Containerized Culture

A single oyster species, the eastern oyster (Crassostrea virginica), is grown by aquaculture operations up and down the East Coast. But even with this single species of oyster to cultivate, no two growing operations are alike in the Chesapeake Bay.

“If you’re opening a burger franchise, there’s nothing you’re going to do when you walk through that door to make it better. They’ve already perfected it, right? You might as well just go in and use their system because it’s got a good reputation, they’re going to get the best burger out the door, the quickest,” says Ted Cooney, founder of Madhouse Oysters on Hooper’s Island. “This is the complete opposite.”

The water conditions in different areas, different gear types, and different harvest methods mean that what works for one oyster farm is vastly different from another.

“There are so many changes you can make to improve the quality of the oyster or improve the workday for the worker, because it’s backbreaking no matter what you do. The technological changes are driven by one or the other, or both,” Cooney says.

Maryland’s farmed oysters are grown to market size in areas of the Bay and its tributaries known as leases. Leased areas are reviewed and issued to the oyster grower by the  Maryland Department of Natural Resources . Although the size and scope of each farm varies, farmers raise oysters in one of two ways: either directly on the Bay bottom or in containers. Floats and cages, the containerized gear used to hold oysters while they grow, rest along the Bay bottom or are suspended in the water on a farmer’s leased area.

Humans have cultivated oysters for much of our history, but growing oysters in gear is a newer method in Maryland. Containerized growing allows farmers to grow single oysters in bags or cages, rather than as clumps of oysters directly on the bottom of the Bay. These single, loose oysters are not constrained in shape and size by the other oysters growing around them, resulting in a picturesque exterior perfect for serving on the half shell at restaurants.

But producing a prettier, pricier oyster is also more labor-intensive. The tiny oyster seed, attached to sand-like bits of ground-up oyster shell, are barely enough to fill a coffee filter. But within a year, they can grow large enough to fill several dozen grocery bags. That means from roughly March to November, when the water is warm enough for oysters to be growing, the oyster farmer must pull the cages of oysters up out of the water, remove the oysters, and transfer the oysters into new bags and cages as they outgrow the space.

Oysters grown in containers can also be manipulated to influence their size and shape. The farmer can tumble the oysters in a metal cylinder to chip off the outer lip of the shell, which encourages the oyster to grow a deeper shell that looks irresistible on a serving platter. Lifting the cages out of the water also gives the farmer a chance to rinse the mud and gunk off the cages so that the oysters get enough water flow and algae to eat. And sorting through the oysters helps growers distribute the heavy oysters into manageable groups—a lesson Cooney learned the hard way during his first year of farming oysters. By the end of the season, he had nearly 80 cages of oysters out in the Bay.

“Around Thanksgiving, I went to pick up my last five cages, which was all I needed to do for the winter,” Cooney recalls. “The boat was going to sink if I picked up this one because it was in the water way longer than it should have been. It was overfilled. So I left all five and went home. I was already so stressed, I thought I was going to lose my mind.”

He didn’t lose his mind, or give up on his oyster farm, but the experience produced the company’s name, Madhouse Oysters.

Although no two oyster farms are alike, there’s one thing nearly all farmers will agree upon: oyster farming is a labor of love.

“This is hard work that requires a lot of muscle. Your profit margins are pretty thin, so paying people exorbitant wages is not really an option,” says Matt Gray, an oyster researcher at the  University of Maryland Center for Environmental Science (UMCES) . “So, another way around this is investing in technology where you can leverage mechanics and reduce some of the backbreaking labor.”

To make the work more manageable, some growers have invested in larger vessels and mechanical winches to drag the oyster cages onto the boat. Oyster bags can be cleaned on the boat, rather than having to be hauled periodically back to land to be cleaned. Over time, Cooney invested in machinery that could sort and package his oysters on the boat too. He has also developed a prototype machine that will allow him to power wash his oyster cages and floats on the boat, rather than bringing them to land.

