(DRAFT) - Taxonomy
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
TAXONOMY
NAME - crab, Atlantic marsh fiddler
OTHER COMMON NAMES - calling crab, fiddler crab, fiddler, mud fiddler(Williams 1984), mud fiddler crab(Wheeler 1978) and marsh fiddler crab(Ward et al. 1976)
ELEMENT CODE -
CATEGORY - Aquatic Crustaceans
PHYLUM AND SUBPHYLUM - Arthropoda, Mandibulata
CLASS AND SUBCLASS - Crustacea, Malacostraca
ORDER AND SUBORDER - Decapoda, Reptantia
FAMILY AND SUBFAMILY - Ocypodidae,
GENUS AND SUBGENUS - Uca,
SPECIES AND SSP - pugnax,
SCIENTIFIC NAME - Uca pugnax
AUTHORITY - Smith
TAXONOMY REFERENCES - 206
Taxonomy - 1 (DRAFT) - Status
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
STATUS
Coded Status
See Comments
REFERENCES FOR STATUS - 206
COMMENTS ON STATUS -
Fiddler crabs are the most abundant and conspicuous invertebrates in many
slat marshes. They are probably the most thoroughly studied of the shore
crabs in North America. Although there are 15 species along the North
American coast, the Atlantic marsh fiddler is the only one endemic to the
temperate Mid-Atlantic coast of the United States. The Atlantic marsh
fiddler, red-jointed fiddler, and the sand fiddler are the three major
species on this coast and make up the greatest animal invertebrate biomass
in the salt marsh intertidal zone. The Atlantic marsh fiddler is the most
abundant of these *206*.
The ecological influence of fiddler crabs in the salt marsh is large. Their
activities and byproducts can significantly influence the transfer of energy
and nutrients within the marsh ecosystem. The sensitivity of these crabs to
pollutants and their role in the balance of the salt marsh ecosystem, are
major reasons for the inclusion of the Atlantic marsh fiddler in this
series *206*.
Status - 1 (DRAFT) - Distribution
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
DISTRIBUTION
Distribution - 1 HABITAT ASSOCIATIONS
NATIONAL WETLAND INVENTORY CODES
NWI NWICLS NWIMOD NWISPEC
Estuarine, intertidal UB3 2
Habitat Associations - 1 (DRAFT) - Food Habits
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
FOOD HABITS
TROPHIC LEVEL -
OMNIVORE
REFERENCES FOR TROPHIC LEVEL - 206
LIFESTAGE FOOD FOOD PART
General Plankton Not Specified
General Tracheophyta Not Specified
General Benthos Not Specified
General Detritus - Organic Not Specified
General Microorganisms Not Applicable
General Crustaceans Not Specified
General Annelids Not Specified
General See Comments; Food
REFERENCES FOR GENERAL FOOD - 206
REFERENCES FOR LARVAE FOOD - 206
COMMENTS ON FOOD -
Fiddler crabs emerge in great numbers from their burrows at low tides and
feed. The Atlantic marsh fiddler feeds by scrubbing muddy particles of
substratum. Its mouthparts are structured to manipulate and feed on
particulate organic matter in muddy substrates. Male fiddlers are reported
to spend more time feeding than females, probably compensating for the fact
that males have only one chela (the smaller claw) that is functional in
feeding. Some Atlantic marsh fiddlers forage far from their burrows. Some
adults have been seen to feed underwater *206*.
The crabs significantly reduce the abundance of meiofauna (crustaceans,
nematodes, and segmented worms), probably by feeding on them *206*.
In foraging, fiddlers actively sort out indigestible from digestible items
and place indigestible material aside in the form of balls which break up
and return to the ecosystem beginning on the next tide. Undigested material
passing through the gut of the fiddler is deposited as fecal pellets. These
pellets often blanket the marsh, and can persist through successive tidal
cycles *206*.
COMMENTS ON LARVAE FOOD -
The zoeae of all three Atlantic species of fiddler crabs are carnivorous
*206*.
