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First record of the Australian ascidianEudistoma elongatum in northern NewZealandPeter J. Smith a , Mike Page b , Sean J. Handley b , S. MargaretMcVeagh c & Merrick Ekins da National Institute of Water and Atmospheric Research Limited ,Private Bag 14901, Wellington, New Zealand E-mail:b National Institute of Water and Atmospheric Research Limited ,P.O. Box 893, Nelson, New Zealandc National Institute of Water and Atmospheric Research Limited ,Private Bag 14901, Wellington, New Zealandd Queensland Museum , P.O. Box 3300 South Brisbane, Brisbane,4101, AustraliaPublished online: 19 Feb 2010.

To cite this article: Peter J. Smith , Mike Page , Sean J. Handley , S. Margaret McVeagh &Merrick Ekins (2007) First record of the Australian ascidian Eudistoma elongatum in northernNew Zealand, New Zealand Journal of Marine and Freshwater Research, 41:4, 347-355, DOI:10.1080/00288330709509924

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New Zealand Journal of Marine and Freshwater Research, 2007, Vol. 41: 347-3550028-8330/07/4104-0347 © The Royal Society of New Zealand 2007

347

First record of the Australian ascidian Eudistomaelongatum in northern New Zealand

PETER J. SMITHNational Institute of Water and Atmospheric

Research LimitedPrivate Bag 14901Wellington, New Zealandemail: p.smith@niwa.co.nz

MIKE PAGE

SEAN J. HANDLEYNational Institute of Water and Atmospheric

Research LimitedP.O. Box 893Nelson, New Zealand

S. MARGARET McVEAGHNational Institute of Water and Atmospheric

Research LimitedPrivate Bag 14901Wellington, New Zealand

MERRICK EKINSQueensland MuseumP.O. Box 3300South Brisbane 4101Brisbane, Australia

Abstract A colonial ascidian was first reported bymarine farmers in Houhora Harbour, Northland, NewZealand in early 2005 and subsequently found onoyster racks in Parengarenga Harbour and the Bay ofIslands. The Northland ascidian was identified witha combination of morphological characters and DNAcytochrome c oxidase I (COI) sequence data, asEudistoma elongatum, a species native to Australia,where it is found from northern New South Walesto Northern Queensland, and distinguished fromEudistoma circumvallatum, the only reported speciesin this genus from New Zealand. Ascidian larvae

M07030; Online publication date 9 November 2007Received 8 June 2007; accepted 19 July 2007

are weak dispersers and long distance dispersal ofE. elongatum is likely to be enhanced by vectorssuch as oyster barges and/or movement of culturedoysters. In its native range, E. elongatum is restrictedto areas with a minimum winter sea temperatureof 16°C. Assuming similar biological limitationsapply in New Zealand, the spread of E. elongatummight be restricted to northern New Zealand (northof latitude 37°S).

Keywords colonial ascidian; invasion; biosecurity;mitochondrial DNA

INTRODUCTION

An unusual colonial ascidian was reported bymarine farmers in Houhora Harbour, Northland,New Zealand in early 2005 (Handley 2005) and laterfound on oyster racks in Parengarenga Harbour andthe Bay of Islands. The sudden appearance of thisascidian may represent an invasion of a recentlyintroduced species or a native species undergoinga local population explosion. The ascidian wasprovisionally identified as belonging to the genusEudistoma, and possibly Eudistoma elongatum(Herdman, 1886) based on the long stalked headswhich are unusual in this genus (M. Page unpubl.data). Eudistoma elongatum is native to Australia,ranging from northern New South Wales to centralQueensland (Kott 1990).

