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CRAB PREDAT10N ON GREEN TURTLE(CHELONL4MYDAS) EGGSJNCUBATED ON A NATURAL BEACH
ANDlN TURTLE HATCHER]ES
AhmadAlilandKamarruddin[brahim2
イ M∂血eF伝わe〟e5尺e50U′℃eSDeve′叩m即加dMan∂9emenf加pa伽1e咄
SoutheastAsianFISheITeSDevelopmentCenteI;21080Chende/Tng,77)Il)nganu,Malaysla. 2
7t/rtIeandMa血eEcosystemCenter(TUMEq,DeparhentofFjsheriesMalaysia,23050
Du〃9Un,福相〃99∂爪ノ,M∂/∂yS胤亡-m∂//了kdm55@y∂わ00.COm
ABSTRACT
AstudyofcrabpredEltionongreenturtle(CheIoniamydas)eggswasconductedonanaturalbeachofMak
Kepit,PulauRedangandatturtlehatcheriesinGeligaandChendorduringMarch-September2002・Theobjectives
WeretOquantifycrabp「edationonturtleeggsonnaturalbeachandhatcheriesandtodeterminetheeffectiveness
Ofp[asticmeshfencingforpTeVentingcrabpredation・AtotalDf658nestscompriseofthoseonnaturalbeach(214),
hatcher】es(429)andexperimentalplot(15)wereinvestigated・ResultshovvedthatmoTtalityofgreentur[leeggsin
thestudyareaduetoghostcrabpredationisnotanimportantthTeataSthemagnitudeofdepredationwasonlyl・3%
(rangeO.4%-2.7%).Twospeciesofcrabs,i・e・,Ocypodeceratophtl7aImusandOcypodekuhJliweTereCOrded・The
useofO.5cmmeshedplasticnetEontofencesurroundingnestsdowntolmdeepundeTSandsurfacewasproven
effectiveinpreventingcrabsfromentenngthenestsintu「tlehatcheries・Thispreventivemethodwasrecommended
foradoptionintheoperationofturtlehatcheries,aSitwaseffectiveandeco-friendIysound・
Keywords:ghostcrabpredation,Cheloniamydas.Ocypodespp,naturaIbeach,turtIehatchery
]NTRODUCT10N
The green turt]e,Chelonia mydasis known to
nestextensivelyonselectedsandybeacheson廿1emainland
and offshoreislands of Peninsular Malaysia.Highest
COnCentrations of nesting green turtles occur on the
isLandofPulauRedang.foIEowedbyGeEigaandPaka,all
islocatedinthestateofl七rengganu.lnthestateof
Pahang】theonlygood greenturtlerookerylSlocated
atChendor,Whereas PantaiSegariofPerakisa main
rookeryforthisspeciesonthewestcoastofPeninsular
Malaysia. There are also nesting of green turtles
reportedintheotherareasbuttheirnestingnumbersare
considered small(Kamarruddin,1994).Thisreportalso
concIuded thatthe nesting season ofgreen turtlesin
Peninsular MaEaysia occursthroughouttheyearwith
PeaksinJune-JulyperiodL
Eggsandhatchlingsofseaturtlesaresubjecttoa
numberofnon-human predators.There are manyspe-
Cies ofpredators that prey upon the10ggerhead turtle
Carettacaretta.Theireggsandhatchlingswerereported
to be predated bythe nineLbanded armadillo,Dasypus
novemcintus(Drennen etal.,1989).Theywerealso
Preyeduponbyanumberoftheotherpredatorssuchas
theAtlanticghostcrabs,Ocypode quadrata(Sundn,
2001).thesurfcrabs,ArenaeuscrIb/笥,(uS(Frick.2003),
Varanidlizards,「aCCOOnS.COatis,feraldogs.coyotes,
Shorebirds,Vultures,Wild boars,and ghost crabs
(Fowler,1979;Mrosovsky,1983;Cornelius,1986;
Connant,1991;Eckert,1992;BbmiresandGuinea.2001).
