Northward spread of tropical affinity fishes: Caranx crysos (Teleostea: Carangidae), a case study from the Mediterranean Sea

Abstract

The blue runner Caranx crysos is a thermophilic species poorly investigated in the Mediterranean Sea. Although considered a typical inhabitant of the southern regions, it has recently established in northwest Sicily and, according to the data presented in this study, is now regularly caught in the central-southern Tyrrhenian Sea up to the Gulf of Naples. Some occurrences of the species were also documented in the Gulf of Taranto (Ionian Sea) and in more northerly localities of the Tyrrhenian Sea, such as Gaeta and Civitavecchia. These recent distributional records are in contrast with historical literature and museum collections which depict this species as very rare in the Italian seas and only sporadically occurring above the Strait of Sicily. In this paper, literature and museum collections were thoroughly investigated in order to obtain a satisfactory understanding of the species distribution in the Mediterranean. In addition, the hypothesis of a recent displacement of the northern limit of this species distributional range in the Mediterranean is discussed.

Keywords:

• Caranx crysos
• thermophilic species
• northward spread
• Mediterranean Sea

Introduction

In recent years the progressive northward spread of tropical and subtropical fish species has been well documented in the western Mediterranean (Quignard & Raibaut 1993; Francour et al. 1994; Riera et al. 1995; Quignard & Tomasini 2000; Vacchi et al. 2001). These findings have been generally explained by the ‘meridionalization’ of the colder sectors of the latter sea possibly caused by water warming (Riera et al. 1995) and by a more generalized ‘tropicalization’ process presently investing the whole Mediterranean (Andaloro & Rinaldi 1998; Bianchi & Morri 2003).

Among the native fishes with a tropical or subtropical affinity occurring in the Mediterranean (Tortonese 1964), the blue runner Caranx crysos (Mitchill 1815) may be considered one of the least known with respect to its general morphology (Tortonese 1952) and biogeography (Tortonese 1961). Very few papers dealing with its biology are presently available (Assem 1999, 2000; Mirto et al. 2002; Sley et al. 2009) and a critical treatment of the species past and present distribution in the Mediterranean is missing. Although CIESM (2008) includes C. crysos among a list of southern species recorded out of their known Mediterranean distributions, no mention with regard to the extent of such northerly expansions is given. The species is essentially distributed in tropical and subtropical regions of the Atlantic Ocean, including the Mediterranean Sea (Tortonese 1961). According to Fischer et al. (1987), C. crysos can be found throughout the Mediterranean, excluding the Adriatic Sea. ¹ This is in contrast with Tortonese (1952, 1961, 1975), who described the Mediterranean population of C. crysos as relatively scarce, the species being more or less frequent in the eastern and southern sectors but only sporadically reported along the northern coasts of the western basin. Furthermore, Tortonese (1975) regards some old citations of the species from northern localities as unreliable, either because they are based on questionable museum material (Nice and Genoa) or they are listed in general fish catalogues without precise indication of date and/or locality of capture (Catalan Sea). This view complies with Doderlein (1878) who considered C. crysos as very rare for the Sicilian seas and, according to the literature, only during the last decade has this species been recorded with unusual abundance and frequency in northwest Sicily (D'Anna et al. 1999; Mirto et al. 2002; Vega Fernández et al. 2003; Andaloro et al. 2005). Such conflicting data on the distribution of C. crysos in the Mediterranean were already noted by other contemporary authors (Vacchi et al. 1999), suggesting that a more complete picture of the species biogeography in this region is needed.

In this paper, we document the presence of C. crysos from the central-southern Tyrrhenian Sea and Gulf of Taranto (Ionian Sea). Records of the species available in the literature along with data obtained from museum collections were reviewed in order to present a more complete description of the species' distribution in the Mediterranean Sea.

