Scripps marine biologist asks what ocean acidification could do to coral reef systems

By Claire DisCenza

When you think about carbon emissions in the context of the world’s oceans, your mind likely jumps to the commonly-discussed issues of climate, rising water levels, and intensified storms. Yet changes in the atmospheric carbon levels are affecting marine systems in many other less-publicized ways.

Since joining Scripps Institution of Oceanography in 2010, marine biologist Martin Tresguerres has been studying one of these “other” consequences of increased global carbon: ocean acidification.

In a research discussion titled “Ocean Acidification: Can Corals Cope?” Tresguerres presented his laboratory’s work as the November installment of the Jeffrey B. Graham Perspectives on Ocean Science lecture series hosted by the Birch Aquarium.

“Now that CO2 has been constantly increasing, what we have is a net increase in the rate of CO2 influx into the oceans,” Tresguerres said.

While atmospheric CO2 is a gas, once dissolved into the oceans, CO2 combines with water to form bicarbonate ions and hydrogen ions. These hydrogen ions are an acid, and as such have the potential to cause detrimental problems. Because the main component of shells is calcium carbonate, a compound easily dissolved in acid, these ions could pose a real threat.

“There is the concern that either the shells might dissolve, or at least they might have more trouble,” said Tresguerres. “[The organisms] might have to expend more energy to secrete the shell.”

A second threat results from the fact that these hydrogen ions are highly reactive.

“When you change the concentration of hydrogen ions, proteins change shape,” Tresguerres said. Because their function is linked to physical shape, altering proteins in such a way impairs everything from normal reproductive activity to blood circulation.

“It can lead to pretty much anything you can imagine depending on the magnitude of the pH stress.

“Given the effects of pH stress, it is not surprising that all living organisms have the ability to regulate the pH,”continued Tresguerres. “We are constantly producing CO2 in our cells. Every cell on the planet must have the ability to do that, if not, they die.”

At Scripps, Tresguerres studies how various marine organisms sense acidification, and how they adapt the added stresses caused by this lowering of pH.

“One of the things we’re doing in my lab is not only looking at potential effect of ocean acidification, but first we need to know how the animal works. We know much less about invertebrates such as corals,” Tresguerres said. “We want to study how corals work in the first place, and then see how changes in the ocean acidification may affect those organisms.”

Tresguerres recently received a National Science Foundation (NSF) grant to study the unknowns in coral physiology. His lab is using fieldwork as well as cell cultures to study the currently-unknown function of individual cell types.

But he is not embarking on this project alone. Tresguerres’ lab has been developing worldwide collaborations in order to pool knowledge and resources towards understanding pH stress. “By getting all of these different experts, it means we do not have to develop every single thing,” Tresguerres said. “The original question is: Can corals cope? We don’t have an answer yet, but most likely corals are not happy.

“The key thing here is how each of these things affect coral physiology, and what happens when you combine them. And after we know that, after we know the mechanisms, then we can get the information to try to establish policies to prevent them.”