Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | C sig- 13 δ Discussions Biogeosciences ). Species distribution suggests ) or restricted to deeper mud volca- S) and investigate the intra-specific vari- 34 δ 17348 17347 erent species may explain the high diversity of ff N and 15 δ C, Lamelisabella denticulata 13 δ ´ sp., ario, and M. R. Cunha “Bathymodiolus” mauritanicus erent resources by the di are the most widespread, whereas other species were found in a single ff Polybrachia erent species may adjust their position within the sediment according to their ff This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. The finding that hydrothermalnature, vent tubeworms very have distinct a from significantly the depleted values of other typical deep-sea invertebrates led Rau to exploit di chemosymbiotic species found inedge the of Gulf the of chemosymbioticseep Cadiz. species chemoautolithotrophic This production in study in the increases thisture Gulf trophic the area ecology and of knowl- studies. provide Cadiz, a highlight starting the point relevance for fu- of 1 Introduction particular needs and intensity andvalues variability found of for the selected chemicalies, species substrata with supply. are Isotopic thiotrophy in as accordancemixotrophy the with emerging dominant values as nutritional found secondary pathway, insources and strategies. (expressed other with The in stud- methanotrophy heterogeneity the high and in variance terms of of nitrogen and nutrient sulphur values) and the ability stable isotope analyses ( ation of isotope signatures withinbivalve and chemosymbiotic between species study have sites.mud been Twenty siboglinid volcanoes identified and during and nine our wereSiboglinum found studies. living Solemyids in bivalvesmud fifteen and volcano tubeworms (e.g. of thenoes genus (e.g. that di Previous work in the mudchemosymbiotic volcanoes species, from namely the bivalves Gulf andgive of siboglinid an Cadiz polychaetes. overview revealed In of a this the high studydetermine distribution number we and the of life role styles of of those autotrophic species symbionts in in the Gulf the of nutrition Cadiz, of selected species using Abstract Biogeosciences Discuss., 9, 17347–17376, 2012 www.biogeosciences-discuss.net/9/17347/2012/ doi:10.5194/bgd-9-17347-2012 © Author(s) 2012. CC Attribution 3.0 License. Departamento de Biologia & CESAM – Universidade deReceived: Aveiro, 28 Aveiro, Portugal November 2012 – Accepted: 30Correspondence November to: 2012 C. – F. Published: Rodrigues 7 ([email protected]) December 2012 Published by Copernicus Publications on behalf of the European Geosciences Union. Chemosymbiotic species from the GulfCadiz of (NE Atlantic): distribution, life styles and nutritional patterns C. F. Rodrigues, A. Hil 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent S val- ff 34 S below δ 34 δ erent life habits ranging from ff ´ ario et al., 2010; Oliver et al., 2011); 17350 17349 ´ enio et al., 2008; Rodrigues et al., 2008; Oliver et al., erent anatomical organization particularly in relation to ff ´ ario and Cunha 2008; Hil er from the other chemosymbiotic bivalves in the way that they are ff N values than heterotrophs or marine phytoplankton and the ´ ario et al., 2010). Frenulata, the most specious clade of siboglinids, live 15 δ ering a multitude of physicochemical niches that can be exploited by species erent carbon fixation pathways involve distinct isotopic fractionation (e.g. car- ff ff erent anatomical features, physiology and symbiotic associations. ff (Fisher, 1990; Conway et al., 1994; MacAvoy et al., 2002). erences in both fluid geochemistry and composition of the microbial assemblages 4 erent mud volcanoes reveal a predominance of thermogenic sources with varying erentiate animals with thiotrophic symbionts from those with methanotrophic sym- Siboglinid polychaetes are represented in the Gulf of Cadiz by a high diversity of Symbiotic bivalves in the Gulf of Cadiz include members of five of the six fami- The Gulf of Cadiz is an extensive cold seepage area including over 40 mud volca- Previous work in the Gulf of Cadiz mud volcanoes (South Iberian Margin) found The di ff ff ff in a variety of reducing environments including shelf and slope sediments, cold seeps, 2011). These bivalves have di the structure of theviewed gill by which Taylor in and alldeep Glover, of sediment 2010), burrowers them and to areMytilidae) epifaunal also modified further bysate to very di species. house di Bathymodiolin thecapable mussels symbionts of (family (re- co-hosting sulphur-their and filter feeding methane-oxidizers ability symbionts (Fisher and et al., that 1993; they Duperron keep etfrenulates al., (Hil 2008). column o with di lies known to hostVesicomyidae, and chemoautothrophic Mytilidae bacteria: (G Solemyidae, Lucinidae, Thyasiridae, di degrees of thermal maturityHensen (Mazurenko et al., et 2007; al., Nuzzo et 2002,genic al., 2003; 2008) methane and, Stadnitskaia in and et some other cases, al.,(AOM)-related partial hydrocarbons 2006; recycling methanogenic mediated of archaea thermo- by in anaerobicDi the oxidation shallow of sediments methane (Nuzzoresponsible et for the al., AOM 2009). activityical have composition major of consequences in the the hydrocarbons quantity reaching and chem- near-surface sediments or the water fluid sources and transport mechanismsgeochemistry determining of the the intensity porewater of and the sediments. fluxes and the noes at depths between 2002005). and The 4000 molecular m and (Pinheiro isotopic et composition al., of 2003; the Van hydrocarbon Rensbergen gases et present al., in the Especially relevant for the distribution of chemosynthetic species is the variability in the bination of biogeographic, historical and environmental factors (Cunha et al., 2012). 