First record of the non-indigenous portunid crab Charybdis variegata from the western Atlantic coast

Biological invasions are a present and growing environmental problem because non-indigenous organisms may affect the structure and functioning of native communities. In the marine environment there are records of invasive species in almost all phyla, including crustaceans, and the portunid crabs of the genus Charybdis are among the most widespread invasive groups. We report the first record of Charybdis variegata (Fabricius, 1798) from the western Atlantic coast. This species was collected on an intertidal rocky shore near Santos Harbor, São Paulo state, Brazil. Of 311 portunid crabs sampled, 309 individuals belonged to the non-indigenous Charybdis hellerii (A. Milne Edwards, 1867), one was a native Cronius ruber (Lamarck, 1818), and one was identified as the non-indigenous Charybdis variegata. This individual was a juvenile female measuring 27.5 mm in carapace width. The taxonomic traits used for species identification, as well as a morphological comparison between C. hellerii and C. variegata are presented. The introduction route and establishment status of this species are also discussed.

In the family Portunidae, at least two species originating from the Indo-Pacific have successfully spread through the world: Scylla serrata (Eldredge and Smith 2001;Tavares 2011;Tavares and Mendonça 2011) and Charybdis hellerii (Galil 2000;Junqueira et al. 2009).This latter species is one of the most frequently recorded invasive species around the world.On the Atlantic coast of the Americas, this species was first recorded in Cuba in 1987 (Gómez and Martínez-Iglesias 1990).In the following years there were northern and southern range extensions of C. hellerii on eastern American coasts (Campos and Türkay 1989;Lemaitre 1995), including the Brazilian coast (Calado 1996;Carqueija and Gouvêa 1996;Negreiros-Fransozo 1996;Tavares and Mendonça 1996;Mantelatto and Dias 1999;Ferreira et al. 2001;Lima Junior et al. 2008).
Charybdis hellerii has biological traits that are helpful during invasion of new areas, such as

Materials and methods
In July of 2011, the rocky shores of Ponta da Praia (23°59′28.9″S;46°18′17.0″W),located in Santos Bay, São Paulo State, Brazil (Figure 1) were visited during low tide on four days, to sample portunid crabs.During two hours per day, two people collected the crabs manually among the rocks, totaling 8 hours of capture effort.All crabs were carefully packed in plastic bags and taken to the laboratory for identification.The native crabs were identified according to Melo (1996).Non-native crabs of the genus Charybdis were identified by characteristics described by Wee and Ng (1995) and Padate et al. (2010).The single specimen of the non-native crab C. variegata found was measured for carapace width (including and excluding spines) with digital calipers (0.1 mm).

Animal samples
A total of 311 portunid crabs were collected; 309 were individuals of the non-indigenous crab C. hellerii with carapace width ranging from 17.70 to 70.75 mm (without spines), one was the native crab Cronius ruber (Lamarck, 1818) with carapace width of 30.8 mm without spines, and one was a new, non-indigenous portunid crab.The specimen was a juvenile female of Charybdis variegata, with a carapace width of 24.0 mm (without spines) and 27.5 mm (with spines) (Figure 2 A).

Taxonomic traits
The genus and subgenus of the non-indigenous specimen were determined by the following specific characters (from Wee and Ng 1995): 1) extent of the frontal-orbital border distinctly less than greatest breadth of carapace; anterolateral border of carapace oblique and arched, cut into six or seven teeth, Genus Charybdis (Figure 1, A); 2) posterior border of carapace forming a curve with postero-lateral border; merus of cheliped with distal spine on posterior border (Figure 1A); and 3) "antero-lateral border divided into six teeth of which at least five are large", Sub-genus Charybdis (Figure 1, A-I and  2, B-I).
The identification of Charybdis (Charybdis) variegata was based on Padate et al. (2010), considering: 1) transverse ridges on carapace posterior to the last antero-lateral tooth present The juvenile female collected provided several taxonomic traits typical of C. variegata (as described by Leene 1937): 1) the second anterolateral tooth is only slightly smaller than the first tooth; 2) the last antero-lateral spine is much longer than the fifth tooth, especially in the female; 3) the inner lobule of the outer part of the lower orbital border is sharply dentiform; and 4) whereas the hands of the chelipeds are unequal in size and shape in the male, in the female they are nearly the same, as is shown in Figure 2.
Finally, to facilitate distinguishing between Charybdis variegata and C. hellerii, even by

