Boll. Mus, lst. biol, Uniu. Genoua,58-59: 181-197,1992-1993 Q994)
SOUTHERNSPECIES IN THE LIGURIANSEA (NORTHERN MEDITERRANEAN): NE T RECORDSAND A REVIE\í.
SPECIETERMOFILE IN MAR LIGUR-E: NUOVE SEGNALAZIONI E REVISIONECRITICA CanroNme BieNcHr'& C.q.m-q.Monru' ENEA-CRAMS.Teresa, CP I-19100La Spezia ' 316, lsrituto di Zoologia, Università, via Balbi 5,1-76726 Genova
ABSTRACT A total of 20 epibenthic species, which can be qrralified as waÍn-water elements, are reponed in the Ligurian Sèa. Their increased occlrrence in the last few years deserves attention as a po*ible biological effect of climatjc change and conseqúent sea water warming.
Kny wonos Marine biogeography, dispersal, climatic change, benthos, Ligurian Sea,Mediterranean 5ea
INtnoouctloN From a biogeographical standpoint, the Mediterranean Sea constitutes a well-defined unit (Bnrccs, 1,974;Yvnrv.ErJ, 1980). Nevertheless, the vastness of the basin, its tormented geological history (Mar-ooNeoo, 1985), and the many climatic and hydrological influences upon it, caused an obvious differentiation within the marine biota of this sea (CIESM, 1981; ?ÉtÈs, 7985; Tonrorunsr, 198). Thus, up to ten different "biogeographical sectors" are usually distinguished within the Mediterranean (PÉnÈs& Ptceno, 7964; Fneot, 1974). As a whole, the major differences in species composition and community physiognomy occur alorrg a North-South axis. The Tyrrhenian Sea is the sector inhabited by the most typical Mediterranean flora and fauna, with most endemic species and Argnntt 9pE rl"E oceanc by TeI 4 Liguria 5 ?*^ and D, tl z 7 \\ Tyrrher ,g (Casrsr !r 2 ú of occurf( k LIGURIAN SEA have alway I "therm
^:r^^ ,\ ò l LC), thanks o1o ) 7, In t. TUSCAN freque presen c411 them t oencutptteGo to criti, F frame' o 12$ o È Mernp.t CORSICA i-t War z routln N a scient: TYRRHENIANSEA i. ENEA I Cafflel Archip IÈ:: i aimed ì transe, i ':5r4,;;ffiî;:t"n{',;;##,l';*rt;er years i,. (Gulf i[*3,']*fl#t'rs,.';if#i:àq1'fr ponofino (incruding Rapallo,and ó;;;ì;,;';;à"ò,^n"r, ij camogri, surt of the è#;;'iir;i;àì;; (incluAingTino) and coastnear La i of Tigulio); 6) punu pt^n^rir'll èinq,-r.î.r", 8).islands Lig 10) Capraia;tr) Élba;12) Giglio "!, ép"iir,'qiLghorn: i' BltNcr fì the pr percentage of i Atlantic-Mediterranean elements, plus a fairly high ì affinities' The Ligurian Sea' situated to the R-Esur-r 6;;;t with subtropical li by a very marked if .rtrln, is colder, ànd thus characterized At and by the presence of some diminution of the subtropical element :: water l;"À cold-temperate wat^ers which seem to be missing #;;l;; (Rossr, 1969; literatr elsewhere. This gives thfo tigurlan Sea a boreal affinity AreEnrerlr et al., 1981; CerreNEoVmrn et al., 1988). The physical oceanography of the Tyrrhenian and Ligurian seas is summarized by T,rrr (1985), whereas a closer view of different aspects of Ligurian Sea oceanography can be found in FeNuccl et al. (7990) and DecNrNo et al. (1990). The biogeographic boundary befween Tyrrhenian and Ligurian Sea can be set at the Tuscan Archipelago (Cesrnru et al., 7988; Lenolcct et al., 7990) (Fig. 1). Of course these kinds of boundaries are never sharp, and occurrences of southern, warm-water species in the Ligurian Sea have been reported from time to time. Such occurrences have always been explained as being tied to the presence of "thermophilic oases" (Tonroxnse, 7958; S,q.ne,1985) at particular sites, which were supposed to enjoy warmer local conditions thanks to topography and shelter from cold northern winds. In the last few years, we found some of these speciesto be more frequent and widespread in the Ligurian Sea than expected. The present paper is intended to report these findings, and to review them together with literature data. Fin:rlly, an attempt will be made to critically discuss the occurrence of warm-water species within the frame of different hypotheses.
