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The cold, salty wind blows over the marsh, invisible, detected
only through the swaying of the knee-high cordgrass and the faint ripples on the surface of the creek. The marsh is
empty, seemingly devoid of life, with no sound save the subdued whistling of the wind. Suddenly, our two vehicles pull
up on the hastily built gravel track, just avoiding the thick, oozing mud of the marsh. The doors slide open and slowly
we file out. As I shield my eyes from the sun to get a better look at my classmates, I realize what an oddly dressed
bunch we are. Wearing an inconsistent and multicolored assortment of boots, sweatshirts, hats, and jeans, we are out of
place in the green and brown hues of the marsh. We ignore this fact and unload our equipment. Noisily, we trudge off
into the marsh.
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We have come to the marsh today with one main goal, one sole purpose
in destroying the serenity of the marsh morning. We are after the fiddler crab, a denizen of the marsh that will do
anything to avoid getting caught, measured, and eventually thrown back into the marsh, seemingly miles away from its
warm, comfortable, and secure burrow. Weeks before the expedition, we began our preparations for this epic skirmish,
building scales out of various odd materials in our garages, collecting equipment from the school storage closet, and
researching the fiddler crab. We invested hours of our time in this endeavor, just as one prepares for battle. However,
our ultimate intent is not malicious. Our goal is to discover if the fiddler crab will experience substantive change
over the coming decade. As I pensively observe the marsh, I ponder the many threats to this population of decapods
during the next decade.
The fiddler conducts its life out of its own personal and unique burrow, and any length of time away from the burrow
means certain death. As he moves away from his home, the crab will become disoriented, and will be an easy target for
the night heron or egret, fierce predators that relentlessly attempt to get their talons on the chalky white carapace of
a terrified fiddler.
The fiddler, at only one to one-and-a-half inches long, makes up in speed what it lacks in size. Its most distinctive
feature is its one enlarged chela, or claw. In this respect, the females have nothing to brag about, having two
uselessly small chelae that assist only in the collection of food. The males, however, with one large, ostentatious
chela, use it to serve many purposes. The large chela is four times longer than the other chela, and is involved in
complex mating rituals. It is also part of incredible shows of territory-defining bravado, as fiddlers will wave their
claws around, but run rather than fight. Finally, the pincer forms a natural sound box that can be used as a rattle in
order to make one crab's presence known to others. This is an important feature since fiddlers travel in herds that
number in the hundreds. Like lizards and their tails, if a male fiddler loses his large chela, it will grow back.
Unfortunately, the new claw only is a little larger than that of a female's. Luckily for the male, the remaining claw
will enlarge to a respectable size.
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Fiddler crab burrows are found clustered together in mud flats, hidden under the
intricate leaves of a familiar reddish plant. If one looks closely, one will see small balls of detritus, or decomposed matter,
surrounding the burrow. The fiddler subsists on the detritus found in the marsh, and these balls are feeding pellets, the
indigestible portions of their daily meals. The fiddlers also retain mud caps that can be pulled over their burrow when privacy or
extra security is required. From its burrow, the fiddler can peek out and remain hidden, as its eyes are on long stalks. Thus these
dynamic creatures live their lives feeding off the detritus, cowering from ravenous predators, protecting their territory, mating
occasionally, but never straying far from their burrow. |
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Our group will collect at least 25 of the fiddlers in a bucket, and
then mass them on our rickety but accurate scale. We met after school on one cold and rainy autumn Wednesday to build
the scale. At that time we had the grandest ideas for ultra-precise spring-controlled contraptions, with visions of a
finished product constructed of metal and plastic. In the end, due to the meagerness of both our resources and our
carpentry skills, we settled on a balance constructed of wood and a precariously balanced wire hanger. Our plan is to
contain the fiddlers in clear plastic cups while we measure them. I collect 10 of the crabs in the first few minutes.
