The freshwater aquarium trade as a vector for incidental invertebrate fauna

14 Pages·2010·0.32 MB·English

BiolInvasions(2010)12:3757–3770
DOI10.1007/s10530-010-9768-x
ORIGINAL PAPER
The freshwater aquarium trade as a vector for incidental
invertebrate fauna
Ian C. Duggan
Received:1February2010/Accepted:20April2010/Publishedonline:30April2010
(cid:2)SpringerScience+BusinessMediaB.V.2010
Abstract The aquarium trade has a long history of non-indigenous species had a greater probability of
transportingandintroducingfish,plantsandsnailsinto beingrecordedinaquariacontainingaquaticplantsand
regionswheretheyarenotnative.However,otherthan in those that were heated. Methods for disposal of
snails, research on species carried ‘‘incidentally’’ aquariumwastesrangedfromdepositingwashingson
rather than deliberately by this industry is lacking. I thelawnorgarden(alowriskforinvasion)todisposing
sampledinvertebratesintheplankton,andfromwater of water into outdoor ponds or storm-water drains
among bottom stones, of 55 aquaria from 43 New (ahigherrisk).Itisrecommendedthataquariumowners
Zealandhouseholds.Irecorded55incidentalinverte- beencouragedtopouraquariumwastesontogardensor
bratetaxa,includingcopepods,ostracods,cladocerans, lawns—already a common method of disposal—as
molluscs, mites, flatworms and nematodes. Six were invasionriskwillbeminimisedusingthismethod.
known established non-indigenous species, and eight
others were not previously recorded from New Keywords Pet trade (cid:2) Craspedacusta (cid:2)
Zealand.Ofthelatter,twoharpacticoidcopepodspe- Melanoides (cid:2) Exotic (cid:2) Invertebrates (cid:2)
cies, Nitokra pietschmanni and Elaphoidella sewelli, Alternative vector
are not native to or known from New Zealand,
demonstrating the aquarium trade continues to pose
aninvasionriskforincidentalfauna.Theremainingsix
specieswerelittoral/benthicrotiferswithsubtropical/
tropicalaffinities;thesemayormaynotbenative,as Introduction
research on this group is limited. A variety of
behaviours associated with the set-up and keeping of The keeping of home aquaria is a popular hobby
homeaquariawererecorded(e.g.,fishandplantsinany globally with, for example, 8% of households in the
homeweresourcedfromstores,wildcaught,orboth, UnitedStatesestimatedtopossessfishtanks(AMVA
and cleaning methods varied), which made predic- 2007). The aquarium trade has been responsible for
tion of ‘‘high risk’’ behaviours difficult. However, the establishment of many fish, plant and mollusc
species into areas where they are not native (e.g.,
Fuller et al. 1999; Mackie 1999; Rixon et al. 2005).
I.C.Duggan(&) Despitethis,littleresearchhasbeenconductedonthe
CentreforBiodiversityandEcologyResearch,
role of the aquarium trade in transporting and
DepartmentofBiologicalSciences,TheUniversityof
introducing species into new habitats. That which
Waikato,PrivateBag3105,Hamilton,NewZealand
e-mail:[email protected] hasbeenconductedhasdealtalmostexclusivelywith
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3758 I.C.Duggan
taxa intentionally (i.e., deliberately) carried by the vector has been found carrying these species (Grig-
aquarium trade (e.g., fish, aquatic plants and large orovichetal.2003).
snail species; Rixon et al. 2005; Cohen et al. 2007; Theaimsofthisresearchareprimarilytoexamine
Changetal.2009).Lessisknown,however,offauna the identity and abundance of small incidental inver-
carried ‘‘incidentally’’, such as rotifers, micro-crus- tebratesinfreshwaterhomeaquaria,andtodetermine
taceansandsnails,likelytobelivingintheaquarium whetherthisvectorprovidesaninvasionriskforthese
water column, associated with the aquatic plants, animals. New Zealand is an ideal place to undertake
and/or living amongst the bottom stones, sediments thisresearch,as:(1)anumberofnon-indigenoussnails
and detritus. Nevertheless, the presence of some are known to have been introduced via this vector
members of these taxa has been noted in home there,while(2)anumberofinvertebrateinvadersexist
aquaria. For example, snail species not intentionally for which no vector has been definitively identified
carried by the aquarium trade were noted in North (particularly crustaceans; e.g., Duggan et al. 2006b).
