Ecology of the New Zealand Rocky Shore Community

Transcription

1 Ecology of the New Zealand Rocky Shore Community A Resource for NCEA Level 2 Biology Darren Smith

2 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Author:DarrenSmith Publisher:NewZealandMarineStudiesCentre Address:185HatcheryRoad,Portobello,Dunedin9014 ISBN:978O0O473O23177O4(PDF) ISBN:978O0O473O23176O7(Softcover) January2013

3 FOREWORD The New Zealand Marine Studies Centre launched a nationwide citizen science projectinseaweek2013.anyonecantakepartinthisprojectwhichaimstomonitor biodiversityandchangesinthenewzealandseashore over time. There are two waysoftakingpartintheproject 1. Marine Metre Squared is a simple way for individuals, families, schools and communitygroupstomonitortheshore. 2. Seashore Survey is aimed at secondary school students to tie in with NCEA standards. This resource book is intended to assist teachers of NCEA Level 2 biology to carry outstudiesofthenewzealandrockyshore. Darren Smith developed this resource when he was on the Endeavour Teacher Fellowship,NewZealandScience,MathematicsandTechnologyTeacherFellowship Scheme This scheme was funded by the Ministry of Science and Innovation andadministeredbytheroyalsocietyofnewzealand.darrensmithwashostedby thenewzealandmarinestudiescentre,departmentofmarinescience,universityof Otago. ForfurtherresourcesandinformationabouttheMarineMetreSquaredprojectgoto mm2.net.nz Wewelcomeyourcommentsandsuggestions. Please marineOstudies@otago.ac.nzorphone

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5 CONTENTS PART1: LifeontheRockyShore Introduction BiodiversityontheRockyIntertidalShore TheIntertidalZones TheAbioticEnvironment TheBioticEnvironment Zonation AdaptationstoLifeintheIntertidalZone:CopingwithStress...12 PART2: SurveyingtheRockyShore Introduction:WhyStudytheRockyIntertidalShore? HowtoCarryOuttheShoreSurvey EquipmentList SurveyMethod PART3: ABriefGuidetoSeashoreSurveys Introduction Transects Quadrats PART4: TheTides...35 BIBLIOGRAPHY...40 APPENDIX1 SurveyDataSheet...41 APPENDIX2 InternalAssessmentResource...44 APPENDIX3 Glossary...52

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7 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology PART1:LIFEONTHEROCKYSHORE 1.1 INTRODUCTION New Zealand has approximately 14,000 km of coastline consisting of rocky shores, shelteredestuarinemudflats,andbeachesofloose,mobilesedimentslikesandand gravel. Our coasts experience a regular, dramatic change in sea level caused primarilybytides.onthenorthandwestcoastsofthesouthislandsealevelsmay fluctuatebyupto4mbetweenthehighandlowtides.onaveragenzexperiences twohightidesandtwolowtidesperday.theintertidalzone,sometimescalledthe littoralzone,istheareaoftheseashorethatisregularlycoveredbytheseaduring hightidesandexposedtotheairduringlowtides. Theorganismslivingbetweenthetidesaretruemarinecreatures,yetareuniquely adapted for life at the interface between the land and the sea. As marine species theyneedtobesubmergedinseawaterforatleastapartofthetidalcycletofeed, respire, excrete, and reproduce and disperse their offspring. However, like terrestrialspecies,theyalsoneedtobeabletosurvivetheharshconditionsthatgo withregularperiodsofexposuretotheairwhentheyareuncoveredbythefalling tide; these include wide variations in temperature, salinity, ph and oxygen availability; being battered by wind and breaking waves; the desiccating effects of wind,sunlightandhighsalinity;andpredationbyterrestrialanimals. So,whenitissuchademandingandhostileenvironment,whyareanyspeciesfound in theintertidalzoneatall?theansweristhattheintertidalzoneoffersunique opportunities ecologicalniches forthosespeciesthathaveadaptedtowithstand thedemandsoflivinginsuchanextreme,changeableenvironment. 1.2 BIODIVERSITYONTHEROCKYINTERTIDALSHORE RockyshoreshavethegreatestbiodiversityofanycoastalhabitatinNewZealand astheyprovidemanyecologicalniches.thesenichesarecreatedbytheabundance andvarietyoffoodtypesinshallowcoastalseas,thestabilityandcomplexityofthe rockysubstratethatcreatesnumerousshelteredmicrohabitatsfororganismstolive inoron,andthewidelyvaryingabioticconditionsfromthelowshoretotheupper shorethatpreventanysinglespeciesfromdominatingtheentireshore. Shallow,coastalseassurroundingNewZealandareveryproductivecomparedtothe open ocean. Nutrients washed from the land and from the decay of seaweeds are plentiful;aslightisnotlimitingattheseshallowdepths,photosyntheticalgaethrive. Rockyshoresalsoprovidestableplatformsforseaweedslikekelpstogrowtoalarge size. These factors mean that seaweed productivity is high and therefore there is abundantfoodforgrazinganimalslikemarinesnails,chitonsandurchins,whichin turncansupportlargenumbersofpredatorslikewhelksandseastars. Assessileanimalsarepermanentlyattachedtosurfacestheycannotmovetoforage orhuntforfoodsoinsteaddependontheirfoodbeingtransportedtothembywater 1