Because I can't find anymore, I decide that they have either become more intelligent or my classmates have collected all
of them. As I know the latter is impossible because of the size of fiddler herds, I continue my search. I learn how to
spot the fiddlers among the thick marsh cordgrass and pick them up while forcing the chela tight against their body. As
I travel deeper into the marsh, the crabs grow in size, and the chance of suffering physical harm from a chela seems
more likely. I also begin to hear a revolting noise every time I step, similar to crisp celery snapping. Soon I realize
that this is the sound of a carapace cracking, and I watch my steps. Eventually, we reach our goal and begin the massing
and measuring process.
The most difficult part is holding the irritated and rapidly crawling fiddlers in the cups of the balance while we
attempt to counterbalance their weight on the other side. Twice the fiddlers escape, and twice we round them back up. We
set up an assembly line where one person measures the length of the chela and the width of the carapace, and the other
two attempt to mass the fiddler. Generally, we are successful, and in the end neither fiddlers nor people are harmed.
I turn the page in my notebook, where I had just recorded the essential numbers for 25 fiddlers, and find a comfortable
spot along the edge of the gravel track. From here I sketch my view of the marsh, glad to be out of the mud and cold
water. The wind hits my face, the same wind that I found so bitingly cold when I was searching for fiddlers among the
grasses. However, a different sensation runs up my spine this time, and a great realization sweeps over me. I suddenly
know I am observing a dwindling and precious resource, and that the fiddler population faces a dangerous and uncertain
future. With as many as 200,000 fiddlers per acre, the fiddler crab is the dominant creature in the marsh. However, I
know from experience how fragile and vulnerable they can be. As I contemplate their future, I realize that although the
population seems secure, there are many potential threats to the fiddler crabs within the next decade.
The greatest threat to the future of the crabs is pollution in all its forms. The most abundant and noticeable type in
the marsh is non-point source pollution. This type of pollution is untraceable because of its many sources. I saw
copious examples of non-point pollution during our expedition. Among the cordgrass, shotgun shells and clay pigeons lay
littered carelessly, left behind by practicing hunters. On the outer perimeter of the marsh were soda and beer cans, now
crushed and flattened by the elements. This type of pollution may not always affect the crabs directly, but may instead
kill another organism in the food web, which destroys the marsh ecosystem. Humans created this problem, but we can also
alleviate it by building basins to hold highway and agricultural runoff, or by planting buffer strips.
Heavy metals such as mercury, copper, and zinc are toxic to fiddler-crab larvae, causing a significant delay in larval
development as well as deformities. These effects leave a fiddler crab defenseless against its predators. Lacking strong
chelae, a fiddler might be unable to dig a burrow or sift through detritus and collect food. It may not be able to walk,
and cannot scurry sideways when schoolchildren attempted to ensnare it. Even at a low concentration, these metals will
reduce the crabs' growth. A smaller-than-average crab would be unable to protect itself from predators or dig a home.
Reproduction can also be affected, and a smaller number of crabs means the fiddlers lose the protection provided by
their herds. Chlorine-induced oxidants have detrimental effects on the survival and development of the fiddlers, and
unfortunately, they are fairly common. Chlorine is used as a disinfectant in treatment plants, whose waste is often
released into estuarine waters. These waters then flow into the marsh and the chemicals enter the detritus on which the
fiddler feeds.
Pesticides are also acutely toxic to the crab larvae. In addition to delayed development and abnormalities, they cause
behavioral aberrations. Imagine the poor crab that was exposed to a toxic pesticide in its youth, and whose bright
future was ruined because it lost its ability to filter detritus correctly, couldn't follow the complex mating ritual,
or didn't run from predators.
Pollutants do not have to be lethal to adversely affect marsh organisms such as the fiddler crab. Pollution can also
have a synergistic, or combined, effect. DeCoursey and Vernberg (1972) and Vernberg et al. (1973, 1977) showed that
temperature, salinity, and contaminant stress interacted and negatively affected fiddler-crab larvae.
Two little-known and understudied threats to the fiddlers are parasites and viruses. There are two main types of
parasites found in fiddler crabs. One consists of worms and protozoans. The other category is bird parasites, the eggs
of which the fiddlers consume when bird excretions mix with detritus. These parasites incubate as larvae inside the
fiddlers, and reach maturity inside the bird when it consumes an affected fiddler. Fiddler viruses are fairly rare,
although scientists have seen cases of multiple infections within a herd.
