In Part 5 of this series, we looked at a group of invertebrates that few people see, and no one is looking for – worms. But in this article, we will be looking at a group that seagrass explorers see frequently and some, like the bay scallop, we are actually looking for – these are the mollusks.
With over 80,000 species, mollusk are one of the more successful groups of animals on the planet. Most fall into the group we call “seashells” and shell collection has been popular for centuries. There is an amazing diversity of shapes, sizes, and colors with the snail and clam shells found in coastal areas worldwide. As snorkelers explore the seagrass beds it is hard to miss the many varieties that exist there.
Seashells have been collected by humans for centuries.
Photo: Florida Sea Grant
One group are the snails. These typically have a single shell that is coiled either to the right or left around a columella. Some are long and thin with a extended shell covering their siphon (a tube used by the animal to draw water into the body for breathing). Others are more round and ball-shaped. Each has an opening known as the aperture where the animal can extend its large fleshy foot and crawl across the bottom of the bay. They can also extend their head which has an active brain and eyes. Snails lack teeth as we know them, but many do have a single tooth-like structure called a radula embedded in their tongue. They can use this radula to scrape algae off of rocks, shells, and even grass blades. Others will use it as a drill and literally drill into other mollusk shells to feed on the soft flesh beneath.
In the Pensacola area, the crown conch (XXX) is one of the more common snails found in the grasses. This is a predator moving throughout the meadow seeking prey they can capture and consume. Lighting whelks, tulip shells, and horse conchs are other large snails that can be found here. You can often find their egg cases wrapped around grass blades. These look like long chains, or clusters, of disks, or tubes, that feel like plastic but are filled with hundreds of developing offspring.
The white spines along the whorl give this snail its common name – crown conch.
Photo: Rick O’Connor
A close cousin of the snail are the sea slugs and there is one that frequent our grassed called the “sea hare”. This large (6-7 inch) blob colored a mottled green/gray color, moves throughout the grass seeking vegetation to feed on. When approached, or handled, by a snorkeler, they will release a purple dye as a “smoke screen” to avoid detection. Snails secrete a calcium carbonate shell from a thin piece of tissue covering their skin called a mantle. The genetics of the species determines what this shell will look like, but they are serve as a very effective against most predators. Most… some fish and others have developed ways to get past this defense. But the slugs lack this shell and have had to develop other means of defense – such as toxins and ink.
This green blob is actually a sea slug known as a sea hare. It was returned to the water.
Photo: Rick O’Connor
A separate class of mollusk are the bivalves. These do not move as well as their snail cousins but there are NO access points to the soft body when the shell is completely closed – other than drilling through. One creature who is good at opening them are starfish. Seabirds are known to drop these on roads and buildings trying to crack them open. But for the most part, it is a pretty good defense.
Bivalves possess two siphons, one drawing water in, the other expelling it, and use this not only for breathing but for collecting food – all bivalves are filter feeders. They will, at times, inhale sand particles that they cannot expel. The tend to secrete nacre (mother of pearl – shell material) over these sand grains forming pearls. Most of these are not round and are of little value to humans. But occasionally…
The pen clam is a common bivalve found in grassbeds.
Photo: Victoria College.
Oysters may be one of the more famous of the bivalves, but they are not as common in seagrass beds as other species. Most of our seagrass species require higher salinities which support both oyster predators and disease, thus we do not see as many in the grasses. Clams are different. They do quite well here, though we do not see them often because they bury within the substrate. We more often see the remaining shells after they have been consumed, or otherwise died. The southern quahog, pen shell, and razor clam are clams common to our grassbeds.
The one group sought after are the bay scallops. Scallops differ from their bivalve cousins in that they have small blue eyes at the end of each ridge on the shell that can detect predators and have the ability to swim to get away. They usually sit on top of the grasses and require them for their young (spat) to settle out. They are a very popular recreational fishery in the Big Bend area where thousands come very year to get their quota of this sweet tasting seafood product.
Bay Scallop.
Photo: FWC
There is another group of mollusk that are – at times – encountered in the seagrass beds… the cephalopods. These are mollusk that have lost their external calcium carbonate shells and use other means to defend themselves. This includes speed (they are very fast), color change (they have cells called chromatophores that allow them to do this), literally changing the texture of their skin to look and feel like the environment they are in at the moment, and expelling ink like some of the slugs. This includes the octopus and squid. Both are more active at night but have been seen during daylight hours.
The chromatophores allow the cephalopods to change colors and patterns to blend in.
Photo: California Sea Grant
As mentioned, shell collecting is very popular and finding mollusk shells in the grassbeds is something many explorers get excited about. You should understand that taking a shell with a living organism still within is not good. Some areas, including state parks, do not allow the removal of empty ones either. You should check before removing.
