Orientation and external morphology of
burrows of the mangrove crab Ucides
cordatus (Crustacea: Brachyura: Ucididae)

camila m.h. dos santos
1,2

, marcelo a.a. pinheiro
1,2

and gustavo y. hattori
2,3

1UNESP, Campus Experimental do Litoral Paulista (CLP), Praça Infante Dom Henrique, s/n, Parque Bitaru, CEP 11330-900, São
Vicente (SP), Brazil, 2Grupo de Pesquisa em Biologia de Crustáceos (CRUSTA), 3Universidade do Estado do Amazonas (UEA),
Centro Estudos Superiores de Itacoatiara, Rua Mario Andreazza, s/n, São Francisco, CEP: 69100-000, Itacoatiara (AM), Brazil

The aim of the present study was to characterize the external morphology and the orientation of burrows constructed by the
mangrove crab Ucides cordatus. Data were obtained from two mangrove forests of similar vegetation dominance
(Laguncularia racemosa) but differing in flooding heights. These mangroves were located near Barra de Icapara, Iguape
City (SP), Brazil, (2485003600S–478590530W). A total of 221 burrows were examined (120 on the high mangrove and 101
on the low mangrove). External morphology of the burrows was recorded by photographs for categorization and description.
The directions of the burrow openings were recorded using a geological compass and the declivities of the ducts were measured
with a clinometer. Females constructed 70.8% at Site A and 69.4% at Site B of the occupied burrows with the opening facing
the margin of the river (P , 0.001), whilst males showed no significant difference in the burrow orientation (P . 0.05) at
either site. In females, the tendency for burrow orientation possibly has a reproductive connotation as larval dispersal
may be favoured and enhanced by the tides. Four groups of distinct tracks related to the morphotypes and developmental
stages of U. cordatus were observed. No sediment constructions associated with the burrows were recorded for this species.
Declivity of the burrows from juveniles was lower than from adults (P , 0.05), probably caused by the differential growth
of the chelipeds in this species.

Keywords: burrows, crab, magnetic orientation, mangrove, Ucides cordatus

Submitted 25 April 2008; accepted 21 January 2009; first published online 15 May 2009

I N T R O D U C T I O N

Burrow construction is a common behaviour in many animal
species, including invertebrates (Matsumasa et al., 1992;
Lomovasky et al., 2006) and vertebrates (Moulton et al.,
2006; Schwaibold & Pillay, 2006). Several crustaceans con-
struct burrows in the sediment to protect against predators
and to avoid adverse environmental conditions (Kinoshita,
2002; Thongtham & Kristensen, 2003). Inside the burrows,
parameters such as humidity and temperature are maintained
at more suitable levels (Atkinson & Taylor, 1988). In some
ocypodoids, morphology of the burrow construction may
also provide indications of the hierarchical territoriality
(Christy, 1982), or the reproductive state of a particular
species (Yamaguchi, 1998). Other ocypodoid crabs construct
elevated sediment structures that are associated with their
burrow opening and are utilized by males to attract their part-
ners for copulation. Such constructions may be in the con-
figuration of pyramids like in Ocypode ceratophthalmus
Pallas (Jones, 1972), or shelters (e.g. in Uca pugilator Bosc
according to Christy, 1982). Moreover, the digging habit of
these crustaceans promotes important bioturbation processes
in the sediment, enhancing the oxygenation and facilitating

the incorporation of nitrogen in mangrove areas (Wolfrath,
1992; Nordhaus et al., 2006).

In general, brachyuran burrows present single openings
and ducts. These may interconnect to produce multiple open-
ings, which maximize foraging and refuge areas (Morrisey
et al., 1999). External morphology of the burrows may vary
with the drainage, sediment consolidation and granulometry
of the sediments (Matsumasa et al., 1992) that in turn will
reflect in the depth and complexity of the structures. As a
result, burrows constructed in sandy sediments typically
present single ducts, whilst multiple ducts and chambers
occur in muddy sediments (Morrisey et al., 1999).

