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

Fiddler Crab
Uca minax
Whitney Montgomery & Daniel Hill
Ecology & Behavior of Manatees & Dolphins in
Belize, Class of 2010 (contact: caryns@sirenian.org)
Taxonomy
Kingdom Animalia
Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Order Decapoda
Family Ocypodidae
Species Uca minax
Ecology
Fiddler crabs inhabit a wide range of tropical
regions. In Belize, their habitats are mangroves
and salt marshes. Fiddler crabs are extremely
populous species. The semi-terrestrial species is
diverse in color and habitat, with the most
distinguishing characteristic being the males’
asymmetrical claws (Fig. 1). They use the large
claw to signal to other crabs within their
vicinity, to attract a mate, and as a weapon used
in combat between other males (Magnhagen,
1991). These behaviors could draw attention to
them from predators. The claw can be up to
50% of an adult male’s body weight. If a claw is
lost, the smaller claw of some species will grow
larger and the crab will regenerate the lost claw
with a new, smaller one.
Figure 1. Fiddler crabs during experiment. (Belize, 2010)
fiddler crab (Belize 2010)
Figure
2. Adult
male
Behavior
Fiddler crabs tend to feed near their burrows, so
that if they feel threatened, they will retreat into
it to seek shelter. The crabs use their small
claws to pick up pieces of sand, filtering out
microscopic bits of algae, microbes, or fungus
with their mouthparts. Crabs live about two
years and molt their shells indeterminately (one
to two times per year) as they continue to grow
throughout their lives. Males wave their larger
claw to attract female attention when ready to
reproduce. Fiddler crab eggs are fertilized
externally and the female fiddler crabs carry
their eggs on their underside in a large mass.
She keeps them safe in her burrow for a two
week period and then journeys down to the edge
of the sea to release the eggs into the receding
tide. The larvae remain in a planktonic state for
a further two weeks before venturing onto land
and setting up a territory of their own.
Conservation
While fiddler crabs are not seriously threatened,
their habitats are under pressure. As human
populations continue to expand, they are
destroying the mangroves and salt marshes
where the crabs live. Fiddler crabs may serve as
an important indicator species for these places.
Fiddler crabs are important to the conservation
of their ecosystems. Some experts believe that
by continually sifting through the sand for food,
their feeding habits aerate the substrate and
prevent anaerobic conditions (Montague, D. L.
1980).