The introduced terrestrial mollusca of South Africa

2010·8 MB·English

by  Herbert, David, G.

The
introduced
terrestrial
Mollusca
of South Africa
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David G. Herbert /
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Digitized by the Internet Archive
in 2016 with funding from
South African National Biodiversity Institute Libraries
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SANBI
Biodiversity Series 15
The
introduced
Mollusca
terrestrial
of South Africa
b
y
David G. Herbert
national
biodiversity
institute
SANBI
Pretoria
2010
SANBI Biodiversity Series
The South African National Biodiversity Institute (SANBI) was established on 1 Sep-
tember 2004 through the signing into force ofthe National Environmental Manage-
ment: BiodiversityAct (NEMBA) No. 10 of 2004 by PresidentThabo Mbeki. The Act
expands the mandate ofthe former National Botanical Institute to include respon-
sibilities relating to the full diversity of South Africa's fauna and flora, and builds on
the internationally respected programmes in conservation, research, education and
visitor services developed bythe National Botanical Institute and its predecessors
overthe past century.
The vision of SANBI: Biodiversity richness for all South Africans.
SANBI's mission is to champion the exploration, conservation, sustainable use,
appreciation and enjoyment of South Africa's exceptionally rich biodiversityfor all
people.
SANBI Biodiversity Series publishes occasional reports on projects, technologies,
workshops, symposia and other activities initiated by or executed in partnership with
SANBI.
The author: Dr David Guy Herbert, Natal Museum, R Bag 9070, Pietermaritzburg
3200, South Africa, and School of Biological and Conservation Sciences, University
of KwaZulu-Natal, R Bag X01, Scottsville, Pietermaritzburg, 3209, South Africa. E-
mail: [email protected]
Technical editor: Gerrit Germishuizen
Design & layout: Sandra Turck
Cover design: Sandra Turck
How to cite this publication
HERBERT, D.G. 2010. The introduced terrestrial Mollusca of South Africa.
SANBI Biodiversity Series 15. South African National Biodiversity Institute,
Pretoria.
ISBN: 978-1-919976-56-3
© Published by: South African National Biodiversity Institute.
Obtainable from: SANBI Bookshop, Private Bag XI01, Pretoria, 0001 South Africa.
Tel.: [phone]. E-mail: [email protected]. Website: www.sanbi.org.
Printed by: 4lmages Design & Printing, 23B De Haviland Crescent, Persequor Park,
Brummeria, Pretoria.
Contents
Abstract
Acknowledgements v
Introduction 1
Materials and methods 4
Abbreviations 4
History 7
Patterns and processes ofintroduction 8
Rate ofintroduction 8
Region oforigin 9
Site ofintroduction 10
Modes ofintroduction and dispersal 10
Current provincial patterns 12
Human mediated range expansion ofindigenous species 14
Identification 15
Eradication and control 15
Checklist and classification ofintroduced terrestrial molluscs in SouthAfrica 17
.
Species treatments 19
Snails 19
Slugs 58
Excluded species 76
SouthAfrican species occurring elsewhere 77
Potential future introductions 78
References 82
Index 108
Aplea for assistance from a rather desperate member ofthe
public concerning Thebapisana.
‘Dear Dr Herbert
I recall in a copy of Veld andFlora some 18 months ago you asked for help
in a snail survey. Well, I am asking for HELP with eradicating snails (those
horrible little white ones) which have become such a huge pest in my garden
that after many years oftrying EVERYremedy on Earth, they have actually
multiplied tenfold instead ofdecreasing! I am truly at my wits end! I don’t have a
garden left and they seem to love the harsh West Coast climate - they don’t mind
the hot, dry summers or the cold, wet winters! Even the birds are tired ofeating
ANY
them! help will be greatly appreciated.’
Saldanha Bay, ll/iv/2002
Abstract
The alien terrestrial molluscfauna ofSouthAfrica is comprehensivelyreviewed. 34
species areconsidered tohave been introducedto thecountry, ofwhich 28 are considered
established and 13 ofthese invasive. The historyofintroduction andrecordingis
summarised and patterns ofintroduction are analysed. Introductions continue at
a rate ofapproximatelytwo species perten years, with no evidence oflevellingoff.
The agriculture andhorticulture industries areconsidered tobe majorcontributors
to the introduction and spread ofalien species. Thecomposition ofthis alien fauna
showsconsiderable similaritywith thatknown from southernAustralia, reflectingthe
similarcolonialhistoryoftheregions andclimatic matchingwith regions oforigin
inwestern Europe and theMediterranean. Each species is discussed in terms ofits
distinguishingfeatures, habitatpreferences, date ofintroduction andfirstrecord, native
range and global distribution, distribution in South Africa, pest status, and similarity
with indigenous species. Furthertaxonomic notes andbiological observations relating
tobehaviour, reproduction andparasite transmissionareincludedwhere relevant,
and references to sources ofadditional information are provided. In addition, some
consideration is givento potentially pestiferous species which are notyetknown tooccur
in SouthAfrica, but which represent a significant futureintroduction risk. New records:
Discus rotundatus Hawaiia minuscula, Vitrea contracta,Aegopinella nitidula.
