Deep-Sea Research II 98 (2013) 374–387

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Deep-Sea Research II

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Deep-sea surface-dwelling enteropneusts from the Mid-AtlanticRidge: Their ecology, distribution and mode of life

Daniel O.B. Jones a,n, Claudia H.S. Alt a, Imants G. Priede b, William D.K. Reid c,Benjamin D. Wigham c, David S.M. Billett a, Andrey V. Gebruk d,Antonina Rogacheva d, Andrew J. Gooday a

a National Oceanography Centre, European Way, Southampton SO14 3ZH, UKb Oceanlab, University of Aberdeen, Aberdeen AB41 6AA, UKc School of Marine Science and Technology, Newcastle University, Newcastle upon Tyne, UKd P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow 117997, Russia

a r t i c l e i n f o

Available online 21 May 2013

Keywords:Acorn wormsHemichordatesTergivelum cinnabarinumYoda purpurataAllapasus isidisBenthicRemotely operated vehicleMid-Atlantic RidgePhotograph

45/$ - see front matter & 2013 Elsevier Ltd. Ax.doi.org/10.1016/j.dsr2.2013.05.009

esponding author. Tel.: +44 2380 596357.ail address: dj1@noc.ac.uk (D.O.B. Jones).

a b s t r a c t

The ecology, distribution and mode of life of three species of surface-dwelling enteropneusts isdescribed, based on ROV observations and samples on the flanks of the Northern Mid-Atlantic Ridge(MAR) at comparative stations north and south of the Sub-Polar Front. Tergivelum cinnabarinumwas mostabundant in the north (mean¼4.56 ind. 1000 m−273.50 s.d.) and occurred at low densities in the south(mean¼1.1971.68 s.d.). Yoda purpurata was dominant in the south (mean¼17.00 ind. 1000 m−2712.32s.d.) but only one individual was found in the north. The within-station distribution of all enteropneustspecies encountered was generally random. T. cinnabarinum was larger (mean total length 142 mm) thanY. purpurata (mean total length 70 mm). Size distributions suggested smaller individuals of both specieson the western side of the MAR. Size and density of enteropneusts were generally higher in areas withhigher carbon flux to the seafloor. A single individual of Allapasus isidis was observed drifting and settlingto the seafloor at the SW site. Traces on the seafloor made by T. cinnabarinum covered a much higherpercentage of the total seabed area surveyed (mean¼0.323%70.155 s.d.) than those of Y. purpurata(mean¼0.034%70.037 s.d.). Stable isotope values for T. cinnabarinum suggested that it was a typicalsurficial deposit feeder. Enteropneusts appear to be abundant and an important bioturbator on thesedimented seafloor of the MAR at around 2500 m depth.

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1. Introduction

Enteropneusts are benthic hemichordates commonly foundburrowing in soft sediment from the intertidal zone to the deepsea (Cannon et al., 2009; Deland et al., 2010). There are approxi-mately 90 described species in the class Enteropneusta (e.g.Spengel, 1893; Van der Horst, 1939). The first records of deep-sea enteropneusts were three damaged specimens of the burrow-ing abyssal species Glandiceps abyssicola, Spengel, 1893, retrievedfrom 4570 m depth in the Atlantic, off Liberia, by the Challengerexpedition (Spengel, 1893). Enteropneusts, such as Glossobalanustuscarorae Belichov, 1971, have been recorded from trench systemsas deep as 8100 m in the Kuril–Kamchatka trench (Belichov, 1971),from 6520 to 7250 m depth in the Aleutian trench (Beliaev, 1989)and from 6200 to 8116 m in the sub-Antarctic trenches(Vinogradova et al., 1974). Another species, Saxipendium coronatum

ll rights reserved.

Woodwick and Sesenbaugh, 1985, has been recorded from hydro-thermal vents on the Galapagos Rift down to 2478 m depth(Woodwick and Sesenbaugh, 1985). Three other enteropneustsare known from moderate depths: Glandiceps talaboti Marion,1876, from 30 to 350 m in the Mediterranean, Spengelia sibogaeSpengel, 1907, from 275 m in the Sulu Sea (Spengel, 1909) andStereobalanus canadensis Spengel, 1893, from the Vøring Plateau(1252–1426 m) on the Norwegian margin (Jensen, 1992; Romero-Wetzel, 1989).

In contrast to these relatively inconspicuous burrowingforms, surface-dwelling motile hemichordates have beenrevealed by sea-floor imagery from the 1960s onwards(Bourne and Heezen, 1965; Heezen and Hollister, 1971). In someparts of the world they are an abundant and conspicuouscomponent of the deep-sea fauna (Anderson et al., 2011),producing characteristic spiral or meandering traces on softsediment bottoms. These traces have also been reported fromthe fossil record (Kitchell et al., 1978). Spiral traces resemblingthose of some enteroneusts are best developed in rocks ofCretaceous age or younger, whereas meandering traces have a

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387 375

longer geological history (Crimes and Fedonkin, 1994). How-ever, despite numerous images, these organisms eluded captureowing to their extreme fragility (Rychel and Swalla, 2008;Smith et al., 2005) and their precise nature remained unclearfor many years. Based on examination of photographs, Lemcheet al. (1976) proposed that they were tentacle-bearing lophen-teropneusts, a ‘missing-link’ group that shared the character-istics of the two main hemichordate body plans: the tentacle-less enteropneusts and the tentacle-bearing pterobranchs.

With developments in ROV technology that enabled preciseand gentle collection, the first deep-sea specimen of a surface-dwelling enteropneust was retrieved from 1901 m in the NE Pacificand described as a representative of a new family (Torquarator-idae), genus and species [Torquarator bullocki (Holland et al.,2005)]. What Lemche et al. (1976) believed was a lophophore, orring of tentacles, proved to be an artefact caused by the mis-interpretation of low-resolution images, and T. bullocki was recog-nised as a true enteropneust (Gage, 2005). A second deep-seaepifaunal species, Tergivelum baldwinae, was described from4100 m depth in the northern Pacific (Holland et al., 2009). As aresult of the increase in the use of ROVs, the rate of discovery hasaccelerated and at least nine unrecognised species have beenidentified from the NE Pacific (in addition to Torquarator bullockiand T. baldwinae), and three unrecognised species from theAtlantic Ocean (Holland et al., 2012; Osborn et al., 2012). Thethree Atlantic species (Osborn et al., 2012) were collected in June2010 on the Mid-Atlantic Ridge (MAR) as part of the ECOMARproject (Priede et al., 2012). Recent observations from Australia(Anderson et al., 2011) suggest that enteropneusts are alsocommon elsewhere in the world.

It is evident that deep-water enteropneusts feed on the surface ofthe sediment, ingesting particles from the substratum, apparentlywith little or no selectivity as they crawl forward leaving behind afaecal trail of undigestible, presumably mineralised, material(Holland et al., 2009). In a time-lapse camera study, T. baldwinaewas seen creating a four-whorl spiral of faeces in 39 h beforeemptying its gut, ascending from the seafloor and presumablyswimming or floating off to another feeding location (Smith et al.,2005). A few observations of trace formation in deep-water burrow-ing enteropneust species have also been made. An unidentifiedenteropneust was found beneath a mound structure surrounded byburrow openings in a box-core sample taken at 2100 m depth in theNE Atlantic (Mauviel et al., 1987). On the Vøring Plateau, Romero-Wetzel (1989) and Jensen (1992) described the occurrence ofStereobalanus canadensis at densities of up to 24 indiv. m−2 withinextensive, mostly horizontal systems of branching burrows withvertical shafts to the surface. A number of animals (2–6) shared theseburrow systems, termed ‘enteropneust nests’ (Jensen, 1992), whichalso contained masses of faecal pellets. High densities of an uni-dentified enteropneust species were also found living on the surfaceof a soft, sandy contourite sediment at 850–1000 m on the easternflank of the Faroe–Shetland Channel off Scotland (Bett, 2001). Multi-opening burrows were found deeper in the channel, but it wasunclear whether the same enteropneusts were responsible for thesestructures (Jensen, 1992).

It seems likely that in some regions enteropneusts may form animportant component of the benthic megafauna that feed on orbury the surface-derived phytodetritus (Smallwood et al., 1999;Vardaro et al., 2009) and hence influence the fate of organiccarbon reaching the deep-sea floor. Megabenthic deposit feedersmay completely turn over deep-water sediment surfaces withinweeks (Bett et al., 2001), potentially dominating consumption offresh organic material arriving at the seafloor. These processescontrol carbon supply to sediment communities, benthic biogeo-chemical processes, and ultimately the sequestration of carbon indeep-sea sediments (Smallwood et al., 1999).

In this study we describe the ecology, distribution and mode oflife of three species of surface-dwelling enteropneusts, Tergivelumcinnabarinum Holland in Priede et al. (2012), Yoda purpurataHolland in Priede et al. (2012) and Allapasus isidis Holland inPriede et al. (2012), based on observations and samples obtainedusing the ROV Isis on the flanks of the Northern Mid-Atlantic Ridgeat comparative stations north and south of the Sub-Polar Front inthe area of the Charlie–Gibbs Fracture Zone. The importance ofthese species to mid-ocean deep-water benthic ecosystems isevaluated and observations made of their behaviour.

