Even though oysters have a hard shell that even humans have a hard time opening, they do have natural predators in our waters that can easily slurp up a couple dozen. Your usual oyster slurping suspects include oyster drills, blue crabs, and fish (such as the black drum). In this article, we will focus on the 3 major predators that contribute the most toward natural mortality in oysters here in the Florida Panhandle.
The Oyster Drill
When it comes to the marine snail world, oyster drills would win an oyster-eating contest. Oyster drills (Urosalpinx cinerea) are marine gastropods that grow to sizes of 0.5 – 1 inch. Oyster drills can be found all along the Atlantic coast of North America and the Gulf of Mexico, and they have been accidentally introduced into Northern Europe and the West Coast of North America. These small but mighty snails have become specialized in consuming oysters. Using chemotaxis, they locate their prey oyster. Once they find it, they secrete an enzyme to soften a portion of the oyster shell. Once softened, they drill into the shell and siphon out oyster meat. Oyster drills have been known to occur in great numbers when the environmental conditions are prime and can wipe out not only entire oyster beds but also clam beds. Oyster drills do have natural predators as well, but these predators also consume oysters.
An Oyster Drill (Urosalpinx cinerea) – Barnegat Bay Shellfish
The Blue Crab
Most of us know about the very tasty blue crab (Callinectes sapidus), but many do not know that it is a major consumer of oysters, especially on an oyster farm. Blue crabs are a decapod crab (meaning 10 legs) of the swimming crab family Portunidae. Blue crabs can indeed swim and their last leg on each side has developed into what are called paddle fins. Juvenile oysters are the main target for blue crabs, but they have been observed eating adult oysters when given the opportunity. On an oyster farm, blue crabs can get into an oyster bag when they are very small. Once inside, they have an all-you-can-eat buffet of oysters, and can quickly wipe out a bag of oysters. Oyster farmers have to be very cautious and must either remove the blue crabs manually or dry their bags out in hopes of destroying any blue crabs. Blue crabs can easily break open a juvenile oyster, but for them to consume an adult oyster, they will wait for it to open to feed before shoving a claw inside of the shell to keep the oyster open. Once they have their claw in the shell, they will use their other claw to consume the oyster.
Blue Crabs (Callinectes sapidus) Pulled Out Of Oyster Bags – Thomas Derbes II
The Fish
Even though oyster-eating fish like black drum (Pogonias cromis) and sheepshead (Archosargus probatocephalus) are much bigger than snails and crabs, they tend to contribute less to oyster mortality on oyster farms. However, during certain seasons wild oysters and other shelled invertebrates can contribute up to 33% of a black drum’s diet (more here). Fish will usually congregate around oyster beds and farms, but they are more interested in consuming oyster predators like crabs and snails. The black drum is a fish that was built for oyster consumption. While black drum lack sharp teeth, they have crushing plates in their throat that can crush an oyster shell which allows the drum to eat the oyster meat. Many oyster farmers welcome these fish on their farms as a free source of anti-fouling and predator deterrent (in the form of consumption).
Black Drum (Pogonias cromis) Caught On A Whole Oyster – Thomas Derbes II
There are many more oyster predators, but these are the top 3 in terms of threat and ability to consume/do detriment to oyster beds and farms in the Florida Panhandle. While oyster drills rank up towards the top, crabs and fish can also greatly contribute to natural mortality.
References
Flimlin, G., & F Beal, B. (n.d.). Major Predators of Cultured Shellfish. https://shellfish.ifas.ufl.edu/wp-content/uploads/Major-Predators-of-Cultured-Shellfish.pdf
And it’s a good thing! Green gill oysters are prized in the oyster community. In the Carolinas and Northern France, green gill oysters are a seasonal, cherished crop and a product of the saying “You are what you eat!” The phytoplankton, Haslea ostrearia, is the typical culprit, and their distribution is measured by direct observation from plankton tows or the occurrence of green-gilled oysters. The exact distribution is unknown, but there are reports of H. ostrearia throughout the Atlantic, Pacific, and Indian oceans. Haslea ostrearia is a beautiful pennate diatom that contains a water-soluble blue pigment known as marennine (More Here). Marennine’s production is stimulated by long photoperiods, blue light, and high light/low cloud weather. It can also be released into the water and into the flesh of organisms (typically oysters) that consume them.
