Investigation of Waterborne Chemical Cues for Coral Larval Settlement

This study aimed to address critical knowledge gaps in coral larval settlement processes. We explored the role of waterborne chemical cues in promoting settlement and metamorphosis, which are fundamental steps for coral sexual propagation. Over 35 bioassays were conducted with seven spawning and two brooding species of coral larvae and demonstrated that dissolved compounds in aquarium seawater can effectively induce metamorphosis and settlement for most spawning coral species. Seawater from a diverse coral reef ecosystem consistently induced settlement, suggesting the critical role of biodiversity in producing effective cues. Filtered aquarium seawater (0.2 µm filtration to remove particles and most bacteria) retained its inductive properties for most species, attributing effectiveness to dissolved compounds rather than bacteria or particles. Using solid-phase extraction techniques with C18 resin, inductive compounds were extracted from seawater. These retained compounds proved effective in settlement bioassays. 4 C3E63B May 2025 Fractionation over C18 columns indicated that polar fractions induced the highest settlement and metamorphosis, providing a pathway for identifying specific biochemical inducers. The isolation and characterization of these waterborne cues may lead to new methods that improve recruitment outcomes, even on degraded reefs with limited natural cues. Our research findings emphasize the importance of preserving species-rich habitats on coral reefs to maintain natural settlement dynamics. Our future directions involve further fractionation and analysis of active compounds to continue to isolate and characterize specific settlement inducers. Plans also include broader testing across coral species and aquarium coral reef environments to refine applications of these cues for restoration projects. This study highlights the importance of integrating chemical ecology into coral reef restoration, paving the way for more effective and sustainable conservation practices.