2. Methods

2.1. Study site

Heezen (1968) estimated that mid-ocean ridges comprise ca. 33%of total global sea floor area and in the North Atlantic account forapproximately half of the lower bathyal habitat, defined as between800 and 3500 m depth (Vierros et al., 2009). Collections and surveyswere undertaken at each of the four main ECOMAR stations atca. 2500 m depth on either side of the axis of the Mid-Atlantic Ridge;the NE and NW stations at ca. 541N and the SW and SE stations atca. 491N (Priede et al., 2013). Soft sediment cover predominates atthese depths (Mitchell et al., 1998) and it is on these substrata thatour work focussed. The northern stations were located beneathrelatively cool waters of the Arctic and Sub-Arctic oceanic provincesand the southern stations beneath warmer waters of the NorthAtlantic Drift. The northern and southern sites are separated by theCharlie–Gibbs Fracture Zone, and lie beneath contrasting surfaceproduction regimes (Longhurst, 1998). In this area, the North Atlanticcurrent crosses the MAR from west to east and corresponds to thelocation of the Sub-Polar Front (Read et al., 2010). In addition to thebathymetric and hydrographic barriers between the northern andsouthern sites, the MAR itself represents a geographical barrier thatpotentially creates faunal differences between the eastern and thewestern basins of the North Atlantic Ocean.

2.2. Sample collection

Enteropneusts were obtained from the seafloor using the suctionsampling system on the Isis ROV. This system enabled very gentlecollection of the animals and retrieval of near-perfect individuals,which acted as voucher specimens enabling us to identify theindividuals seen in the ROV Isis videos and still camera photographs.

2.3. Survey design

Data were collected in June 2010 from the RRS James Cook (cruiseJC048) as part of the UK Natural Environment Research Council(NERC) ECOMAR project. ROV video transects (Supplementarymaterial) were designed to assess the benthic environment andbiology of the four main ECOMAR study sites: NW, NE, SW and SE.Within each study site three habitats were identified: flat (0–21slope), slopes (8–121 slope) and cliffs (301+ slopes). Very fewenteropneusts were seen on slopes so this habitat was excludedfrom our analysis. The area of each habitat was delineated bypolygons using ArcGIS (version 10, ESRI). For each habitat in turn,polygons were selected (largest area first) until 40.5 km2 of seabedwere covered, all remaining polygons were removed automatically.Within the selected polygons 100 lines were generated starting atrandom start points, lines were 500 m long and 151 heading,approximately parallel to the axis of the MAR and its dominanttopography. All lines that intersected with polygon boundaries wereremoved. Four non-overlapping lines were picked at random fromthe remaining lines. These four lines became the ROV sampling

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387376

transects. The sampling unit for all analyses was a 500 m long ROVtransect, resulting in a total of 48 sampling units (32 excluding cliffs).

2.4. Data collection

Data were collected using the NERC ROV Isis, which was equippedwith two high-definition (HD) colour video cameras (Insite MiniZeus), a 3-chip colour standard-definition video (Insite Pegasus),digital still camera (Insite Scorpio) and Hydrargyrum medium-arciodide (HMI) lighting. A set of two parallel lasers (100 mm apart) wasmounted on each HD camera for scaling. One HD camera wasmounted vertically on the tool tray with a HMI light mounted atan angle to illuminate the field of view (1.5 m separation). The otherHD camera was mounted on a pan-and-tilt unit at the front of theROV. The ROV was equipped with both ultra-short baseline naviga-tion (Sonardyne medium frequency USBL) to provide absolute globalposition (accuracy approximately710 m) and Doppler velocity lognavigation (RDI DVL 1200 kHz) to provide very accurate relativeposition (accuracy70.1 m).

On every transect the ROV was run in a straight line, on a setbearing, at a constant speed (0.13 m s−1) and set altitude (2 m). TheROV was flown maintaining Doppler lock on the seafloor, enablingvery precise control. Transect width (2 m; max variation70.1 m)was maintained over an uneven seafloor by adjusting ROV altitude in50 mm steps to ensure that parallel laser beams projected onto theseafloor (100 mm apart on the seafloor) were constantly the samedistance apart on the screen (5% of screenwidth). The HD video fromthe vertical camera was used for all analyses. An additional HDcamera was used to take zoomed-in oblique video to help withspecies identification. Over the 500 m long transect, this techniqueimaged 1000 m2 of seafloor and 2000 m3 of overlying suprabenthicwater. HD video was recorded (AJA KiPro) and stored as fullresolution digital files on a hard drive (DroboPro).

2.5. Video analysis

Full resolution video was viewed on a 27 in. screen usingQuicktime Pro (version 7, Apple Inc.). Enteropneusts and their

Fig. 1. Example pictures of enteropneusts showing (A) Tergivelum cinnabarinum and (C)were (1+2) Total length for Tergivelum cinnabarinum, (1+3) total length for Yoda purpupurpurata only), (4) lip width, (5) main body width, (6) proboscis length, (7) body area

traces were identified and counted as the parallel laser dots passedover them in the centre of the image. Only enteropneusts and theirtraces that could be seen in their entirety were included inanalysis. For size measurements, quality control and later taxo-nomic reference still frames containing enteropneusts and theirtraces were extracted from video using Final Cut Pro (version X10.0, Apple Inc.).

2.6. Data analysis

2.6.1. Size and area measurementsSize measurements were made on still images extracted from

video using ImageJ software (version 1.44) (Abramoff et al., 2004).A straight-line distance between the parallel laser dots (a constant100 mm on the seabed) was used to set the scale of the image.Measurements were made of total length, main body length, headlength, lip width, main body width, proboscis length, body area andtrace area/length (Fig. 1). The segmented line tool and the freehandselection tool were used to make length and area measurementsrespectively. Trace area for T. cinnabarinum was calculated byassuming a complete coverage of a bounding circle (see Fig. 1). ForY. purpurata trace area was calculated from the trace length multi-plied by lip width. Area measurements were only made for traceswith visible enteropneusts. Total areal trace coverage estimates weremade by multiplying average trace areas by total trace densities. Theterm traces was used throughout to include both the faecal trail andthe strip of sea floor on which the sediment has been removed.

2.6.2. DensityDensities of each enteropneust species and all enteropneust trace

types were summed for each transect, plotted, and a two-factorANOVA test (on ranks if data were not normal) was performed withtwo factors: superstation (NE, NW, SE, SW) and slope (flat and 101)using the R programming environment (R Development Core Team,2010).

Yoda purpurata and the measurements taken (B and D). The measurements takenrata, (2) main body length (Tergivelum cinnabarinum only), (3) head length (Yodaand (8) trace area (Tergivelum cinnabarinum only).

Table 1Comparison of mean densities of enteropneusts and their traces on flat areas (0–21gradient) and slopes (8–121 gradient), between superstations and north and southof the Charlie–Gibbs Fracture Zone (as numbers per 1000 m2). Means presentedwith their respective standard deviation (SD).

Tergivelumcinnabarinum

Yodapurpurata

Tergivelumcinnabarinum traces

Yoda purpuratatraces

Station Mean SD Mean SD Mean SD Mean SD

NE 101 5.50 2.65 0 0 187.25 40.09 0 0NE flat 5.00 3.37 0.25 0.50 233.00 60.17 0 0

NW 101 6.50 4.51 0 0 202.25 107.01 0 0NW flat 1.25 1.26 0 0 76.25 27.85 0 0SE 101 0.25 0.50 13.50 7.94 0 0 22.75 11.90SE flat 3.00 0.82 30.50 13.48 64.50 26.81 73.75 48.97SW 101 0 0 8.75 11.84 1.00 0.82 16.50 18.16SW flat 1.50 2.38 15.25 4.50 34.50 35.80 59.50 24.23

NE 5.25 2.82 0.13 0.35 210.13 53.28 0 0NW 3.88 4.16 0 0 139.25 98.87 0 0SE 1.63 1.60 22.00 13.69 32.25 38.69 48.25 42.80SW 0.75 1.75 12.00 8.99 17.75 29.50 38.00 30.35

Overall N 4.56 3.50 0.06 0.25 174.69 85.01 0 0Overall S 1.19 1.68 17.00 12.32 25.00 34.07 43.13 36.23

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387 377

2.6.3. DistributionThe within-transect spatial distribution of T. cinnabarinum and

Y. purpurata and their traces were analysed using a standardizedMorisita index of dispersion (Krebs, 1998). The number of enter-opneusts or traces enumerated in segments of video covering20 m2 of seabed (n¼50 per transect) was used to investigatedispersion. The standardized Morisita index of dispersion wascalculated using the ‘dispindmorisita’ function of the ‘Vegan’library (Oksanen et al., 2011) of the R programming environment(R Development Core Team, 2010).