5 ‰ can be used tothe infer isotopic a signature thiotrophic mode of of thecan nutrition sulphide (Vetter therefore and source Fry, provide (Fisher, 1998) 1995). reflecting informationspecifically Stable and on isotope intraspecifically signatures food (Levesque et resource al., use 2003). and partitioning,a high both number of inter- chemosymbiotic species,(Rodrigues namely et al., bivalves 2008; and Hil siboglinid polychaetes and studies on thevariability in faunal structure, assemblages composition in and the density, which area are show likely high to biodiversity result and from a high com- bionts (Brooks et al., 1987;pool as Kennicutt either et thermogenic al., or 1992)have biogenic (Sassen and lower et to al., identify 1999). the Chemoautotrophsues tend source of to animals methane hosting thiotrophicotrophic bacteria symbionts and are heterotrophs depleted (Brooks relative et to al., 1987). those In with fact, methan- values of et al., 2002). The carbonwith source the for former thiotrophic using and poreCH metanotrophic water bacteria dissolved inorganic is carbon di (DIC) and the latter using bon, sulphur and nitrogen) whichfor elucidating makes the stable nutritional isotope status approachesway of particularly et organisms useful al., in 1994; vent Van anddi Dover seep and environments Fry, (Con- 1994). Carbon isotopic values have been used to food source. Later thisconfirmed finding by was the repeated observation forthis that several symbiotic relationship, cold they the seep host invertebratebon, invertebrates, symbiotic host oxygen and facilitates and chemoautotrophic the reduced bacteria. sulphur-compounds, access and to In metabolic in inorganic byproducts exchange or car- it digests uptakes symbiont the tissue bacterial for its nutrition (Fisher, 1990; MacAvoy and Hedges (1979) to postulate that these worms rely on some non-photosynthetic 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | - ffi speci- that har- ´ ario et al., Polybrachia S). Furthermore, we ¨ ugel, 1987), methane 34 and δ 12, 14 and 32 for C, N and S, C until further processing for S analyses. The ground sam- N and ◦ = Siboglinum poseidoni 34 15 δ y 80 δ − Siboglinum C, ´ ario et al. (2010) or given new code- is the molecular weight of the heavier 13 C and re-grinded. The ground sample 100 ◦ N and x δ × 15  δ 1 C, 17352 17351 − 13 13, 15, 34 and δ = x standard erences in stable isotope signatures between species
ff E erent sites and discuss them in the light of species mor- y ff C and re-grinded. ◦ E/ x  sample
the lighter isotope ( E y y can take up and metabolise dissolved organic compounds at a rate su erent tissues were frozen and kept at ff E/ is the element analyzed (C, N or S), x h E = ´ ario et al., 2011). The anterior end of the tube remains in the top layer of the sed- E Isotopic signatures of methane and gas hydrates for some of the studied mud vol- The samples were analyzed at the ISO-Analytical laboratory (UK)The using isotope the method compositions are reported relative to standard material and follow the The samples were freeze-dried and homogenized with a mortal-and-pestle grinding In this study we give an overview of the distribution of chemosymbiotic species in x respectively). The standard materials torine which limestone the fossil, samples Pee are Deeair compared Belemnite are for (PBD) the for nitrogen ma- carbon (Mariotti,(CTD) (Craig, for 1953); 1983). sulphur atmospheric and (Krouse, 1980). triolite from the Canyoncanoes are Diabolo available from iron the meteorite Nuzzo literature et (Stadnitskaia al., et 2009). al., 2006; Hensen et al., 2007; δ where isotope, and discarded, finally the samplefor was sulphur analysis dried was at re-suspendedand in 60 distilled the water, supernatant shacked for was 5the min, discarded; sample centrifuged this was dried procedure at was 60 repeated 3 timesEA-IRMS and (elemental finally analysis – isotope ratio mass spectrometry). same procedure for all stable isotopic measurements (follow equation). stable isotope analysis. tool and aliquots were separatedple for for carbon analysis wasthe acidified sample with was HCl re-suspended (1M) in until distilled no water, further centrifuged bubbling and occurred; the supernatant was and the di abundant species (five bivalve and seven tubeworm species) were dissected on board Chemosymbiotic species were obtained14 from cruises macrofaunal carried samples outof between collected Cadiz using 2000 during a and varietycessed 2009 on of from board quantitative accordingly and numerous (Rodrigues non-siboglinid locations et quantitative tubeworms in al., sampling were the 2011a). gears Chemosymbiotic sorted and Gulf mens bivalves pro- and were and ascribed identified; tonames species when needed according for to more recently Hil collected. Specimens from the largest and more assess intra and interspecific di occurring at the same andphology di and sediment geochemistry. 2 Material and methods cialized tissue where the endosymbiotic bacteria2011). are In housed (reviewed addition by Hil toSiboglinum the nutrition providedcient to by sustain respiration their but symbionts notSouthward, enough 1981). species for growth of and reproduction the (Southward genus and the Gulf of Cadiz andlected determine species the using role stable of isotope autotrophic analyses symbionts in ( the nutrition of se- (Hil iment or extends intolike the structure. oxygenated bottom Hydrogen water sulphidebours and and, methane-oxidizing oxygen in is endosymbionts the absorbed (Schmaljohannare case by and transported a of Fl across gill- the posterior tube and body wall into the trophosome, a spe- hydrothermal vents and organic falls with their tube spanning oxic-anoxic boundaries 5 5 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , C ` es “B.” 13 Isor- δ are less C range poseidoni 13 δ Polybrachia I. perplexum cf. Lamelisabella Lucinoma as- S signatures and 34 (Mercator, Mekn ` es). The three vesi- δ Solemya elarraichensis Siboglinum C signatures. The overall at Darwin MV respectively). 