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received: 2020-06-02                 DOI 10.19233/ASHN.2020.12
ADDITIONAL RECORD OF THE ALIEN CRAB ACTAEODES TOMENTOSUS 
(BRACHYURA: XANTHIDAE: ACTAEINAE) FROM TUNISIAN MARINE WATERS
 
Raouia GHANEM 
Laboratoire de Biodiversité, Biotechnologies et Changements climatiques (LR11ES09), Université Tunis El Manar, Tunisia 
e-mail: raouia-ghanem@hotmail.fr 
Jamila BEN SOUISSI
Laboratoire de Biodiversité, Biotechnologies et Changements climatiques (LR11ES09), Université Tunis El Manar, Tunisia and Institut 
National Agronomique de Tunisie, Université de Carthage, Tunisia
ABSTRACT
The occurrence of the Xanthid crab Actaeodes tomentosus, an Erythrean species, is recorded for the second 
time from the Tunisian marine waters. A single female was captured by hand on October 2016 during scuba 
diving survey carried out in the Marine Protected Area of Zembra. The specimen was caught at 1 m depth 
anchored to a rock. The carapace length and width were respectively 9.1 mm and 14.3 mm. This record 
constitutes the northernmost extension range of the species not only in Tunisia but also at a Mediterranean 
scale. A. tomentosus is neurotoxic containing the “Tetrodotoxin”, which is widespread in the Indo-Pacific region 
and considered among the most common intertidal coral reefs species. 
Key words: Marine Protected Area, bioinvasion, decapods, diving survey, extension range, Tunisia
NUOVA SEGNALAZIONE DEL GRANCHIO ALIENO ACTAEODES TOMENTOSUS 
(BRACHYURA: XANTHIDAE: ACTAEINAE) IN ACQUE MARINE DELLA TUNISIA
SINTESI
La presenza di una specie eritrea di granchi della famiglia Xanthidae, Actaeodes tomentosus, è stata registrata 
per la seconda volta nel mare della Tunisia. Una singola femmina è stata catturata con le mani nell’ottobre del 
2016, durante un’indagine subacquea condotta nell’area marina protetta di Zembra. Il granchio è stato cattu-
rato a 1 m di profondità, mentre si trovava saldamente aggrappato ad una roccia. La lunghezza e la larghezza 
del carapace erano rispettivamente di 9,1 mm e 14,3 mm. Questo ritrovamento costituisce la segnalazione più 
settentrionale delle specie, non solo in Tunisia, ma anche su scala mediterranea. A. tomentosus è una specie 
neurotossica, contenente la tetrodotossina. È diffusa nella regione indo-pacifica ed è considerata tra le più 
comuni specie di barriere coralline intertidali.
Parole chiave: area marina protetta, bioinvasione, decapodi, indagine subacquea, estensione, Tunisia
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INTRODUCTION
Invasive species are considered as a major threat 
(Azzurro et al., 2019) and the second most common 
cause of species extinction after habitat destruction 
(Bellard et al., 2016). The Mediterranean is the most 
invaded Sea in the world (Galil et al., 2014), and of 
the 821 Non-Indigenous Species (NIS) recorded up to 
date, more than a half are established (Zenetos et al., 
2017). This region is known to support several crab 
invasions (Swart et al., 2018). Over 39 alien Brachyura 
species of Red Sea/Indo-Pacific origin have been well 
documented in the Mediterranean Sea, mainly in the 
eastern Basin (Klaoudatos & Kapiris, 2014). Decapods 
are the best known marine invasive crustaceans due 
to their easy larvae dispersal (Landeira et al., 2019), 
their high reproductive rate and wide environmental 
tolerance allowing an important establishment success 
(Gothland et al., 2014) and particularly the adverse 
environmental and socio-economic impacts that can 
inflict such species. Indeed, some crabs from Portu-
nidae (Portunus segnis (Forskål, 1775), Callinectes 
sapidus Rathbun, 1896) or Epialtidae (Libinia dubia H. 
Milne Edwards, 1834) families have strongly affected 
human health, ecosystems and fishery activities in Tu-
nisian waters (Khamassi et al., 2019; Rjiba et al., 2019; 
Chaffai et al., 2020). 
