Coral reef sponges of the Sahul Shelf — a case for habitat preservation

14 Pages·1994·2.4 MB·

by  John N A Hooper

CO—RAL REEFSPONGES OFTHE SAHUL SHELF
ACASE FOR HABITAT PRESERVATION
JOHNN.A. HOOPER
—
Hooper, J.N.A. 1994 06 30: Coral reef sponges of the sahul shell a case lew habitat
preservation. Memoirs ofthe Queensland Museum 36(1 ): 93-106. Brisbane. ISSN 0079
8835.
Three adjacentcoral Teefsystems were surveyed (Ashmore-Cartier-Hibcrnia reefs) on the-
Sahul Shelf,northwesternedgeoftheAustralian continental plate. 138 species ofsponges
(Porifera)in 77 generaand38 families were found. Althoughspongespeciesdiversity was
similarbetweeneachofreefsystem,therewaslowcongruenceinspeciescompositiondespite
theircloseproximity(about50kmapart):Ashmore-Hibernia(13%);Hibcmia-Cartier(24%),
Carrier-Ashmore(9%similarity).Thespongefaunawasdivisibleintofourfaunislicgroups.
1. Widely distributed (ndo-west Pacific species, known from Burma io New Caledonia,
includingapparentlyopportunisticspeciesfoundpredominantlyoncoralsubstrates.2.Large
populationsofautotrophicsponges,characteristicoftheshallowwater,innersandyzoneand
intertidal zoneson the reefflat, accounting for most ofthecoral reef sponge biomassand
alsofoundonmanyIndo-wcstPacificcoral reefs.Togetherthesetwogroupscomprise only
about 16% of species. 3. Coastal and shelf species morc-or-lcss widespread throughout
tropical Australasia, comprising about 25% of all species recorded. 4. Species found
predominantlyinrestrictedorspecialisedhabitatsonthereefcomprisethegreatestdiveisity
(59%)ofspongesinthesereefsystems,butmostofthesearepoorlydocumented;mdknown
from single or lew localities and isolated records in the literature. Differences in spc
composition between the three reef systems were correlated with both major and minor
differencesinthegeomorphologyofparticularreefsystems.Thesefindingssuggestthai the
concept ofa 'ubiquitous coral reefsponge fauna' is loo simplistic. Different reefs contain
differentfaunas, largely dependenton the presence orabsenceofparticularhabitats.These
data, using sponges as an example, have implications for ihe special management of
biodiversity in coral reefsystems by habitat conservation in preference let preservation ol
particulartaxainthetropicalmarinebenthos.Evidence presented herequestionsthevalidity
ofpreserving only a single reefas being 'representative* ofa system ofreefs, Po/t/wyl
SahulShelf,AshmoreReef,CarrierIsland,HiberniaReef[faunalsurvey. sponpebiadivec
habitatconservation.
John N.A. Hooper. Queensland Museum, PO Box 330U. South Brisbane, QUi *IQL
Australia; 22 July 1993.
As for many other groups of marine raver published (Hooper, unpublished data), wherea:-.
tebrates (Briggs, 1987), northern Australian - spongeslivingonoceaniccoralreefs,ontheedge
southernIndonesianmarinehabitatsmaycontain of the western continental margin, have neither
the highestdiversityofspongespecies in Recent been collected nor studied previously. By corn-
seas, and the region isoften consideredto be the parison, sponge faunas from coral reefs on the
centreofdispersalforIndo-Pacificspecies (Levi, east coast of Australia are comparatively well
1979). In fact, nearly 2000 nominal species of known (e.g. Burton 1934; Bcrgquisl. 1969;
spongeshavebeendescribedfromthisregion,but Bcrgquisl et aL, 1988; Wilkinson 1987, 19KS,
it is still considered tobe barely known (Hooper Wilkinson & Cheshire, 1989), as they arc in
&L6vi, 1994). Largecollectionsofspongeshave several major reef systems in the western Indian
now been made from the more turbid, nutrient Ocean (e.g. Seychelles, Maldives, sec summary
rich shallow coastal waters in both northwest inThomas, 1973).
Australia(review in Hooper, l9SK);md southeast This is the first published report of a sponge
Indonesia (review in van Socst, 19S9, 1990), fauna from oceanic coral reels on ihe
although many ofthese species records have not northwestern continental margin of Australia
yet been published. Similarly, several large col- Thispapereoncentratcsonthequestionofsponge
lections of sponges from deeper water reefs on species diversity of three prominent reefs, Ash-
the shelf and slope on the western side of the more, Cartier, and Hibernia Reefs, comparing
continent exist, but these too remain largely On- differences in speciescomposition betweeneach
MKMOlkSOFTHEQUEENSLAND MUSEUM
I
reef;examiningthevariousfactorsthaipotential- trough,ratherthan terrestrial runoli as is thecase
lycontributetothesedifferences;andcontrasting formost reefscloserto the continent.
