volume 14, no. 2 · 2018-04-04 · 16 ocean challenge, vol. 14, no.2 ocean challenge, vol. 14, no....

Volume14,No.2

EDITORAngelaColling TheOpenUniversity

JohnWrightTheOpenUniversity

EDITORIALBOARD

ChairMarkBrandonTheOpenUniversity

MartinAngelSouthamptonOceanographyCentre

KevinBlackMarineScienceConsultantGlasgow

FinloCottierScottishAssociationforMarineScience

PeterFoxtonformerlyNaturalEnvironmentResearchCouncil(MarineSciences)

SueGreigTheOpenUniversity

TimJickellsUniversityofEastAnglia

JohnJonesUniversityCollege,London

MarkMaslinUniversityCollege,London

SerafimPoulos(EFMSrepresentative)UniversityofAthens

HjalmarThiel Hamburg,Germany

LouisaWattsNaturalEnvironmentResearchCouncilAtmosphericSciencesTeam

Volume14,No.2,2004(publishedAutumn2005)

SCOPEANDAIMS

OceanChallengeaimstokeepitsreadersuptodatewithwhatishappeninginoceanographyintheUKandtherestofEurope.Bycoveringthewholerangeofmarine-relatedsciencesinanaccessiblestyleitshouldbevaluablebothtospecialistoceanographerswhowishtobroadentheirknowledgeofmarinesciences,andtoinformedlaypersonswhoareconcernedabouttheoceanicenvironment.

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TheSociety’sobjectivesare:

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TheSocietyaimstoachievetheseobjectivesthrougharangeofactivities:

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COUNCILFORTHECHALLENGERSOCIETYPresidentDuncanPurdieSouthamptonOceanographyCentre

HonorarySecretaryRachaelShreeveSouthamptonOceanographyCentre

HonoraryTreasurerSarahCornellQUEST,UniversityofBristol

GaryFones

YolandaFoote

RuthParker

JenniferPike

RolandRogers

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JonathanSharples

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Editor,ChallengerWaveLouisaWatts

ExecutiveSecretaryJennyJones(Foraddressseebelowleft)

ADVICETOAUTHORS

ArticlesforOceanChallengecanbeonanyaspectofoceanography.Theyshouldbewritteninanaccessiblestylewithaminimumofjargonandavoidingtheuseofreferences.Ifatallpossible,theyshouldbewellillustrated(pleasesupplyclearartworkroughsorgood-contrastblackandwhiteglossyprints).Copymaybesentelectronically.

Forfurtherinformation,pleasecontacttheEditor:AngelaColling,DepartmentofEarthSciences,TheOpenUniversity,WaltonHall,MiltonKeynes,BucksMK76AA,UK.Tel.+44-(0)1908-653647Fax:+44-(0)1908-655151Email:[email protected]

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Thesubscriptionfor2005costs£40(£20.00forstudentsintheUKonly).IfyouwouldliketojointheSocietyorobtainfurtherinformation,contacttheExecutiveSecretary,ChallengerSocietyforMarineScience,Room251/20,SouthamptonOceanographyCentre,WaterfrontCampus,EmpressDock,SouthamptonSO143ZH,UK;Fax:+44(0)23-80-596149;Email:[email protected]

TheChallengerSocietyWebsiteiswww.challenger-society.org.uk

TheMagazineoftheChallengerSocietyforMarineScience

CONTENTS

NewsandViews

Anopportunityforhistoriansofscience:50yearsofSCORandtheIOCWarrenS.WoosterandSelimMorcos

Theversatilityofgiantalgalviruses:fromshuntingcarbontoanti-wrinklecreamWillieWilson

HiMom!What’sbeenhappening?MireilleConsalvey

NewsfromtheEFMSAssemblyatHelsingborg

YoungScientistNetworkRachaelShreeve

LaunchofEarth,EnvironmentandOceansNetwork(EEON)

ReportfromChallengerSocietyAGM

AttendingtheASLOSummerMeetingAngieMilne

Patterninginattachedorganisms:fromtigerbushtomusselbeds?JoGascoigneandJohanvandeKoppel

Deep-seafish:howresearchersaretacklingthechallengeofdecompressionAlanJamierson

Sealiceandseatrout:aresalmonfarmscausingincreasedparasitismonwildsalmonidsinScotland?PhillipGillibrand,DavidHay,MichaelPenstonandAlexanderMurray

BookReviews

OceanChallenge,Vol.14,No.2 15

Distributionsofplantsandsessileorganisms(i.e.thosethatlivepermanentlyattachedtoapar-ticularsubstrate(sand,rock,soiletc.)canbeextremelypatchy.Infact,patchinessissoubiquitousthatmostofusarenotlikelytoaskourselveswhyitexistsorwhatconsequencesitmighthave.Usually,itisassumedthatsuchpatchinessreflectspatchinessintheunderlyingenvironment–perhapsthereareareaswhichhavemorenutrients,waterorfood,trapmoreseedsorlarvae,oraremoreappropriateforattachmentorgerminationsites.

Thebedsofmussels(Mytilusedulis)inwhichwework,intheMenaiStraitinNorthWalesandintheDutchWaddenSea,occuronapparentlyuniformmud-andsandflatswithnoapparentvariationinanyofthefactorsmentionedabove.Nonetheless,theyareextremelypatchy(Figure1,overleaf),withareasofverydensemusselcoveralternatingwithbarepatchesofmud.Westartedtoaskourselveswhythisshouldbe.Ifthereislittlevariationintheunderlyingenvironment,whatiscausingthispatchiness?

Thepatchinessturnedouttobeevenmoreintriguingthanwethought,whenspectralanalysisofaerialimagestakenofthemusselbedsshowedthatthepatcheswereregularlyspacedratherthanrandom.Themusselshadspontaneouslyformedbands,somewhatsimilartothestripesofazebra,aboutthreemetresapartintheMenaiStrait,andsixmetresapartintheWaddenSea.Tofindoutmoreaboutregularpatterninginecologicalsys-tems,welookedatstudiesthatdescribesimilarphenomena.

Itturnsoutthatsortingintoregularspatialpat-ternsiscommonplaceinaparticulargroupofecosystemsthatincludearidvegetationintheAfrican,AustralianandMexicandeserts,peat-landsinSiberiaandCanada,anddiatombiofilmsonintertidalmudflatsinDutch,FrenchandBritishestuaries.Theseecosystemshaveanumberofcharacteristicsincommon,including:(1)auni-form,flatsubstrate(soilorsediment)and(2)anenvironmentstronglyshapedbyphysicalfactors.

Mostecologicalworkonself-organizedpattern-inginecosystemshasbeendoneinterrestrialvegetationsystemssuchasthewidespread‘tigerbush’,foundforinstanceinNigerandBurkinaFaso.Inthesearidsystems,wateravailability

istoolowforanevencoverageofvegetationtopersist.Thelocalvegetation,however,hasdevelopedaclever‘waterharvesting’strategy.Establishedplantsincreasetheinfiltrationofrain-waterintheirimmediatevicinitybecausetheirrootspenetrateandbreakupthesoil,andtheirleavesshadetheground,therebyreducingsurfaceevaporation.Thismeansthatonasmallspatialscale,plantsaremorelikelytoestablishandthriveintheimmediatevicinityofotherplants.Rainfallinthesearidcountriestypicallydropsinshortbutveryintenseshowersthatquicklysaturatetheuppermostlayerofsoil.Asaconse-quence,waterflowsoverthesurface,andclumpsofvegetationcan‘harvest’waterthathasfalleninthesurroundingarea.However,ascompeti-tionbetweenplantsforsoilwaterisverystronginthisenvironment,plantslivingatsomedistancefromsuchaclumpofvegetationaredeprivedofwater.Thiscombinationoflocalfacilitationbetweenplantsgrowinginclumps,butinhibi-tionofgrowthatlargerdistances,leadstoplantsarrangingthemselvesinpatches(onflatsurfaces)orbands(onslightlyslopingsurfaces),withbaregroundin-between.

Inotherecosystems,thedynamicsofsmall-scalefacilitation/large-scaleinhibitioncanbedrivenbyotherlimitingfactors,suchasnutrientsupplyinpeatlands,forexample(cf.Table1),buttheoverallprincipleisthesame.Itturnsoutthatthissamemechanismforpatternformationhasalsobeenproposedforanumberofnon-ecologi-calsituations,suchasthestripesofazebra,thepigmentationofseashellsandthechemistryofembryodevelopment!Theprinciplethatinter-actionbetweenprocessesactingatdifferentspatialscalescancauseregularpatterningwasfirstsuggestedbytheBritishmathematicianAlan

OceanChallenge,Vol.14,No.2 OceanChallenge,Vol.14,No.216

Turingbackin1952.(HeisbetterknownforbreakingGermancodesduringWorldWarII.)

Inordertotestwhetherthis‘Turing’mechanismcouldexplainthepatterningthatweobservedinourmusselbeds,oneofus(JohanvandeKoppel)developedamusselbedmodel.Heassumedthatlarge-scaleinhibitionaroseasaconsequenceofcompetitionforalgaewhileshort-rangefacilita-tionarosebecausemusselsonsoftsedimentbenefitfromattachingthemselvestoeachothertoavoidbeingwashedawaybythestrongtidalcurrentswhichoccurbothintheWaddenSeaandintheMenaiStrait.

Thismodeldidindeedpredictpatterning,bothinthemusselsandintheiralgal‘prey’intheover-lyingwater(Figure2),withpatternsinthemusselbedswhichlookstrikinglysimilartothepatternsthatweactuallyobservedinthefield(cf.Figure1).Oneparticularlyexcitingoutcomefromthismodelwasthepredictionthatself-organizedpatterninginmusselbedsincreasesmusselproductivity,relativetothatofahomogeneousbedstructure.Further-more,patterningallowsmusselstopersistatalgalconcentrationsthatwouldbetoolowformusselstosurviveinahomogeneousarrangement.Thusself-organizedpatterningmayhavegreatecologicalimportanceformusselsinsoftsedimentsystems.

Thenextstagewastotestforthehypothesizedinteractionbetweensmall-scalefacilitationandlarge-scalecompetitioninmusselbedsinthefield.Todothiswelookedatgrowthinrelationtodensityinreplicatemusselbedsonalargescale(20m×20msquaresofdifferentdensitiesofmussels)andonthesmallscale(0.25m×0.25m

Figure2Patterningwhicharisesoutofaspatialcompetition–facilitationmodelfor(a)musselsand(b)theiralgal‘prey’;thearearepresentedis25m×25mNotethatin(b)thedarkerareasaredepletedinalgaecomparedwiththelighterareas.In(a)themusselpatterninglooksstrikinglylikepat-terningweobserveinthefield(cf.Figure1).

