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

Fiddler Crabs and Hermit Crabs
Uca minax and Pagurus annulipes
Rachel Calhoun and Molly Martin
Ecology & Behavior of Manatees & Dolphins in Belize,
Class of 2010 (contact:cselfsullivan@sirenian.org)
Taxonomy
Kingodom Animalia
Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Order Decapoda
Family Ocypodidae
Species Uca minax
Superfamily Paguroidea
Species Pagurus annulipes
Ecology
Fiddler crabs are found in mangroves, salt marshes,
and on sandy or muddy beaches in the Southeastern
U.S., the Gulf of Mexico, and the Carribean (Kaplan
1988). Their distinctively asymmetric claws easily
identify them. U. minax is a detritivore, consuming
algae, microbes, fungus, and other decaying materials.
They appear to be a common resident along the
brackish intertidal mud flats, lagoons, and swamps of
Belize.
Similarly, terrestrial hermit crabs are found in tropical
areas within the intertidal zone. They also are
detritivores, feed primarily on algae and decaying
materials. They lack a carapace, or shell, so they
“borrow” one from snails, such as periwinkles or
oyster drills. As hermit crabs grow in size, they have
to locate a larger shell, abandoning the previous one.
Aside from this, their soft-coiled abdomens, two pairs
of walking legs, and their asymmetric claws, are also
used to identify them.
Behavior
Fiddler crabs create small burrows in the sediment
that are used for mating, sleeping, refuge from
predators, and ‘hibernating’ during the winter. They
are very active during the day, foraging for food and
digging burrows; they will return to their burrows at
night and during high tide, plugging the entrance with
mud or sand. Shells are an important resource for
hermit crabs, but empty shells are generally low
supply in nature (Kellogg 1976) and may be a limited
resource for hermit crabs (Turra and Denadai 2004).
As a result, hermit crabs will often compete with one
another for shells. Competition may occur in two
Figure 1. Hermit crab on the beach.
ways: 1) hermit crabs may use chemical cues to locate
newly available shells (Mesce 1982),or 2) they may
display ritualized agonistic shell fighting behaviors
and subordinate other individuals of the same species
(Hazlett 1966). This is known as interference.
However, many hermit crab species coexist in coastal
areas and may cause various degrees of niche overlap
(Turra and Denadai 2001).
Introduction
Our research took place during our 13-day research
trip as part of a field marine biology class. We stayed
on a mangrove island in the Drowned Cayes east of
the Belize mainland with the Hugh Parkey Foundation
for Marine Awareness and Education. Both hermit
crabs and fiddler crabs are abundant on the island and
are easily found. After much observation around the
island of both crab species we asked the question of
“How do fiddler and hermit crabs abundances change
with the tides?”
Figure 2. Fiddler crab near a burrow.
Methods
We chose two different areas to use for our research
according to where we found the most of each crab
species. Both areas were counted twice a day for three
days. The area for the fiddler crabs was in a marshy
Hugh Parkey Foundation for Marine Awareness & Education (belizeadventruelodge.com)
Sirenian International (sirenian.org)