Effects of seawater pCO2 on the skeletal morphology of massive Porites spp. Corals

Nicola Allison* (Corresponding Author), Phoebe Ross, Alexander Brasier, Nadia Cieminska, Nicolás López Martín, Catherine Cole, Chris Hintz, Ken Hintz, Adrian Finch

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Ocean acidification alters the dissolved inorganic carbon chemistry of seawater and can reduce the calcification rates of tropical corals. Here we explore the effect of altering seawater pCO2 on the skeletal morphology of 4 genotypes of massive Porites spp which display widely different calcification rates. Increasing seawater pCO2 causes significant changes in in the skeletal morphology of all Porites spp. studied regardless of whether or not calcification was significantly affected by seawater pCO2. Both the median calyx size and the proportion of skeletal surface occupied by the calices decreased significantly at 750 µatm compared to 400 µatm indicating that polyp size shrinks in this genus in response to ocean acidification. The coenosteum, connecting calices, expands to occupy a larger proportion of the coral surface to compensate for this decrease in calyx area. At high seawater pCO2 the spines deposited at the skeletal surface became more numerous and the trabeculae (vertical skeletal pillars) became significantly thinner in 2 of the 4 genotypes. The effect of high seawater pCO2 is most pronounced in the fastest growing coral and the regular placement of trabeculae and synapticulae is disturbed in this genotype resulting in a skeleton that is more randomly organised. The study demonstrates that ocean acidification decreases the polyp size and fundamentally alters the architecture of the skeleton in this major reef building species in the Indo-Pacific Ocean.
Original languageEnglish
Article number73
Number of pages11
JournalMarine Biology
Issue number6
Early online date10 May 2022
Publication statusPublished - 10 May 2022

Bibliographical note


This work was supported by the UK Natural Environment Research Council (award NE/I022973/1) to AAF and NA. The participation of NC and NLM in the study was supported by the University of St. Andrews Undergraduate Research Assistant Scheme. We thank Dave Steven, Mark Robertson, Casey Perry, Mike Scaboo and Andy Mackie for their assistance with the culture system build and Truce Jack, Alex Millar and Innes Manders for assistance with preliminary image analysis. John Still assisted with scanning electron microscopy in the ACEMAC Facility at the University of Aberdeen.

Data Availability Statement

All data generated or analysed during this study are included in this published article as Appendix 2. Additional images of the coral skeletons are included in the supplementary data.


  • coral
  • calcification
  • skeleton
  • polyp size
  • ocean acidification


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