American stores by Rixon et al. (2005) and Keller Further, I aim to elucidate behaviours or factors that
and Lodge (2007), and members of this taxon are contribute tothe presence ofnon-indigenous inverte-
well known to aquarium owners for ‘‘appearing’’ in bratesinhomeaquaria,whichmayprovidestrategies
their tanks (Perera and Walls 1996). This is partic- forthemanagementoftheindustryorprovideadvice
ularly the case for the Physidae, Thiaridae, Planor- for best practices for individual aquarium owners.
bidae and Lymnaeidae, families with representatives Questionstoownersthereforeaimedto:(1)identifythe
that have established non-indigenous populations in sourcesofbiotadeliberatelykeptintheaquaria,which
many parts of the world (Perera and Walls 1996; mayinfluencethepresenceofincidentalfauna(e.g.,if
Pointier 1999; Cowie and Robinson 2003). Despite addition of aquatic plants or live fish food affects
their small size, aquatic invertebrate invaders can incidental faunal composition), (2) determine other
have large ecological or economic effects on the factors that may affect the composition of incidental
ecosystems they invade. For example, zebra mussels faunawithintanks(e.g.,presenceofaquariumheating,
(Dreissena spp.) and the ctenophore Mnemiopsis filtration, and frequency of tank cleaning), and (3)
leidyi were listed amongst the IUCN’s ‘‘100 of the provide information on potential mechanisms that
world’s worst invasive species’’ (Lowe et al. 2000). mightleadtothereleaseofnon-indigenousfaunainto
Theaccumulationofknowledgeofbiotacarriedby naturalwaters.
any particular vector allows for the development of
specificmanagementstrategiestoreduceintroduction
rates.Forexample,studiesofbiotainballastwaterand Methods
sediments(e.g.,Lockeetal.1993;Dugganetal.2005)
hasledtothedevelopmentofballastwaterexchange, Sampling was undertaken over a one year period
or partial ballast water exchange, to reduce invasion between 5 March 2007 and 8 March 2008 for
risk. To date there have been no similar systematic incidental fauna in: (a) the open water of the tanks
studiesthatquantifythenumbersofincidentalspecies and (b) the interstitial water among the bottom
carriedbytheaquariumtradeand,besidesmolluscan sediments. Volunteer participants were recruited by
taxa,littleefforthasbeenmadetodeterminewhether approaching aquarium owners known to the author,
non-indigenousspeciesareevenbeingcarriedbythis using a bulk email message to all University of
vector.Thus,itisnotyetknownwhethermanagement Waikato staff, through two newspaper articles
techniques, outside of existing border control strate- describing the project that asked for participants,
gies, are required to reduce invasion rates for this and by word of mouth. Most participants (37: 86%)
vector.Thisisdespitesmallinvertebratesestablishing were in the Waikato region, while the remainder
populations in regions for which no vectors are yet (6: 14%) was recruited in the Wellington region,
known. In the North American Great Lakes, for approximately 500 km away. Participants were vis-
example—arguablythebeststudiedfreshwatersystem ited at times convenient to them, and where possible
globallyforinvadersandtheirvectors—theharpacti- atatimewhentheyweretocleantheirhomeaquaria,
coid copepods Heteropsyllus cf. nunni and Nitokra so as to provide estimates of the faunal composition
incerta have established populations but no specific and abundances that might be released from aquaria.