When most hear the word worm unpleasant things come to mind. “Gross”, “dirty”, “decaying”, “disease”, “rotten”, are a few. And then there is the whole parasite thing. But then there are those who like them. Gardeners, kids, and fishermen find earthworms in particular pretty cool. They are not the typical creature we look for on a hike, or search for on a TV documentary, and they are certain not at the top of creatures you would be looking for while exploring a seagrass bed – but they are there.
According to the 4th Edition of Robert Barnes’s Invertebrate Zoology (1980) there are at least 11 phyla of worms, and he mentions no fewer than six classes. It is an extremely diverse group of creatures, and many are the bridge between the simple animals and the more complex. In this article we will focus on four phyla of the more common worms, or least the ones most commonly known.
These phyla are divided by body shape and internal complexity. The simplest are the flatworms (flukes and tapeworms), the more complex are the annelids (earthworms and leeches). The vast majority of these animals are very small (less than one centimeter) and not seen by the casual snorkeler. Some of the nemerteans (a phyla of flatworm) and the segmented polychaetes (related to earthworms) are quitter large and are easily seen by us.
The polychaetes may be the most familiar to us. These are segmented worms in the phylum Annelida. They are segmented like their cousins the earthworm but differ in that (a) each segment has a small leg-like structure (parapodia) and (b) they like marine conditions.
Neredia are one of the more common polychaete worms.
Photo: University of California Berkley
They resemble centipedes crawling in and amongst the seagrass blades and are often found within seashells we pick up and explore. They are basically harmless, and many species are the “garbage feeders” doing an excellent job keeping the system clean. We often see their “volcano” like burrows in the sandy areas within a seagrass meadows and many species produce glob-like gelatinous egg sacs that seagrass explorers confuse with jellyfish. There are also those that produce tubes. Some of these tubes are paper-like with bits of shell and other debris embedded in them. They produce these using mucous from their bodies to cement them together, place the tube within the sediment in a vertical position, and then live in them. Other tubeworms will produce their tubes out of shell material (calcium carbonate) forming snake-like structures on the surface of shells and discarded beer cans. And then there are a few called bristle worms. These are large and crawl across the surface of the substrate but have thin spines that extend off their bodies like cactus. Many of these do have venom and can be quite painful.
Polychaetes are the most advanced of the marine worms in the seagrass beds. Possessing a brain that is connected to sensory organs that can detect light and chemicals in the water, they can both find prey, and avoid predators. Prey varies between species. Most polychaetes can invert their pharynx (rather quickly) to grab prey using tooth like jaws. The carnivorous ones feed on small invertebrates (including other polychaetes). Others will use these jaws to scrap algae from shells and grass blades and are scavengers. Most reproduce sexually where there are both males and females and they possess a complete digestive tract (including a mouth and an anus) – as you will see… not worms do. In 1980 there were about 5300 species of them worldwide.
Nemertean worms are another large marine worm, but one few people have seen. This is because they are more nocturnal by habit. They are not segmented but rather are flat and gelatinous. They possess a proboscis that can be “launched” by the worm, that has a stylet (spear) at the tip – like a pole-spear gun. They use this to hunt invertebrates and find them by using their sense of smell. They also reproduce sexually, and there are separate males and females, but many will fragment into smaller worms when irritated. There are two classes and four orders of these worms worldwide.
Most of the remaining worms are either so tiny you will not find them or are endoparasites living within some vertebrate or invertebrate host within the seagrass community. The more famous group are the flatworms. These include the parasitic flukes and tapeworms. However, there is a class of free-swimming flatworms that crawl (or swim) around the “seagrass forest”.
The swimming ones are known as tubellarians. Most are clear or opaque, but in the coral reef community some are very colorful. Flatworms are the more basic members of the worm group. They lack a complete digestive system and must both eat and expel waste through the same opening (the mouth). Some tubellarians feed on small invertebrates which they capture and engulf without using teeth. Others feed on dead and decaying creatures, again – cleaning the environment. There are some that live commensally with mollusk and crustaceans. There is one that is rather large and can be seen on the gills of horseshoe crabs. They do have a simple brain and sense the world by detecting light, a sense of touch, and smell. In 1980 they reported about 3000 species worldwide.
This colorful worm is a marine turbellarian.
