Ocean Acidification

As the level of carbon dioxide in the atmosphere rises, oceans worldwide are become increasingly acidic. Even small changes in ocean acidity make it more difficult for marine organisms to form the shells and other hard parts they need to survive and function normally.

Ocean acidification is a global phenomenon, but it is especially marked on the west coast of the United States where acidic deep ocean waters well up close to the surface. Ocean acidification, in combination with warming waters and shifting ocean currents, has the potential to drastically affect the distribution and ecology of marine resources. Using a combination of newly advanced genomics tools, oceanography, and traditional ecology, PISCO scientists are revealing the impacts of ocean acidification on important early life stages of marine species and its possible consequences for marine ecosystems.

The science of Ocean Acidification

Strongylocentrotus purpuratus
Photo: Michael O'Donnell


Limacina helicina
Limacina helicina
Photo: Michael O'Donnell

The combined effect of a warming climate and anthropogenic carbon emissions is the lead cause of ocean acidification, according to numerous researchers and the International Panel on Climate Change.

Throughout earth’s history, oceans have buffered climate change by absorbing nearly one-third of atmospheric carbon dioxide. But absorbing all this CO2 comes with a price; CO2 dissolved in the ocean reacts with other components of seawater to decrease ocean pH. Since the industrial revolution, oceans have become 30% more acidic (from a pH of 8.3 to 8.1).  Experts estimate that if atmospheric CO2 levels remain the same, by the end of this century, the ocean pH will decrease by 0.4 pH units, which will leave the ocean 150% more acidic than it is today.

The biological impacts of these disturbing trends are uncertain. Research thus far indicates that organisms such as corals, mussels, algae, and plankton that make calcium carbonate shells will be negatively impacted. These calcifying organisms normally rely on a healthy abundance of carbonate ions in the ocean water. With increased acidity, less of these precious ions are available and calcification rates decrease, making it more difficult for the organisms to form their protective shells and skeletons.  The effect of thinner shells and weaker skeletons is not yet known, but it could have serious ecological consequences.

The future is now: Although the most dramatic changes to ocean acidity are predicted for the future, a recent study by NOAA scientists found that acidic waters are already upwelling along the west coast of the United States in the ecologically-rich California Current Large Marine Ecosystem (Feely et al 2008).

PISCO approaches

From the lab to the field, scientists use a combination of approaches to study the biological effects of ocean acidification and ocean warming.

  • The group takes an interdisciplinary consortium approach to the ecosystem questions associated with ocean acidification.  A recent award has launched a new program to establish a platform of research in the California Current.
  • With the leadership of Dr. Gretchen Hofmann, a team of scientists including students and postdoctoral researchers has built a CO2 system that is capable of monitoring pH conditions in seawater tanks.   This allows researchers to raise the young, called larvae, of sea urchins and other invertebrates at low pH conditions that mimic the predicted future ocean conditions.
  • Genomics allow the researchers to investigate the impacts of ocean acidifcation on important cellular growth processes.
  • The results of studies on larvae can be used in developing larval dispersal models that include growth information.
  • PISCO Biodiversity surveys and ecological experiments along the entire CCLME coastal margins are integrated with this work, providing personnel already in-place for field collections and unique long-term biological data about species distributions, growth, and interactions.
  • Oceanographic moorings and ship-based work contribute to PISCO studies of climate change. PISCO-OSU has recently invested in a CO2-pH sensor for its nearshore moorings.

On-going work and recent results

Red Abalone larvae

Haliotis rufescens
Photo: Gretchen Hofmann

A new National Science Foundation award will support a new platform of oceanographic sensors and coordinated ecosystem studies.  

Red abalone, Haliotis rufescens, are the largest of the abalone species, economically and ecologically important, and at risk from ocean acidification. Because of work performed by PISCO scientists and collaborators, a significant amount is known about abalone distribution and ecology. Researchers are now working to understand how our previous knowledge about this species might change because of ocean acidification.

Using a combination of manipulative experiments and genomics-based methods to profile gene expression, PISCO scientists explore mechanisms that are involved in the deleterious impact of ocean acidification on the development and calcification process in embryos and larvae of the purple sea urchin, Strongylocentrotus purpuratus an ecologically important marine invertebrate found along the Pacific coast of North America. Interacting and multiplying effects due to changes in sea surface temperature and salinity, along with ocean acidification, are also major parts of this research.


Feely RA, Sabine CL, Hernandez-Ayon JM, Ianson D, Hales B (2008) Evidence for upwelling of corrosive ‘‘acidified’’ water onto the continental shelf. Science 320:1490–1492.


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