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Mesophotic coral ecosystems of the Indian Ocean reveal a hidden layer of coral biodiversity between shallow tropical reefs and deep ocean habitats. 
Beneath the surface of the oceans lies an extraordinary garden, invisible to anyone who never descends below the waterline.
Beyond the colorful fish that often capture our attention, the underwater world is an extraordinary melting pot of shapes, structures and living architectures. Corals build fragile limestone frameworks, gorgonians spread their fans into the currents, while sponges and countless invertebrates colonize every surface of the reef. To understand how these ecosystems function, one can imagine a gradual descent along a reef wall. As the diver slowly moves deeper, light fades, colors change and the structure of the reef transforms. This descent reveals a succession of ecological layers that organize marine life throughout the Indian Ocean. 
The Builders of the Reef
In the upper layers of tropical reefs live the true builders of coral ecosystems: reef-building corals, also known as hard corals. These tiny animals live in vast colonies and produce a calcium carbonate skeleton that gradually forms the massive reef structures found across tropical oceans. Their survival depends on a remarkable symbiotic relationship with microscopic algae known as zooxanthellae. These algae live within the coral tissues and perform photosynthesis, providing the coral with most of its energy. Because this process requires sunlight, reef-building corals thrive in clear, shallow tropical waters, typically between 23°C and 29°C. When ocean temperatures rise beyond the limits of this delicate symbiosis, corals expel their zooxanthellae. Without these algae, the coral loses its color and turns pale — a phenomenon known as coral bleaching. Bleaching does not immediately kill the coral, but prolonged thermal stress can lead to the collapse of entire reef systems. This fragile balance between coral animals, symbiotic algae and ocean temperature explains why coral reefs are among the ecosystems most vulnerable to climate change. In these shallow waters, biodiversity reaches its peak. Fish, mollusks, crustaceans and countless other species depend on the complex architecture built by corals. 
20 to 30 meters: The Transition Zone
As the diver continues descending along the reef wall, the intensity of sunlight gradually decreases. Warm colors such as red and orange fade first, leaving a landscape dominated by shades of blue. At these depths the ecological structure of the reef begins to change. Reef-building corals become less abundant, while other organisms become more prominent: sponges, gorgonians and filter-feeding organisms that capture organic particles carried by ocean currents. Fish communities also begin to shift. Species adapted to lower light conditions and deeper habitats become more common. This zone marks an ecological transition between the brightly lit shallow reefs and the deeper twilight ecosystems. 
30 to 60 meters: The Twilight Reefs
Continuing the descent, the diver enters what scientists call mesophotic coral ecosystems, often referred to as twilight reefs. Located roughly between 30 and 150 meters, these ecosystems still receive some sunlight, but only faint blue wavelengths penetrate to these depths. Corals capable of living here must adapt to extremely low levels of light. Many species survive thanks to highly efficient symbiotic algae able to capture the limited available energy. In many areas of the Indian Ocean, these depths reveal spectacular underwater landscapes dominated by vast forests of gorgonians, whose fan-shaped structures face the current to capture drifting food particles. The reef architecture becomes more vertical, darker and more dominated by filter feeders. The colorful coral gardens of shallow lagoons give way to structures shaped by currents and suspended nutrients. It is also within these twilight reefs that divers frequently encounter one of the most fascinating organisms of deeper coral ecosystems: black corals. 
Black Corals: Ancient Witnesses of the Ocean
Despite their name, black corals are not always black on the outside. Their internal skeleton, however, is dark and dense, which gave them their name. These organisms belong to the order Antipatharia and are among the most remarkable inhabitants of deeper reefs. Black corals grow extremely slowly. Some colonies may live several centuries, making them among the longest-living organisms within coral reef ecosystems. Because their skeletons incorporate chemical signals from the surrounding seawater as they grow, black corals can serve as natural archives of ocean conditions. By analyzing their structure, scientists can reconstruct past variations in ocean chemistry and climate. In this sense, black corals are not only beautiful organisms but also valuable scientific witnesses of the ocean’s history. A Frontier Still Largely UnexploredFor decades, mesophotic reefs remained largely beyond the reach of scientific research. Traditional scuba diving typically limits exploration to around 40 meters, while many mesophotic ecosystems extend much deeper. Studying these habitats therefore requires advanced techniques: mixed gases, rebreathers, submersibles and remotely operated vehicles. 
Studying these habitats therefore requires advanced techniques: mixed gases, rebreathers, submersibles and remotely operated vehicles.
