In 1973 the United States Congress passed the Endangered Species Act. Controversial at the time, and still is today, the law was designed to help protect, and possibly restore, species that were near extinction within the boundaries of the United States. At the time there was a lot of concern about what was happening to whale populations across the world. These majestic creatures were being hunted by humans for food and other products. The hunt had been going on for centuries but in the mid-20th century it moved to an industrial scale and many populations were on the verge of extinction. The backlash from many around the world was enough for regulators in the United States to take notice.
In the 1970s there was an estimated 1000 manatees in Florida. These animals suffered from the increase of humans in their environment altering the habitat and literally running over them with an increase in boating traffic. Many growing up in Pensacola at the time had never seen a brown pelican and had never heard of an osprey. And then there was the decline of our national symbol – the bald eagle, and other national icons like the bison, bears, alligators, and moose. The loss of wildlife was noticeable.
At the time, if you looked at what was happening from the “30,000 foot” level, you could see the impact. Our barriers islands, which supported dunes that reached 40-50 feet tall, were being cleared at an alarming rate. Being replaced by large concrete structures, parking lots, and amusement parks. This loss of habitat forced the decline of the diversity and abundance of wildlife and the carrying capacity of supported populations declined.
If you looked seaward into the Gulf of Mexico, you saw a change from smaller boats with 75-100 horsepower motors to large vessels with up to four 350 horsepower motors on each boat. The number of these vessels seeking fish increased from hundreds to thousands, to even tens of thousands in some locations. Just visit one of the passes into the Gulf one weekend and you will witness the number of fishing vessels heading out. These boats were heading to fishing sites that at one time supported a species’ carrying capacity that was high and could certainly sustain the human need for food. Today these systems are stressed due to overharvesting.
If you looked towards the estuary, you saw the increase growth on the island produce runoff that made the waters more turbid, creating conditions that stressed many species of fish, invertebrates, and plants. Most notably was the loss of seagrass, which supports at least 80% of the economically important finfish and shellfish we seek. We removed coastal salt marshes, which also support fisheries, and replaced them with piers, docks, seawalls, and manicured lawns. These alterations again supported the decline of needed habitat and the diversity and abundance of coastal species. Creatures that were once common in many locations like horseshoe crabs, blue crabs, and echninoderms were now hard to find in some bays. The prized bay scallop is all but gone in many locations along with the recreational fishery that loved them.
On the mainland side of the estuary, you find the large cities. These are the locations that both the early European colonists and the Native Americans sought. They were at the connection between the freshwater rivers and estuarine habitats that supported their way of life. In the mid-20th century, these communities witnessed massive growth of humans. These humans cleared land, built concrete buildings and roads, decreased suitable habitat for much of the life that existed there, and increased pollution in both the ground and surface waters. Oyster beds began to decline, seagrasses that had reached the upper portions of the bay declined, and salt marshes were removed for a different sort of waterfront.
Much of this had been noticed even in the 1960s. The species that spawned the Endangered Species Act were mostly the large vertebrates that people felt close to, or the need for. Species such as whales, dolphins, manatees, and sea turtles. People were concerned about species like bison, moose, and pelicans. But, as the draft of the law was formed, it included others that were not on their radars like alligators, frogs, and sturgeon. The focus of the effort was the large vertebrates we were concerned about. However, there were numerous small creatures that were being lost that became part of the movement such as river mussels, snails, even beach mice. Then there were the numerous small creatures that will still do not know about.
For decades scientists have written about the world of the tiny creatures that live within the sand grains, and on the surface of seagrass that play crucial roles in the over health of the ecosystem and support, directly or indirectly, the larger creatures we care about. Even with the decision as to which species would be listed as “endangered” we saw favoritism for the large vertebrates that we appreciate. When placed up for listing consideration species like spiders, sharks, and snakes were met with resistance. Though their populations may have needed this protection, we did not want to protect those.
Despite some opposition from the beginning, the Endangered Species Act has had many success stories. Several species of whales are now stable or increasing, manatee populations have more than doubled, pelicans are common, everyone knows what an osprey is now, and viewing a bald eagle in Pensacola – though still exciting – is becoming more common place. Another sign of success are species that have been de-listed from endangered to threatened or removed completely. Alligators, bison, manatees, several species of sea turtles, and even the bald eagle have had this honor.
Over the next few months, we will post articles about species that benefitted from the Endangered Species Act, and species who are still struggling and should benefit from it now. There is no doubt that some humans suffered economically with the passing of this law, but its intent of preserving, and increasing the fish, wildlife, and even plants – that we love and need, as worked.
