There are two facts about our planet that, taken together, raise some big questions. First, coral reefs take up far less than 1% of the ocean floor, yet an estimated 25% of marine species depend on them at some point in their life cycle. Second, reefs have been a near-constant presence in tropical seas ever since complex, shelly animals first appeared over 500 million years ago.
Corals are only the latest in a long lineage of animal groups that have taken up the reefbuilding niche, constructing large mounds from robust shells. So the natural question becomes: have reefs maintained this outsized influence on marine biodiversity for the last 500 million years, or is that dynamic particular to the coral reefs of today?
In this work, I explored that question by producing the first high-resolution 3D reconstructions of Earth’s first reef builders that lived roughly 520 million years ago, in the earliest stages of animal evolution.
What I found is that these ancient reef structures were strikingly similar to modern corals in form and function—capable of withstanding wave energy, likely hosting photosynthetic partners, and creating rough, complex surfaces that enhanced nutrient exchange and provided new habitats for other organisms. Today we understand that the structural complexity of coral reefs—the nooks, crevices, and turbulent flow patterns—is a key reason they support so much life. My research shows that those same physical properties existed over 500 million years ago, when reefs built by archaeocyaths (an extinct group of sponges) introduced what I call a “Reef Roughness Revolution.” This term refers to a sudden increase in seafloor complexity far exceeding anything built by the microbial mats and stromatolites that came before.
Whether these ancient reefs directly helped drive the Cambrian explosion of animal diversity remains an open question, but these findings suggest that the relationship between reef architecture and biodiversity may be one of the oldest and most enduring in the history of life on Earth. Large-scale shifts in our biosphere may be more deeply tied to changes in reef ecosystems than we’ve appreciated.