New study looks at impact of ocean acidification on sea scallops

By Doug Fraser

Posted Dec 20, 2019

BUZZARDS BAY — Shannon Meseck, a research chemist with the National Oceanic and Atmospheric Administration, stood in a T-shirt, jeans and fishing boots as winter sunlight streamed in through the greenhouse windows of the Massachusetts Maritime Academy aquaculture lab. A couple of steps beyond the windows, the Cape Cod Canal raced by, a flat gray sheet of swirls and eddies.

Eight weeks of vital research on ocean acidification were drawing to a close, and Meseck was relieved and pleased. She’d already completed similar research on oysters and surf clams, but analyzing Atlantic sea scallops, the region’s preeminent fishery, was a tougher task.

The seawater at NOAA’s Northeast Fisheries Science Center’s lab in Milford, Connecticut, was too warm for scallops, and filters on the water pumped into the lab stripped out the plankton and algae the scallops feed on. Milford Laboratory director Gary Wikfors, who had done some consulting with the academy when it set up its aquaculture lab years earlier, contacted the academy about a partnership. The research is being funded by a three-year NOAA grant of $172,000 annually.

“It’s hard to get scallops and keep them alive,” said Meseck, who works at the Milford lab. “You have to have a specialized facility to do that. That’s what makes the Massachusetts Maritime Academy such a great place.”

Preliminary results told Meseck she would have enough data to feed into computer models that would tell scientists for the first time how sea scallops, worth more than a half-billion dollars a year to fishermen from New Jersey to Maine, responded to an increasingly acidic ocean caused by high levels of carbon dioxide from fossil fuels and other emissions.

“This will get us the feeding rates, growth rates, assimilation rates needed for models,” she said.

Until now, most researchers had relied on data from other shellfish species to model scallop responses to acidification.

“Right now, there are no publications on ocean acidification research on sea scallops,” she said. “This will be one of the first studies.”

Meseck had come to appreciate what the Massachusetts Maritime Academy lab offered for her research, including a steady supply of unfiltered cold seawater at the right salinity and temperature for growing the scallops, as well as students and staff eager to help in the research.

“If we didn’t have the chance to work with professionals in the field, to meet the scientists that are actively engaged in understanding the problems of fixing the world today, then we’d never get a full grasp of what’s going on,” said Jack Gerrior, a sophomore at the academy.

Gerrior was one of two students hired by Meseck to do the day-to-day management of the study, making sure the CO2 and water were flowing, taking samples, measuring water quality and growing the algae to supplement the natural food supply.

Wikfors said the research will fill an essential piece of the puzzle for sea scallops and give the future some clarity.

“Ocean acidification is in everybody’s face every day as an extreme risk,” he said. “But do we know enough right now to predict what will happen?”

Humans have been dumping carbon emissions into the atmosphere for nearly 260 years. According to the EPA, carbon dioxide from industrial uses and fossil fuels makes up 63% of greenhouse gas emissions, while another 11% comes from forestry and other land uses. About a quarter to a third of the CO2 in the air is absorbed by the ocean, amounting to 520 billion tons since the Industrial Revolution and 22 million tons a day.

CO2 in water becomes carbonic acid and the acidity of the surface waters of the ocean have gone up by 30% since the Industrial Revolution. These chemical reactions bind up the carbon that shellfish need to build their shells.

Also, the higher level of energy required for shell building may mean there is less remaining for other life processes like reproduction. Some studies have shown that shells can dissolve as the excess hydrogen ions in the water begin to strip away carbon atoms from the shell, and Wikfor said there may be respiration issues.

This has led to some notable disaster scenarios by scientists. A predictive model by Woods Hole Oceanographic Institution researchers last year posited that scallop populations could drop by more than half in the next 30 to 80 years under a worst-case acidification scenario.

But Meseck’s studies on oysters and surf clams have shown there is a variability to the response depending on the species. Under extreme acidification, oyster shells grew thin and white, but appeared essentially the same inside. Sea clams were harmed the most, with diminished shell growth and tissue weight.

So far, the preliminary data on sea scallops appears to show a mix of the two with some difference in the growth of the shell as the acidity increased, but not much difference in tissue weight. Sea scallops, she posited, may be putting their energy into tissue growth like oysters do.

NOAA staff assembled a smaller version of their Milford lab inside the maritime academy lab. Seawater pumped from the canal flowed through a wall of white pipes. CO2 bubbled up into the water-filled tubes, creating conditions that mimicked ocean acidification levels that exist today, a worst-case scenario level that scientists believe is far beyond anything that could occur and a third level in between the two extremes.

The water then flowed into rows of plastic boxes, each containing a quarter-sized sea scallop.

Meseck leaned over one of the tiny scallops and pointed to the tiny, amber-colored cilia, thousands of waving arms that ring both sides of the shell. Scallops only open to feed when the 50 to 100 blue eyes along the shell opening spot particles large enough and in numbers great enough to warrant the energy and risk.

Water flowing into the open shell deposits organic and nonorganic matter on a mucous membrane. The cilia sweep these mucous bundles in a kind of bucket brigade to the mouth near the hinge of the shell.

To understand the physiological responses to increased carbon levels in seawater, researchers had to not only weigh and measure the scallops but also determine the amount of food coming in and the waste the scallop was excreting.

Meseck pointed to tiny dark piles on either side of the shell. One was feces, what remains of the algae that passed through the scallop’s digestive system. On the other side of the shell, the inorganic matter like sand and other particles, had been discarded. These would both be gathered and weighed.

Mark Dixon, a biological science technician at the Milford lab, poured water fresh from the canal into funnels with a preweighed fiber filter at the spout. The filter and all it collected would first be weighed then heated to burn off organic matter, leaving the inorganic matter behind. Weighing that gave them a calculation of the amount of food flowing over the scallop.

“It’s really interesting to see such high-end science being put in the ground here,” said William Hubbard, professor of marine ecology at Massachusetts Maritime Academy. “You are doing an experiment that is going to make not just local but national decisions on one of the leading fisheries in the region. For us to see this type of experiment, to see the students getting involved, this is the type of partnership we’re trying to build with the scientific community.”