The crab Ucides cordatus (Linnaeus, 1763) is a member of the
family Ucididae (Števčić, 2005; Ng et al., 2008), and has an
omnivorous feeding habit (Christofoletti, 2005). It is an iconic
species in this environment and occupies a distinguished pos-
ition due to its commercial importance (Glaser & Diele, 2004).
These crabs are distributed along the Brazilian coastline,
where they are found associated with mangrove forests from
Amapá to Santa Catarina State (Melo, 1996). In addition, they
have seasonal reproduction, exhibiting a breeding migration
known locally as andada, a period when they abandon their
burrows and walk on the sediment for mating (Costa, 1972;
Alcântara-Filho, 1978; Fiscarelli & Pinheiro, 2002).

The mating occurs in the burrow opening (Góes et al.,
2000) and spawning takes place approximately two months
later (Pinheiro & Fiscarelli, 2001). Females usually walk to

Corresponding author:
C.M.H. dos Santos
Email: camilamhs@hotmail.com

1117

Journal of the Marine Biological Association of the United Kingdom, 2009, 89(6), 1117–1123. #2009 Marine Biological Association of the United Kingdom
doi:10.1017/S0025315409000502 Printed in the United Kingdom



the river margin to spawn, or they wait until the high tide to
release the larvae in the burrow entrance (Góes et al., 2000).

Despite the great economic importance for the native popu-
lation (Nordi, 1994; Blandtt & Glaser, 2000; Fiscarelli &
Pinheiro, 2002), there is still scarcity of biological–ecological
information about Ucides cordatus, such as the excavatory
and burrow construction behaviour. According to Costa
(1972), burrows from adult U. cordatus display inclined aper-
ture in relation to the sediment surface (458), deepening
abruptly towards the water level. In juveniles, the burrows
have a larger variety of forms and a higher number of openings.
In addition, burrows from U. cordatus are generally excavated
near the vegetation, following patterns seen in other crabs, as
these structures provide a more stable construction (Oliveira,
2005). The crabs usually move and change their burrows,
and it appears that local competition is one reason for this
behaviour (Piou et al., 2007).

Due to this limited scientific knowledge on the external
characteristics of the burrows of U. cordatus, as well as the
declivity of the ducts and orientation of their aperture,
the present study aims to narrow this gap in the literature.
The analyses of these parameters aimed to characterize the
excavatory pattern shown by the different morphotypes of
the species, and to evaluate variations due to flooding levels
in the mangrove forests studied.

M A T E R I A L S A N D M E T H O D S

The present study was carried out at the Environmental
Protection Area of Cananéia, Iguape and Peruı́be (APA/CIP),
in the south of São Paulo State (2485003600S–478590530W),
on an estuarine isle close to Barra de Icapara, Iguape City,
Brazil. In that area, the mangrove forest consisted of
the species Laguncularia racemosa C.F. Gaertn, Avicennia
schaueriana Stapf & Leechman and Rhizophora mangle
Linnaeus, with the species predominance varying by location.
This allowed the delimitation of two areas with the same arbor-
eal species (Laguncularia racemosa) with distinct tidal heights:
Site A (high mangrove, lower flooding height) and Site B (low
mangrove, higher flooding height).

Protocols for collection and analysis of data
Collection of data occurred from 14 to 16 August 2005 in the two
mangrove forests. Quantification of flooding height in the man-
grove was established from the maximum heights of the vertical
distribution of the alga Bostrychia sp., which was recorded from
the base of 10 trees. Site A presented 100% of L. racemosa with
mean algal height of 9.8 + 2.8 cm, whilst in the Site B these
values were 93.3% and 23.2 + 2.7 cm, respectively.

For each study site, 150 burrows with evident opening and
presence of biogenic activity (e.g. tracks, faeces or pellets) were
selected. Concomitantly, orientation points were positioned in
relation to the margin of the river. At Site A (Figure 1), there
was only a single orientation point, as the margin profile was
parallel to the estuary. In contrast, on Site B, the margin
profile was curved and required some orientation points;
hence, the mean was used in the statistical analyses.