While Cooney adapted his operation gradually, learning year by year, some newer growers have designed their operations with technology in mind from the start. Dale Leavitt, one of the founders of Blue Stream Shellfish in Massachusetts, began his oyster growing business with an engineer and investor to cover the upfront costs of technology. His operation uses a sorting machine that measures each oyster with a laser beam, and then sorts it into different containers based on the oyster’s size. He also uses a barge with a mechanized winch system to pull his oyster cages onto the boat.

“Our intention all along was to take advantage of the scale [of operations], and mechanize as much as possible around the farm,” Leavitt says. “We’re using a lot of technology coming out of France and Australia, because they are well beyond us in application of technology to enhance their farming efforts.”

Other growers, like Nick Hargrove of Wittman Wharf Seafood in Talbot County, Maryland, have invested in conveyor belts that use a laser to count oysters and sort them into 100-count boxes. To make shucking easier, he also has a conveyor system modified from a dry-cleaning conveyor that brings buckets of oysters to the shuckers in the shucking room. Before the conveyor belt was installed, staff had to cart the oysters into the shucking room, and then haul the empty shell out.

“We can set the speed on the conveyor into the plant, and that way we can have a steady flow they can keep up with,” Hargrove says. “A bushel of oysters weighs about 80 pounds.”

Alongside the hard-won wisdom growers gain from experience, researchers like UMCES’ Matt Gray are also supporting the growth of the aquaculture industry. One project, led by Gray’s student Brendan Campbell during his PhD research at UMCES, focused on oyster gear that floats on the surface of the water, in order to understand what factors contribute to oyster growth.

“We’re trying to take a little bit of the art out of the process and really understand why an oyster grows the way it does at the surface,” Gray explains. “There’s been a lot of movement and activity toward creating these new types of gear, but we are still trying to understand how it actually works and optimize it.”

The research, conducted at the  UMCES’ Horn Point Laboratory , found that oysters in floating cages grew an optimal shape for the half-shell market, but also grew more slowly. The oysters in floating gear also formed deeper cups as the edges of their shell chipped off from the jostling motion, which can make them more appealing for the half-shell market. The rocking motion and the resulting shell shape is one of the main appeals of floating gear, but whether that was due to wave energy, wind energy, or another source of motion like boat traffic was unclear. Waves driven by wind are more variable than predictable tidal waves, but both can create motion for the oysters in floating cages.

To gain a better understanding of what was happening on the surface, researchers deployed sensors attached to oyster cages to measure their motion. After testing the devices and installing them in the gear, the researchers used meteorological data from the area to determine that wind accounted for about half of the cage movement they observed.

That finding provides oyster growers with a scientific basis for how they can position their cages to maximize natural motion. As part of the same study, the research team also deployed sensors called accelerometers within the gear to understand how much movement oysters experienced within the cages. In higher-energy areas where oysters experienced more jostling, the oysters in the study experienced higher shell growth, but also higher mortality. In more protected areas of the farm, oysters experienced slower shell growth, but higher survival.

“A grower could theoretically look at a plot on their farm and make management decisions,” says Campbell, who tested the sensors during his PhD research at UMCES. “For example, they can use the low mortality zone to grow smaller, more vulnerable oysters, then move animals to the more energetic sites where they can better handle the stress and will grow a more marketably favorable shell.”

Understanding the level of motion can also help farmers make decisions about how often they need to be cleaning their cages. For example, if a grower wanted less motion for their cages, they could clean their cages less frequently. Controlling biofouling, or the accumulation of plants on the oyster cages, can consume a lot of an oyster grower’s time and labor expenses.

“Biofouling is a huge time-consumer. When I worked on a farm, half of what I was doing was cleaning cages,” Campbell says. "If you have the ability to do that half as much, and still get the outcome that you're looking for, you just saved a ton on labor costs."

Not every solution will work for every grower, since each farm has different gear, water conditions, and growth goals for the oysters. More information allows growers to make deliberate choices for their farm, rather than using guesswork and learning through trial and error.

Maryland’s oyster aquaculture industry in its current form has only existed for a little over a decade. Oyster leasing laws were overhauled in 2009, creating opportunity for the industry to expand to containerized culture, in addition to the leases where oysters are grown on the Bay’s bottom.

