While some at Horn Point Laboratory are focused on oyster restoration, geneticist Louis Plough is focused on another way of producing oysters that thrive in Maryland waters.
Plough wants to breed an oyster that excels in low-salinity waters, such as those that characterize the Maryland part of Chesapeake Bay.
Oysters generally grow faster in high-salinity waters, but diseases such as Dermo and MSX, which nearly wiped out the already fragile oyster population, also thrive in those higher salinities.
“We basically get around the disease issue by creating an oyster that grows well in low salinity where disease pressure is lower,” Plough said.
Salinity is the concentration of dissolved salts in water. In the open ocean, salinity measures around 35 parts per thousand (ppt), while freshwater is 0. The waters around Horn Point Laboratory range from 8 to 15 ppt, but spots in the Upper Chesapeake Bay consistently measure below 10 ppt all year.
Plough started a partnership with Virginia Institute of Marine Science’s Aquaculture Genetics and Breeding Technology Center (ABC) oyster breeding program to spearhead the development of a line of oysters that grow well in low salinities to support Maryland’s growing aquaculture industry.
“Currently, farmers don’t have a lot of options for strains that grow well in their backyard,” he said.
There is a need for high-performing, domesticated oysters for the burgeoning oyster culture industry in the north of the Bay.
The idea of growing a specific breed of oyster isn’t new. Virginia and New Jersey have already developed lines of oysters that are resistant to Dermo and MSX. Breeding for disease resistance works well in those areas, where the waters have higher salinities than Maryland, Plough said.
There have also been efforts to produce low-salinity strains for Chesapeake Bay. The unique partnership that combines ABC’s world-class oyster breeding program with Plough’s modern molecular tools may be the difference that allows the Horn Point geneticist to succeed where others could not.
“We have more tools. We couldn’t scan the genome and find genetic markers associated with salinity even five or 10 years ago,” Plough said. “Now, we have the Eastern oyster genome, as well as new tools that can profile the genome cheaply and quickly.”
To breed oysters for tolerance to a specific environmental stress involves collecting oysters, exposing them to that disease or lower salinity, and seeing which ones survive or grow faster. Then the survivors or highest performing oysters are bred together, and the process is repeated over a number of generations. The success of this approach, called selective breeding, is dependent upon the existence of heritable genetic variation in the trait of interest, which then allows aquaculturists to select or breed for it.
As part of his research, Plough needs to measure what is termed the heritability of the trait, which indicates if it’s possible to breed for low-salinity tolerance. Heritability describes what proportion of the variation in a trait (e.g. size or growth rate) is due to genetics versus environmental or other sources of variation. Traits that are highly heritable respond to selection and selective breeding better than traits that are not.
His first step is an exposure trial, which involves exposing 50 families of oysters, produced as part of the ABC breeding program, to low-salinity waters. Then Plough waits to see which oysters do best. From there, he can estimate the heritability of this low-salinity tolerance trait. Those oysters will help Plough find more oysters with low-salinity tolerance through their genes using genomic tools.
“Some will live, some will die, and the question is, are there certain genes the ones that live have versus the ones that die?” Plough said. “We’re trying to understand what specific genes (or regions of the genome) are associated with low-salinity tolerance.”
With these markers serving as a road map, he can help direct the selection of oysters for future generations, improving performance in each.
“There is a need for high-performing, domesticated oysters for the burgeoning oyster culture industry in the north of the Bay.”
Plough hopes his work will meet that need.
Story by Kristi Moore