Hatchlingsofgreenturtleswhenenteringseafromrook-
erybeachesandduringtheswimrfrenzyperiodenroute
96
tonurseryhabitatswereeas11yeatenby
the grouper,PromjcropsIance10tuS
(Witzell,1981).
Theghostcrabs(Ocypodespp)
are fast running crustaceans with a
SPeed of up to3,4m/sec,CaPable of
COVenng[ongdistanceduringforay.This
SPeCiesspendsthegreaterparts ofits
lifein,Or aSSOCiated with a burrow.
Hughes(1966)reported that burrows
havedepththatrangefrom30cmtol.3
mdependingonhow10ngtheyhadbeen
OCCuPiedandtheirpositiononthewave
beach.The burrows were most often
rocatedin positions between highwater
SPnngtideto)uStberowhighwaterneap
tide.Ghost crab coIEectiveEy exhibits
manyfeedingtacticsand activitycycles
(Hermkind,1983).Theyleavetheirburrows
mostly at night and scurry along the
beachinsearchoffood.Althoughghost
Crabsspendmostoftheirlivesonland.
theystillhavegllEsthattheymustkeep
Wetinordertobreathe.Theyperiodically
Shedanexoskeletonwhentheyoutgrowit,
Ghostcrabdepredationonseaturtleeggs
and hatchlingsisfrequentlyobserved.
arthoughtheextentof10SShasnotbeen
quantified.
円9.†M叩5わol〝血9納e/oc8f旧∩50r軌佗eSfu(少S〟eson肋ee∂Sf CO∂SforPe/血SU/∂rんね/∂yS/a-Ma〟Kep/f,Ge旬∂∂ndC/†endor
MATERIALSANDMETHODS
Study sites
ThreestudysitesontheeastcoastofPeninsu[ar
Malaysiawerechosen(Figurel).MakKepit,anatural
WhitesandbeachislocatedontheislandofPu[auRedang
intheSouth ChinaSea.TwoothersitesareturtIehatch-
enesatGeligaandChendoronthemainlandwherethe
beaches areofbrown-tyPe Sand.
Quantification ofcrabpredation-Quantification
DfcTabpredationongreenturtleeggswasmadeatall
threesites.1dentifLCation ofcrabspecieswas based on
thefle[d keys(Lovett】1981)andthecharacteristicsof
burrows(John.1998).The species Ocypode
CeratOPhtharmusischaractensedbyhavingapyramid-1ike
Sand mound adjacentorclosetothe burrow.whereas
Ocypodekuhliicoversitsburrowholewith a moundof
Sand.0.ceratophthalmusisusuallyfoundintheintertidal
ZOneandhasprominenteyestalkswithaLongstem.The
Stemisshorterin O.kuhlii.which generally has round
eyes.StridulationisapparentinO▲kuhliiwhereduring
Observation,raSPlngSOundscould be heardfromthe
burrows.0kuhliialso preferstoconstructburrowson
theisolated area,in contrastwith0.ceratophthalmus
that present everywhere on the beach
Theinformation aboutdepredationofseaturt[e
eggsand hatch‖ngs byghostcrabsin Malayslaisvery
SCanty.John(1998)duringhisstudyatChagarHutang
OntheislandofPulauRedangdocumentedtwospecies
Ofghostcrabs:OcypodeceratophthaImusandOc)pOde
kuhliiand reported thatghost crabswere the most
PrOminentnestpredators(56.67%),Hearsointroduced
acontrolmethodbytrapplngandremovlngaSameanOf
PrOteCtingturtEeeggsfrombeingp「edatedbyghostcrabs・
ln PeninsularMalaysia.theghostcrabs(Ocypodespp)
liveindeepburrowsonsandybeachesofbothmainland
and offshoreislands.