13 δ (Bonjardim MV). Lucinids and from Darwin MV and the least (Capt. Arutyunov, Sagres and Bobmarleya gadensis S values were the most variable 27.2 ‰ ; the most depleted − 34 , mutitentaculate species are only was found in all the 14 MVs. From δ presented lighter 36.8. Despite some overlap of individ- shoing higher average values than (Mercator and Mekn − Axinulus croulinensis species are only found in one MV. It is (Capt. Arutyunov) – and two mixotrophic 54.8 and Ib has the widest distribution in the Gulf of − 1.2 and 7.0 ‰ with was the most widespread chemosymbiotic bi- Polybrachia 17354 17353 − ` Siboglinum es, Yuma, Ginsburg, Darwin and Sagres). An- form conspicuous clumps of dark long tubes cov- Thyasira vulcolutre (Capt. Arutyunov and Darwin MVs) and Siboglinum Christenoconcha regab sp.1 is found in Mercator and Bonjardim, was found in seven MVs at greater depths in the Car- “B.” mauritanicus Siboglinum from Sagres MV. There was a clear segregation between C values below (Fig. 2, Table 2). The “Bathymodiolus” mauritanicus 13 Thyasira granulosa Thyasira vulcolutre δ “Bathymodiolus” mauritanicus and Spinaxinus sentosus species, Polybrachia A. gadirae I. megadesmus erent species showed distinct average ff Solemya elairrachensis Spirobrachia tripeira Acharax gadirae C average values between erences in the isotopic values of both tissues were observed and there- and N values varied between ff Acharax gadirae 13 Ia is present in three MVs and three other species are found in two dif- and 15 δ δ Siboglinum species, at Mercator MV and N range for the chemosymbiotic bivalves (10.5 ‰) was lower than the With the exception of one species of The unitentaculate Frenulata genus The solemyid 15 with an overall range of 45.3 ‰. a relatively narrow range (values between 11.5 and 17.7 ‰). Thyasirids and solemyids depleted for the mytilid and the otherble families 2) (Solemyidae, that Lucinidae never andual showed Thyasiridae) values (Fig. the 2, di Ta- δ (27.5 ‰) Lucinoma asapheus mauritanicus Stable isotope valuesspecies were (Table 2). obtained Although forsignificant analyses di five were carried bivalvefore out species only in and the the average seven gillpresented results and siboglinid per foot specimen tissuesvalues are no were presented. measured Chemosymbiotic in bivalves determined IIa) in Carlosdenticulata Ribeiro and Porto MVsering continuously (Fig. the 1). crater The ofconspicuous species Porto and MV. more The regularly tubes spaced of field but in were the also crater observed of forming Carlos a Ribeiro continuous MV. 3.2 Stable isotope signatures (Rodrigues et al., 2011b) in the Capt. Arutyunov MV. present in MVs belowmore than 1300 m one MV: depth.Va Only in three Carlos Ribeiro of and the Semenovich, and eleven one species species are of found an undermined in genus (Un- worth noticing the presence of the methanotrophic species Siboglinum ferent MVs. The four remaining comyid species wereropodon found always at(Capt. depths Arutyunov) and greater the larger thanmytilids 1000 m: were each twoapheus represented small by a single species inthe only nine one MVCadiz, ( being present in seven MVs from approximately 350 to 3060 m depth (Fig. 1). Sagres, Carlos Ribeiro andmud Porto), volcanoes. with The thyasirids bothcurring were solemyid represented in species by MVs co-occurring two of atCarlos chemosymbiotic the three species Ribeiro) Deep oc- Field and – species occurring mostly at shallower depths: and Capt. Arutyunov) and 14 MVs (Table 1 andMVs Fig. in 1). The the majority Gulfshells of but of these the were Cadiz samples not yielded collected considered from herein. fragmented a or total emptyvalve of occurring siboglinid 24 at eight tubes MVs andand in the in bivalve shallower the El Arraiche Carbonateother field solemyid Province (Mercator, Gemini, (Mekn Kidd) bonate Province (Yuma, Ginsburg, Jesus Baraza) and Deep Field (Capt. Arutyunov, 3.1 Species distribution Chemosymbiotic species were identifiedspecies in (including 15 two mud mixotrophic) volcanoes occurring (MVs) at with 13 MVs 11 and bivalve 20 siboglinid species at 3 Results 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | and erent ff Id from C lower T. vulco- N values ”-shaped 13 A. gadirae Y 15 δ δ Ib that for the ` es and Darwin Id, both in the N ranges were erent mud vol- ff ”- or “ 15 C signatures for T. vulcolutre U δ showed ranges of 13 Siboglinum δ showed the greatest N, respectively. from Porto MV. Most of 16.8 ‰) was found in the Siboglinum 15 Siboglinum − δ 49.8 ‰ ( − S( showed a wide range (37.6 ‰) S ranges, especially and 34 S ranges of 13.4 ‰ in Capt. Aru- δ 34 C and S overall range was lower: 26.1 ‰ δ 34 S. elarraichensis 13 34 δ all from Darwin MV varied by 5.2 ‰. δ Ib, Gemini MV). Values of δ erent sites varied from 3.0 ‰ ( ff the poseidoni A. gadirae N values from 0.2 ‰ (Sagres MV) to 12.2 ‰ 15 cf. 17356 17355 δ presented specimens collected from six di ` ` es MV (Fig. 2, Table 2). es and Darwin MVs, respectively. The four speci- C values varied from -35.9 ‰ in the Lazarillo de 34.7 ‰ in Carlos Ribeiro and Porto MVs). Within Siboglinum − Lamelisabella denticulata 13 “Bathymodiolus” mauritanicus 8.4 (Sagres MV) to 6.5 ‰ (Gemini MV). Within Yuma δ 29.3 ‰ in Ginsburg, Yuma, Jesus Baraza and Sagres 34.7 ‰, with a clear separation of values from speci- varied by 2.7 ‰, between specimens from Sagres and − N values in di − “B.” mauritanicus − 15 Siboglinum δ S measured in 33.1 ‰ ( 31.6 to S. elarraichensis N values lower than 6 ‰ except ). Within the same site − 34 − Ib. The S from If from Mekn δ 15 27.2 to