Storms, tides and seasonal migrations ensure that almost every Wednesday morning beachwalk is different from the one before. The cool waters and extreme low tides of spring can provide us with unique opportunities to discover some of the vast array of shells, shellfish, crabs, tunicates, mollusks, fish and other sea life that inhabit our islands living beach.
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CREATURE FEATURE #23
ZEBRA LONGWING (Helliconius charitonius)
Soon, the weather will warm and the gusty winds of winter will dissipate and spring will be upon us here at Mound House. It is then that we find so many of the numerous species of butterflies that make their home here on the Mound.
Our State butterfly, the Zebra Longwing is found throughout Florida and adults may live for several months. The female lays her eggs on the young leaves and tendrils of the purple passion flower, which will provide food for the caterpillars that emerge. They may produce numerous generations each year and these butterflies can be easily distinguished by the yellow bands on their wide black wings. Mound House has a wide variety of flowering “host”plants that provide food for several species of butterflies.
Creature Feature # 23
SAILFIN MOLLY (Poecilia latipinna)
The sailfin molly is one of the most prolific and beautiful of our forage fishes. Growing to about four or five inches, sailfin mollies are found throughout coastal waters from the Carolinas to Florida and Texas as well as the Yucatan. They are able to survive in a wide variety of conditions from salty to brackish and even fresh water. Here at Mound House, you can find sailfin mollies schooling in the shallows of the kayak and canoe launch, amongst the rocks along our shoreline ,and even in the culvert pipes under our entrance. They are easily recognized by their flattened heads and spotted bodies. On the males, large and colorful blue dorsal fins and tails make these species easily distinguishable. Like other species of forage fishes in our region, the sailfin molly finds its way into tidal marshes and salt flats as well as ponds and ditches where it feeds on mosquito larvae. In fact, one method of mosquito control used here in Lee County decades ago was to excavate a series of ditches from tidal waters and into areas of marsh or standing water so that native fishes, including the sailfin molly could find their way in and feed on the mosquito larvae growing in the formerly stagnant water.
But life is rough for the sailfin molly, they are the target of numerous species of predator fish as well as wading birds and may live less than a year after reaching maturity.
CREATURE FEATURE #22
SHEEPSHEAD (Archosargus probatocephalus)
If you were to spend the day here at Mound House, fishing our rocky, historic shoreline with shrimp or crabs for bait, there’s a very good chance that you would wind up with several of these tasty fish on your stringer. Winter is the time when sheepshead congregate in our cold inshore waters feeding on oysters ,crabs and other crustaceans around the rocks and pilings of the back bay.
The prisoner stripes are a dead giveaway, and the sheepshead’s unique, stubby teeth, made for crushing shells give this fish its name. While they may grow to over 15 pounds, most sheepshead found in our waters are between 2 and 5 pounds.
Either walking the beach at Newton Park or touring the shell wall forming the underground archaeological exhibit at Mound House, you will invariably find the colorful shells of this enigmatic little scallop. Rarely found in the shallows, calico scallops prefer deeper waters and inhabit anywhere from 30 to 1,300 feet of water all along the coast of Florida and into the Carolinas. Scallops are swimmers and mass migrations occur up and down the coast to take advantage of seasonal changes in both the Gulf and Atlantic. Genetic identification of calico scallop populations show that larval scallops from Florida take advantage of coastal currents such as the gulfstream to find their way as far north as North Carolina. Occasionally after storms, live calico scallops can be found washed ashore in great numbers. Given that calicos are a deep water species, this is perhaps how they were harvested by the Calusa and eventually became part of the Mound. Today ,calico scallops are harvested commercially by trawlers ,but this is a true “boom or bust” species with catches ranging from a few thousand to millions of pounds depending on the environmental conditions which cause population cycles to change. Scientists believe that many of the massive calico scallop beds on the seafloor are never found because of how calicos readily migrate to better conditions. Scallops are filter feeders living primarily on a diet of microbial suspensions including bacteria as well as detritus and other organic matter. Calico scallops rarely live beyond two years of age and grow to about 2 inches in size making them somewhat smaller than bay or sea scallops. In addition to frequently finding themselves as the entrée at many of our Islands’ seafood restaurants, calicos are preyed upon by starfish, octopus, squid, numerous species of fish, crabs, rays, and even sharks.
