ASSESSMENT OF CROWN-OF-THORNS (DAP-AG) SEASTAR … · 3 Pictures taken on June 6th 2019 in Two Rocks, a dive site located in the North of Malapascua island, at a depth of about 10m.

Malapascua Island

Logon, Daanbantayan

Cebu 6013

Philippines

SEC Registration No : CN201625259

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http://www.peopleandthesea.org [email protected]

________________________________________________________________________________________________________

ASSESSMENTOFCROWN-OF-THORNS(DAP-AG)SEASTARPOPULATIONAROUNDTHEISLANDOFMALAPASCUA,DAANBANTAYAN,PHILIPPINES

ALICIADALONGEVILLE,PhD.LEADSCIENTIST,PEOPLEANDTHESEA

JUNE2019

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REPORTKEY-POINTS:• Crown-of-Thorns are sea-stars feeding on corals. Their populations sometimes

increasedrasticallyintooutbreaksthatcanreducelivecoralcoverbymorethan90%inaperiodofjust2-3years.

• CebuPENROfficemadearecommendationtodeclareCOToutbreaksthroughouttheprovinceofCebu,andthatfundsarebeingmadeavailabletoLGUstohelpaddresstheproblem.

• COTs spawnunder stress, thus carrying COTs underwater aftermanual extractioncausesmassreleaseofeggsandsperm,whichwillleadtofurtheroutbreaks.

• TwotechniquesarerecommendedtocontrolCOTpopulationswhileavoidingstress-spawning:free-divingremovalsorscuba-divinginjectionsofhouseholdvinegar.

• ReefmonitoringresultsshowthatCOTdensitiesonthereefsofMalapascuaarenowSEVENTIMESthethresholddefininganoutbreak(morethan15COTsperhectare).

• Torespondtotheimportantoutbreakoccurringinthesite‘CoralGarden’,PeopleandtheSeahasdevelopedacontrolprogramoverthepastyearandahalf.

• Free-diving removals of COTs were organized together with various localstakeholderssuchastheMalapascuaTourGuide’sAssociation,theBantayDagatofMalapascua,andlocalandforeignbusinessesandvolunteers.

• Over thepastyear, thenumberofCOTscollectedduring the removal sessionshasconstantly been above the outbreak threshold. Hence, we are committed to thecontinuationofengagementsthatcontributetoeducatedandcoordinatedeffortstoeradicatetheCOTproblem.

• SincethebeginningofJune2019,wehavebeenconductingpopulationassessmentstoobserveCOTdensitiesaroundMalapascua.Outoftheninesitesmonitored,onlytwoshowedCOTpopulationsbelowtheoutbreakthreshold.

• Our most recent observations show alarming abundance of COTs indicating anoutbreakisoccurringintheNorthofMalapascua,asattestedbythefollowingpictures(A,B,C,D)

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PicturestakenonJune6th2019inTwoRocks,adivesitelocatedintheNorthofMalapascuaisland,atadepthofabout10m.(A)and(B)showpilesoflargeCrown-of-Thorns(diameterof30to50cm)predatingontableAcroporaspp.corals.(C)and(D)showthedamagesinflictedbytheCOToutbreaktothereef.Thelargemajorityofhardcoralcolonieshavebeenkilled,andnowappearwhitetogreenishastheirdeadskeletoniscolonizedbyalgae.

(A) (B)

(C) (D)

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1. Crown-of-Thorns(COTs)Acanthasterplanci

COTsarefoundthroughouttheIndianandthePacificOceans,makingthemoneofthemostwidelydistributedofallreefspecies(DeVantierandDeacon,1990).Despiteonlyreproducingonceayear,COTshaveanenormousreproductivepotential(Pratchettetal.,2014).Alargefemale(>40cmindiameter)canproduceupto65millioneggswhileasmallerfemale(<30cm)mayproduceupto2.5millioneggs(KettleandLucas,1987).

AdultCOTsarespecialistcorallivores(De’athandMoran,1998),whichmeanstheypreyoncoralpolypsandcanconsume400cm²ofcoralperday(Carpenter,1997).Inlownumbers,COTscanincreasethebiodiversityofareef,preyingonfastergrowingcorals(e.g.Acroporaspp.), givingway for slower growing corals (e.g. Porites spp.) to succeed.However,whennumbersincreasetooquickly,large-scalepredationofcoralscanleadtohabitatdestruction,astheirfeedingrateexceedstheaveragegrowthrateofthecoral(Fabricius,2013).Thisisknownasan‘outbreak’(Bosetal.,2013).Therearethreestagesofanoutbreak:thebuild-up,which iswhen thenumbersbegin to increase; theoutbreak,which iswhen theCOTsdensity exceeds local resource availability; and the epidemic, which is when the COTsoutbreak has spread to other reefs due to reef connectivity (Hock et al., 2014). A largeoutbreakcanreducelivecoralcoverbymorethan90percentinaperiodofjust2-3years(Chesher,1969;Bucketal.,2016).