Food Habits - 1 (DRAFT) - Environment Associations
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
ENVIRONMENTAL ASSOCIATIONS
G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae
LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
G Water Temperature: Specified in Comments
G
G Relation to Substrate: Occurs in substrate [penetrating]
G Bottom Type [Aquatic]: Mud or silt
G Stability of Bottom: Stable
G Aquatic Habitat Zonation: Shallows with emergent vegetation [littoral zone]
G Coastal Features: Sand beaches
REFERENCES FOR ENVIRONMENTAL ASSOC_ - 206
COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Temperature. The range of the Atlantic marsh fiddleris limited by
temperature extremes. Researchers found that molting in adults is
blockedby temperatures less than 20 degrees C. This temperature is the
same as the summer water temperature at Cape Cod (the upper limit of the
geographic range of the Atlantic marsh fiddler). It was hypothesized that
the air temperature may be more influential than water temperature in
semiterrestrial crabs, and that the northern geographical limit of the
Atlantic marsh fiddler may be determined by the effect of water temperature
on the planktonic larvae.
The Atlantic marsh fiddler, in particular, can eventually acclimate to
lower temperatures, but it dies at 2-3 degrees C. Hibernating crabs dug
from New Jersey marshes when air temperatures were from 1.7 to 5.5 degrees
C were revived. To raise their body temperatures a few degrees, some
fiddler species orient themselves to the sun during low-temperature
periods.
Death from thermal exposure occurs at 40 degrees C in humid air and at 45
degrees C in dry air. Lethal temperatures can occur in nature. For
example, in Georgia marshes were reported to reach lethal air temperatures
of 40 degrees C during the summer. To avoid lethal temperatures and
subsequent desiccation, fiddler crabs move to their burrows or shady parts
of the marsh during periods of high temperatures *206*.
Environment Associations - 1 (DRAFT) - Life History
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
LIFE HISTORY
PHYSICAL DESCRIPTION:
Crabs belonging to the genus Uca are moderate to large in size. The three
species common to the Mid-Atlantic region are Uca pugnax (Atlantic marsh
fiddler), U. minax (red-jointed fiddler), and U. pugilator (sand fiddler).
The carapace of the Atlantic marsh fiddler male averages 15 mm long x 23 mm
wide; that of the female averages 13 mm long x 18 mm wide *206*.
In life, the Atlantic marsh fiddler is mostly brown (with some pale gray in
the gill regions). The anterior part of the carapace and eyestalks range
from blue to blue-green. There are no purple or red spots as are found on
other fiddlers. The frontal region is about two-sevenths of the body width,
with slender eyestalks. The dorsal carapace is flattened rather than convex
as in other crabs. At the intersection of the front and lateral edges of
the dorsal carapace, there is a sharp angle *206*.
Specific identification characteristics are usually descriptive of the male
and often refer to the major cheliped (large claw). In the Atlantic marsh
fiddler, the major cheliped ranges from a dull yellowish orange to
yellow-white. In males, joints of the major cheliped have a yellow or
yellow-brown border. In the northern part of the range, fingers of the
major cheliped are nearly always white. These structures in females are
colored less strongly than males *206*.
The minor (smaller) chela is white. The other appendages--the walking
legs--are usually dark and may be banded. A patch of rows or paired rows of
dense velvety pubescence, as well as sparse rows of stiff hairs, are on the
ventral surface of the merus (the long section of the appendage closest to
the body) of the second and third walking legs. The meral surface of the
second maxilliped usually has 0-75 spoon-tipped hairs *206*.
The large claw of the males occurs about equally on the right or on the left
of the Atlantic marsh fiddler. The weight relationship of the large
cheliped ranges from 2% to 65% of the body weight. Females have two small
chela that are equal in size and are colored similarly to males, but the
color is less vivid *206*.
REPRODUCTION:
Courtship of the Atlantic marsh fiddler consists of a series of visual and
acoustical displays. Visual and acoustical signals replace the standard
chemical communications of most aquatic crustaceans.
Usually in precopulatory behavior, male fiddler crabs display a high
intensity waving of the major cheliped and produce acoustical signals;
however, male Atlantic marsh fiddlers often have lethargic displays.
Acoustical displays by males are produced by vibrating and stamping of the
walking legs on the substrate. The waving of the large claw can be seen at
considerable distances and is weakly circular and very jerky. Displaying
males are not bleached in color during mating to the extent shown by males
of other species of fiddlers, but the major cheliped lightens to light brown
or yellow. Nocturnal reproductive behavior, including acoustical displays,
of the Atlantic marsh fiddler in the southern part of its geographic range,
have been reported.
