Scientists from UC San Diego's Scripps Institution of Oceanography and the Centro para la Biodiversidad Marina y la Conservación in Mexico have developed a tool that identifies mangrove patches facing the greatest risk of degradation.
The tool, called the Mangrove Threat Index and described in a new study published in the journal Frontiers in Ecology and the Environment, aims to provide an empirical argument for conservation before vulnerable ecosystems are lost rather than after, said the researchers. The index yields a single number that local planners and communities can use to prioritize specific mangrove patches for protection.
Mangroves are coastal forests that buffer shorelines from storms, store carbon and provide nursery habitat for many species of fish. Despite the tremendous intrinsic and economic importance of the ecosystem services that mangroves provide, roughly half of the world's mangrove forests are at risk of collapse .
Conservation-minded scientists are often in the position of reporting losses with increasing precision rather than proactively identifying mangroves that face immediate risks from infrastructure, agriculture or urban expansion. Long-term threats such as ocean warming and sea-level rise are captured by climate models, but they don't account for the pressures driving most mangrove loss today.
"We are trying to break the trend of simply reporting how many hectares of mangroves we have lost each year," said Octavio Aburto Oropeza, Scripps marine biologist and study co-author. "We created this index to try to measure the risk of loss so conservation can prevent damage rather than only react to it."
To create the index, the researchers tested whether proximity to human activity could reliably identify which mangrove patches would go on to experience degradation.
The study authors analyzed 530 mangrove patches across 13 regions worldwide, from urbanized coastlines to remote deltas. Scrutinizing 2010 satellite imagery, the team manually mapped patch boundaries and calculated each patch's distance to nearby roads, settlements and agricultural areas. These distances were combined into a single score — the Mangrove Threat Index — scaled from 0 (lowest risk) to 1 (highest risk). To test whether patches with high threat scores were more likely to experience degradation, the researchers compared the 2010 mangrove patches with 2020 satellite imagery and compared their risk classifications against actual losses.
The index proved effective at identifying vulnerable sites. Among patches the index classified as medium-high or high risk in 2010, 78% went on to experience measurable loss of area by 2020, and nearly half of those lost more than half a hectare (1.2 acres). Statistical modeling also revealed that patches with higher index values tended to lose more area, with each unit increase in the index corresponding to a 58% greater likelihood of degradation.
"Mangroves are foundational ecosystems that take decades to recover once degraded. If we want to safeguard biodiversity, coastal protection, fisheries productivity and carbon storage, we need tools that allow us to act early," said Valentina Platzgummer, a scientist at the Centro para la Biodiversidad Marina y la Conservación in Mexico and lead author of the study. "The Mangrove Threat Index provides a science-based way to identify where pressures are accumulating and where timely intervention can prevent long-term ecological and social costs."
The Mangrove Threat Index gives planners, communities and policymakers a tool to act before damage occurs — a shift from reactive conservation to what the authors call preventive governance. Because the index relies on accessible data and straightforward calculations, it can be applied by local decision-makers without specialized expertise. Local authorities could, for example, require assessments for any development proposed in high-risk zones.
"Conservation costs money, but mangroves provide ecosystem services for free," said Aburto. "You can calculate the economic value of the ecosystem services, but without some assessment of risk there isn't a concrete reason for a decision maker to pay for conservation. It's like car insurance — the premiums are calculated not just based on the value of the car but also on the risk of damage."
To demonstrate the index's utility in the real world, the researchers used it to evaluate 17 mangrove sites near La Paz, Mexico. The index identified a site called El Comitán located in a transition zone between urban and undeveloped lands as particularly vulnerable. That assessment guided a community-led restoration effort now underway that was supported by municipal authorities who used the index results to understand the urgency of intervention.
The authors said the framework could also be applied to other ecosystems where degradation risk correlates with proximity to human activity such as seagrass meadows, saltmarshes or freshwater wetlands. The researchers have made all the data and coding needed to reproduce the analysis publicly available, enabling others to apply or adapt the approach.
In addition to Aburto and Platzgummer, Fabio Favoretto of the University of Plymouth co-authored the study. The research was supported by the Baum Foundation and the David and Lucile Packard Foundation.
Read the full paper in Frontiers in Ecology and the Environment, "Beyond conservation pessimism and optimism: a proactive, risk-based approach to protect mangrove systems."