At 60 meters of depth, even a short time spent on the bottom already requires significant decompression stops during ascent. These physiological constraints explain why exploring deep reef ecosystems demands specialized training, careful planning and significant technical resources. Exploring the Hidden Layers of the OceanDuring this progressive descent, based on real diving observations along reef walls of the Indian Ocean, we move through several ecological layers of the reef. From the sunlit zones dominated by reef-building corals to the twilight reefs where gorgonians and deep corals take over, each depth reveals a different organization of marine life. These deeper ecosystems remain among the least studied coral environments on Earth. Yet they may play an important role in the resilience of coral reefs facing rapid environmental change. Exploring these worlds requires technical expertise, scientific effort and a willingness to work at the limits of human diving capability. Because beneath the familiar coral reefs that most people imagine lies another realm — a quieter world suspended between light and darkness, still waiting to be fully understood Frequently Asked Questions about Mesophotic Coral ReefsWhat are mesophotic coral ecosystems?Mesophotic coral ecosystems are coral reef habitats located roughly between 30 and 150 meters depth. They receive limited sunlight and are often dominated by organisms such as gorgonians, sponges and black corals. Why are twilight reefs important?These deeper reef systems host unique biodiversity and may help scientists understand how coral ecosystems adapt to environmental stress such as ocean warming. How deep can divers explore coral reefs?Recreational scuba diving usually limits exploration to around 40 meters, while deeper reef ecosystems often require technical diving, rebreathers or submersibles. What are black corals?Black corals belong to the order Antipatharia. They grow very slowly and some colonies may live for several centuries, making them important natural archives of ocean conditions.
Migration, Encounters and the Quiet Power of the Ocean’s Largest Fish
Sometimes it appears first as a shadow beneath the surface. For a few seconds the mind struggles to understand what it is seeing. Then the outline becomes clear: a wide mouth, a massive body covered with perfectly aligned white spots. The whale shark moves slowly through the water, indifferent to the presence of humans.
The first time I encountered one was in the Bay of San José, in Baja California. I was not expecting to see such an enormous animal. The water was murky and filled with plankton — the whale shark’s favourite food. Out of that thick green haze, a dark mass suddenly emerged only a few metres away. The giant moved quietly through this living soup, calmly filtering the water. For a diver, encountering a whale shark is always a special moment. Despite its enormous size, this giant of the ocean is completely harmless. It feeds almost exclusively on plankton, filtering immense quantities of water every hour. Yet the largest fish on Earth still remains surprisingly mysterious. 
The Largest Fish on Earth
The whale shark (Rhincodon typus) holds the title of the largest fish on the planet. Individuals can reach lengths of more than 12 metres, and some may exceed 15 metres. Despite this immense size, their behaviour is remarkably gentle. Unlike predatory sharks, whale sharks are filter feeders. Swimming slowly near the surface, they open their massive mouths to sieve plankton, fish eggs and other microscopic organisms from the water. Their bodies are easily recognised by a pattern of white spots and pale stripes scattered across dark skin. Each whale shark carries a unique pattern, much like a fingerprint. Scientists now use these patterns to identify individuals and track their movements across oceans. Yet even with modern technology, much of their life remains hidden beneath the surface. 
A Traveller of the Indian Ocean
The Indian Ocean is one of the most important regions for whale sharks. They are regularly observed along the coasts of Mozambique, Madagascar, the Seychelles and the Arabian Sea. But these giants are far from sedentary animals. Satellite tagging has revealed that whale sharks are capable of travelling thousands of kilometres across tropical oceans. Some individuals have been recorded travelling more than 10,000 kilometres, linking distant feeding grounds across entire ocean basins. These movements appear closely linked to ocean productivity. Whale sharks follow plankton blooms, ocean fronts and large spawning events where food becomes suddenly abundant. Certain locations in the Indian Ocean act as seasonal feeding hotspots, attracting these giants for short periods each year. Research conducted in the western Indian Ocean has also shown that whale sharks may use ecological corridors such as seamounts, productive currents and plankton-rich upwellings as stepping stones during their migrations. In other words, the whale shark is not simply a coastal visitor. It is a true oceanic traveller, connecting ecosystems across vast distances. 
The Mystery of Giant Gatherings
In some places around the world, whale sharks gather in surprisingly large numbers. Scientists have discovered that these gatherings are often linked to massive spawning events of fish, where billions of eggs suddenly fill the water column. For whale sharks, such events represent an enormous feeding opportunity. These temporary feasts explain why animals from far away may converge in the same place. Yet these gatherings remain unpredictable, and the life cycle of whale sharks is still poorly understood. Their breeding grounds are largely unknown, and many aspects of their behaviour remain one of the ocean’s great mysteries. 
A Vulnerable Giant
Despite their enormous size, whale sharks are vulnerable animals. The species is currently classified as Endangered by the International Union for Conservation of Nature. Several threats affect whale shark populations:
The fate of these animals ultimately reflects the health of the oceans they inhabit. 