The external morphology of the selected burrows was
described based on the following characteristics: (1) biogenic,
with mud deposition near the opening, which enabled the
occurrence of structural organization (e.g. tower, mounds,

or hoods, and presence of tracks on the sediment); (2) bio-
metric, the diameter of the burrow aperture (BD), using a
Vernier calliper (0.05 mm precision); and (3) physical, the
measurement of the duct declivity from the burrow using a
clinometer and the orientation of the burrow opening in
relation to the magnetic north using a universal geological
compass.

Each burrow was photographed and the occupying speci-
men was captured by hand or using a trap (a small dipping
net). Subsequently, the size was measured with a Vernier cal-
liper (CW, carapace width) and the specimen morphotype
(male or female) was recorded. Two classes of burrow diam-
eter (BD) were considered and used to classify the specimens
in juveniles (BD , 45 mm) and adults (BD � 45 mm). These
classes corresponded to animals with size (CW) smaller or
larger than 60 mm, respectively, according to Pinheiro &
Hattori (2006).

Orientation data of the burrow openings were analysed
using the Rayleigh test for circular distribution (Batschelet,
1981; Zar, 1999) and represented in circular graphs produced
using the program Stereonettw, with each sex being delimited
in each angular band. The G-test was used to compare the pro-
portion of burrows constructed landward and toward the
margin. Declivity data of the ducts were examined using an
ANOVA to compare areas of study, sex and size of individuals.

Burrow characters were examined for relationships with
size at maturity and sex of the specimens. These features
were obtained from field notes or photographs and from the
perception of the crab catcher on the burrows, and this infor-
mation was used in the description of each structural type.

Digital photographs were treated in image software, and
only the red channel of the photographs (Color Mode RGB
8 bit) was used to facilitate the visualization of the nuances
of the sediment. Particular attention was taken on the analysis
of the track morphology and certain areas of the images were
zoomed around 4 times to stress features that were more
evident. These are indicated with an arrow in Figure 3.

Fig. 1. Estuarine isle where the study was performed at Iguape Region, Brazil
(A), and delimitation of Sites A and B in this isle (B).

1118 camila m.h. dos santos et al.



R E S U L T S

Data from 120 burrows were collected on Site A (24 females
and 96 males; 92 juveniles and 28 adults) and from 101
burrows on Site B (23 females and 78 males; 42 juveniles and
59 adults). As the efficiency of the capture of the specimens
by the collectors and the traps was not 100%, only data from
burrows that had the occupant’s sex confirmed were used.
Ovigerous females were not recorded during the study period.

Orientation in relation to magnetic north
At Site A, the margin of the river was located at 198 of the mag-
netic north. The data were divided by sectors and the Rayleigh
test applied (Zar, 1999), which indicated the non-uniform dis-
tribution in the 0 to 3608 interval (Z ¼ 6.97; P , 0.05). No pre-
ferential direction was detected for males using the G-test
(55.2% towards the river margin; G ¼ 0.76; P . 0.05), whilst
70.8% of females constructed burrows with aperture facing
the margin (G ¼ 15.51; P , 0.001; Figure 2 A). On Site B, sec-
torization and the Rayleigh test indicated a uniform distri-
bution of the orientation in the interval 08 to 3608 (Z ¼ 1.37;
P . 0.05). On this site, the margin profile was curvilinear
and it was necessary to calculate the mean angle in relation
to the magnetic north (778). As verified for Site A, no direc-
tional preference was detected in the burrow aperture of
males on Site B using the G-test (53.8% toward the margin;
G ¼ 1.49; P . 0.05), whilst females continued to show a
significant percentage of open burrows (69.4%) towards the
margin (G ¼ 13.79; P , 0.001; Figure 2 B).

