95

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．

REFERENCES

Blamires，S．）．andGuinea，M・L・，2001・Theinfluenceoftemperatureoneggmortality，emergenCeSuCCeSSand hatchIingsexratiofor¶atbacksea（Natatordepressus）atFoBay，NortheTnl融ritory・Australia・http＝／／

www．arbec．com．my／seaturtles／art21julyseptOl・htm

Bustard，R．，1972．Seaturt■eニNaturalhistoryandconservation・lbplingeTPubLication・New’ねrk・31ppr

Comant，11A．，1991．GhostcrabpTedationonemergentseaturtlefromre10Catednestson aBarrierLsland，NorlhCarolina M・Sc・thes弓s，WesternWashingtonUniversity・WashingtonDIC・，50pp・

corneLius，S．E．，1986．Theseaturt■eofSantaRosaNationaLPark・FundaciondeParquesNacionales・Costa Rica．64p．

Drennen，D，DwigntCoo■eyandJohn，E・Dり1989・ArmadillopredationonLoggerheadTurtleEggsatTwoNational WildlifeRefugesinFlorida，USA・MarTneTurtIeNews／etter45＝7－8・

Eckert，S．A．，1992．BoundfordeepwateTS・NaturaLHistory，46（11）；15－19・ Frick，M．G，，2003．Thesurfcrab（Arenaeuscribrarhs）＝Apredatorandpreyitemofseaturtles・MarmeTurue

〟e〝S／efferN0．99，2003．16－18．

FowIer，L．E．，1979・Hatch■ingsuccessandnestpredationinthegreenseaturtle・Cheloniamydas，atlt）rtuguerO・ CostaRica，Ecology60（5）：946－955・

Hermkind，W．F．，1983．MovementpatternsandohentationLln＝ThebiologyofcrustaceanlF・J・Vernbergand W．B，Wernberg（eds）：41－101・

Hopkins．S・RHMurphy，M・Stansel■，K・B・andWilkin＄On・P・M・・1979・Bioticandabioticfactorsaqectingnest

mortalityintheAtlantic．oggerheadturtle・Proc・Ann・ConたS・E・Assoc・Fish＆M／d・Agencjes32：213－223

Hughes，D・A・，1966・Behavioralandeco．og■CalinvestigationsofthecrabOcypodeceratophthalmus （Crustacea：Ocypodidae）・J・Zooll，Lond・150：129－143・

了00

John，A・H・F・，1998・Ghostcrab（Ocypodespp）predationongreenturtIe（Cheloniamydas）nestsandhatchlingsin

ChagarHutang，PulauRedang．Finalyearpro］eCtrePOrt．BacheIorofMarineScience，FacultyofApplied

Scienceandl七Chno10gy，UniversitiPutraMaraysia．92p．

Kamarruddin，l・，1994・TheStatusofrnarineturtleconservationinPeninsuEarMalaysia．En．Nacuetal．（eds）．Proc．

FwstASEANsymposium－WOl＊shoponmarmeturtleconsewation，Manila．PhilipplneS．

Lovett，D・L・，1981・Aguidetotheshrimp，PraWnS．］obsters，andcrabsofMalaysiaandSingapore．Universiti

Per［anianMalaysla．

Mrosovsky，N．，1983．Conservingseaturtre．The Brltish HerpetologicarSociety，London．

Simons，M・J・andJonesNl・B・，1981・Populationand reproduction biologyofthemudcrab】Macrophthalmus

hirtipes（Jacquinot．1853）（Ocypodidae），from marineandestuarjnehabitats．］．Nat．Hjst．15：981－994．

Stancky，S・E・，1982・Non－humanpredatorsofSeaTurtleandtheircontrol．ln．K．A．Bjorndal（ed）．Biologyand

COnSerVation ofseaturtIe．Proc．レlわIldConf On Sea Turt（e Conservation，Washington．D．C．Srnithsonian lnstitution Press，139－142．

SundillG・，2001・ATestofThreeSimpleTrapDesignsforSuitabilityinControlringDrepredationonSeaTurtleNesting

Beaches・UniversityofSouthCarolinaBeufortPritchardsIsland Research＆Education．（http：／／WWW．SC．edu／

beaufort／Pritchar／resOO．htm）

Witzell，W・N・，1981・Predationon」uVenilegreenseaturtles，Cheloniamydas，bygrouper，Promicrc）PS／anceIotus

（Pisces：Serranidae）intheKingdomoflbnga，South PacifIC．BulletinofMa／meScience31（4）：935－936．