MemmersAND METHoDS 'Warm-water species in the Ligurian Sea were observed during routine environmental monitoring work done by the diving scientists of the Centro Ricerche A:mbiente Marino (CRAM) of ENEA in S.Teresa(La Spezia). Periodical SCUBA diving cruises are carried out every year in different sites between the Tuscan Archipelago and the western Ligurian Sea. Underwater work is aimed to survey epibenthic communities and uses mainly line- transects(BnNcHt et al., 1,997).The principal survey areas in recent eorterranean, (\Testern .rchipelago). years have been: Gallinaria Island Riviera), Portofino Reroeooi.Zl (Gulf of Genoa), the islands and coast near La Spezia, and some allo,and gulf coast near La of the islands of the Tuscan Archipelago. Ligurian Sea records of southern species from the literature (see BnNcm et al., 7987, for references) are also taken into account in the present paper. entage of .ed to the Rlsulrs marked : of some A total of 20 benthic species, which can be qualified as warm- : missing water elements, have been observed by ourselves or quoted in the rssr,19ó9; literature. A number of mostly pelagic fishes, more frequently seen in the last three years than ever, have been added to these by Regularly BnNcsI & Monnr (199ù: in this paper, however, we shall discuss (Tuscan 1 exclusively epibenthic species, including reef fishes. Species are reaching referred to in alphabetical orcler within higher taxa, MnrNasz(- listed a se Algae century it noted that Acrotbamnion preissii (Sonder) \lollaston - Found at Gallinaria Pseudo Island, September 7997, on dead Posidonia mats and on stony Capraia Is bottoms, B to 15 m depth. A. preissii is an Indopacific species first Bergeggi i discovered in the Mediterranean near Leghorn (CNerrr & SaRrolu, 1989 r, 196D. Its distribution and ecology in this sea have been recently Q6 m), af Ga summarized by CrNrrrr et al. (7984). rocky wall Caulerpa prolifera (Forsskàl) Lamouroux - Mentioned as the last fiv abundant in the late 50s near Portofino (TonroNrse, 1958, 1962), it on all wes was not found in the BOs,alrhough actively sought (Monrr et al., 1988). However, it was found again in the summer of 1,991(Tur.rnsr & VeccHt, in press). C.prolifera is a warm-water species reaching Sponges its northern limit in the Ligurian Sea, where it was considered by Axinell (1980) Menesz to be in a state of regression. 2fì eX-tf€fTìr - Cystoseira spinosa Sauvageau Found at the Island of Bergeggi 35-40m d in June 1988 and at Gallinaria Island in September 7997; in both 33 m), in cases on dead Posidonia mats, at about 10 m depth. According to occurrenc( GnccoNr & BnuNr(1973), this species can mainly be found in the detailed lir southern part of the Mediterrzlnean. experience - Dasycladus uermícularis (Scopoli) Krasser Found on coarse Southern biodetritic sand at 20 m depth at Gallinaria Island, in September warm-wai( 7997. D.uermicularís is an element of tropical Atlantic origin, Guinea: ir never found before in the Ligurian Sea. According to CrNrru species,4 (7979), the growth of Dasyclad.us in the northwest Mediterranean considerec is restricted to the first few meters depth: the present record, about the r therefore, is to be considererJ not only as the northernmost, but also as particularly deep. Galaxaura oblongata (Ellis & Solander) Lamouroux - Rather Cnidarian common in several sites of t]allinariz- Island in September 7997, Astroid( between 5 and 15 m depth on rocks among other algae. Also seen was founc in July 7992 ^t 10 m at Tino Island (near La Spezia). Regularly seen Scoglio di in the last five yeaîs at Giglio Island (Tuscan Archipelago). G. possiblyit oblongata is a circumtropical species (PapeNnusset al., 7982), the subsec previously found in the Ligurian Sea at Portofino (fonroxEsr, 1958). southern i Its thermophilic character was underlined by Tonromsn (t962). Ibero-Morc Penicillus capítatus Lamarck - Found at Gallinaria Island in Naples,ar September 7991, on dead Posidonia mats, at 10-15 m depth. Island, i.e. C to these by Regularly seen in the last five years ar.Elba and Giglio islands : shall discuss (Tùscan Archipelago). P. ca.pitatus is a tropical Atlantic species, ;, Speciesare reaching the