#20 - LIGHTNING WHELK (Busycon contrarium)
One of the first things Visitors to the Mound House learn is that they are standing upon millions of shells and that the Calusa ,who once inhabited this mound, used these shells not only for food ,but for tools, weapons, jewelry and ultimately, building material. So, as we tour the underground exhibit examining the layers of shells that constitute the mound ,or study the mural, or check out the artifacts on the display shelf, we will find the lightning whelk. Lightning whelks shells from the Gulf of Mexico have been discovered in archaeological sites as far away as the great mounds in Cahokia Illinois. Large lightning whelks were carved out into elaborate drinking gourds as part of ancient religious ceremonies conducted on these mounds by Native Americans .
Closer to home, we find lightning whelk shells dispersed like old cans of spam within the ancient hunting middens of the Calusa dozens of miles from the gulf, these shells were carried by hunters to serve as a quick meal when traveling or at camp.
An edible species of very large predatory sea snail, as such it has a muscular foot to crawl on ,eye stalks and a feeding tube or proboscis. The lightning whelk has a unique sinistral or “left handed” spiral that is not found on other whelks or conchs. A large specimen may be over 15 inches in length and be over 20 years old. The lightning whelk feeds primarily on clams and other bivalves, and smaller whelks can be found just below the low tide mark on our beaches and patrolling the bayside grass flats. As a protective measure, smaller whelks will dig into the mud leaving only the sharp pointed end of their shell protruding and protecting the breathing siphon. This sharp protrusion will puncture the foot of an like The largest of our lightning whelks prefer the bayside to the beach. Using its operculum or “door”, to wedge open a bivalve, such as a quahog clam or cockle ,the whelk extends its proboscis into the bivalve and devours it from the inside out.
As the water temperature dips below 78 degrees, as it does here in November, the lightning whelk will greatly reduce its activity. Likewise, they will be much harder to find on the beaches and patrolling the shallows as they spend the winter in deep water making them much harder to find this time of year.
#19 - GREEN IGUANA (Iguana Iguana)
Here at Mound House, visitors will occasionally encounter one of our non- native residents, the green iguana. Frequently found lounging in the trunks of mangroves on our canal bank ,these vegetarians are native to the Central and South American tropics where living in dense canopy above the water is their preferred habitat. As such, our shady mangrove lined shoreline is the perfect location for these lizards. Scientists believe that our resident population of green iguanas are the descendants of escaped and released pets and have been observed in the wild here in Southwest Florida since the 1960s.
It is important to note that while we do have a few resident iguanas here on Estero Island, these reptiles cannot tolerate freezes and we are at the near northern range of their territory. Outer islands such as Estero, Cayo Costa and Gasparilla islands are warmed by gulf waters in the winter and rarely freeze. As such they have become home to the green iguana.
Juvenile iguanas are bright green and tend to darken into a grey or brown as they age. Larger adult males (and we have one) will have dark stripes and even turn a shade of orange during breeding season. Adult males may reach a length of nearly 5 feet. In many cultures, the iguana is considered to be of great medicinal value. Its body fat has been found useful in the treatment of sore throats ,ear aches and arthritis. In fact, the meat of the iguana is even considered an aphrodisiac in Central and South America.
However, unlike their cousin the gecko, researchers have determined that green iguanas can neither speak in an Australian accent or sell car insurance.
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| Mound House resident iguana |
#18 - AMERICAN WHITE IBIS (Eudocimus albus)
Visitors to the Mound House frequently encounter flocks of white ibis wading the rocky shoreline, perched in the mangroves or patrolling our freshly mowed lawn in search of grubs and insects.
A very distinctive wading bird, the white ibis sports a long curving orange bill, orange legs and brilliant white plumage with black wingtips when mature. Younger white ibis are a brownish white.
The American white ibis can be found throughout the Gulf and South Atlantic coastal regions of the United States ,Mexico and Central America as well as the Caribbean. They are found in a variety of habitats from muddy pools to mangrove swamps, mudflats, cypress forests and even the manicured lawns here on Estero Island.
