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Medit. Mar. Sci., 17/1, 2016, 147-151 147
Mediterranean Marine Science
Indexed in WoS (Web of Science, ISI Thomson) and SCOPUS
The journal is available on line at http://www.medit-mar-sc.net
The occurrence of a single individual of yellowtail tang Zebrasoma xanthurum (Acanthuridae) from Sardinia island (Italy),
probably released from an aquarium, is reported. This observation represents the rst record of this species in the Mediterranean
Sea. General information on the Acanthurid shes and other non-native species in the Mediterranean is discussed in the light of
the ongoing ecological change taking place on rocky reef ecosystems with consideration of implications on the aquarium trade.
Keywords: Non-native shes, surgeonsh, Acanthuridae, accidental introduction, aquarium trade, ecosystem shifts, Tyrrhenian
First record of the acanthurid sh Zebrasoma xanthurum (Blyth, 1852) in the Mediterranean
Sea, with some considerations on the risk associated with the aquarium trade
P. GUIDETTI1, L. MAGNANI2 and A. NAVONE3
1 Université Nice Sophia Antipolis, CNRS, FRE 3729 ECOMERS, Parc Valrose 28, Avenue Valrose, 06108 Nice, France
2 Porto San Paolo Dive Center, Via Pietro Nenni, 14A, 07020 Porto San Paolo OT, Italy
3 Marine Protected Area of Tavolara-Punta Coda Cavallo, Via Dante 1, 07026 Olbia, Italy
Corresponding author: email@example.com
Handling Editor: Murat Bilecenoglu
Received: 25 August 2015; Accepted: 16 December 2015; Published on line: 29 January 2016
The Acanthuridae is a widespread teleost family,
comprising of 84 species, with tropical and subtropical
afnity (Eschmeyer, 2015). Within the acanthurids, the
yellowtail tang, Zebrasoma xanthurum (Blyth, 1852),
is distributed throughout the Western Indian Ocean, in-
cluding the Red Sea, the Persian Gulf and Maldives (see
Froese & Pauly, 2015). There have also been isolated,
individual recordings from the marine waters off Boca
Raton, Palm Beach County, Florida, US (Bartley, 2006)
and off Hoi Ha Wan Marine Park, Hong Kong (Myers et
Z. xanthurum is reported to occur on coral- and
rocky-reefs (Sommer et al., 1996) within the 2-20 m
bathymetric range and between 24 and 28°C sea water
temperature (Baensch & Debelius, 1997). It is a typical
herbivorous grazer, generally feeding on benthic algae.
Natural predators are primarily large serranids (e.g. ge-
Z. xanthurum has a reported maximum length of
37 cm, however it is commonly observed around 10-20
cm (Froese & Pauly, 2015 and references therein). The
body is blue in color with a yellow tail, the head displays
numerous black spots, and in some locations black hori-
zontal lines can be displayed along the sides of the body.
Similarly to other species belonging to the Zebrasoma
genus, the yellowtail tang is characterized by large dorsal
and anal ns accompanied by an extended snout used to
feed upon algae. The tips of the pectoral ns are often
yellowish (Carpenter et al., 1997).
There are no specic conservation measures in place
for this species. The yellowtail tang is not commercially
important for sheries and is considered a minor species
in the aquarium trade. Consequently, the IUCN has clas-
sied this sh as ‘least concerned’ (Myers et al., 2012).
In this work we report the rst known occurrence of
Z. xanthurum (Blyth, 1852) in the Mediterranean Sea and
discuss the ongoing changes in rocky reef ecosystems
throughout the basin and implications of the aquarium
Materials and Methods
On the 3rd of August, 2015, a single individual of
Zebrasoma xanthurum was observed (L. Magnani) at
Tavolara Island, in a site located within the borders (spe-
cically in the buffer zone) of the Tavolara-Punta Coda
Cavallo Marine Protected Area (Sardinia, Italy; Medi-
terranean Sea; Fig. 1; 40.8847220 N; 9.7097220 E). The
specimen occurred on a rocky bottom covered by mac-
roalgae interspersed with Posidonia oceanica patches at
about 16-17 m depth. Identication was based on photo-
graphs performed while on SCUBA.
Subsequent to the rst sighting, 33 dives (15 in Au-
gust, 10 in September and 8 in October) at the same site
were made (during daytime by the three authors of this
ms) to identify behavioral traits (e.g. feeding and interac-
tions with other shes) via in situ observations, and by
analyzing video footage and pictures. Three dives were
made by the authors in August 2015 with HD video to
148 Medit. Mar. Sci., 17/1, 2016, 147-151
help with ne-scale observations of behavior. The main
behavioral features observed were: 1) location of the sh
(where it was observed more frequently) and general pat-
terns of movement; 2) events of interaction with other
shes; 3) events of feeding.
