Ancient Glow: Bioluminescence Traced to Octocorals About 540 Million Years Ago

In the ocean's deepest, darkest reaches, some animals make their own light. A new analysis suggests the ability to produce bioluminescence first appeared in the common ancestor of octocorals during the Cambrian, roughly 540 million years ago — more than twice as old as the previous oldest record.

“We wanted to figure out the timing of the origin of bioluminescence, and octocorals are one of the oldest groups of animals on the planet known to bioluminesce,” said Danielle DeLeo (Smithsonian Institution), the study's lead author.

Octocorals are colonial animals made of many small polyps. Unlike stony corals, they typically have softer skeletons and are named for the eightfold symmetry of each polyp. Some species emit light, usually when disturbed, but the ecological purpose of the glow remains debated: it may attract prey, or act as a defensive signal that draws larger predators to consume small grazers damaging the coral.

The research team combined a genetic family tree of 185 octocoral taxa (published in 2022) with new field observations of living species that glow. Fieldwork by Manabu Bessho-Uehara (Nagoya University) and Andrea Quattrini (Smithsonian Institution) documented bioluminescence in five octocoral types not previously reported to glow, expanding the dataset available for analysis.

Using ancestral-state reconstruction and several statistical models, the researchers estimated whether ancestral octocorals likely produced light. All methods converged on the same conclusion: the most recent common ancestor of living octocorals very likely had bioluminescence about 540 million years ago.

That timing places the origin of bioluminescence in the Cambrian, an era of rapid animal diversification when light-sensitive marine invertebrates with simple eyes already existed. The coincidence suggests possible ecological interactions between early light producers and light detectors, which may have influenced the evolution of glowing traits.

Why this matters

Finding such an ancient origin reshapes how scientists think about the evolution of light production and highlights bioluminescence as a very early animal adaptation. It also raises new questions: if the common ancestor of octocorals glowed, why do relatively few living octocoral species still display bioluminescence? How and why was the trait lost in many lineages?

Next steps

Researchers plan to investigate how and when bioluminescence was lost across octocoral branches and to study the ecological contexts that favored either retention or loss of the trait. Those studies could reveal more about Cambrian ecosystems and the selective pressures that shaped early animal behavior.

The study was published in Proceedings of the Royal Society B: Biological Sciences. An earlier version of this article appeared in April 2024.