Eudistoma circumvallatum (Sluiter, 1900), the onlyreported ascidian in this genus from New Zealand,was first described from Cook Strait in 1900, andsubsequently Otago (Brewin 1946), Stewart Island(Brewin 1958a; Millar 1982), the Hauraki Gulf(Brewin 1950,1958b), and Cape Kidnappers (Brewin1952). The genus Eudistoma exhibits considerablevariation in external morphology, but there is anapparent lack of internal morphological variationand the zooids are difficult to distinguish amongspecies, which can create difficulties for speciesidentification, especially in preserved material(Kott 1990). It is possible that E. circumvallatum

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348 New Zealand Journal of Marine and Freshwater Research, 2007, Vol. 41

is conspecific with E. elongatum (P. kott pers.comm.) and that the Northland population is native;alternatively the Northland specimens may representa recent invasion of E. elongatum.

DNA sequence data are being used to assessthe taxonomic status of colonial ascidians withvariable morphologies (Lopez-Legentil & turon2005). Invasive species may show morphologicalsimilarities, or differences, to specimens from thesource population, but would be expected to showlow intra-specinc DNA sequence divergence with thesource population and high inter-specific divergencewith congeners. In this study, we used morphologicalcharacters and a DNA marker to identify the Northlandascidians. We selected a region of the mitochondrialDNA cytochrome c oxidase i gene (cOi) for theDNA analyses. The 18S rDNA has been the mostwidely used DNA marker for phylogenetic studiesof ascidians (Stach & Turbeville 2002; Yokobori etal. 2006), but there is only one entry for Eudistoma18S in GenBank (AB21069). COI sequences areavailable from a phylogenetic study of 37 speciesof ascidian that included 13 species in the familyPolycitoridae, and 4 species in the genus Eudistoma(Turon & Lopez-Legentil 2004) (GenBank entriesAy600973-74, Ay609977-78).

MATERIALS AND METHODS

Specimen collectionNew Zealand specimens of Northland Eudistomawere collected from oyster racks at three sites:Parengarenga and Houhora harbours, and the Bayof islands (Fig. 1), where the ascidian appearedduring 2005-06. Specimens of the native specieswere collected from one site on the Otago Peninsula(South island), where E. circumvallatum had beenreported historically (Brewin 1946). Sub-tidalsearches were also made for Eudistoma at greatBarrier island, where E. circumvallatum had beenpreviously collected by the National Cancer Institute(Nci) in 1999 (m. Page unpubl. data). representativecolonies from each collection were sub-sampled fordNA studies and the balance of the colonies werenarcotised for 4-6 h with 3-4 methanol crystals per100 ml sea water at room temperature (c. 18°c), andthen fixed in 10% formalin solution by volume.

Australian specimens of E. elongatum werecollected from two sites off the Queensland coastand registered in the Queensland museum (NorthStradbroke Island QMG325031 and MooloolabahG327511); tissue samples were preserved in 90%

ethanol for DNA analyses. Two specimens of theintroduced Styela clava from northern New Zealandwere used as internal controls for dNA extractionsand sequencing reactions.

Eudistoma specimens were examined under adissecting microscope (40× magnification) for colonymorphology, and a slice taken along the length ofthe colony to determine the internal arrangement ofzooids. Zooids were dissected out for measurementof body dimensions. Haemotoxylin was used tostain the tissue to resolve the internal structure. Keymorphological characters used for distinguishingspecies were: colony morphology, zooid size, thenumber and structure of muscle bands in the thoraxand abdomen, and the number of stigmata in thebranchial sac (table 1).

DNA laboratory extractionand COI amplificationIndividual colonies were sliced open and c. 500 mgzooidal tissue scraped from the internal surface.three dNA extraction protocols were evaluatedfor the extraction of dNA from six ascidianspecimens (two from each site at houhora andParengarenga harbours, and Queensland). totalgenomic DNA was extracted from 200 to 500 mgof tissue by: (1) homogenisation and digestion withproteinase-K at 55°C for 4 h, followed by extractionwith phenol/chloroform, then chloroform/isoamylalcohol, and precipitation with 70% ethanol at-20°C; (2) digestion in CTAB (cetyl dimethylethylammonium bromide) extraction buffer (1.4 mMNaCl, 20 mMedtA, 100 mMtris-HCl pH8.0,0.2%mercaptoethanol, and 2% CTAB) overnight at 65°C,followed by extraction with chloroform/isoamylalcohol, and precipitation with 70% ethanol; and (3)homogenisation with the Qiagen Dneasy ™ isolationkit, following manufacturer's instructions (Qiageninc., United States).

the dNA pellets were air dried and re-suspendedin 40 µl sterile water and stored at -20°C.