8 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology movementinthesea.foodsuchasmicroscopicphytoplanktonandzooplankton is plentiful in the nutrientorich coastal seas. This plentiful food supply supports manydifferentspeciesoffilterfeedinganimalsinlargenumbersontherockyshore whichextracttheplanktonfromthewaterwhensubmergedbythetidee.g.mussels, oysters,bryozoans,seasquirts,anemonesandbarnacles. Rocksurfacesprovidearelativelypermanent,stableplatformforanimalsandalgae to attach to or shelter beneath in a dynamic environment exposed to strong water currents and wave action. The rock provides a stable anchorage for many sessile organismsandallowsthemtogrowtoalargesizewithoutbeingdislodged.witha plentifulsupplyoffood,theirrelativelylargesizemeansthattheycanproducemany offspring.rockyshoresgenerallyhaveathreedimensionalstructure.thiscomplex habitat provides many different spatial niches. Crevices between and under rocks andboulderscreatemicrohabitatsthatprovideshelterfromtheheatinganddrying effects of the sun and the wind, protection from breaking waves, and a safe refuge fromlargerpredators. Oneofthemostsignificantfactorsincreatingalargenumberofecologicalnichesin theintertidalzoneisthewidelychangingabioticconditions.nosingleorganismis adaptedtowithstandthefull,extremerangeofabioticconditionsacrosstheentire intertidalzoneandcopewiththehighlevelsofpredationandcompetitionfoundin the lower shore; rather, different species have adapted to withstand the biotic interactions and tolerate a particular range of abiotic conditions found at a particularshorelevel:thesearetheunderlyingfactorsthatleadtozonationonthe rockyshore. 1.3 THEINTERTIDALZONES Thereareseveralmaintidalzonesrecognisedontheseashore.Theseareshownin Figure1. Splashzone High MHWS Intertidalzone: Subtidalzone Mid Low MLWS Figure1Classificationofseashorezones. 2

9 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology The splash zone is not a truly tidal zone as it is above the height of the average spring high tide (mean high water springs, MHWS) and so is not normally submerged except in exceptional conditions such as perigee, during low pressure weather systems when the water is not held down as much by atmospheric pressure,orduringstrongonshorewindswhenseawaterispushedontothecoast. Although terrestrial, the splash zone is influenced by wave action and wind, with surfandsaltspraywettingtherock.onveryexposedcoastswithlargewavesand surf,thesplashzonecanbeseveralmetreswide. The intertidal zone is the area of the shore between MHWS and the height of the averagelowtidesduringlargespringtides(meanlowwatersprings,mlws).itcan be subdivided into the high, mid and low intertidal shore. The high shore is regularlycoveredbyseawaterduringthehighestpartofthetidesonlyandgenerally spendsmoretimeexposedtotheairthansubmergedbywater(figure2).themid shoreisexposedtoairandsubmergedbywaterforapproximatelyequalperiodsof about6hourspertidalcycle.thelowshoreisrarelyexposedformorethanjusta few hours at low tide. The rise and fall of the tides is the single most important factorinfluencinglifeintheintertidalzone. The subtidal zone is the region of the shore below MHWS. This part is only ever uncoveredbyexceptionallylowspringtides.itisafullymarinezonebut,beingnear totheseasurface,ithasahigherlightintensity,dissolvedoxygenconcentrationand waveactionthantheseafloorindeeperwater. MHWS Verticalheightontheshore Midshore MLWS Percentageoftimeexposedtoair Figure2Aerialexposuretimechangeswithverticalheightonatidalshore. 3