Why whale sharks matter in the Indian OceanWhale sharks (Rhincodon typus) are the largest fish on Earth and one of the most iconic species of the tropical oceans. In the Indian Ocean, they move across vast distances, linking feeding hotspots, plankton-rich waters and seasonal marine events. Understanding whale shark migration is essential for marine conservation, because these animals do not belong to a single coastline. They cross national borders, depend on healthy ocean productivity, and remain vulnerable to boat strikes, fishing pressure and poorly managed tourism. This article combines field experience, underwater photography and scientific context to explore whale shark behaviour, migration and conservation in the Indian Ocean. A Quiet Encounter with a Giant The whale shark is not my favourite shark to observe underwater. Unlike other species, there is almost no real interaction with the animal. It moves slowly, calmly, focused on feeding, largely indifferent to the diver nearby. And yet, every encounter remains unforgettable. Seeing such a massive animal glide peacefully through the water reminds us of our true scale as humans on this planet. In the ocean, the largest creature is not always the most aggressive or powerful. Sometimes the giant is simply the most noble, calm and composed. In a world often shaped by human conflicts and the desire to dominate, these quiet giants offer a different lesson. Strength does not always come from force. Sometimes it comes from presence, patience and balance with the natural world. And perhaps that is why encountering a whale shark remains such a powerful moment in the ocean. Whale Shark FAQWhat is the whale shark?The whale shark (Rhincodon typus) is the largest fish on Earth. Despite its enormous size, it is a gentle filter feeder that mainly eats plankton and small marine organisms. Do whale sharks migrate across the Indian Ocean?Yes. Satellite tracking has shown that whale sharks can travel thousands of kilometres across the Indian Ocean, following productive waters and seasonal feeding opportunities. Are whale sharks dangerous to humans?No. Whale sharks are harmless to humans. They are slow-moving filter feeders and are generally considered one of the gentlest giants of the ocean. Why are whale sharks vulnerable?Whale sharks face several threats, including boat strikes, accidental capture in fishing gear, habitat pressure and poorly managed wildlife tourism.
Several times a week, I return to the site of Ngouja, in Mayotte.
A simple place, almost still, where time seems to slow beneath the surface. 
There, I find the lagoon’s green turtles.
I watch them graze on the short seagrass with a calm, almost meditative rhythm — like silent herds feeding beneath the water. Their movements are slow, deliberate, repeated — an ancient behavior that seems to belong to a different pace than our own. Beneath them, the seagrass meadows stretch in dense, living patches. They shape the landscape quietly, without ever demanding attention. And yet, as I watch them, another image comes to mind. The Mediterranean. For years, I have moved above the seagrass beds of Posidonia oceanica. A different kind of landscape — denser, more structured, almost forest-like. Where Ngouja feels open and dynamic, Posidonia evokes stability and time. Two environments. Two rhythms. But the same question keeps returning: What do these seagrass ecosystems truly share, beyond their appearance? And what do they reveal about the state of our oceans today? 
Two Worlds, One Function
At first glance, everything seems to separate tropical seagrass meadows from their Mediterranean counterpart. In Ngouja, seagrass is composed of multiple species. It grows quickly, adapts, and recolonizes. Its dynamics are fluid, responsive — but also fragile. In the Mediterranean, Posidonia oceanica follows a different tempo. Endemic to this sea, it expands only a few centimeters per year. Over centuries — sometimes millennia — it builds thick underwater structures known as “matte,” creating one of the most stable coastal ecosystems on Earth. On one side, a fast-growing, adaptive system. On the other, a slow, long-term builder. And yet, despite these differences, their role is the same. Seagrass meadows are among the hidden foundations of coastal oceans. They act as nurseries for countless species, shelter juvenile fish and invertebrates, feed turtles, stabilize sediments, and help maintain water clarity. They also protect coastlines by absorbing wave energy. Without them, entire ecosystems begin to unravel. 
An Invisible Climate Role
But their importance extends far beyond biodiversity. Beneath the surface, seagrass meadows play a critical role in regulating the global climate. They capture carbon dioxide — much like terrestrial forests. But more importantly, they store it. Over time, dead leaves, roots, and organic matter accumulate in the sediment below, forming a long-term carbon reservoir. This carbon can remain trapped for centuries, even millennia. On average, seagrass meadows can store up to 140 tonnes of carbon per hectare. Per unit area, they can be up to 30 to 40 times more efficient than forest soils at storing carbon over the long term. In the Mediterranean alone, Posidonia oceanica captures an estimated 5.7 million tonnes of CO₂ each year. A remarkable figure for such a discreet ecosystem. But this balance is fragile. When seagrass meadows are damaged — by anchoring, pollution, coastal development, or rising temperatures — the carbon they have stored can be released. The system reverses. What was once a carbon sink becomes a source. 
Resilience and Fragility
In Ngouja, tropical seagrass gives the impression of a living, resilient system. Its fast growth allows it to recover under the right conditions. But this apparent resilience comes with vulnerability. Increased turbidity, sediment runoff, or human pressure can lead to rapid decline within just a few years. In contrast, Mediterranean Posidonia tells a different story. It is slow. Extremely slow. But it builds over time. It stabilizes the seabed, stores vast amounts of carbon, and creates long-lasting habitats. When destroyed, recovery can take decades — or may not occur at all on a human timescale. Fast resilience on one side. Deep resilience on the other. Yet in both cases, the same conclusion emerges: These ecosystems are essential and fragile. 
A Silent Decline
Globally, seagrass meadows are in decline. Their disappearance is rarely dramatic. It does not make headlines. It does not burn or collapse suddenly. It happens slowly, underwater, often beyond our awareness. In the Mediterranean, significant losses have already occurred, particularly near urbanized coastlines, ports, and anchoring zones. In the Indian Ocean, data remains limited, making the situation harder to quantify. But pressures are clear: sedimentation, runoff, and coastal development. Less visible than coral reefs, seagrass ecosystems suffer from a lack of recognition. And therefore, a lack of protection. 
Protecting the Invisible
Protecting seagrass does not always require complex solutions. Sometimes, the answers are simple: Limiting uncontrolled anchoring in favor of eco-moorings. Reducing sediment and pollution runoff. Managing coastal development. Strengthening marine protected areas. But all of this depends on one essential step: Recognizing their value. Because it is difficult to protect what remains unseen. 
