Continued expansion of Percnon gibbesi
(Crustacea: Decapoda: Plagusiidae) into
western Mediterranean waters
f.c. fe
’
lix-hackradt
1,2
, c.w. hackradt
1,3
, j. trevin~o-oto
’
n
1
and j.a. garci
’
a-charton
1
1
Departamento de Ecologı´a e Hydrologı´a, University of Murcia, Campus Espinardo 30100, Murcia, Spain,
2
CAPES PhD
Scholarship and
3
CNPq PhD Scholarship
Since its first record in Spanish waters in 2000, Percnon gibbesi has expanded its distribution southwards. In the summer of
2009 it was observed in the south-east Mediterranean Sea including inside a marine reserve. Its widespread presence during
the last year in many coastal sites of the Murcia Region indicates its fast colonization ability and the potential risk of com-
petition and displacement of native crab species, which should be studied carefully.
Keywords: biological invasion, marine introduction, Percnon gibbesi, Mediterranean Sea, Murcia Region
Submitted 1 December 2009; accepted 15 January 2010
For the western Mediterranean region, 110 exotic species have
been registered, most of them being thermophilic species orig-
inating from tropical seas (Galil, 2008). The most recent case
of an alien species in the western Mediterranean is Percnon
gibbesi (H. Milne-Edwards, 1853). It is a small crab belonging
to the family Plagusiidae with a subtropical distribution,
ranging from California to Chile, Florida to Brazil, and
Madeira to the Gulf of Guinea (Manning & Holthuis, 1981).
Its first Mediterranean record came from Linosa Island
(Italy) in 1999 (Relini et al., 2000), and subsequently it has
been recorded in the Balearic Archipelago and the northern
Spanish coast (Garcia & Reviriego, 2000; Mu¨ller, 2001;
Deudero´ et al., 2005), Sardinia, Tyrrhenian Sea, Sicily and
Malta (Pipitone et al., 2001; Mori & Vacchi, 2002; Sciberras
& Schembri, 2007). More recently, it has been discovered in
Greek waters (Cannicci et al., 2006; Thessalou-Legaki et al.,
2006), Turkey (Yokes & Galil, 2006), Lybia (Elkrwe et al.,
2008) and Taranto Gulf (Ionian Sea, Italy) (Crocetta &
Colamonaco, 2008). The origin of P. gibbesi is attributed to
Atlantic waters (Abello´ et al., 2003) and both natural dispersal
through larval drift and adult movements (Pipitone et al.,
2001; Abello´ et al., 2003; Elkrwe et al., 2008) and/or incidental
transport through commercial and recreational vessels (Mori
& Vacchi, 2002; Cannicci et al., 2006) could be responsible for
the rapid dispersal of P. gibbesi. According to Cannicci et al.
(2006), shipping transport appears to be an important
second vector, acting on dispersal of alien species beyond
the first location of introduction. Furthermore, when distri-
bution patterns of the eurythermal P. gibbesi is compared
with other alien temperate grapsoid species, it is possible
that Mediterranean rising temperature values, registered
over the last few years, could have given an advantage to the
fast spread of P. gibbesi (Zaouali et al., 2007).
Here we enlarge the distributional range of P. gibbesi south
into the Iberian Peninsula, western Mediterranean. Indivi-
duals of P. gibbesi have been observed at various sites
during snorkelling and dive assessments along the coast of
Murcia (Spain) (Figure 1). Observation sites comprise Cabo
de Palos region and Isla Grosa, including the Cabo de
Palos–Islas Hormigas Marine Reserve (37838
′
N0842
′
W)
which includes a no-take zone. It has been also recorded
southwards at Cabo Tin˜oso and Cabo Cope rocky coasts
(Figure 1). All observations were done between spring and
summer of 2009, around 1–3 m deep, where specimens
were found mainly on rock boulders hideouts. Based on
frequency classification of Humann & DeLoach (2002) the
species could be categorized as common according to the fre-
quency of encounters. In addition, photographs were taken to
check species validity and are also provided here (Figure 2).
In their review on the status of Marine Protected Areas
(MPA) in the Mediterranean Sea, Abdulla et al. (2008) out-
lined that, although P. gibbesi was registered by six different
Mediterranean MPA managers, they agreed that its presence
in a given MPA represents a negligible risk for environmental
health. However, the fast expansion achieved in the past six
years in Mediterranean waters, reaching densities of 1.5 +
0.5 to 11.9 + 7.1 ind m
22
(Sciberras & Schembri, 2007), is
promoted by its ability to occupy disturbed areas (Cannicci
et al., 2006) and to resist changes of temperature (Calado,
2006). Percnon gibbesi occurs along rocky shores and in the
subtidal zone, among boulders covered by algae. It is an her-
bivorous species feeding on both hard and soft algae and
microzooplankton (Galil et al., 2002). Puccio et al. (2006)
suggest that the feeding behaviour of P. gibbesi could give it
an advantage over other similar species, by allowing the inva-
sive species to explore a broader feeding niche. On the other
hand, the fast rate of population establishment of P. gibbesi
is likely due to its high fecundity, long larval life span, and
Corresponding author:
F.C. Fe´lix-Hackradt
Email: fabiana.cezar@um.es
1
Marine Biodiversity Records, page 1 of 3. # Marine Biological Association of the United Kingdom, 2010
doi:10.1017/S1755267210000175; Vol. 3; e22; 2010 Published online

the occurrence of large megalopa larvae that produce robust
juveniles (Crocetta & Colamonaco, 2008; Elkrwe et al.,
2008). Together, these biological characteristics may enhance
the competitive capacity of P. gibbesi, resulting in the most
invasive decapod species in the Mediterranean Sea (Zaouali
et al., 2007). This could cause the displacement of autochtho-
nous species such as Pachygrapsus marmoratus Fabricius,
1787, and should be cautiously assessed in selected localities
along its geographical distribution ranges.
The number of alien species registered in the Mediterra-
nean Sea have been increasing over the last few decades,
possibly caused by a number of factors—pollution, eutrophi-
cation, destruction and fragmentation of habitats, fisheries
overexploitation, fast-expanding mariculture, enlargement of
the Suez Canal, increase in maritime traffic, and climate
change—that could be acting in a complex and synergistic
form (Galil, 2008). Continued anthropogenic impact over
the ecosystem could change the Mediterranean fauna
completely, replacing existing species by new exotic ones.
Therefore, it is highly recommended that specific manage-
ment measures should be produced in order to prevent such
catastrophes.
For P. gibbesi its eurythermic capacity, cleaning function,
colourful body, together with ‘reef-safe’ (not harmful to
other organisms in an aquarium) characteristics, make it a
widely commercialized species at Portuguese aquarium
shops reaching values of 6–8 Euros ind
21
(Calado, 2006).
This may give a cue to a potential harvesting activity as a
useful management tool to control the spread of this invasive
species.
Fig. 1. Murcia coast (Spain) and location of sites where Percnon gibbesi was found.
Fig. 2. Percnon gibbesi photographed at Cabo de Palos coast (left) and Cabo Cope (right), Murcia, Spain.
2f.c.fe’ lix-hackradt et al.