Cylindrical, pylon-like structures with helix recesses enhance coral larval recruitment

The decline of coral reefs requires scalable restoration strategies to enhance natural recovery processes such as coral larval recruitment. Previous research has shown that conical structures with helix recesses substantially increase settlement and early survival. However, the applicability of this microhabitat design with helix recesses in broader engineering contexts has yet to be assessed. Hereby, we tested (1) whether helix recesses can be transferred from conical dome geometries to space-efficient cylindrical pylon-like geometries, and (2) whether they can be implemented with different materials. In a field experiment in Kāneʻohe Bay, Hawaiʻi, coral recruitment was monitored over six months on cylindrical and conical structures incorporating an optimized helix profile. Cylindrical modules supported recruitment densities similar to those on conical designs, demonstrating a successful transfer of the microhabitat design to compact geometries. Planar recruit densities were ∼300 times higher across all structures, compared to those observed on nearby natural reefs. These results show that the helix recess design is functionally robust across both module shapes and materials. Cylindrical structures with integrated helix recesses, therefore, represent a practical, low-cost design element that can be incorporated in coastal engineering and restoration projects to enhance coral settlement.