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Mound House Happenings shares the latest in ongoing projects, site improvements, scheduled programs and events, plus interesting facts and photos on our unique archaeology, history and ecology.

Mound House

Mound House
October 15, 2013

Friday, May 18, 2012

"Creature Features" #1 - #11

Each week, Parke will write a quick summary of a special creature typically found during his Guided Beachwalk's on Wednesday mornings. Please check under the "Creature Features" tab to the left to stay updated! Below is what he has written so far:

#11 - ATLANTIC WHITE SLIPPER SHELL (Crepidula fornicata)

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.

Slipper Shell

#10 - MOLE CRAB (Emerita sp.)

“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.   

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.   

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”.   

Moon Snail

#6 - ROUGH PEN SHELL ( Family Pinnidae)
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.       

Rough Pen Shell
#5 - GHOST CRAB (Ocypode quadrata)

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.     

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.  

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.        

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.

Sea Pork