A portion (c. 620 base pairs) of the COI gene wasamplified by polymerase chain reaction (PCR) in50 µl volumes in a Cetus 9600 DNA thermocycler(Perkin-Elmer Corporation, United States), using the"universal" primer pair HCO-2198 and LCO-1490(Folmer et al. 1994). Amplifications were carriedout using a low annealing temperature (39°c), basedon previous studies with ascidians (m. mcveaghunpubl. data). The amplification included an initialdenaturation of 95°C for 4 min, followed by 30cycles of 94°C for 60 s, 39°C for 60 s, and 72°C for90 s, with a final extension at 72°C for 10 min.

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Smith et al.—First record of Eudistoma elongatum 349

Fig. 1 Location of Eudistomacollection sites in New Zealand. North Cape

38 "00.00 —

0 15 90 180 Kilomelres 175=00.00

I

Amplified products were separated in 1.4%agarose gels in a TBE buffer (25 mM Tris, 0.5 mMEDTA, and 25 mM boric acid), stained with ethidiumbromide, and viewed under ultraviolet (Uv) light.Samples that produced a single amplified productof appropriate size (c. 620 bp) were purified usingthe QIAquick gel extraction kit (Qiagen Inc. UnitedStates), and sequences determined using the ABITaq DyeDeoxytm Terminator Cycle SequencingKit according to manufacturer's directions (AppliedBiosystems Inc., United States) and analysed on anABI prism autosequencer.

DNA sequence analysesCOI sequences were edited in CHROMAS 2.3 (Tech-nelysium, Australia), and aligned in the BIOEDIT5.0.9 program (Hall 1999), against the COIsequences for Eudistoma (GenBank accession no.Ay600973-74, Ay609977-78) and other membersof the Polycitoridae family: Cystodytes spp.(GenBank accession no. AY821784; AY523042-44,AY523048-49, AY523053, AY523056, AY523060-63, AY523070, AY523073) and Clavelina spp.(GenBank accession no. AJ866716, AJ884573,AY603104-106). COI sequences for species of

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350 New Zealand Journal of Marine and Freshwater Research, 2007, Vol. 41

Pseudodistoma, members of the family Polyclinidaewhich show a close association with Eudistoma(Turon & Lopez-Legentil 2004), were also includedin the initial alignments (GenBank accession no.Ay600970, Ay600979; AJ748708-18).

Phylogenies were explored with neighbour-joining (NJ) and maximum likelihood (ML) methodsusing MEGA v3.1 (Kumar et al. 2004) and PAUPv4.0 (Swofford 2000). Modeltest v3.06 (Posada& crandall 1998) was used to determine the best-fit model(s) using likelihood ratio tests, and thet rN + g model (tamura & Nei 1993) used toconstruct phylogenetic trees. Gaps in the sequenceswere treated as missing data. Support for eachinternode was evaluated by bootstrap replications(Felsenstein 1985) with 1000 pseudoreplicates forNJ, and 200 for ML trees. GenBank data for fourmediterranean species of Eudistoma were included(AY600973-74, AY600977-78) and sequence datafor other members of the Polycitoridae were usedto root the trees. In addition to trees, the sequencedata were summarised in matrices of sequencedivergences and identities to show inter-specificdivergences among the Eudistoma.

Eudistoma sequences obtained for this projecthave been deposited in the GenBank nucleotidesequence database: accession No. EF619346-51.

RESULTS

extensive searches were made at 10 sites atgreat Barrier island in an attempt to collect E.circumvatallum specimens, but no specimens werefound at any of the sites.

