Effect of Temperature on Burrowing Behavior of Fiddler Crabs, Uca pugilator

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Effect of Temperature on Burrowing Behavior of
Fiddler Crabs, Uca pugilator Tiffany Dziuba and
Marilyn Testa Department of Biology, Coastal
Carolina University
Trial Set-up -Hot Dirt was heated to 28-30C
using a heating pad beneath the container and a
heat lamp held above the dirt. The light was
removed before each trial. -Control The dirt
was allowed to conform to room temperature of
18-20C. -Cold Dirt was cooled to 8-10C by
placing the container in an ice-water bath.
Introduction Uca pugilator, the sand-fiddler
crab, is commonly found in marshes and mud flats.
Burrows are an important factor in a fiddler
crabs habitat. They provide shelter from adverse
environmental conditions, tides, and predators,
as well as a location for mating and egg
maturation. Burrowing behavior improves
oxygenation, drainage, and enrichment of the
surface through sediment turnover (Chesapeake
2002). This is important for fiddler crabs
because much of their food is extracted from the
substrate near their burrows (Caraco et al.1990).
Burrowing is also an effective way for fiddler
crabs to thermoregulate. Uca pugilator exhibit
maximum activity in temperature ranges between
18-25C and are inhibited between 11-12C (Powers
and Cole 1976). Crabs experience a variety of
temperatures that vary daily, seasonally, and on
an annual basis. The objective of this experiment
was to test the effect that temperature had on
burrowing behavior. We observed the time it took
a crab to burrow in mud that was hot, cold, or at
room temperature.
Results
The horizontal bars represent the average amount
of time it took for the crabs in each temperature
group to burrow. The minimum and maximum time are
plotted at the bottom and top of the line,
respectively. Crabs in the cold group did not
take significantly longer to burrow than crabs in
another group (F3.12, d.f.2, P gt.051).
Discussion Temperature did not have a
significant effect on the burrowing time of
fiddler crabs. The regulated variable was soil
temperature, not that of the crabs, however,
crabs are known to quickly reach the temperature
of their surroundings (Smith and Miller 1973). In
effect, we assumed that this did not hinder our
results. We were surprised that crabs in the cold
treatment did not differ in burrowing time
because locomotor activity is known to be limited
at temperatures lower than 11C (Powers and Cole
1976). Moisture levels may have differed between
trials due to increased evaporation in the hot
treatment. This could have caused burrowing time
to increase. Suggestions for further research
include increasing the number of replicates and
accounting for differences in crab size.
Methods -Male fiddler crabs were collected from
Oyster Landing, near Murrells Inlet, SC. -Nine
deep, plastic containers were filled with dirt
from the collection site. The dirt was brought to
a consistent, uniform temperature before each
trial. - A single fiddler crab was placed in
each container until it burrowed or until
30-minutes passed. Each of these trials was
considered one replicate. Twenty-five trials were
conducted at each temperature. No fiddler crabs
were used more than once.
Although a greater number of crabs in the hot
group actually burrowed than in the cold group,
the average time to burrow did not significantly
differ between groups (see next figure).
References Caraco, T., et.al. Risk-sensitivity
ambient temperature affects foraging choice.
Anim. Behav. 1990. 39338-345. Chesapeake Bay
Program-Fiddler Crab. Access via Internet
2002.http//www.chesapeakebay.net/info/fiddler_cra
b.cfm Smith, W. and P.C. Miller. The Thermal
Ecology of Two South Florida Fiddler Crabs Uca
Rapax and U.Pugilator BOSC. San Diego
1973. Shields, J. The Fiddler Crab, Uca pugnax.
1999. Access via Internet 2002.
http//www.vims.edu/jeff/fiddler.htm Powers, L.
and J.F. Cole. Temperature Variation in Fiddler
Crab Microhabitats. Biol. Ecol. 1976.21141-157.