After the overhaul, leases no longer had minimum or maximum sizes. Leaseholders were no longer constrained to lease oyster grounds only in the county where they lived, and county-wide aquaculture bans along Maryland’s Eastern Shore were overturned. The list of leasing laws, formerly stretching to more than 30 pages, now fits succinctly in several pages.

Easing leasing regulations allowed growers to employ container farming practices, expanding beyond the traditional aquaculture method in which oysters are grown on the bottom of the lease and harvested with a dredge. In 2013, oyster aquaculture accounted for 22,428 bushels of oysters harvested in Maryland. That number had more than tripled four years later, when growers harvested more than 74,000 bushels of oysters in 2017, according to the Maryland Department of Natural Resources. In 2021, growers harvested more than 90,000 bushels of oysters. Nearly half of the total harvest in 2021 was from oysters grown in gear, with the remainder of the year’s harvest coming from oysters grown loose on the bottom.

As research continues to provide information for oyster growers using cages and floats, aquaculture operators can make more informed decisions about their farm from the start.

“What we would like to do is help growers figure out what gear works best, and reduce the amount of trial and error that is typical at a lot of farms,” Gray says. “If we know the environmental conditions of a given site, and someone says they want to grow oysters here, we can look around and say, ‘We think gear X will do well here because of these environmental constraints.’ The industry is moving in these new directions and figuring out how to grow oysters differently—it’s an exciting time.”

The oysters used for aquaculture are carefully selected—they’re the hardiest against stresses like low salinity levels, produce the most meat, and are resistant to diseases oysters may encounter in the Bay.

Land-based farmers have used genetic tools to breed higher-producing plants or the hardiest cattle for decades, but these genetic tools have only been recently developed for oyster aquaculture. The Eastern Oyster Breeding Consortium, a collaboration of scientists along the East Coast, is working to understand the genetics of the eastern oyster.

The  Aquaculture Genetics and Breeding Technology Center at the Virginia Institute of Marine Science (VIMS ABC)  has developed the oyster broodstock lines used for most aquaculture in the Chesapeake Bay. Different genetic strains of oysters, known as family lines, are bred for a range of salinity environments in the Bay. Using genetic markers, which are DNA sequences with known locations on chromosomes, researchers can monitor family lines of oysters for generations. Understanding oyster genetics helps hatcheries select oysters with the best chance for survival and growth.

Each year, the VIMS ABC spawns oysters for each of their family lines and grows the oysters out in the Bay. Then, based on those oysters’ survival and growth, as well as their genetic traits, the best of the batch are used for the next generation of that oyster family. The lab’s data allows researchers to home in on oyster families that are good for specific traits.

“The elegant thing about family breeding is that we understand how highly heritable these traits are, like survival, growth rate, and shape,” explains Jessica Small, director of VIMS ABC. “Since we know how heritable they are, we know how much pressure we need to put on them from a breeding strategy to create gains.” 

Ming Liu, an oyster genomics researcher at  Morgan State University , has developed a line of oysters native to Maryland that is tolerant of low salinities often found in Maryland’s portion of the Chesapeake Bay.

Evaluating an oyster based on its growth and survival in the Bay means that researchers must wait at least one growing season before they can select the best-growing oysters to use as parents for the next generation. By linking an oyster’s characteristics to specific genetic sequences, researchers can ensure that the oyster’s fast growth and hardiness are traits that it will pass on to its offspring when it spawns. If a desired feature like resistance to a particular disease is genetically determined, researchers can identify the variations in DNA that are linked to that feature. Then, they can select oysters with those genetic markers for breeding.

“That method has been widely applied in agriculture, where broodstock have been chosen based on their associated genetic markers,” Liu says.

Understanding the genetic markers underlying the traits of interest in oysters can give researchers a baseline for addressing future challenges, such as the emergence of a new disease.

This is a developing area of science for oysters, but Liu says it is an important one. “Right now, low salinity is a big challenge, but maybe some new disease or new challenge will appear in the future,” Liu says. This genetic research ensures that Maryland’s oysters are prepared for the range of conditions they will experience while growing out on oyster farms.