Oysters are not only powerful filterers, they also provide a home and habitat for many marine organisms. Most of these organisms will fall off while the oysters are being harvested or cleaned, but some will stay behind and can be found inside or outside of your oyster on the half shell. Seeing some of these creatures might give you the “heebie jeebies” about eating the oyster, they are perfectly safe and can either be removed or, in some cases, consumed for luck. These creatures include mud worms (Polydora websteri), “pea crabs” (Pinnotheres ostreum or Zaops ostreus), and “mud crabs” (Panopeus herbstii, Hexapanopeus angustifrons or Rhithropanopeus harrisii).
Mud Worms (Polydora websteri)
A Mud Worm in an Oyster – Louisiana Sea Grant
One of the more common marine organisms you can find on an oyster is the oyster mud worm. These worms are typically red in color and form a symbiotic relationship with the oyster. Mud worms can be found in both farmed and wild harvest oysters throughout the United States. These worms will typically form a “mud blister” and emerge when the oyster has been harvested. Even though the worms look menacing and unsightly, they are a sign of a fresh harvest and a good environment. Mud worms do not pose any threat to humans and can be consumed.
If you find a mud worm on your next oyster and are still unsure, just simply remove the worm and dispose of it. Dr. John Supan, retired professor and past director of Louisiana Sea Grant’s Oyster Research Laboratory on Grand Isle, mentioned in an article that oyster mud worms “are absolutely harmless and naturally occurring,” and “if a consumer is offended by it while eating raw oysters, just wipe it off and ask your waiter/waitress for another napkin. Better yet, if there are children at the table, ask for a clear glass of water to drop the worm in. They are beautiful swimmers and can be quite entertaining.”
“Pea Crabs” (Pinnotheres ostreum or Zaops ostreus)
“Pea Crabs” are in fact two different species of crabs lumped together under one name. Pea crabs include the actual pea crab (Pinnotheres ostreum) and the oyster crab (Zaops ostreus). These crabs are so closely associated with oysters that their species name contains some form of the Latin word “ostreum” meaning oyster! Pea crabs are known as kleptoparasites and will embed themselves into the gills of an oyster and steal food from the host oyster. Even though they steal food, they seem to pose no threat to the oyster and are a sign of a healthy marine ecosystem.
A Cute Little Pea Crab – (C)2013 T. Michael Williams
Pea crabs are soft-bodied and round, giving them the pea name. Pea crabs can be found throughout the Atlantic coast, but are more concentrated in coastal areas from Georgia to Virginia. While they might look like an alien from another planet, they are considered a delicacy and are typically consumed along with the oyster. If you are brave enough to slurp down a pea crab, you might just be rewarded with a little luck. According to White Stone Oysters, “historians and foodies alike agree that finding a pea crab isn’t just a small treat, it’s also a sign of good luck!”
“Mud Crabs” (Panopeus herbstii, Hexapanopeus angustifrons or Rhithropanopeus harrisii)
Smooth Mud Crab – Florida Shellfish Lab
Just like pea crabs, “mud crabs” is another name for two different species of crabs commonly found in oysters. These crabs, the Harris Mud Crab (Rhithropanopeus harrisii), Smooth Mud Crab (Hexapanopeus angustifrons), and the Atlantic mud crab (Panopeus herbstii) to name just a few, reach a maximum size of 2 to 8 centimeters and are hard-bodied, unlike the pea crabs. Mud crabs can survive a wide range of salinities, but need cover to survive as these crabs are common prey for most of the oyster habitat dwellers, such as catfish (Ariopsis felis), redfish (Sciaenops ocellatus), and sheepshead (Archosargus probatocephalus). These crabs are not beneficial to an oyster environment as they will seek out young oysters and consume them by breaking the shell with their strong claws. If you find a mud crab in your oyster, this is one to dispose of before consuming. However, these crabs typically live on the outside of an oyster and are typically only found when you buy a sack of oysters and do not have an effect on the quality of the oyster.