As I write this article it is mid spring, and the rays are bedding on the edges of our seagrass beds. The most common species seen is the Atlantic Stingray (Dasyatis sabina). They are often found in the sandy areas near the grass where they bury in the sand to ambush potential prey. This time of year, their numbers increase as the females are preparing to releasee their young in summer. Mating occurs in early spring and the females will deliver live young1.
According to Hoese and Moore2, there are eight families and 18 species of rays and skates found in the Gulf of Mexico. These are cartilaginous fish found in the same class as sharks but differ in that their gills slits are on the ventral side (bottom) of the body and their pectoral fins begin before the gill slits do on the side of the head. Most are depressed (top to bottom) and appear like pancakes, but not all of them. Sawfish and guitarfish appear more like sharks than rays.
Of the 18 species listed, seven can be found in the estuaries and may be associated with nearby seagrass beds. Two are species of sawfish, which are rare in our bays these days.
The sawfish.
Photo: University of Florida.
There are two members of the eagle ray family, the cownose ray and the eagle ray, which can be found in our bays. These resemble manta rays but differ in that they lack the characteristic “horns” of the manta (often called the Devil Ray because of them) and they do possess a bard on their tail, which manta’s do not. These are more pelagic rays spending their time swimming in the water column and hunting for buried food.
The cownose ray is often mistaken for the manta ray. It lacks the palps (“horns”) found on the manta.
Photo: Florida Sea Grant
The butterfly ray does resemble butterflies in shape having wide “wing-like” fins and a very small tail. It behaves similar to stingrays burying in the sand and ambushing smaller prey.
Two of the more familiar stingrays are found in our grassbeds, the Atlantic Stingray and the Southern Stingray. The Atlantic Stingray’s disk is more round in shape while the Southern Stingray’s is more angular shaped. The Southern Stingray is larger (disk width about five feet, Atlantic disk width is about two feet) and prefers estuaries with higher salinity. The Atlantic Stingray is very common and can tolerate freshwater, thus is common throughout the bay.
The Atlantic Stingray is one of the common members of the ray group who does possess a venomous spine.
Photo: Florida Museum of Natural History
Stingrays are notorious for their venomous bards and painful stings. They actually try to avoid humans and are frequently spooked by our activity fleeing as soon as they can. However, there are times when people accidentally step on one buried in the sand, or hiding in the grass at which time they will flip their whip-like tail up and over to drive their barb into your foot forcing you to move it – and you do move it – while you yell and scream. The ray then will swim away and can regrow a new barb.
The bard is a modified tooth. It is serrated on each side and there is a thin sac of venom along the flat side of the barb. When it penetrates your foot there is pain enough there. But the natural reaction of your body to an open wound is to close it, this reaction can pop the venom sac and release the toxin. The chemistry of the toxin is not life threatening to humans but is very painful. This experience is something you do want to avoid.
Like their shark cousins, rays do have rows of small teeth which they use to crush small invertebrates including shelled mollusks. They lie in the sand to ambush prey moving in and out of the seagrass beds. They possess two spiracles on the top of their heads which provide water to the gills when they are lying on the seafloor or buried in it.
Like sharks, males can be identified by the two claspers associated with the anal fin and the females usually have two uteri where the young develop. In skates, and some other rays, the young are deposited into the environment within a hardened egg case often called a “mermaids purse”. We see these washed ashore in the beach wrack. Young stingrays usually develop within the female and are born “live” in summer.
Though there is fear of this animal from some seagrass explorers they are a small threat unless you step on one. To avoid this, when in and around the sandy areas of a grassbed, move your feet in what we call the “stingray shuffle”. This is sliding your feet across the surface of the sand instead of stepping. The pressure generated from this movement can be detected by the ray several feet away and they will immediately move away.
Despite the fear, they are amazing creatures and play an important role in the overall health of the grassbed community.
References
1 Snelson, F.F., Williams-Hooper, S.E., Schmid, T.H. 1988. Reproduction and Ecology of the Atlantic Stingray, Dasyatis sabina, in Florida Coastal Lagoons. Copeia. Vol. 1988, No. 3 (Aug 1988). Pp. 729-739.
2 Hoese, H.D., Moore, R.H. 1977. Fishes of the Gulf of Mexico; Texas, Louisiana, and Adjacent Waters. Texas A&M University Presse. College Station TX. Pp. 327.