Material and methods

From November 2007 to January 2009, specimens of Caranx crysos were collected in the central-southern Tyrrhenian Sea by means of trammel net, surrounding gear, and trawl (see Figure 1 and Table I). Some of these specimens were caught by commercial fishing vessels operating in the study area, others were collected by hook and line around aquaculture cages off Vibo Marina (southern Tyrrhenian) and at ‘La Cala’ harbour, Palermo (northwest Sicily). Captured fish were immediately frozen and later transported to ISPRA or to SZN laboratories where basic morphometry (to the nearest millimetre) and meristics were recorded. Each fish was also weighed by means of a digital balance to an accuracy of 0.1 g. Underwater visual censuses (UVC) in six different sites within the study area (see Figure 1 and Table I) were carried out during summer–autumn 2008. All censuses were performed by snorkelling during daylight on rocky and/or mixed bottoms in shallow water (up to 6 m) by using the random course technique (Harmelin-Vivien et al. 1985). Photographs documenting the presence of this species at Gaeta (41°12’N, 13°34’E) and at Salerno (40°40’N, 14°45’E) were obtained from F. Leone and A. Amato, veterinarians working at the local fish auction facilities. The latter also furnished six additional specimens captured by a bottom trawler off Marina di Schiavonea (39°39’N, 16°32’E) in the Gulf of Taranto (Ionian Sea).

Table I. Records of Caranx crysos in the Mediterranean Sea in chronological order

