Jamie Sewell of Warren prepares his boat for a scallop diving off the coast of Cushing in January 2015. Gabe Souza/Staff Photographer, file

A new study co-authored by federal scientists and Massachusetts Maritime Academy staff and students suggests that increased ocean acidification could pose a threat to the sea scalloping industry in the Gulf of Maine and elsewhere along the Atlantic seaboard.

It marks the first time that the impact of ocean acidification on sea scallops has been studied to this extent.

In an eight-week research project, scientists with the National Oceanic and Atmospheric Administration collaborated with the academy to conduct the study at the school’s aquaculture lab on Buzzards Bay in Massachusetts. They concluded that ocean acidification could significantly depress Atlantic sea scallop productivity in the years ahead.

Their study, which was published March 1, also found that pH levels – the measure of acidity – in the Gulf of Maine are dropping faster than at other locations on the East Coast, meaning acidity is increasing. Ocean acidification rises as the ocean absorbs more carbon dioxide from the atmosphere.

Ocean warming may also further hinder sea scallop population growth, endangering one of the most valuable fisheries in the United States – worth $670 million in 2021, according to NOAA.

But the study also suggests that sea scallop populations could adapt to a changing ocean environment.


Maine’s commercial scallop fishery is the state’s third most valuable fishery, although it has experienced several ups and downs in previous decades, including a near collapse in 2005, when it landed just 33,000 pounds of scallop meat valued at about $272,000, according to state Department of Marine Resources data.

The fishery has stabilized, bringing in 506,000 to 796,000 pounds of meat each year since 2013, valued at $4.6 million to $9.4 million. In 2020, scallopers harvested about 659,000 pounds of scallop meat. Valued at about $6.8 million, scallops were Maine’s third most lucrative catch in 2020, well behind the $406 million lobster and $15.6 million softshell clam fishery.

At the Maine scallop industry’s peak in 1981, it hauled in 3.8 million pounds of meat valued at $15.2 million.

Valued at about $6.8 million, scallops were Maine’s third most lucrative catch in 2020, well behind the $406 million lobster and $15.6 million softshell clam fishery. Carl D. Walsh/Staff Photographer, file

Maine scallop landings accounted for just over 1 percent of the U.S. scallop market in 2020. That same year, almost 49 million pounds of sea scallop meat was harvested in the United States, valued at about $486 million, according to the National Marine Fisheries Service’s commercial landings database, with the majority coming from Massachusetts, Virginia and New Jersey. In 2019, before the pandemic, the fishery was valued at around $572 million.

During the NOAA study at Massachusetts Maritime, scientists exposed the scallops to three different carbon dioxide levels and measured their growth and metabolism, including feeding, respiration and excretion rates.

The results demonstrated that juvenile scallops are vulnerable to ocean acidification and warming temperatures during short-term exposure. Less is known about their ability to acclimate when exposed to these conditions throughout their lives, or whether they can genetically adapt across multiple generations.


“Scallops have been around for 250 million years,” NOAA scientist Dvora Hart said. Hart co-authored the study and has been studying sea scallops for 24 years. “They may have something in their genome that allows them to adapt to increased carbon dioxide, but the only way to tell is to do the experiments.”

NOAA scientists will follow up on the 2023 study’s findings with a three-year study to understand whether scallops can adapt to changing ocean chemistry over multiple generations. They are using bay scallops because they are genetically similar to sea scallops and mature and reproduce more quickly.

The next study will measure survival, growth, development time, and physiological processes including feeding and respiration. Researchers aim to find out if second or third generations of scallops grown in more acidic conditions show signs of adapting to it.

While the ocean absorbs about a quarter of the carbon dioxide produced by human activities, the pH of ocean water varies based on oceanographic dynamics, depth and season. Sea scallops live on the seafloor from Canada to North Carolina. Survey data show that acidity is increasing in northern areas, including the Gulf of Maine and Georges Bank, more rapidly than in other areas. Bottom water on the Northeast continental shelf is also warming three times faster than the global average.

“We tend to think of ocean acidification and climate change as off in the future, but the data show that environmental conditions in some areas of this scallop’s range are already approaching those we used in this experiment,” NOAA research chemist and study co-author Shannon Meseck said. “We now know the range where we can expect to see effects on scallop growth.”

Maine has been aware that ocean acidification could negatively affect shellfish fisheries for years. In 2014, the Legislature created a new 16-member state commission, the first of its kind on the East Coast, to study the issue.


Mark Green, a professor in the Natural Sciences Department at Saint Joseph’s College in Standish, is considered a leading expert on ocean acidification. Green, who teaches environmental and marine science courses, was a member of the 2014 Maine commission to study ocean acidification’s impact on shellfish.

Contacted Wednesday night, Green said the entire world should be concerned about the state of the oceans and Maine is no exception. He said scallops are worth millions of dollars to the state’s economy, and that it is probably well past time to push the panic button.

“Add that to lobster, soft shell clams, hard clams, oysters, mussels, surf clams and it’s billions of dollars that could disappear from the Maine economy,” Green wrote in an email. “It won’t happen overnight. It will be a slow and steady decline (it will probably accelerate as critical tipping points are reached). But it will happen.”

He suggested that shellfish populations in the future might have to be raised using aquaculture with juveniles reared in hatcheries where seawater chemistry can be controlled and juveniles can get big enough to move past their most vulnerable stages of development.

The only way to stop ocean acidification is to stop using the atmosphere as a “giant open sewer” for CO2 emission, Green said.

“Ocean acidification is sometimes referred to as ‘climate change’s evil twin.’ They are different ramifications of the same thing – excess CO2 in the atmosphere. What stays in the atmosphere warms the planet and the oceans and what dissolves in the ocean acidifies the ocean,” he said.

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