Feeding primarily on small fish, crabs and crayfish as well as insects, the white ibis readily adapts its feeding behavior to match availability. During the breeding season, ibis gather in large flocks. They are territorial and defend their nests against intruders with elaborate displays of bill snapping ,lunging and biting.
Sometimes, the American white ibis can be found foraging in mixed species flocks that include the glossy ibis, the scarlet ibis and even wood storks. Many of the white ibis observed on Estero Island will move inland to the coastal marshes as waters recede with the onset of the dry season. These lowered water levels concentrate forage species such as minnows and crayfish into much smaller areas making feeding easier for the ibis.
Native American folklore holds that the white ibis is the last bird to seek shelter before a hurricane and the first to emerge after the storm, making the ibis a first a harbinger of danger and later optimism as the “all clear” sign that the hurricane has passed. Fittingly, the white ibis is also the mascot of the Miami Hurricanes.
# 17 - THE MANGROVE TREE CRAB (Aratus pisonii)
There is an impressive array of wildlife living on the Mound House site. Some on land, some in the surrounding waters, and some perfectly at home in either environment, such as this weeks’ subject : THE MANGROVE TREE CRAB
The mangrove tree crab makes its home among the roots and branches of the mangroves that line our shore here at Mound House. They can be seen crawling high up into the top limbs or even crossing the road on occasion, making their way home after a long evening or on the way out to dinner. Thriving on a diet of plant and animal material including mangrove leaves, seagrasses, worms and small crustaceans, the mangrove tree crab is perfectly adapted to is unusual environment where it lives both in the water and on land. This makes the mangrove tree crab an important link in the conversion of plant biomass into zooplankton, which serves as component to the base of the estuarine food chain. Though extremely fast and able to scamper out of the way of most visitors, mangrove tree crabs are small and seldom exceed the size of a quarter.
Predation is tough on the mangrove tree crab. As larvae, they are preyed upon by a variety of other zooplankton, filter feeders like barnacles, hydroids and anemones. As adults, larger fish ,wading birds and even other crabs target this species.
CREATURE FEATURE #16 – FLORIDA STONE CRAB (Menippe mercenaria)
Slow moving, thick shelled and armed with enormous claws that can exert a force of over 19,000 pounds per square inch, the stone crabs which inhabit the rocky shoreline of Mound House are a remarkable testimony to millions of years of evolution. They are adapted to life on the sea floor with juveniles and young adults living in the estuaries and larger adults moving offshore to burrow in the the deeper grass flats or to inhabit rocky limestone ledges. They are well camouflaged with a mud colored carapace and sandy underside. Feeding on carrion and even seaweed if need be, the powerful stone crab prefers using its claws to break into shells of clams, oysters, conchs, whelks and other marine mollusks.
On the other hand, stone crabs are a celebrated Florida delicacy and, in season, their delicious powerful claws can be found served with melted butter and a side salad at your favorite seafood restaurant.
Stone crabs are harvested by commercial trappers, recreational trappers and even divers from October until May. Remarkably, the stone crab is a renewable resource. By law, only the claws may be taken, and the crab is released alive back into the water where it will regenerate new claws within a year.
#15 - SMOOTH BUTTERFLY RAY ( Gymnura micura)
Summer is the time in which the full and new moons bring extreme low evening tides to the beaches of Estero Island, and it is during these low tides that the sand bars become exposed for a few hours at sunset, separating the waves form the shore and leaving the water between sandbar and beach shallow, clear , calm… and teeming with marine life that is rarely seen in the turbulence of the waves washing ashore on a high tide. One of the more unusual species to be observed during this time is the smooth butterfly ray. He is a master of camouflage, and you must look closely to find him. Usually found on soft sandy bottoms, the butterfly rays found on our shores tend to be a light sandy color that blends in nearly perfectly with the bottom. They are wider than they are long, with a very short tail displaying two distinct horizontal bands. These small rays feed on fish, invertebrates and crustaceans. Butterfly rays are common throughout the Gulf of Mexico, the northern coast of South America, and the Atlantic coast of Africa. If you are wading in the shallows looking for one, these rays tend to move slowly away ,gliding just above the bottom and will often stop to fan themselves into the sand nearly disappearing from sight. Although this species of ray is harmless and has no poisonous spine, be sure to shuffle your feet, lest you step on him and feel the stinging pain of butterfly ray resentment.