presented small intraspecific variation between sites (2.0 ‰) “B.” mauritanicus. δ − 34 27.2 to δ − Acharax gadirae collected in the Yuma MV showed the widest range of Thyasira vulcolutre A. gadirae 33 ‰ in the Sagres MV; − Siboglinum S (6.5 and 5.7 ‰). The lowest value of Siboglinum Thyasira vulcolutre 34 δ A. gadirae C values for 40 ‰ were found for 13 C values for Siboglinidae worms varied between − δ ) to 6.1 ‰ ( 13 25.7 and 11.9 ‰) (Fig. 2, Table 2). Solemyds, lucinids and thyasirids bivalves are sediment dwellers whose burrows Intra-specific variation of isotopic signatures could only be examined for one species Isotopic signatures of The intraspecific range of δ − span oxic-anoxic interfaces in the seafloor.burrows Whereas (Stewart solemyds form and “ Cavanaugh, 2006), lucinids and thyasirids maintain an anterior 4.1 Distribution and life styles The combination of form andwhich chemosymbiotic function species studies have are evolved to essentialstand exploit their to their current understand environment distribution. and the Because to wayssymbionts the under- in can association be between seen an as1994) eukaryote an and the adaptation its chemistry to profile bridgewhich of oxic-anoxic species interfaces the are (Cavanaugh, sediments able is to inhabit expected a to particular play site a (Dando role et in al., determining 2008). MV, ranges of 1.5 and 3.5 ‰ were registered for 4 Discussion sites (more than 20 ‰).as In well as within the sameMVs volcano respectively). (2.2, 10.6 and 3.0tyunov ‰ in MV Gemini, and Mekn 29.8 ‰species). in The six Carlos specimens Ribeiro of MV (comparable to theof overall range Frenulata, for the Tormes MV to (Gemini MV) and the within the same species and0.5 site ‰ for all in studied Capt. species3.0 (3.8 Arutyunov ‰). ‰ The in MV Darwin and MV for 2.4 ‰ in Carloswith Ribeiro high variability MV within for the same site (14.2 ‰ in Yuma MV) and between di mens of Solemya elarraichensis and negligible variation withinthe thyasirid the same siteCarlos (0.2 Ribeiro to MVs but 0.6Carlos ‰).The most Ribeiro of (range the ofvariability variation within 2.4 the ‰). was same observed site among (7.1 ‰ specimens in Darwin from MV). lutre 2, 0.5 and 0.4 ‰ in the Gemini, Mekn The canoes ranged from mens collected above ( MVs) and below 2000 mthe ( same site variability was much smaller (1.3 ‰ in four specimens from Yuma MV). Capt. Arutyunov MV, andthe for species one presented specimens in the shallow Geminiing and Lazarillo from de 8.2 Tormes MVs to presentedvalues 12.2 values of ‰. rang- Similarly, thesespecimen two of specimens also presented relatively high 3.3 Intra-specific variation within and between study sites showed more depleted signatures and( much wider Capt. Arutyunov MV) and than 5 5 25 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | “Bathymodi- Lamellisabella spp.). At shallower MVs, have only been found in sp.1 (at Mercator MV only) are erent sources of nutrients. Siboglinum ff erent behaviours and chemical path- ff use to the upper sediment. Polybrachia ff 17358 17357 Bobmarleya gadensis erent species that can show wide ranges of sizes and ff redi and Barry, 2002; Taylor and Glover, 2010). Finally, ff species and also 50 cm) below the seafloor (Hensen et al., 2007; Nuzzo et al., 2008) was found in dense aggregations inhabiting the narrow fissures be- ∼ Siboglinum Spirobrachia tripeira , erent geochemical settings. Solemyids are widespread but were always found ff The only epibenthic chemosymbiotic bivalve known in the Gulf of Cadiz, In the Gulf of Cadiz the methane-sulphate transition zone, where most microbial ac- Frenulata are generally described as tubeworms that extend over oxic-anoxic bound- the smaller mixotrophic species and may occur in relatively high densities and are olus” mauritanicus tween the large carbonatesmall slabs (young) individuals that are pave rarelimited the suggesting amount of crater a favorable habitat strong of where intraspecific Darwinreach higher competition concentrations the MV; of for seafloor. aggregations reduced the Unlike compounds of manyof other cold Cadiz seeps, are chemosymbiotic predominantly bivalvesvery burrowing in di species the Gulf that areat found very in low a densities. variety Thyasirids are of represented MVs by with several species; the juveniles and only the slim found but always insmall more frenulates modest in abundances MVs (Cunhaand with et shorter a al. species variety may 2012). of demandthem The geochemical less to presence exploit concentration settings, lower of of suggests concentrations reduced that that compounds, di smaller allowing This holds true fordenticulata frenulate species, forMVs example (Porto, Bonjardim the and long Carlostrations frenulates are Ribeiro, deep respectively) ( where highand sulphide the concen- presence oftaining gas larger hydrates biomasses. reservoirs In is Capt.highly likely Arutyunov variable; to the MV ensure sediments geochemical are fluxes gradientssustain frequently capable are disturbed very of steep by high but sus- gas densities hydrate dissociation of and smaller frenulates ( tivity occurs, is in most casesmore. more An than exception 30 cm is belowmeasured Capt. the seafloor near Arutyunov and MV the often at where surfacewith 80 high (Hensen cm long or methane bodies et were concentrations al., expected were insediments 2007). mud where volcanoes Burrowing with high bivalves wider sulphide redox and concentrations boundaries, are frenulates living deep in below the sediment interface. tiple symbioses obtaining fromof chemosynthetic sulphur- symbionts and including methane-oxidizers the(Fisher in co-ocurrence et addition al., to 1993; Duperron receiving et nutrition al., from 2008). filteraries feeding in the sediment,posterior with tube the body anterior buriedthe end in on