Oysters: A Dive into Bivalve Aquaculture

Oyster repopulation may be key to restoring ocean health

A World of Oysters

"He was a bold man that first ate an oyster," said Irish author and satirist Jonathan Swift. 

Given their unique appearance and texture, one can't help but wonder who was brave enough to try oysters for dinner. The truth is that oysters, also known as bivalve mollusks, have been a part of the human diet and adored for their pearls for thousands of years. Scientists even found evidence of humans eating shellfish an estimated 164,000 years ago. They're a great source of protein and contain several key nutrients like calcium, iron, vitamin D, and iodine. Today, dining on oysters is considered a luxury experience. Yet, beyond being lavish meals and pearl jewelry collections, oysters have the potential to play a much bigger role in sustainable agriculture.

Belonging to the Ostreida order, oysters can be found in all four oceans where waters are temperate and warm. Because soft and sandy floors leave them susceptible to being buried, oysters thrive in habitats with hard floors. Within the Ostreida order, there are true oysters and pearl oysters. True oysters are those we tend to find on our dinner plates, while pearl oysters are those that we harvest for pearls. Although all oysters have the ability to create pearls, not all of them create the durable, long-lasting gems we find strung together as necklaces. True Oysters can be found all over the world, but within the United States, there are five species that are harvested. Crassostrea Virginicas, or Atlantic Oysters, make up 85% of the harvested oysters in the U.S. They include Blue Point, Wellfleet, Malpeque, and Beausoleil oysters which all live in some parts of the Atlantic Ocean. Across the country, we have three different species. Kumamoto Oysters are found both on the west coast and in Japan. Their sharp and pointy shells are similar to Pacific Oysters, also called Crassostrea Gigas. Pacific Oysters are smaller but are the most cultivated oyster in the world. Within this category includes the Totten Inlet and Fanny Bay oysters. Also on the west coast are Olympia Oysters, which are the size of a quarter and are the only oysters native to the west coast.

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A Harmonious Habitat

Oyster reefs are typically found in salty waters close to the coast. Oysters can find a home as far north as the Canadian coast and all the way south to Argentina. No matter the ocean, the invertebrate thrives as long as it's in warm water between 68 and 90 degrees Fahrenheit. Once oysters become settled, they begin to fuse together, forming beds or reefs. As a result, they become a home for other marine creatures. Mussels, barnacles, and sea anemones are known to find refuge on oyster reefs, with several species laying their eggs there. Among them are anchovies, flounders, and shrimp. In some cases, reefs offer protection from storms and tides. 

Along with providing shelter for other ocean life, oysters are essential for balancing the environment they live in. They are natural ecosystem engineers, meaning they maintain their habitats. For example, water quality where oysters are present is usually much better since they filter water to feed and breathe. During this process, oysters remove and feed on plankton and other small particles in the water. Their ability to feed directly from the water makes them suspension feeders. They can also consume bacteria, nitrates, and ammonia. This is especially important because too much nitrogen in water can cause an overgrowth of plants and algae. Overgrowth often leads to the blockage of light to deeper water and a lack of dissolved oxygen. Filter feeders, like oysters, help keep the ecosystem healthy. One oyster alone can be capable of filtering 190 liters in just one day. 

The State of Oyster Reefs

In the Americas, indigenous groups successfully harvested oysters with minimal damage to the ecosystem. Unfortunately, today oyster beds aren't as prominent as they once were. The Chesapeake Bay has seen 99% of its oyster population vanish due to human activity. Overfishing and other changes to the environment have slashed their numbers. The culprits include erosion from development, excessive nutrient pollution, and unsustainable harvesting. Without thriving oyster beds, the surrounding waters and wildlife lose natural filters, shelter, and barriers from strong tides.

The 19th century saw a huge availability of oysters, which led to cheap prices. In London, oysters were commonly consumed by the lower class, where the shellfish often served as a substitute for more expensive meats. In 1864 the residents of London consumed 700 million oysters, and 12,000 people worked in oyster fisheries across the United Kingdom. Around the same time frame in the Chesapeake Bay, there was a peak harvest of oysters in the 1884-85 season. Fifteen million bushels were harvested in this time frame, and tong harvesting was the main method of collection.

The Chesapeake Bay has seen 99% of its oyster population vanish due to human activity.

To fish oysters with tongs, they must be scraped from their beds and then collected with tongs. Dredging was another common way to snatch oysters from their beds. However, this method is very damaging to the reefs. A dredge looks like a giant scoop with metal teeth and a net to collect its harvest. Dredges are dragged along oyster beds, collecting everything in the path. Their use is typically limited, and yet there has still been notable damage to the oyster count in places like the Chesapeake Bay.

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A Solution to Overfishing

Oyster farming is by no means a new practice. In fact, the classical Roman civilization is believed to have had the first oyster farmers who created systems to grow and cultivate their own oyster beds. More recently in history, the eastern oyster was brought to the California coast in 1875 when the native oyster numbers were struggling. After two hundred years of overfishing, professionals in the industry are looking to continue collecting oysters while also replenishing the population. The states of Virginia and Maryland, in particular, have focused on these efforts. In order to repopulate the waters, scientists and watermen had to join forces. Nearly two hundred years ago, watermen would take hundreds of thousands of oysters from the Potomac River in the 19th century. Now, instead of harvesting, today's watermen are planting baby oysters that were designed in a lab. The lab-bred species is called Triploid Oysters. They were engineered with genes that are both disease resistant and with faster growth patterns. The three-year project involved two dozen watermen working with scientists on the mission. The main goal was not reproduction, but rather successful growth in the wild. These particular oysters were sterile, and because of low numbers, the specific locations of the babies were left unmarked to hide from oyster poachers.