2.6.4. Biomass calculationsEstimates of enteropneust biomass were made from body

volume, which was assumed to equal biomass given a relativedensity close to that of water. Body area was the most accurateway to assess volume as it took into account the variations in bodywidth across the animal. Body area was combined with themeasured body width to assess volume. By assuming the animalwas cylindrical, volume could be calculated using standard for-mulas. The body area was converted to cylinder height by dividingby the measured body width. When simplified, the equation usedto estimate body volume expressed in terms of body width (w)and body area (a) was

volume¼ 0:25⋅w⋅a⋅π

2.7. Stable isotope analysis

Tissues from two individual enteropneusts (T. cinnabarinum)were dissected from freshly collected material and then frozen at−80 1C in glass vials. In the laboratory, the tissue was freeze dried,ground using a pestle and mortar and separated into aliquots forcarbon and nitrogen stable isotope analysis (SIA). Aliquots forcarbon SIAwere lipid extracted, following Reid et al. (2012), becauselipids are depleted in 13C relative to protein and variation in lipidcontent between species can confound trophic interactions (Postet al., 2007). About 0.1 N HCl was added to the carbon aliquot toremove any carbonates that had adhered to the tissue. Sampleswere redried at 50 1C for 48 h. Sample analysis was undertaken byIso-Analytical (Crewe, United Kingdom) using a Europa ScientificElemental Analyser coupled to a Europa Scientific 20-20 MassSpectrometer. Internal laboratory standards were used for correc-tion and quality control, which are traceable to International AtomicEnergy Agency (IAEA) standards IAEA-CH-6 and IAEA-N-1. Anexternal standard of freeze dried and ground white fish muscle(Antimora rostrata) was also analysed (δ13C, n¼7, mean¼–18.86‰70.05 SD; δ15N, n¼7, mean¼13.34‰70.17 SD).

3. Results

3.1. Species presence and abundance

A total of 92 T. cinnabarinum and 273 Y. purpurata individualswere counted in the video surveys. T. cinnabarinum was thedominant species in the north and Y. purpurata was dominant inthe south. Y. purpurata was not found in the NW area and only oneunambiguous individual was observed in the NE area. A singleindividual of A. isidis was recovered from the SW area.

T. cinnabarinum densities (Table 1; Fig. 2) were around fourtimes higher at the northern sites (mean¼4.56 ind. 1000 m−273.50 SD) than the southern sites (mean¼1.1971.68 SD). Thisvariation led to significant differences between superstations(two-factor ANOVA on ranks F¼11.031, df¼3, 24, po0.001).Across all the sites density was slightly higher on the 101 slopes(mean 3.06 ind. 1000 m−2712.28 SD) than on the flat plains

(mean 2.69 ind. 1000 m−2738.66 SD), but the differences werenot significant (two-factor ANOVA on ranks F¼0.306, df¼1, 24,p¼0.585). This pattern was also true for just the northern sites.However, if only the southern sites were considered there was ahigher density of T. cinnabarinum in the flat areas (mean 2.25 ind.1000 m−271.83 SD) than on the 101 slopes (mean 0.125 ind.1000 m−270.35 SD). These differences led to a significant inter-action of slope and superstation (two-factor ANOVA on ranksF¼7.236, df¼3, 24, po0.01) on the density of T. cinnabarinum.Although density was generally higher to the east (Table 1) than tothe west of the MAR, there were no significant pairwise differ-ences between either the NE and NW (Tukey HSD p¼0.268) or theSE and SW (p¼0.441) sites.

At the southern stations densities of Y. purpurata (Table 1) werehigher and more variable (mean¼17.00 ind. 1000 m−2712.32 SD)than those of T. cinnabarinum in the north. Since only oneindividual Y. purpurata was seen at the northern superstations(flat site A05_9 in the NE), these stations were not included insubsequent analysis. Two-factor ANOVA showed significant differ-ences between slope levels (F¼5.452, df¼1, 12, po0.05) but nosignificant differences between the two southern sites (F¼3.949,df¼1, 12, p¼0.070) in the densities of Y. purpurata. The overalldensity of this species was higher in the flat areas (mean 22.88 ind.1000 m−2712.37 SD) than on the 101 slopes (mean 11.13 ind.1000 m−279.67 SD).

3.2. Size and morphometrics

T. cinnabarinum has a mean total length of 142 mm (Tables 2and 3), approximately twice that of the other dominant species,Y. purpurata. Size–frequency distributions (Fig. 3) show a normaldistribution of total lengths for T. cinnabarinum. There is someindication of a bi-modal distribution at the NE site. For T. cinnabar-inum, total length has a significant positive relationship with mainbody length (main body length¼0.48 total length+13.45, R2¼0.81),lip width (lip width¼0.12 total length+11.72, R2¼0.74), body width(body width¼0.06 total length+6.37, R2¼0.65), proboscis length(proboscis length¼0.03 total length+2.70, R2¼0.54), body area(body area¼10.32 total length−426.06, R2¼0.89) and biomass(biomass¼209.68 total length−13,918.86, R2¼0.81). T. cinnabarinumreached larger sizes at the northern compared with the southernsuperstations (max size¼398 mm in the north, 231 mm in the

NE−0 NE−10 NW−0 NW−10 SE−0 SE−10 SW−0 SW−10

Tergivelum cinnabarinum density

Den

sity

(no.

m−3

)0

4

8

NE−0 NE−10 NW−0 NW−10 SE−0 SE−10 SW−0 SW−10

Tergivelum cinnabarinum total length

mm

0

100

250

NE−0 NE−10 NW−0 NW−10 SE−0 SE−10 SW−0 SW−10

Tergivelum cinnabarinum individual biomass

g

0

20

40

NE−0 NE−10 NW−0 NW−10 SE−0 SE−10 SW−0 SW−10

Yoda purpurata density

Den

sity

(no.

m−3

)

0

20

40

NE−0 NE−10 NW−0 NW−10 SE−0 SE−10 SW−0 SW−10

Yoda purpurata total length

mm

0

40

80

NE−0 NE−10 NW−0 NW−10 SE−0 SE−10 SW−0 SW−10

Yoda purpurata individual biomass

g

0

4

8

12

Fig. 2. Density, total length and biomass of Tergivelum cinnabarinum and Yoda purpurata for ECOMAR substations. The x-axis labels indicate the station name and slope levelError bars represent 1 standard deviation.

Table 2Mean morphometric data for Atlantic enteropneusts. SD¼standard deviations,n¼104 (T. cinnabarinum) and n¼220 (Y. purpurata). NA: not measured.

Units T. cinnabarinum Y. purpurata

Measurement Mean SD Mean SD

Total length mm 142.0 81.6 69.6 23.4Main body length mm 79.9 45.0 NA NAHead length mm NA NA 26.1 6.8Lip width mm 27.9 11.4 41.3 13.3Body width mm 14.8 6.7 11.3 3.3Proboscis length mm 6.8 3.2 15.8 4.6Body area mm2 975.2 891.5 653.2 360.6Biomass g 16.7 19.3 6.5 5.0

Table 3Comparison of mean total length (mm) of T. cinnabarinum and Y. purpurata at thefour stations.

T. cinnabarinum Y. purpurata

Station mean SD mean SD

NE 101 168.84 89.13 NA NANE flat 190.20 93.85 NA NANW 101 107.33 50.47 NA NANW flat 157.80 55.66 NA NASE 101 NA NA 68.73 20.69SE flat 98.11 48.68 71.13 25.32SW 101 NA NA 65.62 19.81SW flat 125.46 74.06 69.78 23.99

NE 180.10 91.43 NA NANW 115.21 53.69 NA NASE 93.11 48.68 70.39 23.94SW 125.46 74.06 68.38 22.63

Overall N 156.23 85.32 NA NAOverall S 106.05 58.52 69.63 23.43

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387378

south). Two-factor ANOVA (on ranks) showed significant differencesin the total length of this species between superstations (F¼7.71,df¼3, 98, po0.001), but no significant effect of slope (F¼1.63,df¼1, 98, p¼0.205) or interaction between slope and superstation

NW

total length0 100 200 300 400

NE

total length0 100 200 300 400

0

2

4

6

0

2

4

6

8

SW

total length100 150 200

0

10

20

30

SE

total length0 50 0 50 100 150 200

0

10

30

50

Fig. 3. Total length (mm) frequency histograms for Tergivelum cinnabarinum at the NE and NW site and for Yoda purpurata at the SE and SW site. Note different scales on x-axis for northern and southern sites.

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387 379

(F¼1.475, df¼1, 98, p¼0.227). Pairwise tests (Tukey HSD) revealedthat total lengths of T. cinnabarinum are significantly greater in theNE than in the NW area (po0.001) and in the NE compared withthe SE area (po0.05); however, there were no other significantdifferences.

Y. purpurata had a mean total length of 69.6 mm (Table 3;Fig. 2). The distribution of total lengths (Fig. 3) skewed towardssmall individuals, with large animals (up to 153 mm total length)being rarer. Total length for this species had a significant positiverelationship with head length (head length¼0.22 total length+10.85, R2¼0.58), lip width (lip width¼0.38 total length+14.91,R2¼0.44), body width (body width¼0.09 total length+5.08,R2¼0.39), proboscis length (proboscis length¼0.14 total length+5.72, R2¼0.54), body area (body area¼12.62 total length−225.68,R2¼0.67) and biomass (biomass¼166.53 total length−5140.34,R2¼0.61). The two-factor ANOVA (on ranks) test did not revealany significant differences in the total lengths of Y. purpuratabetween the southern superstations (F¼0.468, df¼1, 216,p¼0.495) or between the different seabed slopes (F¼0.342,df¼1, 216, p¼0.559) or with the interaction between the two(F¼0.282, df¼1, 216, p¼0.596).