variety the the of sediment. top morphologies However(length layer this and of of width), simplified di depth the description penetration sedimentfeatures hides in that and the may the sediment influence and the tube ability thickness, to all exploit important di byssal threads to hard substrates,on sometimes chemosynthetic forming tight symbionts aggregates.are located Their needed in reliance in their thement gills (Duperron, surrounding implies 2010). fluid, Bathymodiolin that mussels as occurwhich reduced in they a may compounds do broad be range not attributed of environments have to access their nutritional to flexibility: the they anoxic are sedi- capable of hosting mul- exhibit such athat diversity it of is morphologies likelyways and to that live acquire they in reduced utilizefour, sulphur such 2005). a from Regarding a Vesicomyidae the number most wide environment species ofusually live (Taylor variety shallowly di and with burrowed of Glover, the in 2000; sediment habitats posterior Du- the half sulphide of uptake the is shell throughuptake protruding the is (Krylova foot through and that the Sahling, protrudesbathymodiolin gill 2010) into mussels (Go and the (family sediment, Mytilidae) while oxygen are mostly epibenthic and live attached by duce long ramified burrows. In somea thyasirids negative the length relationship and number with(Dufour of the and burrows show concentration Felbeck, of 2003)able to hydrogen and “mine” sulphide it insoluble sulphides in hassition (Dando the be et strategies sediment al., proposed are 1994, available that 2004). for Details lucinids some of and sulphur lucinid acqui- thyasirids and are thyasirid species but both groups inhalant connection to the surface (Taylor and Glover, 2000; Dufour, 2005) and pro- 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | “B.” ; Ta- 50 ‰ is sim- S values ≥ − poseidoni 34 C ¨ S. cf. posei- ugel, 1987; Isorropodon δ T. sarsi cf. 13 Id from Capt. δ S. Thyasira vulco- C values for and ´ enio et al., 2008)) 13 , that also harbour C and are in the range of T. vulcolutre probably due to the δ have more depleted 13 δ Id were less depleted Siboglinum C signature of the species 13 sp. 2 may have been pooled and δ B. childressi L. asapheus T. vulcolutre T. methanophila Siboglinum collected in Norwegian fjords which “B”. mauritanicus and , highly depleted S value (above 6 ‰) found in Polybrachia 34 species ( δ ) was only found in one of the deeper MVs. 17360 17359 S. cf. poseidoni from Darwin MV (Rodrigues et al., 2011b, 2013) S. poseidoni erent species and/or ontogenic phases may adjust ff . However, more depleted values may reflect local Thyasira from the Capt. Arutyunov MV (Rodrigues et al., 2011b). “B.” mauritanicus S. cf. poseidoni C values measured in 13 δ S are much higher in 64 ‰ when purely thermogenic) or biogenic ( 34 δ L. asapheus . The presence of microbial symbionts was confirmed in most of ≤ − “B.” mauritanicus Cristineconcha regab C 13 S. cf. poseidoni C values for fixed via sulphide oxidation and are in line with values reported for other is one of the dominant species found in the near surface of gas satu- δ C than (species confirmed as part of the “childressi” group (G 2 13 13 δ δ erences in any of the studied species, which as suggested in previous studies ff may indicate thiotrophy. Because of their small size and morphological similarity is only found at the deeper (more active) MVs. The small vesicomyid “B.” mauritanicus The isotope values of other bivalve and siboglinid species are consistent with use of The isotope signatures of Carbon isotopic values have been used to identify the source of methane as either Average values of isotopic signatures of methane due to assimilation of pore water bicarbonate derived species elsewhere. The values reported for lucinids fromsymbionts other (Table S1). locations that The areilar stable known carbon to to isotope that harbour composition thiotrophic ble registered of S1) for and other indicatesthe that nutrition the of autotrophic the bacteria host.in Chemoautotrophy make the is a usually nutrition substantial consideredseems contribution of to to to be thyasirids more be than important the of case lucinids in (Van Dover the and Gulf Fry, of 1989), Cadiz, which since also are in accordance witha values dual previously symbiosis reported but for dominance of methano-oxidizing bacteria (Rodrigues et al., 2013) (Table S1). seawater CO together in the analysis, which complicates the interpretation ofhigher the results. than 5 ‰,studies can revealed the be occurrence taken ofof a as dual methane-oxidising evidence symbiosis bacteria with for andbacterium the methanotrophy. presence a (Rodrigues However, two molecular less et phylotypes al.,pendent abundant of 2013). phylotype their of Isotopic nutrition, values amauritanicus symbionts, for sulphur-oxidising life mytilids cycle are and variable site and location. de- nutrition and molecular studiesdizing have bacteria already showed theHowever, it occurrence is of arguable that methane the oxi- doni average of it is possible that co-occurring juveniles of Table S1). Nevertheless the values here reported are compatible with methanotrophic than values previously reportedis for known to harbour methane-oxidizing bacteria (Schmaljohann and Fl thermogenic ( when purely biogenic) methaneharbouring methanotrophic (Schoell, symbionts, 1980). The Arutyunov MV, and are consistent with the inferredMV thermogenic in particular, origin and of the methane Gulf in of the Cadiz Capt. in Arutyunov general (Nuzzo et al., 2008). the studied species withtion molecular (Rodrigues characterization et and al., Fluorescent 2010,isotopic in signatures 2011b, situ of 2012, the hybridiza- 2013; two Rodrigues bivalveicant tissues and analysed di Duperron, (foot and 2011). gill) The