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Thefreshwateraquariumtrade 3759
Samples were collected from the interstitial water owner; live food bought from a pet store), how often
among bottom sediments using a modified 50 mL thetankwascleaned,howoldthetankwas,andhow
volumetricpipettewith rubber bulb. The tapered end thewaterwasdisposedofaftercleaning.Itwasnoted
of the pipette was removed to increase the bore size whether tanks were lit, had heating, and/or had
to 5 mm. The end of the pipette was placed into the filtration.Arulerwasusedtoestimatethevolumesof
aquarium sediment (usually comprised of aquarium water in the tank and area comprised of inorganic
stones[5 mm), and water was sucked from among sediments (i.e., aquarium stones, rocks), as well as
the stones in *50 mL aliquots while moving the the sizes of the sediments.
pipette horizontally through the stones. Water from Samples were returned to the laboratory for enu-
the pipette was emptied into a measuring cylinder merationandidentificationusingdissectingandcom-
until a total of approximately 250 mL of water was pound microscopes. Particular attention was paid to
collected for each tank. Two tanks contained no snailsandsmallcrustaceans,taxathathaveextensive
bottom stones; in these the sampling was undertaken invasionhistoriesinNewZealandandelsewhere(e.g.,
similarly, running the base of the pipette across the Winterbourn 1973; Grigorovich et al. 2003; Duggan
bottom of the glass. Water was typically sampled et al. 2006a). The volume of inorganic sediment,
depending on the method used by the aquarium comprising of mainly uneaten food and faeces, was
owner to clean out their tank, so as to replicate taxa estimatedfromeachsamplebymeasuringtheareaof
likely to be washed from the tanks while cleaning; detritus in the sample containers of the preserved
this involved either pouring off water after removal zooplanktonsamples.
ofthefish(smalltanks),siphoning,orusingajug(or Because of the wide variety of behaviours and
similar container) to remove water. Water samples environmentalvariablesassociatedwithaquaria,even
were collected to a measured volume of approxi- withinindividualhouseholds(Table 1),trendsintank
mately5 L,althoughsmallervolumeswerecollected fauna were analysed on a tank by tank basis, rather
in the smallest tanks (i.e., the smallest tank sampled thanbyhousehold.Relationshipsbetween(a)species
hadatotalvolumeofonly2.4 Labovethesediment). abundancesinthewaterandsedimentcomponentsof
Samples were concentrated using a 40 lm sieve and tanks and (b) tank environmental factors recorded,
the material retained was preserved in[50% ethanol were examined using Pearsons correlations (continu-
(final concentration). A visual inspection was con- ousdata;e.g.,temperature)orMann–WhitneyUtests
ductedforsnailsonplants,glassaquariumsides,and (categorical data; e.g., lighting). Mann–Whitney U
among the sediments, and representative individuals tests were only carried out on categorical data where
werecollected;thiswasbecauseonlysmall(\5 mm) samplessizesweresimilarbetweengroups.Datawere
snails were collected using the pipette method. A transformed for statistical tests (usually log (x ? 1))
small volume of surface water was also collected, to improve normality. The frequencies of occurrence
from which specific conductance, temperature (YSI ofcommonnon-indigenousspecies(i.e.,thosespecies
30 conductivity and temperature meter) and pH withfiveormoreoccurrences)wereexaminedrelative
(Oakton Ultra Basic pH Testr) were immediately tofactorsthatmayhaveleadtotheirintroductioninto,
measured. and their survival in, tanks.
Questionnaires were used to elucidate how inci-
dental species might be entering the tanks, and to
understandhowtheymightbeintroducedfromhome Results
aquaria into natural waterways. Each participant was
questioned to determine the numbers and types of Tank attributes
fish,plantsandsnailsdeliberatelyaddedtoeachtank
over time since set up, those extant in the aquaria at Fifty-five aquaria belonging to forty-three people
the time of sampling, and the sources of the biota were sampled. Thirty-four households had single
intentionally placed in the tank (i.e., bought or wild tanks, while four had two tanks each; all of these
collected). Participants were also asked what sorts of tanks were sampled. Where greater than two tanks
food had been added to the aquarium (store bought were present, only a subset or representative tanks