The individual acanthurid observed at Tavolara Is-
land had a total length (TL) of 11-12 cm, and the typical
blue livery with yellow tail, yellowish tips of the pectoral
ns, numerous black spots on the head, and some black
horizontal lines on the body. The caudal n had a linear
margin and the soft portion of the dorsal n was higher
than the spiny portion (specic to the Zebrasoma). This
combination of characteristics allowed for its univocal
identication as a subadult Zebrasoma xanthurum. This
result was further conrmed thanks to in situ observa-
tions, by analyzing pictures and videos, and with two
experts of acanthurids (see Acknowledgements). Dur-
ing all observations, the specimen appeared to be in a
good state of health. The individual actively moved over
rocky bottoms covered by macroalgae, rich in boulders
and crevices, and over patches of the seagrass Posidonia
oceanica. Preference for these habitats suggest suitable
refuge and food. The sh was always observed at one of
two locations and each location was roughly ten square
meters. The individual regularly moved between the two
locations found at 12-14 and 16-18 m depth. Movement
patterns were ‘stop-and-go’, typical of many herbivorous
shes picking at (roughly every 10-15 sec.), and feeding
from, benthic algae that settled on rocks and boulders.
Furthermore, it also fed on epiphytic algae growing on
the leaves of P. oceanica and on other large-sized mac-
roalgae (e.g. Codium bursa).
Other shes observed in the same locations included
typical Mediterranean sh fauna associated with rocky
reefs and P. oceanica. Fish communities of the Tavolara-
Punta Coda Cavallo MPA has been surveyed annually
since 2005 for which a more detailed description can be
found at Di Franco et al. (2009). Based on our eld ob-
servations, the specimen of yellowtail tang at Tavolara
did not interact with other shes except for pairs of the
pomacentrid Chromis chromis, a species well known to
actively defend their nests during the reproduction phase.
Multiple observations (n=11 events observed) of defense
behavior of individual C. chromis against approaches
of the yellowtail tang resulted in the yellowtail tang to
move elsewhere. Relatively large individuals of the ser-
ranid, Epinephelus marginatus, were present in the area
with some observed within close range of the yellowtail
tang. Although representing a potential predator, we did
not observe any predatorial behavior, attraction, or in-
terest towards the yellowtail tang. At times (n=6 events
observed), the yellowtail tang would swim a few meters
into the water column and angle its body at about 45°.
This was assumed to be behavior aimed at attracting
cleaning shes. Nonetheless, this behavior never resulted
in cleaning from Symphodus melanocercus, the only spe-
cie present known to perform the function. With regard
to interactions with divers, generally, the yellowtail tang
at Tavolara was unaffected by diver presence allowing us
to approach the sh for optimal observations.
Fig. 1. Location of Tavolara Island (Sardinia, Italy; central Tyr-
rhenian Sea); the site where the specimen of Zebrasoma xan-
thurum was recorded.
Fig. 2. Photograph of the individual Zebrasoma xanthurum (~11-
12 cm total length) that was observed swimming on rocky reefs
and Posidonia oceanica patches at Tavolara (photo: L. Magnani).
Medit. Mar. Sci., 17/1, 2016, 147-151 149
The sh was last observed in the Tavolara-Punta
Coda Cavallo MPA on September 21st, 2015. At that time
water temperatures at the observation depth (15-20 m)
was 23-24 °C.
Discussion and Conclusion
This observation represents the rst record of the yel-
lowtail tang in the Mediterranean and further conrmed by
the species absence from a recent report of acanthurids by
Langeneck et al. (2015). Including this this observation of
the yellowtail tang, ve species belonging to the Acanthu-
ridae have, to date, been reported from the Mediterranean
Sea. These species include: Acanthurus monroviae (Stein-
dachner, 1876), A. chirurgus (Bloch, 1787), A. coeruleus
(Bloch & Schneider, 1801), Zebrasoma avescens (Ben-
nett, 1828) and Z. xanthurum (Blyth, 1852). As noted by
Langeneck et al. (2015), Acanthurus monroviae was, un-
til recently, the only surgeonsh species reported from the
Mediterranean Sea. However, in the last years, the list of
acanthurid shes recorded from the basin has increased sig-
nicantly from one to ve species (see above).
The increasing number of non-native shes in the
Mediterranean (Zenetos et al., 2012) demands considera-
tion about pathways of introduction during climate change
(thermophilous species). This will help to identify future
scenarios and trajectories of Mediterranean marine eco-
systems, and to eventually adopt appropriate measures for
management or adaptation (Thresher & Kuris, 2004; Zene-
tos et al., 2012; Katsanevakis et al. 2014).