#14 - LOGGERHEAD SEA TURTLE (Caretta Caretta)
The loggerhead is the most common of the five species of sea turtle in Florida and summer is nesting season here on Fort Myers Beach. All sea turtles are listed as endangered and threatened marine species and as such are protected by State and federal law. This is why the nest sites that we see on the beach are carefully protected with stakes, ribbon and cautionary signs. Each nest may contain up to 100 eggs buried in the sand and these tiny hatchlings, only two inches in length, can grow to be over 38 inches long and more than 400 pounds. But as hatchlings, they are at the greatest danger, non only from predators such as raccoons and sea gulls, but from fish and sharks as they enter the water. Unfortunately, many sea turtle hatchlings never make it to the water, hatching at night, they become disoriented by sea side lights on the beach and wander inland where they die from sun exposure ,predation or exhaustion.
Sea turtles live on a diet of, crabs, shrimp, marine mollusks and even jellyfish and have done so, virtually unchanged, for over 200 hundred million years.
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| Loggerhead Sea Turtle |
One of the most attractive shells found on our beaches here on Estero Island is the olive shell. This small marine snail has a shiny delicately patterned shell and grows to about 2 1/2 inches in length. They can be found on the sandy bottom just below the low tide line and often burrow under the sand feeding on coquinas and other small bivalves as well as carrion. This marine snail lacks the operculum or “door” that so many of our marine mollusks have, and lives most of its life with its mantle (fleshy exterior of the body) wrapped around the shell, this constant polishing is what gives the olive shell its smooth, shiny appaerance. The olive shell has the distinction of being the State shell of South Carolina.
Here at Mound House ,our student visitors learn string these shells onto cordage braided from plant fibers, making bracelets and necklaces in the same way the Calusa did centuries ago.
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| Olive Shell Varieties |
#12 - BLUE CRAB (Callinectes sapidus)
In the shallows just off our beaches, the grass flats on the back bay, on pilings, up against seawalls, in the mangroves, the blue crab can be found most anywhere in the waters around Estero Island. They were a staple food source for the Calusa, for early settlers, and are a prized seafood today. They are both predator and prey, and about as omnivorous as a crab can be feeding on detritus, scavenging as well as capturing live fish or even cracking clams and oysters. The blue crab is a remarkable swimmer and can scuttle off rapidly on its swimmer legs when disturbed. If you are out on the bay side of Estero Island ,look for the round floating buoys of the crab trap marker. The blue crab is an important commercial species here in Florida. The inshore crab boats are distinct with their stacks of wire cages and entourage of pelicans and seagulls following along behind the boat to capture bycatch that is thrown overboard by the crabber.
On the beach, you may find the blue crab out in the shallows just offshore on the open on the sandy bottom, where he hides himself by fanning out the sand and burrowing in just underneath the surface.
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| Florida Blue Crab |
The Atlantic white slipper shell is a one sided shell with an arched back and a concave shape. They are white with brown markings and up to about an inch and a half in size when full grown.
These shells attach themselves to a hard object in the water (including other shells, or even each other!). They spend their lives in one place and are filter feeders. The creatures’ foot is on the underside of the shell and this is what it attaches itself with in a suction cup fashion. Also on the bottom of the shell is a shelf that extends about halfway up the length of the shell, thus giving them a resemblance to a house slipper.
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| Slipper Shell |
#10 - MOLE CRAB (Emerita sp.)
#9 - LEAST TERN (Sterna antillarum)
Moon Snail
“What was that?”
If you wade along the beach, right there along the edge of the surf where the waves roll and recede, you may notice, for the briefest of moments, these tiny sand colored creatures, less than an inch long, scurrying away before you, or disappearing under the sand in a flash as they dig themselves in before the next wave washes ashore. The mole crab, or “sand fleas” as they are known around here, are a small but very important crustacean that lives under the surface, in the wash zone of our beaches.
