Invertebrate biodiversity and conservation in Tasmanian caves

5 Pages·1997·1.7 MB·English

by  N E Doran

Memoirs ofthe Museum ofVictoria 56(2):649-653 (1997)
INVERTEBRATE BIODIVERSITY AND CONSERVATION IN TASMANIAN CAVES
N. E. Doran, S. M. Eberhard', A. M. M. Richardson, and R. Swain
Zoology Department, University ofTasmania, GPO Box 252C, Hobart, Tas. 7001, Australia
'NSW National Parks and Wildlife Service, PO Box 733, Queanbeyan. NSW 2620, Australia
Abstract
Doran,N.E.,Eberhard,S.M., Richardson, A.M.M. and Swain,R., 1997. Invertebratebiod-
iversity and conservation in Tasmanian caves. Memoirs ofthe Museum ofVictoria 56(2)
649-653.
Tasmanian caves support a diverse invertebrate fauna, representing the richest known
assemblages ofcave obligate species in temperate Australia. Current studies have yielded
much valuableand unusual information regardingspider,amphipod andcricket speciesin
particular, while highlighting their sensitivity to environmental disturbance.
Introduction limited. In Tasmania, the barren appearance of
Cave ecosystems offer unique opportunities to caves is increased by the absence ofany major
vertebrate usage; roostingbatsand birds arenot
evolutionary biologists because of their often
present (most probably due to the low tempera-
highly adapted fauna combined with theirwell-
ture ofTasmanian caves), nor are any cave fish
defined abiotic environmental parameters. known. The only visiting vertebrates are
Despite its barren appearance and slow rate of humans and the occasional rodent, macropod,
change, the cave environment can be remark-
or snake seeking shelter. In spite of this,
ably speciose, and Tasmanian caves have
Tasmanian invertebrate cave assemblages are
recently been identified as hosting the richest amongst the richest known in temperate zone
assemblages of cave obligate invertebrates in
Australia.
temperateAustralia(Eberhardetal., 1991).This Caveanimals,orcavernicoles,areessentiallya
high biodiversity combined with Tasmania's heterogeneous assemblage occupying different
location at a climatic and geographic extreme, regionsofcaves, andtheirclassification isbased
and its relative abundance ofundisturbed sites, around their relationship to particular cave
makes the region extremely valuable for the zones. While there are many systems for such
study ofthe evolutionary history ofAustralian classification, the simplest (Vandel, 1965; with
cave biota. expansion by Howarth, 1983) divides animals
In Tasmania as elsewhere, however, land into four groups as follows.
management and land degradation problems
Troglobites are obligate cave species, strictly
pose a significant danger to caves and their adapted to subterranean habitats and unable to
fauna.Currentstudiesofthelifecyclesofcertain survive outside them. These animals often dis-
cave animals have highlighted their sus- play a large suite ofdistinctive morphological,
ceptibility to environmental disturbance physiological, and behavioural adaptations,
(Richardsonetal., inpress,andourunpublished many quite bizarre, and their domain is that of
data), whileatthesametime indicatingboththe the deep cave.
practical benefits that further study may pro- Troglophiles are facultative cavernicoles that
vide, and the high scientific and conservation commonly live and reproduce in caves, but are
values ofthese delicate ecosystems. not totally confined tothem; they may be found
in similar sheltered, cool, dark and humid
General background
epigean microhabitats.
The deceptive first impression that caves are Trogloxenes are occasional cavernicoles that
depauperate is based on a combination of the regularly inhabit caves, usually near the
small size of many cave organisms, their fre- entrance, for refuge and a favourable microcli-
quently sparse distributions, and their cryptic mate, butmustperiodicallyreturntothesurface
nature^ since animals more frequently occur in to feed, usually at night. Such animals often
the smaller cracks, crevices, and folds of cave require direct access to both the epigean and
formations to which human access is severely hypogean environments in order to survive.
649
650 N.E. DORAN
Accidentals are surface animals which wan- ensured theanimal'ssurvival duringthe rapidly
der, fall, or are washed into caves, but cannot fluctuating conditions of the Pleistocene
survive there. (Goede, 1967).
