The Nature Conservancy’s oyster restoration efforts in the Chesapeake Bay have primarily focused on supporting wild oyster populations, but the Bay’s oyster aquaculture industry is the largest on the East Coast, providing sustainable seafood and green jobs. There is some evidence that it can have positive impacts on the ecosystem—but those impacts have never been fully quantified.
To develop a better understanding of the specific connections between oyster aquaculture, water quality and ecosystem health, TNC partnered with the Virginia Institute of Marine Science (VIMS) and four oyster growers to answer the question:
Can oyster aquaculture make the Bay cleaner, faster?
Wild oyster populations in the Chesapeake Bay have declined to less than 1% of their historical numbers. With that decline, the Bay has lost the oysters’ capacity to filter sediment and algae and remove nitrogen and phosphorus—harmful pollutants in excess—from the water.
We worked with VIMS and four oyster growers—Big Island Aquaculture, Chapel Creek Oyster Company, Lynnhaven Oyster Company and White Stone Oyster Company—on this two-year study. The growers graciously allowed us to work in and around their operations as we collected data to quantify aquaculture's influence on water quality and ecosystem health.
After sampling and studying environmental variables at each of the four oyster farms including water currents, water clarity and chemistry, and sediment type (and the creatures that live in it), our research indicates that oyster aquaculture is a low impact way of producing animal protein.
The data indicate that the oyster aquaculture industry can help to restore water quality in our rivers and bays. For every 100,000 oysters grown and harvested annually, six pounds of nitrogen and phosphorus pollution are removed from the Bay. Oyster farms may also reduce wave energy and help protect vulnerable shorelines.
As oyster aquaculture grows, so will the food and water quality benefits to the Chesapeake Bay.
The Virginia oyster farmers who participated in the study with us are:
- Big Island Aquaculture, Gloucester
- Chapel Creek Oyster Company, Mathews
- Lynnhaven Oyster Company, Virginia Beach
- White Stone Oyster Company, White Stone
Bruce Vohgt and his son Daniel started Big island Oyster Company in Guinea, Virginia in 2011. They are located in the extensive marshes near the mouth of the York River and grow their oysters in a hanging bag setup. Daniel keeps a close eye on the oysters as they grow, occasionally moving them around their grounds to compensate for varying growth rates.
Bruce and Daniel have noticed what they feel is an increase in both the number of species and the quantity of fish in the area since they began their operation.
Trey Sowers has been farming oysters on the Piankatank River since 2011. His company, Chapel Creek Oyster Company, grows the oysters in cages that sit on the bottom of the river. Trey uses a winch on his boat to haul the cages off the bottom and onto the boat where he can sort through the oysters.
Trey has seen changes in the area where his cages are over time including more underwater grasses and more fish. He hopes that by working with The Nature Conservancy on this project, the findings will confirm his belief that the area is getting healthier.
Lynnhaven Oyster Company is a grower for Cherrystone Aqua-Farms. Owner Norman "Hap" Chalmers started farming oysters as a hobby which then grew into a business. They grow their oysters using a bottom cage system in the Lynnhaven River near the mouth of the Chesapeake Bay.
The Whites Stone Oyster Company, located in White Stone, VA, was started in 2013 by Tom Perry. White Stone uses a floating rack system where the oysters are contained in mesh bags that are secured to the racks. Most of these racks are located in the Chesapeake Bay just off of Windmill Point.
After the oysters are harvested, they are processed and sorted at the company's facility on Antipoison Creek in White Stone, and then bagged for shipment to restaurants around the Bay region.
Tom hopes that by working with The Nature Conservancy he will gain additional information about the area where he grows his oysters which will allow his operation to be more productive.
There are two general types of oyster aquaculture—intensive and extensive.
Intensive aquaculture involves growing oysters in bags and cages either floating in the water or secured just above the bottom. The oysters are routinely checked and sorted until they grow to market size in 2 - 3 years.
Intensive aquaculture typically uses seed oysters which are small, unattached baby oysters. This method produces more uniform and high quality oysters which are ideal for the half shell market.
Extensive aquaculture involves placing young oysters on existing natural or man-made reefs and then later harvesting them—usually after two years.
Extensive aquaculture uses spat on shell oysters which are baby oysters (spat) attached to recycled oyster shell, also know as "clutch". With spat on shell oysters, there are usually several spat attached to each shell. Most of the oysters produced by extensive aquaculture are for the shucked oyster market.
The Nature Conservancy and VIMS collected a large suite of data to measure environmental variables at each of the four oyster farms including water currents, water clarity and chemistry, and sediment type and the creatures that live in it.
White Stone Oyster Company uses a floating cage system to grow their oysters. Each cage holds three mesh bags of oysters. To harvest the oysters, the cages are hauled on board the boat and the bags removed.
Big Island Aquaculture grows their oysters in bags suspended from floats. Oysters are harvested by simply removing the bags from the floats.
Water Quality Mapper
Attached to the rear of the research vessel is a water quality sensor that samples the water every 10 seconds as the boat moves through the oyster farm.
It measures parameters such as dissolved oxygen, water temperature, salinity, and chlorophyll. Chlorophyll is a plant pigment that is used to determine the amount of phytoplankton in the water.
Using this system, scientists can generate a picture of water quality around the entire oyster farm and possibly see what, if any, impact the oyster farm is having.
In the Chesapeake Bay, sediment and plankton can stick together to form larger particles called flocs. These flocs both absorb and scatter sunlight as it shines through the water—meaning there is less light available for underwater grasses.
Oysters can potentially consume these flocs and excrete more compact particles which then sink, helping to improve the clarity of the water.
Underwater grasses are an important part of the Chesapeake Bay's ecology. They're a food source for waterforl and provide habitat for commercially important species like striped bass, blue crabs, and bay scallops.
Seagrass beds also have a role to play in mitigating the impacts of climate change. Five acres of eelgrass can soak up enough carbon dioxide to offset driving a car 15,000 miles a year. According to a 2012 study by Florida International University, coastal seagrass can store more than twice as much carbon per square kilometer as terrestrial forests.
Chapel Creek and Lynnhaven Oyster Companies grow their oysters in cages that sit on the bottom of the river.
Excessive nutrient pollution in the Chesapeake Bay causes phytoplankton to multiply to levels that cloud the water and reduces the amount of oxygen in the water for fish and crabs to breath.
Diver Collected Sediment Cores
Divers swim down to the bottom at several locations inside and outside the oyster farm to collect sediment cores. These cores are then examined to determine sediment type, the amount of organic matter and types and quantities of animals living in the sediment.
Scientists can lower this piece of equipment over the side of the boat and grab sediment samples from the bottom. They are using this method to characterize the sediment in and around the oyster farms.
This piece of equipment has several sensors mounted to it that measure water quality characteristics such as temperature, salinity, pH, clarity and particulates.
Scientists lower this sensor over the side of the boat to determine both how much light is being absorbed and how much is being scattered by particles in the water.
The Acoustic Doppler Profiler (ADP) sits on the bottom and measures the speed and direction of currents moving through each oyster farm.
Life in the Sediment
We are examining the creatures that live in the mud, both under the oyster farms and just outside of them, to see if there are differences that might indicate impacts from oyster farming.
Benefits and Impacts of Oyster Aquaculture
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Oyster Aquaculture Impacts: Addendum
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