An Overview of Ocean Acidification

Its July and salmon are running on the Kuskokwim river again. Here in Alaska, we are fortunate that we have managed to keep our salmon stocks as strong as they are. Further south, our salmon’s cousins are not faring as well. There are many reasons our southerly neighbors are struggling to recover their salmon stocks, but this article is going to focus on ocean acidification.

It is important to understand what ocean acidification is and how it affects marine wildlife so that we can develop plans to monitor and mitigate its effects on the wildlife we depend on. Ocean acidification is a climate related issue that is occurring globally. It is an issue that is difficult to monitor due to the remote nature of the problem, the length of time that this problem has taken to develop, and the difficulty in collecting pH measurements of large bodies of water globally.

Ocean Acidification is the term used to describe the reaction that occurs when excess carbon dioxide from the atmosphere enters the earth’s oceans. The turbulence of the earth’s oceans absorbs CO2, among other gasses, from the atmosphere. The oceans act as a natural sink for CO2, which in the past has helped reduced the amount of CO2 in the atmosphere. However, in the centuries since the industrial revolution of the late 19th century, the amount of CO2 absorbed has increased the global acidity of the oceans by approximately 30%. (PMEL… c2019)

This drastic increase in the acidity of our oceans is currently impacting marine wildlife. As the acidity of our oceans increases, the availability of minerals used by marine wildlife to grow shells and carapaces decreases. Some examples of wildlife directly affected are krill, crabs, oysters, clams, corals and some planktons (NWF… c2019). Ocean acidification is also contributing to the migration of species in the oceans. As ocean conditions change by becoming more acidic, species that were once limited in their range have begun to shift into new areas that have become more suitable to their physiology (Bowen et al. 2015). Current models of the food web as related to salmon predict that that this may be a positive impact for salmon (Reum et al. 2015).

A recent study from the University of Washington has shown that an increase in acidity can interfere with a salmon’s ability to smell. A salmon’s sense of smell has multiple uses including reproduction, navigation, hunting, and predator avoidance. The researchers observed that the salmon exposed to higher CO2 concentrations were able to detect scents, however, it appeared that the salmon were unable to recognize what the scents were and remained indifferent. The researchers hope that the findings from their study will help spur more conservation action from local authorities (Salmon… 2018).

In addition to the direct effects on salmon and other marine wildlife, increased CO2 concentrations in the ocean have the potential to reduce the amount of dissolved oxygen in water. This can reduce the amount of marine wildlife a localized body of water can support, (Johnson-Colegrove et al. 2015, Takeshita et al. 2015).

Freshwater acidification is a related, albeit less studied topic at this point, but just as important to the health of salmon. One recent study suggests that freshwater acidification can have negative impacts on salmon development, such as body length and yolk conversion efficiency, and inhibited sense of smell (Ou et al. 2015).

As climate change continues to progress, observing and recording its effects will become more important to developing adaptation strategies and managing wildlife. Monitoring ocean acidification at this time may only be possible for government agencies and academic researchers, due to the remote and widespread nature of the problem. However, more accessible bodies of water such as rivers, estuaries and lakes are also susceptible to acidification and can more easily monitored by citizen scientists on a regular basis. An example of relevant data to collect would be temperature, pH, and dissolved oxygen content.

Sam Bundy, Environmental Program Assistant

Literature Cited:

Bowen, A., G. Rollwagen-Bollens, S. M. Bollens, and J. Zimmerman. 2015. Feeding of the invasive copepod Pseudodiaptomus forbesi on natural microplankton assemblages within the lower Columbia River. Journal of Plankton Research 37(6):1089-1094.

Chinook Salmon. [accessed 2019 Jul 5]. https://www.nwf.org/Educational-Resources/Wildlife-Guide/Fish/Chinook-Salmon

Johnson-Colegrove, A., L. Ciannelli, and R. D. Brodeur. 2015. Ichthyoplankton distribution and abundance in relation to nearshore dissolved oxygen levels and other environmental variables within the Northern California Current System. Fisheries Oceanography 24(6):495-507.

National Oceanic and Atmospheric Administration, Crozier L. 2015. Impacts of Climate Change on Salmon of the Pacific Northwest. Seattle, WA: Northwest Fisheries Science Center.

Ou, M., and coauthors. 2015. Responses of pink salmon to CO2-induced aquatic acidification. Nature Climate Change 5(10):950-+.

Reum, J. C. P., and coauthors. 2015. Evaluating community impacts of ocean acidification using qualitative network models. Marine Ecology Progress Series 536:11-24.

staff SX. 2018 Dec 18. Salmon may lose the ability to smell danger as carbon emissions rise. Phys.org. [accessed 2019 Jul 5]. https://phys.org/news/2018-12-salmon-ability-danger-carbon-emissions.html

Takeshita, Y., and coauthors. 2015. Including high-frequency variability in coastal ocean acidification projections. Biogeosciences 12(19):5853-5870.

What is Ocean Acidification? PMEL Carbon Program. [accessed 2019 Jul 5]. https://www.pmel.noaa.gov/co2/story/What is Ocean Acidification?