Publ: Espec. but. Esp. Oceanogr. 23. 1997: 23-33 P UBUCACIONES ESPECIALES L"lSTlTUTO ESP.I\NOL DE O CEANOGRAFIA ISSN; 021-1-7378 . ISBN: 81 ~19 1 -O 299-5 Ib Ministerio de Agriculrura, Pesca yAlimentacion , L997

Bathyal zones of the Mediterranean continental slope: An attempt

c. C. Emig

Centre d' ologie de Marseille (UMR-CNRS 6540) , Station Mari ne d 'Endoum e, Rue de la Batterie-des-Lions. 13007 Marseille, France.

Received Febru ary 1996. A ccepted August 1 99 6.

ABSTRACT

On the con tine ntal slop e, th e bathyal can be divided into two zones, the upper bathya l and the middle bath yal, at the shelf break, which represents th e boun dary betwe en the coastal shelf environment an d the deep realm , located at about 100-110 m dep th. T he upper bathyal, previ­ ously considered a transitional zone, is characterised by distin ct physical, geological an d biol ogi­ cal features. Its bath ymen-ic extension is directly related to slope physiography, and its lower boun dary ge ne rally corresponds to the mud line. T his belt is governe d by specific abiotic factors with stee p physical grad ients (e.g., hydro dynam ics, salin ity, oxygen , temperat ure , sedirnen ts}. Major change in tbe benthic fauna is associated with major ch ange in these abiotic factors. The three main biocoeno ses are dominated by suspen sion-feed ing species, which are exclusive to th e Mediterran ean upper bathyal. Dep ending on water parameters, the limit between th e phytal and aphyta l systems gene ra lly occurs with in th e upper bathyal. The second zone, the middle bath yal, is poorl y docum en ted; however, it can be divided into several subzones whos e limi ts appear to be related to water-mass characteristics: the upper-middle slope , the lower-m iddle slope , an d th e lower slope .T he lower bathyal zone deve lops into th e bathyal rise and plain .

Key words: Medi terranean Sea, con tin en tal slope, bathyal zonation, biological oceanograp hy, physical oceanography, geological oce anography.

RESUMEN

L os zonas btuiales del talud continental medi ternineo: un en say o

En el talsui continental, el -piso bauai se puede dividi·r en banal superiory batial medio. Sn timue supe­ ri ar (100-110 m) corresponds al reborde del talud, suuada entre dos domisuos muy distintos: el de la plala­ [orma y el profundo. Aruerumnerue considerada coma «zona de tronsicum» entre etpiso circaluoral y et ba­ tial, el Ltuiol superior se caraaerua 1'01' sus particularidadesfisicas, geol6gicas y biol6gi.cas. 511, extension botimetrica dcpende de la Jisiografia deltalu d, qu e induce los efectos de los facnnes abuiticos y asi proooca una disnibucum. del beruos en d auurones con dominancia de Los suspensivoros }' la casi ausenciade sedi­ menuuion. El batial supenor comp rende generalmerue el limiieentre el sistema fital y el ajtal segttn la trams­ parencia de las aguas. El batial medi a empiexa a pm·t.i., de la. lin ea de fa ngo (mud line) qu.e marca un (',(J.t1/.+ bio abrupto de la energia. Aunque faltan estudios daa llados, a partir de Los datos disponibles se puede jJrojJoner un esqlJ,mna de la. umacuni del batiai media: el talud: medic superior, el talud media inferu n; etta­ lud. inf erior. Por tanto, el boliol inferior se exuende en la llanura batial.

Palabras cla ve: Mar M editemineo, talud continental, zonacum. batial, oceanografia biologica, oceanografiafisica; oceanografia geol6gica.