3.3. Ecology, behaviour and locomotion

Examination of the northern species, T. cinnabarinum, indifferent stages of trace formation provided evidence of itsbehaviour. This species, which was not found living on steep rockyslopes or on bare rock, appeared to land curled up on the sedimentsurface (Fig. 4A). It then began a gradual movement (too slow to beseen with the ROV) in a regular spiral away from the landing site

(Fig. 4C). Traces were both clockwise (55.6% observations withassociated animal; Fig. 4C) and anticlockwise (44.4%; Fig. 4D) indirection. It was not possible to ascertain if particular individualenteropneusts always formed traces in the same direction. Occa-sionally (9.5% of observations), T. cinnabarinum created ‘S’ shapedswitchback traces (Fig. 4B) by making one or more 1801 turnsduring the trace formation. In all cases, as the enteropneustmoved, it created a strip of cleared sediment as wide as its lip(Fig. 4C). The enteropneust never covered the same area ofsediment twice and a narrow ridge of undisturbed sediment wassometimes seen between whorls (Fig. 4D). T. cinnabarinum traceshad typically three (maximum observed of five) complete whorls,following which the enteropneust lifted off from the sediment. Inall cases where the lifting-off behaviour was observed, the animalhad moved back towards the centre of the trace (from one to threewhorls from the centre; Fig. 4E). As observations were madeduring the video transects, and the movements of T. cinnabarinumwere slow, only brief snapshots of behaviours could be obtained.In two cases (05 June 2010 at 19:12 at NW 9 and 11 June 07:37 atNE 9 shown in Fig. 4F), T. cinnabarinum was observed to lift offfrom the sediment proboscis first. In the remaining five observa-tions the animal adopted a hooked posture, the central veils (seePriede et al., 2012) appearing to lift first (seen on 11 June 2010 at07:07 at NE 9, on 11 June 2010 at 07:58 at NE 11 [shown in Fig. 4G],on June 11 2010 at 15:53 and 15:47 [shown in Fig. 4H] at NE 2 andon June 11 2010 at 16:59 at NE 3), with the veils clearly elevatedabove the sediment compared with the proboscis. The posteriortrunk (lateroventral fold) remained entirely on the sedimentsurface in all observations except two (both on June 11 2010, oneat 16:59 at NE 3, the other at 15:47 at NE 2 [shown in Fig. 4H]), in

Fig. 4. Example pictures of Tergivelum cinnabarinum showing: (A) animal shortly after arrival at a new site, (B) forming switchback trace, (C) forming clockwise trace,(D) forming anticlockwise trace, (E) returning to the centre of the trace, (F) initiating lift-off with proboscis raised above the sediment, (G) lift off with 'hooked' posture,where veils are elevated above proboscis and posterior trunk, (H) near complete lift-off. Scale bars represent 100 mm.

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387380

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which the animal is just touching the sediment surface with theend of the posterior trunk. We never observed T. cinnabarinumdrifting in the water column.

Y. purpurata was seen living on a range of substrata, from softsediment (Fig. 5A), to pteropod shells (Fig. 5B) to steep rocky slopes,including on bare rock (Fig. 5D). This species created an irregular, oftenserpentine trace (Fig. 5C). very different from that of T. cinnabarinum.The trace was highly variable in length, commonly short (mean2.4 body lengths72.1 SD), but sometimes extending to 13.5 bodylengths. Where animals were seen with traces, the trace was typicallywell formed with little sign of erosion (Fig. 5C). Y. purpurata was notobserved drifting or lifting off from the sediment.

Fig. 5. Behaviour of Yoda purpurata showing: (A) animal on soft sediment, (B) animal ontwo individuals in close proximity. Scale bar represents 100 mm.

On 22 June 2010, the unique individual of the third species,A. isidis, was encountered at Station 43 ROV Isis dive 174 (SW).It was spotted drifting above the sea floor at an altitude of ca. 15 cm;the camera focussed on it at 04:01:00 h. It had a horizontal posturewith the body curled up in a loose helix of about 1.5 turns (Fig. 6A).The height above the sea floor increased to ca. 50 cm. It was driftingwith the bottom current and changed posture slowly to a flat spi-ral (Fig. 6B) until 04:04:01 h when, possibly in response to theproximity of the ROV, it started to extend the anterior part ofthe body. At the same time, the proboscis changed from a roundedto a conical shape (Fig. 6C). It finally straightened its body untilit was orientated almost horizontal above the sea floor (Fig. 6D).

pteropod shells, (C) well developed trace, (D) animal on bare rock, (E) observation of

Fig. 6. Behaviour of Allapasus isidis. This single specimen of approximately 130 mm body length was observed drifting above the sea floor (A) with a horizontal posture withthe body curled up in a loose helix, (B) in a flat spiral position, (C) with extended anterior part of the body and more pointed proboscis, (D) with a straightened body,(E) apparently controlled descent to the sea floor with body tilted into a vertical position and the head down.

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387382

Once the posterior region was uncurled (at 04:05:08 h), the bodytilted into a vertical position with the head down (Fig. 6E). Theenteropneust then continued drifting in a vertical posture until04:05:37 h, when it began to descend head-first to the sea floor.No body movements were involved in this manoeuvre; it simplyfloated downwards apparently driven by slightly negative buoyancy.The proboscis touched the sea floor at 04:05:55 h, the descent havingtaken 18 s from a height of ca. 0.5 m. Descent velocity was thereforeestimated as 3.8 cm s−1. The animal then lay on the sea floormotionless with the body straight and proboscis resuming a roundedshape, until 04:11:30 h when the ROV closed in to collect it. Thissingle individual was designated the holotype of A. isidis. No furtherinformation was obtained and so it is unknown whether this speciescan burrow or browse on the sea floor.

From the standard drag equation the downward force F actingon the enteropneust is given by

F ¼ 12ρU2CdA

where ρ is the density of sea water, U is the sinking velocity, Cd is thedrag coefficient and A is the area. If we assume that the underwaterweight of the enteropneust does not change with posture, then F isconstant. For the floating horizontal enteropneust with body length13 cm and maximum diameter 1 cm: area Af¼1.3�10−3 m2 and thedrag coefficient Cdf¼0.5 assuming an irregular shape close to asphere. For the descending vertical enteropneust: area Af¼7.85�10−5 m2 and the drag coefficient Cdf¼0.09 assuming an elongatedstreamlined shape. The enteropneust descended at an assumedconstant velocity of 3.8 cm−1 or 0.038 m s−1.

Inserting these values into the equation for the floating anddescending conditions, since ρ and F are constants we can solve for Uf

the theoretical sinking velocity for the horizontally floating enter-opneust. The result is a value of 0.004 m s1 or 0.4 cm s−1. A. isidis wasseen floating above the sea floor continuously for 3 min. During thistime in still water it would have descended by ca. 0.7 m. Whilst

eddies in the flow field can lift the animal above the sea floor fromtime to time, posture alone cannot account for the behaviour weobserved. During the floating phase the animal must have been closeto neutral buoyancy and for the descent it somehow must havereduced its buoyancy.

From our observations it is evident that the centre of mass ofA. isidis is anterior the centre of buoyancy. When it straightenedout its body in mid-water the animal automatically tilted into thevertical head down posture. Curling the body into a spiral or helixalters the relative positions of the centres of mass and buoyancy sothat a more or less horizontal posture is adopted. This change inposture increases drag and consequently reduces sinking speedbut is insufficient to account for the ability of the animal to driftabove the sea floor. We hypothesise that in making the transitionfrom floating to descent it must have been able to change itsbuoyancy, possibly by expelling dilute fluid from the body.

It was not possible to ascertain if any of the enteropneustspecies were able to select their feeding sites by choosing when totransition between drifting in the water column and feeding onthe seafloor. If Y. purpurata does drift between feeding sites, thenthe fact that it was observed on small, presumably low-food,patches of sediment on steep rocky slopes, and occasionally on therocks themselves, suggests that it was not very selective.

We did not observe any interactions between enteropneustindividuals. More than one T. cinnabarinum was never seen ona single still frame from the video and individuals of T. cinnabar-inum and Y. purpurata were not observed within close proximity toeach other. On the other hand, individuals of Y. purpurata wereobserved within 100 mm of other individuals on one occasion(SE flat 3), although no traces ever crossed over each other.

3.4. Within-transect distribution of enteropneusts and their traces

T. cinnabarinum was almost always significantly randomlydistributed within the transect (Standardised Morisita Index −0.5

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387 383

to 0.5). Only one transect had a significantly clumped distribution(SE_A12_01_flat) and this transect only yielded four individualanimals, three of which occurred within a 9 m long section of thetransect. This area had no visually different features from theremainder of the transect.