Specimens of Eudistoma were collected fromoyster racks in Houhora and Parengarenga harboursand the Bay of Islands between November 2005 andJune 2006. The ascidian formed numerous long,ropey, cylindrical zooid-bearing heads up to 30 cmlong and 0.5-0.7 cm in diameter (Fig. 2A,B). Thecylindrical heads often had wart-like side branches,also bearing zooids. Freshly collected colonieswere generally cream coloured with orange fleckscaused by concentrations of bright orange larvae inthe zooid's atrial cavities. The test was gelatinousbut firm, with numerous faecal pellets distributedthroughout. The zooids opened separately to thesurface of the colony and did not form systems.

The zooids were typically small and of similardimensions to those of E. circumvallatum. however,the thorax of the Northland specimens was slightlylarger, measuring 2.0-2.4 mm in length and 2.0 mm

in diameter (Fig. 2C). Both branchial and atrialapertures had six low lobes on short siphons. theatrial cavity contained 6-8 small larvae measuring0.5 mm trunk length. There were 20 fine ungroupedlongitudinal muscles and numerous fine radialmuscles in the body wall, which was thin andtransparent. Stigmata formed 3 rows of 17-20stigmata per row. The abdomen was typical forthe genus with an oesophageal neck approximately6 mm long and a smooth shield-shaped stomachtowards the posterior part of the abdomen (Fig. 2C).there was a small posterior stomach at the distalend of the gut loop. the stomach was not pigmentedand was larger than that of E. circumvallatum. twolarge ova and numerous testis follicles crowded theposterior end of the gut loop. Faecal pellets werecommon along the length of the rectum. Larvae weresmall, measuring 0.5 mm trunk length; the larval tailreached halfway across the anterior end of the trunkwith 4 ampullae and 3 adhesive organs.

colonies of the native species E. circumvallatumwere found attached to boulder sides and tops atthe low tide mark at Aquarium Point, Portobello,on the Otago Peninsula. t h e colonies formedpart of a species-rich ascidian fauna on bouldersexposed to high tidal flow past the point. Eudistomacircumvallatum had small inconspicuous cushion-shaped colonies with up to 80 small cream-colouredzooids embedded in a soft transparent gelatinoustest. Colonies were <25 mm in height and 15-20 mmin diameter (Fig. 2D); a few colonies arose froma short stalk 3-5 mm long. Artificial substrateswere also investigated for the presence of colonies.however, E. circumvallatum was not found oneither concrete or wooden wharf piles adjacent toAquarium Point.

The zooids did not form systems, and openedseparately to the surface. Atrial and branchialapertures had 6 distinct lobes, the atrial aperturewas on a short siphon. The thorax was relativelysmall, and often contracted, measuring 1.0-1.2 mmin length. it had 9 longitudinal bands of groupedmuscle fibres, which extended over the atrial siphon,and 12-20 transverse muscle bands. The branchialsac had 3 rows of 9-12 stigmata.

The abdomen had a long oesophageal necktypical of the genus, varying in length from 7 to9 mm. t h e distal end of the abdomen containingthe gut loop was wider than the thorax. there wasa small globular smooth stomach situated towardsthe posterior end of the descending limb of the gutloop (Fig. 3). t h e stomach, the duodenal regionand small posterior stomach were pigmented bright

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Smith et al.—First record of Eudistoma elongatum 351

Fig. 2 A, young Eudistoma elongatum colonies attached to an oyster rack pile, on an oyster farm in Houhora Harbour,New Zealand; B, extent of fouling problem caused by E. elongatum on oyster racks in Houhora Harbour; C, zooids ofE. elongatum (top) and E. circumvatallum (bottom) demonstrating differences in size of thorax and stomach coloration.(L, larvae; t , thorax; A, abdomen; S, stomach). Note, the stomach of E. elongatum is partially obscured by gonads;and D, E. circumvallatum (centre of frame) colony on boulder top, Aquarium Point, Otago Peninsula.

