As the East End mopes its way through a third-straight disastrous bay scallop season — desperate scallop lovers are forking over upwards of $45 per pound for cousins of the Peconic Bay scallop, imported from Martha’s Vineyard — scientists are working on ways that humans might help steel the local population against the conditions that have led to the massive die-offs of the iconic shellfish just as they had seemed on the verge of a historic rebound.
A Stony Brook University research team has begun using genetic sequencing to try to identify common traits in the smattering of bay scallops that have survived the latest massacre, which scientists say appears to be caused primarily by climate change and warming waters in the Peconic Estuary, in the hope of being able to help boost the numbers of scallops that will survive in ensuing years.
The scientists have already sequenced the genome of the Peconic Bay scallops that have produced large “sets” of juvenile scallops the last three years, only to see them die as adults before they are harvestable. Now they are comparing the sequences of some of the survivors in search of common genetic imprints that might hint at a natural resistance to the conditions that killed off their brethren.
If a distinct genetic signature can be identified, the scientists may be able to select individuals of the same ilk and breed them in captivity and release their offspring into the wild to increase the numbers of resistant individuals.
Natural selection would likely accomplish the same thing over decades, if the wild stock was able to weather the changing environmental conditions causing the die-offs, but researchers hope they can speed the natural evolution to give the scallops a better chance at recovery.
“It is something that farmers have been doing for thousands of years, of course, and we have done this with oysters and clams already, selecting for resistance to disease,” said Dr. Bassem Allam, the Stony Brook University School of Marine and Atmospheric Sciences professor who is leading the gene sequencing effort. “We do not make any changes to the genomes of the organisms. We don’t do anything to them. We’re just relying on the natural abilities of the selected organisms to breed more resistant offspring.”
Natural selection has long been known to allow shellfish to develop traits that help them survive and thrive in areas with environmental conditions different from what others in their subspecies may experience.
Allam has received two grants this year for the work, from the U.S. Department of Agriculture and New York Sea Grant, but the scientists had already begun their sampling efforts in the spring of 2020, collecting individual scallops both before the summer die-off and after, and some of the newborns from the class of 2021 and 2022.
This winter, the Stony Brook team will start controlled spawning in laboratories of scallops that survived the 2021 die-off. The offspring produced will then be used to further sample for survivability, both in the wild and in the laboratory, where the scientists will subject them to high water temperatures, tracking how individuals survive and recording their genetic sequences.
“We know it happens naturally, that some individuals will develop resistance to one environmental condition or another,” Allam said. “We have multiple strains of oysters that are resistant to disease or high salinity or water temperatures. There is some natural selection that happens in the wild — oysters that grow above Tappan Zee Bridge are adapted to very low salinity — but it can be made faster with human intervention.”
While this year’s harvest has been a total bust from a commercial standpoint, researchers from the Cornell Cooperative Extension Marine Program say that the die-off in their survey sites this year was not quite as extensive as it was last year — about 95 percent mortality, compared to 99 percent. That slightly better outcome may have been a product of certain factors — like the arrival of a voracious species of stingray — not aligning this year in the same way they did in 2020, but it also could be a sign that the scallop population is already naturally selecting for better resistance to higher water temperatures.
The scallop die-offs began in the summer of 2019, when researchers and baymen who had been watching local waters said they were seeing the largest “set” of young-of-the-year bay scallops in decades. Talk had turned to optimism that the iconic but delicate shellfish had finally regained a solid foothold in the Peconic Estuary after more than 20 years of inconsistent recovery from the devastation of the “brown tide” algae blooms in the 1980s and 1990s.
Then, quite suddenly, the vast majority of that hoped-for foundation for recovery died.
Scientists began analyzing the surviving scallops and ecological data from around the region in search of an answer and fairly quickly came to the conclusion that the cause had been two outside factors and a component of the animals’ natural life cycle that were combining to weaken the scallops to the point that they simply died where they sat.
A previously unknown microscopic parasite was discovered to be infecting most adult scallops, which scientists said would likely weaken them — not enough to kill them on its own but making them more vulnerable to other stresses.
And water temperatures that year were found to have nearly reached levels known to be fatal to the local scallops much earlier than they had historically, enough so that the warm waters coincided with the time the shellfish would go through their annual spawning cycle, which naturally weakens them further.
The triple whammy appeared to be over-stressing the adults on the back side of the spawn and they simply died where they sat.
The saving grace of the pattern was that the scallops were able to spawn successfully before they died and left behind a large new generation.
But then the cycle recurred in 2020, at even greater levels of mortality. Scientists are exploring whether the onslaught of a newly common species of stingray, the cownose ray, which feeds voraciously on shellfish, may have contributed to the higher mortality in 2020. The rays had been present in 2019, but were not known for sure to have ranged deep in the Peconics.
A Stony Brook University graduate student is currently working on a separate analysis of the cownose ray’s impacts on the scallop die-off — though the general consensus is that the stingrays are not the main factor in the die-off since researchers found the gaping, vacant shells of most of the dead scallops, which would have been crushed to smithereens had schools of stingrays been the culprit. Scientists are hoping to set up a word-of-mouth network of local baymen who fish with fixed “pound traps” throughout the Peconic Estuary to track when the cownose rays arrive in local waters next summer.
Other factors, like the “rust tide” algae blooms that have plagued the bays since the mid-2000s, have also been considered as a possible fringe factor contributing to some additional mortality, but not the main slaughter. There were no rust tide blooms in 2019 at all, so they could not have been a factor in the initial die-off.
Steven Tettelbach, Ph.D., a researcher for the Cornell marine program who led a state-funded effort to track the scallop die-off as it progressed last summer, said that rust tide blooms were present in 2020 and especially widespread this year, but that the bulk of the die-off had already occurred by the time the blooms emerged in most places. It’s not clear how much the blooms may have added to the mortality in certain places, he said.
Whatever the combinations, from a scientific standpoint, Tettelbach said there are signs of hope — natural and human-assisted — for an otherwise bleak future facing bay scallops in this year’s slightly less complete die-off.
“It wasn’t basically zero, like last year,” he said of the scallops’ survival rate. “Maybe the scallops are responding and starting to evolve. That’s our hope.”