Withoutintervention,COTsoutbreakswillcausethedisappearanceofthecoralsinaregionwithin only a few years. Although coral reefsmay recover fromoutbreaks, thismay takedecades,witharangeofanywherebetween5and100years(Pratchettetal.,2017)beforethecoralswererestoredtoahealthyreef,withmostreefsestimatedtotake10-25yearsforfullrecovery(Fabriciusetal.,2010).Highlyimpactedcoralreefsmayneverbefullyrestored(BerumenandPratchett,2006).

This problem of COT outbreaks has gained attention in several parts of the Philippinesrecently.AsreportedinSunstar(April2019)theCebuPENROfficemadearecommendationtodeclareCOToutbreaksthroughouttheprovinceofCebu,andthatfundsarebeingmadeavailabletoLGUstohelpaddresstheproblem.

2. Controlprograms

OnceaCOToutbreakhasstarted,naturalregulationofthestarfishpopulationbypredationisnotpossibleandactivemeasureshavetobetakentobringthenumberofCOTbacktoalevel that canbe sustainedby theecosystem.COTcontrolprogramsare typicallyused toregulatethepopulationandlimitcoraldamagesthatwouldthreatenthehealthandresilienceof theecosystem(Boström-Einarsson&Rivera-Posada,2016).TheDENRtechnicalBulletin2017-13 (Guidelines on the implementation of Environmental standards for diving andsnorkeling)encourageslocallydeclaredandmanagedMPAstoadoptthe“GreenFinsCrownofThornsCleanupGuidelines”aspartoftheprescribedCodeofConductoftheGreenFins

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Approach. These guidelineswould ensure that COT control initiatives are conductedwithecologicalinterestattheforefront.

As stated above, COTs have extremely high fecundity (reproductive capacity). As manyspeciesofseastars, theyalsospawnunderstress,asamethodofensuringthecontinuedsurvivalofthespecies.Hence,carryingCOTsunderwateraftermanualextractioncausesmassreleaseofeggsandsperm,whichcould leadtofurtheroutbreakswithinacoupleofyears(GreatBarrierReefMarineParkAuthority,2017).

Twomain techniquesare commonlyused toactively controlCOTpopulations: free-divingremovalsforshallowsites,andscuba-divinginjectionsofhouseholdvinegarforsiteswherefreediving is not possible. Both methods have to be carried out in accordance to strictguidelinesinordertoavoidCOTsstressspawningandpreventinjuryoftheparticipants.

- Manualremovalsprocedure:free-diverscollecttheCOTsusingtongstoavoidinjuries.COTsshouldbeimmediatelybroughttothesurfaceandplacedinbucketstoavoidstressspawning.Waterfromthesebucketsshouldbeburiedonlandandneverthrownbackintotheocean,asitcontainseggsandspermofthecollectedseastars.

- Householdvinegarinjectionsprocedure:scuba-diversinjecta20mLdoseofasolutionofhouseholdvinegarataconcentrationofabout4%atthebaseofthestarfisharmusingaveterinaryneedle.Forthecontrolprogramtobeefficient,allthestarfishintheareahaveto be injected,which usually requires several visits to the sitewithin 15 days (GreatBarrierReefMarineParkAuthority,2017).

3. Resultsofthereefmonitoring

People and the Sea has been monitoring the coral reefs around Malapascua since thebeginning of their activities on the island in early 2015. Part of thatmonitoring includesrecordingtheabundanceofcoralpredatorssuchasCOTs.Hence,PeopleandSeahasthreeyearsofdatashowingtheevolutionofCOTsontensurveysitesaroundMalapascua(Figure1).

ResultsofthemonitoringshowthatthemeandensityofCOTsinMalapascuahasincreasedby440%since2016,andnowreaches0.015(±0.005)individuals/m2(105individuals/ha).TheCOTcontrolguidelines,publishedbytheGreatBarrierReefMarineParkAuthority,statethatasiteisexperiencinganoutbreakiftheirdensityexceed15individuals/ha.COTdensitiesonthereefsofMalapascuaarenow7timesthatthreshold.