Don’t Be Afraid
Hopefully this article has helped shed some light on the creatures you might experience when shucking or consuming oysters. Here is a helpful online tool to help identify some marine organisms associated with clam and oyster farms (Click Here). While most of the organisms can be consumed, we recommend the mud crabs be disposed of due to their hard shells. Remember, some of these organisms can bring you luck and with college football season around the corner, some of us might need all the luck we can get! Bring on the pea crabs!
Many of us are given that Birds and the Bees talk; another majority have had to give it as an adult to their kids. It is usually an awkward talk, but someone had to step up to the plate and put on a straight face. I am happy to be the one today to discuss one section of the Birds and the Bees of the Sea, batch spawning. Batch spawning, also known as broadcast spawning, is the coordinated release of gametes (sperm and eggs) into the water column. Batch spawning is not just relegated to fish, many species of invertebrates also batch spawn. Some of the most commonly encountered batch spawners include Florida Pompano (Trachinotus carolinus), Eastern Oyster (Crassostrea virginica), Red Drum (Sciaenops ocellatus), Red Snapper (Lutjanus campechanus), and Gag Grouper (Mycteroperca microlepis), to name a few. In fact, most gamefish species in the Gulf of Mexico are batch spawners. This has its advantages, but also has its major disadvantages. We will dive headfirst into a few representative species of saltwater organisms that batch spawn, and their respective life stages to help shed some light on reproduction in the marine world.
Baby Snapper – Thomas Derbes II
Eastern Oysters are a perfect representative for invertebrate batch spawning. I have gone over their life cycle in a previous article (Click Here), but I will just quickly go over their spawning habits and life history. Eastern Oysters typically spawn during the changing of the seasons, particularly from Spring to Summer and Summer to Fall. As humans, we see these changing temperatures and weather fronts as an opportunity for a new wardrobe, but these changes are triggers for oysters to spawn. Once one oyster releases their gametes into the water all of the mature oysters in the area will start releasing their gametes. Waiting to sense for other gametes in the water is a very smart tactic. This allows for a coordinated spawn between masses of oysters and (hopefully) increases the fertilization rate of the eggs. Since oysters cannot move, batch spawning is the most beneficial way for them to reproduce. Females can release anywhere from 2 to 70 million eggs in one spawning event, with only a dozen or so becoming adults. Since they are batch spawners, the larvae are left unprotected by the parents and suspended in the water column for the first few weeks, leaving them susceptible to predation by filter feeders and bad water quality. Once the larvae have reached the pediveliger stage, they will settle out and “walk” along the bottom of the estuary until they find a suitable place to call home, usually another oyster or hard substrate. After 1-3 years, the oyster will mature and begin batch spawning when conditions are ripe, and the cycle continues!
The Oyster Life Cycle – Maryland Sea Grant
Fish in the Lutjanidae (snapper) family are the perfect representative for batch spawning with fish. Snappers of all species are known to congregate and have mass spawning events typically around a full moon. The mutton snapper (Lutjanus analis) of South Florida and the Florida Keys are very well known for their ability to form massive congregations of tens of thousands of fish along the reef starting in April. Once the spawning commences, the mutton snapper will form a small subgroup of up to 20 fish in the late afternoon. This subgroup will travel to depths of up to 100ft to perform their spawning event. During this event, the female will signal to the males that she is about to release her eggs. The males will then rub up against the side of the female snapper, helping her release eggs while simultaneously releasing their milt (sperm). When the milt is released, the sperm is activated by the seawater and begins to swim. Eventually, the eggs are fertilized and an embryo is formed.
Massive Two-spot red snapper aggregation ready to spawn in Palau – R.J. Hamilton
18 – 24 hours later, the embryo is now a larval fish consisting of a yolk sac and lacking a mouth, eyes, and most organs. The yolk sac consists of amino acids and other nutrients that provide energy to the developing larvae. These larval fish have until their yolk sac runs out to develop the lacking vital organs, which usually takes between 24 – 48 hours. Only a very small percent of juvenile snapper make it to adulthood due to predation during their larval stage and predation as a juvenile. In fact, sharks and other large predators will prey on the snapper as they congregate and spawn, and filter feeders like manta rays are known to pass through an active spawning congregation to consume all the fertilized eggs and larval fish.