The within-transect distribution of spiral traces (made byT. cinnabarinum) was random in the majority (21/32) of transects(Standardised Morisita Index −0.5 to 0.5). Despite this pattern, 11transects, including transects from all superstations, had clumpedwithin-transect distributions of spiral traces (Standardised Mor-isita Index40.5). There were no clear patterns in the distributionof this species between transects (Fig. 7).

Longitude

Latit

ude

Latit

ude

Tergivelum

Yoda p

SW

1 m-2 0.

-36.21 -36.19

53.96

53.98

54.00NW

Longitude

-28.66 -28.62

48.725

48.740

48.755

SW

-28.66 -28.62

Longitude

Latit

ude

48.725

48.740

48.755

Fig. 7. Maps of population densities of enteropneusts within the four ECOMAR sites. Thethe circle is proportional to the density of Tergivelum cinnabarinum (top) and Yoda purpuThe thick horizontal line represents 1 km in distance on the seafloor.

Y. purpurata was also almost always significantly randomlydistributed within the transect (Standardised Morisita Index −0.5to 0.5). Again this species had a significantly clumped distributionin one transect (SW A11_04_flat), in which 19 individuals wereobserved. At six places along the transect there were two indivi-duals of the southern species within a section of seaflooro5 mlong. These areas were not visually different from the remainder ofthe transect. The remaining 13 individuals were spaced furtherapart.

The within-transect distribution of traces made by Y. purpuratawas random in the majority (22/32) of transects (StandardisedMorisita Index −0.5 to 0.5). Despite this pattern, 10 transects,

Longitude

Latit

ude

Latit

ude

cinnabarinum

urpurata

SE

5 m-2 0.1 m-2

-34.195 -34.180 -34.165

53.0

54.0

55.0

NE

Longitude

-27.85 -27.80 -27.75 -27.7049.00

49.06

49.12

SE

-27.85 -27.80 -27.75 -27.70

Longitude

Latit

ude

49.00

49.06

49.12

centre of each circle represents the location of an individual transect and the area ofrata (bottom) found at that transect. Latitude and longitude are in decimal degrees.

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387384

including transects from all superstations, had significantlyclumped within-transect distributions of traces (StandardisedMorisita Index40.5). There were no clear patterns in the dis-tribution of Y. purpurata between transects (Fig. 7).

3.5. Biomass

Estimates of the biomass of enteropneusts from photographsreveal that T. cinnabarinum has a mean individual biomass of 17.9 gwet weight in the north (20.0 SD, n¼94) and 8.2 g in the south(8.9 SD, n¼10). As a species it contributes an average of 52 g wetweight biomass 1000 m−2 at the northern stations (where it ismost abundant) and 13 g wet weight biomass 1000 m−2 at thesouthern stations (using overall mean biomasses; Table 2; Fig. 2).Y. purpurata has a mean individual biomass of 6.5 g (5.0 SD,n¼220) in the southern stations. It contributes negligible biomassat the northern stations and around 99 g wet weight biomass1000 m−2 at the southern stations.

3.6. Trace density and bioturbation potential

A total of 3195 spiral traces made by T. cinnabarinumwere observed in the videos. Individual spirals covered a meanseafloor area of 18469.6 mm2718266.0 SD The density of thesetraces (mean¼175 ind. 1000 m−2785 SD) was much higher(mean¼38.8 times animal densities760.4 SD) than the numbersof animals observed. There was a fairly constant proportion ofanimals to traces at each superstation. As in the case of the animaldensities, spiral trace densities were much higher at the northernsites, particularly in the north east, and significantly differentbetween superstations (two-factor ANOVA on ranks F¼43.576,df¼3, p-valueo0.001). Across all stations, spiral trace densitieswere significantly different with slope levels. The NE had thelowest variation in density with slope, but the NE had distinctlylower spiral trace densities on the flat seabed areas than at higherslopes. In the south, spiral trace densities were much higher on theflat areas than on the slopes (F¼6.928, df¼1, po0.05). Because ofthis contrast between the north and south, there was a significantinteraction of slope and superstation (F¼10.150, df¼3, po0.001)in spiral trace densities. The traces made by T. cinnabarinum onlycovered a small percentage of the total seabed area surveyed(mean¼0.323%70.155 SD).

In total, 840 traces made by Y. purpurata were observed in thevideos. Individually, they each covered a much smaller area of theseafloor (Table 4; mean¼7851.4 mm2710298.9 SD) than thespiral traces of T. cinnabarinum, and their density (mean¼43 ind.1000 m−2736 SD) was also lower. Although trace density washigher (mean¼2.7 times animal densities71.5 SD) than thenumbers of animals observed, this ratio was again much lowerthan for T. cinnabarinum. Like those of the animal itself, thedensities of Y. purpurata traces were not significantly differentbetween the southern superstations (two-factor ANOVA on ranksF¼0.04, df¼1, p¼n.s.). However, as in the case of T. cinnabarinum,

Table 4Trace measurements of Atlantic enteropneusts. The area of individual traces forTergivelum cinnabarinum assumes complete coverage of a bounding circle, while forYoda purpurata it assumes a coverage of trace length� lip width.

Units T. cinnabarinum Y. purpurata

Measurement mean SD mean SD

Trace area mm2 18469.6 18266.0 7851.4 10298.9Trace density No. m−2 0.175 0.085 0.043 0.036

Traces per animal No. 38.8 60.4 2.7 1.5% cover of traces % 0.323 0.155 0.009 0.009

trace densities were significantly higher on the flat areas com-pared with the slopes (two-factor ANOVA on ranks F¼11.97, df¼1,po0.01). The traces made by Y. purpurata covered a percentage(mean¼0.034%70.037 s.d.) of the total seabed area surveyed thatwas an order of magnitude less than that occupied by those ofT. cinnabarinum.

3.7. Stable isotopes

T. cinnabarinum had a mean δ13C value of −18.41 (7 0.05 SD)and δ15N value of 9.60 (70.26 SD).

4. Discussion

This study shows a clear contrast in the geographical distributionof the two enteropneust species, with T. cinnabarinum predominatingnorth of the Sub-Polar Front and Y. purpurata to the south. The speciesappear to be responding to differing regimes of food supply from thesurface. Densities of T. cinnabarinum were significantly higher at thenorthern superstations, and highest at the NE. Sediment traps at1000 m off the seabed had significantly higher mean organic C flux atthe NE site (2.05971.985 mgm−2 d−1) than the NW site (0.77770.215 mgm−2 s−1 d−1) (Abell et al., 2013). T. cinnabarinum was alsolarger in the NE, which is consistent with the expected positiverelationship between body size and food supply to the benthos (Rexand Etter, 1998) that allows organisms to maximise the net energygain for a given food input. There were no apparent differences indensity or size between the flat and sloped transects, but there is noreason to believe that these habitats receive differing amounts oforganic matter. Densities of T. cinnabarinum at our northern sites wereconsiderably higher than those of T. baldwinae at the relativelyoligotrophic Station M in the NE Pacific (4100m depth), althoughthe animals were very similar in size (Smith et al., 2005). However,more recent density estimates for T. baldwinae at deep (2712–3954m)sites elsewhere in the Pacific were much higher (up to 9.5 ind.100 m−2; Table S2) than at either Station M or the MAR (Osborn et al.,2012). Otherwise, densities at the MAR were generally fairly similar tothose of enteropneust populations elsewhere, particularly those atdepths which would be expected to have comparable levels of organicinput (Table S2). Densities of T. baldwinae increased by an order ofmagnitude within a year (between 2003 and 2004) at Station M,suggesting that enteropneust populations can respond quickly toincreased food availability (Smith et al., 2005).

Apart from a single example, Y. purpurata was only found at thesouthern superstations. Here, density was highly variable betweentransects but highest overall at the SE superstation. There were nosignificant differences in the input of organic matter recorded insediment traps between the SE and SW areas (SE: 2.08871.018mg m−2 d−1; SW: 2.38772.687 mg m−2 d−1; based on 1000 m offseabed sediment trap data; Abell et al., 2013). Y. purpurata alsoshowed little difference in body size between the eastern and thewestern populations. Although T. cinnabarinum was the larger ofthe two species, Y. purpurata was much more abundant, leading toa greater total enteropneust biomass in the south than in the north(Fig. 2). Although no data exist for congeners of Y. purpurata, mostreported enteropneust densities are lower than the mean valuesrecorded on the MAR (Table S2).

Counts made from the ROV transects indicate that enterop-neusts were one of the more abundant megafaunal taxa at theMAR (C.H.S. Alt, unpublished data). They represent a largerproportion of total megafauna at the southern sites (SW: 1.59%;SE: 2.83%) than at the northern sites (NW: 0.25%; NE: 0.16%). Onaverage, T. cinnabarinum was the 20th (NW) and 15th (NE) rankedmegafaunal species in terms of density at the northern sites (of113 and 83 species respectively). The corresponding rankings for

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387 385

Y. purpurata at the southern sites were 12th (SW) and 6th (SE) (C.H.S. Alt, unpublished data). The majority of the species with higherdensities than enteropneusts were also deposit feeders.