Fresh out of the water Grayson Bay Oyster with green gills! – Brandon Smith, Grayson Bay Oyster Company
Pensacola Bay, and surrounding areas, had a pretty mild fall in terms of rainfall, and the bays have turned a beautiful green-blue hue as the bays have risen in salinity and phytoplankton typically found in the Gulf of Mexico were able to survive. Brandon Smith, owner of Grayson Bay Oyster Company, was out working his farm January 7th, 2024, and sent a text to me saying “take note of the green gills,” and I was very shocked and happy to see actual, green-gilled oysters in our local waterways. He graciously harvested a few dozen to examine (and let me taste test), and I was able to confirm the presence of green gills in the oysters. After further research on H. ostrearia, it seems as though the pennate diatom made it into our bays and is the culprit of this wonderful surprise.
A local Grayson Bay Oyster displaying green-gills – Thomas Derbes II
When I shucked my graciously donated oysters from Grayson Bay, I was reminiscing on the first time I came across green-gilled oysters. The first batch of green gill oysters I ate came from an oyster farm in North Carolina called N. Sea Oyster Company. Their green-gilled beauties “Divine Pines” were requested by a wedding I was catering for, and I was able to slurp down one to get talking and tasting notes. The seasonal Divine Pines offered a sweet yet salty taste and became one of my favorite out-of-area oysters to serve at events and to personally consume. While beautiful, the green-gilled oysters are usually only found in the fall/winter months. These green-gilled Grayson Bays were very comparable and offered a salty yet very sweet and minerally finish. The H. ostrearia is responsible for not only the green gills, but the sweet tasting notes, and I highly recommend adding any green-gilled oyster to your fall/winter raw bar selection.
References:
Turpin, Vincent & Robert, J-M & Philippe, Goulletquer & Massé, Guillaume & Rosa, Philippe. (2008). Oyster greening by outdoor mass culture of the diatom Haslea ostrearia Simonsen in enriched seawater. Aquaculture Research. 32. 801 – 809.
When you sit down and enjoy some fresh, farmed oysters during the summer, you might notice that the oyster is not watery but yet plump and full of meat, unlike the usual wild oysters. These farmed oysters are very special and are called “triploid oysters.” What makes an oyster a triploid? Well, it all starts in the oyster hatchery and involves using tetraploid male oysters to breed with diploid female “wild” oysters.
Before we dive into triploids, let’s go over some definitions. A diploid organism contains two sets of chromosomes. As humans, we have two sets of chromosomes, and the pair is formed by a chromosome from the mother and a chromosome from the father. Triploid organisms contain three sets of chromosomes and while very rare, triploidy does happen in the wild. Tetraploid organisms have four sets of chromosomes and are usually only formed in a laboratory setting using pressure or other means to cause tetraploidy. When you breed a tetraploid oyster with a diploid oyster, the result is a triploid oyster.
A hatchery worker keeping an eye on spawning chambers with diploid oysters – Thomas Derbes II
Inside of an oyster hatchery, you will see many small breeding chambers for the oysters. When a hatchery decides to spawn oysters, they place a single wild diploid oyster in each chamber. During spawning, the hatchery will introduce a cycle of cold then warm water and this cycle is repeated until a spawn is triggered. Hatchery workers will closely watch the oysters and will shut off the water supply to any oyster that has spawned so they can trap the gametes in the chamber. You can determine the sex of an oyster by watching it spawn; a female oyster “claps” out her eggs while a male opens slightly and releases sperm into the water. When spawning for triploid oysters, the hatchery workers will only obtain the eggs from female diploid oysters and discard any diploid sperm to avoid cross contamination. During the spawn, a worker will strip the sperm from male tetraploid oysters and once all female diploids are done spawning, they will introduce the tetraploid sperm to the diploid eggs. After 30 minutes, fertilization rates are calculated and stocking densities are formed.