Well, I hope I didn’t scar anyone too badly. Batch spawning is fairly common in the marine biology world, and you can sometimes experience a spawning event without even knowing it. As for positives, this allows for many eggs to be fertilized at a time multiple times a season and for the larval fish and shellfish to be distributed through the estuary and reef via tides and waves. A major negative is the vulnerability of the juvenile and larval fish and shellfish, but the sheer number of eggs produced and fertilized helps outweigh the high potential for predation and unexplained loss of fertilized eggs and juveniles.
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 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!
You might say this is a strange title – “meet the barnacle” – because everyone knows what a barnacle is… or do they?
As a marine science instructor, I gave my students what is called a lab practical. This is a test where you move around the room and answer questions about different creatures preserved in jars. Almost every time that got to the barnacle they were stumped. I mean they knew it was a barnacle but what kind of animal is it? What phylum is it in?
Going through a thought process they would more often than not choose that it was a mollusk. This makes perfect sense because of the calcium carbonate shell it produces. As a matter of fact, science thought it was a mollusk until 1830 when the larval stage was discovered, and they knew they were dealing with something different. It is not a mollusk. So… what IS it? Let’s meet the barnacle…
Barnacles along the seashore is a common site for many.
Photo: NOAA
The barnacle is actually an arthropod. Yep… the same group as crabs and shrimp, insects and spiders. Weird right…
But that is because the creature down within that calcium carbonate shell is more like a tiny shrimp than an oyster. It is in the class Cirripedia within the subphylum Crustacea. It is the only animal in this class and the only sessile (non-motile) crustacean.
Barnacles are exclusively marine. This has been helpful when conducting surveys for terrapins or assessing locations for living shorelines – if you see barnacles growing on rocks, shells, or pilings, it is salty enough. There are over 900 species described and they live independently from each other attached to seawalls, rocks, pilings, boats, even turtle shells. Louis Agassiz described the barnacle as “nothing more than a little shrimplike creature, standing on its head in a limestone house kicking food into its mouth.”
This image from a textbook shows the internal structure of a barnacle. Notice the shrimplike animal on its back with extendable appendages (cirri) for feeding.
Image: Robert Barnes Invertebrate Zoology.
The planktonic barnacle larva settles to the bottom and attaches to a hard substrate using a cement produced from a gland near the base of their first set of antenna (crustaceans, unlike insects and spiders, have two sets of antenna). It is usually head down/tail up and begins to secrete limestone plates forming the well known “shell” of the animal. Some barnacles produce a long stalk near the head end (called the peduncle) which holds the adhesive gland and it is the peduncle that attaches to the hard substrate, not the head directly. The goose neck barnacle is an example of this. We find them most often in the wrack along the Gulf side of our beaches attached to driftwood or marine debris.
Lucky was found in the Gulf of Mexico. He had been there long enough for these goose neck barnacles to attach and grow.
Photo: Bob Blais
The “shell” of the barnacle is a series of calcium carbonate plates they secrete. These plates overlap and are connected by either a membrane or interlocking “teeth”. The body lies 90° from the point of attachment on its back.
There are six pairs of “legs” which are very long and are extended out of the “doors” of the shell and make a sweeping motion to collect planktonic food in the water column. They are most abundant in the intertidal areas were there are rocks, seawalls, or pilings.
Most species are hermaphroditic (possessing both sperm and egg) but cross fertilization is generally the rule. Barnacles signal whether they are acting males or females via pheromones and fertilization occurs internally, the gametes are not discharged into the water column as in some mollusks and corals. The developing eggs brood internally as well. Our local barnacle (Balanus) breeds in the fall and the larva (nauplius) are released into the water column in the spring by the tens of thousands. The larva goes through a series of metamorphic changes until it settles on a hard substrate and becomes the adult we know. They usually settle in dense groups in order to enhance internal fertilization for the next generation. Those who survive the early stages of life will live between two and six years.
So, there you go… this is what a barnacle is… a shrimplike crustacean who is attached to the bottom by its head, secretes a fortress of calcium carbonate plates around itself, and feeds on plankton with its long extending legs. A pretty cool creature.
Reference
Barnes, R.D. 1980. Invertebrate Zoology. Saunders College Publishing. Philadelphia PA. pp. 1089.