10 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology The main environmental gradient influencing life in the intertidal zone is the time spent exposed to air. Aerial exposure time increases with height on the shore as submergencetimedecreases.differencesinaerialexposuretimecausebigchanges inenvironmentalconditionsoverafewverticalmetresasshowninfigure3,anditis Splashzone Intertidalzone Increasingaerialexposuretime Increasingrangesofdissolved O2andsalinity,temp.andUV andsuspendedfood availability Increasingdissolvednutrients Increasingbiodiversity,predation andinterspecificcompetition Increasinggrazingandpredation fromterrestrialanimals Subtidalzone Figure3Trendsinenvironmentalfactors(gradients)withverticalheightonatidalshore. gradients in these environmental factors that mainly determine the vertical distributionofintertidalorganisms. 1.4 THEABIOTICENVIRONMENT Abioticorphysicalfactorsliketemperature,salinity,pHanddissolvedoxygenare generally quite stable in the seawherethewateractsasalargereservoirthat buffersshorttermchanges.however,theseseafactorstendtovarymorewidelyon land.theintertidalzonealternatesbetweenterrestrialandmarineconditionseach dayasthetiderisesandfalls.asmostintertidalspeciesaremarine,largevariations in these abiotic factors are a major source of physiological stress; the upper vertical distribution limit for most intertidal species is determined by their tolerancetoaparticularlimitingabioticfactor Temperature In the far south of mainland New Zealand, the average sea temperature ranges between11 15 Cfromwintertosummer,whereastheairtemperaturecanvary by9 C.InsubOtropicalnorthernNewZealandtheaverageseasonalseatemperature rangeisjust2 C,between18 20 C,whereastheaverageairtemperaturesvaries byabout7.5 C. 4

11 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology However, these are average temperatures; it must be remembered that in the temperatepartsofnewzealandinwinteritisquitepossibleforintertidalorganisms toexperiencelowtideswithairtemperaturesof17 Cduringthemiddleoftheday and O4 C just 12 hours later maybe even more with wind chill. As the sea temperature may be 11 C at the same time, the organisms can experience rapid changesinbodytemperatureastheyarecoveredanduncoveredbythetide. As temperature increases, the risk of desiccation also increases. High air temperatures coupled with low humidity and coastal breezes mean that the evaporationrateishigh Salinity Salinity is a measure of the amount of dissolved minerals or salts in water. The salinity of the open sea remains fairly constant at between 33 and 35 parts per thousand (one part per thousand is equivalent to 1 g salt dissolvedin1lwater). However,intheintertidalzoneorganismscanexperiencelarge,rapidchangesinthe salinityoftheirenvironmentduetochangesintheweatherandclimate.onahot, breezyday,evaporationoffreshwaterincreasessalinityintidepools,crevicesandin sediments.incontrast,largeamountsofrainfalldilutestandingwaterontheshore, decreasingitssalinity Dissolvedoxygenconcentration Oxygendissolvedinthesearesultsfromphotosynthesisofmarineproducerslike phytoplankton and macroalgaeanddiffusionbetweentheairandtheseaatthe watersurface.theoxygencontentoftheseaisapproximately50timeslessthanthe airat25 C. As seawater temperature increases, dissolved oxygen concentration decreases. As standing water in tide pools and crevices warms, the oxygen concentrationcandecreasebelowapointthatorganismscanobtainenoughtomeet theirrespirationbysimplediffusion Nutrientavailability Important nutrients for algal growth like iron, magnesium, nitrate and phosphate aredissolvedinseawater.therefore,theyincreaseinconcentrationdowntheshore asseawatersubmersiontimeincreases Waveaction Themainstressfromthecoastalmarineenvironmentistheamountofwaveaction. ShoresthatreceivealotofwindOdrivenwavesareknownas exposed.theeffectof breakingwavesontheshoreistodrivesaltwaterhigheruptheshorethanbythe tide alone. This increases the width of the intertidal zones by regularly wetting a regionareaoftheshore(figure4). Another effect of wave action is to create a mechanical stress on intertidal organisms.thereisalotofenergyinbreakingwavesandorganismsneedtobeable towithstandrepeatedbatteringbythewaves.acubicmetreofwaterhasamassof 1000kgoronetonne,alargewavewillcontainseveralcubicmetresofwatersowill transferalotofenergyontotheshoreasitbreaks. 5