dry, dead or frozen food; live food caught by the were sampled; one household had three tanks (one
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3760 I.C.Duggan
Table1 Tanksetup,
Pertankbasis(/55) Perhouseholdbasis(/43)
environmentalvariables,
andownerbehavioursfor
Fish 31tropicalfishtanks 22tropicalfish
sampledhomeaquariaona
20goldfishtanks 17goldfish
pertankandperhousehold
basis 4mixed(i.e.,tropicalfish 4mixed(i.e.,3householdshadtropicalfishand
andgoldfishinthesame goldfishinthesametank,1indifferenttanks)
tank)
Plants 44with 32with
11without 10without
?1withtankswithandwithout
Tankvolume Ave:56.2L Ave:116.6L
(excl. Min:2.4L Min:2.4L
sediments)
Max:303.4L Max:1157.7L
Volumeof Ave:5.22L Ave:11.9L
stones/gravel Min:0L Min:0L
Max:31.92L Max:169.4L
Heating 30heated 22heated
25notheated 19notheated
?2withtankswithandwithout
Filter 39external/internalfilter 27external/internalfilter
4undergravelfilter 3undergravelfilter
12nofiltration 11nofiltration
?2withtankswithandwithout
Lighting 31lit 22lit
14notlit 20notlit
?1withtankswith/without
sampled), one-four tanks (two samples), one-five proportionstockedapplesnails(Pomaceabridgesior
tanks (three sampled), one-nine tanks (four sampled) P.canaliculata;9.1%).Allownersfedtheirfishwith
and the other fourteen tanks (three sampled). Thus, processedfoodboughtfrompetstores,althoughsome
the average number of tanks present in each house- supplemented this with live bought (e.g., Daphnia;
hold was 1.8, although the typical household 18.2%) or live caught food (e.g., mosquito, chiron-
(median) had only one. Each aquarium was sampled omidorotherinsectlarvae;38.2%),whichcouldalso
once only during the study. allow introduction of incidental fauna to aquaria.
There was a great variety of behaviours involved Variousfactorsweremeasuredthatmightaffectthe
with the keeping of aquaria that might affect the survival and abundance of animals in tanks. The
species composition of incidental fauna, or the temperature of heated tanks ranged from 18.7 to
presence of non-indigenous species, in the tanks 28.8(cid:3)C(average25.4(cid:3)C),whileunheatedtanksranged
(Table 1). Most owners (67.4%) sourced their aquar- from10.2to25.1(cid:3)C(average18.3(cid:3)C);thelattervaried
ium inhabitants from stores only, with only a small seasonally.Specificconductancerangedfrom99.9to
proportion having everything in their tanks wild 4170.0 lS cm-1 (average 621.3 lS cm-1), and pH
caught(4.7%;oneownerhadcollectedallnativefish rangedfrom4.4to9.5(average6.7).Mostaquariahad
and plants, while the other had collected all non- filtrationandlighting,andmoretankswereheatedthan
indigenousfish,plants,andsnailsfortheiraquarium). not(Table 1).
Theremainderhadamixtureofstoreboughtandwild
caught inhabitants (usually bought fish with wild- Species composition and abundance in aquaria
collectedplants).Alltankscontainedfish,whilemost
(80.0%) had also added plants that may aid in the Fifty-five incidental invertebrate species were
introductionofincidentalfaunatotanks.Onlyasmall recorded (Table 2). Species belonged to a variety of
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Thefreshwateraquariumtrade 3761
Table2 Listofspecies
Water Sediments Notknown Established
identifiedfromaquariumwater
fromNZ NIS
andwaterfrominterstitial
sedimentsfromNewZealand
Rotifers
aquaria
Cephalodellaforficula X X
Colurellauncinata X
Cupelopagisvorax X
Dicranophorusepicharis X X
Keratellavalga X
Lecaneaculeata X X
Lecanebulla X X
Lecaneclosterocerca X X
Lecanedecipiens X X
Lecanehamata X X
Lecaneinermis X X X
Lecaneludwigiiludwigii X X
Lecaneludwigiiohioensis X X
Lecanelunaris X X
Lecanenana X X X
Lecanepyriformis X X
Lecanerhytida X
Lecanesignifera X X X
Lepadellaacuminata X X
Lepadellaovalis X
Lepadellapatella X
Limnaismelicerta X X
Proalessp. X X
Ptygurasp. X X
cf.Sphyriaslofuana X X
Squatinellagellii X
Squatinellamutica X X
Testudinellapatina X X
Bdelloids X X
Copepods
Acanthocyclopsrobustus X X
Eucyclopsserrulatus X X
Microcyclopsvaricans X
Paracyclopssp. X
Nitokrapietschmanni X X X
Phylognathopusvigueri X X
Elaphoidellasewelligp X X
Epactophanesrichardi X
Cyclopoidnauplii X X
Harpacticoidindet X X
Harpacticoidnauplii X X
Cladocerans
Alonacambouei X X
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3762 I.C.Duggan
Table2 continued
Water Sediments Notknown Established
fromNZ NIS
Chydorussphaericusgp X
Molluscs
Ferrisiaspp. X
Gyrauluscorinna X
Lymnaeastagnalis X X
Melanoidestuberculata X X
Physaacuta X X
Planorbariuscorneus X X