Figure1Apatternedmusselbed(Mytilusedulis)intheMenaiStrait,NorthWales.

Inthemodel,interactionbetweentheeffectsofcompetitionforfood,andtheadvantagouseffectsofmusselsattachingthemselvestooneanother,resultsinamusselbedpatternverylikethatobservedinreality

Musselbedsmayshowpatterning,evenwhentheunderlyingsubstrateisfairlyhomogeneous

g m−2 g m−3

(a) (b)

OceanChallenge,Vol.14,No.2 OceanChallenge,Vol.14,No.2 17

Bycontrast,atthesmallscale,highdensitiesofmusselsmeanmoreshellgrowthinwinter

Table1Examplesoffacilitationofgrowthinrelationtophysicalstressinvarioussessilebiota.

System MechanismRelationwithphysicalstressorresourcelimitation

Regularpatterning?

MusselGeukensiademissa

Protectionfromhighsummertemperaturesindenseclumps

Changefromcompetitioninlowintertidalzonetofacilitationinhighintertidalzone

Notreported

MusselBrachidon-teslemilaevisandbarnacleChthalamusanisopoma

Densebarnaclesprotecteachotherandsmallmusselsfromhighsummertemperatures

Barnaclesurvivalandmusselrecruit-mentincreaseswithbarnacledensityafterexposuretohighsummertemp-eraturesatlowtide

Yes

AcornbarnacleSemi-balanusbalanoides

Protectionfromthermalstressindenseclumps

Strongcompetitioninlowintertidalzone,facilitationinhighintertidalzone

Notreported

Saltmarshplants AmeliorationofsoilsalinityandO2content

Changefromcompetitiontofacilita-tionalonggradientofincreasingsoilsalinity

Notreported

Intertidalalgaeonsilt

Reductioninsedimentshearstressbyalgae

Bimodaldistributionofsedimentsiltcontentandchlorophyll-ainareasofhighbottomshearstress,unimodalwherelowshearstress

Yes

Alpineplants Ameliorationofeffectsoflowspringtemperatures

Changefromcompetitiontofacilita-tionupaltitudinalgradient

Yes

Semi-aridecosystems(tigerbush)

Increasingsoilwatercontentbyshadingandrootpenetration

Facilitationstrongestindriesthabitats Yes

Peatlands Increasednutrientsupplywheretranspirationratehighest

Modelpredictspatterningwherenutri-entconcentrationslow,continuousvegetationwherenutrientconcentra-tionshigh

Yes

squaresofdifferentdensities).WestartedtheexperimentinAprilwithmusselsofequalmeansizethroughouttheexperimentalbed.Wedividedthedataintosummerandwinterdata-sets,toallowforunderlyingdifferencesinmusselgrowthrateswithseason.

Theresultsoftheanalysisweresurprising.Inthesummer,itwasveryclearthatcompetitiondominatedinteractionsbetweenmussels,atbothlargeandsmallscales.Highdensityalwayshadanegativeeffectonmusselgrowth,bothatthelargescaleandatthesmallscale(Figure3).Wecorrectedgrowthoverthewinterusingtherela-tionshipbetweengrowthanddensityobservedforSeptember,sothattheeffectofgrowthovertheprevioussummerwasremoved.Forthiswintergrowthincrementtherewasnosignificanteffectoflarge-scaledensity.However,small-scaledensityhadastrongpositive(facilitative)effectonwintergrowthincrement,bothforgrowthinshelllength(Figure4,p<0.0005)andmeatdryweight(notshown).Thismeansthatmusselsinhighdensityclumpsorpatches(withlotsofnearneighbours)growbetteroverthewinterthanmusselswithfewernearneighbours–asurprisingresult.Overall,wedidindeedhavelarge-scalecompetitionandsmall-scalefacilitationinour

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Figure4Shellgrowthoverwinter,plottedagainstmusseldensity.Here,wintershellgrowthhasbeendeterminedbysubtractingthegrowthovertheprevi-oussummer(calculatedusingtheSeptemberlength–densityrelationshipshownabove)fromthetotalgrowth.Forthiswintershellgrowthincrement,theeffectofsmall-scaledensityisreversed,withmusselsindenserquadratsgrowingmoreonaverageoverthewinter.Thesamerelationshipisseenformeatgrowth.

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Figure3ShelllengthinSeptember,plottedagainstmusseldensity.Musselssampledfromhigherdensityquadrats(0.25m×0.25m)hadlessshellgrowthoverthesummerthanmusselssampledfromlowerdensityquadrats(meatgrowthwasalsolesswheremusseslswereathighdensity).TheexperimentstartedinAprilwithmusselsofequalmeanlengththroughouttheexperimentalmusselbed,sodifferencesinlengthinSeptemberreflectdifferencesingrowthoverthecourseofthesummer.

Highdensitiesofmusselshaveastrongnegativeeffectonsummershellgrowth

OceanChallenge,Vol.14,No.2

patternedmusselbed–butthecompetitionandfacilitationwereseparatedintimeaswellasinspace,withcompetitiondominatingatallspatialscalesinsummer,butfacilitationbeingstrongatthesmallspatialscaleinwinter.

Itisinterestingtoaskwhythereshouldbeaswitchfromcompetitiontofacilitationatthesmallscaleonaseasonalbasis.Itisplausiblethatcompetitionshouldbereducedinwintersincelowerwatertemperaturesmeanthatthemusselsaremetabolicallylessactive.Butwhyshouldtherebepositivebenefitsfromahighlocalden-sityinwinter?Webelievethattheanswerliesinthephysicalandmechanicalstressesimposedonmusselsbythestrongerwindsandlargerwavesduringthewinter.Itiswellknownthatmusselsproducegreaternumbersofattachment(byssal)threadswhenwaveenergyisgreater,andalsothatbyssusproductioncantakeupasignificantamountofamussel’senergybudget.Itseemslikelytousthatonsoftsediment,wheretheonlyformofhardattachmentsubstrateisothermus-sels,musselsindenseclumpsmaysavesignifi-cantamountsofenergybybenefitingfromeachothers’byssalattachments.

Moregenerally,ourresearchfitsinwellwiththeliteratureonfacilitativeinteractionsinothersystemsofattachedorganisms.Itprovidesfurthersupportfortheideathatfacilitationismostlikelyinenvironmentsthatarephysicallystressful,andthatinteractionsmaychangefromcompetitiontofacilitationupagradientofphysicalstress(asfoundinthetransitionfromsummertowinterintheMenaiStrait).Wehavecompiledatablewhichshowssomeexamplesofthesetypesofinteractions(Table1).

Whatnow?Wearelookingforothersystemswhichmightshowsimilardynamics,astheprin-ciplesputforwardinourstudiesareturningouttobemorecommonthanwethought,inboththeintertidalzoneandthesubtidalzone.Forexam-ple,anintriguingimageofsubtidalhorsemusselsbeds(Modiolusmodiolus)offtheLleynPeninsulawaskindlyprovidedtousbytheCountrysideCouncilforWales(Figure5).Thispictureseemstoshowregularpatterningintheseorganismsaswell–wecan’twaittohaveacloserlook!

JoGascoigne*isapostdocattheSchoolofOceanSciences,UniversityofWalesBangor.Herspecialinterestsarepopulationdynamics,Alleeeffects,extinctionriskandconservationandtheinterfacebetweenbiologyandphysics.

JohanvandeKoppel†isatheoreticalecologistattheNetherlandsInstituteofEcology.Hisinterestsfocusontheimplicationsofpositivefeedbackforthedynamicsandspatialstructureofecologicalcommunities.Hecurrentlyintegratesmathemati-calmodelsandempiricalinvestigationsinordertounderstandthespatialstructureofestuarineecosystems.

*MenaiBridge,Wales,LL595AB.†CentreforEstuarineandMarineEcology,NetherlandsInstituteofEcology(NIOO–KNAW),POBox140,4400ACYerseke,TheNetherlands.

Figure5Aside-scansonarimageofsubtidalbedsofhorsemusselsModiolusmodiolusonasand/gravelsubstrate.Thesebedshaveadistinctivewave-formpattern,similartothepatterningofthemusselsintheMenaiStrait.(Thebanddownthemiddleistheship’strack;thediagonalbandmaybeatrawlingscar.)ImagebycourtesyofBillSanderson(CountrysideCouncilforWales)andIvorReesandJimBennell(UniversityofWalesBangor).

AcknowledgementsThankstoHelenBeadmanofNERC,CamilleSaurel,MichelKaiser,GwynneParry-JonesandIvorReesofUniversityofWalesBangorandKimMouldofMytiMusselsLtd.

Figure2isfromJ.vandeKoppel,M.Rietkerk,N.Dankers,andP.M.J.Herman(2005)Scaledepen-dentfeedbackandregularspatialpatternsinyoungmusselbeds.AmericanNaturalist165(3).

Figures3and4arefromJ.Gascoigne,H.Bead-man,C.SaurelandM.Kaiser(2005)Densitydependence,spatialscaleandpatterninginsessilebiota.Oecologia(inpress).

Patterningmaybecommonbelowthelow-tidemarkaswellasintheintertidalzone

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Modiolus modiolus reef


Sincetheearlydaysofdeep-seabiologyduringthepioneeringHMSChallengerexpedition(1872–76),ithasbeenapparentthatbringingdeep-seafishtothesurfaceresultsintheirdeath.Thereasonforthisistheeffectofdecompression:fishlivinginthedeepoceanhaveevolvedtosurviveatpressuresseveralhundredtimesgreaterthanthoseonland.Thishighpressureinhibitssimplelaboratoryexperimentsandimpedesattemptstoanswerthemostbasicbiologicalquestions.Scientistsarethereforeleftwithadilemma:dowestudytheseanimalsinthedeepseaatgreatexpense,ordowebringthemtothesurfacedead?Bothpathscreateimmensetechnologicalchallenges,manyofwhichhavebeensolvedwithgreatinnovationandimagination,withtheaimoffurtheringourunderstandingofthedeep-seacommunity.Discussedherearesomeofthereasonsourknowledgeofdeep-seafishlagsbehindthatofshallow-waterspecies,andsomeofthetoolsthattheresearchcommunityhavedevelopedtonarrowthegap.

