Contrasting heat stress response patterns of coral holobionts across the Red Sea suggest distinct mechanisms of thermal tolerance

Christian R. Voolstra*, Jacob J. Valenzuela, Serdar Turkarslan, Anny Cárdenas, Benjamin C.C. Hume, Gabriela Perna, Carol Buitrago-López, Katherine Rowe, Monica V. Orellana, Nitin S. Baliga, Suman Paranjape, Guilhem Banc-Prandi, Jessica Bellworthy, Maoz Fine, Sarah Frias-Torres, Daniel J. Barshis*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

63 Scopus citations


Corals from the northern Red Sea, in particular the Gulf of Aqaba (GoA), have exceptionally high bleaching thresholds approaching >5℃ above their maximum monthly mean (MMM) temperatures. These elevated thresholds are thought to be due to historical selection, as corals passed through the warmer Southern Red Sea during recolonization from the Arabian Sea. To test this hypothesis, we determined thermal tolerance thresholds of GoA versus central Red Sea (CRS) Stylophora pistillata corals using multi-temperature acute thermal stress assays to determine thermal thresholds. Relative thermal thresholds of GoA and CRS corals were indeed similar and exceptionally high (~7℃ above MMM). However, absolute thermal thresholds of CRS corals were on average 3℃ above those of GoA corals. To explore the molecular underpinnings, we determined gene expression and microbiome response of the coral holobiont. Transcriptomic responses differed markedly, with a strong response to the thermal stress in GoA corals and their symbiotic algae versus a remarkably muted response in CRS colonies. Concomitant to this, coral and algal genes showed temperature-induced expression in GoA corals, while exhibiting fixed high expression (front-loading) in CRS corals. Bacterial community composition of GoA corals changed dramatically under heat stress, whereas CRS corals displayed stable assemblages. We interpret the response of GoA corals as that of a resilient population approaching a tipping point in contrast to a pattern of consistently elevated thermal resistance in CRS corals that cannot further attune. Such response differences suggest distinct thermal tolerance mechanisms that may affect the response of coral populations to ocean warming.

Original languageAmerican English
Pages (from-to)4466-4480
Number of pages15
JournalMolecular Ecology
Issue number18
StatePublished - Sep 2021

Bibliographical note

Publisher Copyright:
© 2021 The Authors. Molecular Ecology published by John Wiley & Sons Ltd.


  • CBASS coral bleaching automated stress system
  • coral bleaching
  • coral holobiont
  • coral metaorganism
  • heat stress
  • ocean warming
  • short-term acute heat stress assays
  • thermal resilience
  • thermal tolerance


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