Radixauricularia X X
Othertaxa
Ostracods X X
Mites X X
Oligochaetes X X
Flatworms X
Springtails X
Chironomid:Paratanytarsusgrimmii X
Indeterminatechironomids X
Nematodes X X
Craspedacustasowerbii X X
taxonomic groups, and included rotifers, copepods, were typically similar (usually \10% difference),
cladocerans, molluscs, ostracods, mites, flatworms, exceptformolluscs,whichwerenotfoundamongthe
chironomids, nematodes and cnidaria. These were water fraction (but in 43% of tanks overall), mites,
primarily mobile benthic species (e.g., substrate- alsomorefrequentlyfoundamongsediments(78.2%)
associatedrotiferspecies,cyclopoidandharpacticoid than water (30.9%), and rotifers, more frequently
copepods,snails,oligochaetes),withfewtrulyplank- occurring in water (94.5%) than sediments (76.4%).
tonic representatives (e.g., Keratella valga, recorded Averageabundancesoftaxaweregreatlyaffectedby
as a single individual in one tank; Table 2). Average having high abundances in few or single tanks; for
densities of animals in the water component were example, cladocerans were on average the most
499.9 ind. L-1 and in sediments 966.1 ind. L-1, abundant taxon in the water fraction across tanks
although these numbers were influenced by some (average 374.0 ind. L-1), but were present only in 5
tanks containing many individuals (i.e., the data was of 55 tanks; one tank had over 25,000 ind. L-1.
non-normally distributed). Thus, the median abun- Rotifers were next most abundant, with average
dance of animals in the water fraction was 13.3 ind. numbersof79.2ind.L-1,butthemedianacrosstanks
L-1, and in sediment 241.8 ind. L-1, indicating that was only 5.5 ind. L-1. Rotifers dominated the
the sediments typically have far greater abundances sediments, averaging 402.9 ind. L-1 (median 47.2),
thantheopenwater.Onaverage,theareacomprising followed by cladocerans, mites and copepods.
the bottom sediments was 10.6% of that in the water Relationshipsbetweentotalnumbersoforganisms
fraction. Rotifers were the most frequently occurring present in the water and sediment fractions and tank
taxon overall (present in 96.4% of the 55 tanks variables were weak or non-existent. A significant
sampled), followed by mites (85.5%), oligochaetes negative relationship was determined only for the
(56.4%), copepods (49.1%) and molluscs (43%); number of animals in the water column and the
these were the only taxonomic groups present in volume of organic sediments present (i.e., the more
greaterthan20%oftanks.Percentageoccurrencesof faecesandfoodremaininginthebottomofthetanks,
each taxon between the water and sediment fractions the less animals were found in the water column);
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Thefreshwateraquariumtrade 3763
however, this had a low correlation coefficient Examining the data for the 36 aquaria where all
(R = -0.329; P = 0.014). No relationships were inhabitants were derived from aquarium stores (no
found for temperature, specific conductance, pH, wild caught components), all of the common non-
time since last clean, age of tank, tank volume, indigenous species were found, indicating that stores
sediment size (inorganic), number of fish, or the have acted as a route for these species to enter
presence or lighting (all P[0.05). aquaria. Too few data were found for aquaria
containing only wild caught specimens; however,
Species notpreviously known from New Zealand noneofthethreetankscontainedanyofthecommon
non-indigenousspecies,althoughonetankhadPhysa
Eight species not previously recorded from New acuta, now a very common species throughout New
Zealand, and six known established non-indigenous Zealand. Lymnaea stagnalis was also only found
species,wererecorded.Fivesnailspecieswereknown once, in one of the wild caught tanks, indicating this
invaders in New Zealand: Planorbarius corneus species may not be spread via stores. The other
(11tanks), Melanoides tuberculata(10tanks), Physa variable that seemingly related to the presence of
acuta (6 tanks), Radix auricularia (3 tanks), and common non-indigenous species was heating; all
Lymnaea stagnalis (1 tank). Additionally, a small groupswererecordedmorefrequentlyinheatedtanks
cnidarian medusa, likely Craspedacusta sowerbii, than non-heated (Fig. 1). No discernable patterns
was also recorded on one occasion. Species recorded wereobservedforfiltration,additionoflivefood,and
thataredefinitelynotnativetoNew Zealand,butare lighting (graphs not presented).