Thelargestcomponentoftheworld’soceanisthedeepsea(2000–6000mdeep).Muchofthisoverliesthevastabyssalplains,characterizedbygentlyundulatinglandscapeswithanaveragedepthof4000m.Inhabitingtheabyssalplainsarethegrenadiersor‘rat-tails’(Coryphaenoi-desspp.ofthefamilyMacrouridae),knowntocontinuallyforage,swimmingimmediatelyabovetheseafloorinsearchoffood(Figure1,overleaf).Rat-tailsarethemostabundantfishinthedeepsea,andplayafundamentalroleinthedisper-saloforganicmatteronthedeepseafloorbyconsumingandscatteringanimalcarcases.Forthesereasonstheyhavebeenthesubjectofmanystudies,particularlyinthelast30years.

Researchingthesefishistechnicallyproblematicbecauseoftheremoteand(tous)hostilenatureoftheirenvironment,whichischaracterizedbylowtemperatures,absenceoflightand–inparticular–extremelyhighhydrostaticpressure.Whenrat-tailsarebroughtupfromtheirnaturalhabitattheyarekilledbytherapidchangesinpressureandtemperature.Asaresult,ourknowledgeofthesedeep-seafishisconsiderablylackingcomparedwiththatoftheirshallow-watercounterparts,forwhichsophisticatedlaboratoryexperimentsareeasilyundertaken.Describedherearesomeofthetechnicalsolutionsthathavehadtobedevel-opedtoallowustoanswereventhemostbasicbiologicalquestionsaboutthem.

EffectsofdecompressionIntherelativelyfood-scarceenvironmentofthedeepsea,grenadiershavealowmetabolicrateand,tooptimizeenergy-use,achieveneutralbuoyancybymeansofawell-developedswim-bladder.Thebladderisfilledwithgasbydiffu-sionfromthebloodviaabiochemicalmecha-nism.Forneutralbuoyancy,theinternalgaspressureistypicallyequaltotheambientpressure(400baronaverage).Incontrasttooil(usedinsharkbuoyancyregulation),gasisextremelycompressible,andthenatureofhigh-pressuregasswimbladdersdoesnoteasilyaccommodatetheexpansionofgaswhichresultswhenthefisharebroughttothesurface.Grenadiershavenoopeningintheswimbladder,andthereisnoconnectionbetweentheswimbladderandthroat.Therefore,whentheyneedtoriseinthewatercolumn,theymustresorbswimbladdergases,ifthevolumeoftheswimbladderisnottoincrease.Therateofgasexpansionversustheresorp-tionratedeterminestheseverityoftheeffectsofdecompression.Attheascentratestypicalofconventionalsamplinggear,apressuredecreaseof50barinducesuncoordinatedmovementandtremors,at100barconvulsionsoccur,andhigherratesstillresultinparalysisandnearlyalwaysdeath.Astheirgasbladdersexpandwithdecreas-ingpressure,deep-seafishfrequentlysufferstom-acheversion,whichoftenpushesotherinternal

19


organsoutthroughtheirmouths(Figure2)andinducesinternalbleeding.Similarly,internaleyefluidexpands,forcingtheeyesoutofthehead(cf.titlegraphic).However,itisthoughtthatifthedecompressionperiodislongenough(e.g.severaldays)fishcouldsurviveatatmosphericpressure.Withmostdeep-watersamplingtechniques(e.g.trawling),slowascentswouldbeimpractical:ascentratesaretypically50mperminute(apres-suredecreaseof~5barperminute).Alongwiththeeffectsofrapiddecompression,fishalsosufferthermalshockasaresultofthethetemperaturechangebetweenthecolddeepseaandsurfacewaters.

Tounderstandthebiologyandecologyofdeep-seafish,specimensmustbestudiedaliveaswellasdead–althoughinbothcasestherewillbeside-effectsofcapture.Therearebasicallythreewaystocounteracttheproblemsoffishdecom-pression.Thefirstistoobservedeep-seafishinthedeepsea;thesecondistodecompressthefishandmanagetheeffectsofcapture;andthethirdistobringtheanimalstothesurfaceunderpressure.

InsituresearchManytypesofinvestigations,suchasbehaviouralresearch,requirethatdeep-seafishbestudiedalive.Thiscurrentlyrestrictssamplingandobser-vationtoinsitustudies.Observationsandlimitedexperimentationcanbeundertakenusingautono-mousobservationplatforms,mannedsubmers-iblesorremotelyoperatedvehicles.Autonomousobservationsaremadepossiblebytheuseoflandersorfreevehicles(i.e.ROVs).Landersarenotattachedtotheship,andfreefalltotheseafloorwithpre-programmedphotographicorvideoequipmentmountedinsideaframe.Theyreturntothesurfacebyjettisoningballastweightsinresponsetoanacousticcommandfromasur-facevessel.Inthestudyoffish,baitistypicallypositionedinthefield-of-viewofthecameratoattractscavengers.Informationonabundance,depthdistribution,speciesassemblages,andinteractionsbetweendifferentspecies,isread-ilyobtainable.Longer-termplatformshavebeendeployedtoinvestigatetheconsumptionoflargerfoodsourcessuchasdolphincarcases,orofbaitintroducedperiodicallyinthestudyofseasonalpatternsandmigration.

Baitedlanderexperimentshavebeendeployedallovertheworldformanyyears,mostfrequentlyduringthelast10years,andwerepioneeredusingtheScrippsInstituteofOceanographyFVVlander(FVV=FreeVehicleVideo)andtheUniversityofAberdeenAUDOSlander(AUDOS=AberdeenUniversityDeepOceanSubmersible)inthe1980s(cf.Figure3).Unbaitedlong-termsystemshavealsobeenused,suchasBathysnap,developedattheInstituteofOceanographicSci-encesintheearly1980s.

Unbaitedsystemsofferaninsightintothenaturaloccurrenceofanimalstravellingacrosstheseafloor.Althoughthenumberoffishobservedmaybefarsmallerthaninabaitedexperiment,thereistheadvantagethattheanimalsrecordedarenotrestrictedtoscavengers.

Figure2Theeffectsofdecompressionondeep-seafish(mainlyrat-tails)takenfromadepthof4000minthenorth-eastAtlantic.Thefishsurroundingthedolphincarcasehaveinternalorgansprotrudingoutoftheirmouths,asaresultofswimbladdergasexpandingduringtheascenttothesurface.

Figure1Deep-seagrenadiersphotographedbyacameraonabaitedlanderinthenorth-eastAtlantic,atadepthof4200m.Asmallrat-tailisapproachingthebait,whilethelargefishintheforegroundisexploringthelander.(Thescalebarsshownare10cmapart,andthecamerais2mabovetheseafloor.)

Rat-tailsarethemostabundantscavengingfishinthedeepsea,andcangrowuptonearly1mlong

Decompressioninvariablyresultsindeathfordeep-seafishbroughtupbyconventionalsamplinggear


Imagesfrombaitedlandershaveprovidedusefulinformationabouthoworganicmatter(food)isfoundanddispersedonthedeepsea-floor

Figure3Deep-seagrenadiersobservedinsitu,feedingonadolphincarcaseat4000mdepthinthenorth-eastAtlantic.Whileforagingclosetothebait,thefishadoptahead-down–tail-uporientation,andusetheirsensitivetactileandgustatorysensestolocatetheirfood.(ThisvideoimagewasobtainedduringtheLargeAbyssalFoodFall(LAFF)project,whichinvestigatedhowlargecetationcarcasesare‘processed’inthedeepsea.)

Amajorlimitationoflanders,however,isthattheyremaininonesitethroughoutthedeploy-ment,anditisnotpossibletorespondtoevents,ormanipulatehexperimentsinrealtime.Mannedsubmersiblesandremotelyoperatedvehiclesdo,however,havesuchfacilities,albeitatfargreatercostandwithlimitedavailability.Thesepilotedand/orremotelycontrolledvehiclescansurveylargeareasofseafloor,locateparticularareasofinterest,andsampleandmanipulateexperimentalequipmentontheseafloor.Agreatdealofinfor-mationcanbeobtainedusingthesetechniques,whicharenon-destructiveand,comparedwithtrawlingforexample,arearelativelynon-invasivesamplingmethod.

MetabolicstudiesItisnotpossibletoanswerthequestion‘Whatisthemetabolicrateofadeep-seafish?’usingconventionallaboratoryexperiments,becausethefishdieduringcapture.In1978,DrKenSmithJnrfromScrippsInstituteofOceanographyinSanDiego,designedanexperimenttomeasuretheoxygenconsumptionofgrenadiersfromamannedsubmersible.Acylindricaldevicesuckedindi-vidualrat-tailsintoawatertightchamber.Thisallowedtheoxygenconsumptionofthefishtobemeasuredwhiletheanimalwasatitsnaturalpressure,provingforthefirsttimethatdeep-seafishhaveamuchslowermetabolismthantheirshallow-watercounterparts.

Buildingontheideaofmeasuringoxygencon-sumptioninsitu,theUniversityofAberdeen’sOceanlabdevelopedamorecomplexexperi-mentallandercalledtheFishRespirometerorFRESP.TheFRESPattractedgrenadierintoanareainviewofacameraand,onthebasisofexistingknowledgeofwhenpeaknumbersoccurredatthebait,awatertightboxwasdroppedoverthebaitcapturingfishinside(Figure4,right).Justthreeyearsago,thistechniqueachievedthefirstcom-pletelyautonomouscaptureandmeasurementofoxygenconsumptionofdeep-seafish,andatafarlowercostthanusingamannedsubmersible.Tocomplementthefindingsonmetabolicrate,

Aberdeenscientistsasked‘Whatisthemaximumenergyoutputofadeep-seafish?’,i.e.‘Howfastcanitswim?’Simplyobservingthefishdoesnotprovidesuchinformation,asinthefood-scarceenvironmentofthedeepseatheyoftenconserveenergybyswimmingveryslowly;andagainconventionallabexperimentsarenotpossible.TheSprintlanderwasdevelopedbyOceanlabtoanswersuchquestions.

TheFRESPlanderallowstheoxygenconsumptionofdeep-seafishtobemeasuredinsitu

Figure4TheFRESPlandertriggersawatertighttraptocapturegrenadiersandmeasuretheiroxygenconsumptiononthedeepseafloor.