Table 1 Key morphological characters for distinguishing Eudistoma elongatum and E. circumvallatum and foridentification of the Northland, New Zealand specimens. Descriptions for E. elongatum from kott (1990), and for E.circumvallatum from Brewin (1946) and specimens collected at Aquarium Point, Otago Peninsula.

character

Colony morphology

Zooid size andmusculature

No. stigmata/rowStomach, shape, size

and pigmentation

E. elongatum

Club-shaped to longcylindrical3 mm (when contracted),20 longitudinal muscle bands

20Small smooth

E. circumvallatum

Small cushion shaped

8-10mm (relaxed);9 longitudinal musclebands (grouped), 12-20transverse bands

9-12

Globular, small, yellow

Northland specimens

Long cylindrical

8-9 mm (relaxed), 18longitudinal muscles,numerous fine transversemuscles

17-20Shield-shaped, non-pigmented

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352 New Zealand Journal of Marine and Freshwater Research, 2007, Vol. 41

B

1 mm

Fig. 3 A schematic drawing of A, the large shield-shapedstomach of Eudistoma elongatum and B, the small globularstomach of E. circumvallatum.

yellow giving colonies a subtle yellow coloration(Fig. 2C). Faecal pellets were common in the anterior2/3 of the rectum. gonads or larvae were not presentin specimens.

DNA analysesOnly the CTAB DNA extraction method resulted inDNA products that consistently amplified with thecOi primer pair in the initial tests, so this methodwas used for subsequent DNA extractions. Sequencedata were collected for 616 base pairs of codingsequence of COI in 10 specimens of Eudistoma fromnorthern New Zealand, 2 specimens of E. elongatumfrom Queensland, Australia, and 3 specimens of E.circumvallatum from Otago, southern New Zealand.Additional Eudistoma COI sequences were obtainedfrom GenBank, to give COI sequences for 19specimens of Eudistoma. in this expanded Eudistomadata set which included four mediterranean species,but which excluded E. circumvallatum from Otago(see below), 219 bases were variable and 134 baseswere parsimony informative.

in the Northland-Queensland Eudistoma cOidata set 8/616 bases were variable and 6/616 wereparsimony informative. There were two haplotypesamong the Northland specimens (Fig. 4) that differedat 6 base positions, of which only one resulted inan amino acid substitution (serine to glycine). Only

one of these haplotypes was found in the smallersample of 2 specimens of E. elongatum fromQueensland. The net sequence divergence amongall the Eudistoma species, including the four entriesin GenBank but excluding E. circumvallatum fromOtago, ranged from 0.150 to 0.273, and was 0.001between the Northland specimens and E. elongatum(Table 2).

COI sequences from the two specimens ofStyela clava (family Styelidae) from northern NewZealand aligned with the GenBank entry for S. clavafrom France (Accession No. Ay16607) with a netsequence divergence of 0.01, over 607 bases.

COI sequences for the Otago specimens of E.circumvallatum did not align with the EudistomaCOI data set above, and consequently divergencetimes between E. circumvallatum and E. elongatumwere not estimated. A GenBank search of tunicateCOI sequences showed that the closest match tothe E. circumvallatum sequence was a species ofDidemnum in the family Didemnidae.

DISCUSSION

the ascidian specimens collected from houhoraand Parengarenga harbours and the Bay ofIslands agree closely with the description for E.elongatum (kott 1990). Eudistoma elongatum canbe separated morphologically from the New Zealandnative species E. circumvallatum predominantlyon the basis of colony morphology; the size andmusculature of the thorax; the number of stigmata;and the shape, size, and pigmentation of the stomach.Eudistoma circumvallatum collected at AquariumPoint resembled specimens described by Brewin(1946) from Portobello, apart from a lack of larvae.Brewin (1946) did not record the presence of asmall post-stomach noted in this study; but maturegonads in Brewin's specimens may have obscuredthe small post-stomach. Based on the morphologicaldescription and the low COI sequence divergence,we conclude that the Northland ascidian specimensare E. elongatum.