Photo: University of Alberta
The parasitic flatworms include the famous flukes and tapeworms. These live within the bodies of their hosts feeding on mucous, cells, tissue, and blood (yep – here is the “gross” “disgusting” thoughts we mentioned at the beginning). They possess tough skin to protect them from the digestive enzymes of their host. Most reproduce sexually but are hermaphroditic (each worm being able to produce both sperm and egg). Most require secondary hosts to complete their life cycle. For example, they may live in the gut of a spotted seatrout but will need to complete their larval stage in the gut of a mollusk. So, the eggs are released with the feces of the trout, the larva find a mollusk and enter, develop, and then expelled again via feces to once again find a trout. It’s a wonder they can do this – but they do.
The human liver fluke. One of the trematode flatworms that are parasitic.
Photo: University of Pennsylvania
The tapeworms cycle differs in that their head is round and has a series of hooks they use to embed into the intestinal tract of their host. The rest of their body is flat and segmented (each segment called a proglottid). These proglottids are released into the environment to find another host.
You may now be afraid of becoming infested with parasitic worms if snorkeling in seagrass beds. Fear not… these animals are VERY specific about the host they can survive with – and you are not one of them. Most seagrass explorers do not think of worms when they visit this community, and probably will not see any, but they are there and play an important role in keeping the system healthy.
Since 2007 Florida Sea Grant has worked with partners, and trained volunteers, to assess the status of the diamondback terrapin in the Florida panhandle. This small emydid turtle is the only one that lives in brackish water and prefers salt marshes. Very little is known about this turtle in this part of the country, and the Panhandle Terrapin Project has the goal of changing that.
Female diamondback terrapin.
Photo: Rick O’Connor
Terrapins have strong site fidelity, meaning they do not roam much, and spend most of their day basking in the sun and feeding on shellfish – marsh snails being a particular favorite. Like many species of turtle, they breed in the spring. Gravid females leave the marsh seeking high dry sandy beaches along the shores of the estuary to lay their eggs. Unlike sea turtles, she prefers to do this on sunny days – the sunnier the better. She typically lays between 7-10 eggs, and they hatch in about two months. The hatchlings spend their early months on shore, hiding under wrack and debris feeding on small invertebrates before heading to the marsh where the cycle begins again.
The project has three objectives each year. One, to survey known (primary) nesting beaches for nesting activity. The number of nests, tracks, and depredated nests can be used to calculate a relative abundance of these animals using those beaches. Two, survey potential (secondary) nesting beaches for any presence of nesting activity. Three, tag terrapins using the old notch method, PIT tags, and a small few with satellite tags. This will help us track terrapin movement and better understand how they use the habitat.
Since the project began, we have been able to verify at least one terrapin in each of the seven panhandle counties being surveyed and have identified nesting beaches in four of those. Relative abundance is rather low when compared to other regions within their range, but those beaches remain active.
The nesting season historically begins in late April and 2023 has been busy early. Seven hatchlings that overwintered in their 2022 nests emerged and were found by volunteers, and others. Two depredated nests were located, and one nesting female was captured and tagged. The volunteers will continue to survey the rest of the spring and much of the summer. Reports of these turtles are important in our assessment. If you believe you have seen a terrapin, contact Rick O’Connor – roc1@ufl.edu – (850) 475-5230 ext.1111. and let us know where.
Female terrapin fixed with a satellite tag for tracking.
Photo: Rick O’ConnorSmall terrapin hatchling released on Santa Rosa Island.
Photo: Rick O’Connor
The Florida Fish & Wildlife Conservation Commission and UF/IFAS Extension – Florida Sea Grant have partnered to implement an innovative community-driven effort to restore scallop populations, and we need your help! “Scallop Sitter” volunteers are trained to assist in Bay, Gulf and Franklin Counties. The goal of the program is to increase scallop populations in our local bays. Scallop sitters help reintroduce scallops into suitable areas from which they have disappeared.
Volunteers manage predator exclusion cages of scallops, which are either placed in the bay or by a dock. The cages provide a safe environment for the scallops to live and reproduce, and in turn repopulate the bays. Volunteers make monthly visits from June until December to their assigned cages where they clean scallops (algal and barnacles can attach), check mortality rate and collect salinity data that helps us determine restoration goals and success in targeted areas.
1. Click on the “reserve a spot” to select the county you are participating in.*You must provide your name, contact information and date of birth to secure an FWC permit for your cage!
2. You will be sent a registration survey via email (closer to the scallops, cage & supply pickup date or you may fill out a survey onsite) , view the virtual training link: https://myfwc.com/research/saltwater/mollusc/bay-scallops/sign-up/
and you’ll receive an invite to our Panhandle Scallop Sitter Facebook Group.
DEADLINE for steps 1 & 2 are May 25th!
