What This Atoll Can Teach Us About Protecting Vulnerable Islands

Aldabra Atoll is defying rising seas, proving that nature can adapt — if we let it

I will never forget the first time I learned what an atoll was.

The idea that a volcanic island could sink beneath the waves, leaving behind a perfect ring of coral, felt almost like a magic trick… except it was real, happening over thousands of years and built by living organisms.

Just thinking about the scale of it blew my mind. These weren’t just islands; they were the product of something much older, built by geological and biological forces. I remember tracing their shapes on a map, imagining how an entire landmass could disappear yet leave behind a thriving ecosystem built by tiny coral polyps.

Years later, when I first set foot on an atoll as a biologist, the concept became something I could feel beneath my feet. Seeing the delicate balance of life that depended on this structure — reef fish darting between corals, seabirds nesting above, sea turtles pulling themselves onto sandy beaches to lay their eggs — made it even more incredible. It wasn’t just in the books anymore.

But there was always an unease in the back of my mind. Atolls, by their very nature, are vulnerable. They exist only as long as the conditions that created them remain somewhat stable.

However, rising sea levels, coral bleaching, storms… any disruption to that delicate equilibrium could mean the difference between survival and disappearance.

That’s why research like this study on Aldabra Atoll, located east of the Tanzanian coast in the Western Indian Ocean, matters. It challenges the idea that all atolls are on the brink of vanishing, showing instead that some can adapt… at least for now.

Satellite view of Aldabra. Aldabra Atoll in the Indian Ocean is one of the largest raised coral reefs in the world — Source: NASA Earth Observatory image by Wanmei Liang, using Landsat data from the U.S. Geological Survey

But let’s look at the methodology of this study first.

To track the atoll’s shoreline changes, researchers analyzed aerial images from 1960 and compared them with high-resolution satellite images from 2011.

Using a Digital Shoreline Analysis System, they mapped changes across 85% of Aldabra’s coastline. The goal? To determine how much of the shoreline has eroded, accreted (gained land), or remained the same over a 51-year period.

As someone who also has a background in paleontology, I love long-term experiments.

A Dynamic but Stable Shoreline

And what did they find?

Well, the results were surprising: 61% of the shoreline had not changed at all. No, not at all.

Of the remaining 39%, erosion and accretion were almost evenly split — 12% of the shoreline eroded, while another 12% gained land. On average, the shoreline shifted by 0.25 meters per year, a much lower rate than the global average for atolls.

In some areas, the changes were dramatic. The lagoon shoreline saw the most movement, with certain stretches gaining over 200 meters as sandy beaches transformed into mangrove habitats. Meanwhile, some of the ocean-facing cliffs held firm, resisting erosion far more effectively than expected.

What’s happening here is not so different from what you see when you pour sand on a beach and let waves wash over it. Some of the sand will wash away, but if the conditions are right, new sand will accumulate elsewhere. The balance between loss and gain is what determines whether an island shrinks or holds its ground. And Aldabra is managing to maintain that balance despite its exposure to rising seas.

