Strahl, J. | Search bioRxiv

bioRxiv2023

Trade-offs in a reef-building coral after six years of thermal acclimation

Evidence is growing that reef-building corals have the capacity to acclimate to new and challenging thermal conditions by increasing their thermal resistance. This raises hopes for their future persistence in a warming world. However, potential trade-offs that accompany such resistance gains, have remained largely unexplored. We provide the first report on the physiological trade-offs in a globally abundant and ecologically relevant coral species (Pocillopora acuta), after a long-term exposure to an elevated temperature of 31 {degrees}C in comparison to conspecifics cultivated under a cooler control thermal regime. At both temperatures, corals consistently appeared to be visually healthy throughout a six-year period. At 31 {degrees}C, corals had increased metabolic rates (both respiration and photosynthesis) that resulted in higher biomass accumulation and total energy reserves compared to the corals from the ambient regime. Further, the composition of coral host tissues shifted in favor of lipid build-up, suggesting an altered mechanism of energy storage. The increase in biomass growth came at the cost of declining skeletal growth rates and the formation of higher density skeletons. In the long-term, this trade-off will result in lower extension rates that can entail major ramifications for future reef building processes and reef community composition. Moreover, symbionts at 31 {degrees}C were physiologically more compromised with overall lower energy reserves, possibly indicating a stronger exploitation by the host and potentially a lower stress resilience. Our study provides first insights into a successful thermal acclimation mechanism that involved the prioritization of energy storage over skeletal growth, entailing higher demands on the symbionts. Our observation in this 6-year study does not align with observations of short-term studies, where elevated temperatures caused a depletion of tissue lipids in corals, which highlights the importance of studying acclimation of organisms over their relevant biological scales. Further investigations into trade-offs at biologically relevant scales and how they unfold under an acute heat stress will help to provide a more comprehensive picture of the future coral reef trajectory. Importantly, these insights will also help improve interventions aimed at increasing the thermal resilience of corals which anticipate to use thermal preconditioning treatments for stress-hardening. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=96 SRC="FIGDIR/small/549699v2_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@139b33corg.highwire.dtl.DTLVardef@1264477org.highwire.dtl.DTLVardef@158f7c9org.highwire.dtl.DTLVardef@1f3c35a_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2017

Functional genomic analysis of corals from natural CO2-seeps reveal core molecular responses involved in acclimatization to ocean acidification

Little is known about the potential for acclimatization or adaptation of corals to ocean acidification and even less about the molecular mechanisms underpinning these processes. Here we examine global gene expression patterns in corals and their intracellular algal symbionts from two replicate population pairs in Papua New Guinea that have undergone long-term acclimatization to natural variation in pCO2. In the coral host, only 61 genes were differentially expressed in response to pCO2 environment, but the pattern of change was highly consistent between replicate populations, likely reflecting the core expression homeostasis response to ocean acidification. Functional annotations highlight lipid metabolism and a change in the stress response capacity of corals as a key part of this process. Specifically, constitutive downregulation of molecular chaperones was observed, which may impact response to combined climate-change related stressors. Elevated CO2 has been hypothesized to benefit photosynthetic organisms but expression changes of in hospite Symbiodinium in response to acidification were greater and less consistent among reef populations. This population-specific response suggests hosts may need to adapt not only to an acidified environment, but also to changes in their Symbiodinium populations that may not be consistent among environments. This process adds another challenging dimension to the physiological process of coping with climate change.

genomics↗