Reef show architectural expertise with complex shapes for survival

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From the coral reefs of the tropics to the oyster reefs of temperate estuaries, nature's most diverse ecosystems are built by "master architects." A study published in Nature revealed that the complex shapes of these reefs are not random-they follow precise geometric rules that maximize survival.

The collaborative research of the University of Hawaiʻi at Mānoa Hawaiʻi Institute of Marine Biology (HIMB) and Macquarie University in Sydney, Australia, offers a proven guide for reviving damaged marine habitats and protecting the vital seafood sources that communities depend on.

"This work shows that there are universal architectural rules for reef persistence," said Joshua Madin, a senior author of the study, HIMB research professor, and a principal investigator of the HIMB Conservation Innovation Group. "Nature has already solved the design problem. Our job is to read that blueprint and scale it up to help reefs grow faster and survive longer."

Geometry of survival

Using high-resolution 3D mapping and field experiments in Australia, the team engineered concrete structures spanning a wide range of surface complexities. They discovered that while simple structures left juvenile oysters exposed to predators, and overly complex structures offered diminishing returns, survival peaked at a specific, optimal combination of height and fractal dimension-exactly the geometry found in thriving natural reefs.

"Reefs are not just piles of skeletons or shells," said Juan Esquivel-Muelbert, the study's lead author from Macquarie University. "They are finely tuned three-dimensional machines. Their shape controls who lives, who dies, and how fast the reef grows."

While the fieldwork focused on oysters, the theoretical principles were developed at HIMB and apply directly to coral reefs.

R3D project

The study provides the biological validation for cutting-edge restoration work currently underway in Hawaiʻi. The geometric principles utilized in this paper are a driving force behind the UH project Rapid Resilient Reefs for Coastal Defense (R3D), a project funded by the Defense Advanced Research Projects Agency that is deploying immense, geometric reef modules off the coast of Oʻahu.

By mimicking the "optimal geometry" of coral reef, using the same principles identified in the study, these artificial structures are designed to do more than just break waves-they are engineered to attract coral larvae, protect them from predators and grow into a thriving coral reef.

"We are applying these exact principles to coral restoration here in Hawaiʻi," said Madin. "Recent work at HIMB testing these 3D-printed designs showed we could increase the settlement and survival of corals by 80-fold compared to natural reef surfaces. By building with the right geometry, we can jump-start the feedback loops that allow reefs to build themselves."

Global solution for degraded coasts

With more than half of the world's coral reefs and 85% of oyster reefs lost or severely degraded, the need for effective restoration is urgent. This study moves the field beyond using generic concrete blocks or riprap, offering a quantitative framework for engineering restoration structures that work across different ecosystems-from saltmarshes to coral reefs.

"If we can capture the right combinations of shape and complexity, we can design restoration structures that function like healthy reefs within a few years," said Madin. "This is about integrating nature's own engineering into coastal infrastructure to protect our shorelines and support marine life."

Photo captions:

Image 1: Experimental set-up showing modules, half of which were caged to exclude predators of oysters. Credit: Juan Esquivel-Muelbert

Image 2: Oysters build reefs by iteratively growing on previous generations. Credit: Juan Esquivel-Muelbert

Image 3: Coral experimental modules ready for deployment at the Hawaiʻi Institute of Marine Biology. Credit: Allison Nims

Image 4: Coral babies (green splodges) growing experimental modules at the Hawaiʻi Institute of Marine Biology. Credit: Marion Chapeau