Date of occurrence	Specimens	Size (mm)	Sampling method	Locality of occurrence	Reference	Notes
1817	1	146 TL	–	Alexandria		MNHN 0000-5857 Holotype of Caranx fusus
IX.1867	1	–	–	Palma de Mallorca	Barceló (1868)	Collected at local fish market
ante 1878	4	<20 TL	–	Palermo and Sicily	Doderlein (1878)
7–12.X.1878	2	90, 110 TL	–	Malta		MZUF 1005
XI. 1882	1	–	–	Messina	Tortonese (1952)
I.1883	1	–	–	Palermo	Tortonese (1952)
1878–1892	6	148–450 FL	–	Palermo and Sicily		MZUP: AN311; P202; P204; P220; P221; P233
20.VI.1892	1	105 TL	–	Naples		MZUF 2781
26.VIII. 1911	1	20 TL	Boat-seine	South Crete	Schnakenbeck (1931)
1916	–	–	–	Phaleron	Athanassopoulos (1917)
07.IX.1924	1	300 FL	–	Jaffa		BMNH 1924.9.7.9
1930	1	–	–	Orontes River (Syria)		MNHN 2001–2758
01.XI.1938	1	320 TL	–	Haifa		BMNH 1938.11.1.36
1943	1	305 TL	–	North Rhodes	Tortonese (1947)
1945	1	–	–	Lake Timsah (Egypt)	Tortonese (1961)
1951–1953	>1	80–180 TL	Purse-seine	Haifa	Ben Tuvia (1953)
31.III.1960	2	175, 143 TL	–	Haifa		MSNG 38098
08.X.1964	5	120–145 TL	–	Nahr el Maut (Lebanon)		BMNH 1967.2.1.105–109
VIII.1965	2	125, 110 TL	–	Beirut		MSNG 40114
VII.1993	1	417 FL	‘Moruna’ net	Calvià (Mallorca)	Riera et al. (1995)
XII.1994	1	246 TL	Mid-water trawl	Karatas	Başusta & Erdem (2000)
X.1995	1	24 TL	Boat-seine	Milazzo	Costa (1999)
VII–XI.1995–1996	516	<200 TL	Surrounding net around FADs	Gulf of Castellamare (NW Sicily)	D'Anna et al. (1999)
V–VIII.1996	∼30	20–70 TL	Visual census	Ustica	Vacchi et al. (1999)
XI.1996	2	246, 297 TL	Mid-water trawl	Karatas	Başusta & Erdem (2000)
V.1996; IV.1997	55	–	Bottom trawl	Yumurtalik Bay	Başusta et al. (2002)
10.II.1998	1	200 TL	–	Termini Imerese		MSNG 49921
VI.1998–VII.1999	490	10–250 TL	Trammel net; purse-seine	Alexandria	Assem (1999; 2000)
VI–X.1999	271	20–80 TL	Surrounding net around FADs	Gulf of Castellamare (NW Sicily)	Mirto et al. (2002)
IX–XII.2000	1	222 TL	Longline	Iskenderun Bay	Cekic & Başusta (2004)
2000	1	225 TL	–	Gökova Bay	Ögretmenet al. (2005)
VII. 2000–IX. 2001	>1	Small size	Surrounding net around FADs	Koroni and Finikouda (SW Peloponese)	Vassilopoulou et al. (2003)
I–X.2001	91	Juveniles	Visual census	Gulf of Castellamare (NW Sicily)	Vega Fernández et al. (2003)	Censused around aquaculture cages
IV. 2001	>1	–	Visual census	Anfeh (Lebanon)	Harmelin-Vivien et al. (2005)
VI.2002	58	450 TL (mean length)	Purse-seine	Lampedusa	Andaloro et al. (2005)
X.2004	2	∼240 TL	Trammel net	Gaeta	Leone pers. comm. (2008)	Documented by photograph
VI.2004–V.2006	1668	85-358 FL	Purse-seine; trammel net	Gulf of Gabes	Sley et al. (2009)
03.VII.2007	1	172 TL	Trammel net	Salerno	Amato pers. comm. (2008)	Documented by photograph
20.XI.2007	2	335, 370 TL	Purse-seine	Civitavecchia	Present report	SZN-OST647
13.XII.2007	7	150–170 FL	Surrounding net	Mergellina	Present report	SZN-OST648
III–XI.2008	Several hundreds	160–405 TL	Trammel net; surrounding net	Tripoli (Libya)	Present report	Observed at Tripoli fish market
15.IV.2008	400 kg	150–180 TL	Boat-seine	Palermo	Present report	‘Neonata’ fishery
V–IX.2008	42	170–241 TL	Surrounding net	Palermo	Present report
V–IX.2008	22	171–186 TL	Surrounding net	Vibo Marina	Present report
VI–X.2008	5	∼150–180 TL	Visual census	Carini (Palermo)	Present report
VI–X.2008	4	∼160–170 TL	Visual census	Vibo Marina	Present report
06.VIII.2008	1	∼200 TL	Visual census	Scario	Present report
27.VIII.2008	1	368 TL	Spear-gun	Civran (NE Adriatic)	Dul0icic et al. (2009)
15.IX.2008	50–60 kg	180–185 TL	Surrounding net	Pozzuoli	Present report
18.X.2008	1	∼180 TL	Visual census	Serapo (Gaeta)	Present report
31.X.2008	12	95–140 TL	Hook and line	La Cala (Palermo)	Present report	Collected from the wharf
31.X.2008	6	170–220 TL	Bottom trawl	Schiavonea (Gulf of Taranto)	Present report	Collected at Salerno fish auction by Dr A. Amato
X–XI.2008	31	116–180 TL	Hook and line	Vibo Marina	Present report	Collected around tuna cages
13.XI.2008	1	∼150 TL	Visual census	Miliscola	Present report
19.XI.2008	1	∼180 TL	Surrounding net	Portici	Present report	On exhibition at SZN Public Aquarium
02.XII.2008	1	210 TL	Bottom trawl	Monte di Procida	Present report
16.XII.2008	3	170–190 TL	Surrounding net	Sapri	Present report	Collected at Salerno fish auction by Dr A. Amato
21.XII.2008	1	175 TL	Trammel net	Ischia	Present report
12.I.2009	1	120 TL	Trammel net	Monte di Procida	Present report
BMNH: Natural History Museum, London; MNHN: Museum National d'Histoire Naturelle, Paris; MZUF: Museo di Storia Naturale ‘La Specola’, Florence; MSNG: Museo Civico di Storia Naturale ‘G. Doria’, Genoa ; MZUP: Museo di Zoologia, University of Palermo; SZN: Stazione Zoologica Anton Dohrn, Naples. The symbol ‘–’ stands for: data unavailable or not furnished by the author(s).

Figure 1. Study area and location of investigated sites (see Table I for more detailed information).

