Search for: All records

Coral reefs are among the most diverse and complex ecosystems in the world that provide important ecological and economical services. Increases in sea surface temperature linked to global climate change threatens these ecosystems by inducing coral bleaching. However, it is not fully known if natural intra- or inter-annual physiological variability is linked to bleaching resilience or recovery capacity of corals. Here, we monitored the coral physiology of three common Caribbean species ( Porites divaricata, Porites astreoides, Orbicella faveolata ) at six time points over 2 years by measuring the following traits: calcification, biomass, lipids, proteins, carbohydrates, chlorophyll a , algal endosymbiont density, stable carbon isotopes of the host and endosymbiotic algae, and the stable carbon and oxygen isotopes of the skeleton. The overall physiological profile of all three species varied over time and that of P. divaricata was consistently different from the two other coral species. Porites divaricata had higher energy reserves coupled with higher contributions of heterotrophically derived carbon to host tissues than both P. astreoides and O. faveolata . Consistently higher overall energy reserves and heterotrophic contributions to tissues appear to buffer against environmental stress, including bleaching events. Thus, natural physiological variability among coral species appears to be a stronger predictor of coral bleaching resilience than intra- or inter-annual physiological variability within a coral species. 

Climate change poses a major threat to coral reefs. We conducted an outdoor 22-month experiment to investigate if coral could not just survive, but also physiologically cope, with chronic ocean warming and acidification conditions expected later this century under the Paris Climate Agreement. We recorded survivorship and measured eleven phenotypic traits to evaluate the holobiont responses of Hawaiian coral: color, Symbiodiniaceae density, calcification, photosynthesis, respiration, total organic carbon flux, carbon budget, biomass, lipids, protein, and maximumArtemiacapture rate. Survivorship was lowest inMontipora capitataand only some survivors were able to meet metabolic demand and physiologically cope with future ocean conditions. MostM. capitatasurvivors bleached through loss of chlorophyll pigments and simultaneously experienced increased respiration rates and negative carbon budgets due to a 236% increase in total organic carbon losses under combined future ocean conditions.Porites compressaandPorites lobatahad the highest survivorship and coped well under future ocean conditions with positive calcification and increased biomass, maintenance of lipids, and the capacity to exceed their metabolic demand through photosynthesis and heterotrophy. Thus, our findings show that significant biological diversity within resilient corals likePorites, and some genotypes of sensitive species, will persist this century provided atmospheric carbon dioxide levels are controlled. SincePoritescorals are ubiquitous throughout the world’s oceans and often major reef builders, the persistence of this resilient genus provides hope for future reef ecosystem function globally.

 

Mass bleaching events are predicted to occur annually later this century. Nevertheless, it remains unknown whether corals will be able to recover between annual bleaching events. Using a combined tank and field experiment, we simulated annual bleaching by exposing three Caribbean coral species ( Porites divaricata , Porites astreoides and Orbicella faveolata ) to elevated temperatures for 2.5 weeks in 2 consecutive years. The impact of annual bleaching stress on chlorophyll a , energy reserves, calcification, and tissue C and N isotopes was assessed immediately after the second bleaching and after both short- and long-term recovery on the reef (1.5 and 11 months, respectively). While P. divaricata and O. faveolata were able to recover from repeat bleaching within 1 year, P. astreoides experienced cumulative damage that prevented full recovery within this time frame, suggesting that repeat bleaching had diminished its recovery capacity. Specifically, P. astreoides was not able to recover protein and carbohydrate concentrations. As energy reserves promote bleaching resistance, failure to recover from annual bleaching within 1 year will likely result in the future demise of heat-sensitive coral species.