Of the ve acanthurids presently reported from the
Mediterranean, A. monroviae (usually occurring from An-
gola to southern Morocco, Atlantic Ocean, and probably
entered via Gibraltar), observations are sporadic and this
species if considered as a ‘vagrant’ in the areas where it has
been recorded (i.e. Algeria, Israel and NW Mediterranean
; Langeneck et al., 2015 and references therein). Observa-
tions of the other four acanthurids (A. coeruleus, A. chirur-
gus, Z. avescens and Z. xanthurum) have been sporadic, or
from only a single record, indicating these to be related to
intentional/accidental releases from tropical aquaria.
As a global and generally unregulated business, the
aquarium trade is emerging as an important pathway of in-
troduction of non-native marine species (Padilla & Williams,
2004). Padilla & Williams (2004) suggested that releases
may take place intentionally or accidentally, via dumping of
unwanted organisms, the deliberate release from captivity
or by the draining of water containing adult organisms or
their sexual (eggs, larvae) or asexual propagules.
The consequences of invasion (sometimes happening
after introductions) of non-native species to marine ecosys-
tems can result in serious ecological impacts and dramatic
socio-economic costs. Some authors have stated that the
probability for aquarium species to be released is higher in
close geographical distance to large coastal cities (Johnston
& Purkis, 2014). We suggest that in some regions, where
mega-yachts (often equipped with tropical aquaria) are fre-
quent, releases from aquaria can also be frequent especially
during high tourism seasons. From our best knowledge,
there is has been no precedent in the scientic literature con-
cerning introductions from mega yachts, however this is the
avenue that we hypothesize for our recorded individual of Z.
xanthurum in NE Sardinia.
Prevention of releases and possible invasions will re-
quire education and outreach, but also adequate legisla-
tion along with appropriate enforcement efforts to address
aquarium amateurs, shops and industry (Padilla & Williams,
2004; Côté et al., 2013). However, once an introduction has
occurred, eradication or efcient population control through
active removal may be considered the most effective ac-
tions, as natural ecosystems generally do not have the ca-
pacity to limit the expansion of non-native species (Côté et
al., 2013; Hackerott et al., 2013). For instance, the example
of the lionsh (Pterois volitans and P. miles) remains para-
digmatic. The dramatic invasion of the Indo-Pacic lionsh
to the western Atlantic and Caribbean has been attributed to
the aquarium trade. Inter-specic ecological processes such
as predation and competition with native shes has not limit
the lionsh expansion (Hackerott et al., 2013). The success
of the lionsh seems to be due to a combination of life his-
tory traits (e.g. early maturation/reproduction, ecological
plasticity) and the characteristics of the recipient ecosystem
(e.g. favorable climatic conditions, overshing of native
large predators; Côté et al., 2013). Likewise, this successful
invasion has had detrimental and rapid ecological impacts
on native communities (see e.g. Côté et al., 2013). Lionsh
(P. miles) have recently been reported in the eastern Medi-
terranean. However, given the geographical proximity and
connection with the Red Sea via the Suez Canal (where the
lionsh is present), these records from the Levantine basin
are attributed to lessepsian migration (Oray et al., 2015 and
references therein). Despite modelling studies that sug-
gested invasion by the lionsh to the Mediterranean to be
unlikely (Johnston & Purkis, 2014), new records of lionsh
continue to occur (Oray et al., 2015 and references therein)
perhaps providing a warning signal that should be recog-
nized before potential catastrophic damages occur to native
Mediterranean species and ecosystems.
The yellowtail tang, Z. xanthurum, is not a predator
like the lionsh, but rather a herbivorous sh. Until now,
the accidental/deliberate introduction in herbivorous tropi-
cal shes to the Mediterranean via the aquarium trade has
not caused signicant ecological impacts. Nevertheless, the
possible consequences of the increasing number of observa-
tions, should be considered. Non-native herbivorous shes
(notwithstanding the pathway of arrival) have the potential
to dramatically alter native Mediterranean communities. For
instance, the invasion of rabbitsh (Siganus spp.) from the
Red Sea to the eastern Mediterranean resulted in barrens; a
phenomenon that generally arises from urchin over-graving
(Sala et al., 2011). Tropical shes like acanthurids may nd
the Mediterranean temperatures during summer to be ap-
150 Medit. Mar. Sci., 17/1, 2016, 147-151
propriate for survival. Surface waters in Sardinia during Au-
gust 2015 were 26-28°C at surface, and 24-26°C at 16 m
depth. These temperatures, unusual in the past but becom-
ing more frequent in recent years, are probably related to
climatic changes resulting in the warming of marine waters
(Bianchi, 2007). This trend is likely to make Mediterranean
waters increasingly suitable to receive thermophilous spe-
cies (Raitsos et al., 2010).
