Award: IOS-1937770

Over the past several decades, global coral reef ecosystems have experienced a substantial decline in coral cover. In recent years, deeper reef systems have gained considerable interest as they appear to be buffered from impacts affecting shallow-water coral reefs and may, therefore, serve as important areas of refuge for coral survival.Yet conditions differ dramatically from shallow to deep reefs, requiring adaptation or acclimation. Here, we aimed to determine how the morphology and physiology of scleractinian corals changes across vertical depth gradients and what mechanisms drive these changes. Three core questions guided the project: (1) Are changes in morphology, physiology, and gene expression consistent across different environmental conditions? (2) Are these traits intrinsically or extrinsically controlled? (3) How are these traits inherited and what impact do they have on recruitment success? To address these questions, a three-tiered approach was employed: (1) comprehensive assessments of coral morphology, gene expression, and environmental factors across depth gradients in the Gulf of Aqaba and the Caribbean; (2) reciprocal transplants of adult corals between shallow and mesophotic reefs to assess acclimatization; and (3) studies on larval ecology, settlement, and recruitment. The research combined molecular techniques, fluorescence imaging, and environmental monitoring to provide a holistic understanding of coral adaptation. The results of this research yielded significant insights into coral adaptation mechanisms. First, we found that morphology shifted across depths without corresponding genetic divergence, suggesting that corals adjust skeletal structures in response to local environmental conditions. Corals also exhibited unique symbiont assemblages and photophysiological adjustments associated with depth, which enables them to optimize light capture. Likewise, stable isotope analyses demonstrated shifts in coral reliance on autotrophy versus heterotrophy based on depth and light availability. However, thermal tolerance of corals was found to be similar across depths, suggesting the capacity for refuge from increasing temperatures on deeper reefs that tend to be buffered during heat waves. Next, we found differences in rates of growth, survival, and gene expression for corals transplanted across depths, which provide evidence for molecular-level acclimatization to new environmental conditions. Finally, we found differences in larval ecology and settlement between shallow and deep reefs that were species and location specific. However, juvenile morphology and physiology were found to be determined more by environmental conditions than parental history, suggesting the capacity of corals to adapt to new conditions during their early life stages. These findings contribute to the broader understanding of coral reef ecology, photophysiology, and adaptation to environmental stressors, which will help predict how corals may respond to future conditions. The results of this project contributed to 14 peer reviewed publications and were shared with the scientific community at multiple local, regional, and global scientific conferences, with the general public through invited lectures at the Cayman Islands National Gallery, the Smithsonian Tropical Research Institute, the Boston Sea Rovers, and onboard the Explora Journeys cruise line, as well as being broadly distributed through social media and the popular press. Over the course of the project, 13 young scientists were trained in field and laboratory techniques, ranging from undergraduate students to postdoctoral researchers, each gaining expertise in mesophotic coral research, bioinformatics, and fluorescence imaging techniques. In addition, a five-day Coral Ecophysiology Workshop was held at the Central Caribbean Marine Institute facility in the Cayman Islands that provided hands-on experience and trained 10 early-career coral reef scientists. Overall, this project has significantly advanced knowledge on coral adaptation while fostering a new generation of marine scientists. The integration of field studies, molecular analyses, and international collaborations has positioned this research as a critical contribution to coral reef conservation efforts worldwide and provide a foundation for future studies on coral adaptation and mesophotic reef conservation. By improving our understanding of coral resilience mechanisms, this research informs strategies for reef management and climate adaptation, ensuring the long-term health of coral ecosystems that contribute significantly to economic stability and global health. Last Modified: 04/17/2025 Submitted by: GretchenGoodbody Gringley