Sea urchins are one of the more commonly encountered creatures when snorkeling in our seagrass beds. At times these little pin cushions can be found in great numbers. In some locations there have been too many and community events have been developed to remove some. In the western panhandle they have all but disappeared. But for many parts of the panhandle, they are a noticeable member of the seagrass community.
According to the Florida Department of Health, most sea urchin species are not toxic but some Florida species like the Long Spined Sea Urchin have sharp spines can cause puncture injuries and have venom that can cause some stinging. Swim and step carefully when snorkeling as they usually are attached to rocks, both on the bottom and along jetty ledges. Photo by L Scott Jackson
Sea urchins belong to the phylum Echinodermata. The term echinoderm means “spiny skin” and is a good name for this creature. This group also includes the sand dollars, sea cucumbers, and the most famous member, the sea stars. Echinoderms are considered advanced and primitive at the same time. Advanced in the sense of organ development, sensory perception, and food gathering. Primitive in the sense that they have radial symmetry, like many of the more primitive invertebrate groups; bilateral symmetry is considered more advanced. The entire phylum is marine, they have no freshwater, nor terrestrial members, and they do like the water salty – at least 20 parts per thousand, and some need it higher than that.
As mentioned, the sea stars are the “star” of the group. They usually have five arms that radiate from a central disk region. On top there are usually small knobs or bumps which are the remnants of their “spiny skin”. Some species, though none in our area, have elongated spines. Beneath the arms is a radial canal which houses a series of gelatinous suckers called tube feet. The sea star can fill these with water using a unique system called the water vascular system. The tips of the tube feet or concave and, when full of water, can create a suction cup that is used for pulling themselves along the bottom and for grabbing food. These canals all meet within the central disk in what is called a ring canal and the water that fills them is sucked in by the sea star through a screen-like structure on the top of the central disk called a madreporite (“screen sieve”). The central disk is where the mouth is located, and it is located on the bottom. Food is worked into the mouth, digested, and excreted through an anus on the top of the central disk. Most species have some form of eye at the end of each arm and have a good sense of smell and taste.
Sea stars are predators, collecting small organisms they are fast enough to catch (which is not many really). But they can also take on larger slow prey, like shellfish. When they approach an oyster, which is sessile and cannot run away, they will grab each of the valves (shells) of the oyster with one of their arms. They will draw water into their water vascular system creating suction on the tube feet and “stick” onto the shells. They will then force the oyster open. Once open they will invert their digestive tract out of their body in a process called evisceration, consume the oyster, then retract the digestive tract leaving two empty shells on the seagrass bed floor. These empty shells are often found by snorkelers – though there are other predators of bivalves.
The Florida Orange Sea Star.
Photo: Florida Sea Grant
Sea urchins differ from their sea star cousins in the way their body is laid out. Imagine you had a five-armed sea star laying on the ocean floor. Imagine taking each of the five arms and rolling them upwards so that the tips of each touch above the central disk. Can you imagine this looking like a ball? A sphere? Now cover the now exposed underside of the arms with long spines (quills) and the tube feet extend between the quills. You have a sea urchin.
Another difference would be the mouth. At the terminus of each arm near the mouth is a single tooth. With five arms, there would be five teeth. Scientists call this set of five teeth Aristotle’s lantern and the urchin uses this to scrap algae from rocks, shells, and grass blades. They are herbivores, moving along feeding on a variety of seaweed and seagrasses in the system.
There is concern with many snorkelers that the quills (spines) of the sea urchin are venomous. That is the case with some species around the world, but not in our area. That said, they are sharp, and the purple urchin (more common in our rock jetties and artificial reefs) hurts. Their quills are sharp and often break off in the skin causing discomfort, much like a splinter. You do not want to handle them, but if you do – handle them with care.
Sand dollars are close cousins of the sea urchin and are in the same class (Echinoidea). If you can imagine taking a round sea urchin and squashing it flat like a pancake, you have a sand dollar. There are also echinoderms in this group that are not as round as sea urchins, but not as flat as sand dollars and are called heart urchins, or sea biscuits. These can be found in grassbeds at the eastern end of the panhandle, but are more common in south Florida.
The sea cucumber is an echinoderm more often found in rocky or coral reef communities, but there are some found in the seagrass beds. To see the relationship between them and their cousins, imagine taking a round sea urchin, lie it on its side, and extended the body so that it is no longer a round ball but an elongated worm-looking creature… sea cucumber. These are primarily scavengers and deposit feeders within the community.