After these courtship displays, the female usually follows the male to his
burrow to mate. Although herding (the male physically maneuvering the
female to his burrow) is found in other species of fiddler crabs, it is
seldom seen in the Atlantic marsh fiddler. Copulation usually takes place
Life History - 1 (DRAFT) - Life History
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
in the burrow, but has been observed on the surface of the marsh in nature;
in captivity, mating has been observed underwater. Unlike mating in some
other crabs, fiddlers mate while the exoskeleton of the female is in a
hardened state *206*.
EGGS. The fertilized eggs are carried on the abdomen of female intermolt
Atlantic marsh fiddlers until they hatch and are released. Clutches of
1,500 to 94,000 eggs were found in one study. Other reports of the Atlantic
marsh fiddler clutches range from 4,500 to 23,700. The size of the clutch,
commonly known as the sponge, is probably related to the size of the female.
Researchers have found that eggs hatched over a period of 2 hours. The
larvae were released (with the aid of abdominal contractions) in phase with
the nocturnal high tide. In laboratory experiments, isolated females
released their larvae in synchrony with those females in the wild.
Researchers found that larval release coincided with the lunar cycle in the
Delaware Bay, and that the Atlantic marsh fiddler released larvae during the
spring and neap tides. It is hypothesized that the synchrony with the
nocturnal high tide maximum allows minimal exposure of the ovigerous females
to predation and provides the zoeae with a favorable tidal current upon
which to be swept from the marsh into the coastal waters. Researchers
concluded that the timing of the release of zoeae probably is a response to
selective pressures that cause larval mortality such as lethal high
temperature, low salinity, and predation by planktivores *206*.
LARVAE. After hatching, the planktonic larvae of the Atlantic marsh fiddler
pass through five zoeal stages (each lasting from 7 days to a month) and one
megalops stage of 4 days to a month. Most published information on larval
and postlarval stages of fiddler crabs is on sand fiddlers; however, the
Atlantic marsh fiddler larvae are similar in most respects to those of sand
fiddler larvae though they are smaller. The zoeae of all three Atlantic
species fiddler crabs are carnivorous.
The zoeae of the three common Mid-Atlantic fiddlers make up a significant
portion of the estuarine plankton. The distribution of zoeae appeared to be
stratified in the water column, and surface waters were preferred by first
and second stage zoeae. Third stage zoeae were found in intermediate
depths, and fourth and fifth stages were in greater depths *206*.
METAMORPHOSIS AND JUVENILES. Megalops larvae of the Atlantic marsh fiddler
metamorphose into the first crab stage (lasting from 3 to 4 days) and settle
to the substratum. The second crab stage lasts 4 to 5 days and the third
stage lasts 7 days. While in these stages the crabs are weak, cling to
objects, and are not capable of burrowing *206*.
LIMITING FACTORS:
Predators. Fiddler crabs, including the Atlantic marsh fiddler, are a food
source for many other animals. Fiddler crab parts have been found in stomach
contents of adult pigfish (Orthopristis chrysoptera), channel bass
(Sciaenops ocellata), and bighead searobin (Prionotus tribulus). Fiddler
crabs are an integral part of the diet of the white catfish (Ictalurus
catus).
Some wading shorebirds and marsh birds take fiddlers as part of their diet,
including the white ibis (Eudocimus albus) and clapper rail (Rallus
longirostris). Researchers have reported fiddler crabs in the diet of
egrets, ibis, and herons. Cattle egrets (Bubulcus ibis) and snowy egrets
(Egretta thula) also prey upon fiddlers.
Some species of crustaceans, e.g., red-jointed fiddlers and the blue crab,
Life History - 2 (DRAFT) - Life History
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
(Callinectes sapidus) prey upon fiddlers. According to one report, raccoons
(Procyon lotor) in Georgia salt marshes and elsewhere take fiddler crabs as
a normal part of their diet *206*.
Parasites and Commensals. The Atlantic marsh fiddler has not been
extensively studied for its parasites and commensal organisms. Researchers
have reported on trematodes and cestodes that parasitize fiddler crabs. One
researcher noted apostome cysts on the gills and in the molts of the crabs
from Woods Hole, MA. Another report extensively examined the ciliate
commensals on the gills of North Carolina crustaceans and described a new
species of apostome ciliate found as a small oval resting stage in the bases
of gills of the Atlantic marsh fiddler. These commensals can reach great
numbers (greater than 100) on the gills and may clog the gills to some
extent, reducing the oxygen absorbing capabilities of the crab *206*.