While oyster farms are for commercial purposes, they can still provide the same shelter and water quality benefits that wild oysters provide.

Some professionals believe oyster farming is the best and most sustainable method for bringing back the oyster population. Others argue that it is not wide-scale enough to replenish the oceans. While oyster farms are for commercial purposes, they can still provide the same shelter and water quality benefits that wild oysters provide. The main cultivation methods of oyster farming are bottom/beach cultured, rack-and-bag cultured, suspended tray cultured, and bag-to-beach cultured. The bottom cultured process involves raising oysters on tidal beaches. Rack-and-bag oysters on the other hand are literally grown in bags that are attached to a steel reinforcing bar. The bags still allow the oysters to grow properly and must be placed in an area with low tides. Oysters grown with suspended trays hang in deep waters in mesh trays or nets. This method keeps them hidden from predators and other dangers. Lastly, farming oysters using the bag-to-beach method combines two techniques in one. Oysters start in bags, and before harvest season, they are placed along beach floors. Doing so helps strengthen their shells and meat by exposing them to a tougher environment.

Man-Made Reefs

The approach to healing the oyster population has been addressed through different means. While some projects focus on cultivating new oysters, others decided to build reefs that would attract the baby oysters already in the water. The success of reef development heavily depends on the selected location. Tidal conditions, current conditions, water depth, and the type of ocean floors are important factors that can make or break a reef's success. 

More than fifteen years ago, marine biologist, David Schulte, began an oyster restoration project with the U.S. Army Corps of Engineers after studying similar projects in other parts of the world. The Lynnhaven Oyster Restoration Project he worked on received three million dollars for the endeavor. The team created a new method for building reefs which included making the structures to be much larger, a whopping one hundred acres in comparison to the typical acre of reef space. Schulte and the team designed the reefs to be taller to help combat the risk of being covered by sand and mud. Altogether, this method was much more expensive in comparison to other restoration projects. While it was an ambitious undertaking, the goal was to get oyster numbers back to what they once were so many years ago. For every square meter, there were a thousand oysters that could be found on reefs. Scientists estimate that during their peak, oysters could filter the entire Chesapeake Bay in just a few days. After 99% of the oysters were lost, it took a year to do the same level of filtering with the oysters that were left. Thankfully, the reef restoration led to a significant increase in the oyster population. It soon became the biggest restored oyster bed in the world.

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A Helping Hand

Organizations like the National Oceanic and Atmospheric Administration are also key players in habitat restoration. NOAA Fisheries provides services to guarantee there are sustainable fisheries, safe sources of seafood, healthy ecosystems, and conservation of protected resources. Located in five regional offices, the federal agency consists of scientists, policy managers, and enforcement officers. Because U.S. fisheries are some of the largest in the world, organizations like the NOAA are fundamental in maintaining a sustainable system.

Because U.S. fisheries are some of the largest in the world, organizations like the NOAA are fundamental in maintaining a sustainable system. Over 70 oyster restoration projects have been funded with the help of NOAA's Restoration Center.

Over 70 oyster restoration projects have been funded with the help of NOAA's Restoration Center. Projects have included collecting old oyster shells for reef development, building linear reefs to stabilize shorelines, and creating hatcheries for oyster reproduction. Unsurprisingly, the center has an office in the Chesapeake Bay and is currently working on restoring the oyster population by 2025.

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A Sustainable Career

The old methods of oyster harvesting proved to be devastating for oyster populations everywhere. The abundance of oysters that existed in the 19th century led watermen to falsely believe that oysters would always remain plentiful. The fierce competition that arose amongst watermen, combined with their harmful dredging practices, destroyed reefs and wiped out a vital part of the Chesapeake Bay and other similar ecosystems. The knowledge of this unfortunate history and the knowledge we have on oyster biology can work together to give the industry a better chance at existing in harmony with the oyster population. Farming oysters would allow professionals to build and maintain numbers while also making a living. Furthermore, focusing on population growth and maintenance can ensure that oysters won't be wiped out the same way they were years ago. It is no secret that without the continual growth of healthy oysters, there isn't a promise of a sustainable career for traditional watermen. Instead, oyster farming leaves room for both the industry and the ecosystem to coexist.

Advantages of Oyster Agriculture

The ecological benefits of oyster agriculture are the same benefits as naturally occurring oysters. By prioritizing oyster numbers, water quality improves with the increased filtering by oysters. The rebuilding of oyster reefs gives marine life a place to seek shelter and lay eggs. The period in which oyster fishing was at an all-time high was the same period where industry regulation was nonexistent in all sectors. The second Industrial Revolution was a time when child labor laws were unheard of, let alone regulations to protect wildlife. Modern oyster agriculture is a crucial opportunity to correct the wrongs of the past. While it remains uncertain if locations like the Chesapeake Bay will see the same thriving numbers as before, efforts of repopulation have the potential to notably improve the ecosystem's conditions. 

Business Takeaways
  • Oysters are essential to the ocean's ecosystem, providing a home for different species and improving water quality while they feed.
  • The oyster population has significantly decreased due to overfishing and environmental changes.
  • Oyster farming and other restoration efforts have made significant improvements in oyster numbers on the east coast.
  • Restrictions on oyster harvesting methods are necessary to preserve the ecosystem.
  • When comparing careers, oyster farming has more longevity than traditional oyster harvesting.