Behind the Catch

The “Other” Global Ocean Problem: Ocean Acidification in New England

Atlantic sea scallops. Scallops are one New England species impacted by ocean acidification. Image via NOAA Fisheries.

This is the second blog in our series, Behind the Catch, in which we’ll explore New England’s waters and fisheries from a scientific perspective. By examining the region’s fundamental ecology, we can better discuss and tackle marine conservation issues.

As a (bad) joke, marine scientists have called ocean acidification the “other” global ocean problem, “The Other CO2 Problem,” or even climate change’s evil twin.

Don’t be fooled by this playful language though. Ocean acidification (OA) poses very serious biological and economic threats to marine ecosystems around the world. Unfortunately, compared to sea surface warming and sea level rise, OA has historically gone “under the radar” and until recently, most climate models underestimated the rate and severity of OA. In this blog, we explain the science behind this pervasive ocean problem and why it’s a challenge for New England’s waters.

Carbon Sinking

Globally, oceans are acidifying 10x faster than they have in 300 million years. As a carbon sink, the ocean is supposed to sequester CO2 among other gases from the atmosphere, helping to regulate the greenhouse effect to an extent. In fact, a quarter of all carbon emissions end up in the ocean.

But in today’s world, where there is too much CO2 in the atmosphere, too much CO2 enters the ocean. Since the industrial revolution, human emissions have deposited over 530 billion tons of CO2 into the seas.

Before industrialization, the average ocean pH was 8.2, and today it is 8.1. While that may seem like a small difference, the –0.1 change in pH really means that the ocean contains 30% more hydrogen ions than it did just a few hundred years ago. Consequently, the blue planet’s chemistry is changing drastically.

A Chemical Double-Whammy

The reaction works something like this:

When CO2 mixes with seawater, it forms carbonic acid. Carbonic acid disassociates or breaks down into one hydrogen ion and one bicarbonate molecule. Bicarbonate then dissociates into two hydrogen ions and one carbonate molecule.

For every COmolecule that enters the ocean, three hydrogen ions are created. This creates two major problems for ocean life.

First: The more hydrogen ions a solution has, the more acidic it is. So when CO2 enters the ocean and undergoes this process, the water acidifies—hence, ocean acidification. Acidified seawater can weaken or even dissolve animals’ shells and bone structures. OA may also reduce survivorship in oysters, coral, and maybe even fish larvae.

Second: As the concentration of hydrogen ions increases, the water’s concentration of carbonate decreases. This is a problem because calcifying animals—such as clams, mussels, and lobsters—rely on carbonate to build their shells and bones. But excess hydrogen ions obstruct this process. When this occurs, organisms must devote more energy to acquiring carbonate, which means they have less energy for everything else. This added stress can impact growth rates and development.

A Cold, Fresh (and Acidic) New England

According to the World Ocean Atlas, the Northeast is one of the U.S. regions most vulnerable to OA. This can be explained by the Northeast’s oceanographic connection to the Arctic and its extensive river system – two fresh and cold water inputs.

Fresh water diminishes the Gulf of Maine’s the ability to absorb acids without undergoing pH changes. This is because fresh water naturally has what’s known as a lower “buffering capacity” than seawater. So as the Gulf of Maine freshens, it becomes unable to take in acids without becoming acidic.

Also, cold water is better at retaining gasses than warm water is. As the Gulf of Maine receives cold Arctic water, its capacity to retain CO2 increases. More CO2 means more fuel for OA’s chemical reaction. Interestingly, the recent warming trend in the Gulf of Maine could help mitigate OA’s effects, though this remains a very new idea.

While algal blooms, pollution, upwelling, and fertilizer runoff have also exacerbated acidification in the Gulf of Maine, the region is predisposed to OA primarily because of its natural freshness and temperature.

Implications for Fisheries Management

Ultimately, the only thing that can stop OA is to reduce global CO2 emissions, but there are still productive steps that local management can take.

For example, the science on OA is still fairly new. Investing in ecological monitoring and other research efforts can help us develop our understanding of this issue, identify vulnerable species – including important fisheries – and develop a better plan of action. Thankfully, the U.S. House of Representatives recently passed the Coastal Communities Ocean Acidification Act, originally introduced by Maine’s Rep. Chellie Pingree, which requires NOAA to publish an OA vulnerability assessment every seven years.

In the meantime, fishermen might benefit from diversifying their target species. Given that OA sensitivity is variable, any one (or more) of the popular shellfish fisheries—mussels, oysters, clams, scallops, etc.—could collapse. If fishermen branched out, they would be proactively reducing the risk of overfishing a vulnerable stock and be better situated to adapt to change.

Without a doubt, OA will have far reaching economic and ecological effects—the bulk of which remain difficult to predict. But with continued research, advocacy, and persistence, perhaps we can mitigate OA in New England and beyond.

Clayton Starr is a guest writer for Talking Fish. He is a recent graduate from Bowdoin College where he earned a bachelor’s degree in Environmental Studies and English with concentrations in Marine Science and Creative Writing. Clayton hopes to communicate science to spread understanding and, ultimately, to inspire climate action.


Sources

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