Project description:Mesophotic coral reefs have been proposed as refugia for corals, providing shelter and larval propagules for shallow-water reefs that are disproportionately challenged by global climate change and local anthropogenic stressors. Yet, knowledge of the capacity of coral larvae to adjust to different depth environments is still limited. In this study, planulae of the reef-building coral Stylophora pistillata from 5-8 and 40-44 m depth in the Gulf of Aqaba were tested in a long-term in situ translocation experiment for their ability to settle and acclimate to reciprocal depth conditions. We assessed survival rates, photochemical, physiological and morphological characteristics, as well as gene expression variations in juveniles grown at different depths, comparing them to non-translocated adults, juveniles and planulae. We found high mortality rates among mesophotic-origin planulae, irrespective of translocation depth. Gene expression patterns suggested that deep planulae lacked settlement competency and experienced increased developmental stress upon release. Symbiont photochemical acclimation to depth occurred rapidly within 8 days, with symbiont populations showing changes in photochemical traits but no symbiont species shuffling between deep and shallow juveniles. In contrast, coral host physiological and morphological acclimation were less evident. We observed minimal overlap in gene expression patterns between different life stages and depths, indicating that gene expression significantly depends on life stage. The study also identified a set of DEGs associated with initial stress responses following translocation, lingering stress response, and environmental effects of depth. In conclusion, though our data reveal rapid symbiont acclimation, host acclimation to match deep coral phenotypes was incomplete within 60 days for planulae translocated to different depths. These results have implications for understanding the ecological significance of mesophotic reefs as potential larval sources in the face of environmental stressors.
Project description:Scleractinian corals are the major builders of the complex structural framework of coral reefs. They live in tropical waters around the globe where they are frequently exposed to potentially harmful ultraviolet radiation (UVR). Coral eggs and early embryonic stages are thought to be the most sensitive life stages of corals to UVR given that they are highly buoyant and remain near the sea surface for prolonged periods of time. Here we analyzed gene expression changes in different larval stages of the Caribbean coral Montastraea faveolata to natural levels of UVR using high-density cDNA microarrays (10,930 clones). We found that larvae exhibit low sensitivity to natural levels of UVR during most time points analyzed as reflected by comparatively few transcriptomic changes in response to UVR. However, we identified a time window of high UVR sensitivity that coincides with the motile planula stage and the onset of larval competence. These processes have been shown to be affected upon UVR exposure, and the transcriptional changes we identified explain these observations well. Our analysis of differentially expressed genes indicates that UVR induces a stress response and affects the expression of neurogenesis-related genes that can be linked to swimming and settlement behavior at later stages. Taken together, our study provides further data to the impact of natural levels of UVR on coral larvae. Furthermore, our results might allow a better prediction of settlement and recruitment rates after coral spawning events based on UVR climate data.