Examplesofthe first three ofthesegroupsare In contrast, very littlehasyetbeen discovered
presented in the following section. about the troglobitic amaurobiids (Family
Amaurobiidae), which inhabit deeper parts of
Components ofthe Tasmanian cave fauna the cave not prone to external seasonal influ-
ence. These spiders do not spin webs, but wan-
ThecavernicolousfaunaofTasmaniaconsistsof
der widely, although they may display some
five major phyla, Platyhelminthes, Nemertini,
degree of territoriality (our unpublished data).
Aschelminthes,Annelida,andArthropoda,with
The amaurobiids are often locally abundant,
the arachnids, crustaceans, and insects being
and thejuveniles at least are depigmented and
particularly well represented (Eberhard et al., display some degree ofeye reduction (M. Gray,
1991). Ninety percent ofthe recorded Tasman-
pers comm.).
ian cave genera are arthropods, and most ofthe
cave obligate species belong to this phylum. In Amphipods (Malacostraca)
thecourseofnumerouscavestudiesand surveys Several genera and species of troglobitic
carried out by the authors, the followinggroups amphipodsin theSuperfamily Crangonyctoidea
have received particular attention. inhabit streams and pools in Tasmanian caves.
The stream dwelling Antipodeus sp. (Family
Spiders (Araneae)
Paramelitidae), the generic placement ofwhich
Tasmanian caves support an interesting and
diversespiderfauna, including Hickmania trog- is currently under review (W.D. Williams, pers
ltroodgyltoepsh(itlhee,Taasnmdanainan uCna-vneaSmpeidder)amwahuircohbiisida cdwoemlml.er),,oisraaqsutyagtoibciotrnotg:laobnitoeb.liIgtatisefgoruonudndawtasteevr-
spiHdierc,kmwahniicah itsroagtlroodgyltoebsit(eF.amily Austrochili- TerrailmsimteesriCnanvoertatheMronlTeaCsrmeaenkia(,seienfcolluldoiwnignLgistetcle-
tion). In contrast to terrestrial troglobites, this
dae) is the largest spider in Tasmania, with a
leg-span ofup to 18 cm when fully grown, and Species displays distinct seasonal tendencies,
ctoonTsatsrmucatnsiaa,weabndofthuepotnol1y2k0nboyw6n0scpme.ciEensdienmtihce adenpdenitdsenlitfeucypcolen atphpeeayresarltyo cbheanaglemsostindsirtercetalmy
flow. Mating occurs from late-winter to spring,
genus, /-/. troglodytes is of high systematic and and over the summer months the amphipods
zoogeographic interest. Its closest relatives live may display protective burrowing behaviour
in Chileand Argentina, and it isofconsiderable prior to stream drying (our unpublished data).
evolutionary significance as it possesses major Thisburrowingallowstheamphipodstosurvive
physical traits of both the primitive (liphistio-
morph and mygalomorph) and advanced (ara- seasonal dry spells, and appears to be triggered
(perhaps by increasing calcium concentrations
neomorph) spider groups. While the species is
no longer considered a direct evolutionary link in the water)beforethepoolsdry. Theseamphi-
cbleotswesetenatrhaenseeogmrooruppsh,sittiosctohnesiadnecreesdtroanlesopfitdheer bpyodsthgeensetrraelalmy,feaeldthoonugdehtrdiitfufsertehnatt issizcearrcliaesdseisn
type from which thev all diverged (Marples, appear to have their own preferences amongst
the selection that this material offers.
1968).
Hickmania troglodytes builds large pear Crickets (Orthoptera)
shaped egg sacs which hang from the roofand Cavecrickets(FamilyRhaphidophoridae)are
sidesofthe cave. Theyoungtakeapproximately easily the most common trogloxenes in Tas-
nine monthstoemerge from thesesacs, a period mania, the two main genera being Micropathus
significantly longer than the one to two months and Parvotettix. Whilespecies from both genera
typicalofepigeanspiders,andtheirlifespan may may inhabit the same cave, species from the
cover decades (Doran, unpublished data). The same genus appear not to coexist (Eberhard et
egg sacs themselves are of intricate internal al., 1991). Micropathus species are most com-
design and are highly resistant tofungal growth, mon in the moister western and southern parts
which can over-run other organic materials in ofTasmania, wheretheyareestablished in large
caves in a matter ofdays or even hours. A very colonies, and the distribution and derivation of
ancient member of the Tasmanian fauna, //. the species-complexes may have been influ-
troglodytes' stronghold is the twilight and tran- enced by Pleistocene glaciation (Richards,
sition (early) zones of caves, which may have 1971a). Cavecricketsaregenerallyomnivorous,
BIODIVERSITY AND CONSERVATION IN TASMANIAN CAVES 651
and leavethecaveat nighttofeedon forest floor yielded over 55 taxa (Houshold and Clarke
invertebrates and materials (Barr, 1968), 1988).