TheobJeCtiveofthisstudywastoquantifyghost
Crabpredationongreentur[leeggsatanestingbeach
(MakKepit)andin hatcheries(GeligaandChendor)Lln
addition,aneXPerimentwasconductedbyfenclngaPlot
Ofhatcheryareavvhereeggswereincubatedwiththe
aimtounderstanditseffectonreducingcTabspredation.
lnformation derivedfromitwould be used forhatchery
managementpurposes・
97
Nestswereexcavatedandtheircontentsexamined
Within aweekafterthe emergence ofhatchlings.The
PreSenCeOfcharacteristicsnipmarksoneggshellswere
attributed to attack by ghost crabs and were easily
distinguishablewith marksleftbytheotherpredator
SuChasflreantS.Thesumofthenumbersofunhatched
eggsandemptyshellsremovedfromanestusedasan
approximation oftotalclutchsize(Fowler,1979).The
incubationofC.mydaseggsfor214cIutchestoDkplace
atMakKepitbeachfrom25Marchunti112September
2002.whereasatotalof357clutches(atGeliga)and72
Clutches(atChendor)wereincubated duringthe period
OflAprilto13September,andlAprilto6September,
2002,reSPeCtively.The emergence success was
Calcu[atedaspercentageofeggsthatresultinhatchlings
thatemergefromthenest.
Hatchery Experiment
An experimentalp10t WaS COnStruCted within
Chendor’sproductionhatchery.Thetotalareaofthep10t
WaS15m2(5mx3m).1twasfenced rightunderthe
Sand surface with one-meterdepth ofO.5cm(internaJ
diameter)mesh size ofnetlon plasticto protectcrab
encroachment(Figure2).FifteenfullcIutchesofgreen
turtleeggstakenfrom Chendorbeachduringaperiod
Of26June-29July,2002were transplantedintothe
experimentalhatchery.The quantification of crab
Predationinthee〉(Perimentalhatcheryfollowed similar
marmers as described for clutches on the natural
beaches and production hatcheries.
F桓Ure2・加eよpeJTme/1ね/pわf8rC/1e/1dor/1∂似1eJγ
RESULTS
Incubationparameters-Highemergencesuccess
WaSreCOrdedforgreentu111eeggsincubatedatanatura(
beach and two hatcheries(lbblel).The vaEues range
from81・38%(+22・30)forinsituincubationatMakKepit
beach,81.87%+26.35forartiflCialincubationatChendor,
and82.47%+18.28forartificia)incubationatGeliga
Wererelativelyhighandtherewasonlyslightdifference
among them.The emergence success ofeggsin the
experimentaEhatcherywas73.52%+27.52,areduction
OfaboutlO%fromthenaturalandhatcheryfiguresand
is obviouslydepicted bya sIgniflCantSmallnumbersof
theincubated eggs.The mean depth ofnestsin both
hatcherieswasin a rangeof13-16cm shalloweTthan
that of nests on naturalbeach.
Tablel:A summary oftheincubation parameters and crab predation on green turtle(Chelonia
mydas)eggsincubated on naturalbeaclland turtle hatcheries
Paramete「 MakKepitBeach GeligaHatchery ChendorHatchery E叩erimenlalHalchery
lbtalno.of clutches 214 357 72 15
1もtalno.ofeggs 20,294 33,409 6,549 1.374
Mean clutch size 96.6 93.6 91.0 91.6
Meannestdepth(Cm) 76.7 60.2 63.1 61.0
Mean Emergence 81.38% 82.47% 81.87% 73.52%
SuCCeSS
S.D.(Standarddeviation) !22.30 !18,28 !26.35 !27.32
No.ofnestspredated 78(36.0%) 81(22.7%) 36(50.0%) 0
bycrabs
No.ofeg9Sp「edated 244(1.0%) 145(0.4%) 180(2.7%) 0
byc「abs
Range(C「ab-P「edated 0-6 0-7 0-23 0
e∈IgS/clutch)
Meanno.ofeggs/cIutch 1.14 0.41 2.50 0
Predatedbycrabs
S.D.(Standarddeviation) !1.80 !0.93 !4.19
98
Crab predation
Crabpredationongreenturtleeggsincubatedat
allsitesis summarisedinlbblel.Nest examinations
madeon643clutchesofturtIeeggsfromanaturarbeach
andtwoproductionhatcheriesrevealedthatthemortality
Ofeg9Sdueto ghostcrab predation wasverysmal[・
Thisisreflectedbythemeanvaluesofthepredationrate
thatrangesfrom O,4%-2,7%onlyoTl.3%combined.