3. Pick up your scallops, cage & supplies!
Pickup Information (all times local)
St. George Sound Volunteers
Date: Thursday, June 1st
Time: 10:00 AM – 1:00 PM
Location: FSU Coastal & Marine Lab (across the canal – see road signage)
3618 US-98, St. Teresa, FL 32358
St. Joseph Bay Volunteers
Date: Thursday, June 8th
Time: 10:00 – 1:00 PM
Location: St. Joseph Bay State Buffer Preserve Lodge
3915 State Road 30-A, Port St. Joe, FL 32456
St. Andrew Bay Volunteers
Date: Thursday, June 16th
Time: 10:00 AM – 1:00 PM
*We know issues happen from time to time with scallop populations. It’s a bummer. If you loose a significant amount of scallops early in this year’s program, we will do our best to accommodate our volunteers with a “second wave” scallop stocking event in August. Also, looking for other ways to help our program? We plan to offer cage building workshops in the fall, stay tuned!
This sounds similar to the idea that has been discussed about protecting some species of sharks. Do we really want to do this?
It reminds me of an interesting situation that was created when they passed the Marine Mammal Act in 1972. The law seemed simple enough. Citizens wanted to protect our marine mammals – such as whales, dolphins, and manatees. But it also included the polar bear, a dangerous animal. If you lived in a community where polar bears existed, and had one enter town that could possibly be a threat to the citizens, could you shoot it? A colleague of mine had a brother who worked with Alaska Fish and Game. We asked this question. He told us that – yes, if you were threatened by one you would shoot it. But you would have to defend yourself in court that it was defense and that you were not actively hunting the bear.
It seems odd to some that we would even consider protecting a creature that is potentially lethal to humans. But, as has been said so many times before, though they are potentially lethal, they rarely are. Rattlesnakes are different from polar bears in they do not seek us out when they are near us. They actually try to avoid us. In the United States only 5-6 people die each year from venomous snakes bites1. Comparing this to the number who die in car accidents, gun violence, or opioid overdose, there is no comparison. So, though the potential is there it is a very low risk. We can also note that many who bitten by snakes were trying to catch or kill the animal.
On the other side of the coin, these animals do us a service by controlling disease caring rodents. When predators select and kill prey, they tend to select one that is easy to catch and kill. Most predators not only have teeth, but hands and claws to grab the prey. The only thing a snake can do when it sees a rodent is grab it with its mouth and hold on. Many snakes do this, almost 90% of those in Florida do. But a few have venom. This can be injected into the prey so that the snake does not have to hold on, making the process much easier. It makes sense for snakes to have venom and is surprising that more do not. However, this venom was meant for killing prey, not for defending against predators. And rattlesnakes, like other venomous snakes, do not want to use it on humans if they can avoid it. As my professor told us in college venom is “expensive”. It is a complex cocktail of proteins they must produce, and they do not want to waste it.
So, though it seems strange that a state or federal agency would even consider protecting dangerous animals, they do. These creatures play a vital role in the ecology of local systems and if their numbers decline that role is not filled and the spin-off results could have larger negative impacts on us.
The U.S. Fish Wildlife Service has been petitioned to list the eastern diamondback rattlesnake (Crotalus adamanteus). This animal inhabits several habitats within the coastal southeastern United States. The National Council of Air & Stream Improvement, Inc. – a scientific research organization that provides technical information on environmental issues concerning forestry and forestry products – is conducting a survey to better understand its distribution and habitat preferences. They are asking people to report sightings of this snake. You can do so by visiting the following link. Please take photos.
The eastern diamondback rattlesnake is a classic serpent found in xeric habitats like barrier islands and deserts. They can be found in all habitats on barrier islands.
Photo: Bob Pitts
The word “jellyfish” tends to initiate a similar response in most people – “scream”, “run”, “this is going to hurt”. Being stung by a jellyfish is not pleasant and is something most would prefer to avoid. Our beaches warn us when they are out by flying a purple flag.
When exploring the seagrasses, this is not the first animal people thing they will encounter. Few associate jellyfish with the seagrass community. But within any community there are those we call residents (they reside here) and those we call transients (just passing through). It is the second group that we can place most jellyfish, at least the ones we are concerned about.
The sea nettle.
Photo: University of California at Berkley.
Jellyfish are animals, but not your typical ones. They are obviously invertebrates but differ from most others by having radial symmetry (having a distinct top and bottom, but no head nor tail). They possess ectoderm and endoderm (so, they have a skin layer and some internal organs) but they lack the mesoderm that generates systems such as the skeletal, circulatory, and endocrine. Though they do not have a brain, they do have a simple nervous system made up of basic neurons and some packets of nerve cells called ganglia. They seem to know when they are not in the upright position and know when they have stung something – which initiates the feeding behavior. But they are pretty basic creatures.