nortÉern limit of its range in the Mediterranean. VtrrNnsz-(1980)reviewed its distribtrtion in the Ligurian Sea and listed a series of historical records, concluding that in the present century it appears to have become rarer (however, it should be did his researchin the seventies). I at Gallinaria noted ihat Meinesz pseudocblorodesmis (zanardini) Boergesen - Found at ind on stony furcellata Island in Seprember 1985 r.l m depth), at the Island of c speciesfirst capraia 1988 (2-15 m), at Paraggi (near Portofino)^in June -u & Sanrom, Beigeggi"d6 in June "t Portofino in April 1997 06 m) and Jtiv 7993 (6'5 reen recently Dl9}t *i m), at Gallinaria Island in Septemhrcr 7997 (7-11 m), always on walls. Regularly seen ar cigho Island (Tuscan Archipelago) in entioned as .*t v the last five years. P..furcellata is a circumtropical species common 958, 7962), it western Mediterranean coasts (Mewasz, 1980). (Monm et al., on all 1991(TuNnsr :ies reaching Sponges :nsidered by Axinella potypoides schmidt - w'e discovered in September 1991 an exrremety rión population of this species at Gallinaria lsland, at I of Bergeggi (30- 35-40 m depth, and ànother small p'pulation at Punta Manara 991;in both rhe .a ù, in July 1gg3. TonroNnsr (1g58) was the first ro norice Accordingto occurrence of A. poljpoides in the Ligurian sea. Up.tz(1982) gives a found in the detailed list of iti reòords in the Mediterranean. According to our experience, this species seems to be by far more abundant in the d on coarse southern Italian seas (e.8., Sardinia, epulia). A. polypoides is a r September warm-water species ranging from the Mediterranean to the gulf of ìntic origin, Guinea: in the north-eatt Atlantic it is substituted by the sibling g to crNELu soecies A. dissimills (Bowerbank), which has sometimes been editerranean c'onsidereda synonym (see DoNaorv et al., 1985, for a discussion ;ent record, about the distinction between the tlvo species)' rrnmost,but ux - Rather Cnidarians :mber 1991, Astroid.escalycularis (Pallas) - A ,Jead colony of a-dozen polyps deep at e. Also seen was found in September 7989 uncler a overhang 6'5 T gularly seen Scoglio di Mezzo Franco (Giglio Island, Tuscan Archipelago): pelago). G. porJibly it settled in one of the prerzious years, but did not survive al., 7982), ihe subsequent winter. A. calycularis is a rypical and well known >ilnss,1958). southern épecies, thriving ln the s;outh-west Mediterranean and 1962). Ibero-Moroècan Gulf. The northern limit of its range is the region of a Island in Naoles. and it has never been found alive north of Ventotene i m deprh. islind, í.e.about 4Oo4B'N(Zrenovlus, 1980)' Halocordyle disticba (Goldfuss) - Although the hydroid fauna of Cn'tstacet the Ligurian Sea has been well past (see studied in the Bonno & Calcir Fnrsr, 1986, for references), this was species found only once: species i Rapallo (near Portofino), 1948 (Rossr, 7950: June Pennaria d.). k depth. C seems to have become more freouent in verv we recent vears: Sea,but heard of its occurrence at C<>goleto(near Genoa) in the summer of C. ornati 1988, and we saw it at Tino Island and in other sites of the Gulf of typical th La Spezia in August 1987, July 1989, July 1990, July 1992, and October 1993, as well as at Portofino in 7993, always on rocks July Ecbinod.t in shallow waters (3-9 m clepth). H. disticha is a circumtropical Centr, species which can be seen in the southern Mediterranean during summer (Momr & BoeRo,19iì6). Portofinc Ligurian Pbyllangia moucbezi (Lacaze-Duthiers) - A living colony was the 70s ( collected in November 1992 aL 35 m depth at Gallinaria Island knowler (Monnr, I99ò. Another colony was found at 28 m depth at Tino Meditert Island (Gulf of La Spezia) in November 1993. Previously recorded in member the Ligurian Sea by Rossr(1957: Coenocyatbusm.), P. moucbeziis App considered by Zrenowus (1980) to be almost absent from the colder Sea. parts of the Mediterranean. since 19 longispir could b Molluscs transpofl Cbaronia lampcts lampas (L.) - We heard of the occurrence of Chae this species on two occasions: in the late 70s, at Quarto (near Septemb Genoa), and the late 80s near La Spezia. DE Loxcrs (1987: as C. at about rubiconda) reports a fincling