although they may also prey onjuvenile spiders
withinthecave(ourunpublisheddata).Toadult Comparisons with temperate mainland
spiders, beetles and other animals, the crickets Australia
provideamajorsourceoffood input tothecave, Few data have been published forcaves in tem-
either directly as prey, or through their drop-
perate mainland Australia, but the literature
pingsandeggs.Thelatterareburied insiltbanks includes over 6 troglobites from the Nullabor
ofthe deep cave, and possibly provide the sole
Plain (e.g., Richards, 1971b; Knott, 1983), at
food source for troglobitic beetles specially
least 6 more from five cave areas in Victoria
adapted to retrieve them.
(Davey and White, 1986), 2 troglobites and 5
troglophiles from Wombeyan Caves (Smith,
Major sites and regions examined 1982) and 2 species of troglophile from Bun-
gonia Caves in New South Wales (Wellings,
In the MoleCreek region ofnorthernTasmania,
1977), and 25 species of aquatic cavernicole
71 invertebrate taxa have been recorded from from a cave at Yanchep in Western Australia
Kubla Khan and Genghis Khan caves
(although the number ofstygobiontic species is
(Eberhard, 1990b), including 3 species each of not given; Jasinska and Knott, 1991). Against
fanlnaetlwiodrsm,smyarnidapsopdrisngatnaidlsm,oll5usscpse,ci6esspeeacicehs ooff these figures, it would appear that Tasmania is
comparatively rich in troglobitic diversity.
crustaceans, 21 arachnids and 23 insects.
Althoughabout 9ofthesespecieswereacciden-
1 Conclusions
tals, at least 1 1, and possibly more, are troglo-
bitic.Thediversityofspeciesrecorded hereisby WhiledatacurrentlyshowthatTasmaniancaves
far the highest for any single Tasmanian cave support substantially higher biodiversity than
(Eberhard et al. 1991). caves in temperate mainland Australia, such
Precipitous BlufF, far southern Tasmania, comparisonswill remain rathercrudeuntilsam-
supports the richest assemblage ofcaveobligate pling strategies and sampling intensities can be
species presently known in temperatezoneAus- in some way standardised, and until all karst
tralia, with at least 15 troglobiticorstygobiontic areas have been surveyed. However, Tasmania
species recorded among a total cave fauna of is likely to remain an extremely rich source of
some 32 (+ +) species (Eberhard et al., 1991). cavefauna, whoseageand diversity is related to
Thisarea has the most highly cave adapted rep- thegeology and geomorphic history ofthe karst
resentatives in several animal groups, including systems in which it is found.
amphipods, beetles, molluscs, and harvestmen, As caves are entirely dependent on outside
while the hydrobiid mollusc and opilionid (har- sources for their energy input, and as their
vestmen) faunas are particularly notable for the environmentsareslowtochangeand/orpredict-
diversity ofspecies represented. able, these ecosystems are highly vulnerable to
Ida Bay, far southern Tasmania, has 31 external events, which may even occur at some
recorded cavernicolous species including 5 tro- distance from the caves themselves. Two major
globites (21% of the fauna) from one survey sources of food input, cricket guano and water
(Richards and Oilier, 1976), and 30 species carriage, areat high risk from land usepractices
hianrcdl,udi1n9g901a)1.trTohgleosbeitfeisg(ur3e6s%)exicnlaudneotahcecrid(eEnbtearl- tEhvaetnaftfheectdissurrurpotuinodninofgHfoorwestleavenldswianttoerthqeuaclaivtey.,
or surface fauna, and cover such groups as the whether by an increase or decrease, can have
opilionids, pseudoscorpions, aranaeids, crus- devastating effects on the cave fauna. While
taceans,collembolans, hemipterans,andcoleop- water levels may fluctuate enormously during
terans amongst others (Eberhard et al., 1991). thenormal yearlycycle, this isgenerally predict-
MountAnne(southernTasmania)and Mount able,andexceptionallysevereconditionsduring
Ronald Cross (central to western Tasmania) the normal season are not as potentially cata-
support at least 5 and 3 troglobitic species strophic as relatively minor floods occurring at
respectively (Eberhard, 1987, 1989), while at unusual times, or even the absence offloods at
Bubs Hill (western Tasmania) at least 6 definite the expected time (Howarth, 1983).