When you view a jellyfish the first thing you see is the “bell” and the tentacles – we always see the tentacles. The bell is usually round (radial), could be bell-shaped, or could be flat. It is made of a flexible plastic-like jelly material called mesoglea. Most of the mesoglea is actually water. When you place most jellyfish on the dock and come back in a few hours there may be nothing but a “stain” of where it was. It completely evaporated. There are some exceptions to this, like the moon jelly and the cannonball jelly, who leave thick masses of mesoglea for long periods of time.
Image: Wikipedia.
If you look closer at the “bell” you will see shapes within the mesoglea. Some are stripes, and may have color to them, others look like a clover leaf. These are the gonads of the animal. Jellyfish are hermaphroditic (the gonads can produce both sperm and egg), and they reproduce by releasing their gametes into the water column when triggered by some environmental clue to do so.
Around the edge of the “bell” many have a thin piece of tissue called the velum that can undulate back and forth and allow the jellyfish to swim. Swimming can involve moving up or down in the water column, or turning around, but the swimming action is not very strong and the tide and current actually plays a larger role in where the animals go – like pushing them through a seagrass bed.
Under the “bell” is a single opening, the mouth, that leads into a simple gut (the gastrovascular cavity). This serves as the stomach of the creature. But there is no anus, when the jellyfish has digested its food, the waste is expelled through the same opening – the mouth. This is called an incomplete digestive system.
Jellyfish are predators and hunt small creatures such as baitfish. Though they know whether they are upside down or not, and may be able to detect light, most have no true eyes and cannot see their prey. Some species may be able to detect scent in the water and undulate their velum to try and move towards potential food, but most drift in the water and hope the tide carries them to dinner. To kill their prey, they extend tentacles into the water. These tentacles are armed with stinging cells known as nematocysts. Each nematocyst holds a coiled harpoon with a drop of venom at the tip. They are encased in a cell membrane and are triggered when an object, hopefully food, bumps an external trigger hair that will fire the harpoon. This will then trigger the release of many nematocysts and the potential prey will be “stung” by many drops of venom. The venom can either kill or paralyze the prey at which time the tentacles bring it to the mouth. Many jellyfish have venom that is painful to humans, like the sea nettle and moon jelly, others have a mild venom that we do not even notice. Some have a very strong venom and can be quite painful, like the Portuguese man-of-war which has put some in the hospital. The famous box jelly of Australia has actually killed humans. We do have box jellies in the Gulf of Mexico, but they are not the same species.
This box jellyfish was found near NAS Pensacola in November of 2015.
Photo: Brad Peterman
As the tide pushes these transients through the seagrass meadows, their tentacles are extended and small baitfish like juvenile pinfish, croakers, and snapper become prey. But there are resident jellyfish as well.
With the Phylum Cnidaria (the stinging jellyfish) there are three classes. Class Scyphozoa includes the bell-like jellyfish that drift in the water column with extended tentacles – what are referred to as medusa jellyfish. But there are two other classes that include benthic (bottom dwelling) jellyfish called polyps.
Polyp jellyfish resemble flowers. The “bell” part is a stalk that is stuck to a rock, pier, or seagrass blade. Their tentacles extend upwards into the water column giving the creature the look of a flower. Instead of drifting and dragging their tentacles, they hope to attract prey by looking like a hiding place or other habitat. The sea anemone is a famous one, and a good example of the polyp form. But it also includes corals and small polyps known as Hydra. Hydra are tiny polyps that are usually colorless and can easily attach to a blade of turtle grass. Here they extend their tentacles into the water column trying to paralyze small invertebrates that are swimming by or grazing on the epiphytes found on the grass blades.
The polyp known as Hydra.
Photo: Harvard University.
Another jellyfish that drifts in the current is Beroe, what some call the “football jellyfish” or “sea walnut”. This a relatively small blob of jelly that lacks tentacles but rather has eight rows of cilia/hair (ctenes) along its side that move quickly and move this animal through the water. But like their medusa cousins, not against the tide or current. These jellyfish do not sting, they lack nematocysts, and hence are in a different phylum known as Ctenophora. Kids often find and play with them when they are present, and they are luminescent at night. These stingless jellyfish feed on small plankton and each other and are another transient in the seagrass community.
The non stinging comb jelly.
Florida Sea Grant
There are certainly species of jellyfish to be aware of and avoid. But as you look deeper into this group there are harmless and fascinating members as well. Most of these Hydra are very small and hard to see while snorkeling, but they are there. Another creature to try and find while you are exploring and play “seagrass species bingo”. Have fun and stay safe.
