Coral under pressure in Caribbean Netherlands

In the 38 years that Erik Meesters has been a coral researcher himself, he has seen iconic coral reefs disappear: "Anyone who has seen coral while diving is enchanted by it. I’ve seen 500-year-old coral colonies. Bonaire had one that was 6 metres tall. That coral is now dead. And that makes me sad."

In 1973, the late professor Rolf Bak of NIOZ, the predecessor of Wageningen Marine Research, started monitoring coral reefs in Curaçao and Bonaire. Today, researchers from Wageningen Marine Research are working with local management organisations to monitor the situation on the BES islands of Bonaire, Saba and St Eustatius. Meesters: "Our research is the world's longest-running study on corals. The trend is unmistakable: decline."

On Bonaire, Saba and St Eustatius, Meesters and his colleagues are working with nature managers on the islands: Stinapa on Bonaire, Stenapa on St Eustatius and the Saba Conservation Foundation on Saba. Together, they keep an eye on the coral. In the 17 September 2025 edition of Nature, Meesters and colleagues published an analysis of more than 400 sites in the tropical western Atlantic. In the article, they show, among other things, that above the reef the water depth will increase and coral reefs grow too slowly. Message: with warming above two degrees Celsius, most reefs will erode by the year 2100. Not only is this leading to the disappearance of highly valuable ecosystems, but coastal defences provided by coral are also decreasing."

He explains what happens to coral when seawater warms up: "Coral is a skeleton made of calcium covered by thin animal tissue with algae cells. Those cells give the coral colour and provide energy: they convert sunlight into sugars and the coral uses the surplus to create the calcium skeleton. In the tropics, where you find the warm coral reefs, the seawater temperature has hardly fluctuated after the last ice age. In recent decades, we are seeing that the temperature is rising at a much faster rate than normal and also fluctuating more. The heat peaks in those fluctuations are particularly harmful to the symbiosis between the coral and the algae in the coral tissue."

As a result, the algae disappear from the animal tissue layer and the coral loses its colour: “In a short space of time, you then see white fields of coral skeletons. Within around three days, those skeletons usually become overgrown with other algae, giving them a brownish-green colour. Without the symbiotic algae from the tissue layer, the coral starves and dies. Unfortunately, we have been seeing that happening more and more in recent years."

And that makes him sad: "I think it is a bizarrely beautiful and important ecosystem. In addition, coral has great social value for the BES islands. Every year, over 180,000 tourists visit the islands by plane. Many of them come especially for the coral reefs. Moreover, because of their importance for wave breaking, the islands rely on the reefs for coastal protection. A healthy reef can grow with rising sea levels. If a reef fails to grow but instead erodes, the waves can come much further inland."

All ecosystems recover quickest when conditions change in their favour. The same applies to coral. Tackling pollution sources is an important step, says Meesters: "In Bonaire, wastewater is a problem. Most households still have cesspools. Because the subsoil is very often composed of lime, everything from those wells eventually ends up in the groundwater, and thus also in the coastal zone. Especially during tropical rainstorms, many wells overflow, causing their contents to flow directly to the sea. We sometimes measure extremely high concentrations of nutrients in coastal waters indicating sewage pollution."

There are solutions. Meesters lists them: "Central sewerage system where possible, or lockable septic tanks that can be drained. It would also be good if buffer zones were created on the land with vegetation that prevents water from running off so quickly. These don’t need to be expensive measures."

The reality is frustrating. In Bonaire, for example, a sewerage system was constructed on a limited scale, but in the meantime the island population has grown significantly. As a result, the net returns are negligible. And yes, for the sake of coral reefs and all other fragile ecosystems, fossil fuel use must be drastically reduced. Masters outlines the paradox: "The BES islands are heavily reliant for their income on tourists who fly there for the coral. Saba deliberately opts for more expensive tourism to reduce pressure. That’s a good first step.”

Local measures alone will not save the coral, he stresses: "The world really needs to try to stay below two degrees of warming. We are well on our way to exceeding that. This is disastrous for coral reefs. Even if fossil emissions are significantly reduced at some point, warming will continue for several hundred years."

On the subject of coral recovery projects, often a combination of ecological and technological measures, Meesters has clear views: "They are taking place, but on a scale nowhere near enough to stem the tide. Even if these projects increased tenfold, it would not be enough to save coral reefs. “We really need to do a better job: invest in sewers and landscape buffers, curb pollution and turn the dial on fossil emissions.” Otherwise, we have to accept that unique ecosystems like coral reefs will largely disappear."

• Ministry of Agriculture, Fisheries, Food Security and Nature
• Stinapa
• Stenapa
• Saba Conservation Foundation