Declivity
No difference was found between the burrow declivity from the
two mangrove sites studied (F ¼ 2.29, P . 0.05), and a similar
pattern was found when the burrow inclination was compared
between males and females (F ¼ 1.23, P . 0.05). The analysis
between juveniles (CW , 60 mm) and adults (CW � 60 mm)
found that the inclination of the burrows in juveniles (5 to 408;
17.9 + 0.78) was lower than in adults (10 to 308, 20.3 + 1.18)
(F ¼ 13.31, P , 0.001).

External morphology
In most of the burrows of U. cordatus, the opening was ellipsoid
or circular, and only a few of them were associated with mud
deposits, which were 2 to 4 cm in height. Mud deposition on
the burrow aperture was not related to sex, mangrove area or
specimen size. No observation of any sedimentary structure
(e.g. tower, mound and hood), or use of mud balls or trenches
in association with the burrows were recorded. Nevertheless, it
was possible to characterize the morphotype of the species
from the tracks left on the sediment, and these were identified
as: (1) adult females, producing tracks that were fine, delicate,
superficial and larger than those from males (Figure 3 A); (2)
juvenile females, making tracks that consisted of grooves of
reduced size, but difficult to distinguish (Figure 3 B), from unoc-
cupied galleries; (3) adult males, with punctuated and deep
tracks on a lightly brushed sediment (Figure 3 C); and (4) juven-
ile males, with tracks similar to those from females, but more
superficial (Figure 3 D).

Fig. 2. Distribution orientation of burrows of Ucides cordatus from Site A (high
mangrove) and Site B (low mangrove); Site A (high mangrove) with 55.2% of
male’s burrows (P . 0.05) and 70.8% of female’s burrows (P , 0.001) towards
the margin; Site B (low mangrove) with 53.8% of male’s burrows (P . 0.05)
and 69.4% of female’s burrows (P , 0.001) towards the margin.

Fig. 3. Photographs of the external morphology of burrows of Ucides cordatus.
(A) Burrow of an adult female, arrow indicating tracks larger, delicate and
superficial, without deeper points; (B) burrow of a juvenile female, without
evident tracks; (C) burrow of an adult male, arrow indicating shorter tracks,
punctuated over a brushed surface; (D) burrow of a juvenile male, arrow
indicating more superficial tracks.

orientation and morphology of ucides cordatus burrows 1119



D I S C U S S I O N

Female preference constructing the burrow openings facing
the margin has possibly a reproductive implication. This con-
struction would optimize their water access during the larval
release and would favour the larval dispersal due to the tidal
action (Freire, 1998; Goés et al., 2000). Thus, the river
would function as a reflector of natural light and a visual
cue for ovigorous females migrating to the water line for
larval release. This behaviour has been previously described
for other semi-terrestrial brachyurans (Bliss et al., 1978).
However, other orientation mechanisms may also be used
by the females. Luschi et al. (1997) verified the influence of
polarized light in the orientation of Dotilla wichmanni Man,
but this might not be used by all brachyuran species, since
Daumer et al. (1963) have not observed the same for crabs
of the genus Ocypode. Furthermore, there have been sugges-
tions that orientation in many crustaceans occurs by detection
of the geomagnetic field (Lohmann et al., 1995), visual stimuli
(Zeil, 1998), or even by anemotaxis (Vannini & Chelazzi,
1981). The mechanism involved in the orientation may
change ontogenetically according to the crab necessities
and/or environmental conditions. Winn & Olla (1972) and
Herrnkind (1983) reported that during the early stages, crus-
taceans show a tendency to orientate by chemical cues, whilst
in adults visual cues are more decisive, particularly in relation
to polarized light and sun position. Hence, larval dispersal in
the burrow entrance during high tide (Goés et al., 2000) may
be driven by chemical cues to direct them toward the river,
while the females use the river as a visual cue.