not yet recorded as having non-indigenous popula-
tions, were the harpacticoid copepods Nitokra pie- Release
tschmanni(9tanks)andElaphoidellasewelli(1tank).
Additionally, rotifer species not recorded from New A variety of methods were used for disposal. Of the
Zealand, Lecane aculeata (1 tank), Lecane inermis 55 tanks examined, 19 disposed of their washings
(3 tanks), Lecane nana (1 tank), Lecane signifera exclusively on the garden (16 of 43 owners), 27 put
(3tanks),Limnaismelicerta(3tanks),andaspecimen theirwashingsexclusivelydownthesink(19owners)
conformingmostcloselytoSphyriaslofuana(1tank), and 5 tanks had their washings either poured on the
were also recorded. garden or poured down the sink (4 owners). Two
As all tanks contained fish, the frequency of the tanks had never had water removed, one because it
more common ([5 occurences) non-indigenous taxa wasanewtank(1 monthold),whiletheotherowner
wasrelatedtootherfactorsthatmayhaveledtotheir did not feel the need to remove water, even after
introduction and survival to tanks; all snails were having the tank for 2 years. Of the remaining tanks,
combined and treated as one group, but Melanoides one was disposed of in an external fish pond, while
tuberculata, Planorbarius corneus and Physa acuta another was emptied into a storm-water drain acces-
werealsocommonenoughtobetreatedindividually. sible outside the window from the aquarium. Tank
All six rotifer species were treated as a single group, cleaning behaviours varied greatly among partici-
as none were found in greater than five tanks pants, ranging from tanks never having water
individually. The introduction of aquatic plants removed to regular complete cleanings (including
showed clear patterns of introduction (Fig. 1). Snails rock scrubbing). On average, 48.3% of any tanks
were only found in aquaria with aquatic plants, contents were expected to be emptied during each
whereas they were absent from all aquaria without cleaning, and tanks were cleaned on average every
aquaticplants.Therotifersnotpreviouslyrecordedin 2.7 months. With an average tank volume of 56.2 L
NewZealandshowedasimilarpattern.However,the (Table 1), it is estimated that 118.7 L per tank per
harpacticoid Nitokra pietschmanni was found in year(or159.7 Lperhouseholdperyear)aredisposed
relativelyequalproportionsintankswithandwithout of. Assuming approximately 8% of households pos-
introduced macrophytes; as adults and nauplii of this sesshomeaquaria(AMVA2007),andthatthereare1.6
taxon were commonly found in the water column, million households in New Zealand (December 2009
they are perhaps introduced to tanks with the water estimate from Statistics New Zealand: www.stats.
surrounding fish. govt.nz),itisestimatedthat12.8 9 104householdsin
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3764 I.C.Duggan
Fig.1 Percentages of tanks in which common (C5 occur- Zealand home aquaria, for a aquariums with and without
rences) non-indigenous species, or species not known from aquariumplants,binaquariawhereallconstituentswerestore
New Zealand, were recorded, from a survey of 55 New bought,andcinheatedandnon-heatedaquaria
123
Thefreshwateraquariumtrade 3765
New Zealand own home aquaria. Thus, 20.4 million remainingtankshadadditionsofspeciesfromnatural
litres of aquarium waste might be expected to be waters,butestablishedpopulationsofN.pietschman-
disposed ofperyearinNew Zealand,fromacountry ni are not known from New Zealand, despite a
of only 4.4 million people. At an average concen- number of surveys for this group (Chapman and
tration of animals of 539.6 ind. L-1 in each tank, Lewis 1976). The second harpacticoid, Elaphoidella
11.09 109 animals might be expected to be washed sewelli, is known from Asia, Africa, and India, and
fromtanksperyear.Acrossalltankstheharpacticoid was found in only one aquarium. All inhabitants in
copepod N. pietschmanni, the most common and that aquarium were also store bought. The common
abundantofnon-indigenousspeciespresent,averaged Asian native distribution of N. pietschmanni and E.
