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Research Highlights

Corals reshuffle genes to adapt to carbon dioxide hike

Published online 30 June 2018

Scientists show how their “Swiss cheese” hypothesis explains how corals tolerate ocean acidification.

Louise Sarant

Corals enduring high levels of seawater acidity were shown to have increased DNA methylation in certain genes.
Corals enduring high levels of seawater acidity were shown to have increased DNA methylation in certain genes.
© Eric Tambutté
In a new study in Science Advances, an international team of marine biologists has unveiled the mechanism in which some corals acclimatize to ocean acidification through gene regulation. 

Following two years of experimentation, the researchers––including scientists from the King Abdullah University of Science and Technology (KAUST), Saudi Arabia––are now a step closer to understanding how the cauliflower coral Stylophora pistillata, a type of colonial reef-building coral, adapts to seawater acidity. 

“We exposed our coral colonies to different ocean acidification treatments in which we increased CO2 concentrations to values expected by the end of the century, as well as more extreme scenarios,” explains Manuel Aranda, assistant professor of marine science at KAUST and co-author of the study.

Acidification typically results from excess carbon dioxide that leads to higher carbon uptake by oceans and freshwater bodies. 

High carbon concentrations eventually impede corals’ ability to grow calcium carbonate skeletons, a fact that led the scientists to first hypothesize that the genes related to calcification might be the ones to undergo the biggest changes.

They were proven wrong, however. During genome sequencing, the changes that had taken place in methylation patterns––the epigenetic mechanism that ultimately controls gene expression––came as a surprise. 

“The largest changes in methylation levels occurred in genes related to cell growth and stress response, not in the genes related to calcification,” says Yi Jin Liew, geneticist at KAUST’s Red Sea Research and the study’s lead author. 

The greatest modifications occurred in the coral colony soaked in the lab’s most acidic tank, with a pH of 7.2. 

As well, the corals cultivated in that tank had enlarged cells and polyps, and larger cavities for the soft-bodied animal to retreat to. 

Hence, the “Swiss cheese hypothesis,” coined by Aranda in the lab; the idea that if corals make bigger holes (or calyxes), they need less “cheese” (or calcified skeleton), and can still grow at the same speed despite high acidity levels. 

“This study’s findings are encouraging, especially since so little is currently known about the adaptive capacity of corals to changing ocean chemistry,” says Gabriel Grimsditch, a coral expert at the UN Environment Programme’s marine and coastal ecosystems branch in Nairobi.

According to Jin Liew, measuring gene methylation levels can potentially be used to acquire a ‘snapshot’ of coral health. 

doi:10.1038/nmiddleeast.2018.72

  1. Liew, Y.J. et al. Epigenome-associated phenotypic acclimatization to ocean acidification in a reef-building coral. Science Advances http://dx.doi.org/10.1126/sciadv.aar8028 (2018)