Conclusion
From Ngouja to the Mediterranean, seagrass meadows tell the same story. That of ecosystems both discreet and essential — capable of sustaining life and regulating the climate, while remaining largely invisible. Two worlds. Two rhythms. One vital function. And perhaps, one shared urgency: To learn how to see what we have long overlooked.
At the surface, the Indian Ocean does not appear different. Waves form, reefs breathe, currents continue their course. Yet within its very structure, something is changing: the salinity of certain regions in the southern Indian Ocean has been measurably and persistently declining for several decades.
A Change Detected Over Decades : This shift is not based on isolated observations. It relies on long-term oceanographic datasets dating back to the 1960s, compiled in the World Ocean Database maintained by NOAA:
https://www.ncei.noaa.gov/products/world-ocean-database These trends have been confirmed and refined by the Argo program, a global network of autonomous floats measuring temperature and salinity throughout the water column since the early 2000s: https://doi.org/10.1016/j.pocean.2009.03.004 Analyses indicate that parts of the southern Indian Ocean show a significant decrease in surface salinity. This signal fits within a broader intensification of the global hydrological cycle under climate change, as highlighted by Durack et al. (2012) in Science: https://www.science.org/doi/10.1126/science.1212222 and reinforced by the latest IPCC assessment (AR6 – Working Group I): https://www.ipcc.ch/report/ar6/wg1/ While global mean ocean salinity remains close to 35 PSU (Practical Salinity Units), that average conceals growing regional contrasts. Subtropical regions dominated by evaporation tend to become saltier, whereas certain tropical zones and parts of the southern Indian Ocean are becoming fresher. This pattern aligns with climate projections indicating that wet regions become wetter and dry regions become drier (IPCC, 2021). 
Why Salinity Is a Fundamental Physical Parameter : Salinity, together with temperature, determines seawater density. Density governs water mass dynamics and drives the global thermohaline circulation, as described by Talley (2013) in Oceanography:
https://doi.org/10.5670/oceanog.2013.07 Cold, salty water is dense and tends to sink, contributing to deep circulation that redistributes heat, nutrients, and oxygen across the planet. Warmer or fresher water is lighter and remains near the surface. If salinity declines, density decreases. Vertical mixing becomes less efficient and stratification intensifies. Stronger stratification limits exchanges between nutrient-rich deep waters and the sunlit surface layer. These exchanges are essential to the functioning of the ocean’s biological pump, a key process regulating carbon uptake and marine productivity, discussed in detail in the IPCC AR6 report: https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-5/ 
Potential Consequences for Marine Ecosystems : The direct biological effects of moderate salinity decline vary by species and region. However, the underlying physical mechanisms are well established. Persistent changes in stratification can influence nutrient availability, alter plankton distribution, and cascade upward through marine food webs.
In the Indian Ocean, where coral reefs and coastal fisheries play major ecological and socio-economic roles, these structural shifts add to existing pressures from warming and acidification (IPCC, 2021). They represent a gradual reconfiguration — less visible than coral bleaching events, but potentially just as consequential over time. 
A Marker of an Intensifying : Water CycleSurface salinity is now recognized as a robust tracer of hydrological cycle intensification. A warmer atmosphere can hold more water vapor, modifying precipitation patterns and increasing regional contrasts (IPCC, 2021).
In the case of the Indian Ocean, the observed freshening reflects a progressive reorganization of the system. It is not immediately visible to the naked eye, but it influences water mass stability, regional circulation, and potentially atmosphere–ocean interactions, including those that contribute to monsoon dynamics. 
A Climate Paradox — Freshening in a Warming : World At first glance, the idea that parts of the Indian Ocean are “freshening” may sound contradictory in the context of global warming. But freshening does not mean cooling. It refers to a decline in salinity, not temperature. In fact, ocean warming and surface freshening are often linked through the same mechanism: an intensified hydrological cycle.
As the atmosphere warms, it holds more moisture, leading to stronger rainfall in some regions and enhanced evaporation in others. Where precipitation and freshwater inputs increase, surface waters become less saline even as they continue to warm. The result is not a cooler ocean, but a more stratified one — warmer at the surface, fresher at the top, and increasingly layered. This apparent paradox illustrates how climate change does not produce uniform responses, but rather a complex reorganization of ocean structure. 
Why the Ocean Is Salty — And Why That Matters : To understand why these variations are significant, it is useful to revisit a fundamental question: why is the ocean salty? Ocean salinity results from a dynamic balance established over millions of years. Rainwater dissolves minerals from continental rocks. Rivers transport dissolved ions to the sea. Submarine hydrothermal systems add additional chemical elements. When seawater evaporates, the water leaves but the salts remain. This cycle, explained by NOAA: https://oceanservice.noaa.gov/facts/whysalty.html has maintained a relatively stable global salt balance on geological timescales. A rapid regional shift in salinity does not mean the ocean is “losing its salt” globally. Rather, it indicates that the distribution of freshwater is changing enough to alter the physical structure of the water column. 