,
Acknowledgements
I am grateful to: DrWillem Sirgel (UniversityofStellenbosch) for sharingadditional
informationregarding distribution records and forcommentingon the manuscript;
the Wildlife and Environment SocietyofSouthAfrica forfacilitating my‘Snailiens’
project and the many SouthAfricanteachers and schools thatparticipated in the
data collection; Prof. ThierryBackeljau for identifying arionid slugs; Drs GeofBaker,
Suzanne Charwat andAngela Lush (SouthAustralian Research and Development
Institute) forprovidinginsightinto the alien mollusc problems inAustralia; Mary Cole
and Linda Davis forassistance with field surveywork; DrDavid Robinson (UDSA,
APHIS) for information andhis ongoinginterest in this project; Ben Rowson (National
Museum ofWales) for assistance with photographs and literature queries. As always,
I am also much indebtedto Linda Davis forconverting mycamera lucida drawings
ofgenital anatomyinto scientific illustrations ofhigh quality. I also acknowledge
the UniversityofKwaZulu-Natal foruse ofautomontage facilities at its Centre for
ElectronMicroscopy. Lastly, butbyno means least, I thank Gerrit Germishuizen forhis
meticuloustechnical editingand SandraTurck forthe design and layout.
The publication ofthis
reviewwas generously OI*B
sponsoredbythe Centre
for Invasion Biology
(Stellenbosch University) national DST-NRFCentreof
and the National Research biiondsitvietrustiety EInxvcaesliolnenBcieolfoogry
Foundation (SABI). S A N B
I
V

SANBI Biodiversity Series 15 (20103
Introduction
Aliens species, particularlythose that become invasive, have enormous economic and
environmentalconsequences. Pimentel et al. (2005) estimated annualeconomic costs of
approximatelyUS$120 billion resulting from invasive alien species inthe USAalone.
Biodiversitycosts may also be considerable and introduced species are recognised as
one ofthe most significantthreatsfacing Earth’sbiota (Clout 1995, 2002), resultingin
the homogenisationofonce diverse faunas (McKinney & Lockwood 1999; Cowie 2004).
The economic impactofmanyterrestrial snail and slug pestsinthe agriculture sectoris
wellknown (Barker 2002a), and instances where introduced freshwater molluscs have
resulted in high economic costs include zebra and quagga mussels (Dreissena spp.) and
theAsian clam (Corbiculafluminea) in North America (Pimentel etal. 2000), and apple
snails Pomacea spp.) in Hawaii and SoutheastAsia (Cowie 2002).
(
Forterrestrial species, these economiccosts mayrelate to directimpacts ofthe mol-
luscs themselves, such as theirfeeding, faecal and mucus soilingofcrops, and clogging
ofharvesting machinery. Alternatively, costs maybe associated with indirect impacts or
downstreamconsequences such asthetransmission ofparasites and diseases, the con-
tamination ofproduce leadingto its down-grading at pointofsale or rejectionby quaran-
tine officials atports ofentry, andrejectionofsnail-infestedpasturebylivestock (Baker
2002). Manyterrestrial gastropods are known to serve as intermediate hoststo econom-
icallyimportant livestock parasites, particularly platyhelminths and nematodes (South
1992; Boray & Munro 1998; Godan 1999; Otranto & Traversa 2002; Grewal et al. 2003;
Morandet al. 2004), some ofwhich may also affecthumans (Kliks & Palumbo 1992;
Spratt 2005), andtofunction as vectors ofcrop plant pathogens (Mead 1961; Godan
1983; South 1992; Boray & Munro 1998; El-Hamalawi & Menge 1996; Alvarez etal.
2009). Less obviousindirectcosts, resultingforexample from changes in tilling/burn-
ingregimes aimed at snail control, mayinclude increased soil erosion and lowered levels
oforganic matterenteringthe soil, leadingto altered nutrient cycling processes (Baker
2002). In terms ofbiodiversitycosts, the impact ofthe rosywolfsnail Euglandina rosea)
(
on the native snail fauna ofislands in the south Pacific is now widelyviewed as a worst
case scenario resultingfrom ill-conceivedbiological control initiatives (Civeyrel & Sim-
berloff1996; Coote & Loeve 2003; Lydeard et al. 2004). Six species ofmollusc arelisted
amongstthe top 100 worst invasive alien species in the world (IUCN-ISSG 2000).