these differences to the reef gcoraoiphokigy. Ashmore, Carticr and Hibernia Reels are part
Tlvesedatahave implications 10the conservation of a larger system of exposed coral reefs, sub-
and selectionofcoralreefs ashabitat preserves. merged eoTal shoals and drowned reels running
Detailed descriptions ofhabitats, stations sur- along the northwestern margin of the Australian
veyed, and methods of collection are given by lontinent. Althoughonly9ofthesereefsarcnow
Russell & Hanley <1992) and Hooper (1992). fully exposed, classed as 'platform reefs'
Three reefsystems were studied. Ashmorc Reef [Rowley Shoals (Imperieuse, Gierke and Mer-
wasvisitedinMarch 1981 iRV "Hai Kung*)July maid Reefs; 18-I7°S), Browse Island |T4°S|
(
1986 (MV -Coral Reefed') and August 1987 Scott Reef (I4°S). Seringapatam Reef (13.5°S>.
• viV *Re*:fSeeker'): CarrierIslandanil Hibernia CarticrIsland, AshmoreReefandHibemiaReef],
Reef were visited in May 1992 <PV 'Rachel'). itis thought that this whole area once contained
Sponges were collected along random transects, many more active coral reefs during times of
using SCUBA, to depths of 30m. Underwater lowersealevels,comparabletosomeareasofthe
photography, using both 35mrn-sti!I and 8mm- Great Barrier Reef (Edgerley, 1974; Van Andel
videu formats, were used to supplement manual Si Vecvers. 1967; well illustrated in Butlin,
collectionsofsamples-Speciescomposition,dis- 1979).Despitetheabsenceofanextensivebarrier
tribution and abundance of sponges were deter- reef on the Sahul Shelf it is nevertheless still
mined from taxonomic studies ofsamples (using classed as a major reef province (Burnett et al..
methods described by Hooper, 1991) and com- 1991).
(u.i.iir-r ana yscsofphotographictransects,. Only
twospecieswereunabletobedifferentiated i'rom GnoMORmoLGOYor-theRfi
photographic* records [fCeStospongiaWStudinaria
(Lamarck) and JC bergquistia FromontJ, which calAlsehdmoar'eshReeleff.atIotlli's)a, l2a7rgkempllaotnfgo,rm14rekemf(woifdtee,n
'mpedtogetherinthisstudyunder(heformer
name. The taxonomicscheme (Tabic 1) follows owniltyh oanltahrgeenocritrhcuemrfnersiednet,iaalloaurgteershraeelfl,owb,rovkeerny
Ipei :t al. (in press). heavily silled central lagoon, and several sjnd
RESULTS ANDDISCUSSION coys (Fig. 1). Ashmorc Reef is situated on a
platform projecting from the westernmost ridge
of the Sahul Shelf, averaging about 50in depth,
withdrop-offsto200malmostimmediatelytothe
Said • Shi west andsouth. The prevailing swell and wind is
laAndsh;moir:cvR'eSe,f<I122°3IWT'HS), I2a3nfdiQHriEbKeCranritaicRreIesf- tfhreomrteheefsSoumtohrpohrosloougthye,astb,eiwnhgicohriiesnrteaftleedcteeadsti-n
(ll'SK'S. 123*22*E) henear Ibeouteredgeofihc with the outer reef best defined on the
Australian continental margin in the Timor Sea, southern and southeastern margins. Maximum
about 350km off the Kimbcrlcy coast (840km spring tidal range is 4.7m, and there is no im-
west of Darwin. 640km NNB of Broome), and pounding of water within the lagoon due to
115km from the southern Indonesian island of several large breaks in the outerreef.
k:-h Thesereefsaresituated on the Sahul Shell, The Lithothamnmn vczi crest is unbroken on
at the edge of the Australian plate, at a zone of thesouth andsoutheastern sides, with somecoral
Mibduciion with the southeastern Indonesian boulder accumulations on the windward side,
(SCC illustration in Michaux, 1991: fig. 2i. whereas it is broken by several passages on the
The Sahul Shelfconsist* of a shallow central northern (leeward) side, leading into twoShallow
; ! i- (called Ihe Bonaparte Depression. <l40m lagitons (maximum46m deep), many submerged
depth) rising toridges2U-50mdeepontheouter patch reefs ('hominies'), and three low.