did(Cary not show et signif- al., 1989)symbiont is to an the host. indication of a high degree of carbon flow from the bacterial their position within the sedimentvariability according of to the chemical their substrata particular supply. needs and intensity4.2 and Methanotrophy vs. thiotrophy Overall the isotopic signatures ofof the a chemosymbiotic thiotrophic mode species of indicateand nutrition the for prevalence most species with the exception of lutre megadesmus rated sediments in Capt. Arutyunovthe MV larger (Cunha et species al., ( 2012).These Also distributions for suggest the that vesicomyids, di often found closer to the sediment surface while the larger species, 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | N Si- 15 and δ erent ff erence present ff Solemya N values 15 L. asphaeus 11 ‰ group” δ − Acharax Calyptogena paci- erences were found ff C and more enriched S. elarraichensis and 13 erence in discrimination erentiated life styles, dif- but because of the small δ ff ff , specimens from deeper specimens from Porto and C of 13 δ erent sources of nitrogen since ff is found. A. gadirae Acharax A. gadirae fixation. Whereas symbionts of are more depleted, but are in accordance erences in isotope values between species 2 ff erent pools of nitrogen, or discriminating dif- ff 17362 17361 Calyptogena magnifica N ammonium values occurring at the sediment T. vulcolutre , which are probably a consequence of metabolic 15 C values and in the same range of values found erent forms of the enzime ribulose 1,5-bisphosphate 13 A. gadirae ff s presented more depleted δ 30 ‰” group with a form I RubisCO and the “ − erences between the two species. Symbionts of co-generics of Acharax gadirae ff from the deeper mud volcanoes were similar to those found for s. Oliver et al. (2011) ascribed . Previous studies have shown that the di 2 CO 13 C isotopes by the two forms of RubisCO can explain the disproportion in Ib collected from three of the shallowest mud volcanoes are probably re- Solemya elarraichensi N values between solemyid species, suggesting that they are using di A. gadirae 13 15 erent species in these mud volcanoes, which could also explain the di ff δ C values of the chemoautotrophic symbiosis between two groups of chemosym- (Southward et al., 1994; Fisher, 1995), which suggests that bivalves expressing 13 N signatures than S. elarraichensi Nitrogen isotope values measured in both chemosymbiotic bivalves and frenulate When compared with previous data, the values of When compared with other taxa that also present form II RubisCO (e.g. vent vesti- It is worth noticing that within our samples of Overall 15 up and metabolise dissolved organic compounds (Southward and Southward, 1981). range reflects a dilutionwater of interface the (Lee and very Childressi, 1996; Carlier et al., 2010). tubeworms showed a wideabove range 6 ‰ of (value values, indicatedence including by of Levin one chemoautotrophic and species symbionts). Michenerboglinum with These (2002) relatively as high upper values limitlated were for to the found pres- in thein fact addition that to these the animals nutrition can provided explore by di their symbionts they may be capable of take those of other species of the samein genera the (Table S1). However, several di chemical species of nitrogen,ferently tapping after di acquisition of their nitrogen source. Furthermore, it’s likely that the MVs presented more depleted for Carlos Ribeiro mud volcanoes tosize the of new the species available specimens theof same a authors di raised the possibilityin of the the isotopic existence signatures. mentiferans) the values found for with the values foundfica for the bivalves RubisCO form II maytributing have to other the factors carbon than fractionation. this enzyme structure and kinetics con- expressing a form II (Robinson and Cavanaugh, 1995). both species are known tocarboxylase/oxygenase use di (RubisCO) for CO species present RubisCO formthe form I II (Scott of ettors the against al., enzime 2004), (Duperron symbionts etagainst of al. 2012), whichthe has lower discrimination fac- biotc invertebrates: the “ may be expected (Becker et al., 2011).is Co-occurrence particularly of interesting phylogenetically close and species inand the solemyids. Gulf of Cadiz it may be observed both forδ thyasirids and morphological di The high diversity ofplained chemosymbiotic by species a found combinationThe in of number historical the of species and Gulf coexisting contemporary in of atyunov factors single Cadiz MV) (Cunha MV and may may et be in be as al., most highthere ex- 2012). cases as is nine with resource (e.g. no Capt. partitioning. apparent Aru- Thisferentiated zonation may metabolic pattern, occur pathways and which by strategies suggests means or that ofresource by di partitioning a combination occurs, of consistent these. di If chemical Becker et al., 2011). Methanelower isotopic MVs (higher signature thermal is maturity considerably ofoccurs less methane; than depleted Nuzzo in et at the al., shal- deeper 2009) where MVs where 4.3 Resource partitioning from microbial sulphate reduction coupled to methane oxidation (Scott et al., 2004; 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | er- ff S values 34 δ S signatures. 