Land snails and slugs are undoubtedlyadept hitchhikers and, with human assistance,
manyspecies have now become widely distributed across the globe (Smith 1989; Rob-
inson 1999). Evidence from archaeological investigations indicates that ship-mediated
translocation ofland snails is a process ofsome antiquity, withone Mediterraneanex-
ample datingfrom 3 300years BP (Late BronzeAge) (Welter-Schultes 2008), another
perhaps 5 000 years BP (Giokas et al. 2009). DNAdata also suggestthat ancient trade
routes have been important in the dispersal ofsnails within theMediterranean (Fioren-
tino et al. 2008 andreferencestherein).
The introductionofland snails to SouthAfrica almostcertainlybegan with the arrival
ofthe Europeancolonists in the late 1600s and early 1700s. In orderto survive in an
essentially unknown land, these early settlers mustfrequentlyhavebrought familiar
crop plants with them. Thesetheyknew how tocultivate andtheycould therefore guar-
antee a food supplyin their newbut unfamiliar home. Janvan Riebeeck, forexample, is
known tohave importedvine cuttings (wrapped in moist soil) to the Cape as early as the
1650s (Hughes et al. 1992) andin 1652 he established the Dutch EastIndia Company
gardens as a victualling station inwhatis now CapeTown (McCraken & McCraken
1988). As the colony grew, subsequent settlers imported ornamental flowers, shrubs and
SANBI Biodiversity Series 15 (2010]
trees to growin their gardens. Later still, in the midto late 1800s, formalbotanical
gardens with a widevarietyofnon-native plants were established in a numberoftowns
(McCracken & McCracken 1988). Thisimportedhorticultural stock almostcertainly
did notcome alone. The plants were often rooted in containers, inwhichthe soil would
undoubtedlyhave contained a range ofinvertebrates, either as adults or as eggs, and
plant pathogens from theiroriginal homes. No doubt manyofthese failed to establish
viable populations in their new environment, butothers have, to varying degrees, been
able to exploitthis opportunityto theirown advantage. The periodic introduction ofnon-
indigenous species is now an ongoingphenomenon and likelyto occur with increasedfre-
quencyas globalised trade expands. Westphal et al. (2008) have shown that the greater
the degree ofinternational trade, thehigherthe numberofinvasive alien species. Given
that many terrestrial gastropods are pests ofcommerciallyimportantcrops, diseasevec-
tors and competitivelyefficientcolonisers ofnative habitats, itis importantthat we take
stockofhow far this process has progressed, monitor the spread ofthose species already
introduced, identify new introductions at an early stage, be alert to the possibilityofthe
introduction offurthertramp species, particularlythose ofeconomic significance, and
implement effective measures so as to minimise the risk offurther introductions.
Thetotal numberofconfirmed introductions ofnon-native terrestrial molluscs in South
Africa now stands at 34, ofwhich 28 appearto have established self-sustainingpopula-
tions. However, although some were undoubtedlyintroducedin the 1600s and 1700s, our
knowledge ofthem dates onlyfrom the first studies ofthe SouthAfrican malacofauna,
whichessentiallybegan inthe mid-1800s. The earliest record ofan introduced snail in
SouthAfrica dates from 1846 when William Benson, on avisitto Cape Town, collected
Oxychilus cellarius and Valloniapulchella (Benson 1850) [despitebeingon crutches]. By
this time, the common European garden snail, Cornu aspersum, was also probably well
established, eventhough the first confirmed record forthe species dates onlyfrom 1855.
With a growingpopulation and increasingtrade, the accidental importation ofalien
molluscs has continued, with discoveries ofnew introductionsbeing made on a regular
basis.
Many molluscancolonists are speciesthat thrive in association withhumans (synan-
thropic); indeeditis largelybecause ofthis habitthatthey are such effective globe-trot-
ters. Deprivedoftheir natural predators andwith the opportunityto exploit unoccupied
ecological niches, manyintroduced species have faired extremelywell in parts ofSouth
—
Africa where the climate is favourable to such an extentthat they now constitute sig-
nificant pests, particularly forgardeners and crop growers. Alien snails and slugs gen-
erally presentfar more ofa problem than do the indigenous species, which co-existin a
long-establishedbalance with their naturalcompetitors, predators and diseases. No data
are availableregardingthe economic costs ofalien pest snails and slugs in SouthAfrica,
but Pimentel (2002) estimatedcrop loss andcontrol costs for alien invertebrate pests in
SouthAfrica tobe US$1 billionper annum. In 1989, Boray & Munro (1998) estimated
thatinAustralia, which has a similar alien gastropod fauna and similarclimatic re-
gimes, the cost ofdamage causedbyterrestrial molluscs amountedto atleastA$50
million per annum, most ofwhich is causedbythe alien species. Theyfurtherestimated
thatA$10 million was spent per annum onchemicalcontrol ofsnails inAustralian do-
mestic gardens alone.