According to Corsini-Foka & Kondylatos (2015), 
four alien xanthid crabs occur in the Mediterranean 
Sea; Atergatis roseus (Rüppell, 1830), Actaea savignii 
Fig. 1: Map of northern Tunisia (redrawn from Capapé et al., 2020) indicating the capture sites of Actaeodes 
tomentosus (ref. INAT- IXAN-Ac-tom0) from the Tunisian waters. 1. Marina of Hammamet. 2. Zembra Island.
Sl. 1: Zemljevid severne Tunizije (prerisano iz Capapé in sod., 2020) z lokaliteto, kjer je bila najdena rakovica vrste 
Actaeodes tomentosus (ref. INAT- IXAN-Ac-tom0) v tunizijskih vodah. 1. Marina v Hammametu. 2. Otok Zembra.
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(H. Milne Edwards, 1834), Xanthias lamarckii (H. Milne 
Edwards, 1834) and Actaeodes tomentosus (H. Milne 
Edwards, 1834), this latter is the most frequent species, 
worldwide distributed particularly in the Indo-Pacific 
region, from the Red Sea, Aden, Somalia, Kenya, Tan-
zania, Mozambique and S. Africa to the Western Indian 
Ocean islands up to Australia, Japan and Hawaii Islan-
ds (Serène 1984). 
A. tomentosus was recorded for the first time in 
the Mediterranean Sea in the shallow coastal waters 
of Rhodes Island (Corsini-Foka & Kondylatos, 2015). 
In January 2015, three specimens, two non-ovigerous 
females and one male, were collected from the marina 
of Hammamet, located in eastern Tunisia among biofo-
uling (Ounifi Ben Amor et al., 2016). 
A larger trend in recorded alien species in the 
last decades have been locally reported as a main 
consequence of a heavy biological invasion of mixed 
origins. More than 150 NIS fauna have been recorded 
at present. Among them crustacean decapods consti-
tute the main group of alien fauna, more than 50% 
according to Ounifi-Ben Amor et al. (2016) and Ben 
Souissi et al. (2019). 
In order to implement effective management plans 
for marine ecosystems, an accurate and updated spa-
tio-temporal data on species biogeography is required 
(Katsanevakis et al., 2020). Records of “New-Comers” 
should not be limited to their first observation. In fact, 
species distribution knowledge constitute a prerequisi-
te to assess their invasion potential and its progress and 
therefore the establishment of the best conservation 
measures.
MATERIAL AND METHODS
During a periodic assessment of climate change 
impacts on marine biodiversity carried out mainly 
in Tunisian Marine Protected Areas (MPA’s), a single 
female of Actaeodes tomentosus specimen was col-
lected by hand at 1 m depth anchored to a rock during 
scuba diving survey on 15 October 2016 performed in 
Zembra MPA (37°04’645’’N and 11°02’960’’E) (Fig.1). 
The crab was identified as A. tomentosus following 
Serène (1984) and was subsequently preserved in 
95% alcohol, and deposited in the Collection of cru-
stacean species at the Institut National Agronomique 
de Tunisie under the catalogue number: INAT- XAN-
-Ac-tom01. 
RESULTS AND DISCUSSION
The collected specimen was a female exhibiting 
the typical morphological characters of A. tomentosus 
following Serène (1984). The crab was easily identified 
by numerous dark granules throughout the carapace 
and appendages, especially on the outer face of both 
movable and fixed dactyls. (Fig. 2). The carapace 
length (CL) and width (CW) were respectively 9.1 mm 
and 14.3 mm. The ratio CW/CL= 1.58 is near the value 
(1.55) reported for the species by Serène (1984).
Fig. 2: Actaeodes tomentosus (ref. INAT- XAN-Ac-tom01). A. Dorsal view. B. Ventral view. Scale bar = 5 mm.
Sl. 2: Actaeodes tomentosus (ref. INAT- XAN-Ac-tom01). A. Hrbtna stran. B. Trebušna stran. Merilo = 5 mm.