Sea Cucumber
Photo by: Amy Leath
Being a resident of the western panhandle, we have noticed a mass decline of echinoderms in our grassbeds. As a kid in the 60s and 70s we never saw large numbers, as they do in the eastern panhandle, but we did see them. Now they are gone. One suggestion as to why has been salinity. Our bay system over here has more river discharge than those further east and the lower salinity may not support larger populations. The increased development of the years, and the methods of dealing with stormwater, may have created a system that echinoderms do not like. Whatever the reason, finding sea stars and sea urchins in our grassbeds is rare.
The eastern panhandle still has them. And, at times, too many. In recent years there has been an increase in sea urchin populations in St. Joe Bay that has led to overgrazing of the turtle grass. This could lead to a decline in suitable habitat for bay scallops, which the community depends on economically. The state currently sponsors a “Sea Urchin Round Up” event using humans to help control the overabundance of sea urchins.
Echinoderms are a visible, and interesting, part of our seagrass community.
My wife and I like to sit on our back porch and watch the sunset each day. We do not make all of them, but we try to make as many as we can. We often see small bats darting in all directions feeding on bugs. Recently we were enjoying a particularly great sunset. The sky was a light blue with streaking clouds of dark gray, purple, orange, and white. It was amazing. As the streetlight came on, we could see a swarm of termites gathering around it. There were a lot of them, but we also noticed the increase in bats. There was a dozen at least, probably more, zipping in and out, darting in all directions. We enjoyed watching them and wondered where all of them were roosting.
Bats sometimes move into buildings when they can’t find the natural structures they prefer (caves and large trees with cavities).
Many people are afraid of these creatures. They have been associated with Halloween, horror, vampires, and rabies. They are creatures of the night, and that is unsettling in itself for many. But, as biologists say with most creatures, these stories and legends are just that… stories and legends. Some members of their population do carry rabies, but most do not and the transmission of the disease to humans is rare. The animals are small furry mammals that eat an enormous number of insects each evening, including flying termites and mosquitoes. Many help pollinate plants and help disperse seeds. They are really pretty cool.
There are around 1400 species of bats worldwide1, 13 of these are from Florida2. Though some species feed on fruit and nectar, most feed on insects and consume about half their body weight each evening doing so. The Bat Conservation International states that insect consuming bats may save U.S. farmers $23 billion dollars a year in pesticide use due to their insectivorous diet1. The agave plant, the one used to produce tequila, is primarily pollinated by bats. The 13 species found in Florida are all insectivores feeding on beetles, mosquitos, moths, and other agriculture and garden pests. They are truly beneficial.
Bats are mammals, having fur covered bodies, live birth with young nursing on milk, and being endothermic (warm blooded). Most connect bats with the mammalian order Rodentia (rodents) – often calling them “flying rats”, but – due to the type of teeth – they are actually in their own order Chiroptera. They are the only true flying mammals in the world, the flying squirrel is actually a glider, not a true flyer. They live in a variety of habitats in Florida including pine forests, hardwood forests, riverine systems, lakes, and in urban areas. They most often roost in the crevices of dead trees, beneath the dead fronds of palms, and in Spanish moss. But when available, they will use caves and are notorious for using buildings, culverts, and the underside of bridges.
They fly using wings that are actually thin skin between their extremely elongated fingers. They breed in the fall and give birth to a single pup in the spring. One of the legends is that they are blind. As mentioned above, this is a legend. Bats can see well and see better than we do in dim light. They do have the ability to use high frequency sounds to “echo” off objects in the dark (echolocation) which helps them find, and follow, their insect prey at night. You can notice this hunting tactic as the sun sets and view the bats darting in all sorts of directions chasing their prey.
Most of the 13 species of Florida bats can be found in the Florida panhandle, with the gray bat only found in Calhoun and Jackson counties and nowhere else in the state. Rabies is a concern with bats, and it is true that an infected bat with the disease can transmit it to humans, but this is very rare. That said, anyone who is bitten by a bat should seek medical attention. The animal was also connected with the transmission of COVID during the early period of the pandemic3. Bats, like many other mammals, can pass infectious diseases and there is also a fungal growth associated with their droppings that has caused medical problems with some humans. If working in an area where bat guano is abundant, a mask is recommended. If an injured animal is found in your yard, wear a pair of gloves and take it to your local wildlife rehabber.
Florida bats do face problems in our state with the loss of habitat. We often remove dead trees and cut dead fronds from palms. The benefit we receive from them (consuming thousands of pest insects each night) leads to a need for their conservation. To date, the white-nose syndrome, which has infected many bats north of us, has not reached Florida but is of concern. Despite the fear many have of this animal, they are quite beneficial and should be allowed to exist in our panhandle habitats.