23 c. C. Emig Meduermnean baih)'at zones

INTRODU CTION edge sector is a poorly known e nviron m ent because it lies between two distinct zones of inter­ The upper part of the Mediterran ean continen­ es t, the coastal-shelf environment and th e dee p tal slo pe was previously regarded as a «transitio nal».. realms (figu re 2). T hus, it is n ot surprising th at th e zone between th e circalittora l zone and the bathyal shelf-to-slo pe transition remains a biological and zo ne (Peres and Picard , 1964; Carpine, 1970; Reyss, physical «no man's land» (Vanney an d Stanley, 1974; Falcone tti, 1980; Emig, 1985; Peres, 1982; 1983). Bella n-Santini, 1983; Ab e1l6, Vallad ares and The Mediterranean shelf-to-slope morphology Castellon , 1988). All these au thors have noted th e on soft substrates presents two major types of pro­ importan ce of th e batbym etric depth range files (figure I ), on which the shelf break occurs at betwee n ] 0()..1 50 to 200-300 m, which generally about 100 to 120 m. H owever, in Type Il, th e co nti­ includes the limi t be tween th e phytal and aphytal nental sh elf break is ge ne rally co nsidered to be at a systems (Emig, 1989b ). Bu t th ey failed to take in to depth of abou t 150 m, which corresponds to th e account th e importance of abiotic facto rs, i.e., edge of a large an d flat bathyal offshore te rrace; slo pe physiography and physical characteristics, in but th e tr ue co ntinental shelf break , ofte n missed , order to exp lain th e biologi cal specificiry of this lies shoreward and co rresponds to th e edge of a zone (Emig, 1985, 1989a, 1989b) whose limits have short scarp of about 5--20 ID (figure 1) (Ernig, never been clear ly defined. H owever, Ercegovic 1989a, 1989b; Savoye and Piper, 1993) . (1957) an d Peres and Picard (1964) defined th e T he lower limit of th e u pper bathyal zone is extension of the «transitional» zone , from the in dicated by the mud line, wh ich is kn own to in di­ lower boundar y of th e circalitto ral , i.e., th e lower cate an abrupt change in the en vironmental condi­ limit of multicellular algae, down to th e lower limit tio ns (Blake an d Doyle, 1983) and serves as an of unicellular algae. Conse quently, the «true» energy-level marker (Stanley, Addy an d Behrens, bathyal zone was considere d to begin beyond th e 1983). Located a depth of between 160 and 300 m, transitional zone, be tween 200 and 500 m. O th er this limi t is rel ated directly to slo pe mo rphology authors use arbitrary (15 0 m ) or economical (200 (figure I ), which gove rns th e influence of the pre­ m) zone defin itio ns of th e upper lim it of the vailing abiotic factors: th e weake r the inclin e the bathyal, based on artificial considerations, never shallower in depth is this limit (Em ig, 1989a, scientific on es. 1989b). Thus, like th e upper limit of th e upper A review of the northwestern Mediterranean bathyal, th e lower limit does n ot co incide with a bathyal zone, with new information fro m sub­ bathymetric expression. mersible cam paigns along th e con tin ental slope, makes it possib le to reco nsider the position and impor tan ce of th is zone on th e co n tinen tal slope. Physical characteristics On the other hand, few faunistic surveys were pe r­ fo rm ed in the Mediterranean bathyal, and com­ The upper bathyal zo ne is a high -energy sector parisons of data an d results are difficu lt, becau se characte rised by grad ient variations of th e prevail­ th ey were obtained in different ways. Co nsequently, ing abiotic factors, i.e., hydrodynamics, salinity, n either local nor biogeographic comparisons can tem pera ture, oxygen, sedimen ts (figure 2) .In th e be made. Neverth eless, except th e upper bathyal entire northwestern basin there is a main current, zo ne, the o ther ba thyal zones are unlikely to be th e Liguro-Provencal-Catalan current, that follows d efined and characterised at present, although a the co n tinental shelf break and co inc ides with a ge neral tendency can be