Reports on the orientation in Brachyura are rare in the
crustacean literature. Amongst these reports, the migration
of the red crab (Gecarcinus lateralis Freminville) is particularly
remarkable (Bliss et al., 1978). Adults travel several kilometres
from the forests to the beach to spawn, whilst their juveniles
make their way back closing the life cycle (Bliss et al., 1978).
Nevertheless, this topic requires more studies on the existence
or absence of an orientation pattern during migration, or in
the case of U. cordatus, during the burrow construction.

The direction of the burrow openings showed a non-
uniform distribution on Site A and this may be explained by
the female tendency for constructing the burrows facing the
river margin, which presented a straight profile. Nonetheless,
we verified an uniform distribution pattern at Site B that is cer-
tainly a result of the curvilinear profile of the margins in this
area. The orientation points available to the females probably
have produced the spurious uniformity observed.

Morphological characteristics such as the duct declivity are
of extreme relevance in agonistic displays or territory defence
behaviours (Christy, 1982), but descriptions are very limited
in the literature. For ocypodoids, this subject has been investi-
gated previously only for species of the genus Uca (Genoni,
1991; Wolfrath, 1992; Lim & Diong, 2003) and only Lim &
Diong (2003) have carried out precise measurements of the
declivity of the burrows and comparison between sexes. For
the crab U. cordatus, such information is still rare. According
to Costa (1972), juvenile and adult burrows present similar
slope (458) and are constructed with the pereopods. This is
in contrast with the results of the present study, which demon-
strates that the declivity of the ducts is different between juven-
iles and adults. Such discrepancy may be due to the absence of a
systematic collection of data by Costa (1972), who made only a
visual description of the differences.

The heterochely appears to influence the declivity of the
duct (Clayton, 1988) and the direction of the burrow
opening (Vaninni, 1980). Lim & Diong (2003) verified signifi-
cant differences in the burrow declivity between sexes in Uca
annulipes, and the authors suggested heterochely (males) and
homochely (females) as the causes for the observed pattern.
Conversely, this could explain the patterns observed in
Ucides cordatus because heterochely is found in both males
and females (Alcântara-Filho, 1982; Melo, 1996), but occurring
with an increase in the growth rate of the claws in relation to the
cephalothorax at the onset of sexual maturity (Pinheiro &
Hattori, 2006). Consequently, it is expected that such morpho-
logical alterations affect the excavatory behaviour of the crabs.
This is evidenced in the distinct patterns between juveniles and
adults expressed by the differences in burrow declivity.

Power (1975) noted that granulometric differences may
cause alterations in the burrow declivity in some species of
the genus Uca. This is evident in mangrove areas where gran-
ulometry may vary significantly as a function of the flooding
level, with sandier sediments in less flooded areas (Site A)
and muddier in the more frequently flooded areas (Site B)
(Hogarth, 1999; Little, 2000). Nevertheless, the present study
has not evidenced correlation between burrow declivity and
flooding height, which suggests that granulometry does not
influence the duct inclination of burrows in Ucides cordatus.

Burrow morphology in mangrove crabs may vary according
to depth (Takeda & Kunihara, 1987), drainage, and sediment
composition and consolidation (Rossi & Chapman, 2003;
Ribeiro et al., 2005) of the site. Although the subject has been
studied in a few brachyurans (Power, 1975; Vannini, 1980;
Christy, 1982; Thongtham & Kristensen, 2003), a detailed analy-
sis has not been carried out in U. cordatus. The only description
for this species refers to the circular/ellipsoid format of the open-
ings (Oliveira, 1946; Costa, 1972; Alcântara-Filho, 1978), and
particularly the information on the tracks of this species con-
tinues to be empirical rather than scientific (Fiscarelli &
Pinheiro, 2002).