There was a disparity between the morphologicaland cOi data for E. circumvallatum. A study of COIsequence data in 14 species of ascidians also reportedthat COI sequence data were incongruent with both18S sequence and morphological data (Stach &Turbeville 2002). The authors suggested that thisincongruence was because the cOi region evolvestoo rapidly to allow resolution of relationships ofhigher ascidian taxa (Stach & Turbeville 2002).

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Smith et al.—First record of Eudistoma elongatum 353

81; 65

100; 100

99; 100 85;8o1

81; 8593; 95

94; 95 r

Eudistoma Houhora Harbour

• E. elongatum Mooloolaba

E. elongatum Stradbroke Is

Eudistoma Parengarenga Harbour

Eudistoma Russell, Bay of Islands

Eudistoma Parengarenga Harbour

Eudistoma Russell, Bay of Islands

Eudistoma Opua, Bay of Islands

E plumbeau AY600978

E. planum AY600977

£. posidoniarum AY600974

- E banyulensis AY600973

— C. lepadiformis AY603104

•C.p/cfaAY116598

0.02

Fig. 4 Phylogenetic relationships of tunicate species in the genus Eudistoma based on partial cytochrome c oxidaseI (COI) gene sequences. The tree has been rooted with two other members of the Polycitoridae family (Clavelinalepadiformis and C. picta). Scale bar represents an interval of t rN+g genetic distance. Numbers at nodes are bootstrappercentages, based on distance (after 1000 replicates) and maximum likelihood (200 replicates); codes after speciesnames are GenBank accession numbers.

Table 2 Net cytochrome c oxidase I gene sequence divergence among species of Eudistoma and the Northland, NewZealand specimens.

E. plumbeauE. planumE. posidoniarumE. banyulensisNorthlandE. elongatum

E. plumbeau

0.1980.1860.1850.2220.227

E. planum

0.2640.2600.2690.273

E. posidoniarum

0.1500.2540.257

E. banyulensis

0.2130.217

Northland

0.001

however, cOi might be expected to be useful atlower taxonomic levels (Stach & Turbeville 2002),and has subsequently been used in a phylogeneticanalysis of 37 species of ascidians, which included4 species of Eudistoma (turon & Lopez-Legentil2004).

Stach & Tubeville (2002) also suggested thatthe presence of pseudogenes might explain theirincongruent results with COI sequences. Pseudogenesare genomic DNA sequences similar to known genesequences, but are non-functional and are regardedas defunct relatives of functional genes that havearisen through duplication or retrotransportation.The lack of indels and stop codons in the 37 speciesof ascidians studied by Turon & Lopez-Legentil

(2004) indicated that pseudogenes were not presentin these species. Likewise there were no stop codonsin the COI sequence obtained for E. circumvallatum;furthermore if there were multiple pseudogene dNAsequences similar to the mitochondrial COI gene, thenclear sequences would not have been obtained withthe universal primers used for the COI amplification.these limited observations would indicate that the E.circumvallatum COI sequence is not a pseudogene,but contamination cannot be ruled out. Further studieswith additional DNAmarkers and regional specimenswould be desirable to resolve the molecular phylogenyof E. circumvallatum, and other species in this genusidentified from Meyer Island, at the Kermadec Islands(m. Page unpubl. data)

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354 New Zealand Journal of Marine and Freshwater Research, 2007, Vol. 41

Biology and movement controlOn the east coast of Australia, E. elongatum iscommon in muddy habitats and on wharf piles inprotected waters, throughout its range from JervisBay, New South Wales (NSW) to Hervey Bay,Queensland (Kott 1990). Based on the known nativegeographic range and minimum water temperatureson the NSW coast, a tentative prediction can bemade on the likely southern limit to the spread ofE. elongatum in New Zealand. Jervis Bay (35°S)is the southern recorded limit for the distributionof E. elongatum on the NSW coast (kott 1990). ifminimum water temperature limits the distribution ofE. elongatum to water bodies above the 16°c winterisotherm, then the distribution of E. elongatum islikely to be restricted to northern New Zealand,north of latitude 37°S. An unconfirmed report of anE. elongatum specimen attached to an oyster shellin Golden Bay (northern South Island, winter seatemperatures 11°C) may not represent an establishedpopulation (m. Page pers. obs.).