Eight specimens collected within this study were preserved in 70% ethanol and deposited in the SZN zoological collections (see Table I); the remaining specimens are preserved frozen at ISPRA laboratory. Extensive literature searches, including investigations of systematic collections, registers and databases of the main Italian and foreign museums, was also carried out. With the exception of Museum National d'Histoire Naturelle, Paris (MNHN), all specimens referable to C. crysos included in museum collections were examined by the first author (PNP). Stored samples of C. crysos that were not provided with date and locality of capture on the label were excluded from this study. Old citations of the species included in general fish catalogues without indication of locality and date of occurrence were also excluded. All the data gathered (field, literature, museum collections) were summarized and used to develop a correlation analysis of the species' distribution according to latitudes and years (Figure 2a, Table I) and an updated point-map of its geographical distribution in the Mediterranean Sea (Figure 2b, Table I). To quantify the strength of the linear relation between these two variables (latitudes and years), the Pearson correlation coefficient (r) was calculated and tested for significance. Records of the species' shown in Table I are presented in chronological order along with information regarding number of specimens, size range, site of capture, fishing gear/sampling method, reference and/or acronyms of institutional depositories. In some cases (e.g. very abundant landings) kilograms were used instead of the number of specimens. Fork lengths (FL) are given when that was the only measurable parameter (due to caudal-fin damage) or when it was the only length measurement reported in the references cited.

Figure 2. Distribution according to latitudes and years (a) and geographical distribution (b) of Caranx crysos in the Mediterranean Sea. * Literature data; • museum collections; ○ present study record. Surface isotherms of February are also shown (climatological source: Bianchi 2007).

Results

A total of 130 specimens ranging from 95 to 370 mm total length (TL) and weighing between 15.1 and 620 g wet body weight (BW) were collected during this study. The biometric, meristic and morphological characteristics of all examined specimens were in accordance with descriptions of the species given by Smith-Vaniz (1986) and can be described as follows: 47–49 scutes along the straight part of the lateral line (23–39 in Caranx hippos); 9–13 gillrakers (including rudiments) on the upper limb and 23–26 on the lower limb (36–40 in C. rhonchus) of the first gill arch; spiny dorsal fin lower than the soft dorsal fin (in contrast with C. rhonchus which presents dorsal fins of similar size); the terminal ray of dorsal and anal fins closely positioned to adjacent ray (in C. rhonchus they are partially detached, forming a sort of finlet); upper jaw with an irregular series of moderate canines flanked by an inner band of small villiform teeth (in contrast with lessepsian species Alepes djedaba, which is devoid of the latter). Colour (fresh): greenish–grey dorsally with spots of golden iridescence behind the eye and on the pectoral axil; belly white, with a rose tint on flanks and dusky blotch on the upper margin of the opercle. Fins grey–yellowish and tips of caudal fin darker. Individuals smaller than 140 mm TL were generally more yellowish and juveniles occasionally presented fainted dark vertical bars on the sides (Figure 3a).

Figure 3. Caranx crysos. a, Juvenile from La Cala harbour, Palermo (photo P. N. Psomadakis); b, stuffed specimen, catalogue no. P233 held at MZUP (photo M. Sarà); c, adult from Civitavecchia deposited at SZN, catalogue no. OST647 (photo P. N. Psomadakis); d, two individuals captured at Gaeta (photo F. Leone). Scale bar: 10 cm.

During visual census investigations, no individuals were observed at Santa Marinella (north of the study area). One individual for each site was recorded at Gaeta, Miliscola and Scario, while nine individuals were censused between Carini and Vibo Marina (south of the study area). All specimens of C. crysos sighted during UVC showed an ‘inquisitive’ behaviour, approaching the diver in mid-water from the side or from the back. Sighted specimens of C. crysos ranged from 150 to 200 mm TL (estimated) and were always recorded as single individuals.