These figures weTe derived fromindividualsite that
TeCOrdedeggdepTedationatChendorhatcheryas2.7%
fo”owed byMakKepitand GeIigaasl.0%and O,4%,
respectively.The varues ofthe percentage ofeggs
Predated byc「absseemedinagreementwiththemean
numbers ofpredated eggs perclutch,i.e,2.5+4.19
eggs/CIutch(n=72),1.14+1.8eggs/clutch(n=214)and
O.41+0.93eggs/clutch(n=357).
The percenta9e Of nests being predated by
CrabsseemedhighestforthoseinthehatcheryatChendor
(50.0%),followed by the naturalnests at Mak Kepit
(36.0%)andinthehatcheryatGeriga(22.7%).Similarly,
the rangeforcrab-Predated eggs/clutch was recorded
highestatChendorhatchery(0-23eggs/clutch)・Onthe
Otherhand,SuChavaluewasslightlyhigheratGeliga
hatchery(0-7eggs/clutch),followedbyMakKepitbeach
(OL6eggs/Clutch).Twospeciesofghostcrabs.i・e・,0・
CeratOPhtha/mus and Okuhliiwere recorded during
thisstudybutefForttounderstandthemagnitudeofegg
depredationbyeachspecieswasnotattemptedatthis
Sta9e・
An interesting result was recorded at the
experimentalhatchery.Thedata(lbbIel)cEearlyshowed
thattherewas no ghostcrab predation ataIlatthis
Site as reflected by a”15clutches were safely
incubated.The useplasticmesh netting provedto be
effective in deterring ghost crabs from entering the
fenced hatchery.
WerenOtimportantpredatorstogreenturtleeggsasthe
mortalityrateofO.4%-2.7%orl・3%overalrwasvery
littLe.Sucha10WmOrtalitycouldpTObablybeassociated
with the presenceofhuman being(theworkers)that
lookedafterallthree-hatchlingproduction sites.Result
OfthisstudyisincontrasttoJohn(1966)whoreported
thatghostcrabs,Oqpodewe「ethemostprominentnest
Predators,COntributing56.67%ofnestmortalityatChagar
Hutang.aturtIebeachlocatednexttoMakKepitbeach,
both areon theisland ofPulau Redang.The probable
answertothe ghostcrab-humaninteractionis aLso
foundina reportofCornelius(1986)whostatedthat
ghostcrabshavebeenreportedtobeprominentpredators
OfturtIeeggsinareaswherebiggerpredatorsareab-
SentOrSParSe.GhostcrabburrowsDCCurnngneartUrtle
nests throughout the incubation period provide an
entrance for other predators to infest or prey on the
nest.John(1966)reportedthatghostcrabdensityat
ChagarHutang beach ontheislandofPulau Redang
WaShighestatthebeginningofthenestingseason(jn
May)withacountof177.88crabs/100m.Thedensity
decreased throughoutthefo1low【ng mOnthswith43.44
Crabs/100minOctober,Thedropmaybelargelydueto
theincreaseinhumanactivitiesonthebeachduringthe
nestingseason.Hughes(1966)aFsoreportedthatghost
Crab activity[S COrrelated with human or predator
activity.Thebreeding cycle Dfthespeciesitselfcould
have caused a dec[inein abundance.rtis noted that
Ocypodjdae has distinct breeding seasons that are
reguIated by exogenousfactors(Simons andJones,
1981).Thepredationofeggsbyghostcrabsinthisstudy
is considered small if compared with other predators
such asvaranidlizardsthat caused51,9%mor[aFityof
flatbackturtle,Natatordepressus eggsin Australia
(BlamiresandGuinea.2001)・
Taking into consideration that the mean
emergencesuccessofeggsatthreestudiedsiteswas