A Silent but Structural Transformation : Public discussions about ocean change often focus on rising temperatures or acidification. Yet salinity reveals a complementary and essential dimension: how accumulated energy in the climate system redistributes freshwater and reshapes ocean structure.
If temperature tells us how much the ocean is warming, salinity tells us how it is reorganizing. Beneath the apparently unchanged surface of the Indian Ocean, this transformation is already measurable. It is gradual, physically consistent with climate projections, and potentially decisive for marine ecosystems and circulation patterns in the decades ahead. From the Heart of Voh to the essence of mangroves Mangroves protect coastlines, store carbon and sustain life — yet they are vanishing. From the Heart of Voh to the shores of Mayotte, this is the story of a fragile ecosystem at a turning point.  I first discovered the power of mangroves not by walking through the mud, but through an image: Yann Arthus-Bertrand’s aerial photograph of the Heart of Voh in New Caledonia. Seen from above, this improbable shape draws a heart within the mangrove forest. To me, it captures what mangroves truly are: a quiet, often overlooked ecosystem — yet vital, a coastal heart beating for the planet. Mangroves are tropical and subtropical forests growing in the intertidal zone, where saltwater, freshwater and land meet with the rhythm of the tides. They are made of highly specialized trees and shrubs — mangrove species — able to survive extreme salinity and flooding. Globally, scientists recognize around 70 true mangrove species, spread across the coasts of more than 120 countries. But to describe mangroves as “just forests” is misleading. They are a keystone ecosystem, a biological crossroads where water, carbon, nutrients and marine life cycles converge.  What a mangrove does — an ecosystem working for usA mangrove is not a line of trees along the shore. It is a living system, constantly active above and below the surface, helping coastal environments remain in balance. In its waterlogged, oxygen-poor soils, mangroves lock away vast amounts of carbon. This carbon — captured from atmospheric CO₂ — can remain stored for decades or even centuries. For us, the meaning is simple: as long as this carbon stays buried, it does not fuel climate change. When a mangrove is destroyed, that stored carbon can be released, adding to the greenhouse effect. Facing the sea, mangroves act as a natural buffer. Their tangled roots slow waves, trap sediments and stabilize shorelines. Where mangroves remain, they reduce erosion, dampen storm surges and protect coastal communities from increasingly violent weather. (UNEP overview: https://www.unep.org/explore-topics/oceans-seas/what-we-do/protecting-restoring-blue-carbon-ecosystems) Below the surface, mangroves are a giant nursery. Thousands of organisms find shelter here: fish larvae, juvenile sharks, crustaceans, mollusks, birds and reptiles. For many species, this is their first refuge before reaching the open sea — a growth space that later sustains reefs and fisheries (FAO module: https://www.fao.org/sustainable-forest-management-toolbox/modules/mangrove-ecosystem-restoration-and-management/en). They also play a quiet but essential role in water purification by trapping sediments and filtering nutrients, helping protect nearby ecosystems such as seagrass meadows and coral reefs. For all these reasons, mangroves cannot be treated as scenery. They are a natural infrastructure, silent yet indispensable.  Major losses… and a fragile recoveryFor decades, mangroves have been cleared, fragmented and transformed — often out of sight. Aquaculture, agriculture, urban expansion and infrastructure have steadily eaten away at these amphibious forests. With the satellite era, monitoring has become far more precise. The global reference today is Global Mangrove Watch. According to this dataset, between 1996 and 2020 the world lost 5,245 km² of mangroves, about 3.4% of the global total (Source: Bunting et al., 2022, Remote Sensing; platform update via Wetlands International: https://www.wetlands.org/global-mangrove-watch-platform-updated-with-the-latest-data-to-2020/). That is nearly the size of the U.S. state of Delaware — an entire living coastline erased in a single generation. Data from the FAO (Food and Agriculture Organization of the United Nations) confirm this trend: the rate of loss has slowed since the 2000s, but it has not stopped (FAO global assessment 2000–2020: https://openknowledge.fao.org/server/api/core/bitstreams/7f15adf1-2756-4e86-a6dd-77d0fc26d97c/content).  The Women of the Mangrove. The Mamas Shingos of MayotteIn Mayotte, along the edges of the lagoon, groups of women known as the mamas Shingos still harvest shellfish and small marine life in the mangrove at low tide. Their movements follow the same rhythm as the tides, passed from generation to generation. They also collect seawater and let it slowly evaporate in shallow basins under the sun, leaving behind coarse crystals of salt. It is a quiet process, shaped by patience and heat — a transformation of the sea itself into something that can be shared, traded, and preserved. For them, the mangrove is not a concept. It is food, income, knowledge, and identity. When the mangrove recedes, it is not only an ecosystem that disappears, it is a way of living, a fragile balance between survival and nature. Their presence reminds us of something essential: protecting mangroves is not only about carbon or coastlines. It is about dignity, continuity, and the right to remain connected to the living world.  Blue carbon: a real promise — but not a magic solution“Blue carbon” is now a central argument for protecting mangroves — and rightly so. They store enormous amounts of carbon, especially in their soils. When a mangrove is destroyed, this carbon can be released into the atmosphere, worsening climate change. Globally, mangroves store around 6.4 billion tonnes of carbon in their biomass and soils equivalent to more than 23 billion tonnes of CO₂. That is roughly equal to over five years of total European Union emissions. But reality is more complex. Mangrove soils can also emit other greenhouse gases, such as methane (CH₄) and nitrous oxide (N₂O) — far more powerful than CO₂. Depending on local conditions, these emissions can reduce part of the net climate benefit (Rosentreter et al., 2021: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GB006858). This does not mean mangroves are “bad” for the climate. It means their impact depends on the site, the ecosystem’s health, and how it is protected or restored. The key message is this: mangroves are a powerful climate ally, but they cannot be reduced to a single carbon number. Protecting the whole ecosystem matters more than counting tonnes of CO₂.  