Climate Change Is Affecting Our Seafood, Too

By Maya Gilchrist, Environmental Science, 2018

It is no surprise that climate change is at the forefront of today’s most pressing issues, concerning scientists and policymakers alike. Recently, approximately 400,000 people from all across the United States marched in solidarity down the streets of New York City to demand action to counter global climate change, marching for “The People’s Climate.” World leaders have held numerous referendums to attempt to address this issue. However, for many, the actual impacts of our climate’s changing composition may seem like a distant issue.

As it turns out, however, the earth’s warming temperatures are beginning to affect life in more ways than we may think. Detrimental to marine processes and life, climate change may be responsible for what is — or more importantly, what is not — on our dinner plates in the future.

In 2013, 36 gigatons of carbon dioxide were released into the atmosphere as a byproduct of human industries, especially the burning of fossil fuels. Since 1990, there has been a 61% increase in emissions, meeting humanity’s record high. The effects that these emissions have on our air quality and on our atmosphere may be astounding.

However, what is not as widely discussed are the effects on ocean acidification, and the impacts that carbon dioxide emissions are having on the quality of our oceans and all the marine life that resides within it. While the majority of carbon dioxide emitted makes its way into the atmosphere, over 25% of it is absorbed in the world’s oceans. In the past, this process has been crucial to the normal reduction of atmospheric warming, but there is only so much that the oceans can handle before crossing its threshold.

When water absorbs carbon dioxide, the gas is dissolved, leaving carbonic acid as a product of its reaction. Increasing levels of carbonic acid lead to greater overall acidity in the water. Seawater is naturally basic, but its pH has been creeping towards the neutral and acidic end of the spectrum. Currently, the average pH of the earth’s oceans is 8.1, which is 0.1 units lower, or more acidic, than that of pre-industrial times. It is projected to decrease by another 0.5 units by the end of the 21st century. This may not seem like much, but to the many marine species that depend on very specific circumstances to survive, this difference could be severe.

Smaller life forms are the first to be hit by the negative impacts. A 2010 study found that there was an inverse relationship between carbon dioxide levels and levels of dimethylsulfide (DMS), a byproduct of phytoplankton production. With higher levels of carbon dioxide in the water, fewer phytoplankton are produced. This can be attributed to decreasing amounts of nutrients at the surface of the water. Despite their small body mass, fluctuations in phytoplankton populations could have tremendous repercussions on the oceanic ecosystems as a whole.

As phytoplankton is at the base of the marine food chain, biological production is projected to decrease accordingly in all ocean regions. According to the scientists leading the study, “ocean acidification is a driver for substantial change in ocean ecosystems this century, potentially leading to long-term shifts in species composition.”

However, larger species are also directly impacted by the ocean’s increasing acidity. A 2013 study examined the sensitivities of five different marine taxa to ocean acidification. Based on predictions for future acidity levels, negative impacts were predicted for all five taxa: corals, echinoderms, mollusks, crustaceans, and fishes. While crustaceans and fishes were found to be the most resilient, the first three taxa were especially impacted by the acidity due to the calciferous nature of their protective shells. These shells are worn down by acidic waters, and their growth is stunted by the dramatically increased presence of carbonic acid.

These negative effects have already been seen in the 2007 mass death of oyster larvae in Netarts Bay, Oregon. The Whiskey Creek Shellfish Hatchery is the state’s leading center for oyster production. Pipes leading in from the bay feed this hatchery, one of the largest in the nation. Hence, when the larvae suddenly began dying, researchers looked at the source of incoming water. However, a few years later, scientists at Oregon State University were able to pinpoint the problem elsewhere: ocean acidification.

Oyster larvae make their shells from calcium carbonate, by capturing carbonate and bicarbonate ions in the water and combining them with calcium ions. Acidification of the ocean has reduced the number of available ions, cutting the number of carbonate ions present in the water by roughly 16%. As a result, the oyster larvae find it much more difficult to gather enough ions to build their shells in time and often die.

Ocean acidification effects have yet to cause alarm to East Coast aquaculture industries, but they are not safe from harm’s way. Sarah Cooley, a marine scientist at the Woods Hole Oceanographic Institute, estimates that the East Coast has only a few decades before it starts feeling the effects of acidification.

So what does this mean for us? While we in the United States may not feel the other effects of climate change for quite a bit of time, our fisheries and aquaculture are being impacted today. If carbon dioxide emissions are not reduced, the kinds of food we are so used to eating, like seafood, may not be there for us in the future.

This article was originally published in NUSci Issue 21.