Species found in Florida:
Mexican Free-tailed bat
Southeastern myotis
Evening bat
Eastern red bat
Seminole bat
Northern yellow bat
Tricolored bat
Gray bat – endangered; only found in Calhoun and Jackson counties.
In terms of diversity and abundance, the Phylum Arthropoda is the most successful in the Animal Kingdom. Between them all, there are over one million species. They can be found in all habitats, from the deepest part of the ocean to the highest places in the mountains, from the polar region to the most extreme deserts. Most are insects, but there are also arachnids, centipedes, millipedes, and the ones most common to the marine environment – the crustaceans. With the numerous species within this group, and new ones being discovered all the time, the classification of arthropods is constantly changing. Currently Crustacea is considered a subphylum and there are about 30,000 species within.
Insects are one of the most abundant forms of life on the planet. Photo: Princeton University
There are several keys to the success of arthropods. Number one, their shell. It was seen with the mollusk that having a hardshell to protect your soft body was a winner. However, mollusk make their shells from heavy calcium carbonate. Though this provides excellent protection against most predators, it did slow them down considerably making it much easier for predators to catch them. It is understood that in the world of defense, speed is important. The arthropods make their shells from a strong, but much lighter material called chitin. This material is strong but serves as the creatures’ exoskeleton and must be shed periodically as the animal grows.
Number two, their legs. The name “arthropod” means jointed foot and one glance at the legs of any of these, you will see why scientists call them this. To increase speed animals, need to break contact with the surface of the ground. Birds are the best, lifting off and flying – the fastest form of location there is. The slug-like mollusks have their entire bodies in contact with the sediment, as the “slug” along the bottom of the sea. Many creatures have developed legs and walk, this is the case of the arthropods. Some hop great distances, like the flea. Others can actually swim, like blue crabs. And many of the insects have wings and can fly. But these jointed legs, along with a lighter shell, have been very effective defense for these creatures.
Number three, their sense organs and brain. Though not as intelligent as octopus and squid, arthropods are very aware of their environment and very quick to respond to trouble or a food source. Drop a piece of cheese during a picnic and see just how fast the ants find it. Heck don’t drop the piece of cheese and see how quickly they find it! These animals have a series of hairs, bristles, and setae connected to their shell that can detect movement and pressure changes in the environment. There are canals, slits, pits, or other openings in the shell that can detect odors. And then they have their compound eyes. Compound in the sense there are more than one lens. Each lens does provide an image of the target (in other words, they do not see 100 images of you) but rather each provides a level of light intensity sort of like individual pixels in a computer image, or the image we see when the camera displays “squares” of light so that you cannot read someone’s license plate, or the logo on their t-shirt – we see this on TV news and shows often. Compound eyes do not produce as clear an image as our eyes, but they are MUCH better at detecting motion, and there is an advantage to this. Try stomping on a cockroach, or swatting a fly, and you will see what I mean.
And number four, a high reproductive rate. You see this in many of the “prey” type species. Most arthropods are dioecious (males and females) and can produce millions of offspring at rates that you could never consume them all. So, they survive and can quickly support gene flow and adaptation. These are well designed animals.
Blue crabs are one of the few crabs with swimming appendages.
Photo: Molly O’Connor
In the crustacean world we find several groups. They differ from their arthropod cousins in that they have 10 jointed legs, and two sets of antenna (one set long, the other short). They include at least 30,000 species including the shrimplike cephalocarids, the shrimplike branchipods, the shrimplike ostracods (common in the deep sea), the roachlike copepod (part of the plankton we spoke about in another article in this series), the mystacocards, branchiurans, the familiar barnacles, krill, the roachlike isopods, flea like amphipods, and the most familiar of the group – the decapods – which includes the crabs, shrimps, and lobsters. It is this last group we will focus on.
There are three basic body parts to an arthropod. The head, thorax, and abdomen. In crustaceans the head and thorax are fused into one segment called the cephalothorax (the head of a shrimp or crawfish). The abdomen is what most call the shrimp and crawfish tail (the part we usually eat).
Insect body parts.