34 erent degrees of δ ff erent fractionation ff erences in carbon isotopic N found in these study may ff 15 S values were highly variable N values indicate that organic δ 34 15 δ erences in the δ ff C may result from the assimilation erent MVs or within the same MV ff 13 δ erent MVs which is plausibly explained ff erent species may have di ff 17364 17363 erences maybe lower at shallow MVs as high ther- ff ´ ario et al., 2010; Oliver et al., 2011). Here we report (Fisher, 1995). As proposed by other authors (Carlier et al., 2 C fractionation occurring during DIC fixation by endosymbionts, erent distribution patterns (Vanreusel et al., 2009). It is therefore ff 13 δ S values of animals with chemoautolithotrophic sulphur-oxidizing sym- 34 δ C isotopic signatures that nevertheless are relatively consistent within species re- In the Gulf of Cadiz the thiotrophy is the dominant nutritional pathway, with methan- Similar arguments can be used to explain the di In general, there was considerably less intra-specific variation between specimens 13 time-series sampling of chemosymbioticments species should coupled be with undertaken geochemical to measure- better understand the interplay between temporal and otrophy and mixotrophy emergingδ as secondary strategies. Wesulting found from a specific metabolic wide pathways. spanare Contrastingly of most the likely highly the variable resultscales. of The the diversity high and variability the of distributionreflect of the chemosymbiotic the sulphide species environmental pool in heterogeneity at the in local Gulf termsment and of of Cadiz of regional nutrient life-styles sources, that but allows also an resource assort- partitioning at local and regional scales. Future pared with other seep locationsSea such and as the the Gulf mudfor volcanoes of the in Guinea Eastern first (Hil Mediterranean nutritional time patterns. on Our the resultsproduction distribution highlight in the and this relevance area life of and seep styles provide chemoautolithotrophic a of starting these point for species future and trophic ecology study studies. their that the three microbial3) consortia are known active with toprobable di perform that this a reaction diversity (ANME-1, ofchemosymbiotic -2, metazoans. sulphide and sources is - available locally for exploitation by the 5 Conclusions The number of chemosymbiotic species found in the Gulf of Cadiz is high when com- reflecting high variability into the Becker sulphide et pool al., onsulphate (2011) a and this very sulphide small pattern between spatial of chemosymbioticconsortia. scale. invertebrates high It According and variability sediment is is microbial knownand consistent AOM with that activity the in are cycling reflected the of by Gulf very of diverse microbial Cadiz, community the compositions and environmental setting variations among individuals of the same species either in di bionts reflect their reducedrelative abundance sulphur of source reduced compounds (MacAvoy available. et al., 2005) and probably the of DIC of diversefrom origins the depending variable onwith the the MV, isotopic and fractionation in dependingof variable on each proportions, the individual as growth but reported rate, also and for other therefore studies on (Carlier theThere et size is al., little 2010). fractionation between sulphideof and sulphate sulphide or oxidation organic sulphur by asTherefore, chemoautolithotrophic a result bacteria (reviewed in Canfield, 2001). (from one MV to another).mal These di maturity of the gasescomposition is (Nuzzo consistent with et moreences al., limited di in 2009). the However, isotopic thereMVs. signatures The were of observed intra-specific relevant chemosymbiotic variation species intra-specific in both the di within and between 2010) we hypothesize that the inter-specificresult variations of from species-specific types offactor symbionts occurring characterized during by the di assimilationparticular of case dissolved of inorganic frenulate nitrogen, tubeworms,access di and and that abilities in to the exploit dissolved organic compounds. collected from the sameby volcano a than from higher di variation in the composition of hydrocarbon pools at larger spatial scales derived from superficial waters. Onnitrogen the is contrary, of low local origin,(Levin, presumably 2005; resulting MacAvoy et from al., the 2008), activitylight and of are nitrate autotrophic possible or bacteria due to ammoniumues, assimilation possibly by of fixation isotopically the of symbionts N or, in the case of the very negative val- Furthermore, because of the shallower depth they may have access to organic nitrogen 5 5 25 15 20 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ´ ario, A., Ravara, A., and Pfannkuche, O.: Macro- 17366 17365 . , Mar. Ecol-Prog. Ser., 280, 181–187, 2004. ´ enio, L., Hil ˆ encia e a Tecnologia (FCT, Portugal). AH was also supported by Thyasira sarsi Thanks are due to the chief-scientists for the invitation to participate in ˜ ao para a Ci the bivalve mollusc tween sediment chemistry and frenulateDeep-Sea pogonophores Res. 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R., G Sahling, H., Galkin, S. V., Salyuk, A., Greinert, J., Foerstel, H., Piepenburg, D., and Suess, E.: 5 5 25 20 15 10 30 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | erent quanti- ff ) WW B.T7 B.T8, B.A8 W B.A9, S.L1 WW B.L1, B.S1 W S.S1 W B.S2, B.S3, S.S2 B.S4 WW S.S3 W B.S5, B.S6, S.S4 W B.A1 W B.A2, B.S7 W B.A3, B.A4, S.S5 B.A5 WW B.B1, B.B2 W B.S8, B.B3, B.B4 W B.S9, B.B5, B.B6 S.S6 WW S.S7 W S.S8 W B.T1 W B.T2 W B.A7, B.S10, B.T3, S.S9 B.T4,W B.T5 B.T6 W S.P1 W B.A6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 S 9.212.3 1.2 0.4 1.4 0.9 5.4 1.0 8.4 16.8 8.2 7.7 17.35.3 0.2 25.7 1.7 10.74.2 1.9 6.4 0.5 9.4 1.4 21.8 1.3 11.2 4.0 2.0 0.8 16.014.0 2.5 0.6 2.4 8.4 0.6 0.5 27.621.9 1.7 34 − − δ − − − − − − − − − − − − − − − − − − − − − − 25.36 25.36 30.44 38.72 49.47 59.92 43.97 46.40 04.38 05.46 06.33 05.45 04.98 11.47 11.48 11.51 20.01 20.05 19.97 20.05 20.02 05.54 25.27 25.32 00.03 12.26 ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ N 1.3 0.6 1.1 2.5 2.3 0.3 3.40.1 0.3 1.5 0.1 1.4 0.2 11.9 1.9 0.70.4 0.1 16.6 17.2 0.5 0.0 1.2 0.3 17.7 17.7 15 − − − δ − − − − − − − − − N 07 NN 08 08 N 09 NN 06 N 06 N 06 N 06 N 06 N 07 N 07 N 07 N 07 07 NN 07 N 07 N 07 N 07 N 07 N 07 N 07 N 07 N 