Our estimates of biomass, although speculative, suggest thatenteropneusts made up a substantial proportion of megafaunalbiomass, at least in terms of wet weight, on the MAR and in thebathyal Atlantic generally. Trawls at the northern sites captured anaverage of 1493 g (NE) and 326 g (NW) wet weight of invertebratemegafauna 1000 m−2 (Alt et al., 2013), which is only six timesmore than our estimates of the biomass of T. cinnabarinum. In theSE area trawls captured 546 g wet weight of invertebrate mega-fauna 1000 m−2 (Alt et al., 2013), which is also approximately sixtimes more than our estimates of the biomass of Y. purpurata.These values should be treated with some caution as ROV-baseddensity estimates show that the relative abundance of enterop-neusts is not this high (C.H.S. Alt, unpublished data). The trawldata, however, do appear to be reliable. They were similar to thevalues for total invertebrate megafaunal biomass (as wet weight)from elsewhere in the bathyal Atlantic (Priede et al., 2013); forexample, 367 g 1000 m−2 on the east Atlantic margin (PorcupineSeabight, B. Bett, unpublished data) and 285–2222 g 1000 m−2 onthe west Atlantic margin (south of New England, Haedrich et al.,1980), both from around 2500 m depth. Even allowing for errors inbiomass estimates as a result of inefficient trawl sampling(Thurston et al., 1994), it would appear that enteropneusts wereimportant contributors to megafaunal biomass, at least in terms ofwet weight. However, the torquaratorids have minimal muscula-ture, are gelatinous and are extremely fragile (Osborn et al., 2012)so, although no measured values are available, the relativeproportion of organic carbon in enteropneusts is likely to beconsiderably lower than for other megafaunal organisms.

4.1. Behaviour

Enteropneust traces appear to represent discrete, near-continuous feeding events, with the formation of individual tracesseparated by the movement of the enteropneust from one feedingarea to another in the water column (Smith et al., 2005). In thecase of Y. purpurata there is another less likely possibility. Thetraces formed by this species did not always have a clear startingpoint and there were often gaps along their length. This observa-tion suggests that the length of the cylindrical trace may dependon how quickly it is eroded. However, this would have requiredthe enteropneust to have moved very slowly or stopped duringtrace formation in order to allow time for the trace to undergosignificant erosion (likely several days to weeks).

The trails of T. cinnabarinum at the MAR are very similar to thoseobserved in the east Pacific (Smith et al., 2005) and off Australia(Anderson et al., 2011). Smith et al. (2005) saw an enteropneust, nowdescribed as T. baldwinae (Holland et al., 2009), forming trails invarious forms from tightly wound spiral coils to wandering, switch-back loops. Their time-lapse observations showed the same ani-mal creating both configurations in a single foraging period. LikeT. cinnabarinum, the Pacific species formed clockwise and antic-lockwise spirals in approximately equal numbers and switchbackloops were less common than spiral loops (Smith et al., 2005). Bothforms of enteropneust trace have been observed in photographs fromacross a range of geographic locations from the Antarctic Belling-shausen Basin (Kitchell et al., 1978) to the abyssal Pacific (Bourne andHeezen, 1965) and the Australian margin (Anderson et al., 2011).Traces resembling the enteropneust spirals and switchback loopshave been recorded in the fossil record as Spirodesmos and Palaeo-helminthoida respectively (Kitchell et al., 1978) from at least the earlyMesozoic (Wetzel et al., 2007). Some late Palaeozoic spiral traces areillustrated by Seilacher (Seilacher, 2007) and meandering traces have

an even longer history (e.g. Crimes and Fedonkin, 1994), althoughthere is no evidence that they were made by enteropneusts.

T. cinnabarinum appears to be a typical surface deposit feeder; ityielded δ13C and δ15N values between those of the holothuriansPeniagone spp. and Paelopatides grisea, both of which consumesurficial sediments (Reid et al., 2012). Species of Peniagone oftenhave the lowest δ13C and δ15N values of deposit feeders in deep-seafood webs (Drazen et al., 2008; Iken et al., 2001), indicating theyassimilate freshly deposited phytodetritus. The feeding behaviour ofenteropneusts has presumably evolved to optimise deposit-feedingeffectiveness (optimal foraging theory) in the varying resourcehabitat of the deep sea (Jumars et al., 1990). It is interesting thatthe genus Tergivelum makes a spiral trace, unlike Y. purpurata andmost other deposit feeders. The spiral trace is presumably an efficientmechanism to capture all surficial organic matter within an area, butit also suggests that this animal is selecting areas with particularlyhigh resource availability. The wandering strategy adopted by otherdeposit feeders, including Y. purpurata, should be equally effective.This species appears to maximise feeding efficiency by having verywide lips (�1.5� the width of T. cinnabarinum), which may preventeffective spiral trace formation.

The observations here of ‘active’ drifting in Atlantic deep-seaenteropneusts, in conjunction with observations of Pacific species(Osborn et al., 2012), show that at least three species use changesin body posture to catch demersal currents for movement betweenfeeding locations. Similar feeding behaviours are observed inT. cinnabarinum and holothurians in the genus Peniagone. Indivi-duals of both taxa feed in areas where phytodetritus is presentbefore lifting off the seafloor and ‘swimming’ or drifting in near-bed currents. Our short-duration observations of gut contentsbeing voided prior to drifting support the hypothesis that enter-opneusts use their gut contents as ballast (Osborn et al., 2012;Smith et al., 2005) in a similar fashion to swimming holothurians(Miller and Pawson, 1990). These adaptations allow the enterop-neust to make reasonably rapid, long distance movements toincrease their feeding range (Osborn et al., 2012) and potentiallyenhance their utilisation of spatially and temporally heteroge-neous deep-sea food resources (Billett et al., 1983). While lift-offafter voiding the gut is readily understood, our observations andcalculations for drifting and descent in A. isidis suggest that thisspecies can also increase its density, although the mechanism forthis change remains obscure.

4.2. Within transect distribution of enteropneusts and their traces

The predominantly random distribution of enteropneusts atour MAR sites suggests that T. cinnabarinum or Y. purpurata are notactively selecting foraging sites. At metre scales, resources such asfood (quality or quantity), or suitable sediment habitat, usuallyvary spatially (Snelgrove et al., 1992) and/or temporally (Billettet al., 1983) and display non-random distribution patterns (Felleyet al., 2008). Aggregations of deep-sea organisms in response toresource availability are common (Billett and Hansen, 1982;Snelgrove et al., 1992) and it is likely that enteropneust distribu-tion would not be random if active site selection was occurring.Time-lapse observations of T. baldwinae also suggest that siteswere not actively selected (Smith et al., 2005). At station M in thePacific, this species landed on a patch of seafloor that was notobviously enriched in detrital organic matter compared with areaswith no enteropneusts (Smith et al., 2005). However, neither ofthese observations provides conclusive evidence against activeforaging site selection.

Enteropneust traces, presumably those of T. cinnabarinum,observed in submersible video records made in 2003 at the MARhave a significantly clumped distribution (Felley et al., 2008). Thescale of dispersion analyses was finer in our analyses (20 m2)

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387386

compared to analysis in Felley et al. (2008) (1 min of videorepresenting approximately 100 m2 of seafloor), but the analysesseem relatively robust to small changes of area. Re-running ourdispersion calculations at 100 m2 scale makes little difference tothe outcome. The difference in dispersion patterns observed canbe explained by a difference in methodology. The dispersionanalysis in Felley et al. (2008) was performed across all theirtransects, which covered multiple habitat types and thereforeaddressed the broad-scale habitat preferences of enteropneusts.Our dispersion calculations, on the other hand, assessed within-habitat dispersion of enteropneusts (within one quantitativetransect pre-selected to represent one habitat) and finer-scalepatterns.

4.3. Enteropneust traces and bioturbation potential

Trace densities were considerably higher in the present studythan those derived from submersible dives at the MAR in 2003(Felley et al., 2008). This discrepancy may represent a change inenteropneust density or activity over time. However, the 2003study extended into deeper waters and quantification was basednot on area but on minute-long segments of submersible video. Ifit is assumed that each minute covered approximately 100 m2 ofseafloor, then trace densities were considerably lower at equiva-lent depths in 2003 than in 2010 (approx. 2–140 traces ha−1 in2003 compared with 1750 traces ha−1 in 2010). Of course, thesedifferences could be a result of spatial heterogeneity or lowerresolution video, rather than temporal variation. The density ofenteropneust traces in the present study is comparable to totaltrace densities measured elsewhere (Table S2). These observationsadd weight to the impression gained from the enteropneuststhemselves that these animals are important bioturbators ofsurfical sediments in the Atlantic and elsewhere.

The duration of traces on the seafloor of the MAR is importantas it may allow quantification of enteropneust feeding activity(trace production rate), as well as being an indicator of the rates ofimportant ecological functions, principally bioturbation (tracedestruction rates). In the Pacific, the trace made by T. baldwinae,which took 37 h to form, degraded rapidly and was virtuallyindistinguishable after 8.5 days (Smith et al., 2005). This observa-tion represents a ratio of construction time (39 h) to degradationtime (203 h) of �0.2. Assuming the rates of degradation in the oneobserved trace were normal, there will be a maximum of 6.5 dis-tinguishable traces per animal (if they continually produce traces).For T. cinnabarinum there were many more traces per animal (38.8ratio between number of animals and the number of traces), eitheras a result of an increase in trace formation rate or a reductionin the destruction rate compared with Smith et al. (2005). InY. purpurata there were fewer traces per animal (2.7 ratio betweennumber of animals and the number of traces), possibly a result oflower enteropneust activity rates. However, this pattern does notappear to be associated with reduced flux of organic matter to theseafloor (Abell et al., 2013).