3-month-old triploid seed – Thomas Derbes II
Why Would a Farmer Want to Grow a Triploid Oyster?
There are many benefits for a farmer to raise triploid oysters. First and foremost, triploid oysters are sterile. This is a major benefit for the farmers during the summer months. During the summer, wild diploid oysters spawn, and when they spawn, the meat turns very thin and watery. In the Panhandle of Florida, the harvest of wild oysters is prohibited in the summer and only farmed oysters can be harvested.
Another added benefit is the increased growth rate of a triploid oyster compared to a diploid oyster. As mentioned above, triploid oysters lack the ability to spawn. Since a triploid oyster does not have to spend energy producing gametes, it puts all of its energy into growing its shell and meat. A typical diploid oyster could take more than two years to reach harvest size, where a triploid oyster can reach harvest size within 8 months (commonly 12-24 months but there are usually some fast growers in a batch).
There are more benefits of triploid oysters including selective breeding for disease resistance and environmental sustainability. With the use of triploid oysters for oyster farming, wild stocks go relatively unaffected and help contribute to more sustainable aquaculture practices. I hope this brief explanation of triploid oysters will help you understand more about the somewhat unknown world of oyster aquaculture. With demand for oysters on the rise, triploid oysters hold great promise in meeting the needs of an ever-growing oyster aquaculture industry.
When you hear about oyster farming, you typically hear the word “seed” and how it is highly important to the future of the farm. While it might not be a typical seed that produces agricultural crops like corn, this seed is a living, breathing (albeit in the water) organism that produces a beautiful, cupped oyster. Depending on market size demand and requirements, it could take anywhere from 8 to 24 months to reach “shucking ready” size. Let’s take a dive into the timeline of an oyster, from seed to shuck.
A cooler full of R6 oyster seed headed out to the farm – Grayson Bay Oyster Company
Oyster farmers typically buy seed from an oyster nursery or hatchery, where they carefully spawn male and female oysters together in individual spawning chambers. Depending on the farmer’s needs, they can produce either diploid or triploid oyster larvae (more on triploids next week). These larvae are free-swimming for the first 2-3 weeks of their life until they develop into pediveligers (Oyster 101). Hatcheries will, for lack of better terms, mix the pediveligers with very tiny grains of ground-up oyster shells. These pediveligers will then attach to a single grain and begin to form into a “seed” oyster. Seed costs range and vary from year to year, and this cost is usually one of the biggest financial purchases oyster farmers can make. Seed is sold by size, starting at 6 millimeters (typically called size R6), and by increments of 1,000. Hatcheries and nurseries are located all along the Gulf Coast, but Florida law requires seed put in the Gulf of Mexico waters and estuaries must come from Gulf of Mexico hatcheries, and the same rules apply to Atlantic waters.
Oyster Seed (>R16) – Thomas Derbes II
Once purchased, these seed oysters make it to their homes in beautiful nutrient-rich waters and grow at a steady rate, and can reach an overall size of 2 inches in 4 to 9 months. During those months, the seed are filtering gallons of water per oyster per day, helping sequester carbon in their shells and consuming large amounts of plankton and algae that could contribute to the eutrophication of the bays. Oyster farmers will check on the seed almost weekly, changing bag mesh sizes and sorting the seed by size. Farmers will also take this opportunity to check for any oyster predators and swiftly evict them from their all-you-can-eat buffet. Sorting is done by using a “tumbler” that has a long drum with holes of varying sizes. This tumbler also helps clean the oyster and chip away at the lip of an oyster shell, causing the oyster to grow deeper and create a beautiful cup.
Farmed oysters do not have a size limit, but most farmers stick to a 2.5 to 3-inch size oyster. These oysters have filtered over 7,000 gallons of estuary water individually and sequestered a very generous amount of carbon, in the form of calcium carbonite (more here), in their shells in their first year of life. Once deemed ready for harvest, farmers will pull them out of the water and get them quickly in the fridge, following strict biosecurity guidelines and regulations to provide a safe product year-round.