discerned . pe rmanent sh elf/ slope density front; thi s flow is in tensified by th e p revailing win d s and separates th e co n tinental fresh waters on the she lf fro m the Upper bathyal zone saltier an d usually warmer open-sea waters (Salat and Fo n t, 1987;Millot, 1987; Wang et al., 1988; T he upper lim it of th e bathyal zone lies at th e Emig, 1989a; Monaco et al., 1990; Fo n t, 1990; Emig con tin en tal shelf break, defined by physical, ge o­ an d Garcia-Carrascosa, 199 1;H uthnan ce, 1992). logical and biological characteristics (figures 1 and The near-bo ttom curren t, weak or abse nt on the 2). Although of primar y im p ortan ce, because of lower par t of th e contine ntal shelf, increases by sev­ maj or gradient change s, the Mediter ran ean sh elf- eral tens of meters at th e level of the shelf edge; its

24 PubL Espec. Inst. Esp. Oceanogr: 23. J997: 23-33 ;p [) 1': n ~ -G, X "~ r- ~ ~ ~ ~ ,,'b'",," J' .5' ~ ~ :? ~r ,,§' C;<#' l;: .... ;g :--;1 ec ~

Profile Type I

Profile Type II I ~ il

Figure 1. Block-diagrams of the bathyal biocoe noses d istribu tion along the uppe r con tine n tal slope sector accordin g to the slope gradient on th e two main profile types, 1 and ~ n, with the sides showing th e sedimen tation prism since the last Wiirm glaciatio n (hatch ing) .For profile location s (Provence and Corsica) and explanation see Emig (1989a, [ 1989b, 1989c), Em ig and Oarcta-Carrascosa (199 1). Th e numbers indicate the depth in metres. Between do tte d lin es, the strongest velocity zone of the near-bottom CU lTCn LS .. an d their main di rections (arrows) . Biocoenoses: (UBM): upper barhyal mud; (SD) : shelf detritic; (BDS): bath yal deu-itic sand ; (MBM): middle bathyal mud. 't ~ ""o- ~ c. C. Emig Mediterranean bathyal w nes

1000 ~ ~ "' '''~ '''.J''- ~ '''' ''' "' ...... "' ..... "' ,...'" Mediterranean 4.5-4.7 38.4-38.5 Deep ~ Depth in m P c 5•%. 02 mill Water masses Lower BATHYAL

Figure 2. Diagram of diffe re nt,parameters ofthe surrounding in me Bathya l Zone (drawn after data from var­ ious authors}. bathymetric ex tension, velo city and direction are the northwestern Mediterranean Sea (figure 2): d irectly related to slope physiography (figure 1) . low annual tempe rature variatio n (about 2 DC) T he velocity shows a ver tical gradient (figure 1) and wh ich be comes co ns tant beyond abo ut 200 m varies fro m about 0.5 up to 2 kno ts or more, an d d ep th (th e Mediterranean h omo th ermy), low sometimes causes large ripple marks or undulations salinity increase, and sharp decrease of oAJ'gen on th e bottoms (Reyss and Soyer, 1965; Emig, 1987) . whi ch, howeve r, is kn own to be higher than bio­ Consequen tly, sedimentation is absent or weak in logical consump tion.T h e lower boundary corre­ the upper bathyal, which appears to be a resuspen­ sponds to th e lowe r lim it of the fron tal structure, sion lone with minor accumulation of particles and across which the hydrol ogical pro per ties ch ange in which the fauna is characterise d by high densities sharp ly (Huang a nd Su , 1991), an d to th e begin­ of suspension-feeders. At th e lower limit of th e sec­ ning of the oxyge n m ini mum laye r (O ML) which tor, th e bottom curren t velocity drops off by several is related [ 0 the Levan tine intermed iate water tens of meters, while the su bstrate becomes muddy m ass with a salinity m ax imum an d homo th er my (Reyss and Soyer, 1965; Emig, 1989a;Emig and (figure 2) . Garcia-Car rascosa, 1991): the mud line is eas ily T he C jN ratio in th e sed irnen ts decre ases detected in the case of a ch an ge fro m sandy to from 12 to 10 (Carpine, J970) . T he change of muddy substrates, but remains pro blematical when sediment oc cur in some tens o f meters, related to this lin e occurs shoreward to the shelf edge. the hydrodynamics, at both lim its of the Upper In the surrounding water co lu m n several Bathyal (Emig, 1989a; Emig and Garcia-Carrascosa, o th e r gra d ien ts charac te rise th e up per bathyal in 199J ).