ai San Lorenzo, near Imperia. consider Tnr,rplt*qDo(I99I) summarized. the distribution of Ch. l. lampasin the in the L Mediterranean: it occurs only in the western basin, being rare in the (P,c,sroRI northern sector. According to Russo et al. (7990), the specimens found in cold areas may be rlerived from allochtonous larvae, since This Ìast Cb.l.lampas has a planktonic, long-term, free-swimming larva that the (teleplanic). misinterl Patella ferntginea Gmelirr - \7e found this species to be very Hace comrnon at CapÍaia Island (Tuscan Archipelago) in the summer of April 19 "Í 1985.It has been reported from the Ligurian Sea proper only fwice, calied and only in very recent years (De LoNGrs,1987; Poncunoou & Capraia Mnrru., 1991).ln an older str,rdyof the species of Patella in the gulf depth. I of Tigullio (east of Portofino), Zornzzt (1942) did not menrion it. this thet According to PoRcHEDou& Mnena (1991), who also provided a several distribution map, P. ferruginea is a warm-water species which & Caxu, entered the Mediterranean during the Riss-Wrirm interglacial apparen (Tyrrhenian II), and is now threatened with extinction also because (Tonror of human harvesting. \992. fauna of Crustaceans Bosno & Calcinus tubularis (L.) - We reccgnized a specimen of this Llyonce: in a vermetid tube at Gallinaria Island, 7992, 3 m ia cl.). k species June C. tubula4s is widely spread throughout the Mediterranean ears:We depth. but more common in its southern parts (Znnowlus, 1978: as rmmerof Seà, C. ornatus). PÉRES& Ptceno (7964: as C. ornalzs) consider it as a : Gulf of thermophilic element. )92, and rypical on rocks ntropical Ecbinoderms (Phl\íppi) - at n during Centrost@hanus longispinus We saw a specimen Portofino i[June 7990 at about 30 m depth. Its occurrence in the of ony was Ligurian Sea was discovered for the first time at the beginning (1991) a Island thè 70s (Tonroxnse, 7975a). Fnexcoun updated and analysed in the at Tino knowledge about the distribution of C. longispinus the only orded in Mediterranean, confirming the thermophily of this species, Mediterranean utcbeziis member of the tropical family Diadematidae in the in the Ligurian Sea re colder Sea. Apparently it has become more colrurlon since i995. Francour assumed that Ligurian specimens of C. longispinus arise from a distant zone of reproduction: the lawae .orrld be emitted in the south of Italy (Naples, Sicily) and be transported by the "Liguro-ProvenEal' (lurrent. rence of Cbaetuster longipes (Retzius) - This species was discovered in to (near Seotember 7997 at Galbnaria Island and turned out to be abundant 7: as C. at about 40 m during subsequent dives in 1992. TonroNssr 0957) mperia. considers C. longipes to be a thermophilic species: previous records esin the in the Ligurian Sea date from 7956 (TonroNrse, 7957) and 7964 re in the (Pesrozuxó & Ce.Nu,196r. However, it is perhaps an infrequent eclmens species also in the rest of the Mediterranean (TonroNnse,19(r5a). le, stnce This last opinion is shared by Zrnnowlus(1991), who expliciry states ró tatvd that the presumed thermophily of C. longipes is likely to be a misinterpretation. be very ttacétta attenuata (Gray) - \7e sa'w this species at Portofino in "coralligenous" nmer of April 1991, at m depth on the bottoms of the so- 37 "Formiche" y rwlce, càtl"d "Seccadell'Isuelo". It was very common at the of Eoou & Capraia Island (Tuscan Archipelago) in September 7985, 75-20 m the gulf depth. Tonromrsr (195D was the first to notice the occurrence of ntion it. this thermophilic species at Portofino: his records were confirmed vided a several times in subsequent years (e.,9',TonroNESe, 1962; PasroruNo ; which & CaNu, 196r. Although the Portofino population of H. attenuata is rglacial apparently persistent, ilts presence also at Gallinaria Island in 7957 because (iònrontsB, 1953) was not confirmed by our searching in 7991 and 7992. do not aL - Opbidiaster opbidian.us (Lamarck) A specimen of O. specÍnenl (Tuscan opbidianus was found at Capraia Island Archipelago) in no infom the summer of 7985 at 15 m depttr. In the Ligurian Sea proper, it no real l has been found around Portofino promontory in 1896 and 7956 scattered (Tonroivess, 195D, and in 