A new record of the West African fiddler
crab, Uca tangeri, from Gran Canaria
(Canary Islands)
A specimen of West African fiddler crab, Uca tangeri, was collected in October 2011 on the north-east coast of Gran Canaria (Canary Islands). This species is frequent along the shores of the east Atlantic from Portugal to Angola, but is very rare in the Canary Islands. There is only a previous record from 1971, but that did not report the place where it was found in the archipelago.
INTRODUCTION
Uca tangeri (Eydoux, 1835) is a common crab in marsh land,
mud flats, often near river mouths, along the west coast of
Africa from Morocco to southern Angola. It is also present
on the coast of Portugal, but it does not occur in the
Mediterranean (Holthuis, 1981; Manning & Holthuis, 1981;
Schneider, 1990).
According to Burggren & McMahon (1988), U. tangeri
with a maximum carapace length of 33 millimetres (47 mm
carapace width) is the largest species in the genus Uca
(Holthuis, 1981; Lloris & Rucabado, 1998). The most
notable feature of this species is the dimorphism of the
chelae. Males have one small chela (smaller than observed
in females) and the other is enormously enlarged. The small
chela is mainly used for feeding while the large one is used
for agonistic and mating displays (Christy & Salmon, 1984;
Burggren & McMahon, 1988). The waving and vertical movements
of the larger chela, together with quick movements of
the small one during feeding, have given the genus its
popular name of ‘fiddler crabs’ (Burggren & McMahon,
1988). Fiddler crabs live in burrows and galleries created
into the mud and used for protection during high tide, emerging
when galleries are exposed at low tide (Altevogt, 1959;
Montague, 1980).
There are no reports of the presence of this crab at Madeira
and Cabo Verde archipelagos. However, Garcı´a-Cabrera
(1971), in a paper about similarities of Canary Islands and
Antilles marine fauna, reported the presence of U. tangeri in
the list of brachyuran species of both areas, but without site
specification. Because of this lack of specificity and because
there are no previous or later references to that of
Garcı´a-Cabrera in this archipelago González – Pérez (1995)
excluded this crab from the species catalogue of crustaceans
of the Canary Islands. Also, the citation of U. tangeri for the
Antilles is probably due to confusion with other species of
the Uca genus.
MATERIALS AND METHODS
On the night of 3–4 October 2011, a single male specimen of
U. tangeri (Figure 1), with carapace length 28.0 mm, carapace
width 33.7 mm, and 33.3 g of wet weight, was collected from
the Las Canteras Beach (20808′27.23′′N–15826′09.42′′W),
north-east of Gran Canaria (Canary Islands, central-east
Atlantic). The crab had the left chela (73.2 mm) 4.2 times
larger than right one (17.2 mm). The specimen was captured
by hand while it was walking on the sand, along the beach
strand, in the limit of sea waves during low tide.
During the night of 3–4 October there was low tide
(20.6 m) and the sea surface temperature was 248C (the
minimal low tide recorded in Gran Canaria had been
21.5 m). The moon was in its first quarter. The weather
was warmer and winds were light and variable from the northeast
at coastal areas, and from the south changing to west at
high areas of the island.
RESULTS AND DISCUSSION
This is the first corroborated record for U. tangeri from the
Canary Islands. According to García-Cabrera (1971), in the
Canary Islands only 15% of marine species are in common
with the neighbouring African coasts. Mainland and island
ecosystems are very different. The African waters are colder
and less saline than the island ones, with shallow bottoms
that extend beyond 120 km without reaching the 500 m
depth. These bottoms are rich in marine vegetation and able
to accommodate populations of great interest and biomass.
However, the islands are of volcanic origin and their shelves
are markedly narrow and steep. The coastal areas are quite
diverse, with predomination of volcanic and stony shores,
and they present a great variety of microclimates and
marine biotopes (Bas et al., 1995; Brito et al., 1996, 2001).
And, probably due to the microclimates and marine biotopes,
the absence of river estuaries, adequate muddy areas, and that
beaches support a high human pressure (tourism is the main
industry in the Canaries), the population of U. tangeri in the
island should be very low, and limited to few individuals
that live restricted to some small areas.
On the other hand, it is possible that this specimen could be
a consequence of occasional larvae drifting transport between
the African coast and the Canary Archipelago, as it has been
documented for fish larvae (Rodrı´guez et al., 1999, 2004),
and the subsequent process of settlement and growing of an
isolated individual.
ACKNOWLEDGEMENT
I thank Desire´e Herna´ndez-Hormiga for her assistance in the
specimen collection, measuring and rearing.
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J.J. Castro
Departamento de Biología
Universidad de Las Palmas de Gran Canaria
Edificio Ciencias Ba´sicas, Campus de Tafira
35017 Las Palmas de Gran Canaria, Canary Islands, Spain
email: jcastro@pesca.gi.ulpgc.es
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