26 Publ. Espec Inst. Esp. Oceanogr 23. 1997: 23-33 c. c. emig M editerranean bathyal zones

Geological characteristics els and pebbles), a characteristic of the BDS bot­ tom (Falconetti, 1980; Emig, 1989a, 1989b) . The T he Recent imprint, since the last rise in sea su bstratum of th e SD is sand y mud (gravel , sand, level (the Wurrn glaciatio n, 17 000 years), is clearl y mud)(P icard, 1965; Emig, unpubli sh ed data). evident in the upper bathyal : th e continen tal shelf On m uddy substrata, the tr ansiti on from the cir­ break lies at the outer edge of th e deposits forming calitto raJ m uddy detritic (MD) and terrigenous a narrow prograding wedge or prism located at th e mud shelf (TMS) biocoenoses to an upper bathyal ou ter part of th e contin ental shelf (figure 1). T he . mud biocoenosis (UBM) remains hypothetical, shelf edge is in equilibrium wi th th e present en vi­ due to lack of research. However, fr om the data of ronmental co nd itions ; its progra dation d uring the G uille (1970) , Picard (1971) , Salcn-Picard (1982), Late H ol ocene has been negligible and its depth Alber telli, Della Croce an d Fraschetti (1991) and coincides with a «depositio nal equilibrium » level Albertelli and Fraschetti (1992), one may argue (Mougeno t, Boillot an d .J. P. Rehault, 1983; that there is a faunistic change at the level of th e Monaco et al., 1990; Co u r p and Monaco, 1990 ; shelf edge, with the ap pearance of domin ant Savoye and Piper, 1993). T he relative absence of species , particularly the oph iurid Amphiura fili­ Recent sedim ent supply in the upper bathyaJ (fig­ [ormis (Muller, 1776), reaching 8-34 % of th e fauna, ure 1) shows that sedim ents are mainly re worke d accord ing to Sale n-Pica rd (1982) and Albertelli, relict (Wurrnian) sedimen rs with th e OCCLU'fenCe of De lla Croce and Fraschetti (19 91) , and th e poly­ Q uater nary thanatocoenoses visible by submarine chaete Maldane glebifex Grube, 1860, while th e char­ o bservation and generally located at a depth of acteris tic species from both circalittoral MD and between 180 to 20 0 m (Gautier and Picard, 1957 ; TMS biocoenoses are abse nt in th e up pe r bathyal. Blan c, 1968; Em ig, 1987 ) . In th is hypothetical UBM, some species can reach high densiti es in some areas, i.e ., the echinoderrn Brissopsis lyrifera Fo rbes, 1841, the p ennatularia Biological characteristics Fu n icula quadrangularis (P allas, 1766) an d the sponge Thenea muricata (Bowerbank, 1858). The circali ttoral ex tends down to the lower limit Within th e upper bathyal biocoenoses, the Iau­ of m ulti cellular algae (Peres and Picard, 1964): nistic distribution develo ps in to belts re lated to th e from subm arin e obser vations of th e coastal detritic prevailing factors (hydrodynamics an d th e related bioco enosis (CD) , ca lcareous red algae do n ot sedimentary conditions). Consequen tly, these bel ts extend beyond th e shelf-break and, afte r a short are mainly suspensio n-feeder o nes. The direction transitional zone of some tens of m eters, the an d veloci ty of th e bOtt0111 currents create live dis­ bathyal detritic sand biocoenosis (BDS) begins, or tributional zones in the BDS (tile highest velocity at th e sides of submarin e ca nyo ns, tbe shelf-edge zone is reported in figure 1) , i.e., th e di stribution­ detritic biocoenosis (SD) (figure 1). The SD has al zo ne s of Gryphus uitreus, whi ch can reach up to been traditionally considered a circalit to ral bio­ 700 individuals .z m? (Em ig, 1987, 1989a, 1989b; coenosis, som etimes co nfuse d with the BDS, but Emig a nd Arnaud, 1988; Emig an d Garcia­ belon gs with out an y doub t to th e upper bathyal Carrascosa, 1991) or the distributio n belt (between (Laubier and Em ig, 1993). T he continental shelf 100 to 140-150 m ) of the ech in odcrrn Neolampas ros­ edge corresp onds to th e upper limi t of the di strib­ tellata Aga ssiz, 1869 rep o rted previously by ution of at least two excl usive upp er bathyal Fa lco netti (1980) as belonging to th e circalittoral. spec ies, th e brachiopod Gryphus vitreus (Born, In th e SD, the crinoid Leptomeira phalangiu m can 1778) in the BDS an d the crinoid Leptornetra pha­ reach up to 30-50 individ uals/ m ' (Reyss, 1971) an d langiurn (Muller, 1841) in the SD, while the mud in th e UBM Amphiura filifo,.,nis reaches lip to 28 line corresponds to the lower limit of their exten­ in d ivid uals ymz (Albenelli and Frasch etti, 199 2) . SIOn . Su cb a bel t distribution explains the relative het­ The su bstratum of the BDS is well-sorted sand erogeneity of the fauna beyond tile shelf-edge, as (gravel, co arse and fine sand ), clogged by a fine reported by previo us authors, as well as th eir argu­ fractio n which can reach 60 %, an d co ntains a large men ts for co nsidering the upp er bathyal a transi­ detritic p ro portion of small h ard substrates of tional zone. en dogenous origin (fragments of mollu sc and bra­ The upper bathyal biocoenoses seem to be char­ ch iopod sh ells, of sponges, bryozo ans, co rals, grav- ac te rised by lower spe cies and individual rich n ess