1964 (PasroRINo& CRNu, 1965). O. speclesgl opbidianus is a thermophilic species of east tropical Atlantic origin, Algae which in the Mediterranean is more frequently found south of beginnin Naples (TonroNess, 7965a). reference diving ir Fisbes warm-wz Sparisoma (Euscarus) c'retense(L.) - Three specimens (green in southt phase) were observed in September 1991 at Giglio Island (Tuscan Some Archipelago) on rocky bottoms less than 10 m deep. S. cretenseísa rather t2 subtropical east Atlantic and south-eastern Mediterranean species findings (TonroNnsn, 1975b), not kn(lwn in Italian seas north of Sicily (BtNt, previous 1968).lt reproduces from liugust to October and has floating eggs the casr (TonroNEss,I975b). Cbaetasi Tbalassoma pauo L. - The first time we saw this species in the How' Ligurian Sea was in September L991 at Gallinaria Island, in very records shallow waters (1-3 m depth). In the sumrner of the same year it unquest had been seen at Portofino by amateur divers, and in October 1985 studied it had been encountered in the Cinque Terre, not far from La Spezia 1965b, 1 (RerrNr et al., 1988). We met it again in the summer of 1992 recogni, (Gallinaria) and 1993 (Portofino). Previous records in the Ligurian 1gg3.rt Sea were very scarce: one r;pecimen in December 1902 at Camogli, the intt near Portofino (TonroNnsE& TRorrI, 1949), and two in l9II at photogt (1973), Portofino (TonroNesn, 1965b). According to KLAUSEvnz have be Thalassoma is a postglaciai tropical invader of pre-Mediterranean- explain Tethys origin. In the Mediterranean Sea it is by far more common in case ol rhe southern part (BrNr, 1968; ToRroNesn,1975b). High temperatures reliabili are crucial for the sexual maturation of the species and possibly of soutl (BIu, reproduction does not occur every year 1p6B): we saw mature Disc and September 1992, males only rwice in the Ligurian Sea Qune saltatri pauo to reproduce in and Gallinaria Island). T. is known June July and ea, and has pelagic eggs (Tonrt>Npsn,1975b). hypoth w'e ar( DrscussroN deservr The main problems in discussing records of southern species in talkinS the Ligurian Sea are the sparsenessof the data and that many of the ToRrol records, especially the old ones, are incomplete. It is often Russo impossible to know exactly the year of occurrence of a certain Centro species, because authors ol' systematic and/or floro-faunistic works how long before publishing they collected their nofO. do not always state Similarly, tindings of the adults of ìongliving species give 'lago) in specimens. about the exact year oî settling. There is, unforn:nately, 'roper, lt no information series of surveys. The data are very irregularly nd 1956 no real historical rather 'random'. In manl' surveys, the recording of a t65). o. scattered and reflects the presence of a relevant specialist! : origin, speciesgreatly instance, have been poorly studied since the outh of Algaè, for beginning of the present century (see BannnRISel al., 7979, for reférencei). However, we have fifteen years expeiience of scientific diving in the Ligurian Sea and we never saw, before 1991, the warm-water species listed above, although we regularly saw them ( orcen in southern ltaly in those years. (Tuscan Some of the presumed warm-water invertebrate species are tnseis a rather rare and localized even in the Tyrrhenian Sea: thus, new species findings may not be clues to recent settlings,but simply records of (BrNr, iy previously overlooked populations. This could be true especially in ng eggs the case of the sponge Axinella polypoides and the sea-star Cltaetaster longipes. s in the However, many of the records remain of great interest. The records of the oînate wrasse, Tbalassoma pauo, appear year it unquestionable. The Ligurian Sea fish fauna has been adeqr-rately ,er1985 studied since the beginning of the 19th century (see TontoNEse, r Spezia I965b, for references). Tbalassomais a well known fish, easy to >f t99z recognize: it has been found in 7902, 7977, 1'985, 799I, 7992, and Ligurian 1993. lt is difficult to believe that it w:ls present but overlooked in ìamogli, the intervening years. It is a preferred subject for underwater 7977 at (197r, photography, and many'photographic