Ocean acidification and the shifting goldilocks zone of cold-water coral growth

Cold-water corals build three-dimensional frameworks that support a wide range of marine life and provide important ecosystem services. These reefs provide a shelter and feeding grounds to myriads of organisms, and they act as long-term carbon stores. Previous modelling work has shown how their survival depends on prey capture within a hydrodynamic Goldilocks zone, where currents are strong enough to deliver food but not so strong that they prevent coral polyps to catch prey. But flow conditions and food availability are only part of the story; ocean acidification is emerging as a serious challenge to the persistence of cold-water coral reefs, threatening their skeletons and putting in danger all the marine life that depends on them.

In aragonite under-saturated waters, dead coral frameworks can dissolve. Experiments have shown that once living tissue is lost, exposed skeleton becomes porous, fragile, and prone to crumbling. This process steadily erodes the complex frameworks that these corals have built over centuries. To explore this mechanism in more detail, a numerical model was developed using Smoothed Particle Hydrodynamics (SPH) to capture the balance between reef growth, dissolution, and recovery under different acidification scenarios.

The results reveal that, although living corals can continue to grow, the supporting dead skeleton is far more vulnerable. Once dissolution rates exceed calcification rates, reef accretion becomes negative, and colonies fragment into smaller, isolated patches. Simulations also show that, if acidification pressures ease, surviving colonies can regrow and rebuild lost structure, though recovery times are strongly dependent on the extent of initial damage. In some cases, regrowth is fast early on where the competition is reduced, but long-term recovery depends on whether the reef framework remains intact enough to support additional expansion.

The coupling of reef growth and energetic demands models with dissolution processes offers a more complete perspective on how cold-water corals respond to ocean acidification. It highlights that while colonies can persist and survive, the loss of dead framework leads to a decline in habitat complexity. Future expansion of this model will create a predictive tool for that will be able to guide conservation strategies and inform the design of restoration initiatives, accounting for different environmental stressors.