Publ. Espec Inst. &p. Oceanogr: 23. 1997: 23-33 27 c. C. Emig Mediterranean balh)'al zones when compared to the ove rlying circalittoral bi o­ geographic area, contradicting Bellan-Santini's coenoses; in general, the muddier the substrate, (19S3) statement that this boundary lies at th e the lower the richn ess. However, the analysis of lower limi t of the circalittoral zone, as well as the recently published data by Albertelli, Della Croce definition of the lower limi t ofthe transitional zone and Frasch etti (1991) , Albertelli and Fraschetti proposed by Ercegovic (1957) and Peres and (1992) an d Tselepides and Eleftheriou (1992) Picard (1964) . from m u ddy sh elf-to-upper slope tr ansects show that the mac rofauna increases in species and indi­ viduals, mainly of suspension-feeders and detritus­ Middle bathyal zone feeders, in the uppe.r bathyal zone (figu re 3) . Within the SD an d m iddle bathyal mud (MBM) There is a rapid transitio n over several tens of bio coenoses on the northern Mediterranean coast, meters from the upper bathyal zone to the middle there is a geographic decrease in richness from the bathyal zone, i.e., from the u pper bathyal bio­ west to the east (Carpin e, 197 0) , which n eeds con­ coenoses to the MBM . T he substrate becomes firmation because o pposite to the cyclonic circula­ m uddy, with th e appearance of burrowin gs having tion. various diameters (Em ig and Arnaud , 19S8; Emig Th e extension of circalittoral species into the an d Carcia-Carrascosa, 1991) . O ver the co n tinen­ upp er bathyal occurs in general down to a depth of tal slope in the middle bathyal , with in creasin g 130-140 m , where th eir presence is probably limit­ depth, a ge neral decrease in the size of the m ac­ ed by abio tic factors, i.e. , ligh t, pressu re or/ and robenthos is recorded (Carpine, 1970; Peres , 1985; hydrodynamics, particularly for polychaetes an d Sarda an d Cartes, 1993; Stefanescu and Cartes, echinoderrns, wh ile the ex tension of 1vfBM species 1992) , as well as a quantitative decrease in th e mac­ in to th e upper bathyal is limited by the substrate, at robenthos (fig ure 3) and an in crease in diversity leas t in th e SD and BDS. Never theless, species related to increased en vironmental stability, associ­ which occur at the same time in the circalittoral ated wi th in creasin g depth (Sanders, 1965; Sanders and bath yal are generally co nsidered as circ alittoral and Hessler, 1969; H aed rich, Rowe and Po l1oni, spec ies which ex ten d into the bathyal, rarely th e 19S0; Abell6, Vall adares and Ca ste1l6n, 19S8) . contrary. For example, several brachiop od species, Nevertheless, fo ur of th e five grenadier fish species i.e., Megerlia truncata (Linnaeus, 1767) and Megathiris occurring in the m iddle bathyal follow th e bigger­ detruncata (Gmelin , 1790), co nsidered respectively as deeper ph enom enon (Massuti, Morales-Nin and a shallow-water species and an eurybathic species Stefanescu, 1995). (Logan, 1979), h ave their maximum density in There are several faunistic stock changes within the upper bathyal, between 100 an d 150 m (Em ig, the middle bathyal zone, which consequently can 19S8). be divided in to several distributional zones (figure 4), based m ai nly on recent data from crustacean and fish distribution. However, these zones can be Phytal-aphytal boundary related to several previous proposals, such as th at of Per es (19S5) , who divided the up per slope into T his boundary can be estimated by the percent­ two zones below the transitional one: from 200 to age of the Gryphus vi/reus shells infested with th e 500 m and from 50 0 to 1 000 m. Car pine (19 70) green alga Ostreobiu m sp . Bornet and Flahau t. proposed the followi ng limits: transitional zone, Occurring generally within th e upper bathyal zone, 150-250 m ; upper bathyal , 250-550 m ; m iddle its dep th varies in relation to the water transparen­ bathyal, 550-2000 m; an d lower bathyal, I 500­ cy, i.e., between LSO and 210 m in normal water 3000 m . co nditions in Corsica, but it can be restricted to The cr ustacean assemblages occurring o n the 125-135 m under turbid water con ditions (Emig , upper an d on th e lower-middle slo pe correspond 19S9c). Along the Proven cal coast, becan se o nly a to hi ghly differen tiated faunistic communities, small number of shells is infested with Ostreobium whose differences can be attribute d to hyd rological sp. , this boundary is estimated at about 150 m differences. The upper community is associated depth . Such results in dicate that the phytal-aphytal with the warmer intermediate waters, and the boundary is independent of benthic zonation , and lower zone with the deep-water mass, which has a that its depth can flu ctuate even within a restricted fairly co nstan t temperature throughout the year

28 Pubt. Espec. Inst. Esp. Oceanogr 23. 1997: 23-33 ;p r> ?t: r> t;; ." ~ ~ 1· ~ 1;1

Cl "il ~ g ~ I ,... ji 8 ~ species i ,.,to 1 2 00 ru ~ ..- u ~ ~ ~ e---e Numb er IIf s p~cic slm~ ~ wi th biornass :g ~ Vl 0---0 Mean num ber of spec ies/O. ! 10: :--;'l ~ 1000 50 § o---a M ean abundance ~ .c. '" < <:>-- -OOiOlllllS$ '" 800 +40 Biornass dryWt glm2