Previous reports (Baensch & Debelius, 1997) have sug-
gested that the optimal temperatures for Z. xanthurum range
between 24 and 28°C. Thus, we believed that our observed
individual at Tavolara would thrive during the summer, but
mortality would ensue during winter’s 12-14°C. Unfortu-
nately we were unable to conrm this because the specimen
disappeared from the study area at the end of September
2015, while the water temperature was still tolerable. The
absence of the sh suggests that it moved elsewhere or that
it had been successfully attacked by a predator.
Langeneck et al. (2015) stated that the absence of
lessepsian acanthurids in the Mediterranean Sea was due
to their close ecological association with coral reefs; a fea-
ture absent in the Mediterranean Sea (Goren et al., 2011).
Based on the preliminary observations from this study,
the absence of coral reefs, per se, does not seem to pre-
vent Z. xanthurum from surviving (at least temporarily)
in the Mediterranean. Other coral-reef associated shes
have also displayed short-term survival in the Mediterra-
nean (e.g. Chaetodon austriacus and C. larvatus; Goren
et al., 2011, Salameh et al., 2011). Thus, it would seem
that thermal barriers or local predators limit the expan-
sion of many thermophilic shes accidentally released in
Mediterranean waters rather than the absence of coral-
reefs. This is in agreement with Golani et al. (2013) who
stated that Lessepsian migrants and thermophilic Atlantic
species may display a signicant rate of establishment
and invasion success, while tropical species accidentally
introduced (seldom become invasive.
Despite pathway or mechanism, more thermophilous
shes are entering the Mediterranean Sea and they are
increasingly nding conditions conducive for their sur-
vival. They often establish in the warmer southern and
eastern sectors of the Mediterranean basin, and occasion-
ally expand north- and westwards (Azzurro, 2008). This
phenomenon of geographical expansion encompasses a
variety of thermophilic organisms including macroalgae,
plankton, invertebrates and shes (Bianchi, 2007; Galil
et al., 2014). Furthermore, these expansions are con-
sidered one of the most detectable indicators of climate
change in the Northern hemisphere (Perry et al., 2005
and references therein included).
In the last two decades the number of non-native shes
recorded in the Mediterranean has increased signicantly
(Azzurro, 2008; Golani et al., 2013). Most are typically
herbivorous, like Siganus spp. and the ve Acanthuridae.
In the areas where species of Siganus become established,
rocky reef habitats have been dramatically and rapidly
degraded. Furthermore, profound ecosystem shifts occur
where rocky reefs covered in macroalgae are converted to
coralline barrens, a trajectory that is hardly reversible (Sala
et al., 2011; Guidetti et al., 2014). In a recent study carried
out at the Kos Island (Aegean Sea, Greece), Bianchi et al.
(2014) has noted a dramatic regime shift occurring over
the last 30 years. At this site they recorded a rise in sea sur-
face temperatures 1-2°C, human pressures have increased
signicantly and multiple invasions by non-native species
has occured. These changes are further seen in the benthos
where once ourishing macroalgal forests have been re-
placed by sponges and wide barrens. The authors (Bianchi
et al., 2014) attributed these profound changes chiey to
the overgrazing by non-native herbivorous shes (Siganus
luridus and S. rivulatus), whose establishment and spread
have been probably favored by sea warming in combina-
tion with local human impacts (Bianchi et al., 2014; Giak-
oumi, 2014). From this perspective, given that Acanthurid
shes are also herbivores, their potential introduction and
spread across the Mediterranean coastal waters could in-
crease the degradation of Mediterranean rocky reefs. The
shift from macroalgal beds to barrens implies signicant
changes in biodiversity, 3-D architecture of habitats, and
a number of ecosystem functions (including several goods
and services provided to society) (Guidetti, 2006). This
ecosystem shift is attributable to overshing and other hu-
man impacts, climate change and the introduction of non-
native herbivorous species (also including some inverte-
brates like the crab Percnon gibbesii; Evans et al., 2015).
In the worst case scenario, the increase of temperatures
and continued biological introductions combined with
human resource usage, will interact resulting in irrevers-
ible, negative consequences, especially for Mediterranean
Many thanks are expressed to J. Langeneck and P.
Louisy, who conrmed the identication and provided
valuable information about the species object of this
study, and to Bianchi C.N., who provided interesting ele-
ments for discussion. Special thanks to J. Plass-Johnson
for his useful comments and the revision of the English
language, to the two referees and the handling editor, for
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