edges and contiguous with the KimberJey cavi vegetated, permanently exposed sand cays. The
13 eastern side On the northern and southern outer reef slope is initially gentle,
northwestern edges of the Sahul Shelf the con- producing a broad shelf 150m wide with exten-
tinental margin drops away rapidly to >20()0m sivespurandgroove formalions, beforedropping
depth,wheretheAustralianandIndonesianplates down more steeply in close proximity tothe reef
meet{Timortrough).All threereefslieveryelose Abutting the inner side Of the southern reefcrest
tothisdrop-off,and they are probably influenced is a reefflat composed ofcoral rubble and slabs,
' .i ^eaicrextent by oceanic upweliing from the coral sediments and live coral rxvils The inner
CORAL REEFSPONGES OFTHESAHULSHELF 95
beachrock FIG. 1. Geomorphology
| Lrthr-tharHhioiiit:"!t:ri-';f ofHibernia,Cartierand
12 sanfl Ashmore Reefs, Sahul
Q shallowpoats O stationssampled" Shelf, indicating major
[~] coralrubble G SindL'uorrubble habitat types, compiled
gi coralpinnaeb entento(outerreefmargin fromaerialphotographs
|F16|q33 drlreeaeetgefiopcafulnllaaatwgtceitdtnhnppatchrest QMggj fsBftafHlnJrfidtalwfwlint,lhnrtrii:fonorto.iilv\ne,tfshaoinrcdkme,attsCioornaslpatches ((fiA1cu9es9)t,2r)Ra,ulsisBaenelrlSruy&rv(He1ay9n9lO3ef)y,-
ri sandWithpatchlepf branchtncicoralthickets
and from unpublished
collection data (NT
Museum, Darwin).
1 -
'* MEMOIRSOFTHEQUEENSLANDMUSEUM
sand flat is very extensive, occupying possibly isaraisedplatform reef,7 7kmlong,2.2kmwide,
half the inner reef area, composed of carbonate with a nearly continuous outer reef around its
sediments (mostly foraminiferan and mollusc perimeter,adeeplagoon,andnocay(Fig. 1).The
debris), sparseThalassiabedsandalgal turf.The Lithothamnion reef crest is well defined only
macrobenthoshereappearstobepoorinstructure along the southern and western margins, indicat-
and diversity. The northern outer reef slope is ing that the prevailing swell and wind may come
initially sheer but (hen the slope Tapers to 50m from thisdirection.
depth,becomingcontinuouswiththeSatuilShelf Although virtually continuous, with well
The northern reef flat is more narrow, with little developed coral boulders cemented the leef Hat,
wi noinnersandflat,andgenerallycarriesaricher the reef margin \& sunken slightly on its north-
benthos than does the sand flat on the southern easternedge,allowinglimited vessel passageJiil-.>
margin(compiledfromNTMuseum unpublished the lagoon, but there is obvious impounding of
data, and Berry, 1993). wnter within the lagoon during low tide. The
CurfterIsland, Thereefisorientated easi-wesi, lagoon is large, Occupying more Than half the
fJvrion.mtjothneawpelsattefronrmedagbeouotf5t0h-e7S0amhudleeSpheplrfo,jeacntdinigs sruerevfesyaerdea,ilaanvderdaegeeps(aablotuhtou3gh0mnotdeypetthc,odmrpolpepteilnyg
also exposed to swell and wind predominantly to below 60m in places) Surrounding the inner
from thesouthernside.This windwardpartofthe margin ofthe reef, relatively homogenous on all
reefliesclose totheedgeoftliL-coatincntalslope, sides is a well developed reef Hat. There is an
rising directly from about 180m from the south extensive back red margin of branching cowJ
However, Cartier Island has a very* different thickets at both the western and eastern margins,
morphology from both Ashraon; and liber although in the west these thickets drop quickly
I
ni«i Reefs (Fi£ to very fine cornlline sand slopes, and at the
Illsanoval-sh1aped raised platlouu ieef.4.Skill noitheast inner margin there is an extensive coral
long 2_1km wide. IjlLs a lagoon, and possesses l- slope forming the lagoon entrance
mergiegldc dounrvienggemstproidngHitniddecs.ayThifeialUtbheatcfotcmtets\ fllb1 Throu>g,hroiustingthe30la5g0omonIarrocmlatrhgeelpoagtucuhiire"e°f0p1in8-
reef crest is only noticeably developed un llu* dominant feature oi' the lagoon. The outer reel
island's southwest, which also has un extensive Slope on the southern and western sidesof1liber-
coral bouldci /one behind the reef crest. The lUa Reef is extensive, although spur and groove
osuubtsetranrteeifalsllyopme-oOrpetehxeteisnlsainvde'stshoaunththaatmiofweAssth\-% afsortmhaetoitohnesrwreerefes.nuOtnsetehnetnoorbtehaesrnweslildedetvheerleopiseda
more Reef, running about 500m seawards from sheerslope loabout 50m, whereason the easi, mi
igthwreco<or*veneeff1co0rresmstaotdiMoenr3se0amtnheddreempaatinheyexOltanergnostihcveaevesirpsnulrsanabdnc'd-s asinddeiRrpuuisblsbeeldlelfs&reoemHmasNnltTocydM,oum1si9ne9au2t)me tuhnepuobultiershreedefdaarteaa,
southeast, the outerreefslope is much narrower.
