By Jeremy Cox, Chesapeake Bay Journal
Xuetao Li thrusts a metal cylinder into the creek’s squishy bottom and wriggles it until he’s satisfied it can go no deeper. A moment later, the doctoral student at Morgan State University in Maryland is yanking the apparatus upward. The sediment packed inside tumbles out onto a waiting metal screen.
It’s now the job of his professor, Ming Liu, to sift through the gray mud, like a prospector searching for gold. And in a way, he is.
A few months earlier, Liu and his colleagues had planted dozens of young soft-shell clams in the bottom of St. Leonard’s Creek as part of trials to refine their growing methods. If those efforts are successful, he said, they could result in a cleaner Chesapeake Bay and a new source of income for Maryland aquaculture operations.
“Many growers want a second aquaculture [option] to increase or enhance their business resilience,” said Liu, who leads the shellfish-growing program at Morgan State’s Patuxent Environmental and Aquatic Research Laboratory (PEARL) in Southern Maryland.
For now, the only shellfish species available to the state’s growers on a large scale is the Eastern oyster. That iconic bivalve brings in millions of dollars a year. But it’s not necessarily a money-maker in years when oyster diseases run rampant or so much rain falls that salinity levels plummet, causing widespread die-offs.
Soft-shell clams, meanwhile, have water-filtering abilities similar to those of oysters and are much more tolerant of the low-salinity environment in the Maryland portion of the Bay. And the Bay’s relatively warm waters help clams grow to market size much faster than in Maine, the state that accounts for 60% of the country’s soft-shell clam supply.
But that warmth — and the promise of more to come from climate change — could unravel Maryland’s “clam-bitions.”
Liu’s lab has already cleared the first important hurdle for clam aquaculture in Maryland: establishing a large-scale breeding program. The scientists are now able to produce hundreds of thousands of tiny soft-shell clams, or “seeds,” at their small hatchery, and they’re planning to expand their operations at PEARL so they can produce more in coming years.
Lately, the milestones have started piling up. The researchers have demonstrated they can grow the clams to market size — about 2 inches in length — within about a year. By contrast, oysters can take up to three years to be ready for harvesting.
Through careful experimentation, scientists worked out the “lethal temperature threshold” for Maryland-bred soft-shell clams: 84 degrees. The lab then began using selective breeding to develop clams with genes that make them more tolerant of the Bay’s warming waters.
That, too, has produced promising results, with the heat-resistant juvenile clams experiencing an 85% survival rate in hot weather, compared to 70% among those with no special breeding.
Developing a soft-shell clam for Maryland’s oyster growers would be a game changer, said Patrick Hudson, owner of True Chesapeake, an oyster farm in St. Mary’s County and a restaurant of the same name in Baltimore.
A few years after starting his oyster operation in 2011, he started noticing soft-shell clam shells in the water that he pumped from St. Jerome Creek into tanks used for raising baby oysters. A neighbor told him that clams hadn’t been spotted in the waterway since the 1970s. That was before diseases and declining water quality all but wiped out the Bay’s commercial wild clam fishery.
Hudson soon began raising clams on his oyster farm. “It was really exciting, and we thought we were off to the races,” he recalled.
But the fledgling clams all died when summer heat peaked. So, he approached Liu at PEARL about refining the process in the hope of creating a new industry statewide.
The lab, after its initial successes, ran into similar obstacles. When young clams grow into adults, their heat tolerance goes way down, Liu said. In a major trial last year, all 350 adult clams died from a prolonged heat wave that’s typical in the Bay region.
“That presents a big challenge,” Liu said. “How do we grow them through the summer?”
Wild clams appear to have adapted to the Bay’s warmth by plodding into cooler, deeper waters, Liu said. (A clam can move by extending and retracting a fleshy, tongue-like “foot” outside its shell.) They can also burrow several inches into the bottom sediment to protect themselves.
Farm-grown clams wouldn’t have that luxury. The oyster operations that would adopt them are typically located in shallow waters where the oysters, with harder shells, can access more warmth and nutrients.
In June and July this year, Liu’s team experimented with planting clam seeds beneath specially made nets with oyster shells sewn into their strands. They hoped that the shells would offer shade to protect the vulnerable clams below and provide a hard surface to which oyster larvae floating through the water could attach themselves.
The initial results weren’t as successful as Liu had hoped for. He checked the nets located just beyond the lab’s pier on a sunny afternoon in early October, but he and his colleagues could only find about 10% of the original clams. And most of them were no longer alive.
Liu suspected that some of the loss was caused by the inhospitable condition of the muck in some locations and by starting with too few seeds. But he wasn’t discouraged. Next time — and there will be a next time, he vowed — he plans to deploy 100 seeds per mat, instead of 40.
Perhaps that’ll do the trick. And if not, there are sure to be more attempts, Liu said, as long as the project’s funding continues.
