Internal Feedback Shapes Coral Reefs
Charles Darwin’s first monograph, published in 1842, proposed a theory that linked coral-reef formation to underwater mountains and sea-level changes. Miguel Álvarez-Alegría and his colleagues at the University of the Balearic Islands and the Spanish Research Council now show that reef structures can form without the need for preexisting geological formations [1]. Instead, their mathematical model relies on internal feedback mechanisms, including coral growth, resource competition, and accretion dynamics.
Coral reefs are formed from the accumulation of aragonite (calcium carbonate) exoskeletons secreted by individual coral polyps. Álvarez-Alegría and colleagues developed a model of reef development that combines various terms that have been studied previously—polyp physiology and mineral erosion, for example—but that have not been considered together. Their model describes the temporal evolution of polyp density and the buildup of aragonite at a given location. Crucially, it includes a self-limiting feedback loop, in which aragonite accretion negatively affects polyp survival by exposing the coral to drying.
In a 1D version of the model, the team observed evolving structures that resembled reef patterns found in nature. These patterns arose from the interaction of waves of reef growth traveling in opposite directions. This excitation-like instability is distinct from the Turing-type instabilities that are commonly invoked in biological pattern formation and that have been put forward to explain coral-reef development specifically.
The finding demonstrates that mathematical models can reproduce the temporal development of atolls and fringing reefs—two common reef structures—on the basis of purely internal factors, in an approach that the researchers say is complementary to Darwin’s theory. It offers a simplified framework for evaluating the resilience of coral reefs in the face of increasingly complex environmental stressors.
–Rachel Berkowitz
Rachel Berkowitz is a Corresponding Editor for Physics Magazine based in Vancouver, Canada.
References
- M. Álvarez-Alegría et al., “Excitable dynamics and coral reef formation: A simple model of macro-scale structure development,” Phys. Rev. Res. 7, 023196 (2025).