Territorial behaviour at the burrows has been reported for
males of many ocypodoid species, with the construction of
specific structures (Christy, 1982; Oliveira et al., 1998; Wada
et al., 1998; Yamaguchi, 1998; Burford et al., 2001). In U. cor-
datus, no construction associated with the burrow was
recorded in the study period, only a small elevation of the
opening in relation to the sediment. This feature characterizes
excavatory and cleaning activities from the burrows, which is
common amongst these animals (Costa, 1972; Fiscarelli &
Pinheiro, 2002). Therefore, it is presumable that U. cordatus
does not utilize mud constructions as a demonstration of ter-
ritorialism such as in other smaller sympatric crab species.

According to Góes et al. (2000), Ucides cordatus copulates at
the burrow opening during the andada (the reproductive
migration), when males produce large quantities of foam
around their bodies. These authors suggested the presence of
pheromones in the foam composition, which could enhance
the chemical attraction of the females. Moreover, the foam
volume also maximizes the size of the males on the sediment,
making the crabs more visible to their partners and enhancing
sexual recognition and formation of pairs. This would explain
the absence of sedimentary structures near the burrow openings
in this species (e.g. hood, mound, pyramid, etc.), a common
character in other ocypodoids (Jones, 1972; Christy, 1982).

Burrows of juvenile U. cordatus may have more than one
opening (Costa, 1972; Alcântara-Filho, 1978). In the majority

1120 camila m.h. dos santos et al.



of brachyurans, burrows have a single opening and duct, but
some of these burrows are interconnected forming multiple
openings that maximize a safe foraging area and serve as a
communal refuge against predation (Morrisey et al., 1999).
In the present study, only burrows with a single opening
were observed, despite the fact that juvenile burrows with
multiple openings were previously recorded on the same estu-
arine isle (Hattori, 2006).

Differences observed in the tracks of this species are related
to the different morphological characteristics between the
morphotypes. Males show numerous developed setae covering
the entire ventral area, from the 2nd to the 4th pairs of pereo-
pods, which produce brushed tracks. In females, setae are not
well developed, but abundant on the locomotor appendages
(Pinheiro & Fiscarelli, 2001). The finest grooves on the
female tracks are attributed to the more styliform dactyls of
their pereopods (Fiscarelli & Pinheiro, 2002), with the depth
of the tracks depending on the weight of the specimen. Males
have larger size and weight than females (Alcântara-Filho,
1982; Alves & Nishida, 2004; Pinheiro et al., 2005), particularly
after puberty moult (CW .60 mm) (Pinheiro & Hattori, 2006)
when males leave deeper, punctural tracks, whilst females leave
shallow, but widespread grooves. Similarly, juvenile tracks are
more superficial and difficult to distinguish, and are easily con-
fused with adult female tracks by the crab collectors.

The information obtained demonstrates the adaptations of
the crab to the mangrove environment, which is expressed as
behavioural and morphological adjustments. The present
study is important for the management optimization of this
fishery resource in Brazil, as the external morphology of the
burrows allows the estimation of density and population struc-
ture by a non-invasive technique. The use of a non-invasive
method has proven to be useful to estimate the size of speci-
mens in burrows (Hattori, 2006). This technique may be
helpful, particularly, considering the reduction of the popu-
lation stocks in many regions (Gondim & Araújo, 1996;
Machado & Gondim, 2000).

Additional information on the orientation of the female
burrows and testing the efficiency of the pattern proposed
by this study of external morphology of the burrows could
lead to future studies.

A C K N O W L E D G E M E N T S

We acknowledge the financial support by FAPESP (Projeto
Uçá II, Proc. # 02/05614-2 to M.A.A.P.; and Scientific
Initiation Scholarship to C.M.H.S., Proc. # 05/00269-3). We
also thank MSc Bruno S. Sant’anna, Daiane F. Oliveira
and Bruno Sayão for their assistance in fieldwork and
Dr Ronaldo A. Christofolleti for help with statistical analysis.

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Correspondence should be addressed to:
C.M.H. dos Santos
UNESP, Campus Experimental do Litoral Paulista (CLP)
Praça Infante Dom Henrique, s/n, Parque Bitaru
CEP 11330-900, São Vicente (SP), Brazil
email: camilamhs@hotmail.com

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