2012 COURSE DATES: AUGUST 4 – 17, 2012 - Sirenian International

area on the north part of the island near the lagoon.
The area for the hermit crabs was on the east part of
the island only a few meters from the edge of the
beach. Presence or absence of a breeze, temperature
estimation, precipitation, the substrate moisture, and
tide were taken before each data collection. We noted
the presence and activity levels of each species in and
around the study area before and after collecting data.
We counted the number of fiddler crab burrows within
a 10x10 ft area within the marshy area. This area had
a small mangrove tree that marked one corner.
Vegetation coverage in the area was estimated by
looking at what percentage of the soil was covered by
vegetation. The study area was divided in half and
each person counted the number of burrows on each
side to make counting easier and switched which side
they counted in the afternoon.
In the second area where hermit crabs were counted
we demarcated a 15x15 ft study area with a palm tree
in the eastern corner of the box and the number of
hermit crabs on the beach was recorded. Next, the
number of hermit crabs either climbing the tree or
hidden in the braches of the tree were counted. Hermit
crabs in the tree often crowded in crevices and would
move when we got near making them more difficult to
count. Therefore, each person counted and then
shared numbers and an average number between
counts was agreed upon. Also observations of hermit
crabs in the area especially those near the water of the
beach were recorded.
Results
The density of both crab species did not vary much
with tide level (Fig. 3). The high tide for the fiddlers
had the lowest density but it was also the only data
taken during high tide whereas three data sets were
taken during low tide and two taken during an ebb
tide.
The average density of fiddler crabs per square foot
was 13 times greater than the average density of
hermit crabs per square foot although the fiddler crab
area was smaller. Most of the hermit crabs found were
located in the crevices of the palm tree in the area and
only a total of eight hermit crabs were found on the
beach over all three days. The fiddler crab burrows in
the designated area averaged 128.7 for each data
collection and hermits found in the palm tree averaged
21 for each data collection.
Discussion
We did not observe any major differences in the
abundance of either crab species during different
times of the tide. We did see six times more fiddler
crabs than hermit crabs in a smaller area but neither
species fluctuated too much with the tides. It is hard to
draw any absolute conclusions from our data because
we only took six data sets over three days and did not
cover all the tides fairly. If we had more time to take
more sets we would have more reliable data.
Additionally, we did not have enough data to do any
statistical analyses, so no certain conclusions can be
made. However, this study seems to suggest that tides
do not seem to directly affect either species’ numbers
or their activity. Interestingly, the high tide did not
reach the study site of the hermit crabs, which means
that their decrease in density or relocation to the tree
does not appear to be directly correlated with tides.
There appears to be another reason as to why hermit
crabs hide in trees, which could be predator
avoidance.
References
Hazlett, B.A., 1966. Social behavior of the Paguridae and
Diogenidae of Curacao. Stud. Fauna Curacao Other
Caribb. Isl. Vol. 23, 1 –143.
Kaplan, E.H. 1988. “Fiddler Crabs of the Southeastern
U.S., Gulf of Mexico, and Carribean.” Southeastern
and Caribbean Seashores. p 334-338
Kellogg, C.W., 1976. Gastropod shells: a potentially
limiting resource for hermit crabs. J. Exp. Mar. Biol.
Ecol.Vol. 22, 101–111.
Mesce, K.A., 1982. Calcium-bearing objects elicit shell
selection behavior in a hermit crab. Science. Vol. 215,
993–995.
Turra, A., Denadai, M.R., 2001. Desiccation tolerance of
four sympatric tropical intertidal hermit crabs
(Decapoda Anomura). Mar. Freshw. Behav. Physiol.
Vol. 34, 227– 238.
Turra, A., Denadai, M.R., 2004. Interference and
exploitation components in interespecific competition
between sympatric intertidal hermit crabs. Journal of
Experimental Marine Biology and Ecology Vol. 310,
183– 193.
Hugh Parkey Foundation for Marine Awareness & Education (belizeadventruelodge.com)
Sirenian International (sirenian.org)