08 N 08 08 N 09 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 S (mean and standard error – SE) for the www.pangaea.de C 34 13 δ δ 35.44 47.27 47.26 33.70 17.92 09.60 06.44 25.30 19.09 59.15 24.97 25.82 25.05 22.68 23.53 23.52 23.52 39.71 39.69 39.66 39.64 39.71 02.20 47.24 47.25 27.56 33.038.7 38.241.0 0.2 44.549.8 3.043.7 2.736.9 3.6 4.2 1.1 3.6 6.0 35.9 8.2 5.7 33.1 12.2 28.029.3 0.328.3 0.6 0.329.2 0.3 0.3 28.8 0.1 1.2 0.6 28.2 1.5 0.2 27.2 0.4 0.434.7 1.931.6 0.334.0 0.3 2.7 0.7 32.0 0.4 0.2 0.532.3 4.832.9 5.1 0.3 0.3 33.0 0.8 7.1 0.4 32.4 0.9 4.2 0.5 33.5 0.4 5.7 0.3 1.132.7 5.2 0.2 33.2 2.0 0.2 33.2 0.2 0.4 54.3 0.7 3.9 4.3 51.4 4.4 0.254.8 0.4 2.2 0.250.0 4.347.7 0.7 1.0 49.5 0.5 1.8 0.3 29.8 2.1 0.134.9 0.4 11.634.9 0.6 4.4 0.034.1 4.1 11.5 0.6 0.3 36.8 3.6 0.2 0.9 34.6 0.4 2.1 1.3 35.4 1.8 2.6 0.7 34.4 1.0 2.7 1.435.3 0.3 4.8 1.0 2.2 0.4 3.4 2.2 0.9 34.6 5.1 0.7 0.5 0.8 0.0 8.7 6.5 ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − − 17374 17373 N and 15 δ C, sp.1 Ib If Ia Id Ib Ib Ib 13 δ 157169 2200 m 2199145 m 35 35 3860 m 35 190#1217#1 1322 m225 1321 m 35 35 1320 m 35 Siboglinum cf. poseidoni Siboglinum cf. poseidoni Lamelisabella denticulata Siboglinum Siboglinum Siboglinum Polybrachia Siboglinum Siboglinum Acharax gadirae Acharax gadirae Acharax gadirae Acharax gadirae Acharax gadirae Solemya elarraichensis Solemya elarraichensis Solemya elarraichensis “Bathymodiolus” mauritanicus “Bathymodiolus” mauritanicus “Bathymodiolus” mauritanicus “Bathymodiolus” mauritanicus “Bathymodiolus” mauritanicus “Bathymodiolus” mauritanicus Lucinoma asapheus Thyasira vulcolutre Thyasira vulcolutre Thyasira vulcolutre Siboglinum Bivalvia Acharax gadirae Acharax gadirae Acharax gadirae Acharax gadirae Solemya elarraichensis Solemya elarraichensis Solemya elarraichensis Solemya elarraichensis Solemya elarraichensis Solemya elarraichensis Solemya elarraichensis Thyasira vulcolutre Thyasira vulcolutre Thyasira vulcolutre Thyasira vulcolutre Thyasira vulcolutre Siboglinidae – Frenulata Siboglinum 151938A 444 m 430 m 35 494 m 35 35 AT569 358 mAT528 35 AT586 489 mAT524 35 AT604 701 mAT605 960 m 34 AT607 1030 m 35 AT391 975 m 35 AT608 983 m 35 AT664 1105 m 35 1115 m 35 AT544 1128 m 35 AT546 35 1330 m 1345 35 m 35 AT667AT615 1562 m 2200 m 36 35 AT597 3061 m 35 032 1109 m 35 057 2175 m 35 S.S6 S.S7 S.L1 S.S4 S.S5 S.S8 S.P1 S.S9 S.S3 Species Species code nameB.A2 B.A3 B.A4 B.A5 B.A6 B.S1 Mean SE Mean SE Mean SE B.S8 B.S10 B.B1 B.B2 B.B3 B.B4 B.B5 B.B6 B.L1 B.T5 B.T6 B.T7 S.S2 B.A1 B.A7 B.A8 B.A9 B.S2 B.S3 B.S4 B.S5 B.S6 B.S7 B.S9 B.T1 B.T2 B.T3 B.T4 B.T8 S.S1 MSM01/03 M2007 TTR16 TTR16 TTR17 JC10 TTR14 MSM01/03 MSM01/03 MSM01/03 JC10 MSM01/03 Sampling details of specimens collected for stable isotope analysis. Di Stable isotope values of ` es TTR15 Bonjardim TTR15 MVMercator TTR15 Station Code Depth Latitude Longitude Species code GeminiKiddLazarillo de TormesMekn M2006 Yuma M2007 Ginburg TTR14 Jesus Baraza TTR14 TTR12 Captain Arutyunov TTR16 TTR14 SagresCarlos Ribeiro TTR16 TTR17 Porto MSM01/03 Darwin TTR16 erent specimens here studied. Species codes according to Table 1. ff Table 2. di Table 1. tative and non-quantitative samplers wereand used. station Station number code as is used composed in by PANGAEA the database cruise ( name Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 28 B If; ; 4.

, Va; Isor- ; 26. sp.1; Luci- ; 29. A ; 23. Ib; 13. Ia; 12. Acharax 29 ; 27. Polybrachia Lamelisabella Lamelisabella ; 24. Siboglinum Polybrachia Siboglinum Siboglinum Siboglinum Va; 8. Thyasira granulosa S for Bivalvia ( Axinulus croulinensis Ie; 16. 34 ; 11. ; 20. Undetermined IIa. If; 17. sp.; 3. δ sp.3; 7. Ia; 12. Thyasira vulcolutre S S for Bivalvia (A, B) ; 30; 34 δ Lamelisabella denticulata . C vs. Isorropodon perplexum vs Polybrachia osymbiotic osymbiotic species distribution. 13 ; 28. C C poseidoni Siboglinum δ 13 δ Siboglinum sp.; 3. Polybrachia Christineconcha regab Siboglinum cf. Lamelisabella ; 22. sp.3; 7. Bathymodiolus” mauritanicus Solemya Solemya (Petrasma) elarraichensis N and N N and . Mean values of species and respective Id; 15. ; 23. ; 11. 15 15 Ie; 16. ; 2. δ δ . Spirobrachia Spirobrachia tripeira sp.2; 6. ; 26. “ ; 25. (mixotrophic species); 31: vs Spinaxinus sentosus (mixotrophic species). Siboglinum C ; 20. Undetermined IIa. Bivalvia species; 21. 13 17376 17375 C vs. Lamelisabella δ Polybrachia poseidoni 13 Siboglinum ; 29. Lucinoma asapheus δ ; 2. Siboglinum cf. sp.2; 19. Polybrachia Vc; 10. ; 27. sp.2; 6. Ic; 14. Id; 15. Acharax Acharax gadirae sp.1; 5. Bobmarleya Bobmarleya gadensis Isorropodon perplexum Isorropodon megadesmus Siboglinum Siboglinum Axinulus croulinensis Thyasira granulosa ; 24. Spirobrachia tripeira Polybrachia

. ; 22. Thyasira vulcolutre ; 30; Siboglinum Polybrachia ) species from the Gulf of Cadiz. Mean values of species and respective Siboglinum Vc; 10. D , sp.1; 18. Bobmarleya gadensis Polybrachia Vb; 9. ; 28. sp.2; 19. C Ib; 13. Solemya (Petrasma) elarraichensis ; 4. sp.1; 5. Ic; 14. Mean values (after Table II) of Map of the Gulf of Cadiz showing the chemosymbiotic species distribution. Siboglin- ; 25. standard error are are error in A. standard also represented and and Frenulata (C, D) species from the Gulf of Cadiz Figure Figure 2. Mean values (after Table II) of

Polybrachia Siboglinum Polybrachia Siboglinum 3 4 2 1 5 Bathymodiolus” mauritanicus Siboglinidae Siboglinidae species: 1. Figure Figure 1. Map of the Gulf of Cadiz showing the chem . denticulata 8. Siboglinum Spinaxinus sentosus Bivalvia Bivalvia species; 21. 17. “ (mixotrophic species) Christineconcha regab Fig. 2. Vb; 9. Siboglinum 18. Fig. 1. idae species: 1. Polybrachia ropodon megadesmus (mixotrophic species); 31: and Frenulata ( standard error are also represented in A. gadirae noma asapheus 2 1 3 4 5 7 6 9 8 13 12 10 11