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The future of coral reefs in a warming world depends on corals’ ability to recover from bleaching, the loss of their symbiotic dinoflagellate algae (Symbiodiniaceae) during marine heatwaves. Heat-tolerant symbiont species can remain in symbiosis during heat stress, but often provide less photosynthate to the host than heat-sensitive species under ambient conditions. Understanding how heat stress changes the dynamics of this tradeoff between stress tolerance and mutualism contribution is crucial for predicting coral success under climate change. To test how symbiont resource allocation affects coral recovery from heat stress, we exposed the coral Montipora capitata hosting either heat-sensitive Cladocopium C31 (C) or heat-tolerant Durusdinium glynnii (D) to heat stress. D regained symbiont density and photochemical efficiency faster after heat treat- ment than C, but symbiont recovery did not restore coral biomass or calcification rates to pre-bleaching levels in the initial recovery period. D populations also contributed less photosynthate to the host relative to C, even during heat stress. Further, higher-density symbiont populations of both species retained more photosynthate than lower-density populations, and corals receiving less photosynthate exhibited reduced calcification rates and lower intracellular pH. This is the first evidence that symbiont density and carbon translocation are negatively related, and the first to establish a link between Symbiodiniaceae carbon translocation and coral cellular homeostasis. Together, these results suggest the energy demand of symbiont regrowth after bleaching reduces their mutualism contribution and can thus delay host recovery. Reestablishing a beneficial endos- ymbiosis imposes additional costs as holobionts overcome stress, and may explain latent mortality among coral populations after alleviation of heat stress in the field.
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Coral growth persistence amidst bleaching events
Abstract As mass bleaching events decimate stony coral populations, production of calcium carbonate is diminished on reefs, dampening their capacity to keep pace with rising sea levels. However, perturbations to the calcification process of surviving wild corals during bleaching are poorly constrained, owing to the lack of suitable techniques to retroactively extract this information from coral skeletons at sufficient resolution. Here, we use novel Raman spectrometry techniques to test the biogeochemical response of long‐lived corals before, during, and after bleaching. Maintenance of high aragonite saturation state (ΩAr) in the coral calcifying fluid is key to driving rapid skeletal growth but would be expected to decrease when corals become energetically depleted without their symbionts. Contrary to this expectation, our results demonstrate that corals upregulate calcifying fluid ΩArduring bleaching and for at least 2 yr after recovery. This indicates that the calcification process of coral‐bleaching survivors is unexpectedly resilient.
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- Award ID(s):
- 2117987
- PAR ID:
- 10428996
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography Letters
- Volume:
- 8
- Issue:
- 5
- ISSN:
- 2378-2242
- Format(s):
- Medium: X Size: p. 734-741
- Size(s):
- p. 734-741
- Sponsoring Org:
- National Science Foundation
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