DISTRIBUTION PATTRRNS
choppingvertically toabout 200mdepth inavery
OF MARINL INVERTEBRATES
short distances whereas cm the northern side it is
almost sheet lor aboni iOtn depth but then the
platcau levels al about 5(V70crt, prolific coral brom the known distributions 01 a lew marine
substrate merging imocorallinesand The invertebrate groups on the outer shelf reel sys-
i
reef margins on the island's north and cast arc temsofthe western continental margin (e.g. Wil-
diffuse, composed of consolidated navemenj li ii. 1978; Bern. 1986, 1993: WifccWl & Allen,
leading almost directly into sand and patch reel. 1987; Morean & Well*, 1991: PfcArct & Walker.
Anextensiverubble-sand p&WJl ieefHatoccupies 1991;Morgan, 1992;MarshctaL, 1993), several
mo.vi ofthe island's subtulal -/one including Iwo biogeQgraphic models have hecn proposed and a
small shallow pools. Abundant Thalassia and number ofpertinent factors have hecn identified
photntrophicspongeswerepresentonthe reefHal thai potentially contribute lo these distributions
Russelplil&edlfliaonilneyN.fT19M92u,seanudmBeurnrpyu,bl1i9s0h3e)d. data, facIttoirssw,oarstthhwehyilreelhaetreedtsopborniegfelypospuumlmatairoinsse,siihl.iCC
Hthetnia Rrvf. ll lies on the noittiwesteiu etljje this information is relevant to the irtierpceiation
oftheSahulShelf, rising from about 00mdepth ofspecies dtsrtributipn patterns.
1
on all sides bin dropping to 300m quite close to Dvtpersatpotential. Phyla with both demersal
the northwestern edge of the reef Hibemia Reef and pelagic larval strategics arc known to have
CORAl REEF-SPONGES OFTHESAHULSHELF H
differing distributions and dispersal abilities. open ones {e.g. Vr'\? ei al.. 1991)]. Whichever
This explanation has been used lo (partially) ex- hypothesis i\ correct, sponge survivorship ap-
plain observed differences in distributions of pears tobe Stronglychemically mediated.
echinoderms on some of these oceanic, outer Sponges arc predominantly heterotrophic, ob-
shelfcoral reefs of Western Australia (Marshct taining their nutrients from filter feeding
al . 1993). By comparison, phyla with pelagic suspended partu le> in the water column As
larval strategics may be much more widely dis.- hetcrotrophsmanyspeciesarcefficientinsurviv-
liibuted throughout Iiulo-west Pacific reef sys- ing in high silt, high energy environments, but
tems (e.g. corals). The third dispersal strategy, they arc also relatively slow growing as com-
phyla with only short-lived, demersal larvae pored with other benthic marine invertebrates
(such as sponges with a creeping blastula larva), suchasascidiansandcorals. Heterotrophicspoil
poseanenigma in termsofresolving theirpoten- ges do not generally compete well with sclerac-
tial for only short-range dispersal versus con- tinian corals, tor example, in rlear waters (the
firmed observations on relatively wide latter have a competetive advantage in using
distribution^ fel a small number Ol specie* nutritienis pioduced by the pholosynihelu ac-
BrXh vivipary (brooding larvae) and ovipary tivitiesoftheirsymbiotic zooxanthellae).
(broadcasting gametes) are common sexual Autotrophic (photolropha) sponges obtain
reproductive strategies in sponges. Over short some nutrients from the photosynthctic by-
distances (or short periods of time) ftdkUal products of symbiotic cyanobaetcria. Unlike
reproductive products are undoubtedly effective mostheterotrophicspecies,autotrophs have rela-
inrecruitmentofreefsponges, but for longrange tively fast growth rales and are the predominant
dispersal their effectiveness is questionable primary producer? "' some clear water reef
[short lived demersal larvae, short lived gamcies habitats (e.g. reef flats) (Wilkinson. 1987).
(e.g. about <24 hours)) However, il is suspected Autotrophs ure more efficient competitors in
that asexual (clonal) modes of dispersal are these habitats, but their distribution is severely
widespread, particularly in tropical sponge restricted to shallow, clear waters Generally,
populations (e.g. Baiicrshil) & Uergquisl, 1990) however, sponges survive well in high energy
where fragments ofadult sponges 'tumbleweed' environments and under relatively adveise con-
aCrtttS the substrate (although pelagic rafting in ditions (surge, swell, current, sediment loadsj.
sponges is probably minima): Boury-Esnault & These conditions often cause fragmentation and
Lopes, 1985).This doesnotexplainhow alleged fragmentscan readilydisperseandreattachlothe
ly widely distributed Indo-west Pacific species seabed.
