INTRODUCTION
The Genus Uca contains about 100 species of
semi-terrestrial marine crabs which includes fid-
dler crabs, sometimes called ‘calling crabs’
(Rosenberg 2019). Fiddler crabs are members of
the Family Ocypodidae of brachyuran crabs,
marine animals that recently invaded the land.
They are active on the surface at low tide, feeding
on soil debris, bacteria, and algae (Zeil et al.
2006). Sandy beaches, mudflats, mangrove areas,
and salt marshes are all locations where fiddler
crabs can be found. Fiddler crabs rely on the sed-
iment which they use for food, burrowing, and for
collecting bacteria, debris, and benthic macroal-
gae (Ribeiro and Iribarne 2011). The intertidal
zone and the nearby marine and terrestrial habi-
tats are connected by fiddler crabs, which are rec-
ognized as ecosystem engineers and significant
connectors of energy flow. According to a recent
study, fiddler crabs are the primary food source
for some fish and may be more important than
was previously thought as food for predators
(Grande et al. 2018).
Fiddler crabs are recognized for having
extraordinary claws. Male claws are much larger
compared to those of females, who have claws of
the same size. They stay close to their burrows to
quickly escape from predators, as well as find
shelter from the heat and water loss (Macintosh et
al. 2002).Male fiddler crabs use their minor claw
for feeding and the major claw for displaying and
fighting. Major claws are typically brightly col-
ored and four to five times longer than minor
claws, making up around one-third of the total
body mass of the crab. Female fiddler crabs have
two tiny claws almost always cryptic (Rosenberg
2001). Fiddler crabs can tolerate a wide range of
salinities, high temperatures, and low levels of
oxygen (Nagelkerken et al. 2008). Fiddler crabs
attract a female for mating by waving their
enlarged claw. Courtship activity of male fiddler
crabs peaks semi-monthly and coincides with the
peak in the temporal distribution of receptive
female fiddler crabs. A female fiddler crab mate
once a month, 4-5 days prior to one of the semi-
monthly spring tides. The relationship between
the timing of reproduction and tide cycles may
represent an adaptation to maximize the likeli-
hood that the last stage of planktonic larvae will
be carried by tidal currents to substrates suitable
for adults (Swanson et al. 2013). They protected
themselves against other fiddler crabs or preda-
tors using their enlarged claws (Bergey and Weis
2006). Burrows are the most crucial resource for
the reproduction and survival of fiddler crabs, and
males must defend them for females to be attract-
ed to them. Each fiddler crab concentrates its ter-
ritorial defenses on a single burrow (Mautz et al.
2011). Research on the behavior of fiddler crabs
is critical to understanding when and how much
sediments impact and how they affect the overall
functioning of ecosystems. As with other inter-
tidal invertebrates, their activity is significantly
influenced by tides. According to several studies,
fiddler crabs only engage in surface behaviors
including feeding, burrowing, and mating during
low tide and stay in their burrows during high tide
(Reinsel 2004; Sanford et al. 2006; Zeil and
Hemmi 2006; Dugaw et al. 2009). Fiddler crabs
can significantly influence the ecology of man-
grove communities, acting as ecological engi-
neers by adjusting resources accessible to marsh
plants and by changing the physical, chemical,
and biological characteristics of these communi-
ties of soft sediments (Smith et al. 2009). Fiddler
crab bioturbation would improve the oxygenation
of the sediments and promote the growth of man-
grove saplings (Macusi and Tipudan 2021). Vari-
ous species of fiddler crabs, each have different
behaviors like feeding, mating, walking, etc., can
be found in the same habitat in many tropical
environments (Nordhaus et al. 2009; Shih 2012).
Because there are few studies of fiddler crabs
in the Philippines, this paper provides a new
understanding of the species. The objective of
138 MARINE AND FISHERY SCIENCES 36 (2): 137-147 (2023)