False good solutionsThe first trap is to confuse planting with restoring. Planting mangroves without restoring water flows, tides and sediments often leads to failure. The result may look reassuring — but the ecosystem does not function. Another risk is turning blue carbon into a communication tool, where the credit becomes the goal rather than the ecosystem itself : https://mangroveactionproject.org/wp-content/uploads/2024/07/SOWM-2024-HR.pdf). A necessary shiftThese mistakes do not come from bad intentions, but from a misunderstood urgency. Faced with collapse, we wanted quick, visible action. But science now shows that mangroves cannot be rebuilt like a park. They are shaped by water, tides, sediments and time. By confusing speed with effectiveness, we sometimes created the illusion of rescue. This shift in understanding marks a turning point: to protect is not to replace — it is to allow life to continue.  Real solutionsThe most effective solution is still the simplest: protect the mangroves that remain. Every hectare preserved avoids emissions, shields coasts and sustains nurseries. When restoration is necessary, it must start by restoring natural hydrology, then letting regeneration do its work. It is slower — but infinitely more durable.  Conclusion :
So the heart can keep beatingThe Heart of Voh is not just a famous photograph. It is a fragile symbol, suspended in time. Nothing guarantees it will still be visible tomorrow — or that other mangroves will have the chance to trace, by chance, what we recognize as a heart. Protecting mangroves is not about saving a distant landscape. It is about preserving a vital function of the planet — a discreet but essential organ, without which our coasts, oceans and climate become more unstable. If we want future generations to still glimpse a heart beating from the sky — in Voh or elsewhere then mangroves must no longer be a backdrop we watch disappear, but a living system we choose to protect. Because in protecting mangroves, we are not only defending the shoreline We are protecting the very heart of our world.
Why is forest loss making tropical heatwaves lethal for fruit bats?
During tropical heatwaves, the first signs are subtle. Flying foxes also known as fruit bats—remain motionless in full daylight, wings spread wide in a desperate attempt to regulate their body temperature. Normally nocturnal and active at dusk, they now hang silently from exposed branches, unable to escape the heat.
Across the Indian Ocean region, such scenes are becoming increasingly common. Heatwaves are not new in tropical environments. What has changed is the disappearance of forests—the natural climate buffers that once enabled flying foxes to survive extreme temperatures. 
A keystone species under pressureFlying foxes play a critical ecological role across islands and coastal forests of the Indian Ocean. As long-distance pollinators and seed dispersers, they actively contribute to forest regeneration, biodiversity maintenance, and the recovery of degraded ecosystems.
Their survival depends on stable microclimates. Dense forest canopies provide shade, humidity, and air circulation—essential conditions for thermoregulation in these large-bodied bats. Unlike smaller species, flying foxes are particularly vulnerable to overheating when exposed to direct sunlight for extended periods. When forests remain intact, heat rarely becomes fatal. When forests disappear, even moderate heatwaves can turn deadly. 
Deforestation in the Indian Ocean: a gradual erosion
In Madagascar, Mayotte, and other islands across the region, deforestation rarely takes the form of a single dramatic event. Instead, forests are progressively fragmented through fuelwood extraction, agricultural expansion, urbanisation, and infrastructure development. Each cleared area may appear insignificant in isolation. Together, however, they dismantle the forest’s ability to function as a thermal refuge. Mature trees used for generations as communal roosts are felled or left isolated, forcing colonies into exposed landscapes with no viable alternatives. In island ecosystems—where space is limited—this loss is particularly severe. 
Why heat becomes lethal without trees : Flying foxes regulate body temperature primarily through evaporative cooling and behavioural adaptations: seeking shade, adjusting roosting posture, or moving short distances to cooler areas. Without forest cover, these options vanish.
Exposed bats experience rapid dehydration and severe hyperthermia. During extreme heat events, individuals may fall from roosts or die while still clinging to branches. Mass mortality events—once rare—are now increasingly documented worldwide, with habitat loss consistently amplifying their scale. In tropical regions, deforestation removes the final margin of survival against heat. 
When habitat loss turns species against each other: flying foxes and lemursForest loss does not affect a single species in isolation. In Mayotte, intense habitat fragmentation has forced species that once coexisted with little interaction to share an increasingly limited number of trees.
Lemurs (makis), themselves forest-dependent and emblematic of regional biodiversity, are now sometimes forced into direct competition with flying foxes for food resources and refuge trees. This inter-species conflict is not natural—it is the product of extreme habitat compression. As space disappears, ecological balances collapse. Stress behaviours increase, temporal niches overlap, and protected species are pushed into conflict despite sharing the same underlying threat. The ecological crisis, in this case, creates conflict between victims—not between culprits and the innocent. 