arcable tocross deep water barriers, ..ml (hfc Bh&eogfaphfc affinities. Precise hiogco-
qsupeosntgieosn' pseerptairnaetnetd lboy dduepeepistarioug<rhfs'.(e.g. New gSrpaopnhgiecallauanffainairtciesstiollf utnhcentnaoiir.t,heranlthAouusgthraliliainv
Caledonia and Great Barrier Reef). now clear that it is composed of several very
Survivorship and growth. Although commen- different elements OloopcrAc Levi, 1994). Levi
sals on sponges are very common (including (1979) and VViedenmayer (1983) speculated that
shrimps, eiabs and holoihurians), predators oj this fauna was predominancy southeastern In-
sponges arc known onlv to include fishes, turtles donesian in origin, hut more recent empirical
and a few other invertebrates such as nudihrauch evidence indicates thai there aic iclutivclv higher
molluscs (e.g. Randall & Hartman. 1968; Me levels ofendemism than expected, ranging froill
Oinlock, 1987). Their fixed, sedentary lifestyle 30-50% (varying between particular families
precludes; sponges from actively evading (Hooper, 1991), with small regional enclaves of
predators or defending ihcmselvc:;, hut they arc endemic species along the western and
thought to becapable ofdoing so using an array northwestern coasts leg. Houtman-Abrolhos Is-
ofnoxiouschemicals (e.g. Bakus, 1981; Bakusct lands, Shark Bay, Darwin Harbour; Hooper &
al.. 1989). which. Bakus & Ormsby (1994) Levi, 1994). By comparison, other areas appear
hypOihegtSC, have evolved for this specific pur- to have very few indigenous species (e.g. Gulfof
pose-. But these 'biologically Active cV'mcals C vapeniana), and lhe.se differences are probahly
llso known Lo be important as ofieii-.r..• ;it least partly due to the differences in age ofthe
mechanisms in competition forspace (eg Buss. Australian coastline, as described and illustrated
1976), and this hypothesis now has some good by JonesA:Toigcrstii ( 1988) Thisexplanation is
empirical support (such as their prevalence in plausible lo account for the colonisation and af-
crowded, cryptic communitiei versus, exposed. finities of the sedentary marine invertebrates.
.
98 MEMOIRSOFTHEQUEENSLANDMUSEUM
such as sponges, an these western oceanic coral histories ofthe tropical reefs on both sides of the
reefs, as (hey were oncesuspectedofbeing con- continent,particularlyreflectedbytheabsenceof
nectedbyeJttettsiveemergent reefsandshallow- a barrier reefon the westcoast (Edgerley, 1974;
water skoals to the Pleistocene continental Burrc-UetaJ.J991).
coastline(e.g. ButIin, 1989). Bothopportunisticandecologicallyspecialised
Itisexpectedthatthethreereefsinvestigatedin sponge faunas have been recorded from many
this study would contain a mixture of both In- Indo-westPacificcoral reefs, from whichearlier
donesian 'colonising' species and Australian workers concluded that general distributions of
'endemic' species, lying as they do on the 'coralreefsponges' wererelatively homogenous
northwesternmarginoftheAustralianplate.This across the Indo-wcstPacific (e.g. Burton, 1934).
mix of faunas has been demonstrated in severe This is implicit in much of the older literature,
otherphylaofmarine invertebrate, such as mol- whcrc3sitisshowninthisstudythatthecomposi-
luscs (e.g. Wells, 1986), Crustacea (e.g. Morgan tionofthereefsponge faunamay vary consider-
& Wells, 1991) and echinoderms <e,g. Marsh et ably depending on the presence or absence of
al., 1993), but not previously for the sponge particularhabitats.
fauna Furthermore, because these three coral
reefsystemsare incloseproximity toeachother, OBSERVED DISTRIBUTIONPATTERNS
each less than about 50km apart and intercon- ANDAFFINITIES OFTHE SPONGE FAUNA
nected by the shallow Sahul Shelf with its
numerous submerged shoals, it is expected that Priortothesepresent surveys the spongefauna
eachreefwouldcontainthesame,oratleastvery of Ashmore. Cartier and Hibcrnia Reet\ W9A un-
similar,spongespecies. known.Thisstudycollected 139speciesal spon-
This null hypothesis is not upheld hy present ges (although only 138 are differentiated, .V.
data ttstudinariaandX. bergquistiacombinedasthey
Habitat availability. Overlaying these could not be distinguished from video records),
biogcographical relationships arc complex pat- belonging to77generaand38 families(Table 1)
terns related to specific ecological requirements Each reefsystem contains the following number
ofparticularspecies. Coral reefs are well known of species: Cartier Island 74 species, Hibcrnia
fortheir heterogeneity (Huston. 1985), andtypi- Reef 73 species ami Ashmore Reef 51 species.
cally contain many more potential niches than Contrary toexpectations,however, thesimilarity
most temperate ecosystems. Sponges occupy betweenthefaunasoneachofthesereefswaslow
many ofthese niches incoral reefsystems,some (F.g.2).
