• Energy Research

AbstractOver this century, coral reefs will run the gauntlet of climate change, as marine heatwaves (MHWs) become more intense and frequent, and ocean acidification (OA) progresses. However, we still lack a quantitative assessment of how, and to what degree, OA will moderate the responses of corals to MHWs as they intensify throughout this century. Here, we first projected future MHW intensities for tropical regions under three future greenhouse gas emissions scenario (representative concentration pathways, RCP2.6, RCP4.5 and RCP8.5) for the near‐term (2021–2040), mid‐century (2041–2060) and late‐century (2081–2100). We then combined these MHW intensity projections with a global data set of 1,788 experiments to assess coral attribute performance and survival under the three emissions scenarios for the near‐term, mid‐century and late‐century in the presence and absence of OA. Although warming and OA had predominately additive impacts on the coral responses, the contribution of OA in affecting most coral attributes was minor relative to the dominant role of intensifying MHWs. However, the addition of OA led to greater decreases in photosynthesis and survival under intermediate and unrestricted emissions scenario for the mid‐ and late‐century than if intensifying MHWs were considered as the only driver. These results show that role of OA in modulating coral responses to intensifying MHWs depended on the focal coral attribute and extremity of the scenario examined. Specifically, intensifying MHWs and OA will cause increasing instances of coral bleaching and substantial declines in coral productivity, calcification and survival within the next two decades under the low and intermediate emissions scenario. These projections suggest that corals must rapidly adapt or acclimatize to projected ocean conditions to persist, which is far more likely under a low emissions scenario and with increasing efforts to manage reefs to enhance resilience.

AbstractShifts from coral to algal dominance are expected to increase in tropical coral reefs as a result of anthropogenic disturbances. The consequences for key ecosystem functions such as primary productivity, calcification, and nutrient recycling are poorly understood, particularly under changing environmental conditions. We used a novel in situ incubation approach to compare functions of coral‐ and algae‐dominated communities in the central Red Sea bimonthly over an entire year. In situ gross and net community primary productivity, calcification, dissolved organic carbon fluxes, dissolved inorganic nitrogen fluxes, and their respective activation energies were quantified to describe the effects of seasonal changes. Overall, coral‐dominated communities exhibited 30% lower net productivity and 10 times higher calcification than algae‐dominated communities. Estimated activation energies indicated a higher thermal sensitivity of coral‐dominated communities. In these communities, net productivity and calcification were negatively correlated with temperature (>40% and >65% reduction, respectively, with +5°C increase from winter to summer), whereas carbon losses via respiration and dissolved organic carbon release more than doubled at higher temperatures. In contrast, algae‐dominated communities doubled net productivity in summer, while calcification and dissolved organic carbon fluxes were unaffected. These results suggest pronounced changes in community functioning associated with coral‐algal phase shifts. Algae‐dominated communities may outcompete coral‐dominated communities because of their higher productivity and carbon retention to support fast biomass accumulation while compromising the formation of important reef framework structures. Higher temperatures likely amplify these functional differences, indicating a high vulnerability of ecosystem functions of coral‐dominated communities to temperatures even below coral bleaching thresholds. Our results suggest that ocean warming may not only cause but also amplify coral–algal phase shifts in coral reefs.

The dataset reports 1) Bibliographic information of each original publication of exotic species impact; 2) number of replicates for controls and experimental treatments; 3) mean ± SD of control and experimental treatments; 4) Hedges’ g effect size and variation of impact; 5) Descriptive information of the recipient sites including latitude, longitude, depth; 6) Descriptive information of the study, including whether it was mensurative of manipulative in the field or laboratory, the level of organization of recorded impacts and the response variable; 7) Descriptive information of the exotic species, including species name, taxonomic group and trophic level; 8) Descriptive information on the recipient species, including taxonomic group and trophic level; 9) Thermal characterization of the recipient site; 10) Latitudinal and thermal characterization of the exotic species range of origin (RO); 11) Characterization of warming projections in the recipient site under RCP4.5 and RCP8.5 projections. Here we provide data on the ecological impacts of exotic marine species on recipient native ecosystems and characterise the thermal niche of both the recipient sites and each exotic species range of origin (RO). In addition, we provide the summertime warming trajectories of the recipient sites under RCP4.5 and RCP8.5 emission scenarios. Together, this dataset characterises the ecological impacts of exotic marine species and the climatic context under which these impacts occur. Overall this database represents 108 studies that have measured impacts of exotic species on recipient marine ecosystems where they were introduced, encompassing 748 observations from 80 sites and 50 species, ranging from primary producers (e.g. seagrass, macroalgae) to predators (e.g. fish, crustaceans, annelids). S.B. received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 659246. S.B., J.S-G and N.M. received funding from the Spanish Ministry of Economy, Industry and Competitiveness (MedShift, CGL2015-71809-P) and Fundación BBVA (project Interbioclima). J.M.P. received funding from the Australian Research Council Centre of Excellence for Coral Reef Studies (CE140100020). D.K.-J. received funding from the Independent Research Fund Denmark (CARMA; 8021-00222B). Author contributions: S.B, J.S-G, N.M and C.M.D. conceived and designed the study. A.A., N.R.G., C.E.L., E.T.A., J.C., D.K-J., N.M., P.M., J.M.P., and J.S-G. constructed the exotic species impacts data set. S.B. and J.S-G., compiled the exotic species range-of-origin dataset and G.J. compiled and analyzed the observed and projected ocean temperature data. S.B. and J.S-G performed the data analyses with contributions from all coauthors. Peer reviewed

AbstractThe term Blue Carbon (BC) was first coined a decade ago to describe the disproportionately large contribution of coastal vegetated ecosystems to global carbon sequestration. The role of BC in climate change mitigation and adaptation has now reached international prominence. To help prioritise future research, we assembled leading experts in the field to agree upon the top-ten pending questions in BC science. Understanding how climate change affects carbon accumulation in mature BC ecosystems and during their restoration was a high priority. Controversial questions included the role of carbonate and macroalgae in BC cycling, and the degree to which greenhouse gases are released following disturbance of BC ecosystems. Scientists seek improved precision of the extent of BC ecosystems; techniques to determine BC provenance; understanding of the factors that influence sequestration in BC ecosystems, with the corresponding value of BC; and the management actions that are effective in enhancing this value. Overall this overview provides a comprehensive road map for the coming decades on future research in BC science.

Understanding the consequences of rising CO 2 and warming on marine ecosystems is a pressing issue in ecology. Manipulative experiments that assess responses of biota to future ocean warming and acidification conditions form a necessary basis for expectations on how marine taxa may respond. Although designing experiments in the context of local variability is most appropriate, local temperature and CO 2 characteristics are often unknown as such measures necessitate significant resources, and even less is known about local future scenarios. To help address these issues, we summarize current uncertainties in CO 2 emission trajectories and climate sensitivity, examine region-specific changes in the ocean, and present a straightforward global framework to guide experimental designs. We advocate for the inclusion of multiple plausible future scenarios of predicted levels of ocean warming and acidification in forthcoming experimental research. Growing a robust experimental base is crucial to understanding the prospect form and function of marine ecosystems in the Anthropocene.