POPULATION ATTRIBUTES:
Growth and Molting Characteristics. Little is known about the molting
habits of the Atlantic marsh fiddler except that molting in adult crabs
occurs 1-2 times per year. Researchers have hypothesized that the burrow is
the likely place for routine molting because it offers protection from
desiccation and predators; available water; and lack of disturbance. During
an extensive two year study in North Carolina, researchers observed no molts
on the marsh surface.
Molting in adult Atlantic marsh fiddlers is temperature dependent and is
completely inhibited at 20 degrees C and below. Researchers determined that
other factors that negatively influence molting are light, extremes in
salinity, and mechanical disturbances. Many physiological changes occur
during the molting cycle of fiddler crabs *206*.
REFERENCES FOR LIFE HISTORY- 206
Life History - 3 (DRAFT) - Management Practices
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
MANAGEMENT PRACTICES
RESULT MANAGEMENT PRACTICE
Adverse Applying insecticides
Adverse Controlling pollution [thermal, chemical, physical]
Adverse Other management practices [specified in comments]
REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 206
COMMENTS ON MANAGEMENT PRACTICES -
The effects of contaminants. Different response patterns to the effects of
radiation (using a cobalt source) were found for the Atlantic marsh, red-
jointed, and sand fiddler crabs along the Mid-Atlantic coast. In the
experiments with male fiddler crabs, natural conditions (e.g., temperature,
salinity) were kept constant. The Atlantic marsh fiddler had a slightly
higher projected LD-50 (16,000 rad) than the other two common sympatric
species. Additionally, the mortality response pattern of the Atlantic marsh
fiddler differed from patterns of other species of fiddler crabs. In other
species, mortality was proportional to dose; however, in the Atlantic marsh
fiddler at dosages from 4,000 to 16,000 rad, mortality was independent of
dose.
In experiments in a New Jersey marsh, it was found that the application of
Temefos (Abate), an organophosphate insecticide, at normal-use levels
significantly reduced the population of the Atlantic marsh fiddler. Temefos
is commonly applied as a granular larvicide for control of salt-marsh
mosquitoes. In other experiments with caged populations of the Atlantic
marsh fiddler, researchers determined lethal and sublethal effects of
Temefos. Further, they found that sublethal doses reduced populations of
crabs in open test plots, but not in closed cages, and hypothesized that the
insecticide propbably impairs the fiddler's escape response, leading to
increased predation.
In an 11-day laboratory experiment, researchers fed Atlantic marsh fiddlers
natural detritus, contaminated with DDT residues (10 ppm) from Long Island
Sound, New York. After 5 days all crabs showed a loss of coordinated
avoidance reaction, which was hypothesized to negatively affect predator
avoidance in natural populations. At the end of the experiment, crab muscle
from the large claw showed a three-fold increase in concentration of DDT
over background level. Other workers have found a three-fold concentration
of DDE (a degradtion product of DDT) in natural populations of fiddlers.
Researchers found other contaminants which affect fiddler crabs (including
the Atlantic marsh fiddler) are PCB's, and the insecticides in
fertilizers, Aldrin and Dieldrin, which are found in agricultural runoff.
Though they found no PCB's in marsh sediments, researchers did find
measurable levels in crabs and hypothesized that fiddler crabs
concentrate these chlorinated hydrocrabons from seawater or from food.
Dieldrin was concentrated in crab tissues and impaired locomotion, killing
crabs at the higher concentrations. Chemical contaminants were responsible
for the drastically reduced populations of fiddler crabs in the marsh.
Other species of fiddler crabs have been found to be sensitive to pollutants
and contaminants. This sensitiviity has been shown for mercury, PCB'c, and
cadmium *206*.
Management Practices - 1 (DRAFT) - References
Species crab, Atlantic marsh fiddler
Species Id M070000
Date 26 AUG 96
References
206 * Grimes, Barbara, Melvin Huish, J. Howard Kerby, David
Moran. 1989. Species Profiles: Life Histories and Environmental
Requirements of Coastal Fishes and Invertebrates (Mid-Atlantic)
--Atlantic Marsh Fiddler. Species Profile Series 82(11.114)
(ed.). U.S. Fish and Wildlife Service, U.S. Army Corps of
Engineers Washington, DC:18.
References - 1