Some oysters are fast growers! These were apart of the same spawn. – Thomas Derbes II
And there you have it, from seed to shuck. With the holidays coming up, and seafood sometimes being a part of the holiday plans, reach out to the local oyster farmers in your area to reserve a dozen or two for your favorite uncle. You can also wow the crowd with this very fancy mignonette recipe below!
Lemon Champagne Mignonette
Juice From 2 Local Meyer Lemons (They’re in Season!)
1 Shallot Chopped Finely
½ cup Champagne Vinegar
¼ cup Red Vinegar
1 tbsp each of Green and Pink Peppercorns
24 Local Farm Raised Oysters (For the Environment!)
1. In a bowl, add the juice of Meyer lemons and shallots. Let it marinate for 10 minutes.
2. Add champagne vinegar, red vinegar, and peppercorns to the lemons and shallots.
3. Chill for at least 30 minutes in the fridge.
4. Shuck oysters and top with freshly made mignonette. Enjoy!
Growing up in the South, I was exposed to many “Old Wives’ Tales,” ranging from not cleaning your house or clothes on New Year’s Day to the one that everyone, including the northern states, knows, “don’t consume oysters in months without an R.” While most “tales” are full of superstition, the “R” tale was one of biosecurity, and was mainly truthful until two new types of “R” came about; Regulations and Refrigeration. The tale came about due to the rise in food poisonings from shellfish in the warmer summer months that do not contain a “R,” such as June and July. The rise in food poisoning came about from the practices used by the oyster “tongers” at the time. Commercial harvest of wild oysters is a very labor-intensive job that requires long days on the water and constant tonging, measuring, and sorting of oysters as they come off the bottom. During the summer, the oysters would sit on the deck of the boat for hours in the heat, causing microorganisms and bacteria to flourish inside the closed oyster. Bacteria, like Vibrio, would replicate to harmful levels inside of the oysters and when consumed by a human, could cause life-threatening illnesses.
That was then, and this is now. While the consumption of wild Florida oysters during the summer is not allowed (closed harvest season for wild oysters during the summer in Florida), you can still find oysters from all over the US, and farmed oysters from Florida are still allowed to be consumed during the summer. Biosecurity is a major factor involving food production and aquaculture, and without biosecurity, the consumption of Florida-farmed oysters would be prohibited. Oyster farmers in Florida must follow a very rigorous biosecurity plan that includes State-issued harvest times, water-to-refrigeration requirements, reporting of harvest and planting, and twice-daily temperature monitoring requirements. The regulations for harvest times and refrigeration requirements have scientific backing, showing a statistical difference in Vibrio concentrations between properly handled oysters and neglected oysters, with properly handled oysters having little to no concentrations of Vibrio. For instance, during the summer months, oyster farmers must have oysters harvested and in the cooler before 11am and down to 45°F within 2 hours of storing in cooler.
A farmer returns early morning from the lease with harvest oysters covered by burlap. This keeps the oysters “cool.” (Photo by: Thomas Derbes)
While there is an increased concentration of harmful bacteria during these warmer months, properly cared-for oysters help limit the growth and proliferation of the bacteria. Another myth is that Vibrio doesn’t exist in cold, winter waters. Vibrio can exist year-round, and people with health risks, including immune-suppressed patients and those with diabetes, should exercise extreme caution when consuming raw seafood. When purchasing seafood for personal consumption, make sure to bring a cooler with ice and place your seafood above the ice, making sure to not allow any fresh water to touch the seafood. When storing seafood at home, make sure they are in a container that can breathe, and cover with a moist paper towel to keep their gills wet. Oysters are typically good for 10-14 days after the harvest date, so make sure you check the tags and consume within time.
Next summer, when you see farmed oysters on the menu, remember the new R’s and order a couple dozen for the table. The need for support from your local oyster farmer is most needed during those months without R, so slurp them down all summer and thank your local oystermen and women!