The specimens caught by surrounding nets and landed at ‘La Cala’ harbour, Palermo were mostly found together with specimens of greater amberjack Seriola dumerili. On one occasion (March 2008) we recorded 400 kg of a size-homogeneous group of C. crysos landed by a boat-seiner targeting Sardina pilchardus larvae, locally known as ‘neonata’. These specimens, averaging 180 mm TL, were captured in shallow waters while feeding on the above-mentioned fish larvae as shown by stomach content analyses of some fresh individuals just upon landing. Starting from the summer season up to October/November, the species is so abundant in this area that it can be fished by hook and line directly from the harbour's dock. Also at Vibo Marina C. crysos is mainly caught by purse-seiners targeting greater amberjack; however, in this locality the species was collected in large numbers around offshore tuna cages by hook and line. These catches consisted mainly of juveniles ranging from 116 to 180 cm TL (see Table I).

In the Gulf of Naples, the species was collected principally by purse-seiners operating in the area of Pozzuoli and Mergellina, but some catches also derived from bottom trawlers (Monte di Procida) and trammel nets (Ischia, Monte di Procida). One specimen captured alive together with a size-homogeneous group of 100–200 individuals of Trachinotus ovatus was taken to the SZN Public Aquarium, where it lived for several months. Six additional specimens coming from Marina di Schiavonea (Gulf of Taranto) and collected at the Salerno fish auction were also taken by bottom trawlers.

No Mediterranean specimens of C. crysos were found in the following institutional depositories: Stazione Zoologica Anton Dohrn, Naples (SZN); Museo di Zoologia, University of Naples (MZN); Museo Civico di Zoologia, Rome (MCZR); Museo Zoologico, University of Turin (MZUT); Museo di Storia Naturale, Milano (MSNM); Museo di Storia Naturale, Trieste (MSNT); Museo Zoologico, University of Pisa (MZP); Musée Océanographique de Monaco (MOM); Museo Nacional de Ciencias Naturales, Madrid (MNCN). Among the material examined within museum collections, one stuffed individual held at the Museo di Zoologia, University of Palermo (MZUP), catalogue no. P233, Palermo, 1884, and labelled as Caranx dentex (synonym of Pseudocaranx dentex) was re-identified to C. crysos. The latter, measuring 505 mm TL (450 FL), is to be considered the largest specimen officially recorded in the Mediterranean Sea (Figure 3b). One cleared and stained specimen (MZUP, catalogue no. AN311, Palermo) belonging to the great Doderlein collection of fishes from Sicily (1862–1892) and labelled as C. dentex was also re-identified to C. crysos. Furthermore, one specimen from Haifa held at the Natural History Museum, London (BMNH), catalogue no. 1935.3.5.21 labelled under the name of Caranx fusus (synonym of C. crysos) and mentioned in Tortonese (1952, 1961, 1975), was re-identified to Alepes djedaba.

With regards to statistical analysis, the linear relationship between the two sets of variables (latitudes and years) extrapolated from records (n = 59) of C. crysos in the Mediterranean, showed a significant negative correlation for the years interval 1867–1965 (r = –0.76, P < 0.01) and a significant positive correlation for the years interval 1993–2009 (r = 0.42, P < 0.01).

Discussion

The presence of Caranx crysos in the southeastern Mediterranean is well-documented in the historical literature and from museum records (see Figure 2 and Table I). At present, the species is commonly found along the entire Levantine coasts of Israel (Golani 2005) and Turkey (Bilecenoglu et al. 2002) up to Fethiye Bay (36°37’N) becoming progressively rarer northwards (Bilecenoglu, personal communication, 2008). Records from the Aegean Sea are concentrated in the southern and central sectors (Papakonstantinou 1988 and references therein included).

In Greek waters, the species seems to have reached the southwestern Peloponnese coast (Ionian Sea) as demonstrated by studies conducted by means of fish aggregating devices (FADs; Vasilopoulou et al. 2003). In the southeastern regions of the Mediterranean, C. crysos is common in Egypt (Assem 1999, 2000) and also in Libya, where is caught mainly in Missurata (Sirt Gulf) by surrounding-nets all year round (Lamboeuf 2000). The species has recently established along the entire Tunisian coast (Bradai et al. 2004), where it can be found with other thermophilic carangids in purse-seine and trammel net landings (Ben Souissi et al. 2005; Sley et al. 2009). Available bibliography exclude the historical presence of C. crysos from Algerian waters (Dieuzeide et al. 1953). The species is presently unknown to investigators working on the Algerian ichthyofauna, but it cannot be excluded that occasional catches may have occurred during the last few decades (Hemida, personal communication, 2009). As with other checklists and technical reports, most of the aforementioned references were useless for the purpose of this compilation due to incomplete capture data. Nevertheless, occasional trips of the first author (PNP) to Tripoli (Libya) confirm the presence of this species in Libyan waters and document its massive presence also at Tripoli, which stands several miles northwest of Missurata.