TheSprintexperimentusedtwo1.5-metreelec-trodesplacedaroundbait.At60-secondintervalsanelectricalpulsestimulateda‘faststart’inthefish.Thiselectricshockwasnotenoughtoharmthefishbutenoughtotriggeranescaperesponse.Byfilmingthesesudden‘sprints’withahigh-speedcameraweobtainedfurtherinformationondeep-seafishphysiology.Thesophisticationofexperimentsthatcanbeundertakenfromland-ers,mannedsubmersiblesandremotelyoperatedvehiclesisincreasingallthetime.

ExsituresearchImperativeassuchresearchsurveysandinsituobservationandexperimentationare,itisoftenscientificallynecessarytophysicallyobtainspecimens.Photographicandvideoobservationsdonotpermitanalysisofchemicalcomposi-tion,dietcomposition,geneticsormorphology.Trawlingiscurrentlythemostcommonmethodofcapturingdeep-seafish,buttrawlingatabys-saldepthsisnotrivialtask.Thousandsofmetresofwarparerequiredtoreachthesedepths,whichlimitsthenumberofvesselscapableofundertakingsuchoperations.Inshallowwaters,trawlinggear‘herds’fishintothemouthofthetrawlwheretheyarecapturedwhentheytire.Indeepwater,wherethereisnolight,herdingisthoughttodiminishandso-called‘filtertrawling’occurs,withalmosteveryanimalinthepathoftheoncomingtrawlbeingcollected.Fishandotheranimalscapturedinatrawlaredrawnintothecod-endwheretheirdelicatescales,finsandprotrudingfeatures,someofwhicharerequiredforidentification,areoftendamaged.

Intheabsenceofalargevessel,fishcanbecap-turedwithoutdamagingthembyusingmooredfishtrapsdeployedinthesamemannerasland-ers.Fishtrapsarebaitedcageswithoneormorefunnelentrances,whichareelevatedabovethebottomandprotrudeintothetrap.Onceinsidethecage,fishtendtoexploretheinteriorstructureseekinganescaperoute,butareunabletolocatethefunnelsagain.Fishtrapsdonotsampleinthesamequantitiesastrawlingbuttheycanbedeployedfromsmallvessels,arerelativelycheap,

andrequireverylittleship-timetooperate.Trapsalsohavetheadvantagethattheylimitbycatch,andeliminateaccidentaldamagetocoralmounds,spongefieldsorotherbiologicalcom-munities,whichisoccasionallycausedduringdeeptrawlingforscientificpurposes.

Bothtrawlingandfunneltrapsprovidematerialforgenetic,morphologicalandchemicalcom-positionanalyses,butspecimensarestillsub-jectedtotheeffectsofdecompression.Stomacheversionduringdecompressionmakesitdifficulttoanswerthebasicquestion‘Whatdodeep-seafisheat?’Furthermore,althoughweknowthatscavengersconsumebaitplacedonlandervehicles,thesearenottypicalnaturaleventsandtherearespeciesofgrenadierthatrarelyapproachbaitandprobablysearchforlivefoodintheformofotherfishorsmallcrustaceansinorontheseafloor.Dietcompositionprovidesinsightsintopredator–preyinteractionsandforagingpatterns,andtheirinfluencesoncommunitydynamics.Suchanalysisisonlypossiblebyremovingfishfromthedeepseawithoutlossoftheirstomachcontents.

AseriesofnovelfishtrapsweredesignedbyJeffDrazenatScrippsInstituteofOceanographytosolvetheseproblems.Thetrapsconsistoflongplastictubeswithanopendooratoneendandapieceofbaitattheentrance,connectedtothetrapinteriorviaafishinghookonatensionedbungeecord.Asthefishtakesthebait,andthenpullsatitwhenitsnags,thebungeecordisreleased,thefishispulledintothetrap,andthedoorshutsbehindit.Thetrapsarerecoveredinthesamewayaslanders,andthefisharesub-jectedtotypicaldecompressioneffects.How-ever,thetrapsarefittedwithextremelyfinemeshfiltersoneitherendtoretainthestomachcontentsaftereversion.Thistechniqueprovidesarela-tivelycheapwayofretrievingstomachcontents.

Figure5Arat-tailwhosescaleshavebeenstrippedoffinthecod-endofatrawl.(Thefishisabout50cmlong).

Fishcapturedinatrawloftenlosescales,finsetc.,neededforidentification


intoapressure-resistantsphereandreturnedtothesurface.Thespherewascoupledtoare-cir-culationandfeedingsysteminthelaboratory,andthesmallfishwaskeptaliveatapressureof200barfor64days.Thehypothesisdrivingthistechniqueisthatdeep-seafishcanacclimatisetolowpressureifslowlydecompressedoverdaystoweeks,anditishopedthat,oneday,deep-seafishcanroutinelysurviveinanaquariumorlaboratoryenvironment.

DiscussionThemorewestudythedeepsea,themoreitthrowsoutnewquestionsthatneedtobeanswered–achallengethatthemarinesciencecommunityisalwayseagertoexplore.Arecur-ringthemeassociatedwithprovidinganswerstodeep-seabiologicalquestionsistheimmenseengineeringinputrequired.Experimentsoftenmakeuseofadvancedtechnology,devisedinresponsetobiologicalquestions.Thismulti-disciplinaryapproachhasbenefitedthesciencecommunityingeneral,andinparticularhasimprovedourknowledgeandunderstandingofthedeep-seaenvironment.Itistheambitionofdeep-seascientistsandengineersalikethatsoonthedeepseawillnotbeseenassuchahostileandproblematicareaofresearch,butanacces-sibleandreadilystudiedenvironment.

FurtherreadingBailey,D.M.,A.J.Jamieson,P.M.Bagley,M.A.Collins,I.G.Priede(2002)Measurementofinsituoxygenconsumptionofdeep-seafishusinganautonomouslandervehicle,Deep-SeaResearch,49,1519–29.

Drazen,J.C.,T.W.Buckley,G.R.Hoff(2001)ThefeedinghabitsofslopedwellingmacrouridfishesintheeasternNorthPacific,Deep-SeaResearch,48,909–35.

Koyama,S.,T.Miwa,M.,Horaii,Y.Ishikawa,K.Horikoshi,M.Aizawa(2002)Pressure-stataquariumsystemdesignedforcapturingandmaintainingdeep-seaorganisms.Deep-SeaResearchPartI,49,2095–2102.

Phleger,C.F.,R.R.McConnaughey,P.Crill.(1979)Hyperbarictrapoperationanddeploymentinthedeep-sea.Deep-SeaResearch,26A,1405–09.

Sebert,P.(2001)Fishathighpressure:ahundredyearhistory.ComparativeBiochemistryandPhysiology,PartA,131,575–85.

AlanJamiesonisapostdoctoralresearchfellowspecializingindeep-seatechnologyattheOcean-lab,UniversityofAberdeen*,UK.Heisprimarilyinvolvedinthedesignofhigh-pressurelandertechnologyforthestudyofdeep-seafish.

Email:http://www.abdn.ac.uk/oceanlab

*MainSt,Newburgh,Aberdeenshire,ScotlandAB416AA.

23

HyperbaricresearchAnalternativetoinsituandexsituresearchistobringdeep-seaanimalstothesurfaceunderhigh-pressureconditions.Thisraisesthebigques-tion:candeep-seafishbeacclimatisedtolowpressure?Thisisperhapsthemosttechnicallychallengingtaskofall.Justascamerasystemsandelectronicinstrumentationarehousedinstrongmetalpressurevesselstoresisttheambi-entexternalpressure,similartechnologycanbeusedtoretaininternalpressure.Thetechniqueinvolvesloweringanopenpressurevesseltotheseafloor,closingit,andreturningittothesurfacewhilstretainingthepressureatclosure,i.e.makingahyperbaricchamber.Thiswasfirstdoneusingasmallvesselforstudyingbacteriaandplanktonindeepseawater.Theideapro-gressedbyincorporatingbaitedfunnelsintotheopenvessel;smallcrustaceanssuchasscavengingamphipodswouldswiminsidethefunnels(similartothosedescribedabove,butsmaller)tolocatethebait.Thevesselwouldthencloseandreturntheamphipodstothesurfaceunderhighpressure.Usingthistechnique,physiologicalexperimentswereundertakenontheeffectsofdecompression/recompressionandmetabolism.SimilartrapsdevelopedbyIFM-GEOMARinGermanyarestillinuse,andnowincorporatetemperatureregula-tion.

Inthe1970s,thebasicprinciplesofthistech-niqueweredevelopedfurtherbyScrippsInstituteofOceanographyinlarger,moreelaboratetrapsforcapturinggrenadiers,andthebaitedbungeemethodofcapturewasagainusedsuccess-fully.Thetrapdesignincorporatedhigh-pressureviewportstoobservethebehaviourandhealthofcapturedspecimens,andhadcertainlimitedexperimentalcapabilities,suchasmeasurementoftheoxygenconcentrationofthewater.How-ever,difficultiesintotallysealingthechamberautonomouslyhaveledtomanyfailuresofthetrap.Also,thecompressibilityoftheequipmentasdictatedbythematerialpropertiestypicallyresultsinsomelossofpressure.

Thehyperbaricfishtraphasrecentlybeenre-designed,andthecurrentdesign,operatedbyMontereyBayAquariumResearchInstitute(MBARI),hasbeenusedwithsuccessonPacificgrenadiers.Thenewtrapascendstothesurfaceveryslowlytoallowforanyminordecreasesinpressurewithintheequipment.Duringprelimi-narydeploymentsofthetrapadeep-seafishwaskeptalivefor48hours,butlaterdeploymentshavemanagedtosustainalivefishfor80hours.

Simultaneously,anotherhyperbaricchamberdesignwasdevelopedinJapanbyJAMSTEC.*TheJapanesecapturemethodinvolvedtheuseofamannedsubmersible.Asmallzoarcidfish(alsoknownasaneelpout)wascapturedandplaced

*JAMSTEC=JapanMarineScienceandTechnologyCen-tre,nowtheJapanAgencyforMarine–EarthScienceandTechnology(IndependentAdministrativeInstitution).