fish-hunting' competitions every year in Liguria since the sixties: how can we ranean- have been held that nobody noticed it, if it was present?Thus, at least in the rmon in explain we can grant these data with a certain 3rafures case of Tbalassoma, examples r:f periodical range exlension rcssibly reliability and take them as Ligurian Sea. mature of southern speciesinto the Ligurìan Sea of Pomatomus r 1992, Discussing the expansion in the saltatrix, a pelagic warm-water fish rnore abundant in the south nd July and east Mediterranean, TonroNesg(1954) suggested two different hypotheses to explain such periodical tange extensions. Although -é are deallng with benthic species, Tortonese's hypothe.ses deserve to be taken into account, since the benthic species we are lcles m talking about have pelagic eggs, larvae, or propag'tla (e.8., r of the 1975b: Sparisoma cretense and Tbalassoma pauo; ; often TontoNrsn, Cbaronia lampas lampas; FneNcoun,7997: certain Russo et al., 7990: nu s: etc.). works Centrostepba n us longispi The first hypothesis stated that an abnormal and relevant j- numerical increase within its normal range caused the expansion of the species even in seas where formerly it seldom occurred. .'l Random increasesin population density due to intrinsic factors are well known in many animal species, and thus such a hypothesis has been invoked in many cases. It could also explain the 16-1tI o"lfl 11 occurrence of Tlsalassom(tpauo in the Ligurian Sea. However, if P we accept that range extensions have simultaneously occurred for others of the species we disrcussedabove, this hypothesis does not ru-]I\ seem tenable anymore. \ The second of Tortonesie's hypotheses stated that changes in -J i/ environmental condítions, chiefly in temperature, favoured diffusion northwards. This hypothesis appears to be more 14]] plausible when many species are involved simultaneously, and 1830 attractive due to the present concern with the biological effects of climatic changes and global warming (Bpruoux et al., 7990; Sournwano& BoercH, 799r. Fig. 2 - Trt Analysing Ligurian Sea temperature data from the hydrological moving a data bank of ENEA-CRAM (BnuscHI& ScoRatNI.1986), Copeno Obsen'xtol (1992) found evidence of cyclic changes in the period 7957-1980, - for instance - a minimum in 1969-71' and fwo maxima in witlr Bein 7958-62 and aL the end of the 1970s. satellite Unfortunately, historicrll, long term data on inshore water this war temperature of the Ligurian Sea are not available. However, air Ligurian temperature data have been collected since 1833 by the along t Meteorological Observatory of Genoa (FroccutNt et al., I9B3), and enrapp we can assume that surface water temperatures in the coastal zone are reasonably correlated with mean annual air temperatures PIcCO, hypotht (Souruwnno et al., 7988). souther From the analysis of air temperature trend it can be easily seen in estal that climatic fluctuations are evident, warmer periods alternating 1968;F with colder ones, although in a rather irregular manner (Fig. 2). 'pseudr Smoothing the data by mo"ring averages over eleven year periods restore( (Sormrwnno et al., I97), the well known warming in the thirties Asa and Forties(CusurNc & DrcrsoN, 1976) can be easily recognized. of Astmror & Gespe,ntNt(7992) gave evidence that the so-called Sea variabt "Tyrrhenian current", flowing northwards berween Tyrrhenian and permar Ligurian seas, exhibits great variation on a year to year and i seasonal basis according to atmospheric-climatic conditions. This could po w'arm Tyrrhenian current is the carrier of long-living pelagic this Iawae, eggs or propagula of southern species: due to variations in Liguriat current intensify, the arrival of allochthonous \arvae ("supply-side": scafclty LEwN, 1986)would be strongly affected by climatic fluctuations. not onl levant rnsion :urred. )rs are )ihesis n the o16 ver, if ed for esnot
