Next-century ocean acidification and warming both reduce calcification rate, but only acidification alters skeletal morphology of reef-building coral Siderastrea siderea

• Published in: Scientific Reports
• Main Authors: Horvath, Kimmaree M., Castillo, Karl D., Armstrong, Pualani, Westfield, Isaac T., Courtney, Travis, Ries, Justin B.
• Format: Text
• Language: English
• Published: Nature Publishing Group 2016
• Subjects: Article; Ocean acidification
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4965865/; http://www.ncbi.nlm.nih.gov/pubmed/27470426; https://doi.org/10.1038/srep29613

Atmospheric pCO2 is predicted to rise from 400 to 900 ppm by year 2100, causing seawater temperature to increase by 1–4 °C and pH to decrease by 0.1–0.3. Sixty-day experiments were conducted to investigate the independent and combined impacts of acidification (pCO2 = 424–426, 888–940 ppm-v) and warming (T = 28, 32 °C) on calcification rate and skeletal morphology of the abundant and widespread Caribbean reef-building scleractinian coral Siderastrea siderea. Hierarchical linear mixed-effects modelling reveals that coral calcification rate was negatively impacted by both warming and acidification, with their combined effects yielding the most deleterious impact. Negative effects of warming (32 °C/424 ppm-v) and high-temperature acidification (32 °C/940 ppm-v) on calcification rate were apparent across both 30-day intervals of the experiment, while effects of low-temperature acidification (28 °C/888 ppm-v) were not apparent until the second 30-day interval—indicating delayed onset of acidification effects at lower temperatures. Notably, two measures of coral skeletal morphology–corallite height and corallite infilling–were negatively impacted by next-century acidification, but not by next-century warming. Therefore, while next-century ocean acidification and warming will reduce the rate at which corals build their skeletons, next-century acidification will also modify the morphology and, potentially, function of coral skeletons.