81.9%.the different of18.1%was derived from the
unhatchedeggsthatincludedl・3%crabpredation・FoT
managernent purposes.a maJOr PrOPOrtion of the
Unhatched eggs recorded from this study requires
furtherinvestigationinordertounderstandwhatfactors
affectingtheirhatching.0pportunisticobservationsmade
duringthestudyperiod recordedsomepTedato「SSuCh
asfEreantSandvaTanidlizards,besidesrootsandfungl,
mayalsocontributetomortalityofturtleeggs・
lntheexperimentalhatchery,theuseofsmall
meshplasticnet10n(0.5cmdiameter)tofence15clutches
(1,374eggs)ofgreenturtlesresultedinzeronumbersof
DISCUSS10N
Anumberofbioticandabioticfactorsareknown
toaffectnestand egg mor(alityin marinetu「tlesrThe
haterateoftheAt[antic10ggerhead(C.caretta)inSouth
CaroEina\〟aSOnly6.1%(Hopkinset.al.,1979).Thiswas
mainlyduetointensepredationbyanimalpredators・He
reportedthatraccoons(Procyonlotor)andghostcrabs
(Ocypodequadrata)destroyed56・1%and2・4%ofthe
OVeraIE458nests.respectively.Poacherstooktherest・
lnthisstudy,Wefoundthatghostcrabs(Ocypodespp)
99
becausethemagnitudeofdepredationisonlyl.3%(range
O.4%-2.7%).Two species of crabs,i.e.,Ocypode
CeratOPhthaImusand Ocypode kuhliipresent.The use
OfsmalImeshedplasticnet10nfenclnglSPrOVenefFective
in preventing crabs from entering the nests in turtle
hatcheries.1tissuggestedthatminimisingeggmortality
through preventive methodis moreappropriatethan
trappLngOrremOVaIofpredatorsasthefencingismore
eco-friendlysound.FurtherstudiesarerequiredtoquantWy
magnitude ofegg mortalityduetootherfactorsthat
contributed a major portion of the unhatched eggs as
reveaLedfrom this study.The nextstepisintroducing
remediaLmeasuresaimlngatPrOducing hatc仙ngswith
ZerOegg mOrtality.
eggsbeing predated byghostcrabs.Themethod has
proven effective in preventing crabs from entering the
nests.ItisbelievedthatminimismgeggmortaEitythrough
PreVentivemethodismoreappropriatethantrapplngOr
removalofpredatorsastheformerisecorfriendlyin
natu「e.
Manyagreethatthereisalinkbetweenghost
Crabsandtheotherpredators.Theinitialharmoccurs
when ghostcrabs maketunnelintothe nestchamber
andbreakopenseveraEeggs.Thisbeginsasequenceof
events,Which normally resultsin entireclutch being
destroyedalthoughthecrabmayactual【yeatonlyafew
eggs.Thisdirectaccessintothenestprovided bythe
ghostcrabsactasapathwayforsecondarypredators
SuCh as redantsandfungi.FungLand harmfulmicroor-
ganismsf.ndasuitablemediumonthebrokeneggsand
SPreadslowly,enCOmPaSS■ngeggSatdi仔erentstages
ofembryonicdeveropment・Ltseemsthataddress【ngghost
crabissuewouldatthesametimeaddresstheproblems
associated with other predation.
CONCLUS10NS
Mortalityofgreenturtleeggsinthestudyarea
duetoghostcrabpredationisnotanimportantthreat
ACKNOWLEDGEMENTS
TheauthorsacknoⅥ11edgewiththankstheDirector
Genera[ofFisheriesMalayslaandtheChiefofMarine
Fishery Resources Development and Management
DepartmentfortheirconsistentsuppoTt・ThisstudywouId
nothavebeenpossiblewithouttheassistanceoftechnical
staffandrangersoftheDepartmentofFisheriesMalay-
Sia.Wethankal10fthem.
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