Discussion
The species Charybdis variegata was first described as Portunus variegatus by Fabricius in 1798, and transferred to Charybdis variegatus by De Hann in 1850.The taxonomic status of Charybdis variegata was updated in 1935 by Chopra (Leene 1937).The biology of C. variegata is poorly studied.Chandran (1968) showed that C. variegata has a biannual breeding cycle based on the hepatosomatic and gonadosomatic indices, which are directly influenced by environmental factors.
The specimen collected in Brazilian waters differs from the key to the genus Charybdis of Padate et al. (2010) in one characteristic.In the description of Padate et al. (2010), all frontal teeth are acuminate at the tip, but in the juvenile female caught in Santos Bay, the two median and two sub-median frontal teeth were blunt.However, this specimen conforms to the description provided by Leene (1937).This author compared the type species of Portunus variegatus Fabricius, 1798 from the Copenhagen Museum with specimens of Charybdis variegatus in the Leiden Museum (three males and one female) collected in Amoy (China), and found several differences, among them the less acute frontal teeth.
Charybdis variegata is a portunid crab originally from the Indo-Pacific Ocean, and was recorded in India (Chandran 1968), Malaysia and Singapore (Wee and Ng 1995), China (Chou et al. 1999), Japan (Yamochi and Oda 2002), and Australia (Stephenson et al. 1957), among other countries.The invasive potential of C. variegata was first reported by Williams et al. (1988).These authors analyzed the species composition of the ballast tanks of cargo vessels (water and sediment) between Japan and Australia, and found two specimens of C. variegata, among other invertebrate species, in the sediment.In the present study, only one individual of C. variegata was found among 311 portunid crabs collected in the vicinity of the largest Latin American port, the Port of Santos.The amount of sampling effort and the record of only one individual of C. variegata suggests that the introduction of this species may be recent and probably occurred in ballast water, as suggested for C. hellerii in the mid-1990s in Brazil (Calado 1996;Carqueja and Gouvea 1996;Mantelatto and Garcia 2001;Junqueira et al. 2009;Ferreira et al. 2009).
After more than 20 years of introduction, dispersal and establishment of C. hellerii in Atlantic waters (Gómez and Martínez-Iglesias 1990;Lemaitre 1995;Tavares 2011), little is known about its biology and environmental impacts.The present record of another portunid crab of the genus Charybdis confirms the prediction by Ferreira et al. (2009), that "(we) do not disregard the possibility of new occurrences as prospective alien species".This new find provides evidence that biological invasions are still occurring in the study area, and that more attention from the Brazilian maritime authorities is advisable.Brazil is engaged in the Global Ballast Water Management Program (GloBallast), and needs to increase the routine of inspection and control of ballast water, as highlighted by Ferreira et al. (2009).

Figure
Figure 1.Location of the study area, Ponta da Praia Beach (white arrow) at the entrance of Santos Harbor, São Paulo State (black arrow), Brazil.

Figure 2 .
Figure 2. (A) Dorsal view of the juvenile female of Charybdis variegata collected in Santos Bay, São Paulo, Brazil.(B) Detail of taxonomic traits used for C. variegata identification: I, Dorsal view of carapace; II and III, pairs of ridges on both right and left mesobranchial area of carapace; and IV, interruption of the ridges in the cardiac area on the carapace (white arrow).Scale bar 1 mm.Photographs by Timóteo Tadashi Watanabe.

Figure 3 .
Figure 3. (A) Dorsal view of a juvenile female of Charybdis hellerii collected in Santos Bay, São Paulo, Brazil.(B) Detail of taxonomic traits used to separate C. hellerii from C. variegata: I, Dorsal view of carapace; II and III, absence of paired ridges on both right and left sides of mesobranchial area of carapace; and IV Continuous ridges of cardiac area on carapace (with arrow).Scale bar 1 mm.Photographs by Timóteo Tadashi Watanabe.