12 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Upperlimitofsprayandsplashbywaves MHWS Splashzone Intertidal zone MLWS Exposed shore Sheltered shore Increasingexposure 1.5 THEBIOTICENVIRONMENT Figure4Theeffectsofexposureonzonation. Theuppershoreisaharshenvironmentandfewerspeciesareadaptedtotolerate theextremeabioticconditionsherethanlowerontheshore,thereforeinterspecific competitionforfoodandspaceislowerforthosespeciesthatcancopewiththese conditions.asaresult,biodiversitygenerallyincreasesdowntheshore.withmore species come more interspecific interactions. Biotic factors in an ecosystem are related to the living parts of that system and include competition for resources, predation,herbivory,parasitismandmutualism. The lower vertical distribution limit for most intertidal species is determined by interspecificcompetition,foodavailabilityandpredationpressure Interspecificcompetition Competition between different species increases down the shore with increasing biodiversity. The main resource that sessile organisms compete for on the rocky shore is living space on the rock. Planktonic larvae and algalspores of sessile organisms need room to settle on, attach and grow. Most seaweeds and many marineinvertebratesarebenthic:theyliveontheseafloorsurface.manyofthese organisms have planktonic larval stages that settle, metamorphose and grow to adulthoodontherockyshoree.g.seaweeds,barnacles,seasquirts,mussels,oysters, and tubeworms. Therefore space on rocky surfaces to attach and grow is fiercely competedforbymanydifferentspecies. Although filter feeders compete for food, plankton abundance is rarely a limiting factor in coastal seas. Similarly, dissolved nutrients are rarely limiting for algae. Like plants, algae are photoautotrophic: they obtain their nutrition by photosynthesis. Marine algae do this in one of two ways: they either drift in the 6

13 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology wellolit surface waters as microscopic phytoplankton, or permanently attach to a solid substrate from which they can grow e.g. seaweeds 1. Seaweeds tend to dominatetheshallowsubtidalandlowintertidalareasofallbutthemostexposed shores.heretheycompetewitheachotherandwithsessileanimalsforattachment space on the rock. As seaweeds can grow they can cover large areas of the rock. Thiscanexcludesessilefilterfeedinganimalsastheseaweedsreducethewaterflow totheanimalslivingbeneaththem 2.Howeverseveralanimalswillburrowunderor allow themselves to be overgrown by seaweeds as this may offer them some protection from predators. As seaweeds grow they also compete with other algal species for light. A dense algal canopy can overgrow other slowerogrowing or smalleralgalspecies,reducingtheamountoflighttheyreceiveandthereforetheir rateofphotosynthesis Predation Predation pressure from marine animals increases down the shore. Predatory animalslikewhelks,seastarsandfisharemobileandasthetiderisestheseanimals moveuptheshoretofeed.theycanpotentiallymovetoanyregionoftheintertidal zone, but the amount of time they can spend feeding decreases with height up the shoreastheaerialexposuretimeincreases.thesepredatorsgenerallydonotfeed when they are exposed to the air and, unlike many of their prey species, are not adapted to tolerate long periods of exposure. Therefore, there is relatively low predation pressure from marine animals in the high shore due to the limited time they can spend feeding in the upper shore. Thehighshoretherefore acts asa habitatpreyrefugefrommarinepredatorsforsessilespeciessuchasmusselsand barnacles,wherethetotalmortalityduetopredationislowerthanitwouldbelower downtheshore. Although the high shore offers a habitat prey refuge from marine predators, shore birdslikegulls,tattlersandoystercatchersdopreyonspeciesintheuppershore whenthetideisout.manyspeciesinthehighshoreshowadaptationstoreducethe risk of predation from seabirds. Some animals like periwinkles, chitons and topshellswillhideininaccessiblerockycrevicesandamongstseaweed;otherslike shore crabs bury themselves in the sediments that often accumulate underneath rocks.manyhighshoresessilespeciespossessstructuraladaptationstowithstand predation from seabirds. Barnacles and mussels have strong shells that are firmly cemented to the rocks to avoid being broken open or dislodged by foraging birds; withtheirrelativelysmallsizethismeansthattheyareapoormealforarelatively large bird and are therefore overlooked by most predators, as larger birds tend to concentrateonlargerpreythatyieldabiggernutritionalbenefitfortheenergycost 1 Notallintertidalalgaearelargeseaweedsormacroalgae.Thesurfaceofthesubstrateiscoveredby athinlivingfilmofbacteriaandmicroalgae.thismicroscopiccommunityisanimportantsourceof foodforgrazingprimaryconsumerslikelimpetsandtopshells.these biofilms arethepioneer communitiesinanecologicalsuccessionontherockysubstrate. 2 Althoughitdoesprovidenewnichesformanyorganismssoincreasesbiodiversity.Thesurfaceof theseaweedprovidesmicrohabitatsforsomeepibionts(epio=surface;biont=organism)likespiral tubeworms,ascidians,bryozoansandhydroids;smallcrustaceans,echinoderms,molluscsandeven fishfindshelterbetweenandbeneaththefronds;andtheseaweeditselfisanimportantfoodsource formanygrazers. 7