Sealicearenaturallyoccurringparasiticcope-pods,partofthemarinezooplanktoncommunity.ThespeciesLepeophtheirussalmonisandCaliguselongatusoftheCaligidaefamilyareparticularlyprevalentonsalmonidsintheNorthernHemis-phereand,inthepast,theiroccurrenceonwildsalmonhasbeentakenasasignthatthefishhaverecentlybeentosea.However,thelargenumbersoffarmedsalmonkeptcloselyconfinedinmarinecageshaveprovidedabundanthostsforsealice,leadingtoenhancedlicepopulationsininshorewaters.Sealicefeedonhostmucus,tissuesandblood,andhighnumbersofparasitesonindi-vidualfishcanleadtoreducedgrowth,secondaryinfections,unsightlylesionsandlossofmarketvalue,andultimatelydeath(Figure1).SuchconsequencesofsealiceinfestationshavebeenestimatedtocosttheScottishfishfarmingindustryabout£15–30millionperannum.

Akeyquestioniswhetherthesealicepopulationsfoundonsalmonfarmshavecausedincreasedparasitismonthewildsalmonidpopulationsfoundintheriversandstreamsthatenterthesamecoastalwatersinwhichthesalmonfarmingindustryislocated.Or,alternatively,aresealiceretainedonthefarmswhereabundanthostsare

Overthepastthreedecades,thedevelopmentofsalmonfarmingintoamajorindustryintheHighlandsandIslandsofScotlandhasbeenofhugebenefittoemploymentopportunitiesintheseruralcommunities,andtotheScottisheconomyasawhole.However,withtheexpansionoftheindustryhascomerisingconcernaboutpotentialadverseenvironmentalconsequencesforthemarineecosystemsinwhichtheindustryisbased.Possibleimpactsrangefromthoseonlocalscales(e.g.theexportofcarbon-richfishwastesandchemicalsusedonfishfarmsites)towiderregional-scaleeffects(e.g.ahypothesizedlinkbetweendissolvednitrogenemissionsfromcagedfishandincreasedriskofalgalblooms).Overthepasttwentyyearsorso,considerableresearchefforthasbeeninvestedinunderstandinglocalimpacts,anddevelopingappropriatepredictivetools,andconsiderableprogresshasbeenmade.Morerecently,scientistshavebeenturningtheirattentiontolesstangibleregional-scaleeffects.Onesucheffectisahypothesized,butasyetunproven,linkbetweenthesealicepopulationsthathavebeenendemiconsalmonfarms,andinfestationsofliceonwildsalmonids(salmonandseatrout).DeclinesinwildsalmonidpopulationsinScottishriversoverthepastfewdecadeshavebeenattributedbysometoextremesealiceparasitismcausedbytheexpandingaquacultureindustry,althoughthedeclineshavebeenwidelyobservedinsalmonidpopulationsthroughouttheNorthAtlanticregion.

readilyavailable?Toanswerthatquestion,weneedtounderstandthelifecyclesandbehav-iouraltraitsofbothsealiceandwildsalmonidsinordertoassesshowthetwomayinteract.

Atlanticsalmon(Salmosalar)aremigratoryfishfoundinthetemperateandArcticregionsoftheNorthAtlanticandtheBalticSea.Atlanticsalmonspawninriversandtheyoungfishremaininfreshwaterfortheirfirst1–5years,beforeenteringthemarinephaseoftheirlifecycle.Thesmoltrun,whentheyoungfish(smolts)migratetosea,typicallyoccursinlatespring,fromApriltoearlyJune.Onceatsea,thesmoltsimmediatelybegintoheadforfeedinggroundsintheopenocean;feedinggroundsintheNorwegianSeaandoffsouth-westGreenlandareknown,andothersmayexist.Afterusuallyspendingseveral(1–4)yearsatsea,salmonreturntotheirhomerivertospawn.

Forthisstudy,ourmaininterestwasintheseatroutpopulationindigeneoustotheRiverShiel-daig.Seatrout(Salmotrutta)areamigratoryformofthecommonbrowntrout.ThelifecycleofaseatroutissimilartothatoftheAtlanticsalmon:followingaperiodoffreshwaterresidence,seatroutmigratetoseaassmolts.However,unlike


Sealiceaffectthehealthoffarmedsalmon,andreduceindustryprofits

Sealice,likemostcaligidcopepods,havealifecycleconsistingoftypicallytenstages:twofree-livingplanktonicnaupliarstages,oneinfectivefree-swimmingcopepodidstage,fourattachedchalimusstages,twopreadultstagesandoneadultstage(Figure2).Femaleadultsattachedtofishreleaseeggsintothewatercolumnwhichhatchintothefirstnaupliusstage.Theselarvaeareplanktonicanddriftwiththeprevailing

salmon,seatroutappeartoremainlargelyincoastalwaters,althoughintruthlittleisyetknownabouttheirpatternsofmovementalongthecoast.Thetendencytoinhabitinshorewatersmaymakeseatroutparticularlysusceptibletosealiceinfestationfromsalmonfarms.Likesalmon,afteraperiodatsea(usuallyayearorso),seatroutreturntotheirnativerivertospawn.

Figure1(a)Naturalsealiceloadonawildsalmon;(b)extremeeffectsofanuntreatedinfectiononafarmedsalmonin1990,beforecurrenttreatmentswereintroduced(lesionsandhaemorrhagingareclearlyseen);(c)sealousewithblood-filledgut.(©Crowncopyright)

Figure2Sea-licelifecycle.Theeggshatchintoplanktonicnauplii,whichdevelopintocopepodidswhichsearchforfishonwhichtolivefortheremainderoftheirlives.Thedifferentstagesareseparatedbymoultsofthehardexoskeleton.

(c)

(a)

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Onlythecopepodidstageofsealiceisabletoinfectfish

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ObservationsofsealicelarvaeOurfieldworkconcentratedonLochShieldaig,partoftheLochTorridonsysteminthenorth-westofScotland(Figure3).RiverShieldaigsupportsafishtrapinitslowerreaches,whichhasbeenestablishedtomonitorthelocalseatroutpopula-tionintheriver.Themonitoringestablishedthatseatrout,heavilyinfestedwithsealice,werereturningearlytotheriverwithouthavingspentsignificantperiodsoftimeatsea.Someofthesefishexhibitedveryhighliceburdens,enoughtocauseeventualmortality.Thisobservationsug-gestedthatthefishwereinfectedwithliceverysoonafterdescendingtheriver.Acoustictrack-ingstudieshaveshownthatintheperiodshortlyaftertheyenterthesea,post-smoltseatroutmoveinandoutwiththetide,swimmingintheinter-tidalzoneformuchofthetidalcycle.Itseemedpossible,therefore,thatitwasherethatseatroutwereencounteringsealiceinsignificantnumbers.

Samplingforsealicelarvaeincoastalwatersisnotstraightforward.Typically,lowlarvaldensi-tiesmeanthatinordertocatchasignificantnumberoflice,largevolumesofwaterhavetobesampled.Thetraditionalmethodofsamplingzooplanktonistotowaplanktonnetthroughthewaterfromaresearchvessel.Inordertocatchsealicelarvae,arelativelyfinemeshsizeisrequiredfortheplanktonnet,andgiventhatlargevolumesofwaterhavetobesampled,thenetstendtogetcloggedupwithotherplanktonanddetritusinthewater.However,wefoundthatthebestmethodwastotowasmallplanktonnetbehindaslowlymovingrigidinflatableboat.

Becauseitwashypothesizedthatsealicemightbeinfectingseatroutintheintertidalzone,plank-tontowswerefirstperformedintheveryshallow

26

LiceconcentrationsweresampledatsiteSintheintertidalzoneattheheadoftheloch,plussevenotherdeepersites

watercurrents.Thenaupliarstagesquitequickly(aboutthreetofourdaysat10°C)transformintocopepodids,whicharestillplanktonicbuthavesomeswimmingcapability.Copepodidstypicallysurvivefor2to8daysat5–15°Cinfullseawater,duringwhichtimetheymustlocateandattachtoahostfish.Theplanktonicphaseofthesealicelifecyclemaythereforelastaroundthreeweeks(althougholderlicemaybecomesenescent),duringwhichtimethelarvallicemaydisperseoverawidearea,dependingontheprevailingwatercirculation.Thekeytotheirsurvivalistofindandattachtoahostduringthisplanktonicphase,eitherafarmedorawildsalmonid.

Theroleoflarvaldispersioninthesealicequesttofindsuitablehostshasreceivedlittleattentionpreviously.DuringsamplingprogrammesinIrishcoastalwatersduringthe1990s,sealicelarvaewereonlyfoundconsistentlywithinandclosetosalmoncages,butwerealsofoundsporadicallyclosetorivermouths.Theresearchersfoundasignificantinverserelationshipbetweendistancefromafishfarmandlarvalnumbers,andcon-cludedthattherewasaveryhighretentionofsealicewithinthefishfarmcages,andthatthelicefoundclosetorivermouthswereaseparatepopulationassociatedwithwildsalmonandseatrout.Thisconclusionwasalsoreachedbyotherresearcherswhoarguedthatlicelarvaedevelop-ingonfishfarmswouldimmediatelyattachtothereadilyavailablereservoirofhostspresentinthecage.Thusitseemedthatsealicefromfishfarmswerenotrelatedtoparasitesfoundonwildfish.Morerecently,however,newstudieshavebeguntosuggestthatthepresenceofsalmonfarmsinlongnarrowfjordicinletsmayresultinincreasedinfectionpressureonwildmigratingsalmonids.

Figure3Ourstudysite,LochTorridononthenorth-westcoastofScotland.LicesamplingsitesareidentifiedasA–GandS.Thelocationsoftwofishfarms(site1andsite2)andRiverShieldaigareindicated.Themodeldomaincoverstheentireareashownataresolutionindicatedbythegridinthelowerleftcorner.

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watersattheheadoftheloch,nearthemouthofRiverShieldag(siteSonFigure3),withtheplank-tonnetbeingtowedeitherfromasmallboatorbywading.Samplingalongtheshorelinebeganin1999andhascontinueduntilthepresentday,withsamplingtypicallyperformedweeklyduringthespringandsummer,andmonthlyduringthewinter,althoughthishasvaried.Sampleswerecollectedfromfour‘sweeps’atdifferentlocationsattheheadoftheloch.

