Some corals resistant to ocean acidification

Percentage change in calcification rates plotted against seawater aragonite saturation state

With atmospheric and oceanic CO2 levels rising and the consequent acidification of the oceans, marine life has to adapt rapidly if they want to stay around. Especially calcium carbonate skeleton building organisms are affected by the rapidly dwindling seawater pH and carbonate saturation state.

Luckily new research in Nature climate change shows that some corals are able to counter the effects of ocean acidification through an ingenious buffering system.

Aragonite

Good news indeed. At least for those marine dwelling organisms with an aragonite skeleton or aragonitic corals, as they seem to be the only ones outfitted with the molecular pumps necessary for regulating their internal pH. The corals are able to manage pH to such an extent that internal changes are only about half of those in the surrounding waters.

And as an added bonus, rising oceanic temperatures may even increase the growth rate of these corals, especially those in colder waters.

Calcite

Not so fortunate are the coral with a calcite skeleton. They lack a pH regulating system and are thus, as ever, highly vulnerable to ocean acidification. But at least as important is the large number of free-floating plankton with a calcite skeleton that are equally vulnerable to acidification but also form a vital part of marine food webs. On top of that they soak up large quantities of CO2.

An aragonite skeleton therefore seems to be the trait to have when it comes to surviving ocean acidification. So a relatively positive outcome would be that organisms with aragonite skeletons gain the upper hand over those with calcite skeletons and manage to partly fill their niches in the ecosystem.

Algae

But since corals, be it with an aragonite or a calcite skeleton, both rely on symbiotic algae as their main source of energy they remain vulnerable, since those algae are highly susceptible to both low pH and high temperatures.

So the question remains whether corals can adapt to their rapidly changing environment and will aragonitic corals stand a better chance? If they don’t the future for marine life, and thus for humans, will look bleak indeed.