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A. tomentosus has been reported in the marina of 
Hammamet on 2015 (Ounifi-Ben Amor et al., 2016), su-
ggesting that the possible pathway of introduction was 
maritime traffic. Since this species has now been found 
in two localities from eastern (Central Mediterranean) 
and northeastern Tunisia (Western Mediterranean) for 
a short time, this record constitutes the northernmost 
extension range of the species not only in the area 
but also in the wide Mediterranean Sea. Such patterns 
suggest that viable populations are progressively esta-
blishing although it is small and cryptic, and probably 
escaped to notice.
The arrival of poisoning species is increasingly 
noted in Tunisian waters (Yahia et al., 2013; Ben 
Souissi et al., 2014; Ounifi-Ben Amor & Ghanem In 
Dailianis et al. (2016). Indeed, cases of intoxication 
by Tetradotoxin (TTX), present in Tetraodontiformes 
fish (pufferfish) were observed in western Tunisia 
during year 2013 (Ben Souissi et al., 2014) and also 
identified in some A. tomentosus from Taiwan (Ho 
et al., 2006), and Saxitoxin and related compounds 
(STXs) were found in specimens from Japan (Deeds 
et al., 2008). Several scientific studies confirm the 
increasing spread and abundance of invasive marine 
species of human health concern, however, informa-
tion on their impacts remains unequally and poorly 
known (Galil, 2018). 
Regular monitoring programs in and around MPAs 
enhance NIS detection to an early invasion stage 
probably allow their eradication (Otero et al., 2013). 
However, the risks that NIS can have in these particular 
habitats are very significant and even harmful (Galil, 
2019). Several Non-Indigenous species have been 
reported the waters surrounding Zembra Island MPA, 
and such habitat constitute a kind of refuge, where 
NIS do not face to fishing pressure occurring in the-
se  unprotected sites (Giakoumi et al., 2019). In fact, 
and according to Ounifi-Ben Amor et al. (2016) and 
Ounifi-Ben Amor & Ghanem In Dailianis et al. (2016), 
of  the 137 non-indigenous faunal species recorded  in 
Tunisia, 25 species were listed around Zembra MPA 
and six species have been observed in its surrounding 
waters. Therefore, in total agreement with Galil (2019), 
it appears that MPAs with an abundance of Non-Indi-
genous populations could be considered as seed banks 
leading to a spill-over effect to neighboring areas. 
ACKNOWLEDGEMENTS
The authors would like to warmly thank anonymo-
us Referees for their valuable comments and their 
suggestions for improving the manuscript. This work 
was partially funded by the French Research program 
BIODIVMEX/MISTRALS. 
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NOVI ZAPIS O POJAVLJANJU TUJERODNE RAKOVICE ACTAEODES TOMENTOSUS 
(BRACHYURA: XANTHIDAE: ACTAEINAE) IZ TUNIZIJSKIH MORSKIH VOD 
Raouia GHANEM 
Laboratoire de Biodiversité, Biotechnologies et Changements climatiques (LR11ES09), Université Tunis El Manar, Tunisia 
e-mail: raouia-ghanem@hotmail.fr 
Jamila BEN SOUISSI
Laboratoire de Biodiversité, Biotechnologies et Changements climatiques (LR11ES09), Université Tunis El Manar, Tunisia and Institut 
National Agronomique de Tunisie, Université de Carthage, Tunisia
POVZETEK
Avtorji poročajo o drugem zapisu o pojavljanju rakovice Actaeodes tomentosus, eritrejske vrste, v tunizijskih 
morskih vodah. Samica te vrste je bila ujeta z roko oktobra 2016 med potapljanjem z avtonomno potapljaško 
opremo v morskem zavarovanem območju Zembra. Primerek je bil ujet na 1 m globine, tesno pritrjen na skalo. 
Dolžina oklepa je bila 9,1 mm, njegova širina pa 14,3 mm. Ta zapis predstavlja najsevernejši primer pojavljanja 
vrste v Tuniziji in tudi v Sredozemskem morju. A. tomentosus je nevrotoksična vrsta, ki vsebuje strup tetrodotoksin. 
Je široko razširjena vrsta v Indo-Pacifiku in pogosta vrsta v bibavičnem pasu na koralnih grebenih. 
Ključne besede: morsko zavarovano območje, bioinvazija, raki deseteronožci, potapljaški pregled, širjenje areala, Tunizija
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