Theresultsfromtheshorelinesamplingfrom1999to2003areshowninFigure4.Thefirststrikingfeatureofthedataisthestrongbiannualsignal.SealicelarvaewerefoundinthelittoralzoneattheheadofLochShieldaigin1999,2001and2003,butwerenotfoundin2000or2002.ThenumberofsamplescollectedatthissiteeachyearandthenumberofdaysonwhichsamplesweretakenaregiveninTable1below.Thehighestestimateddensitiesrecordedwere33,94and143licem−3in1999,2001and2003respectively.ThesamebiannualcyclewasalsoobservedatanotherrivermouthsiteinUpperLochTorridonwhensamplingwasconductedthereduring2001–2003.

AsecondkeyfeatureofthedatawasthatnonaupliarstagesweredetectedatsiteS.AllsealicelarvaesampledweretheinfectiouscopepodidstageofL.salmonis.

Followingtheearlysuccessinsamplingsealicelarvaeattherivermouth,samplingintheopenwatersofLochShieldaigandUpperLochTorri-donstartedinautumn2001.Heresampleswerecollectedbytowingaplanktonnetbehindarigidinflatableboatatfivesites(A–E),withsitesBandDsoonbeingreplacedbyFandG.Repeattowsateachsitewereperformedwiththenetbeingtowedatdifferentdepthstoprovidesomeverticalresolutionintheresults.Theopenwatersamplingwasconductedweeklyunlessadverseweatherconditionsmadesmallboatworkimpossible.

Analysisofthe2001–2002datashowedthatpeakdensitiesintheopenwaterweretypicallymuchlowerthanthoseobservedattheshore-line;averagelarvaldensitieswerelessthan1licem−3comparedwithalmost60licem−3attheshoreline(Figure5(a)).Also,innotablecontrasttotheshorelinedata,bothnaupliarandcope-podidstagesofsealicehavebeenidentifiedintheopenwatersamples.Analysisoftheratioofnauplii:copepodidstagesateachsitesuggeststhattheratiodecreaseswithincreasingdistancefromafishfarm(Figure5(b)).

Figure4Resultsofthesealicesamplingattheshore-lineofLochShieldaig(siteS),showingnumbersofcopepodidsdetectedpercubicmetreofwaterfor1999–2003.Thesampleswerecollectedfromthree‘sweeps’alongtheshorelineattheheadoftheloch.The‘Year1’and‘Year2’labelsatthetopoftheplotrefertoyearsinthefishfarmproductioncycle(seetext).

Figure5Calculated(a)averagelarvaldensities(licem−3),and(b)nauplii:copepodidratio,fromsamplescollectedduringOctober2001–February2002.Notethattheaveragelarvaldensityattheshoreline(siteS)wastwoordersofmagnitudehigherthanvaluesintheopenwater(A–E).

Year Samplingdates nNo.ofdays

1999 03/05/99–02/08/99 24 82000 22/03/00–19/06/00 42 142001 15/03/01–10/09/01 54 182002 01/04/02–09/09/02 17 62003 07/01/03–16/07/03 42 14

Table1PlanktonsamplingatsiteSinLochShieldaig:dates,numbersofsamplescollected(n)andnumbersofdaysonwhichsampleswerecollected.

InterpretingtheobservationsThebiannualcycleofsealiceabundanceobservedattheshorelinesite(Figure4),andhintedatintheopenwaterobservations,closelymatchestheproductioncycleoflocalsalmonfarmsinLochTorridon.InScotland,salmonproductiontypicallyoccursoveratwo-yearcycle.Emptycagesarestockedwithyounglice-freesalmonsmolts,typicallyinearlyspring.Overthefollowing14–22months,thesmoltsgrowtofullsizemarketableadults,whicharethenharvestedoveraperiodofafewmonths.Thecagesarethenallowedtolie‘fallow’(empty)foraperiodoftime(typically6–8weeks)beforerestockingtakesplaceandtheproductioncycleresumes.Statisti-calstudiesofliceburdensonproductivesalmonfarmsinScotland,carriedoutatStrathclyde

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Sealiceabundanceinintertidalwatersfollowsthetwo-yearsalmonproductioncycle

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OpenwatersamplestypicallycontainedlowerdensitiesoflicelarvaethansiteS;sitesclosetofishfarmscontainedrelativelymorenaupliiandrelativelyfewerinfectivestages


University,havedemonstratedthatnumbersofL.salmonisarerelativelylowduringthefirstyearofproductionandrelativelyhighduringthesecondyear,whenthefishreachadulthood.Theyearsof1999,2001and2003,whenhighlarvallicenum-berswereobservedduringourstudy,allcoincidedwiththesecondyearoftheproductioncycleonlocalsalmonfarms.

Theshorelinedatafrom2001and2002werecross-correlatedwitharangeoftimelagsagainstrecordsoftheliceburdensonthenearestlocalsalmonfarm.Theseresultsshowedasignificant(p<0.001)correlationcoefficientofr=0.39forlagsof1and3weeks,suggestingthattheappear-anceofliceattheshorelinelaggedbehindfarmlicelevelsbythisperiod.Itisimportanttonote,however,thatthispositiveassociationbetweenfarmandshorelinelicelevelsisnotregardedasevidenceofcausality,sincebothmayhavebeendrivenbyexternalfactors.

AsshowninFigure5,analysisoftheopenwatersamplesrevealedtwointerestingfeatures:first,thattheaveragedensitiesoflarvalliceinitiallydecreasedwithincreasingdistancefromthelocalsalmonfarmsbutthenincreasedtowardtheheadoftheloch(sitesC,B,AandS);andsecond,thattheratioofnauplii:copepodidstagesdecreasedwithincreasingdistancefromthelocalfarm,fall-ingfromabout2.5atsiteCtozeroatsiteS.ThiscouldbeinterpretedassuggestingthatsiteC,withlargernumbersofnaupliarrelativetocopepodidstages,wasclosertothesourceofthelice,andsiteSfurtheraway.

Thesedataraisedasmanyquestionsastheyanswered.Whydolarvallicenumbersappeartobehighestatthemouthoftheriver,particularlyifthesourceisnotimmediatelylocal?Whatdrivestheaggregationofliceattherivermouth?Arebehaviouraltraitsinvolved,orisitpurelytheresultofphysicaltransportprocesses?Arelicelarvaereleasedbyadultfemalestocoincidewiththespringsmoltrun,orhastheyear-roundpresenceoffarmedsalmonfacilitatedcontinualbreeding?Whattriggersthereleaseofeggstringsbyfemaleadultlice?

Onewayofbeginningtoaddresssomeofthesequestionsisthroughcomputermodelling,whichcanhelpustointerprettheobservations.

Whatdothemodelsshow?Previousresearchershadconcludedthatsealicelarvaereleasedfromadultliceonfarmedsalmonwerelikelytoberetainedwithinfishcagesandwereunlikelytodispersefarenoughtoformpopulationsatthemouthsofrivers.WewantedtotestthatconclusionintheScottishcontext,andthereforeinvestigatedthedispersionoflicelarvaefromsalmoncages.Weusedathree-dimensionalhydrodynamicmodeltosimulatethewatercirculationthroughoutLochTorridonforperiodsofinterestduring2001–2003,whenlicesometimesappearedattheshorelinesamplesiteandsometimesdidnot.Inthisway,wecouldtrytounderstandwhatfactorswereinvolvedintheappearanceoflicelarvaeattherivermouth.Themodelcalculatedwatercurrentsatahorizontal

Figure6Surfaceflowfields(averagedoveratidalcycle)predictedbythenumericalmodelfortheLochShieldaigregion(notekeyarrowforcurrentspeed).(a)Asteadynorth-westerlywindof5ms−1givesrisetoweaklandwardsurfacecurrentsinLochShieldaig;(b)asteadysouth-westerlywindof5ms−1resultsinweaktransversesurfacecurrentsacrosstheloch;and(c)observedwindsproduceagyre-likecirculationintheLochShieldaigbasin,enhancingtheresidualtidalcurrentsgeneratedatthesillbetweenLochShieldaigandUpperLochTorridon.

(a)

(b)

(c)

Loch Shieldaig

UpperLoch Torridon

Outer Loch Torridon

Computedsurfacecurrentpatternsformedthebasisforthelicetransportmodel


resolutionof100mandat15differentdepthsinthevertical;thesecurrentfieldsweresavedeveryhalf-hour.Thewatercurrentswereforcedbythetideandwind.

Thecomputedcurrentfields(Figure6)wereusedtodrivealicetransportmodel.Thismodelsimu-latedthereleaseanddispersionofsealicelarvaefromspecifiedlocationsintheloch.Thesealice,whichwereassumedtobebuoyantandremaininsurfacewaters,asindicatedbytheobservations,arecarriedaroundthelochbytheprevailingcurrents,andalsodisperseasaresultofeddiesandhorizontalmixing(diffusion).Weusedrealobservedwindspeedsanddirectionsinordertotryandreproduceobservedevents.However,someofthemostrevealingresultstodatehavecomefromsimplertestsusingsteadywindspeedsfromfixeddirections.Thesesimulationsallowustoasseshowlicemaydispersefromvariousreleasepointsunderdifferentenvironmentalconditions.

Figure7showstheresultsofselectedmodelruns.Here,liceparticleshavebeenreleasedfromalocationinLochShieldaig(indicatedbythetriangle),andtheirtransporthasbeentrackedfor15days(sincecopepodidsmayonlybeviablei.e.infective,forthislengthoftimeafterhatch-ing).Theplotsshowrelativeinfectionriskforfishresidentindifferentmodelboxesoveramodelrun,assumingthatriskisproportionaltocon-centrationofinfectiveparticlesmultipliedbythetimeoverwhichinfectioncouldoccur.Thethreeplotsshowdispersionoflarvaeresultingfromanorth-westerlywind,asouth-westerlywind,and

arealobservedwindtime-series(cf.Figure6).Mostnotably,underanorth-westerlywind,thelarvaehugthesouth-westcoastofLochShieldaigandaretransportedtotheheadoftheloch,wheretheyaggregate(Figure7(a)).Aggregationunderpurelyphysicalforcingispossibleinthemodelsimulationsbecausethelarvaeareassumedtobepositivelybuoyantandthereforeremainonthewatersurface,evenwhenwaterisbeingdown-welled,asmayoccurattheheadoftheloch.Deadlicesink,andthereforethelicemustbeviablewhentheyformsuchconcentrations.