56.9 ind. L-1, and therefore 7.7 9 108 individuals sewelli is consistent with the predominant global
might beexpectedtobewashed fromtanksper year. regions for aquarium fish culture facilities and
Assuming2of43ownersreleasewaterintopondsor exports (Cheong 1996), which indicates the likely
storm-water drains, more ‘‘high risk’’ methods of pathway for introduction.
disposal, it is estimated that 5.2 9 108 animals in Some or all of the rotifer species not previously
total, and 3.6 9 107 N. pietschmanni, might be recorded may potentially be native to New Zealand,
released into external waterways without treatment. as species found in this study typically have broad
This is likely an overestimate for freshwaters as, distributions,whilelittleresearchhasbeenconducted
although in the Waikato most storm-water is drained inNewZealandofthelittoralorbenthicfauna(Shiel
to lakes and rivers, a high proportion of storm-water et al. 2009). However, of the four Lecane species
in the country will be drained to the ocean. recorded, L. nana, L. signifera and L. aculeata are
noted by Segers (1995) to be more common in
‘‘tropicalandsubtropicalwaters’’,or‘‘warmwaters’’.
This suggests that these species may well not be
Discussion nativetoNewZealand,unlesstheyaretobefoundin
the warmer far north of the country.
Taxonomic composition and non-indigenous A number of known established non-indigenous
species invertebrate species were identified, which shows a
strong signal for the historical importance of this
I recorded a variety of invertebrate species from the vector. Those recorded were primarily snail species:
water column and sediments of home aquaria, Radixauricularia,Planorbariuscorneus,Melanoides
including species possibly present in New Zealand tuberculata,PhysaacutaandLymnaeastagnalis.Most
but not previously recorded, non-indigenous species havebeenestablishedinNewZealandforsometime,
known to have already invaded, and non-indigenous withtheaquariumtradealreadyinferredasthevector
species not yet known to have established. As such, for introduction (Winterbourn 1973; Duggan 2002).
the aquarium trade appears to remain a significant However, some of these taxa still have fairly limited
risk for the establishment and spread of non-indige- distributions in New Zealand, particularly M. tuber-
nous species. culata, R. auricularia and P. corneus, and the aquar-
Of greatest concern, two harpacticoid copepods iumtradethereforestillprovidesopportunitiesforthe
and six rotifer species were identified that are not spreadofthesespecies.Asmallcnidarianmedusawas
known from New Zealand. The harpacticoid Nitokra also recorded;nofreshwater cnidarian native toNew
pietschmanniwasthemostcommon,recordedinnine Zealand, and few globally, are capable of producing
aquaria belonging to seven owners, and was also medusa, but the non-indigenous Craspedacusta sow-
highly abundant. This suggests that N. pietschmanni erbiiisknownfromanumberoflakesinthenorthern
is widespread and abundant in the New Zealand halfoftheNorthIsland(e.g.,Boothroydetal.2002).
