Plentiful, healthy oysters will help keep the Chesapeake Bay clean.
There’s a turning point that happens every single night in the waters of the Chesapeake Bay. It has to do with one the Bay’s most critical — and imperiled — residents: oysters.
The situation for oysters is dire, by any measure. One estimate from the Chesapeake Biological Lab puts the oyster population at just 0.3 percent of historical levels, mostly thanks to overharvesting.
But for many years, biologists and environmental policy makers have also voiced concern about declining oxygen levels in the Chesapeake Bay, a phenomenon caused in part by the demise of underwater plants such as bay grasses.
In deep water, oxygen levels change very slowly. But in coastal, nutrient rich waters, the balance of oxygen is actually fluctuating all the time along the day-night cycle.
Some of the latest research on how water quality in the bay is affecting this cycle and how those changes are affecting oysters happens in a lab at the Smithsonian Environmental Research Center — or SERC — in Edgewater, Maryland.
Andrew Keppel and Denise Breitburg with the Smithsonian Environmental Research Center. (Jonathan Wilson/WAMU)
The Room of DOOM
The Reed Education Center on the 2,600 acre SERC campus sits on the Rhode River, a tributary of the Chesapeake. And the waters of the Rhode are constantly pumped in and out of the lab here — making this what’s called, logically, a "wet lab."
“For our room itself, we’re going through about 20 liters of water per minute through the lab, and that’s just trying to pump as much river water through the room as we can to feed the oysters,” says Andrew Keppel, a graduate student at SERC.
The room he’s talking about isn't just any room. It’s the Room of DOOM.
No, it doesn't have anything to do with the apocalypse. It’s just a clever acronym coined by Keppel and his fellow researcher Rebecca Burrell.
“DOOM came out of Dissolved Oxygen Oyster Mortality,” he explains. “It’s a cool name that we've sort of made work. We've stuck with it even though we've moved on to [researching] growth and disease and other aspects.”
The lab is dominated by 30 oyster aquarium tanks, each filled with river water and different mixes of dissolved oxygen and nitrogen – along with different levels of plankton to feed the oysters.
Everything is monitored by a customized computer program, and researchers know right away if oxygen levels are off thanks to an appropriately sinister alarm: it plays the music that accompanies Darth Vader in Star Wars.
The room of DOOM can even send researchers email and text messages if something goes wrong in the middle of the night.
A tiny baby oyster settled on a plastic tile. The tile provides a clean flat surface for the oysters, and makes it easier for researchers to observe their progress. (Jonathan Wilson/WAMU)
Connections between low-oxygen, acid, and disease
Though it may seem like the room itself is running the show, everything here happens under the watchful eye of Dr. Denise Breitburg — an ecologist who focuses on how we humans influence coastal systems.
She says a main goal of the experiment is finding out what makes oysters more susceptible to Dermo, a disease that has ravaged oysters throughout the Chesapeake Bay.
“It’s a single-celled parasite that the oysters are exposed to as they’re filtering water for food and to get oxygen also,” Breitburg says. “Essentially over-time, the oyster cells are displaced by these ever-increasing numbers of parasite cells and it eventually kills them.”
Breitburg and her team have shown that severe low-oxygen — or hypoxia — hampers oysters’ ability to fight the parasitic infection that causes Dermo. In fact, their work shows that hypoxia can result in two to three times as many oysters becoming infected than in waters with normal oxygen levels.
And in shallow coastal waters, oxygen levels drop drastically on a nightly basis.
During the day, underwater plants and plankton are photosynthesizing, taking in carbon dioxide and putting more oxygen into the water.
“At night, when it’s dark, they’re only respiring and they're not photosynthesizing so what they're doing is they're using that oxygen and they're putting carbon dioxide into the water,” Breitburg says.
Excess carbon dioxide also raises the water’s acidity and Breitburg’s team has recently started monitoring that variable as well.
All of these fluctuations, she says, are exacerbated by the nitrogen and carbon dioxide humans are adding to the mix with polluted runoff and air pollution. This pollution helps create the Chesapeake Bay’s “dead zones” — places with chronically low oxygen levels and fewer living things.
The future role of oysters in the Chesapeake Bay
This is why Breitburg says the future of oysters in the bay is likely to look very different from the past — even if her research points to methods for avoiding their complete disappearance from bay waters.
“Well, wild oysters as the source of food may be a thing of the past, but wild oysters for their role in the ecosystem is something I think that has a lot of promise,” she says.
And Breitburg says in a healthy bay, oysters would play a starring role.
As oysters settle on top of one another, they form reefs which can act as home to fish and other aquatic critters. And as filter feeders, they can also help keep water clean.
But, of course, there’s a limit to how much they can do by themselves and once waters get too dirty or hypoxic, oysters can’t exactly swim away. Next, Breitburg and her team plan to find out if shallow water fish, which — unlike oysters — can swim to more hospitable waters fare any better when facing similar conditions.
Music: "Dock of the Bay (acoustic instrumental)" by The Acoustic Guitar Troubadors from Acoustic Instrumental Memories D1