangrove survival.
The mechanisms driving these spatially opposing patterns are tightly linked to oceanographic changes induced by ENSO. El Niño causes anomalous warming of the central and eastern equatorial Pacific, along with significant alterations in ocean currents and atmospheric circulation. These shifts trigger a notable decline in local sea levels in the Western Pacific, escalating soil salinity and osmotic stress in mangrove root zones. Elevated salinity levels impair physiological functions, resulting in widespread mangrove dieback as documented in several coastal zones. Conversely, the Eastern Pacific’s warmer surface waters during El Niño promote favorable hydrological and nutrient conditions for mangrove expansion. La Niña events reverse these oceanic conditions, effectively flipping the stress and growth patterns between these regions.
The research team incorporated diverse datasets, combining satellite observations with climate and oceanic records, to unravel this global interconnectivity. Aside from LAI, oceanographic metrics such as sea surface temperature, sea level anomalies, and precipitation patterns were analyzed to interpret the environmental drivers behind mangrove fluctuations. By integrating multidisciplinary datasets, the researchers could disentangle the complex interactions between atmospheric phenomena and coastal ecosystem responses, providing an unprecedented holistic view of ENSO’s ecological footprint.
A poignant example illustrating the significance of these findings is the 2015 mangrove die-off in northern Australia, where more than 40 million mangrove trees perished across a 1,200-mile shoreline. This catastrophic event, previously considered isolated, now fits within a broader global pattern of ENSO-induced ecosystem stress, underscoring that localized diebacks are manifestations of wider climate-driven phenomena. The recognition of such systemic vulnerability elevates the urgency of global monitoring and management efforts targeting mangrove resilience.
Professor Daniel Friess of Tulane’s Earth and Environmental Sciences department, a co-author of the study, emphasized the ecological and socioeconomic ramifications of these insights. Mangrove ecosystems support hundreds of millions of people globally, offering protection from tropical storms and serving as carbon sinks that mitigate climate change. However, their survival depends intricately on narrow physical conditions. Understanding how climatic oscillations impact mangrove physiology and productivity facilitates more effective conservation and restoration strategies, tailor-made to withstand future ENSO-related disturbances.
Beyond ecosystem dynamics, the study also raises important questions about climate adaptation and management policies in coastal regions. As ENSO events are projected to evolve amid global climate change, their intensity and frequency could amplify mangrove stress cycles. This exacerbation threatens to erode the invaluable services these ecosystems provide, compromising biodiversity and jeopardizing human livelihoods. Policymakers and ecologists alike must consider these findings to devise adaptive frameworks that enhance mangrove resilience and secure ecological and economic stability.
In terms of methodology, the use of remote sensing technologies represents a crucial advancement in ecosystem monitoring. Leaf Area Index, derived from satellite spectral data, offers a reliable proxy for assessing vegetation health at scales previously unattainable. Coupled with long-term climate indices, this approach allows for continuous, consistent tracking of ecosystem responses to complex climate drivers, a methodology that can be extended to other vulnerable habitats subjected to environmental flux.
The study’s interdisciplinary collaboration, involving institutions such as Xiamen University and the National University of Singapore, highlights the global nature of both the research challenges and the ecosystems under scrutiny. By pooling expertise across geography, ecology, oceanography, and climate science, the team crafted a detailed narrative of ENSO’s tangible impacts, elevating scientific understanding and setting new standards for integrative environmental research.
This landmark study sets the foundation for a new era of ecological enquiry focusing on the intersection of climate variability and habitat resilience. It provides a compelling call to action, encouraging the scientific community, conservation practitioners, and global policymakers to recognize and mitigate the compounded threats ENSO poses to mangrove forests. As climate patterns continue to shift in unpredictable ways, safeguarding these coastal sentinels will require sustained research, innovative monitoring, and proactive ecological stewardship.
Subject of Research: Not applicable
Article Title: Study shows how El Niño and La Niña climate swings threaten mangroves worldwide
News Publication Date: 23-May-2025
Web References: http://dx.doi.org/10.1038/s41561-025-01701-8
Image Credits: Photos courtesy Daniel Friess, Tulane University
Keywords: Mangroves, Environmental sciences, Life sciences, Applied ecology, Aquatic ecology, Ecological dynamics, Earth systems science, Ecotourism, Community ecology, Ecological methods, Ecology, Ecosystems, Trees, Earth sciences, Environmental methods, Climate monitoring, Environmental impact assessments, Environmental monitoring, Climate change adaptation, Climate change effects, Environmental issues, Greenhouse effect, Climatology