Key figures: alarming population declines : The Mauritian flying fox (Pteropus niger) lost approximately 45–50 % of its population between 2015 and 2016, largely due to heat stress and large-scale culling campaigns sanctioned by the government of Mauritius. These actions, alongside ongoing illegal hunting and habitat degradation, were significant contributors to this rapid decline and were part of the reasoning behind the species’ uplisting to Endangered on the IUCN Red List. (decline of ~50 % since 2015 due to culls and other pressures)
During the 2015 cull alone, over 30,000 individuals were killed, making it one of the largest documented removals of fruit bats in the world. (government-authorized national cull of over 30,000 individuals in 2015, with additional tens of thousands culled in the following years) The Livingstone’s fruit bat (Pteropus livingstonii), endemic to the Comoros archipelago and one of the world’s rarest megabats, is currently estimated at about 1,200–1,500 individuals in total across its limited range on the islands of Anjouan and Mohéli. (population estimates ~1,200–1,500) Globally, more than 70 % of large Old World fruit bat species (including many in the genus Pteropus) are now classified as threatened or near-threatened on the IUCN Red List due to a combination of habitat loss, hunting pressure, and climate-related stressors that are affecting their populations worldwide. (Pteropus species are widely listed as threatened due to these pressures) 
The danger of the wrong narrative : As flying foxes move into exposed or human-dominated areas, they are increasingly labelled as pests, invasive, or dangerous. This narrative obscures the real cause of their displacement and often justifies ineffective or harmful responses such as culling or forced relocation.
Removing flying foxes does nothing to address the absence of functional forests. On the contrary, it undermines ecosystem resilience by eliminating a keystone species essential to forest regeneration—precisely when forests are most needed. Killing bats treats a symptom, not the disease. 
Forests as living climate infrastructure : Forests are often discussed primarily as carbon sinks. Yet their role as local climate regulators is equally critical.
For flying foxes, forests are far more than simple habitat. They create the microclimates that buffer extreme heat, retain humidity during droughts, and provide the spatial complexity these large, highly social bats need to roost, thermoregulate, and survive. In a warming world, protecting forest ecosystems is therefore not an abstract conservation ideal it is one of the most immediate and effective defenses against climate-driven mass mortality. The solutions are neither speculative nor technologically complex. They already exist, and they are well understood: safeguarding the last remaining roost trees, restoring forest corridors that reconnect fragmented populations, preserving native large-canopy species that offer shade and thermal stability, and integrating wildlife requirements into land-use and agricultural planning. What is missing is not scientific knowledge, but political will and sustained local engagement. When forests are allowed to stand and regenerate, flying foxes are given back their most powerful ally against a rapidly destabilizing climate. 
Conclusion: a warning written on living bodiesIf flying foxes disappear, the heat they endure today will become our own reality tomorrow. What these animals experience first is not a biological anomaly, but the symptom of ecosystems stripped of their capacity to regulate climate extremes.
Flying foxes serve as early indicators: without forests, tropical regions lose their ability to buffer heat—affecting wildlife and human populations alike. As forests vanish, heatwaves will become more frequent, more intense, and harder to survive. Protecting forests is therefore not just about saving a misunderstood species. It is about preserving the conditions that will allow life—human and non-human—to endure in a warming world.  In the humid forests of southeastern Madagascar, particularly in Ranomafana National Park, researchers have noticed an unexpected pattern. Among certain groups of black-and-white ruffed lemurs (Varecia variegata), birth rates appear to be rising. In a country where more than 90% of lemur species are threatened with extinction, this could easily be seen as hopeful. But in ecosystems under strain, reproduction does not always reflect abundance; it can also reflect uncertainty. Sometimes, to be born is not to grow into a flourishing world, but to arrive already in a state of endurance.  The forests of southeastern Madagascar once formed a continuous canopy stretching over valleys and ridges. Today, much of that continuity has been broken. Forests have been divided into isolated fragments separated by fields, roads and burned clearings. For animals whose entire existence plays out in the trees, the consequences are profound. Movement becomes more dangerous. Groups become isolated. Food availability becomes unpredictable. Seasons shift their meaning. Fragmentation does not only cut the forest into pieces; it interrupts the flow of life itself.  It is in this context that the research led by primatologist Andrea L. Baden through the Ranomafana Ruffed Lemur Project has documented consecutive-year births among some ruffed lemur groups – a pattern unusual for a species known for spacing reproduction because raising young is energetically costly. As reported by Smithsonian Magazine in 2025 (“A Baby Boom Among Madagascar’s Lemurs Isn’t the Good News It Seems”), these births are interpreted not as a recovery, but as an adaptation to instability. When fruiting seasons shift and the reliability of resources becomes uncertain, producing more young can become a short-term attempt to ensure that at least some survive. This interpretation is supported by broader findings published in Scientific Reports (Baden et al., 2019), showing that forest fragmentation corresponds to a fragmentation of gene flow among ruffed lemur populations, reducing their adaptive capacity in a changing climate.  