Ò-,.-oF s '^-in oured more 14 r, and 1830 1850 1870 1890 1910 1930 1950 1970 --ctsof yeors 1990; oC) - Fis. 2 - Trend of aif temperature (annual means, at Genoa, 1833 fo 1993 Bold line logical --o"lrg averages over'eleven-year periodS. From the data oî the Meteorological Observatory of Genoa. '-1980,3PELLO rma ln Being warmer, Tyrrhenian water can be easily recognized in satellite lnfra-red thermal imagery (Fig. 3): entering the Ligurian sea, waf er this warmer current is pushed against the coast by the rather steady gyre (Asrnerot et alj 1980). it flows westwards r\/ lhf: Ligurian-Provengal the coast, and apparently there it remains somewhat ,), and ulóng entrapped (see also the surface temperature maps produced by I zone 'termophilìc Prccó,-1990), perhaps forming the coastal oases' atul'es 'termophilic hypothesized in the pasr. once arrive
AKNOW'LEDGE Thanks are accomplishment occurrence of IZ G.F. Russo(Ischi southern (or prel temperature data ancl unpublishe unpublished rest Spezia) gave inf< Ligurian seas,an( AJ. SoL"rH'ùrARD( suggestions,also the late Prof. ENr
Il mar Ligun flora e fauna; tl alcune occasioni alghe, 11 invertr letteratura. La pr può essere dovr-r fluttuazioni clim temperarura ed i
1ù7ithrespec biota has a bore Ligurian Sea has epibenthic spec together with lit the last fèw yea the individual F-ig.3 ' Satellitc intra-red riremul imagt:ry of the nc.rrthwesternMecliteffanean Sea (AVHRR NOAA 9, March 28th, 198ó). The whites: areas are the warmesr. Historical series hypothesis.
in occurrence of southern species observed in recent years in the Ligurian Sea, therefore, deseives attention as a possible biological effect of climatic cl-rangeand consequent warming of sea water already hypothesized for the northern Mediterranean by Beruorx et at. (1990). AKNOVLEDGEMENTS Thanks are due to the many people whose help has been crucial to the accomplishment of this study. S. ScoRBINI(La Spezia) first drew our attention upon the occunence of ThalassomaPauoin the Ligurian Sea. M.C. Bure (Ischia), M. PANSINI(Genova), G.F. Russo (Ischia), and H. ZrBRoMus (Marseille) provided references of literature on several southern (or presumed so) species. P. Plcco and A.M. Derrm (Genova) kindly provided air temperature data from the Meteorological Observatory of Genoa, including the more recent and unpublished ones. G. Mexzrrrl (La Spezia) gave advice and let us known the unpublished results of his elaborations of Ligurian Sea hydrological data. G. Gesperrm (La Spezia) gave information and bibliography about water exchanges between Tyrrhenian and Ligurian seas, and put at our disposal the satellite infra-red thermal imagery AVHRR NOAA 9. AJ. SoLTTHvARD(Plymouth) critically read an early draft of the manuscript and made useful suggestions, also providing dala and literature references. \7e dedicate the present paPer to the late Prof. ENFrcoToRToNEsE, the father of Ligurian Sea biogeography. RrassuNro 'fredda' Il mar Ligure si differenzia dal mar Tirreno per una maggiore affinità della sua flora e fauna: tuttavia, la presenza in mar Ligure di specie termofile è stata segnalata in alcune occasioni. I rinvenimenti recenti di una ventina dí specie termofile epibentiche (7 alghe, 11 invenebrati, e 2 pesci di scogliera) venSono discussi criticamente con i dati di letteratura. La presenza di specie termofile sembra essere aumentata in questi ultimi anni, e può essere dol,r:ta a due cause, 1) espansioni demografiche a carico delle singole specie; 2) fluttuazioni climatiche che sposîano le frontiere biogeografiche. Serie storiche di dati di temperatura ed informazioni idrologiche depongono a favore della seconda ipotesi.
Suutr.mRv \ìirith respect to the neighbouring Tyrrhenian Se;r, the Ligurian Sea is colder and its biota has a boreal affinity: however, the occurrence of southern, warm-water species in the Ligurian Sea has been reported from time to time. The recent findings of 20 thermophilic epibenthic species (7 algae, 11, invertebrates, and 2 reef fishes) are critically discussed together with literature data. ]iíarm-water species occurrence seems to have increased in the last few years, and may be due to fwo causes: 1) demographical expansions affecting Sea(AVHRR the individual species; 2) climatic fluctuations shifting biogeolraphical boundaries. Historical series of temperature data and hydrological information favour the second hypothesis. ars in the biological iea water ETHOIJX E/
l3 194
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