Because the marshes are their homes, fiddlers are harmed whenever marshes are. One formerly popular practice was diking
the marshes. This involved building earthen dams around the marsh to control tidal flow. This, of course, affects the
marsh organisms in many ways. The dikes restrict water exchange and lower the water quality. Dissolved oxygen decreases,
affecting all underwater organisms and eventually shaking the marsh ecosystem to its roots. Marshes have also been
dredged, effectively destroying thousands of organisms. Luckily for our fiddlers, this marsh is still unspoiled and
beautiful.
More than half of the salt marshes in the United States have been destroyed. They have been filled in order to create
more land for farming and residential areas. They have been dredged or have been diked to created impoundments. The
building of canals has lead to increased water levels, killing cordgrass. By creating ditches and rerouting water flow
as a method of mosquito control, water flows by the marsh, leading to excess dryness in an ecosystem based on
waterlogged soil. Recent federal regulation now protects marshes and the organisms within them. We should continue to
ensure a home for fiddler crabs as well as all the other denizens of the marsh, as they serve an important purpose in
the global ecosystem.
Fiddler crabs are critical to the marsh, as they have important roles in the regulation of primary production as well as
decomposition. Their burrowing enhances the growth of marsh grasses and aerates the soil. They also stimulate the
turnover of important nutrients, and therefore the process of denitrification. It is important that we preserve this key
decapod. If fiddler crabs were to die out, the marsh would die with them. It would become clogged with pollutants,
unable to filter sediments and toxic runoff from our homes and businesses. The coast would be unprotected from erosion,
and storm surges would destroy millions of dollars of real estate. The effects could be truly devastating. Our world is
by no means separate from the fiddler's. Instead, they are intertwined and inseparable. The fiddlers require our
support, and we require theirs.
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| References
Albers, N., and J. Shields. "Parasites and Symbionts of Uca Species from Goodwin Islands," 1992.
Barnes, R.D. Invertebrate Zoology. (Fourth Edition). Philadelphia, PA.: Saunders College, 1999.
Chesapeake Bay National Estuarine Research Reserve in Virginia. "A Fair Bay." Gloucester Point, VA. Retrieved November 29, 1999, from the World Wide Web: http://www.vims.edu/cbnerr/fairbay/october93/
Decoursey, P. J. and W. B. Vernberg. "Effect of Mercury on Survival, Metabolism and Behavior of Larval Uca pugilator," 1972.
Knowledge Adventure, Inc. "Fiddler Crab: Big Claw" (1998). Retrieved November 22, 1999, from World Wide Web: http://www.letsfindout.com/subjects/undersea/rfivioli.html
National Oceanic and Atmospheric Administration. "Subtidal Estuarine Consumers." Washington, D.C. Retrieved November 29, 1999, from the World Wide Web: http://www.csc.noaa.gov/otter/htmls/ecosys/ecology/sconsum.htm#kwd4
Shields, J. Chesapeake Bay National Estuarine Research Reserve in Virginia. "The Role of Fiddler Crabs in Marsh Ecology." (1997). Retrieved November 30, 1999 from the World Wide Web: http://www.vims.edu/cbnerr/research/abstracts97.html
Tunberg, B. G. and T. Carlson. "Mosquito Impoundments Within the Indian River Lagoon, Eastern Florid-Ecological Impact on the Fiddler Crab (genus Uca) Populations." Retrieved November 30, 1999, from the World Wide Web: http://www.gmf.gu.se/old_english_gmf/Researchers/BjornGTunberg.html
Viscido, S. "So What's A Fiddler Crab?" (December 1997). Retrieved November 20, 1999, from the World Wide Web: http://tbone.biol.sc.edu/~steven/fiddler_crabs.html
Wenner, E. South Carolina Department of Natural Resources. "Dynamics of the Salt Marsh." Charleston, S.C. Retrieved November 29, 1999, from the World Wide Web: http://water.dnr.state.sc.us/marine/pub/seascience/dynamic.html
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