t he potential impact of E. elongatum on NewZealand intertidal flora and fauna is unknown. OnNorthland oyster farms, E. elongatum was found onthe underside of oysters and on the rack-rails, andwas most prolific on the racks at about 0.25 m belowthe recommended oyster growing level of extremelow water neap (ELWN) tidal level (Handley 2002,2005). Eudistoma elongatum did not appear to begrowing in the mud substratum beneath the oysterracks, and was not found in the higher intertidalzone above ELWN (Handley 2005). In the June 2005collection, E. elongatum appeared less vigorous inits growth and was smothered by diatoms on themore exposed western side of the oyster farm closeto the estuary channel. The spread of E. elongatumin oyster farms in the Bay of Islands, and the rapidgrowth of colonies on oyster racks, suggests thatthis species is invasive on intertidal aquaculturestructures. The oyster farmers were advised toraise their oyster racks to above ELWN to avoid orminimise the infestations of E. elongatum (Handley2005), which should have minimal impact on oystergrowth rates (Handley 2002).

Eudistoma elongatum probably arrived in NewZealand with human assistance, rather than being self-introduced, because of the limited dispersal abilityof aplousobranch ascidian larvae (Ayre et al. 1998).The method of introduction is unknown, but is morelikely owing to translocation in fouling assemblageson the hulls of slow-moving vessels than in ballastwater, because of the short larval period (Ayre et al.

1998). Eudistoma elongatum was not found in 2006surveys of the Opua marina and Whangarei Port,including marsden Point and the Whangarei townbasin marina in northern New Zealand (g. inglis,NiWApers. comm.). Finding E. elongatum close tooyster growing areas, as opposed to northern ports,implies an introductory route that favoured smallvessels visiting coastal waters rather than main ports.In this way, the invasion and subsequent spread ofE. elongatum may follow a different pattern to thatof other invasive ascidians. A number of ascidiansappear to have been introduced into New Zealandwaters and many were first discovered close to portareas (Cranfield et al. 1998; Kott et al. 2006), whichare considered to be at greatest risk of invasion byexotic species. For example, the leathery tunicateStyela clava was first detected in Hauraki Gulf, closeto Auckland, in 2005 (Davis & Davis 2006) and hassubsequently been found in the ports of Lytteltonand Nelson, in the South Island and the Tutukakamarina in northern New Zealand (g. inglis, NiWApers. comm.).

Long distance dispersal of E. elongatum in NewZealand's coastal waters is likely to be enhancedthrough movement on vessels and/or aquacultureequipment. Control of the spread of E. elongatumin New Zealand may be more feasible than for someother invasive marine invertebrates. the apparentpreference for artificial substrates in the intertidalzone, coupled with their sessile nature, makes E.elongatum readily accessible at low tide for manualclearance. however small juveniles, and sub-littoralpopulations could be easily overlooked if they exist.Some simple management tools such as movingoyster racks above ELWN would decrease the habitatavailable for settlement and growth of E. elongatumand could substantially reduce their populations(Handley 2005). Management of vectors such asoyster barges would reduce the risk of introductionsto oyster farms south of the current distribution ineast Northland.

ACKNOWLEDGMENTS

We are grateful to dr Patricia mather (Queenslandmuseum) for her invaluable taxonomic expertise; garthRichards (Sanford Ltd) for supply of Eudistoma specimensfrom Houhora; and Mike Murray (J.T.H. Fisheries) forsupply of specimens from Parengarenga. We thank Brettrathe from Assassin charters for logistical supportsurveying sites on Great Barrier Island. This project wassupported by Biosecurity New Zealand.

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