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Figure2showstheCOTdensityforeachsurveysitein2016,2017and2018.TheabundanceofCrown-of-Thornshasincreasedineightoutofthetensites.ThetwositeswherenoCOThasbeenobserved(LapusLapusandTwoRocks)arethetwositesdominatedbysoftcoral,whichareofpoorinterestforthestarfishsinceitmainlyfeedsonhardcoral.FoursiteshaveCOTdensitiessignificantlyhigherthantheoutbreakthresholdof15individuals/ha,andfourarerightonthelimit(averageof16.7COT/hainDakitDakit,Lighthouse,BarrioandSunkenDakit;Figure2).Twosites located inCoralGarden,ontheEastcoastofMalapascua,haveshownCOTdensitiesabove theoutbreak thresholdsince thebeginningofourmonitoringactivitiesin2016.

Figure2.

ResultsofPeopleandtheSeareef monitoring ofMalapascua. Density of COTin the ten survey sites in2016,2017and2018

Figure1.

MapofPeopleandtheSeasurveysitesinMalapascua.

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4. PeopleandtheSeaCOTremovals

Torespondtotheimportantoutbreakoccurringinthesite‘CoralGarden’,ontheEastsideofMalapascua,PeopleandtheSeahasdevelopedacontrolprogramoverthepastyearandahalf.Wehavebeenorganizingregularfree-divingremovalsontheimpactedsitesinceJanuary2018.AspartofthiseffortwehaveteamedupwithvariouslocalstakeholderssuchastheMalapascuaTourGuide’sAssociation,theBantayDagatofMalapascua,andlocalandforeignbusinessandvolunteers.The schemewe implemented is low cost and easy to repeat; buckets are floated on thesurfaceandswimmersdivedownusingtongstocollecttheCOT,wheretheyareimmediatelybroughttothesurfaceandplacedinbucketstoavoidstressspawning.InordertomonitortheevolutionofCOToutbreaks,wealsocollectedbiometricdataofremovedstarfish.Thetotal number of starfish collected was recorded, and each individual was weighed andmeasured.Inaddition,oneineverytenCOTswasalsosexedanditssymmetryassessedbycounting the number of missing and/or short arms. The size and weight of a COT isproportionaltoitsageandthenumberofeggsproduced(Kettle&Lucas,1987).Symmetryisanindicatorofthepredation/competitionaffectingCOTpopulation.Hence,thebiometricscan inform us on the age structure, sex-ratio and potential fecundity of COT population,allowingtomeasuretheefficiencyofthecontrolprograms.AnimportantpartofPeopleandtheSeaworkistospreadawarenessofthebestmethodsofCOTremovalrecommendedbytheguidelines.Foreachremovalsession,apresentationwasprovided beforehand to describe the safest and best way to remove COT from theenvironment, alongwith giving some basic information on their biology and the reasonsbehinddoingremovals.In addition, People and the Sea hosted a COT workshop in September 2018 withrepresentatives of the local businesses anddive centres to inform themabout the issuesrelated to COT, best practices in control activities, as well as to share the results of ourcollectionactivities.WearecommittedtothecontinuationofengagementsthatcontributetoeducatedandcoordinatedeffortstoeradicatetheCOTproblem.FromFebruary2018toFebruary2019,PeopleandtheSeaorganizedatotalofthirteen(13)removalsofonehourintheareashowninredinFigure3.Duringthesesessions,atotalofmorethan3300COTshavebeenremoved.

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Figure3.

MapofCoralGardenwheretheCOTremovalsessionshavebeenconductedfromFeb2018toFeb2019.

Figure4showsthetotalnumberofCOTcollectedperone-hourremovalsessions.Thenumberofparticipantspersessionvariedfrom6to14(average10.6).Toaccountforthedifferencesin thenumberofparticipants,wecalculated theCatchperUnitEffort (CPUE)as the totalnumberofCOTremovedduringtheone-hoursessiondividedbythenumberofparticipantbuddyteams,anddividedby60tohavethenumbercollectedperminute.Formanagementpurposes,theGreatBarrierReefMarineParkAuthority(GBRMPA)currentlyconsidersaCPUEof0.1asanactiveoutbreakwhencoralcoverisabove40%(asitisinCoralGarden according to ourmonitoring data). Figure 5 shows the CPUE calculated from ourremovaldata.FromFebruary2018toFebruary2019,theCPUEcalculatedfromourremovaldatavaryfrom0.1to1.48,which isconstantlyabovetheoutbreakthreshold.However, itstarted to decrease over the last threemonths,whichmay indicate that the outbreak isslowingdownthankstothecollectiveeffort.

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Figure4.NumberofCOTcollectedperremovalsessioninCoralGardenfromFebruary2018toFebruary2019.

Figure5.CatchPerUnitEffort(CPUE)calculatedfromCOTremovals:numberofCOTremovedperparticipantbuddyteamperminute.Theredlineindicatesthethresholdofactiveoutbreak(0.1COTSremoved/min).