aquarium trade. To date, this species is known from Sampling in the current study was not designed to
Asia (Japan, China, South Korea) and the Hawaiian collectbenthicattachedspecies;assuch,thepolypsof
Islands (Chang and Yoon 2008). In four tanks, all thisspeciescouldbewidespreadintheaquariumtrade,
fish, plants and snails were store bought, indicating withthesamplingofthismedusaafortuitousevent.For
that stores are the probable source to the tanks; the example, medusa of C. sowerbii have been noted in
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3766 I.C.Duggan
aquaria previously, both in New Zealand and else- study,theremustbesomelevelofregionalism(14of
where(Fish1971;RahatandCampbell1974). 43ownershadeithersomeorallcomponentsoftheir
I did not attempt identifications of many oligo- tankscollectedfromthewild).However,withrespect
chaetes during this study, due to most specimens to non-indigenous species in aquaria, there appear to
consisting of juveniles, but these were common and be both similarities and differences between taxa
occasionally abundant. However, many tanks were recordedinNewZealandandthoseknowntooccurin
observed to contain Pristina species of which, for the aquarium trade elsewhere. Snail species such as
example, three species are believed to have invaded Physa acuta and Melanoides tuberculata are known
the North American Great Lakes (Grigorovich et al. within, and are considered to have established popu-
2003). Combined, this data shows that the aquarium lations from, home aquaria in a number of locations
trade has likely been responsible for a large number globally (e.g., New Zealand and North America;
of invasions into New Zealand’s freshwaters to date PereraandWalls1996;Mackie1999;Duggan2002).
and—althoughmostnon-indigenousspeciesrecorded However,otherspecies,suchasthetropicalAmerican
had already invaded—still poses somefuture risk for species Elminia floridensis, have been observed on
both establishment and spread. plants in aquarium stores in North America (Rixon
The composition of the aquarium fauna was etal.2005),butwerenotdocumentedinmystudy.The
distinctive not only by what was present, but also incidentalfaunainhomeaquariamaydifferdepending
bywhatwasabsent.WhilealargeproportionofNew ontheregionsfromwhichplantsandfisharesourced
Zealand’s historic aquatic invertebrate invaders were from;however,asSingaporeistheprimarysourceof
recorded duringthisstudy(snails,C. sowerbii),most aquarium fishes to global markets, including North
of the recently established invaders are relatively AmericaandEurope(Cheong1996),itisprobablethat
large planktonic species, including Daphnia and some incidental species are widespread. Surveys of
calanoid copepod species (e.g., Duggan et al. faunasinhomeaquariaelsewhere,andinthedominant
2006a). These taxa are not likely to survive in home aquariumfishandplantculturefacilitiesglobally,are
aquaria containing fishes, as they are large bodied, imperativefordeterminingthesepatterns.
and would be easily seen by these visual predators Overall,mostofthetaxaweretypicaloflittoralor
(e.g., Ortega-Salas et al. 2009). Indeed, 5 of the 43 benthic habitats, and not of the plankton. This may
households sampled had bought live Daphnia cul- reflectthehighdegreeofzooplanktivoryinthewater
tures from stores to feed their fish, but no live fraction of tanks, but also that these species possess
Daphnia were recorded in tanks. One of the recent adaptations for attaching to substrates that might
calanoidcopepodinvadersrecordedinNewZealand, allow them to fasten to the aquarium sides during
the North American Skistodiaptomus pallidus, has cleaning (e.g., Duggan 2001), or to the manner in
beenrecordedaslivingwithinsuchcultures(Duggan which they are introduced into the tanks (below).
et al. 2006a; Banks and Duggan 2009). If the
aquarium trade has been the source of these intro- Arrival, survival and abundance in tanks
ductions, they have perhaps been released directly
into waterways from culture samples, rather than It was difficult to determine any single factor, or
being released from home aquaria themselves. Alter- subset of factors, responsible for high abundances of
natively,diapausingeggs,whichbothofthesespecies taxa in tanks; this makes the development of man-
are known to produce (e.g., Dowell 1997), could be agement strategies for owners to reduce the preva-
deposited in tank bottom sediments and hatch lence of species in their tanks difficult. I observed a
following release into natural waters. vastarrayofpractices thatownersused tosetupand
Fewdataexistoftheincidentalfaunacarriedbythe maintain their aquaria, which led to a multitude of
aquarium trade. Although it is probable that benthic possible important factors responsible for survival in
rather than planktonic forms will dominate, it is not tanks,evenamongaquariaownedbyasingleperson.
knownwhetherthesamespeciesexistelsewhere(i.e., Even categorical factors measured had complicating
whether there is a cosmopolitan aquarium fauna). factors. For example, filtration devices used differed,
Certainly, due to the widespread collection of plants which could be set at a variety of different strengths,
and fish from local lakes and ponds in the current and their efficiency will have been affected by the
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