Biology subjects

Roik, A.

Publications and source records attributed to Roik, A..

4 recordsLinked to original sources

bioRxiv2024

Thermal preconditioning modulates coral physiology and heat tolerance: A multi-species perspective

Global warming threatens reef-building corals by challenging their natural adaptive capacity. Therefore, interventions such as stress hardening by thermal preconditioning could become crucial for their survival. Stress-hardening approaches recognize that organisms living in thermally variable environments are better able to withstand marine heat waves. However, a systematic assessment of preconditioning effects on the baseline physiology and thermal tolerance across coral species is lacking. We assessed the changes of thermal tolerance in six stony coral species (Galaxea fascicularis, Porites rus, Acropora muricata, Montipora digitata, and Stylophora pistillata) in three thermal preconditioning treatments of stable-high 29 {degrees}C and variable-high 29 {degrees}C with a daily oscillation of {+/-} 1.5 {degrees}C, compared to corals in stable-ambient 26 {degrees}C. We quantified changes in photosynthetic efficiency and coral bleaching intensity before and after a short-term heat stress assay and up to 30 days later. Stress-hardening success after preconditioning was observed in nearly all preconditioned corals, but the increases in thermal tolerance were species-specific. The greatest increase was recorded in G. fascicularis and A. muricata, with stress responses reduced by over 80 %. In contrast, preconditioning regimes had minor effects on stress tolerance of S. pistillata, making it least receptive to this intervention. After 30 days, most stress-hardened species demonstrated higher survival and recovery rates than their conspecifics from the stable-ambient regime. Notably, both preconditioning regimes affected baseline physiology, especially in the branching species, as indicated by minor tissue paling and decreased photosynthetic efficiency. We conclude that implementing thermal stress hardening protocols will require careful consideration of the species-specific receptiveness and evaluation of the potential trade-offs that can be inflicted with the post-conditioning shifts in physiological baselines.

ecology↗

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↗

bioRxiv2023

Natural thermal stress-hardening of corals through cold temperature pulses in the Thai Andaman Sea

Thermal variability can render corals stress resistant through a phenomenon coined as "stress-hardening induced by environmental priming". Fluctuations that involve high temperature peaks have been commonly investigated, however, the effects of a stress-hardening stimulus generated by cold-water pulses has rarely been studied. Offshore island reefs in the Andaman Sea offer an ideal natural setting to study these effects, as cooling water of internal waves induce strong variability with peak intensity in January to June and absence in August to November. While western island shores are exposed to this stimulus, eastern shores remain sheltered. This study examined (1) whether corals from exposed reefs were more heat stress resistant compared to stimulus-sheltered conspecifics and (2) whether this trait can last in the absence of the stimulus. We quantified the thermal stress resistance in two ecologically important coral species, Pocillopora sp. and Porites sp., from the two island shores, during the two seasons. Coral bleaching intensity and photosynthetic efficiency of algal symbionts were measured as response variables after a short-term heat stress assay (24-48 h, 34 {degrees}C) to assess thermal stress resistance. Stress responses of all stimulus-exposed corals were either undetectable (during the season of stimulus presence) or very weak (during stimulus absence), while corals from the stimulus-sheltered shore responded strongly to heat stress irrespective of the season. Hence, thermal resistance was overall greater in corals originating from the stimulus-exposed shore, but it was slightly diminished during the season of stimulus absence, emphasizing the relevance of stimulus recurrence in maintaining the resistance trait. We exemplify that the stimulus of fluctuating low temperature pulses successfully induced stress-hardening in corals. This suggests that priming stimuli do not necessarily need to transgress certain upper thermal thresholds, but can also touch on lower thresholds to be effective. Even more, we argue that cooling pulses might represent a safer stress-hardening regime, since warming-stress accumulation can be avoided. More research is required to obtain a better understanding of environmental priming, but current findings should encourage the development of artificial stress-hardening approaches to enhance coral resistance in reef restoration efforts.

ecology↗

bioRxiv2017

Coral reef carbonate budgets and ecological drivers in the naturally high temperature and high alkalinity environment of the Red Sea

The coral structural framework is crucial for maintaining reef ecosystem function and services. In the central Red Sea, a naturally high alkalinity is beneficial to reef growth, but rising water temperatures impair the calcification capacity of reef-building organisms. However, it is currently unknown how beneficial and detrimental factors affect the balance between calcification and erosion, and thereby the overall growth of the reef framework. To provide insight into present-day carbonate budgets and reef growth dynamics in the central Red Sea, we measured in situ net-accretion and net-erosion rates (Gnet) by deployment of limestone blocks and estimated census-based carbonate budgets (Gbudget) in four reef sites along a cross-shelf gradient (25 km). We assessed abiotic variables (i.e., temperature, inorganic nutrients, and carbonate system variables) and biotic drivers (i.e., calcifier and bioeroder abundances). On average, total alkalinity AT (2346 - 2431 mol kg-1), aragonite saturation state (4.5 - 5.2 {Omega}a), and pCO2 (283 -315 atm) were close to estimates of pre-industrial global ocean surface waters. Despite these calcification-favorable carbonate system conditions, Gnet and Gbudget encompassed positive (offshore) and negative net-production (midshore-lagoon and exposed nearshore site) estimates. Notably, Gbudget maxima were lower compared to reef growth from pristine Indian Ocean sites. Yet, a comparison with historical data from the northern Red Sea suggests that overall reef growth in the Red Sea has likely remained similar since 1995. When assessing sites across the shelf gradient, AT correlated well with reef growth rates ({rho} = 0.89), while temperature was a weaker, negative correlate ({rho} = -0.71). Further, AT explained about 65 % of Gbudget in a best fitting distance-based linear model. Interestingly, parrotfish abundances added up to 82% of explained variation, further substantiating recent studies highlighting the importance of parrotfish to reef ecosystem function. Our study provides a baseline that will be particularly useful in assessing future trajectories of reef growth capacities in the Red Sea under continuous ocean warming and acidification.

ecology↗