Workflow for shoreline extraction of 2011 (left column) and 1960 (right column) imagery. The example is developed using a southeast section of Grande Terre Island of Aldabra (A). The NIR-Red Ratio (NRR) is applied on the bands of the GeoEye 2011 imagery, and the output (shown) is used to create a water mask based on histogram thresholding (B). The water mask created from B is applied to the GeoEye imagery and an unsupervised classification of the remaining pixels of the 2011 imagery is done to group them into two classes according to their spectral properties. The effect of the classification is to remove water pixels, such as shallow coral heads (blue pixels shown) that are not picked up by the NRR ©. The land polygon is attributed and a polyline layer is extracted from the polygon boundary. The polyline is visually assessed to adjust for errors and a final 2011 shoreline is created (D). The 2011 shoreline is used as the reference layer for the 1960 shoreline and overlaid on the 1960 imagery (E). The 1960 imagery is segmented — pixels are grouped according to similar spectral, spatial, and texture values — so that they represent objects showing land-based features, e.g. edge of limestone reef (F). The segments created simplify the process of tracing shoreline change hence are used for the computer-aided visual interpretation of the shoreline. The shoreline is backdated by interpreting the reference shoreline and tracing the changes. The identified changes can only be accepted with the criteria of a minimum width of 2 m from the reference shoreline to account for the difference in spatial resolution of the two imageries and corresponding uncertainty (G). The polylines of change in 1960 are merged to the polylines that remained the same from 2011 and the rest are eliminated, providing the final 1960 shoreline layer (H). Appendix C for workflow in higher resolution. The workflow was generated from the 2011 GeoEye-1 satellite imagery (left) and greyscale imagery (right) using ENVI NV5 Geospatial software (https://www.nv5geospatialsoftware.com/Products/ENVI) and ArcGIS 10.8.1 (https://www.arcgis.com/index.html) — Constance et al. 2025

What This Means for Islands Facing Climate Change

This study highlights an important point: not all islands are equally vulnerable to sea level rise. Atolls are often seen as passive victims of climate change, but Aldabra shows that some can adapt, at least in the short term.

The key factor is the ability of natural processes, such as sediment movement and reef growth, to continue unrestrained.

But this resilience has its limits. The researchers point out that Aldabra’s unique protection status plays a significant role in its stability. This is because, unlike many other atolls, Aldabra has remained largely untouched by human development.

That means no dredging, no construction of seawalls that alter natural sediment movement, and no overfishing of the herbivores that keep coral reefs healthy. However, if these natural processes are disrupted, the balance could tip quickly toward erosion.

Exploring the research further, one of the most vulnerable areas is Settlement Beach, which has already seen significant erosion. This beach is a critical nesting site for green turtles, and its loss could have serious consequences for the population.

The research station on Aldabra is also at risk, as rising tides and coastal retreat threaten its foundations. “The resilience of Aldabra’s shoreline to sea level rise might be tightly linked to its high protection status,” said lead researcher Dr. Annabelle Constance.

However, if tourism or other human activities were introduced, it could disrupt the island’s delicate equilibrium.

Net shoreline change on Aldabra Atoll from 1960 to 2011. Insets show two areas with the highest accretion (La Gigi) and erosion (Cavalier) recorded across the atoll during the study period. The map was generated using GeoEye-1 satellite imagery (Digital Globe, 2011) and processed with ArcGis 10.8.1, https://www.arcgis.com/index.html. Insets on the map have been modified from GeoEye-1 satellite imagery (left) and orthorectified greyscale imagery captured in 1960 by the Directorate of Overseas Surveys (right) —Constance et al. 2025

Take-Home Messages

Aldabra Atoll is a rare success story: an atoll holding its own against climate change, at least for now. The research highlights that islands are not doomed to vanish overnight if natural processes are allowed to operate without interference.

But it also serves as a warning: human impact can easily tip the balance. What’s happening on Aldabra today is a glimpse into what could happen elsewhere — either positively or negatively — depending on how we manage coastal ecosystems.

This research also reinforces something I’ve seen firsthand while working on conservation projects: nature is incredibly resilient, but only if we let it be.

In a world where rising seas and stronger storms are becoming the norm, protecting the natural mechanisms that allow islands to adapt might be the most effective long-term strategy. This lesson is worth considering, not just for scientists but for anyone invested in the future of our planet’s coastlines.

Meaning all of us.

Do you want to read more stories like this? You can now subscribe to my newsletter and join a community of over 10,000 Earth lovers!

I’m thrilled to have you here. Stay curious, and thank you for being part of this journey!

Best,
Sílvia P-M, PhD Climate Ages

P.S. If you’re an academic feeling unsure about your career path, I’ve put together some free resources to help you gain clarity and take the next step with confidence.