Enteropneust activity was responsible for a relatively largeproportion of the surficial deposit feeding at the ECOMAR sites.This is unexpected because at the MAR enteropneusts onlyrepresent a relatively small percentage of the density of surficialdeposit feeders, the majority of which were holothurians, parti-cularly at the northern superstations (ROV data from C.H.S. Alt,unpublished data). If the total density of surface-dwelling echino-derms is used to provide an approximation of the densities ofdeposit feeders at the MAR, enteropneusts represent 0.84%, 0.17%,13.89% and 5.71% of densities in the NW, NE, SW and SE areas,respectively (ROV data from C.H.S. Alt, unpublished data). Never-theless, enteropneusts are major bioturbators of surfical sedimentsat the MAR. They are responsible for up to 35% of the area of

bioturbated surficial sediment at the NE sites and an importantpercentage of all surficial bioturbation in the other ECOMAR areas(NW: 2.4%; SE: 5.4%; SW: 6.9%) (Bell et al., 2013). Elsewhere, onlythe densities (trace number per unit area) of enteropneust tracesare reported, not the area that they cover. In terms of their density,enteropneust traces seem not to be of major importance in otherareas. For example, Mauviel and Sibuet (1985) found the super-ficial traces (which included the enteropneust traces) represented11.3–51.8% of all traces. When analysed in terms of area, however,it is likely that enteropneust traces would have been considerablymore important, as they are in the MAR, where they represent2.1–6.3% of trace density compared to 2.4–35.1% in terms of area(Bell et al., 2013). This dominance is because of the large size ofenteropneust traces compared with other trace types.

5. Conclusions

Epibenthic enteropneusts are a relatively important group ofsurficial megabenthic deposit feeders in the deep sea. Theyrepresent a significant component of the megafauna in someareas, although, even in our limited study, their density varied atseveral spatial scales. We present the first extensive size–fre-quency and morphometric data on deep-sea enteropneust popula-tions and show that these animals feed over very wide areas ofseafloor, causing extensive bioturbation. Their behaviour is becom-ing better known, but questions still remain that can only beanswered by more extensive observations and perhaps experi-mentation, particularly with regard to feeding site selection. Withincreased access to ROV technology and more sampling effort it islikely that enteropneusts will be found in more parts of the deepAtlantic and beyond and that additional species will be discovered.Although still poorly known, enteropneusts appear to have arelatively important role in benthic ecosystem functions, notablyorganic matter processing and surficial bioturbation.

Acknowledgements

This work was supported by the UK Natural EnvironmentResearch Council as part of the Ecosystems of the Mid-AtlanticRidge at the Sub-Polar Front and Charlie–Gibbs Fracture Zone(ECOMAR) project. We thank the ships’ companies of RRS JamesCook, ROV operators, technicians and assistants who contributedto this project for their help and support. Thanks to James Bell forproviding ECOMAR bioturbation data. W.D.K.R. was supported forthis work by NERC studentship NE/F010664/1.

Appendix A. Supporting information

Supplementary data associated with this article can be found inthe online version at http://dx.doi.org/10.1016/j.dsr2.2013.05.009.

References

Abramoff, M.D., Magalhaes, P.J., Ram, S.J., 2004. Image processing with ImageJ. Biophoton. Int. 11 (7), 36–42.

Abell, R.E., Brand, T., Dale, A.C., Tilstone, G.H., Beverage, C., 2013. Variability ofparticulate flux over the Mid-Atlantic Ridge. Deep-Sea Res. II, 98 (PB), 257–268.

Anderson, T.J., Przeslawski, R., Tran, M., 2011. Distribution, abundance and trailcharacteristics of acorn worms at Australian continental margins. Deep Sea Res.58 (7–8), 970–978.

Alt, C.H.S., Rogacheva, A., Boorman, B., Hughes, J.A., Billett, D.S.M., Gooday, A.J.,Jones, D.O.B., 2013. Trawled megafaunal invertebrate assemblages from bathyaldepth of the Mid-Atlantic Ridge (48°–54°N). Deep-Sea Res. II. http://dx.doi.org/10.1016/j.dsr2.2013.02.003, 98 (PB), 326–340.

Beliaev, G.M., 1989. Deep-Sea Ocean Trenches and Their Fauna. Nauka, Moscow.

D.O.B. Jones et al. / Deep-Sea Research II 98 (2013) 374–387 387

Belichov, D.V., 1971. Kishechnodyshashie (Enteropneusta) Kurilo-Kamachatskojvpadiny (Tuskarory), Glossobalanus tuscarorae n. sp. [Enteropneusts from theKuril-Kamchatka Trench (Tuscarora Deep), Glossobalanus tuscarorae n. sp.].Voprosy Zoologii, Sbornik 2, Kazanskiy Pedagogicheskiy Institut [Problems inZoology, Series 2, Kazan Pedagogic(al) University], Number 61:3–38.

Bell, J.B., Jones, D.O.B. Alt, C.H.S., 2013. Lebensspuren of the Bathyal Mid-AtlanticRidge. Deep-Sea Res. II. 98 (PB), 341–351.

Bett, B.J., 2001. UK Atlantic Margin Environmental Survey: introduction andoverview of bathyal benthic ecology. Cont. Shelf Res. 21, 917–956.

Bett, B.J., Malzone, M.G., Narayanaswamy, B.E., Wigham, B.D., 2001. Temporalvariability in phytodetritus and megabenthic activity at the seabed in the deepNortheast Atlantic. Prog Oceanogr 50 (1–4), 349–368.

Billett, D.S.M., Hansen, B., 1982. Abyssal Aggregations of Kolga hyalina Danielssenand Koren (Echinodermata: Holothurioidea) in the Northeast Atlantic Ocean: apreliminary report. Deep-Sea Res. 29 (7A), 799–818.

Billett, D.S.M., Lampitt, R.S., Rice, A.L., Mantoura, R.F.C., 1983. Seasonal sedimenta-tion of phytoplankton to the deep-sea benthos. Nature 302 (5908), 520–522.

Bourne, D.W., Heezen, B.C., 1965. A wandering enteropneust from the AbyssalPacific, and the distribution of “spiral” tracks on the sea floor. Science 150(3692), 60–63.

Cannon, J.T., Rychel, A.L., Eccleston, H., Halanych, K.M., Swalla, B.J., 2009. Molecularphylogeny of hemichordata, with updated status of deep-sea enteropneusts.Mol. Phylogenet. Evol. 52 (1), 17–24.

Crimes, T.P., Fedonkin, M.A., 1994. Evolution and dispersal of deep-sea traces.Palaios 9, 74–83.

Deland, C., Cameron, C.B., Rao, K.P., Ritter, W.E., Bullock, T.H., 2010. A taxonomicrevision of the family Harrimaniidae (Hemichordata: Enteropneusta) withdescriptions of seven species from the Eastern Pacific. Zootaxa 2408, 1–30.

Drazen, J.C., Popp, B.N., Choy, C.A., Clemente, T., De Forest, L., Smith, K.L., 2008.Bypassing the abyssal benthic food web: Macrourid diet in the eastern NorthPacific inferred from stomach content and stable isotopes analyses. Limnol.Oceanogr. 53 (6), 2644–2654.

Felley, J.D., Vecchione, M., Wilson Jr, R.R., 2008. Small-scale distribution of deep-seademersal nekton and other megafauna in the Charlie–Gibbs fracture zone of theMid-Atlantic Ridge. Deep-Sea Res. II 55, 153–160.

Gage, J., 2005. Deep-sea spiral fantasies. Nature 434, 283–284.Haedrich, R.L., Rowe, G.T., Polloni, P.T., 1980. The megabenthic fauna in the deep-sea

south of New-England, USA. Mar. Biol. 57 (3), 165–179.Heezen, B.C., 1968. The world rift system. Tectonophysics Special Issue 8, 269–279.Heezen, B.C., Hollister, C.D., 1971. The Face of the Deep. Oxford University Press,

London.Holland, D.M., Clague, D.A., Gordon, D.P., Gebruk, A., Pawson, D.L., Vecchione, M.,

2005. ‘Lophenteropneust’ hypothesis refuted by collection and photos of newdeep-sea hemichordates. Nature 434, 374–376.

Holland, N.D., Jones, W.J., Ellena, J., Ruhl, H.A., Smith, K.L., 2009. A new deep-seaspecies of epibenthic acorn worm (Hemichordata, Enteropneusta). Zoosystema31 (2), 333–346.

Holland, N.D., Kuhnz, L.A., Osborn, K.J., 2012. Morphology of a new deep-sea acornworm (Class Enteropneusta. Phylum Hemichordata): a part-time demersaldrifter with externalized ovaries. J. Morphol. 273, 661–671.