In contrast with the southeastern sector, the central and western Mediterranean are poorly documented with historical records of this species (see Figure 2 and Table I). With few exceptions, as in the case of one contemporary individual coming from Termini Imerese (Sicily), catalogue no. 49921 held at the Museo Civico di Storia Naturale ‘G. Doria’, Genoa (MSNG), all other samples preserved in institutional depositories investigated during this study are still represented by the material examined by Tortonese (1952, 1961, 1975). Discounting the questionable records from Nice and Genoa, based on old museological material lacking indication of date of capture, the Civitavecchia specimens of C. crysos presented in this paper (Figure 3c) along with the single individual recently documented at Civran along the Croatian coast (Dul0ic et al. 2009) represent the most northerly records of the species in the Mediterranean Sea. The parallels passing over Civran (45°16’N) and Civitavecchia (42°05’N) are well above that which goes through Palma de Mallorca (39°34’N), where the only reliable captures of this species in the Mediterranean northern sectors have occurred (Barceló 1868; Riera et al. 1995). Historical records of C. crysos exist for some localities of Sicily, including Palermo and Messina (Tortonese 1952). Since this species was considered very rare for the seas of Sicily (Doderlein 1878), its elevated abundance and frequency documented during the last decade (D'Anna et al. 1999; Mirto et al. 2002; Vega Fernández et al. 2003; Addis et al. 2006) may be indicative of a northerly shift in its distribution. No contemporary or historical published record of this species can be found for the central Tyrrhenian Sea. Its presence in this area is attested only by a dated specimen from Naples preserved in the systematic collections of Museo di Storia Naturale ‘La Specola’, Florence (MZUF). However, during our field investigations, the species was collected in different landing sites from the Gulf of Naples (Monte di Procida, Pozzuoli, Ischia, Mergellina, Portici) and readily recognized by local fishermen who referred to it under the vernacular name of ‘sauro-ricciola’, obtained by merging local names used for the horse mackerels Trachurus spp. (‘sauro’) and the greater amberjack Seriola dumerili (‘ricciola’), respectively. In the Latium Maritime district, the species is less well known and besides the Civitavecchia record presented in this study, the only captures of this species are represented by two specimens taken at Gaeta and photographed at the local fish auction on October 2004 (Figure 3d). The absence of C. crysos from historical fish collections (SZN, MZN, MCZR) and regional fish catalogues (Costa 1871; Vinciguerra 1890) supports the hypothesis of a recent expansion of this species into the Tyrrhenian Sea as remarked by the interviewed fishermen. Inadequate sampling methodology may be invoked to explain the scarcity of historical records of C. crysos in the Tyrrhenian Sea, but surrounding gear (which is considered the most appropriate for this species) have been traditionally used either in the central (Targioni Tozzetti 1871) or in the southern sectors, including northwest Sicily (D'Anna et al. 1999). Above 40°50’N (the parallel passing through Naples), the species is very rare and occurs only sporadically, probably in the form of erratic individuals following drifting objects. Besides the single records given by Barceló (1868) and Riera et al. (1995) at Palma de Mallorca, no other reliable occurrences of this species can be found for the Spanish Mediterranean waters. The rarity of C. crysos in the Balearic Islands was confirmed by recent studies using FADs, in which the species was never found (Deudero et al. 1999; Massutí et al. 1999; Riera et al. 1999; Deudero 2001; Addis et al. 2006). Similarly, the species was not found during investigations carried out around offshore buoys in western Sardinia (Addis et al. 2006) and in the Ligurian Sea (Relini et al. 1994, 2000).

