Ocean Acidification Poses A Threat to Mollusks

by SC Reporter Teresa Vazquez

Dr. Jose Leal

Increasing atmospheric carbon dioxide levels are lowering the ocean’s neutral pH thus becoming more acidic and threatening the health of mollusks.

“The more carbon dioxide we have in the atmosphere,” José H. Leal said. “The less carbonate there is for shell making.”

José H. Leal explained the process in his presentation “Shells and Bad Water: Ocean Acidification and its Effects on Mollusks” during a Bailey-Matthews National Shell Museum H2O Lecture on March 25.

José H. Leal is the science director and curator at the Bailey-Matthews National Shell Museum and was the museum’s first executive director after opening in 1995.

His lecture began by highlighting the main factors contributing to ocean acidification: burning fossil fuels and deforestation. The former produces carbon dioxide while the latter removes forests which are vital to carbon dioxide absorption.

With nowhere to go, the excess carbon dioxide in the atmosphere seeps into the ocean, said Leal. Once carbon dioxide is absorbed into the water it aims to find an equilibrium between bicarbonate, carbonate, and carbonic acid.

The absorption results in the formation of carbonic acid by the release of free hydrogen. These free hydrogen atoms then sequester the carbonate ions in the water creating bicarbonate, said Leal.

Prior to the Industrial Revolution, carbon dioxide was absorbed in manageable amounts resulting in a small number of free hydrogen atoms. Thus, the creation of bicarbonate was minimal and there was leftover carbonate for shell making at normal levels, said Leal.

Now, there is a steady increase in the abundance of hydrogen free atoms resulting in a decrease of carbonate ions. These carbonates makes up half of the calcium carbonate couple, which is the main component of shells, said Leal.

Beyond isolating carbonates, the increase in free hydrogen ions is lowering the oceans pH.

“Over the past 200 years, the ocean pH had dropped down to about 8.1 which represents a 30% increase in acidity over those last two centuries,” Leal said.

These changes are negatively affecting the health of mollusks. Mollusks are an important group in terms of global biodiversity, with more than 80,000 named species. They are also important links in the ocean food webs and are important as food for humans throughout the planet, said Leal.

The shell making process takes place in a small space between the animal and the shell where the linkage between the calcium and carbonate occurs. The decrease in carbonate ions makes it harder for them to create their shells, said Leal.

In fact, the shell is more likely to dissolve as it is being built in a more acidic ocean. These creatures are expending atypical amounts of energy making and repairing their shells instead of growing, reproducing, and feeding.

“Imagine you’re used to walking on a street, or jogging in Florida, and then all of a sudden you go to the Andes and have to run uphill,” Leal said. “That’s what the mollusks are doing under ocean acidification. Shell making is like you trying to climb 1000 feet in a very short distance.”

A practical example of this is seen in a study done by Laura Parker in 2013. The paper outlined the impact of ocean acidification on mollusks globally, said Leal. She found that the majority of the 96 species studied were negatively affected.

A study done by the Pacific Marine Environmental Lab in Seattle studied the effects on sea butterflies, an open water mollusk. Leal said the study discovered that the shell would dissolve within 45 days when placed in seawater with increased acidity.

Animals who rely on mollusks for food will also be affected, such as the small krill and large whales that feed on them. Corals which are an essential structure in the ocean will also feel the effects of ocean acidification.

As an avid sheller, and museum member, Debra McBroom said she chose to attend Leal’s lecture to learn about what is affecting the creature she admires. She learned about the importance atmospheric carbon dioxide level has on ocean health and humans.

“If the oceans don’t survive, we don’t survive,” McBroom said. “That’s a great reason for all of us to be interested in doing all we can to reduce ocean acidification and save our oceans.”

Reducing fossil fuel emission and implementing projects to restore forests can help stunt ocean acidification, she said. Although the topic worries her, McBroom was happy to learn there is hope for the oceans and the creatures inhabiting it.

“I want our beaches to have seashells for us and future generations to enjoy,” McBroom said.

The next H2O Lecture will be on April 22, and will cover “Blue Revolution: A Water Ethic for America and Florida.”

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