600 + 30 ' K _~ 0 0.4 CS) '. 400 +20 \ , \ , 0.2 0 / I \ 0--- ~~ ~ - - - ~ - ~ - ~ - ~ ~~ ------200+10 e;j ------

I I I I .,-- Depth in m 200 400 600 800 1000 1200 1400 1600 1800 2 000

;,. f ~

Figure 3. (A): Abu ndance , species richness and biom ass of the macro fauua on the muddy bottom s in the shelf-to-slope sector of the Gulf of Genoa (dam from AJbcn elli, Dclla [ Croce and Frasch eu.i, I99 J; AJbene lli an d Frasch eu.i, 1992).(8 ); On a slope transect in th e Cre tan Sea (Tselepidcs an d Eleftheriou, J992). (C): Biomass of demer sal fish com­ '"a. munities o n. the slope of Catalonia (data fro m Stefanescu , Lloris and Rucabad o, 1993 ). N ~ '""" ~ c. C. Emig Mediterranean. bathj'al zones

(1991) , on muddy substrates in th e Gulf of Gen ova deposit-feeders represen t respectively 63 % in the CIRCALl TTORAL upper bathyal an d 37 % in th e upper-m iddle slope lOO Shelf brea k 120 of th e middle bathyal, while suspens ion-feeders 160 UPPER BATHYAL represent respectively 14 and 7%, and predators 20 250 an d 57 %. Along a Cretan tran sect (Tselep ides and Upper-middle slope Elefth eriou, 1992), polychaete deposit-feeders are dominant between 200-400 m (more th an 50 %) 480 and carnivores (more than 49 %) be low 500 m. In 510 the Catalan Sea, th e upper-middle slope co mm uni­ ty (245-485 m ) shows a predominanc e of 650 mesopelagic species (Cartes, So rbe and Sarda, 1994); th e fish asse mblage on the lower-middle 800 Lower-middle slope slope, between 1000 and 1425 m , is domin ated by Lepidion. lepidion (Risso, 1810) with five subdomi­ ....I < nant species (Stefanescu, Lloris and Rucabado, > J: 1993). I- < So me au thors (Abcllo, Vallad ares and Castellon, m 1988; Mura an d Ca u, 1994) indicate a change in 1200 W th e decapod fauna between 650 and 800 m. ....I 0 1400 Acco rding to Sarda an d Ca rtes (1993), the d iet of 9 these decapods consists lar gely of in£auna or epi­ :E fauna, an d there are differences in th e co mposi­ tio n of th e diet above an d beyond this limit. Lowerslope On th e lower slope , the re is evidence of fau nis­ tic changes, as well as drastic changes in the amount of available energy and a sharp re d uction of th e available trophic resources related to the dis­ tribu tion of mesopelagic organisms and hydrologi­ 1000 cal characteristics (Cartes, 1993; Stefanescu, Llori s and Ru cabado, 1993; Sarda an d Cartes, 1993) _The fauna is dominated by demersal fish species with I

30 Publ: Espec. Ins t. Esp. Oceanogr. 23. 1997: 23-33 c. C. Emig Mediterranean bathyal zones

too poorly documented to allow comparison (see T his also seems to be the ca se in th e Medi­ Monaco et al., 1990; Bourcier, Stora and Cerino, terranean upper bathyal, as suggested by th e data 1993; Gerino et aI., 1995). T hese valleys are geo­ of Alb er te lli an d Cattaneo (198 5) , Albertelli, Dclla mo rphologically important in concentrating and Croce and Fraschetti (.1 991) ,Albertelli and transp or ting sedimen t to deeper areas (Mo naco et Frasche tti ( .1 992) and Tsele pides and Eleftherio u al., 1990), with high dynamic water circulation (1992) on mudd y bottoms (figure 3). H owever, th e (Mille t, 1990). T heir biological im portance is due species and individ ual richness glo ba lly decreases to the input of bigh prod uctivity with abundant . from circalittoral to bathyal in. the Mediterranean, resources, and the occur rence ofrecruitm ent areas as also established by Sh errnan et aL (.1988) in the co ncen tr ating juvenil es of certain species, particu­ northeast Atlantic for the density and biornass of larly in th e middle bath yal zone. Fa un a biom ass four m ajor taxonomic groups. and abun dance are higher than those recorded o n Th e distributional zones in th e Mediterranean th e sur rounding slope areas. mid dle bathyal (figure 4) can be com pared with th e depth boundary on th e Atlan tic co n tinental slo pe at 400, 700 an d 1200 m, which are considered DISCUSSION nearly universal by Hecker (1990) . Nevertheless, this author indicates th e fo llowing zones: upper T he zone herein defined as th e upper bathyal slo pe 180-600 m , upper-middle slope 600-1 300 m, ",..as previo usly considered a transitional zone. not lower-middle slope 1400-1600 m, lower slo pe .1 600­ only in th e Mediterranean but in the ""orld O cean 2000 m , an d a con tin ental rise fr om about 2000 m . (see Zenkevitch, 1963; Peres, 1982; Blake and Acco r ding to Van ney and Stanley ( .1 983), the Doyle, 1983; Zezin a, 1994 ) . However, thi s zo ne sh elf-edge appears as a boun dary of importan ce begin s at the con tinen tal shelf-edge (geomorpho­ comparable to the coastline, separating the coastal­ logical shelf-break) which is ch aracterised by bi o­ shelf environment from the deep realms; it is the logical, physical and ge ological expression, and point wh ere th e first maj o r change occurs in the beyond which the upper bathyal develops as a bel t p hysical gradie n t, and consequen tly, in the biologi­ whose bathyrnetric extension is di rectly related to cal gra d ien t, when entering the . T h is slo p e physiography (figure 1). Con seq uen tly, upper lim it of th e deep-sea zone, the bathyal, future stu dies of bathyal fau na shou ld always indi­ depending bathymetrically o n th e depth of th e cate the slo pe profile from whi ch the data have sh elf-edge, is expressed by biological , physical and been re por ted; rhis is also valid for th e middle geomorphological criter ia which have to coin cide bathya]. In the bathyal, th e major change in fauna with each other and with th e lower boundary of the is directly associated with major environ m ental circalittoral zone. changes, wh ich play a key role in d eterminatio n of T h e transition from the upper bathyal to the the fauna across the shelf-break. T h e biological middle bathyal, whose bathymetric lim it depends ex tension alo ng the slope is given by th e bio­ o n local environmental factors governed by phys­ coenoses occurring in th e upper bathyal, dominat­ iography, also follows su ch multidisciplinary crite­ ed by hi gh densities ofexclusive suspen sion-feeders ria. It co rresponds in general to the mud lin e, whose distributional belts should provide informa­ located between abo ut 165 and 300 111, depending tion regarding flo w str uctures in th e shelf-to-slo pe o n the slo pe physiography, in the n orthwest co n text. Med ite rranean, where this line al so in dicates a The validity of th e bathyal biocoenoses needs to d rastic change in th e energy leve l, as reported in be established with new data, using fau nistic density other ocean areas by Stanley, Addy and Behrens and biom ass an d th e effects of almost abi otic char­ (1983) . acters, to define cir calitto ral and baihyal species As a result of stee p gra die n ts in physical con di­ and the exclusive species of a biocoenosis, whi ch tions, the upper bathyal zone represents an under­ can only be stenotop ic species (Arn aud and Emig, estimated barrier fro m shelf to deep sea, occur ring 1987). T he dis tr ibutional zo nes of fauna deter­ in the World O cean. In the Mediterranean, su ch a mined by abi otic factors need a careful bathyrnetric p hysical barrier m ay partly explain th e sharp fauna and spatial choice of sampling along th e slope. decrea se in th e middle bathyal and the bi ological In th e Atlan tic, infaunal density increases in the poverty of the Medite rranean deep sea. On the u pperm ost slo pe zone (Blake and Doyle, 1983). o ther hand, a lo ng-botto m transport p assing