opportunistic (growing in many habitats on the These discrepancies in fauna! composition
reef) and some highly specialised fawlrkaed to mightbe anartifact oflow sample sizes, wherchy
one or few). Examples of the latter include: accuratecomparisonsbetweenreelsmightnotbe
encrusting mats found on shallow water beach possible due to the relatively low number of
rock; scagrass beds; burrowing into mud and stations from which sponges were recorded. 76
other soft sediments; biocroding coralline sub- stations (from a total of 113 stations sampled)
strates; cryptic encrusting (soaphihe) species, contained sponges: Cartier Island 26 stations,
'living fossil' (reef-building) coralline species HibcrniaReef24 stations, and Ashmore Reef26
found at ihe base of mo$l coral reefs: and the stations. Whilst this explanation is plausible for
remarkableshallow-waterautotrophicfauna.The comparisonbetween Ashmore ReefandtheCar-
ecology and distribution of these autotrophic tier-llibcrmacollections (whereonly 96samples
species, suited to clear water coral reefhabitats. of51 specieswerecollected fromAshmoreReef.
has been well documented on the Great Barrier no underwater video record was manic, and col-
Reef (e.g. Wilkinson 19S7, 1988; Wilkinson & lections were made over three separate trips), it
Cheshire. 1989; Bergquistetal., 1988). but prior certainly is not true for the comparison between
to the present work it was not known whether Cartier Island and Hibernia Reef(where techni-
these werealsoprevalentonthecoralreefsofthe ques were standardised and collecting effon was
western continental margin. By comparison, the comparable). It is considered that observed dif-
species composition ofthe inshore, more turbid ferences in the sponge fauna betweenthese reefs
watersponge faunasdiffersbetweenthewestand a real (biological) origin.
east coasts of Australia (e.g. Hooper, 1991; Based on their known geographical distribu-
Hooper & Levi, 1994), which may be at least tions the sponge fauna was divisible into four
partly explainedbythe very different geological majorgroups.
CORAL REEFSPONGES OFTHESAHULSHELF
9$
*
Roti, Indonesia (115 km)
HIBERNIA REEF
(deep lagoon, impounding of
tidal water, large coral
pinnacles}
ASHMORE REEF <^\
Kimberley coasi (350 km)
{highly silted lagoon,
lagoon drains on tides,
no back reef)
CARTIER ISLAND
{no lagoon, large
spur and groove with cave
formations)
FIG. 2. Similarityin sponge faunas of3 adjacentcoral reefs,Sahul Shelf, indicatingnumberofspeciesoneach
%
reefand similarity in speciescomposition betweenreefsystems.
1. 'Coral reefsponges'- These are widely dis- caicitic substrate (e.g. Cliona celata, Gelliodes
tributed throughout the Indo-west Pacific, from fibulatus, lotrochota baculifera, /. coccinea,
BurmatoNewCaledonia(althoughsomespecies Microciona aceratoobtusa, Thalysias rein-
arerecorded as widespread, fromMadagascar to wardti), or burrowing into both living and dead
Polynesia). The distribution ofthese species ap- coral heads (e.g. Aka mucosa, Oceanapia am-
pears to be somehow closely linked to theactual boinensis, Myrmekioderma granulata,
distributions of the coral reefs themselves, al- Spirastrella vagabunda). All these groups are
though it is speculative how their supposedly relatively well documented in both the contem-
short lived, poorly motile reproductive products porary and olderliterature.
are dispersed across this vast tract of sea (dis- 2. Autotrophic sponges. As expected from
sected by deep trenches). Most ofthese species literature on other coral reefs (e.g. Wilkinson &
are largely opportunistic, living in many or any Cheshire, 1989), autotrophic species were a
zones on the reef. Examples ofthese are Aaptos prevalent (visually dominant) component ofthe
aaptos, Axinella carieri, Cinachyra australien- sponge fauna, with most species recorded from
sis, Cribrochalina olemda. Echinodietywn all three reefs. These sponges (with repre-
mesenterinunty Halisarca dujardini. lanthella sentatives from many families ofPorifera), have
flabelliformis,Jaspisstellifera, Phakellia caver- symbiotic cyanobacteria within their tissues and
nosa,P. conulosayXesiospongiatestudinariaand utilise some or all of the micro-organisms'
X.nigricans.Some 'coralreefsponges' arefound photosynthetic products for their own nutrition.
associatedpredominantly withdead coral, on the Thus they are capable of relatively fast growth
living reef or in rubble zones, bioeroding the rates, large individual biomass, large local
t
LOB MEMOIRSOFTHF.Ql LHNSLANDMUSKUM
population si^e, and they arc apparently respon- and Ashmore Keels, hut completely absent from
sibleforalargeproportionofihecoralreefsiotaI CarrierIsland. Differencesinthegeomorphology
net primary productivity(e.g. Wilkinson, 1987). ofthese reefs (e.g. the extent ofdevelopment of
Autotrophic sponges arc generally restricted to the fore-reef slope, presence and absence of a
the reefs shallow waters, such as shallow lagoon system) may be directly responsible for
lagoons, inner sandy /uticv Mid intertidal zones these observed differences in the sponge fauna.