They must move quickly to survive and escape detection by predators or be washed away and left helpless, in the next wave. As such,Its body is barrel shaped ,and the legs tuck up tightly under the shell to allow the mole crab to quickly dig under the surface and to be able to roll with the waves when on the surface. They live for a year or two, using its antennae to filter feed the detritus and microorganisms that wash back and forth in the surf. In turn, the mole crab is a favorite food of fish ,such as the pompano, sand trout and whiting that feed along our shores. They are targeted by our wading birds such as ibis, sandpiper, and the reddish egret. In addition, the mole crab is a favorite food of his larger cousin, the ghost crab, who feeds in the surf zone at night. As such ,they are the bridge in the food chain between the microbes and organic detritus that wash ashore and the larger predators waiting for them on the beach, or just offshore.
Life is tough in the surf zone.
#9 - LEAST TERN (Sterna antillarum)
The least tern has long pointed wings and a deeply forked tail. It is the smallest of our terns. The adult is gray above ,white below and has a distinct black cap. The least tern is listed as a “threatened” species by the State of Florida.This is due to extensive development of their beach habitat and nesting disturbance from humans as well as pets. Least tern winter in Latin America and nest farther north in the spring, laying eggs in shallow depressions in the sand. As such they are very susceptible to predation and disturbance. At many nesting areas, including those found on Fort Myers Beach, signs and roped off areas warn against disturbing nesting birds.
The least tern feeds on small fish and can often be found just off the beach diving into schools of anchovies or juvenile sardines and herring. Sometimes , terns will dive right next to, or even over, other larger feeding sea birds to get at their prey.
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| Least Tern |
#8 - RED MANGROVE (Rhizophora mangle)
While you don’t find mangrove trees growing on the beach unless they are in a protected embayment, the long pen like objects that children find on the beach and use to write in the sand are the seedlings of the red mangrove. These seedlings are known as “propagules”. The mature seedlings drop into the water from the parent tree where they are carried by tides and currents. As the seedlings float, they absorb water at one end and become bottom heavy. If its voyage ends on a mudflat or calm shoreline, the seedling attaches to the substrate by sending out roots. It will sprout leaves at the other end and eventually become a tree.
In the late summer there are thousands of these propagules washed up on our beaches and some remain well into winter, but the dynamic surf of the beachfront prevents them from taking root. As they die, these propagules decompose providing food for the microorganisms that become the food for the filter feeders such as coquinas, conchs and clams along the shore who in turn become food themselves for the fish and crabs just offshore, who are ultimately the prey of the dolphins and fishermen just offshore. It is within this narrow band of beach, from high tide wrack line to the shallows of the sand bar that we find an entire interdependent ecosystem within the width of a few yards, functional in large part to mangrove seedlings that will never become trees.
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| Red Mangrove |
#7 - MOON SNAIL (Euspira heros )
Also called the “shark’s eye” , these mollusks have a spiraling round shape and come in varying colors from pastels in grey and brown to blue. Moon snails are found on sandy beaches and live subtidally. They are often found washed ashore after a heavy surf or on a very low tide. They burrow beneath the sand and are often passed over, unseen by beach combers. Those washed ashore are a favorite prey of gulls and other shore birds and even a prized delicacy served in European restaurants. These burrowing creatures hunt other mollusks including clams ,mussels and even other moon snails. The moon snail has a sharpened mouth part called a radula that they use to drill a hole into the shell of their prey. The radula is like a tongue with raspy teeth. As they drill, the moon snail excretes an acid that softens and dissolves the shell of its victim as it drills. Then, the moon snail devours its prey. Shells which have been targeted by the moon snail have a distinctive counter sunk circular hole drilled through them, and are ready made for stringing onto a bracelet or necklace, making the moon snail the official “ beach jeweler”.
#6 - ROUGH PEN SHELL ( Family Pinnidae)
#5 - GHOST CRAB (Ocypode quadrata)
The rough pen shell derives its name from the old quill or “pen” that it resembles. Its surface is rough and spiny, often covered in barnacles from where the open top of this clam emerges from the substrate.
The pen shell is anchored by threads called byssus ,that resemble roots. Some members of the pinnidae family are harvested for this fine thread which is used to make sea silk. In the Mediterranean , very high quality sea silk , has been used for over 3,000 years to make robes, gloves, scarves, stockings and other apparel. Items made from sea silk have an attractive golden hue and these items were greatly valued by ancient cultures.