Publ. Espec: Inst. Esp. Oceonogr: 23. I 997: 23-33 31 c. C. E1I1ig Medill-r ranean balh)lUi zones

through the canyon axes a ppear as p a th ways across Canes, J. E., J. C. Sorbe and F. Sarda. 1994. Spatial dis­ the sh e lf break to the Mediterranean deep sea tribution of deep-sea decapods an d eusphausiids near (Courp and Monaco, 1990). the bo ttom in th e northwestern Mediterrane an. J. E"/J. Mar Bioi. £CoL 179: 131-144. Courp , T. and A. Monaco. 1990. Sedimen t dispersal and accumulation on the contine ntal margin of the Gulf REFERENCES of Lyons: sedimentary budget. Cont. Shelf Res. ]0: 1063-1087. Abell6, P., F. J. Valladares and A. Castell6n. 198B. Emig, C. C. 1985. D isu-ibuuo n et synecologie desfonds a Analysis of th e structure of decapod cr ustacean Gryphus uitreus (Bra chiopoda) en Co rse. M a?: Bioi. 90 assemblages o ff the CataJan coast (northwes t (I): 139-146. Mediterranean). Mar Biol. 98: 39-49. Emig, C. C. 1987. Offshore brach iopods investigated by Albertelli, G. and M. Cattanco. 1985. Macrobenthos dei submersible. J. E"/J. Mar BioI. Ecol.l08: 261-273. fc ndi molli del mar Ligure. In: Atti 6" Congr Ass. Ital. Emig, C. C. 1988. Les Brachiopodes ac tuels son t-ils des indi­ Oceanol. Limnol.: 87-98. Univcrsira d i Livorno. cateurs (paleo) ba thymetriques? Cial. Miditerr.15: 6!'>-71. Albertelli, G., N. Della Groce and S. Fraschetti. 1991. Emig, C. C. 1989a.Distribution bathymeu-ique et spa­ Bcnthos della platrafor ma continentale ligu re tiale des population s de Gryphus uitreus (Bra­ (Ch iavari): trasversale Luglio 1989. Rapp. techn. Univ. chiopode) sur la marge contine ntale (Nord-O uest Cenova, 1st. Sci. ambient. mar. 37: 1-1l. Mediterranee). Oceanol. Acta 12: 20",209. Albertelli, G. and S. Frasch etti. 1992. Observatio ns on Enng, C. C. J989b. Observa tions preliminaires sur l'en­ the str ucture of th ree d iffe rent commun ities of the vasement de la biocoenose a Gryphus v itreus contine n tal she lf in the Ligurian Sea. In : Atti 9° Congr. (Brachiopoda), sur la pen te continentale du Nord de Ass. it. Oceonol. Limnol. G. Albertelli et al: (eds.): 351­ la Corse (Mediterrance}. Origincs et conseque nce s. 362. Un iversha d i Ce nova. C. R. Acad. Set. (Paris) 309 (ser. Ill ): 337-342. Amaud, P. M. and C. C. Emig. 1987. La pop ulation , Emig, C. C. 1989c. Distribu tional patterns along the unite fonctionnelle de la bio coenose. In: Aae Coli. Mediterranean contine ntal margin (u pper bathyal) Not. CNRS Biologic des popuuuions (Lyon, 1986): 69-72. using Gryphus uitreus (Brachio po da) densitie s. C. N. R. S., Paris . Palaeogeogc Palaeaclimat: Palaeoecol. 71: 253-256. Be llan-San t..i ni, D. 1983. The Mediterranean be ntho s: Emig, C. C. and P. M. Arnaud. 1988.Observations en Reflections an d probl ems raised by a classification of subme rsible sur la d ensite des populations de Gr)fphus the benthic assemblages. In : Mediterranean Marine vureus (Brachiopodes) le long de la marge contin en­ . M. Morairo u-Aposto lopoulo u and V. tale de Proven ce (Mediterran ee nord-occi de ntaJe ). Kior tsis (eds.). NATO Con! Se>: (1 £Col. ) 8: 19-48. eR. Acad. Sri. (Paris) 306 (ser. Ifl ): 501-505. Plenum Press. New-York, USA. Emig, C. C. and M. A. Oarcia-Carrascosa. ]991. Distrib­ Blake, N.J. and L.J. Doyle. 1983.lnfaunal-sedi mem rela­ uti on of Gryphvs oiueus (Born , 1778 ) (Brach iopoda) tion ships at the shel f-slope break. In: The ShelJbreak: on transect P2 (Contine ntal ma rgin, french Critical Interface on Continental Margins. D. J. Stanley Medite rranean coast) investigated by submersible. and G. T. Moore (eds.). SEPM Spe cial Publ, 33: Sri. Mar 55: 383-388. 381-389. Ercegovic, A. 1957. Principes e t essai d'un classement Blan c, J. J. 1968. Sedime ntary geo logy o f th e des erages bemhiques. Red . Trav. Stn. "!fm: Endoume Med iterranean Sea . Oceanogr. Mar. Bioi: Annu. Rev. 6: 22: ]7-21. 377-454. Falconetti, C. 1980. Bionomie benthique des fonds situis n de Calvi (Co",e). T hese Docteur ran een a de s apports particulaires telluriques et es- Sciences. Universite de Nice: 287 pp. anthropiques. C. R Acad. Sri. (Paris) 316 (Sec. 3) : 91­ Fon t, J. 1990. A comparison of seasonal 'winds with cur­ 196. rents on the continental slo pe of the Catalan Sea Carpine , C. 1970. Ecologie de l'etage bathyal dans la (northwestern Mediter ranean ). j. Geoph),s. Res. 95 Mediterranee occidentale. Mhn. Inst. Oceonogr: (C2) : 1537-1545. (Monaco) 2: 1-146. Oauuer, Y. and J. Picard. 1957 . Bionomie du ban c du Cartes, J. E. 1993. Diets of deep-water pa ndelid shrimps Maga ud (Est des Iles d 'Hyere s}. fuel. Trau: Stn. Mar 0 11 the western Mediterran ean slope. Mar: Ecol. Frog. Endov 1l1e2 1 (12) : 28-40. Set: 96: 49-61. Cerino, M., C. Stora, F. Poyden oi and M. Bourcier. 1995. Cartes.]. E. 1994. Infl uen ce of depth and season on the Benthic fauna and bioturbation on th e Medi­ diet of the deep-water aristeid Aristeus antennatus terran ean continental slope: Toulon Canyon. Cont. along the contine ntal slo pe (400 to 2300 m) in the Shelf Res. 15: 1483-1496. Ca talan Sea (western Mediterranean ) . M w: Biol. ] 20: Cuille, A. 1970. Bion om ie benthique d u plateau conti­ 639-648. nental de la cote catalane Irancalse, 2.Les commu­ Cartes.] . E. an d J. C.Sorbe. 1995. Deep-water mysids of na utes de la macrofaune. Vie Milieu 21 (lB) : 149-280. the Catalan Sea: Species composition , bathymetric Haedrich , R. L., G. T. Rowe and P. T. Polloni . 1980. Th e and near-bottom distribution. J Mar Bioi. Ass. (UK) megabcnrluc faun a in the deep sea south of New 75: 187-197. England, USA. Mar Biol. 57: 165-179.