troglobites and 6 other taxa of uncertain status More direct effects arc also important. Caves
have been recorded (Clarke 1989). Including may be heavily affected by quarrying, rubbish
accidentals, one cave in the Bubs Hill karst has dumping, the in-fillingofentrancesorclearance
DORAN
652 N.E.
ofsurrounding land. Visitors are also a signifi- and release, the impact on the fauna is minimal.
cant potential source ofdisturbance, and some Recordsarealsokeptofthedate,duration,party
cave inhabitants and habitats are particularly number, and course taken through the cave for
vulnerableto them (Richardson et al., in press). each visit, so that the impact on the cave
Indirect disturbance alone, such as light or environment of even these few visits can be
movement, can disturbcavespidersand disrupt assessed.
courtship and mating. Spiders may desert their The benefits ofthis monitoring strategy have
egg sacs ifdisturbed frequently, which probably been many. LittleTrimmerCavehasbeenfound
accountsfortherarityoftheseanimalsintourist to contain a rich invertebrate fauna in keeping
caves. Seepage pools supporting rare syncarid with that observed in other areas of the state,
shrimps (Family Psammaspididae) can be and this diversity is due, at least in part, to the
destroyedbyasinglecarelessfootstep,ascansilt wide variety of substrates and consequently
banks which support many ofthe small terres- habitat typeswithinthecave.Throughthemini-
trial invertebrates deep in caves. The cave malimpactnatureofourprogram,theseanimals
environment is a very special, fragile habitat, andhabitattypeshavebeenabletobestudiedin
into which even scientific visits should be care- an essentially undisturbed state, and this
fullyregulatedtoreducepotential,and veryreal, approach has yielded much valuable infor-
impacts. mation. The species presented as examples in
this paperare present in large numbers in Little
Trimmer, and much of the new information
Future directions: the Little Tri—mmer Cave reported hascome aboutasa direct result ofthe
Biological Monitoring Program a model Little Trimmer program. The slow rate ofcave
study biological processes means that long-term,
Afaunal study designed to beoflow impactwas intensive studies are essential for comprehend-
specifically formulated for LittleTrimmerCave ing the ecology ofcave organisms, and the nine
atMoleCreek,Tasmania, in 1990.Thisprogram month incubation period and apparent lon-
was established at the cave at the beginning of gevityoftheTasmanian Cave Spiderin particu-
1991 and is still ongoing today. lar demonstrate how ideal an opportunity the
Little Trimmer Cave is a well decorated, Little Trimmer program presents.
stream bearing cave of reasonable length (the In view ofthe success ofthe Little Trimmer
major passage is approx. 200 m). Situated in study, we fully endorse the 'sampling with
State forest, it has been gated by the Tasmania replacement' recommendations of Slaney and
Forestry for several years, so that access is lim- Weinstein (at this conference), and believe that
ited to facilitate scientific studies in an undis- such low impact, non-collection studies are the
We
turbedhypogeanenvironment.Visitsareregular way forward in biospeleological research.
and infrequent (ranging from monthly to believe that the Little Trimmer program is an
bimonthly), visitor numbers are restricted, and excellent example ofhowdata collection can be
studiesare designed around conservation ofthe optimised yetatthe sametime balancedagainst
cave environment and its fauna. Movement the needs of faunal conservation.
through the cave is kept smooth and quiet to
minimise disturbance due to noise and sudden
Acknowledgements
vibration, and in all but the most carefully con-
sidered cases the introduction of any foreign Parts ofthe work reported here were supported
matter, particularly organic, volatile, or odor- by grants from both the Australian Research
iferous substances which may attract or repel Council and the National Estate Grants
cavernicoles, is avoided. Pathways are marked Program. Thanks are also given to the Forest
by string to reduce the area exposed to disrup- Practices Unit ofForestry Tasmania, forkindly
tion by researchers traversing the cave, and the offeringand allowingus continued accessto the
greatest care is taken to avoid even the smallest closed environment of Little Trimmer Cave.
animalsandcaveformationsonandabovethese
paths. Substrate Protection Zones are estab-
lished thoughout the cave to preserve the more References
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