The new distributional records of C. crysos for the central Tyrrhenian Sea presented in this study could indicate a displacement of the northern limit of the species range possibly attributable to the ‘tropicalization’ phenomenon presently occurring in the Mediterranean. The recent findings of authochthonous (Psomadakis et al. 2006, 2008a, 2008b) and allochthonous (Psomadakis et al. 2009) thermophilic fish species in the central Tyrrhenian Sea seem to support this idea. Also, the six specimens captured off Marina di Schiavonea in the Gulf of Taranto constitute a new distributional record for this species since no mention of it is made either in national (Tortonese 1975) or regional (Pastore 1976) fish inventories. Apart from the Civran (Dul0ic et al. 2009) and Civitavecchia (this study) records, the present distribution of C. crysos in the Mediterranean Sea (see Figure 2b, Table I) fits quite well within the limits of isotherm 14°C for February (the coldest month in the year), claimed to be the northern boundary for Mediterranean warm-water species (Bianchi 2007). A possible mechanism that could explain the extension of tropical affinity species in colder sectors of the western Mediterranean may be found in the changing surface circulation pattern in the Ionian Sea (Bianchi 2007). According to Briand (2000), the Eastern Mediterranean Transient (EMT) that produced a drastic inversion of surface currents in the Ionian Sea could also have affected the western Mediterranean. At present, it is not possible to correlate changes in species distribution with EMT; however, around 1990, many southern species moved northwards (Bianchi 2007) and, as shown in Figure 2a, C. crysos may be included among the latter. This idea is confirmed by a notable increment in the number of individuals of this species documented in published records during the last 20 years (see Table I). However, the graph in Figure 2a also shows a southerly contraction of the species distribution during the time span 1867–1965, suggesting that northerly shifts in range expansions may have occurred on a cyclical basis, as already remarked by Bianchi (2007) for other thermophilic species inhabiting the Mediterranean. The increase of floating objects like buoys used to delimit Marine Protected Areas (MPAs) and cages for coastal aquaculture, which seem to attract this species (Andaloro & Rinaldi 1998; Vacchi et al. 1999; Vega Fernández et al. 2003), could have contributed to its northerly spread in the Mediterranean providing adequate conditions for recruitment and survival of young fish also. Whatever the reason(s), some sort of large-scale hydroclimatic phenomenon must have taken place in order to explain the simultaneous northward spread of eastern Atlantic (see Brito et al. 2005; Wirtz et al. 2008) and Mediterranean (present study) populations of C. crysos during the last two decades.

Acknowledgements

The authors wish to thank C. Zazo (Servizio pesca SZN), A. Daiola (La Cala harbour, Palermo), S. Biada (Civitavecchia) and A. Amato (AUSL Salerno) who provided specimens of C. crysos for this research. Many thanks also to F. Leone (AUSL, Latina), M. Corsini-Foka (Hydrobiological Station of Rhodes), M. Bilecenoglu (Adnan Menderes University, Aydin, Turkey), F. Hemida (Ecole Supérieure des Sciences de la Mer et de l'Aménagement du Littoral, Algiers, Algeria), F. Costa (Messina), S. Di Muccio (ISPRA, Rome) S. Petrilli (Sapri) and A. Abubaker (Tripoli, Libya) for sharing with us information regarding this species and to S. Lomiri (ISPRA, Rome) for laboratory support. Thanks are also due to M. Bottaro (ISPRA, Rome) for helpful suggestions. Many thanks to staff members of SZN Library service and to A. Romanello (Accademia Nazionale dei Lincei, Rome) for helping with reference search. We are grateful to the following museum curators for making available systematic collections: G. Doria (MSNG), S. Vanni (MZUF); M. Sarà (MZUP); N. Maio (MZN); E. Gavetti (MZUT), M. Capula (MCZR); M. Podestà (MSNM); G. Carnevale (MZP); M. Bruni (MOM); J. Maclaine (BMNH), G. Solis (MNCN). This work is dedicated to the everlasting memory of Giulia Psomadakis.

Notes

1. Following submission of the present paper, the first record of Caranx crysos in the Adriatic Sea (Dul0ic et al. 2009) was published.