Underconditionsofsouth-westerlywind,thelarvaearetransportedintotheupperbasinofLochTorridon,andsomearecarriedalmosttotheheadoftheloch,some16kmaway(Figure7(b)).Theseresultsdemonstratethat,undersuitableconditions,viablelicelarvaecanbetransportedmanykilometresfromthesource.Whetherdensi-tiesofliceatthesedistancesaresufficienttoposeaseriousinfectionrisktowildfishpopulationsisunclear.Thissimulationalsodemonstratesthattransferoflicelarvaebetweensealochbasinsisentirelypossible,andthatneighbouringsalmonfarmsarecapableofinfectingeachother.Inthecaseofrealwindforcing,thelicelarvaearedispersedthroughoutLochShieldaig(Figure7(c)).Thiswouldseemtoraisethepossibilitythatseatroutsmoltsmigratingtoseaduringthistwo-weekperiodwouldencounterinfectivelice,thoughnotnecessarilyinthehighdensitiesthatmightresultfrompersistentnorth-westerlywinds.

Thecleardependenceoflicetransportonwind-drivensurfacecurrentsinthesesimulationsmay

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Thelicetransportmodeldemonstratesthatlicemaydisperseoversignificantdistances,andthatneighbouringsalmonfarmsmayre-infectoneanother

Figure7ResultsfromthelicetransportmodelinwhichparticleswerereleasedfromSite1inLochShieldaig.Concentrationsofcopepodidsonlyareshown(i.e.notnauplii).Theparticlesweresubjectto(a)north-westerly,(b)south-westerlyand(c)(bottomleft)observedwindforcing.Theoutputisinunitsofparticletimestepspergridsquare,forexample10particletimestepscouldmeaneither10copepodidsenteragridsquarefor1timestep,or1copepodidispresentfor10timesteps(orsomeintermediatecombination).

(b)

(a)

(c) Loch ShieldaigLoch Shieldaig

Upper Loch Torridon

Loch Shieldaig

29

0


explainsomeoftheanomaliesofthedatasetfromthemouthoftheRiverShieldaig.Occasion-ally,whenegg-bearingfemaleliceareabundantonthelocalsalmon,licedonotappearattheshoreline;conversely,licehaveappearedattheshorelineinsignificantnumberswhenliceburdensonthefarmwererelativelylow.Thiscouldindicatethattheshorelinelicepopulationisdistinctfromthefarmpopulation,oritcouldbeasignthattheshorelinepopulationdensitiesarecontrolledbytheprevailingwindconditionsatthetime.Themodellingresultstodatesuggestthatlicenumbersattheheadoftheloch(indeed,throughouttheloch)atanyonetimearestronglydependentonwindconditions,andthattheseresultinsporadicpeaksinthepopulationatanygivenlocation.Certainly,themodelresultssug-gestthatalinkbetweenfarmliceandshorelinelicepopulationscannotbediscounted.Workcontinuestorefineandimprovethemodels,incorporatingphysicalcharacteristicssuchastheimpactoffreshwaterinputs,andtheeffectsofdif-ferentassumptionsaboutturbulenceondispersal,aswellasbiologicalcharacteristicsofsealicelarvae,suchasspawning,verticalmigration,andviabilityunderdifferenttemperatureandsalinityregimes.Datatoinformthesedevelopmentsarealsobeinggathered.

Whatdoesthefuturehold?Inrecentyears,salmonfarmersinScotlandhavebeenabletousesomenewlylicensedtreatmentagentsthatseemtobemoreefficaciousagainstallstagesofsealicethanthemedicinesthatwerepreviouslyavailable.Itishopedthatstrategicuseofthesenewproductswillassistsalmonfarm-ersincontrollingtheliceburdensontheirfarms,reducingproductioncostsand,intheprocess,reducingtheparasiteriskforwildsalmonandseatroutpopulationsfromScottishrivers.

ThroughoutScotland,thebattleagainstsealiceinfestationsonsalmonfarmsisalsobeingtakenforwardthroughtheestablishmentofAreaMan-agementGroups(AMGs)andAreaManagementAgreements(AMAs).Thesevoluntaryconcordatsbetweensalmonfarmersandrepresentativesofthewildfishinterestsinlocalisedstretchesofwater(e.g.individualsealochs)facilitateinfor-mationexchangeonliceburdensandpromotecoordinatedsealicetreatmentsbyfarmers.Pastresearch,whichhasbeencorroboratedbythepresentstudy,showsthatfarmsinsharedwatercanquicklyre-infecteachotherwithliceiftheydonotalltreatatthesametime.Strategictreatments,usingthenewlyavailablemedicines,mightfinallybringthesealiceproblemonsalmonfarmsundercontrol.

SamplingforliceinLochShieldaigandLochTor-ridoncontinues.During2005,thesalmonfarmsinLochTorridonareinthesecondyearoftheirproductioncycle,whenpreviousevidencewouldpointtoheavyliceinfestations.ThelocalAMAhasledtoareductionoftheliceburden,bothonthefarmedsalmonandontheindigenoussalmonids.Atpresent,thelicelevelsinLochShieldaigandLochTorridonareatthelowestlevelsinanysecondyearofproductionsincesamplingcommenced.Themonitoringbeingconducted

by FisheriesResearchServices(FRS)willhelptoestablishthesuccessorfailureofthisstrategyinthefuture.

Intermsofthesurvivalofseatroutandsalmonpopulations,itisclearthatparasitismisjustoneofmanythreatsthatsalmonidfishfacewhentheymigratetosea.Increasingpredatornumbers,warmingcoastalandoceanicwaters,marinepol-lution,commercialfishingandfoodshortagesarejustsomeofobstaclesthatthesefishmustsurviveandovercomeinordertoreturntotheirnativerivers.Tacklingthesealiceproblemmayimprovesurvivalchancesalittle,butthethreattowildfishgoesfarbeyondourinshorewaters.

AcknowledgementsMuchoftheshorelinesamplingatLochShieldaigwasperformedandmanagedbyMaggieMcKibben,whohassincemovedontootherthings.SheandMichaelPenstonwereablyassistedinthefieldbyJasonMiltonandColinBlyth.Thesamplingduring1999wascarriedoutbySallyNorthcott,AndyWalkerandAlastairThorne.RobFryerhelpedwiththestatisticalanalysisofthedata.

Furtherinformation/FurtherreadingAtlanticSalmonFederation:http://www.asf.ca/Nasco/nasco2001/index.html;

AtlanticSalmonTrust:http:/www.atlanticsalmontrust.org/

Butler,J.R.A.(2002)WildsalmonidsandsealouseinfestationsonthewestcoastofScotland:sourcesofinfectionandimplicationsforthemanagementofmarinesalmonfarms.PestManagementScience,58,595–608.

Costelloe,M.,J.Costelloe,N.Coghlan,G.O’DonohoeandB.O’Connor(1998)DistributionofthelarvalstagesofLepeophtheirussalmonisinthreebaysontheWestCoastofIreland.ICESJournalofMarineScience,55,181–7.

Johnson,S.C.,J.W.Treasurer,S.Bravo,K.NagasawaandZ.Kabata(2004)Areviewoftheimpactofparasiticcopepodsonmarineaquaculture.Zoo-logicalStudies,43,229–43.

Krkosek,M.,M.A.LewisandJ.P.Volpe(2005)Trans-missiondynamicsofparasiticsealicefromfarmtowildsalmon.ProceedingsoftheRoyalSocietyB,272,689–96.

McKibben,M.A.andD.W.Hay(2004)DistributionsofplanktonicsealicelarvaeLepeophtheirussalmo-nisintheinter-tidalzoneinLochTorridon,WesternScotlandinrelationtosalmonfarmproductioncycles.AquacultureResearch,35,742–50.

Murray,A.G.andP.A.Gillibrand(inpress)ModellingsalmonlicedispersalinLochTorridon,Scotland.SubmittedtoMarinePollutionBulletin.

Pike,A.WandS.L.Wadsworth(1999)Sealiceonsalmonids:theirbiologyandcontrol.AdvancesinParasitology,44,234–37.

Penston,M.J.,M.McKibben,D.W.HayandP.A.Gil-librand(2004)Observationsonopen-waterdensi-tiesofsealicelarvaeinLochShieldaig,WesternScotland.AquacultureResearch,35,793–805.

Revie,C.W.,G.Gettinby,J.W.Treasurer,G.H.Rae,andClark,N.(2002)Temporal,environmentalandmanagementfactorsinfluencingtheepidemiologi-calpatternsofsealice(Lepeophtheirussalmonis)infestationsonfarmedAtlanticsalmon(Salmosalar)inScotland.PestManagementScience58,576–84.

30


PhilipGillibrandisaphysicaloceanographerandmodellerworkingattheScottishAssociationforMarineScience(SAMS)*inOban,Scotland.Hisresearchonphysicalprocessesincoastalwatersincludesmodellingmechanismsofmixingandexchangeinfjords,thedispersaloflarvaeandcontaminants,andthelinkbetweenfjordbasinwaterpropertiesandchangingclimate.Email:[email protected]

*ScottishAssociationforMarineScience,Dunstaff-nageMarineLaboratory,Oban,Argyll,PA371QA.

DavidHayisafisherybiologistworkingattheFisheriesResearchServicesFreshwater(FRS)LaboratoryinPitlochry,Scotland.Hehasworkedwithsalmonandseatrout,andiscurrently

involvedinaprojectonthewestcoastofScotlandstudyingthemarinesurvivalofseatrout,withtheeventualaimofrestoringtheseatroutpopulationintheRiverShieldaig.

MichaelPenstonisaplanktonbiologistattheFisheriesResearchServicesMarineLaboratoryinAberdeen,Scotland.Hismaininterestisexploringdistributionsanddynamicsofsealicelarvaeinthecoastalenvironment.

AlexanderMurrayisanepidemiologicalmodellerattheFisheriesResearchServicesMarineLaboratoryinAberdeen,Scotland.Hisinterestsinmodellingthespreadoffishdiseasesandparasitesincludethedispersalprocessesofpathogensinthemarineenvironment.

31

balancedandclearcontentifnotforitsliterarystyle.

WehaveusedGrantBigg’sbook(firstandsecondeditions)forfouryearsasthestandardtextina24-lectureundergraduatemoduleon‘OceansandClimate’(thisisaThirdYearmoduleinthefour-yearMarineScienceBSc.programmedeliveredbySAMS).Thereisstillnootherbooklikeit,andIwillcontinuetorecommenditasacoretext.