Iken, K., Brey, T., Wand, U., Voigt, J., Junghans, P., 2001. Food web structure of thebenthic community at the Porcupine Abyssal Plain (NE Atlantic): a stableisotope analysis. Prog. Oceanogr. 50, 1–4.

Jensen, P., 1992. “An enteropneust's nest“: Results of the burrowing traits by thedeep-sea acorn worm Stereobalanus canadensis (Spengel). Sarsia 77, 125–129.

Jumars, P.A., Mayer, L.M., Deming, J.W., Baross, J.A., Wheatcroft, R.A., 1990. Deep-seadeposit-feeding strategies suggested by environmental and feeding constraints.Philos. Trans. R. Soc. A 331, 85–101.

Kitchell, J.A., Kitchell, J.F., Johnson, G.L., Hunkins, K.L., 1978. Abyssal traces andmegafauna: comparison of productivity, diversity and density in the Arctic andAntarctic. Paleobiology 4, 171–180.

Krebs, C.J., 1998. Ecological Methodology. Benjamin Cummings, Menlo Park,California.

Lemche, H., Hansen, B., Madsen, F.J., Tendal, O.S., Wolff, T., 1976. Hadal life asanalyzed from photographs. Vidensk. Medd. Dan Naturhist. Foren. Kjøbenhavn139, 263–336.

Longhurst, A.R., 1998. Ecological Geography of the Sea. Academic Press, San Diego,CA.

Mauviel, A., Juniper, S.K., Sibuet, M., 1987. Discovery of an enteropneust associatedwith a mound-burrows trace in the deep-sea - ecological and geochemicalimplications. Deep-Sea Res. A – Oceanogr. Res. Pap. 34 (3), 329–335.

Mauviel, A., Sibuet, M., 1985. Repartition des traces animales et importance de labioturbation. In: Laubier, L., Monniot, C. (Eds.), Peuplements Profonds due Golfede Gascogne. IFREMER, Brest, France, pp. 157–173.

Miller, J.E., Pawson, D.L., 1990. Swimming sea cucumbers (Echinodermata:Holothuroidea): a survey, with analysis of swimming behavior in four bathyalspecies. Smithson. Contrib. Mar. Sci. 35, 1–18.

Mitchell, N.C., Allerton, S., Escartín, J., 1998. Sedimentation on young ocean floor atthe Mid-Atlantic Ridge 291N. Mar. Geol. 148 (1–2), 1–8.

Oksanen, J., Blanchet, F.G., Kindt, R., Legendre, P., O'Hara, R.B., Simpson, G.L., Solymos,P., Stevens, M.H.H., Wagner, H., 2011. vegan: Community Ecology Package. Rpackage version vol. 1.17–19 ⟨http://CRAN.R-project.org/package=vegan⟩.

Osborn, K.J., Kuhnz, L.A., Priede, I.G., Urata, M., Gebruk, A.V., Holland, N.D., 2012.Diversification of acorn worms (Hemichordata, Enteropneusta) revealed in thedeep sea. Proc. R. Soc. B: Biol. Sci. 279, 1646–1654.

Post, D.M., Layman, C.A., Arrington, D.A., Takimoto, G., Quattrochi, J., Montana, C.G.,2007. Getting to the fat of the matter: models, methods and assumptions fordealing with lipids in stable isotope analyses. Oecologia 152 (1), 179–189.

Priede, I.G., Osborn, K.J., Gebruk, A.V., Jones, D.O.B., Shale, D., Holland, N.D., 2012.Observations on torquaratorid acorn worms (Hemichordata, Enteropneusta)from the North Atlantic with descriptions of a new genus and three newspecies. Invertebr. Biol. 131 (3), 244–257.

Priede, I.G., Bergstad, O.A., Miller, P.I., Vecchione, M., Gebruk, A., Falkenhaug, T.,Billett, D.S.M, Craig, J., Dale, A.C., Shields, M.A., Tilstone, G.H., Sutton, T.T.,Gooday, A.J., Inall, M.E., Jones, D.O.B., Martinez-Vicente, V., Menezes, G.M.,Niedzielski, T., Sigurðsson, Þ., Rothe, N., Rogacheva, A., Alt, C.H.S., Brand, T.,Abell, R., Brierley, A.S., Cousins, N.J., Crockard, D., Hoelzel, A.R., Høines, Å.,Letessier, T.B., Read, J.F., Shimmield, T., Cox, M.J., Galbraith, J.K., Gordon, J.D.M.,Horton, T., Neat, F., Lorance, P., 2013. Does presence of a Mid Ocean Ridgeenhance biomass and biodiversity? PLoS ONE 8 (5), e61550.

R Development Core Team, 2010. R: A Language and Environment for StatisticalComputing. R Foundation for Statistical Computing. isbn:3-900051-07-0, URL⟨http://www.R-project.org⟩, Vienna, Austria.

Read, J.F., Pollard, R.T., Miller, P.I., Dale, A.C., 2010. Circulation and variability of theNorth Atlantic Current in the vicinity of the Mid-Atlantic Ridge. Deep-Sea Res. I:Oceanogr. Res. Papers 57, 307–318.

Reid, W.D.K., Wigham, B.D., McGill, R.A.R., Polunin, N.V.C., 2012. Elucidating benthicand pelagic trophic pathways in deep-sea benthic assemblages of the Mid-Atlantic Ridge north and south of the Charlie–Gibbs Fracture Zone. Mar. Ecol.Prog. Ser. 463, 89–103.

Rex, M.A., Etter, R.J., 1998. Bathymetric patterns of body size: implications for deep-sea biodiversity. Deep-Sea Res. 45, 1–3.

Romero-Wetzel, M.B., 1989. Branched burrow-systems of the enteropneust Stereo-balanus canadensis (Spengel) in deep-sea sediments of the Voering-Plateau,Norwegian Sea. Sarsia 74 (2), 85–89.

Rychel, A., Swalla, B.J., 2008. Anterior regeneration in the hemichordate Ptychoderaflava. Dev. Dyn. 237, 3222–3232.

Seilacher, A., 2007. Trace Fossil Analysis. Springer, Berlin, Heidelberg, New York.Smallwood, B.J., Wolff, G.A., Bett, B.J., Smith, C.R., Hoover, D., Gage, J.D., Patience, A.,

1999. Megafauna can control the quality of organic matter in marine sediments.Naturwissenschaften 86 (7), 320–324.

Smith, K.L., Holland, N.D., Ruhl, H.A., 2005. Enteropneust production of spiral fecaltrails on the deep-sea floor observed with time-lapse photography. Deep SeaRes. I: Oceanogr. Res. Pap. 52 (7), 1228–1240.

Snelgrove, P.V.R., Grassle, J.F., Petrecca, R.F., 1992. The role of food patches inmaintaining high deep-sea diversity - field experiments with hydrodynamicallyunbiased colonization trays. Limnol. Oceanogr. 37 (7), 1543–1550.

Spengel, J.W., 1893. Enteropneusten. Fauna und Flora des Golfes von Neapel undder Angrenzenden Meeres. Zool. Stn Neapel. Monogr. 18, 1–756.

Spengel, J.W., 1909. Pelagisches Vorkommen von Enteropneusten. Zool. Anz. 34,54–59.

Thurston, M.H., Bett, B.J., Rice, A.L., Jackson, P.A.B., 1994. Variations in theinvertebrate abyssal megafauna in the North Atlantic Ocean. Deep-Sea Res. I:Oceanogr. Res. Pap. 41 (9), 1321–1348.

Van der Horst, C.J., 1939. Hemichordata. In: Bronn, H.G. (Ed.), Die Klassen undOrdnungen des Tier-Reichs. Akademische Verlagsgesellschaft, Leipzig, pp. 1–737.

Vardaro, M.F., Ruhl, H.A., Smith Jr, K.L., 2009. Climate variation, carbon flux andbioturbation in the abyssal North Pacific. Limnol. Oceanogr. 54, 2081–2088.

Vierros, M., Cresswell, I., Briones, E.E., Rice, J., Ardron, J., 2009. Global Open Oceansand Deep Seabed (GOODS) biogeographic classification. IntergovernmentalOceanographic Commission and United Nations Education, Scientific andCultural Organization, Paris.

Vinogradova, N.G., Kudinova-Pasternak, R.K., Moskalev, L.I., Muromtseva, T.L.,Fedikov, N.F., 1974. Some regularities of quantitative distribution and trophicstructure of bottom fauna from the Scotia Sea and the deep-sea trenches of theAtlantic sector of the Antarctic. Tr. Inst. okeanol. Akad. Nauk SSSR 98, 157–182.

Wetzel, A., Blechschmidt, I., Uchman, A., Matter, A., 2007. Highly diverse ichnofaunain late Triassic deep-sea fan deposits of Oman. Palaios 22 (5), 567–576.

Woodwick, K.H., Sesenbaugh, T., 1985. Saxipendium coronatum, new genus, newspecies (Hemichordata: Enteropneusta): the unusual spaghetti worms of theGalápagos Rift hydrothermal vents. Proc. Biol. Soc. Wash. 98, 351–365.