on the reefflat, and they include species such as Given the close proximity ofthe three reefs to
CarterioSffOngiafoUoscchS, Dysidea herbacea, each other, each lyingatabout the same distance
Haliclona cymifonms, Perichurax heierar- from the edge ofthe continenlal shell", and each
haphis, and Phyllospongiapapyracea. interconnected byashallowplatformwithanuni-
Our present understanding of 'coral reef bet ofsubmerged shoals interdispersed. it is un-
sponges*derivesmainly from knowledgeofboth likely that any differences in dispersal of
these groups (1 and 2), and yet together reproductive bodies between the reefs could ac-
account fof OOly 16% ofspeciesdiversity within count for the observed differences in sponge
theAshrnorc,Cartierand Hibcrnia Reefsystems species composition. Conversely, it is Suggested
J. Coastal and shelfspecies. 25% of the other here that the relatively low levels of similamv
speciesrecordedinthese.surveysareknowntohe between the sponge faunas of Ashmore, Cartier
rnorc-or-lcss widespread in (topical Australasia, and Hibcrnia Reefs is related to the presence or
J on the more turbid coastal reefs and the absence Of particular habitats on each reef (i.e.,
shallowcontinental;shelf(e.g.aClumusp.,Diili\- both major and "minor* differences in the
cus uteraius, Hi&ginsia scabra, Raphidotethya geomorphology of the reefs). The most obvious
enigmatic**, Rcniochalina stuluytmitts, Tcichux differences in n&ef geomorphology arc seen be-
inelta lahyrinthica). tween Carrier Island and the other two reefs (the
4. Resfriitvi! \pon\;\? fauna , The greatest former with large coral caves and overhangs In
diversity 159%) ofsponges in these reefsystems the spur and groove formations of the fore-reel
consists ofspecies wiili restricted or specialised zone, and an extensive reel flat; the latter with
habitats, such as in sheltered waterson the Boor extensive,relatively deepwater lagoonsand their
ofdeep lagoons, at the have and on the sides of associated sheltered-water habitats), less strik-
pinnacles or patch reefs within deep lagoons, in ing, but just as 'effective', arc the differences
spurs and grooves on the reef from, in eaves on between Ashmore Reef and Hibcrnia Reef (the
the upper reef slope, or associated wnh seagrass former with an unusual highly sedimentcd
bedsinshallow sijld flats, Someofthese hahiiats lagoon covering most ofits back reefslope - an
a/e not present in all reef systems (Fig. 1 ), and area which usually has very rich coral growth;
therefore these mitre restricted species are ob-
viously notpresenteither. This component of the and the latter with a nearly continuous outer reet
fauna is very poorly known m the Iileratutc. margin, and extensive system of patch reels
within the lagoon). Thus, the concept of a reta-
species arc either undocumented, with several
new species from this region already confirmed, il', fijy homogenous, ubiquitous coral reefsponge
or with only a few other isolated records in the fauna1, implied in the literature, is an over-
simplification: ecological specialisation, as a re-
literature.
The hypothesis, that the composition of the quirement for survival, is probably more
importantthanpreviouslyrecognised lorsponges
sponge fauna is largely related to the geoinor-
pspheocliofgicyaonfecedoatcahlreexefa,mpilsesf.urPtihaekrorstuLptponrttaetndmtbly letThLaetvio.nl1y97295;%Wioefdealmlnsapyeecri,es1r9e8c5o)rded in this
laris, for example, was only found on the outer study are known from cither (or both) tropical
k.i slope, in spur ami groo\e formations and in Australian and southern Indonesian waters sup-
caves on the foretrel, which are be>l represented ports the notion thai biogeographic affinities >'
at Cartier Island, but was not found at either the sponge tauna on the northwestern continental
Hibcrnia or Ashmore Reef. Conversely, /J nigra shelf is not overwAhelmingly that of southern In-
was collected from Hibcrniaand Ashmore Reefs, donesia (Hooper Levi, 1994), as proposed b>
was; innogtinsgeaenndaptatCcahrtrieeeifsIwsiltahnidn twhheilcahgohoans, bnuot bbuoith fWhieedyeicitoinitaayicin |a19Xm5o)iarndcovamnplSoeexstm(i19x90)o,f
lag<MW- Similarly, Astcropus sifftisshorum is a Australian 'endemics'. Indonesian 'invaders1 .
dominant non-sclcractinarian speciesofthe ben- widely distributed oceanic species ('coral reef
thosinthedeeperpartsofthelagoonsofHibcrnia sponges'
CORAL REEF*SPONGESOFTHESAHULSHELF 101
CONCLUSIONS great company; and Ms Cathy Johnston, Ms
Anne-Marie Mussig, DrLyle Vail and DrHelen
Extrapolation of these. Imdmgs to it conserva- Larsonforassistingincollectingandphotograph
tion strategy for marine resources is appropriate ing sponges from these reefs.
