COS 90-4 - The effect of reef morphology on coral recruitment across multiple scales

Abstract: Coral reefs support marine ecosystems throughout the tropics, yet corals are increasingly threatened by ocean heatwaves. One pathway for rebuilding reefs is to identify habitats where coral larvae are most likely to settle and survive, and to enhance conditions for coral recruitment there. Coral reef morphology, i.e., the structural form of reef substrate, affects many aspects of reef function, yet the effect of reef morphology on coral recruitment is not well understood. We used a combination of Structure-from-Motion photogrammetry and remote sensing to measure reef morphology (rugosity, slope, and other metrics) on a continuum of scales and examined the effect of morphology on coral recruitment in a culturally important Hawaiian fishery. We also measured larval import, reef fish, and adult coral populations to identify conditions facilitating coral recruitment across multiple coral genera. We found that these variables explained 72% of coral recruitment in the study region. Reef rugosity and curvature measured at ≥ 2 m spatial resolution were significantly and positively correlated with coral recruitment; however, reef morphology measured at finer scales (≤ 32 cm resolution) was not significant. Larval import estimated from hydrodynamic models was positively related to Porites and Montipora recruitment, and fish (grazer) density was negatively linked to coral recruitment in all genera. Our results indicate that reef rugosity and curvature at intermediate to coarse scales may bolster coral recruitment in broadcast spawning species, perhaps by altering larval flow dynamics and coral sheltering. Coral reef morphology is an important indicator of restoration potential that can be detected by remote sensing, enabling restoration sites to be efficiently identified.