Where the ruffed lemur expresses ecological stress through shifts in birth rhythm, the Indri expresses it through time itself. The Indri’s voice is one of the defining elements of the Malagasy landscape: long, rising calls that can fill entire valleys at dawn. Many who live near these forests describe the Indri’s call as something more than sound; it is atmosphere, memory, the forest declaring its presence. Yet the Indri reproduces extremely slowly. A single infant may be born only every two or three years and remains dependent for a long time. The species’ survival depends on stability and on continuity of the canopy. When forests fragment too rapidly, the Indri cannot accelerate to compensate. Where the ruffed lemur can attempt to “race” against instability, the Indri can only endure. And endurance has limits. When the Indri falls silent, the forest does not simply lose a species. It loses a way of recognizing itself.  The Sifaka reveals another dimension: the dimension of space. Sifakas are dancers of the canopy. Their movements – weightless leaps between branches, poised landings high above the ground – depend entirely on the presence of tall, closely spaced trees. When the forest is intact, the Sifaka moves as though gravity has loosened its hold. When the forest breaks, the Sifaka is forced down to the ground. There, it moves upright, with a sideways skipping gait that many find charming. In truth, it is not charm. It is exposure. The Sifaka was not made to walk on earth. A Sifaka crossing bare soil is not a playful spectacle. It is a forest trying to hold itself together across a gap where the trees have gone.  The ruffed lemur, the Indri and the Sifaka are responding to the same changes in their environment, yet each expresses those changes differently. One increases births. One cannot speed up at all. One is forced into movements that do not belong to its body. Through them, the forest is telling us something. It is not a single message, but a chorus. A change in rhythm. A change in voice. A change in motion. The lesson is the same: the forest is changing faster than the lives within it can adapt.  As the world approaches COP30, discussions about forest restoration increasingly revolve around numbers: hectares protected, carbon absorbed, funding allocated. But a forest is not defined by surface area or carbon metrics alone. A forest is a structure of relationships. It is pollination, memory, dispersal, seasonal timing, learning passed from mothers to young, movements that depend on architecture. Restoring a forest means restoring continuity. It means allowing seeds to travel again, allowing families to remain in territories that hold their histories, allowing calls to carry across valleys, allowing bodies built for trees to stay in the trees. Conservation cannot be separated from the communities who live among these forests, whose knowledge and livelihoods shape their futures. And long-term field research is not optional; it is what allows us to detect these subtle shifts before they reach a point where recovery is no longer possible.  Ruffed lemurs, Indris and Sifakas share something with us. They have five fingers capable of holding on. They leave traces in the places where they live. And at times, they show gestures that resemble care for the dead. Their future does not run parallel to ours; it reflects it. To protect these forests is not only to safeguard remarkable species. It is to preserve the possibility for life to continue from one generation to the next. What is being born in the canopy today is not just a new generation. It is a chance. Whether it becomes a future depends on the choices we make now.
 Some days change something. Not because of a spectacular event or a scientific breakthrough, but because you can feel it — quietly — a new relationship with the ocean taking shape. Today was one of those days. It began with a simple question on the boat, as it often does. One of the young divers asked me how many sharks are killed every year. When I answered 70 to 100 million, the whole group fell silent. Then came the second question: “But… why?” And that’s when everything started moving: industrial fishing, finning, the disappearance of a predator the ocean desperately needs. Then we talked about the role of turtles in Mayotte -- the gardeners of the lagoon — cleaning seagrass, redistributing nutrients, maintaining a fragile balance very few people know about. These simple exchanges are where sparks begin.  The “Naimi Effect”And then there’s Naimi. When she joined the program, she was preparing for her math–physics baccalauréat, bright, focused, heading toward the classic science path. But dive after dive, something shifted. She started asking different questions. Not just “how does this work?” but “could I work in this field one day?” Today, she says out loud what she barely dared to think a few months ago: she’s considering marine biology. That’s not a small turn — it’s a whole life pivoting, quietly, shaped by experiences underwater, by encounters, by understanding. When a 17-year-old begins to look at the ocean not as a backdrop but as a possible future, it means something real is happening.  Diving Is No Longer a Hobby — It’s a Doorway. The questions are changing. In the beginning they asked: “Is it deep? How long will we stay? What fish is that?” Now it’s becoming:
from experience to vocation. It’s exactly what I hoped for — quietly, secretly that diving wouldn’t just be an activity, but a gateway to a deeper understanding of their island, their lagoon, their future.  A New Relationship with the OceanSharks, turtles, seagrass, reefs… These are no longer abstract words. They’re things they’ve seen, felt, understood, protected. A new relationship with the ocean is taking root. Not through big speeches -- but through accumulated experience:
 And Me, in the Middle of All ThisI watch them evolve, grow, open up.
This isn’t just a project. It’s a transformation. Each time a young diver tells me, “I’d like to work in the ocean too,” I feel that all the hours teaching, filming, reassuring, guiding… they all land somewhere meaningful. The Ambassadeurs du Lagon are no longer teenagers learning to dive. They are slowly becoming the Sentinelles du Lagon -- the future guardians of a world they’re only beginning to understand. And that might be the most beautiful thing I’ll have witnessed here. |
Serge Melesan
Underwater & Fine Art Ocean Photographer Specialist in Fine Art Ocean Photography. Published in Oceanographic Magazine & Earth.org. National Geographic Traveller – Portfolio Winner (2023). Archives
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