Locally Farmed Oyster with French Mignonette (Photo by: Kelly Derbes)
Easy French Mignonette Recipe
Recipe for 2doz Oysters
¼ cup Red Wine Vinegar
¼ cup Champagne Vinegar
1 tablespoon of Finely Chopped Shallot
1 teaspoon of Fresh Crushed Black Pepper
Juice of ½ Lemon
Combine all ingredients together. Spoon over shucked, chilled raw oysters.
There is a term that all oyster farmers dislike, it is almost like that one villain from a famous book/movie series where they shouldn’t say his name. That term is “unexplained spring/summer mortality” and it has been a growing issue along with the expansion of oyster farming throughout the southeast. While the art of oyster farming has been around since the time of the Romans, it is a relatively new venture here in the Gulf of Mexico, and Florida is home to over one hundred oyster farms. These farms are meticulously cared for by the oyster farm crew, with many different anti-fouling techniques and biosecurity measures in practice to provide the customer with a safe, clean product that you can consume even in the months without an R (another article on that coming later). Each year, farm managers can expect a 10-30% mortality event during the transition from winter into spring/summer, hence the term “unexplained spring/summer mortality.” Researchers and scientists from all over the southeast have been actively working to find a cause for this phenomenon, but the answer has been hard to find.
Dead, market ready oysters from one bag. Cause of death, “Unexplained Mortality Event 2022” Photo by: Thomas Derbes II
Our Pensacola Bay has been a hotbed for oysters lately; The Nature Conservancy recently constructed 33 oyster beds along Escribano Point in East Bay, the establishment of the Pensacola & Perdido Bay Estuary Program, acquisition of a $23 million restoration grant with $ 10 million towards 1,482 acres of oyster restoration, and the establishment of oyster farms and hatcheries. In Pensacola Bay, there are currently 5 oyster farms in operation, one of those farms being a family-owned and operated Grayson Bay Oyster Company. Brandon Smith has been managing the business and farm for over 4 years now and has experienced mortality events during those prime spring/summer months. In recent years, they have experienced mortality events ranging from minimal to what many would consider “catastrophic,” and reports from around Florida and the Southeast convey a similar message. Concerned for not only the future of his family farm, but other oyster farms in the Southeast, he has been working with the most experienced institutions and groups in 2022 to possibly get an answer on his and other local “unexplained mortality events.” Each road led to the same answer of “we aren’t quite sure,” but this didn’t deter Smith or other the farmers who are dealing with similar issues.
In 2023, Smith was invited to participate in a Florida-Wide program to track water quality on their farm. This project, led by Florida Sea Grant’s Leslie Sturmer from the Nature Coast Biological Station in Cedar Key, Florida, hopes to shed some light on the changes in water quality during the transition from winter to spring and spring to summer. Water samples have also been taken weekly to preserve plankton abundance and the presence of any harmful algae if a mortality event does occur. With the hottest July on record occurring in 2023, temperature could play a role in mortality events, and now researchers are equipped with the right tools and open lines of communication to possibly find a solution to the problem.
3-month-old seed being deployed out on Grayson Bay Oyster Company’s farm in Pensacola, Florida (2023). Photo by: Thomas Derbes II
As with traditional farming on land, oyster farming takes a mentally strong individual with an incredible work ethic and the ability to adapt to change. The Southeast has a resilient system of oyster farmers who display these traits and continue to put their noses down and “plant” seed every year for the continuation of a growing yet small industry, even through the hardest of trials and tribulations. Through collaboration with local and state institutions, stakeholders, programs, and citizens, oyster farmers are hopeful that they can solve this “unexplained mortality event” and help develop resilient farming techniques. An important message is local farms that have environmental and economic impacts cannot exist without the support of their community.
If you’re interested in tracking water quality on select farms, including Grayson Bay Oyster Company, the website is https://shellfish.ifas.ufl.edu/farms-2023/ and it is updated monthly.
