Lauren Huey stares at an oyster’s gonads.
Her computer shows a picture of oyster tissue preserved and stained in pink and purple hues. Huey, a Virginia Sea Grant graduate research fellow at the Virginia Institute of Marine Science (VIMS), differentiates the gonads, a thick, dark pink ring of eggs, from the rest of the oyster. She’s tracking changes in gonads of Chesapeake Bay oysters over the past 30 years to investigate their tolerance to a disease that has been plaguing them since the 1980s.
Perkinsus marinus, a parasite that causes a disease called Dermo in oysters, was first found in the Chesapeake Bay in 1949. Its presence intensified in the 1980s, contributing to the oyster’s severe decline. While Dermo still causes mortality in some Chesapeake Bay oysters—and most oysters in the Bay are infected by Dermo—they seem to be recovering from historically low numbers.
This might be because the oysters have become more tolerant to Dermo. To check this hypothesis, Huey is going through an archive of oyster tissue. Since the 1960s, VIMS researchers have collected and preserved cross-sections of oysters from Chesapeake Bay. These samples are housed in rooms of wall-to-wall drawers packed with glass slides, each containing a thin slice of oyster tissue.
This archive enables Huey to look at oyster gonads sampled from the James River from 1988 to the present. Which is why she’s peering so intently at the gonads on her computer screen. The number of eggs a mature female oyster produces indirectly reflects its tolerance to Dermo, because eggs tell scientists about an animal’s energy budget. When an oyster makes more eggs, it suggests the oyster is more tolerant to Dermo—because it’s devoting less energy to fighting off Dermo and can spend it on making more eggs instead.
For every year, Huey must analyze between 15 and 20 oyster samples, which takes a couple of hours. First she inspects every sample under a microscope to count the number of eggs. Then she takes a picture of the slide so she can use a computer program to calculate how much of the oyster overall is taken up by gonads.
“Looking at a single oyster, they’re all sort of the same and it’s kind of tedious,” Huey admits. So far, she’s looked at 307 individual oysters spanning 21 years. (In the process, she’s also listened to 21 audiobooks, and numerous short stories, mostly by Edgar Allen Poe and Ray Bradbury.) “But when you put them all together, it tells this story.”
“Looking at a single oyster, they’re all sort of the same, and it’s kind of tedious. But when you put them all together, it tells this story.”
Huey has identified a clear change in oyster reproduction. From 1988 to 2002, she found the number of eggs per oyster to be about the same. But around 2003, the number of eggs shoots up suddenly and significantly. This indicates that these oysters, despite being infected with Perkinsus, started responding better to the parasite, and so were able to make more eggs.
“It’s a story of resilience,” says Ryan Carnegie, a research associate professor in VIMS’s Aquatic Health Sciences department, and Huey’s research mentor. “We’re going back literally decades to uncover the secret of an animal’s success after being harassed by so many different assaults.” Beyond diseases like Dermo, oyster reefs have been damaged by harvest and changes in water quality.
Huey’s data suggests that the oysters evolved a tolerance to the disease—they are still infected by Perkinsus, but seem less affected by it because they are able to devote more energy to egg production. To rule out warm weather as the cause of the uptick in eggs, Huey plans to look at temperature and salinity throughout the years, but she’s still excited by her results thus far.
“To see the sudden shift, and talk to other scientists about it is pretty cool,” Huey says. And she wants to share the story of her research with nonscientists as well.
“Her research is important to everybody who cares about oysters,” Carnegie says. But it is perhaps most relevant to resource managers managing oyster harvest, like the Virginia Marine Resources Commission. Evidence of tolerance might provide justification for conservation tools like oyster sanctuaries. Sanctuary reefs, which already exist in some of Virginia’s waterways, are protected from harvest.
“Sanctuaries, and rotational harvest areas, give animals a chance to evolve disease tolerance,” Carnegie explains. “Lauren’s work reinforces the justification for conducting these sort of significant restoration activities.”
To share her work with resource managers and more broadly with anyone else interested in oysters’ plight, Huey is getting help from Caroline Donovan, her outreach mentor for this project, and Program Manager of the Integration and Application Network (IAN), an initiative of the University of Maryland Center for Environmental Science that produces syntheses and assessments on environmental issues in Chesapeake Bay watershed.
“What’s really cool is that this is very complicated and specific science, and communicating that is something that all scientists need to be able to do,” Donovan says. “So it’s exciting that Lauren is already doing that.”
Huey has already made one infographic in the Advanced Science Communication Seminar, hosted by Virginia Sea Grant and George Mason University. She’s also uploading symbols she’s designed for her infographics to IAN’s free-to-the-public image library. She hopes to complete two more infographics, while also analyzing nine more years of oyster tissue to flesh out this story of resilience.
By Chris Patrick, science writer
Photography by Dennis Quigley, VASG photo intern