Fat mollusks, rockfish and even parasites can be found thriving at oyster sanctuaries in three Chesapeake Bay tributaries, leading scientists to believe that current oyster restoration techniques are working.
Those findings are detailed in a newly released study from the Smithsonian Environmental Research Center and University of North Carolina at Chapel Hill which found more wildlife diversity at sanctuaries than nearby unprotected harvest sites.
One indication of that — two native parasites: the boring sponge and mud blister worm.
They win their names easily enough. The boring sponge drills or “bores” through the shell to make a home while the mud blister worm burrows into the inner shell causing the oyster to form darkened, muddy-looking patches around the worm in self-defense.
“I think a knee jerk reaction for people is to be like, ‘Oh, that's bad, right?’” said lead report author Zofia Beck Anchondo. “But parasitism is the most common ecological relationship and that means that if there are more parasites, that is suggestive that there are more of other things.”
Essentially, they’re a sign of good ecosystem health.
And in their research, which was conducted over the summer of 2019, scientists did find more wildlife like blue crabs, rockfish and summer flounder at the sanctuaries than at unprotected harvest sites. They also found fewer parasites at the harvest sites.
Anchondo and her co-hort say those findings are an indication that the sanctuary restoration projects are working to improve oyster health and numbers. Oysters are the “backbone” of the Chesapeake Bay, they say, as they both filter water and support marine life as a food source and habitat. Due to overharvesting, pollution and disease, the oyster population in the Bay is likely around 1% of its historic levels.
Researchers collected samples from three Chesapeake tributaries: the Choptank River, the Great Wicomico River and the James River. Each site had both an oyster sanctuary and nearby harvest site, where the mollusks can be freely taken, for comparison.
The results aren’t surprising for Matt Ogburn, a co-author and senior scientist with the Smithsonian Environmental Research Center, but they are reassuring.
“For the first time since the science of ecology was founded, we have oyster reefs that are relatively large scale to study,” he said. “ It's really exciting to be able to see now, using data, that the restored reefs are performing the way that we think they should with larger numbers of oysters, better habitat and more species and animals living on them.”
The presence of the parasites are remarkable for a few reasons. While they take a toll on the energy of the individual oyster, they do not kill it.
“They’re not preventing high oyster densities,” said Matt Ogburn, and while more research is necessary, there’s even a possibility that the parasites are good for the oysters’ long-term evolution, he added.
“Restoring the oyster reefs is likely to be helping the oyster population become more resilient to the parasites that are out there now, compared to what would be possible if everything was harvested all the time.”
Evidence of these native parasites go back hundreds of years, Anchondo pointed out. Previous studies on Chesapeake-area shell middens, which are essentially trash dumps from earlier humans, indicate the presence of those parasites, particularly the boring sponge.
“We can track the populations of these parasites through history using those shells, because they leave marks on them,” she said. It’s another indication that the reefs are mimicking how earlier pre-industrial sites would have looked.
While the oysters in the study are not for human consumption, neither parasite is harmful to humans. The only human problem they cause is a marketability one.
“If you are ordering oysters at a restaurant, you want the shells to be pretty, not full of holes,” said Ogburn.
Up next: the researchers are looking at their data for evidence of dermo and MSX, two non-native parasites behind some of the most devastating oyster crashes.