32 Publ. Espec: Inst. 1:.$1'. Or.eanogr 23. 1997: 23-33 c. C. Emig Mediterranean balhyal zones

Hecker, B. 1990. Variation in megafaunal assemblages Reyss, D. and]. Soyer. 1965. E tude de deux va ll ees sous­ on the south of New England. marines de la mer Caralan e (Com pte rendu de Deep Sea &so 37: 37-57 . plongees en soucoupe plongeante SP 300) . Bull. Inst. H uang, D. andJ. Suo1991. On the stability affronts near Ocianogr: (Monaco) 65 (1356): 1-27. shelfbreak. Acta Oceanol. Sinica.10: 167-18l. Salar.]. and]. Font. 1987. Water mass str uctu re near and Huthnance, J. M. 1992. Extensive slo pe currents and offshore th e Catalan coast du ring th e winters of 1982 ocean-shelf boundary. Frog. Oceanogr: 29: 61-196. and 1983. Ann. Geaphys. 5 B: 49-54. Laubier; L. and C. C. Emig. 1993. La faune benthiq ue Salen-Picard, C. 1982 . Contribution a l 'enule dynam ique de p rofc n d e d e Me d iterranee. In : S)I1nposium Medi­ peuptements matins de substrats meubles: les peuplernents temmen Seas 2000, F. R. Della Croce (ed.) . I st: Sci, Amb. macrobenthiques circaliUoraux soumis al'enoasemeni dans Ma'S. Marghcrita Ligure: 397-428. la region prooencale. T hese Do crcur es-Scie nces . Logan, A. 1979. The Recent Brachiopoda of the Un iversite d 'Aix-Marsetlle: 268 pp. Mediterranean Sea. Bull. inst. Oceanogr (Monaco) 72 San ders, H. L. 1968. Marine bcnthic diversity: A com­ (1434): 1-112. par ative stu dy. Am. Nal.. 102: 243-282. Massutf E., B. Morales-Nin and C. Stefanescu. 1995. San ders, H. L. and R. R. Hessler. 1969. Ecology of th e Distribution an d biology offive grenadier fish (Pisces: deep-sea benthos. Science, N.Y. 163: 14 J9-1424. Macrouridae) from the upper and m iddle slope of Sarda, F. and J. E. Cartes. 1993. Relationship between th e northwestern Mediterranean. Deep Sea Res. 42: size and depth in d.ecapod crustacean pop ulations on 307-330. the d eep slope in the western Mediterranean. Deep Sea Millo t, C. 1987. Circulation in the weste r n Medi­ Res. 40: 2389-2400. terranean sea. Oceanol. Acta 10:] 43-149. Savoye, B. and D.J. W. Piper. 1993. Quaternary sea-level Millo t, C. 1990. The Gulf of Lyons hydrodynamics. Cont. change and sed imen tatio n on the continental shelf Shelf& s. 10: 885-894. and slope of An tibe s, French Riviera. Gee-Marine Letters 13: 2~8. Monaco A., P. Biscaye, J. Soyer, R. Pockliugton and S. Heussner. 1990. Particle flu xes and ecosystem Sh erman, K., M. Grosslein, D. Mountain, D. Busch , J. O 'Reilly J. and R. Theroux. 1988.T he continental respon se on a continental margin : the 1985-1988 shelf ecosystem off the northeast coast o f th e United Med iterranean ECOMARGE experiment. Cont. Shelf States. In: Continental Shelves, Ecosystems of the World 27: Res. 10: 809-839. 279-338. H . Postma and J. J. Zi jlstra (eds.). Elsevier. Mo ugenot D., G. Bo illot and J. P. Rehaulr. 1983. Amsterdam , Hollan d. Progradin g shellbreak lypes on passive continental Stanley, D. J , s. K. Addy and E. W. Behre ns. 1983. T he mar gins; some European examples. In: The She!fbreak: mud-line: variability of its positio n relative to shelf­ Critical In terface on Continental J\1argins. D. ]. Stanley break. 1n: The Shelfbreak: Critical Interfaceon Continental an d G. T. MO Ol ~e (eds.). SEPM special Pub!. 33: 61-77. Margins. D. J. Stanley and G. T. Moore (eds.). SEPM Mura , M. and A. Cau. ] 994. Co mm unity structure of th e Special Pub!. 33 : 279-298. decapod crustaceans in the middle bathyal zone of Stefanescu, C. and J E. Cartes. 1992. Benthopelagic th e Sardin ian Channel. Crustaceana p7: 259-266. habits of adu lt specimens of lam panyctus crocodilus Peres, M. 1982. O cea n Managemen t. In : Marine J. (Risso, 1810)(Os teich thyes. Mycophi dae) in the west­ Ecology. O. Kin ne (ed.) 5 ( I ): 9-64 2. Wil ey­ ern Me di terranean deep slope. Sci. lWar: 56: 212-223. Interscience Pu b!. Chichester. Stefanescu, C., D. Lloris and J. Rucabado. 1993. Dee p­ Perca, J. M. 1985. History of the Mediterranean biota sea fish assemblages in the Catalan Sea (weste r n and co lo n iza tio n of th e depths. In: Western Mediterranean) below a depth of 1000 m. Deep Sea Mediterranean. R. Margalef (ed.): 198-232. Pergamon, Res. 40: 695-707. Oxford, En glan d. Tselepides, A. an d A. Eleftheriou. 1992 . South Aegean Peres, J. M. and J. Picard. 1964. No uvea u manuel de (eastern Mediterranean) contine ntal slope bentho s: biouomie benthique. Reel. Trav. Stn. lUG"!: Endoume 31 macroinfaunaJ-environment relationships. In : Deep-sea (47) : 5-137. Food Chains and the Global Carbon Cycle. G. T. Rowe an d Picard, J. 1965. Rec herches qualitatives sur les bio­ VParien te (eds.): 139-156. Kluwer Acad. Publishe rs. coenoses marines des su bstrats meub les d ragablcs de Netherlands. la region marseillaise. Reel. Tmv. Stn. Mm: End oume 52 Vanney, J. R. and D. J. Stanley. 1983. Shelfbreak physio­ (36) : 1-160. graphy: An over view. In: The Sheifbreak: On tical lnterf ace Picard, J. 1971. Les peuplemen rs de vase au large du on Continental Margins. D. J. Stan ley and G. T. Moore Golfe d e Fos. Tethys 3: 569-618. (eds.) . SEPM Special Pub!. 33: 1-24. Reyss, D. ] 971. Les canyon s sous-marins de la mer Wang, D. P., J. Vieira, J. Sala t, J. Tintore and P.E. La Catalane, le rech du Cap et le rech Lacaze-Duthiers, Violette. 1988. A shelf/slope frontal filament off the Ill. Les peuplemen rs de ma crofaun e ben thique. Vie northeast Spanish cc es:]. Ma' &so 46: 321 ~3 32 . Milieu (B) 22: 529-613. Zenkevirch, L. A. 1963. Biowgy of the Seas ofthe URSS. G. Reyss, D. 1974. Les canyon s sous-marins de la mer Alien and Unwin Ltd. London: 955 pp. Catalane, le reeh du Cap et le rech Lacaze-Duthiers, Zezina. O . N. 1994. Bathyal zone of th e ocean as a place IV. Etude synccologiquc des pcuplcme u ts d e macro­ for preservatio n offaunistic relics. Oceonotogj 34: 367­ faune be nthique. Vie Milieu (B) 23: 101-142. 372. (English translation .)

Pu bl. Espec. Inst. Esj). Oc.eanogr. 23. / 997: 23-33 33