Crabs are the ones we most often encounter when exploring the seagrass beds. Not that the others are not abundant, they are, they are just not seen. They differ in that their abdomen is curled beneath their cephalothorax. The most commonly encountered is the famous blue crab (Callinectes sapidus). Most crabs have modified two of their 10 legs into chelipeds (claws) and most folks seeking crabs for dinner are aware of these claws. The blue crab belongs to a group called the protunid crabs which have modified two additional legs into swimming paddles – they can swim. They are often found crawling around the edges, and within, the seagrass searching for food. When detected over sand, they quickly bury themselves and sometimes people step on them not knowing they are there. When spooked they often will emerge with chelipeds extended and when the time is right, will scurry off running sideways with one cheliped pointed at you. They can get quite large and are a popular fishing target for both recreational and commercial fishermen. The males (the ones with the long then telson on their curled tailed) are more common in the upper estuaries. The females (the ones with the more round telson) frequent the lower bay. During breeding season, the males will move to the lower estuary to find a female. Once found he will crawl on her back and “ride” for a couple of days in what commercial fishermen call “doublers”. At some point the male will provide a tube filled with sperm called a spermatophore to the female. He then moves on. The female will store the spermatophore until she feels it is time to fertilize the eggs, then does so. The eggs begin to develop beneath her abdomen in a spongy looking mass. Early in development the mass is an orange color. Closure to hatching it is brown. Females carrying this spongy mass are called gravid and are illegal to harvest in Florida. The larva will be released in the millions as tiny plankton and go through several life stages before becoming young crabs and starting the whole story again. These popular crabs live for about five years.
Male and female blue crabs.
Photo:
Another crab found in the grassbeds is the spider crab (Libinia dubia). This crab does resemble a spider, is slow moving, and very hard to see. It has small chelipeds and feeds on debris and organic material collected by the grasses. They too can get quite large and resemble the king crabs harvested in Alaska.
Stone crabs (Menippe mercenaria) are more often associated with rocky bottoms, or artificial reefs, but they have been found in burrows and crevices within grassbeds. The have wide-stocky chelipeds, which is a favorite with some seafood lovers. Those in the grassbeds do not get as large as those found around the reefs of south Florida, where they support a large commercial and recreational fishery.
The stone crab has been a popular seafood target in Florida for decades.
The hermit crab is a common resident of grassbeds. The most frequently encountered is the striped hermit (Clibanarius vittatus). Like all hermit crabs, they lack an external shell covering their abdomen and must cover their tail with an empty mollusk shell. Their curled abdomen can grab and wrap around the columella within the mollusk shell and carry around their new home. These hermits have been found in a variety of mollusk shells and are found roaming the beaches at low tide feeding on organic debris and cleaning the grassbeds.
A room with a view: a stripped hermit crab sizes up a potential residence
One crab that is often associated with seagrasses is not actually a crab at all. The horseshoe crab (Limulus polyphemus) lacks antenna and is more closely related to the arachnids. This ancient mariner has been plowing the bottoms of estuaries for over 400 million years. They resemble stingrays with their elongated telson and feed on a variety of small invertebrates both in the grassbeds, and in other estuarine habitats. They are quite common in the eastern panhandle and seem to be making a recovery in the western end.
A large horseshoe crab found in Little Sabine.
Photo: Amanda Mattair
Though rarely seen, shrimp are very prolific in our seagrass beds. Pulling a seine or dip net through the grass will expose their presence, usually in high numbers. The most commonly collected species are those known as grass shrimp (Palaemonetes sp.). There are a few species, and all are small and mostly translucent, though one is a brilliant green. Feeding on organic debris within the grassbed these little guys are an important food source for the larger members of the community.
The more famous of the shrimp group are the brown and white shrimp. These are the species we find on our dinner plates and are one of the most popular commercial species in the country. Brown shrimp (Farfantepenaeus aztectus) are also known as bay shrimp and “brownie”. They are a darker brown than the white shrimp and their uropod (the fan on the tail of the shrimp) is lined in a red color. They do not get as large as the whites and are very popular for fried and steamed dishes. The white shrimp (Litopenaeus setiferus) is a larger shrimp, is lighter in color (“white”), and their uropod is lined with a neon green color. Both of these commercially important species spend their juvenile and young adult days in the grassbeds of our estuaries. Later in the fall the adults move into the nearshore waters of the Gulf where they spawn and die. The planktonic larva drift back into the estuary with the incoming tide, finding the grassbeds and the cycle begins again.
The famous Gulf Coast shrimp.
Photo: Mississippi State University
The large diversity of crustaceans within the grassbeds speaks to the importance of this habitat to all marine life. Many are commercially important to the local economy and depend on a healthy ecosystem to survive. All the more reason to protect our grassbeds.
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.