Pen shells are also harvested throughout the world for food and were consumed by the Calusa, our islands first inhabitants. Pen shells have a tender consistency and delicate, delicious flavor not unlike a scallop.(But remember, it is unlawful to harvest live shells on Fort Myers Beach!) In addition, the inside of the shells have a beautiful silvery iridescent interior and these are carved by artisans and shaped into pendants and jewelry, and even plates.
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| Rough Pen Shell |
The name “ghost crab” derives from their sandy pale coloration and prefence for nocturnal activities. During the day, these reclusive 4” to 6” crabs can usually be found deep in their elaborately costructed burrows, sometimes extending 3’ or more underground ,including a terminal chamber and often with a second entrance . These burrows are located well above the high water line and in the sand dunes along our beach. Ghost crabs usually emerge at night to feed on a wide range of items including debris in the wrack line, and coquina clams. As a land crab, they must return to the water occassionally to wet their gills or to spawn, but spend most of their time on dry land.
On of the most remarkable traits of the ghost crab is his speed. When walking ,the ghost crab uses all four pairs of legs ,but runs using only the fist and second pairs of legs,lifting the other two pairs above the ground,and as such appears to be hovering above the sand as he scurries along, a ghostly apparition.
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| Ghost Crab |
#4 - THE PARCHMENT WORM (Chaeopterus sp.)
After the high surf of a storm or a day of onshore winds, the wrack line of debris is piled high and far up on our beach. And there in the jumble of seaweed, mixed amongst the starfish and pen shells is here we’ll frequently find the empty homes of the parchment worm. Usually about a foot in length and resembling a tube of wet paper bag, or parchment, these are the tough but light empty husks left by the parchment worm. Living under the substrate off shore, the parchment worms create this underwater “home in a tube” with an opening to the surface at each end. The parchment worm uses its wing like legs to fan water through the tube and trapping the algal particles on which it feeds.
By the time these displaced homes have washed ashore, the parchment worm is usually gone, having fallen prey to the fish, crabs and shorebirds that feed on them. As such, the parchment worm serves a valuable function in the beach ecosystem, feeding on algae and in turn providing a valuable food source for predators. In time, the decaying husks of the parchment worm as well as the other detritus that washes ashore, will breakdown and decay, serving in turn as food for beach microorganisms.
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| Parchment Worm |
#3 - THE FLORIDA FIGHTING CONCH (Strombus alatus)
As the tides recedes and our intertidal shallows and sandbars are exposed, the fighting conch make his appearance , using the long pointed operculum (the “door” of the shell) these three to four inch conchs emerge from the sandy bottom and can often be seen making their way back to the water. The fighting conch is easily identified by his thick shell with a spiraled point ,blunt spines, and golden tan to caramel coloring. The beaches and sandbars of Estero Island are the perfect habitat for these conchs. Often, beachcombers walking the sandbars at low tide will encounter hundreds of fighting conchs emerging from the sandy bottom after the waves have receded . Despite the name, the fighting conch is a mellow vegetarian, feeding on algae and other plant life on the sandy bottom and thus serving an important role in our beach ecosystem . The distinct name comes from the fighting conchs rapid kicks with which it uses the operculum as a hook to drag itself along and draw the operculum shut to protect themselves from predators and to await the rising tide.
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| Florida Fighting Conch |
#2 - SEA PORK (Family Ascidiacea)
Finding a glistening piece of sea pork washed ashore may leave you thinking you’ve found just a piece of some other creature, resembling a piece of waterlogged pork or fatback (yummy!) This “blob” is actually a living creature, a very complex colony composed of thousands of tiny zooids wrapped in a cellulose housing, each in its own tiny sack like body. This celluloid housing is called a “ tunic” and protects the colony. You will find two external openings near each other that serve to circulate sea water through the sea pork in which nutrients are filtered out as food . Sea pork lives on the bottom and attaches itself to rocks, pilings, jetties or seaweed and is washed ashore by storms and high surf. Bottom feeders such as skates, and even some species of sharks, are known to eat sea pork. There are over 1,000 species of Ascidians worldwide, with numerous species of varying colors including red, yellow ,white , greenish-blue, and even purple appearing on our shores.
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| Sea Pork |