in this forum. OneofIhe main stated functions of
LITERATURECITED
asystemofmarine parks istoprovidea ftSSCI - -it
of generic diversity, to repopulate adjoining
areas, as well as to protect particular habitats, ANDEL. T H VAN & VEEVERS, J.J. 1967. Sub
marine pioeessc.s and rare and endangered marine morphology of the Sahul Shelf,
northwestern Australia. Geological Society 01
species (JvaqoVici, 1984). Within the various
America Bullehn76: 695-700
biogcographical provinces there arc often small BAKUS,G.J. 1981. Chemical defease mechanisms un
"representative1 habitats set aside as protected the GrCAt Barrier Reef, Australia. Science 211:
areas, onthebasisofbeing 'typical' andcontain- 497-499
ingsufficientresources tofulfil theirfundionsas BAKUS. G.J STLBBINS. T.D.. LLOYD. K..
genetic reservoirs. Tins is the existing situation CMANE1.. 11.. WRIGHT, M.T & BAKUS, GE
for Ashmore Reef, declared a National Nature !9X9 1Inpaliabilityanddominanceoncoralreefs
Reserve in I983| with theprimary staled purpose in the I*i|i and Maldivc Islands. Indian Journal ol
to protect marine and terrestrial fauna and flora, Invertebrate ZholDgY and Aquatic Biology I; 34
to protectagainst possible overfishing, and to act BAKU5S3.. G.J. & ORMSBV. B. 1994. Comparison ol
as a representative ofan oceanic, outer shell reel
speciesrichnessamidominance innorthernPapua
and atoll rising from the edge ofthe Sahul Shelf. New Guinea and northern Gulf Of AlasLt In
H\ jdence presented here questions the validity ol Soesl. R.W.M. van ted.), Sponges in Time and
preserving only a single reel as being repre- Space'. (Halkcma; Rotterdam).
sentative' of, and maintaining genetic lesourees BATTERSHILL, C.N. & BERGQUlST, I'.k. 1990
fftf, a system ot reels, For one group ol marine The influence ol Morms Of) asexual reproduction,
invertebrates at least, and supported to a some recruilmeni and survivorshipofBpODgCS. Pp397-
exieni by data from oihcr groups [echinoderms 403. In Kuet/.lei. K. led.). 'New PcfSpOCUVC* in
(Marsh el a).. 1993); molluscs (Wells, 1993)]. it WSapsohnignegtBoino)l.ogy' (Smilhsonian Institution Press-
is suggested that 'adequate biodiversity* may not BKKGQUIST. P.R. 1969. Shallow waier Demospon
be contained within a single reef system. Both Ii"iii Heron Island. Papers ol the University
subtle andmajordifferences in reefgeomorphol- ol Queensland Heron Island Research Station
Ogy appeal to substantially influence some 1(4): 63-72
faunae. Marine sanctuaries should bedesigned to RERGQI 1ST P.R.. avling. a.m. & Wilkinson.
contain enough diversity ofreeftypes to pro\ idc C.ll 19KS Poliose Diciyocentidfi of the
a true reservoir ofgenetic diversity Austiiiiuur( ofni BarrierReef Pubbiieazronedella
Sta/ionc /ooloii^iea di Napoli 1 Marine Ecology
9(4) 291-320.
BERRY, P.p.ted..)l*>Sf». •Eai.f.iilsuiveysofiheKuwIev
ACKNOWLEDGEMENTS
Shoals. Scott Red andSenngapatamReel,north-
western Australia' Records of the Western
Re]setahracnhk SDtiatiLoynl)c. VDarilRu(snsoewllatHaLnil/eayutanIdslaDnrd tedA.)us1t9r9a3l,ianMaMruisneeufma.unSnulpspulrevmeeynsti>f2A5:sh1m-1o0r6e.Reef
Barry Russell (NT Museum), Principal Invfis aAunsdtrCaalrirainerMuIsselaunmd.'.SuRpepcloermdesntof44t:heI-9Wte.stern
ligalOTS Of various expeditions funded by the BOtJRY-ESNAUIX N. & LOPES, M.T. 1985 Les
Australian National Parks and Wildlife Service dtfmospongcs littontlesde PArchipel dea Acorcs
(Australian Nature Conservation Agency), firti Annalcs de L"Institute Oecarioyrapliiciue, Pans
providing me access to these remote faunas; Or (612): 149423
Paddy Berry (WA Museum), through L>r Barry BRIGGS. J.C. 1987. 'Oncography find Plaic fa
Russell, toraccess to an Unpublished uianiiscii|>t tonics. De\dopmcrtls in Palaeontology ami
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R 1991 Asian and soulh-wcstern Pacific Con-
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Wellsforpermitting mc tocitesomeoftheirwork their bioireo^ruphic significance. Australian Svs-
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TABLE 1 List of sponge species collected from Carticr, Hibcrnia and Ashmore Reefs, showing distribution
withinthethreereefsandextra-limitaldistributionwhereknown. Speciesnumbersrefertoasyetunidentified.
possibly new species in NTM andQMcollections.