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Figure 6 shows the average diameter and average weight of COT collected during eachremovalsession.Averagediameterrangedfrom17to21.5cm(mean19.2cm).Averageweightseemswellcorrelatedtodiameter,andvariedbetween129.5and320g(mean221.1g).Bothdiameterandweightremainedrelativelyconstantovertheyear,which indicatesthatCOTpopulationismaintainingaconstantpresenceofreproductiveadults.

Figure6.AverageweightanddiameterofCOTscollectedduringeachremovalsession.

5. Populationassessment

Recently,PeopleandtheSeahasstartedapopulationassessmentofCOTs.Theobservationaltechniqueweemployedisknownas‘SCUBAsearching’,amethodthatprovidesaquantitativemeasureofabundance(Endean,1974).Foreachsite,2-3diversspenduptoanhoursearchingforCOTs.WhenaCOTisobserved,itsdiameteracrossthelongestarmsismeasured.AfterthattheareaaroundtheCOTisobservedforpreyedoncorals(withina2mradius).ThecoralsformandgenusarerecordedtohelpunderstandthefeedingpreferencesoftheCOTs.Figure7showsthelocationoftheninesitesthathavebeenassessedsofar.TheirGPScoordinates,divetimeandnumberofobservedCOTsaregiveninTable1.

Asmentionedpreviously, theCOTcontrol guidelines (publishedby theGreatBarrierReefMarineParkAuthority)statethatasite isexperiencinganoutbreak if theCOTpopulationexceeds15individualsperhectare,whichcorrespondtomorethanoneCOTspottedper20-

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minuteswim.Hence,sitesareconsideredtobeexperiencingaCOToutbreakifmorethan3COTswere observed during a one-hour dive. The number of COTs spotted per hourwascalculatedfromourpopulationassessmentobservationsasfollows:thenumberofCOTswasdividedbythedivetimetogetthenumberofCOTsobservedperminute.Andthatnumberwasmultipliedby60tohavethenumberofCOTperhour.

Figure7.

Map showing the number of COTsobserved in one-hour dive for each sitemonitored during the populationassessmentconductedinJune2019.

Out of the nine sites monitored, only two showed COT populations below the outbreakthreshold(<3COTs/hour).ThesesitesarelocatedbytheDakitisletonthesouthwesternsideofMalapascua(Figure7).AsshowninFigure7,theabundanceofCOTsseemsparticularlyhighontheNorth-Eastoftheisland.TwoRocksisthesitethemostaffected,with127COTSrecordedinjust52minutesandahighproportionofdeadcoral,asshowninthepicturesatthebeginningofthisdocument.Thisoutbreak is locatedatashortdistancefromourreefmonitoringsurveysite, inanarearicherinlargetableAcroporaspp.coralsonwhichCOTsfeedpreferentially(Bos,Gumanao,Mueller,&Saceda-Cardoza,2013).

Hence, our observations show alarming abundance of COTs indicating an outbreak isoccurringintheNorthofMalapascua.Thisoutbreakhasalreadystronglyaffectedthecorals,asevidencedbythepicturestakeninTwoRocksonJune6th2019(page3).Inaddition,severaldive centers have reported similar outbreaks in surrounding areas includingMonad shoal(whichisaprotectedarea)andKalaggamanisland.Boththesesitesareprotectedareas,andthehealthofthesereefsiscrucialfortourismandlocaleconomyastheyarethemostvisitedbydivers.

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Table1.ThetotalnumberofCOTsobservedateachsiteduringthepopulationassessment.

Date Dive Site GPS Coordinates Total Dive

Time (mins) Total COTs Number Latitude Longitude

04/06/19 MermaidSurveySite 11.335 124.109 55 5

05/06/19 MermaidCW 11.335 124.111 45 13

05/06/19 LighthouseBuoy 11.342 124.107 57 13

06/06/19 LapusBuoy 11.347 124.104 54 20

06/06/19 TwoRocks 11.351 124.109 52 127

07/06/19 DakitSurveySite 11.322 124.106 50 0

10/06/19 DakitDakitBuoy 11.323 124.108 53 1

10/06/19 LighthouseWreck 11.342 124.109 55 20

11/06/19 Bantigue 11.350 124.119 40 13

Hence, our observations show alarming abundance of COTs indicating an outbreak isoccurringintheNorthofMalapascua.Thisoutbreakhasalreadystronglyaffectedthecorals,asevidencedbythepicturestakeninTwoRocksonJune6th2019(page3).Inaddition,severaldive centers have reported similar outbreaks in surrounding areas includingMonad shoal(whichisaprotectedarea)andKalaggamanisland.Boththesesitesareprotectedareas,andthehealthofthesereefsiscrucialfortourismandlocaleconomyastheyarethemostvisitedbydivers.

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