MarkInallLecturerinMarinePhysicsScottishAssociationforMarineScience

Continuedoverleaf

systems,thequalityoffigurerepro-ductionleftmuchtobedesired.Thissecondeditionismostwelcome,and,withafewexceptions,thefigureshavebeengreatlyimproved.ThereremainsomeminorerrorsintheGlossary,e.g.definitionsofchlorophyllandprimaryproduction.Overall,though,thetextcontinuestobeauniquelyaccessiblegeneralclimatesystemtextandIwouldrecommendedittoallenvironmentalscienceundergraduatesandinterestedlaypersonsalike.Itprovidesthereaderwithanaffordableintroductiontoavastarrayoftopics,broughttogetherunderthebannerofoceansandclimate.Newsectionsonrecentdevelopmentsinourunderstandingofabruptchangesinclimatebringthetextuptodate.Thebookisauthoritativeandyetpaintsabalancedviewofthecomplexityoftheclimatesystem,drawingfromahugerangeofsourcematerial.Carefulselectionof‘furtherreading’materialisgivenonachapterbychapterbasis.

Thebook’smainweaknessliesinitsboldattempttocoversuchawideanddiversetopicatanintroductorylevel.Oftenoneisleftfindingthegivenexplanationincomplete–forexampleintheexplanationoftheCoriolisforceonlyahintisgivenofthevitalelementoftheEarth’soblatespheriodshape.Ontheotherhand,somelackofdetailisnotnecessarilyabadthing,giventhewellchosenlistsoffurtherreading.Morecritically,thebookcanseemalittlelostattimes,lackingacoherentthreadrunningthroughout:acollec-tionofinterestingfactsandideas,nottightlywoventogether.Thatsaid,itisatextbook,andshouldbepraisedforits

TheOceansandClimate(secondedi-tion)byGrantBigg(2003).CambridgeUniversityPress,273pp.£27.95(flexi-coverISBN0-521-01634-7)(hardcovernolongeravailable).

InthesecondeditionofOceansandClimate,GrantBigghasthoroughlyrevisedandupdatedthesuccessfulfirstedition.Bothaccessibleandcompre-hensive,OceansandClimateman-agestocapturethecomplexityofourclimatesystem,withoutoverwhelmingthereaderintechnicaldetail.Start-ingwithverybroadbreakdownoftheclimatesystemintofivecomponents(Atmosphere,Oceans,Cryosphere,Bio-sphere,andGeosphere),theintroduc-torychaptergoesontoemphasizethekeynotionsoffeedbackmechanismsandmultipletime-scales.Thisintroduc-tionlaysthefoundationsforchaptersondiscipline-basedocean/atmosphereinteractionprocesses(physical,chemi-calandbiological),whicharebroughttogetherinachapterof‘casestudies’oflarge-scaleair–seainteractionphe-nomena.Thejigsawofnaturalclimatevariability,stretchingbacktoPalaeo-zoictime,isthenpiecedtogetherwithincreasingdetailthroughtheQuater-naryandHolocene,andthroughtheinstrumentalrecordsofthelatetwen-tiethcentury.Onlyatthispointarediscussionsregardingsignalsofnaturalandanthropogenicclimatechangeraised,andthisfinalchapterisprobablytheonemostreaderswillreturntoforreference.

Whilstthefirsteditionfilledaprevi-ouslyunoccupiednicheforintroduc-toryundergraduatetextsonclimate

Book reviews

Noteforenthusiastsofthehistoryofoceanography

ThenextissueofOceanChallengewillincludereviewsoftheproceedingsoftwoconferencesconcerningthistopic:ACenturyofDiscovery:AntarcticExplorationandtheSouthernOcean(seep.13)andOceanSciencesBridgingtheMillennia:aspectrumofhistoricalaccounts(ProceedingsoftheSixthInternationalCongressontheHistoryofOceanography)(seep.7).


ChangingSeaLevelsbyDavidPugh(2004)CambridgeUniversityPress,265pp.,£70(hardcover,ISBN0-521-82532-6)and£30(flexicover,0-521-53218-3).

IwasalittlesurprisedwhenIwasaskedtoreviewthisbookafewmonthsago,asIamcertainlynoexpertontidesandsea-levels.However,thisisnotabookaimedatexperts,butratheratthosewishingtolearnaboutthesubject,astatuswithwhichIwassomewhatmorecomfortable.Havingworkedinocean-ographyfor13yearsnow,itwouldbelamentableifIhadnotpickedupatleasttherudimentsofthesubject,andIconsidermyselfatleastknowledgeableenoughtoavoidtheembarrassmentofbeingcaughtoutbythetidewhilework-ingforanestablishmentthatwasonceknownas‘TheLiverpoolTidalInstitute’.

ThefinedetailofthesubjectisalargeandvariedfieldforwhichDavidPughprovidesanicelybalancedoverview,andinreadingthebookIwaspleasedtoseeclearexplanationsoftheinevitablescientificterminologythatisroutinelythrownaroundintheliteratureandatconferences,someofwhichIknew,andsomeofwhichIthoughtIknew.ForthosereadersunfamiliarwiththeworkofDavidPugh,Ishouldaddthathehasalsopublishedthemoreprofession-allyoriented1987bookTides,SurgesandMeanSea-Level:Ahandbookforengineersandscientists(nowoutofprintandveryhardtofindsecond-hand)andisanauthoronover150scientificarticlesrelatedtothesubject.

Thebookbeginsgentlywithanintro-ductiontothehistoryoftidalrecordingandthevariouswaysofrecordingthelevelofthesea,ataskwhichintheshorttermcanbeconsideredasthemeasure-mentoftides,butwhichinthelongertermcanbeusedtodeterminemeansea-levels.Themeasurementmethodsdescribedrangefromoldfashionedfloattidegaugesthroughtothelatesttech-niquesusingsatellitealtimetry.

Thebasicphysicsofthetidesareclearlyexplained,includingaworkedexampledetailingtheanswertotheeverpopularinterviewquestion:whyaretheretwotidesperday?Thebalanceofcon-

ceptualexplanationstomathematicalcontenthasbeenpitchedjustrightforundergraduatelevel.Themathematicsincludedinthisbookhavebeenkepttotheminimumnecessarytosupporttheconceptualdescriptionsandnumerousdiagrams,withseveralmoredetailedtechnicalappendicesattheendofthebookandothersavailablefordownloadfromtheCambridgeUniversityPresswebsite,alongwithelectroniccopiesofanumberofthefiguresforuseasteach-ingaids.

Tidalanalysisandpredictionarecov-eredinsomedetail,withreferencetoboththeanalysisofpointmeasurementsfrominstrumentssuchastidegauges,andtheanalysisofspatiallyvariabledatasuchasthosegeneratedbysatelliteobservations.

Thetopicalsubjectsofsea-levelchangesduetotheweatherandotherextremeeventssuchastsunamisarealsocovered,withdiscussionofanumberofexamplesoflowlyingcoastalareassubjecttoinundationbyhurricanesandtsunamisaroundtheworld.SincethiswaswrittenpriortotheSumatratsunamiofDecember2004theexamplesarefromearliereventsthatwillnodoubtbealmostforgotteninlightofthatmorerecentdisaster.Inaddition,thetableofhistoricalstormsurgeeventsputsintocontexttheseverityoftherecentHurricaneKatrinathathitMississippiinAugust2005,whichhadanestimatedstormsurgeofbetween7and10m,rankingitamongsttheworstonrecord.

Risingmeansea-levelsarediscussedwithreferencetosomeofthelongesttidegaugerecordsheldbythePerma-nentServiceforMeanSeaLevel.Theseincludeseveralrecordsthatappearatfirstsighttoshowfallingmeansea-levels,whichareexplainedbythefactthatinthoselocationsthelandisuplift-ingfasterthanmeansea-levelisrising.Thisinturnemphasizestheimportanceofmeasuringandaccountingforverticalmovementsofthelandonwhichthedatumsrest,whendeterminingabsolutesealevels.

Thequestionofwherethe‘extra’volumeofwateriscomingfrommakesfascinatingreading,withassessments

ofthecontributionstomeansea-levelrisefromthethermalexpansionoftheoceansandthepossibleeffectsofmeltingicesheets;surprisingly(tome),theamountofwaterheldinreservoirsaroundtheworldaccountsforasignifi-cantvolumeofthewaterremovedfromtheoceanbudget.

Thesectiononfloodrisksdemonstratestheimportanceoflongtime-seriesofhighqualitymeasurementsforassessingtheprobabilitiesofextremeevents.Themethodsforcalculatingtheprobabilitiesofsucheventsfromtidalrecordsaredescribed,andthedifferencebetweenthedesign-lifeofastructureandthereturnperiodofafloodeventprovideastarkreminderofthepitfallsofmis-understandingtheuseofsuchprobabil-itystatistics.Theimpactofevenmodestsea-levelriseonthereturnperiodoffloodeventsisshowntobeasignifi-cantissueforlow-lyingcoastalareasineconomicterms,whiletheecologicalimpactsincludelossofwetlandsandtheinabilityoftheslowgrowthrateofcoralreefstokeepupwithpossiblefuturesea-levelrise.

Thefinalchapterofthebookfocussesontheinfluenceofthetideonavarietyofphysicalandbiologicalsituations,fromtidalinletstothetimingoffishspawningsandhatchings.Thereisalsoaninterestingdiscussiononthechangesintidalamplitudesandphasesthroughrecentgeologicalhistory,andtheeffectthatthegraduallywideningEarth–Moonseparationmayhavehadonthetidesoverthepastfewmillionyears.

Ihaveusedagreatmanytextbooksinmycareer,bothasastudentandprofessionally.Thereadabilityofthosetextbooksvariedwidely,fromthosethatalmostmademelosethewilltolive,tothosethatfiredmyimaginationwiththeeleganceofthenaturalworld.DavidPugh’sbookonsealevelsisawellwrit-ten,wide-rangingandup-to-datebookthatIfoundinterestingtoread,raisedtheoddeyebrowandmademethink.Icangiveitnobetterrecommendationthanthat.

PaulS.BellProudmanOceanographicLaboratoryLiverpool

Advancewarningforphotographers...ThesubjectforentriesforthePresident’sPhotographicPrize,

tobejudgedattheChallengerConferenceinOban,inSeptember2006,

willbe‘Flotsamandjetsam’

volume 14, no. 2 · 2018-04-04 · 16 ocean challenge, vol. 14, no.2 ocean challenge, vol. 14, no....

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