14 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology oftheirefforts.theideaofasmall(orlarge)sizeactingasadeterrenttopredators isknownasasizepreyrefuge Foodavailability FilterOfeedinganimalscanonlyfeedwhentheyaresubmergedsoitstandstoreason that they will be more numerous in the lower shore where they spend longer periods covered by seawater. The number of potential food sources decreases as biodiversity decreases down the shore (this is particularly true for those animals thatgrazeonlargeseaweedsthataregenerallyrestrictedtothelowershore).there is also the everopresent risk of desiccation and thermal shock for animals that are active on the exposed shore during low tide. Hence for most intertidal animals, feeding opportunities are limited to the times and regions of the shore that are coveredbyseawater.allofthesefactorsmeanthatopportunitiestofeeddecrease withincreasingheightontheshore. However, for scavenging detritivore animals like isopods (sea slaters) and amphipods(sandhoppers)therearemorefeedingopportunitieshigheruptheshore asplantandanimalremainscollectinthedriftline,wheretheyarewashedupby thehightideandstrandedasthetideebbs. 1.6 ZONATION Biological zonation is the distribution of species into visible bands or zones along (perpendicularto)anenvironmentalgradient. Ontherockyshore,theenvironmentalconditionsmaychangefromfullyterrestrial tofullymarineoverafewverticalmetres.asaresultofthisstrongenvironmental gradient, intertidal species occur in discrete horizontal zones according to their ability to cope with the different physical stresses of the gradient (Figure 5), and their interactions with other species in their habitat (that are also affected by the sameabioticfactors). In the intertidal zone, toleranceforaparticular,limiting abiotic factorusually determinestheupperverticallimitofaspecies distribution,whereasthelowerlimit tendstobesetbybioticfactorssuchasinterspecificcompetitionandpredation. Toleranceistheabilityofanorganismtowithstandarangeofvaluesforanabiotic factor in a changing environment e.g. temperature, salinity, ph and light intensity. Tolerancehasaphysiologicalbasis:therearebiologicalprocessesoccurringwithin the organism that enable it to maintain an internal environment that allows the organism to survive despite the changing external environment. If the external environmentexceedsthetolerancelimitsoftheorganismfortoolong,thenitcannot regulateitsinternalenvironmentanditwilldie.figure6showshowaspeciesmight respond to a changing abiotic factor. The response could be for an individual organismintermsofitsgrowth,respiration,reproductiverateorforapopulation. 8

15 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Barnaclezone Tubeworm/ Oysterzone Seaweedzone Figure5Biologicalzonationonanearvertical1.5mrocksurfaceatPortobello, Dunedin.Here,aerialexposuretimeincreaseswithheight. An organism will have an upper and a lower tolerance limit for different abiotic factors and these determine the tolerance range. Organisms cannot survive the extreme conditions outside this range. An organism will have an optimum range withinwhichitisbestadapted,anditsresponseisthegreatest.eithersideofthe optimumrangelaythephysiologicalstresszoneswheretheorganism struggles to survive as it uses energy and nutrients to oppose the negative environmental conditions,leavinglessforgrowthandreproduction.forexample,inacoldenvirono ment, an organism may have to actively warm itself up by moving to a warmer regionor,ifitisa warmoblooded animal 3,itmayincreaseitsmetabolicrate. 3 WarmOblooded animalsshouldbereferredtoashomoeothermic,meaningthattheynormally maintainarelativelyconstantinternalbodytemperaturethatisindependentoftheenvironmental temperature.similarly coldoblooded animalsmaintainabodytemperaturethatisthesameastheir environment,warmorcold. 9

16 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology ToleranceRange Speciesresponse Lower stress zone zone Lower limitof tolerance Optimum range Optimal value Upper stress zone zone Upper limitof tolerance Valueofabioticfactor Figure6Typicalphysiologicaltolerancecurveshowinghowspeciesrespondtochangingabiotic factorsthattheycannotescapefrom. No two species can occupy the same ecological niche indefinitely; interspecific competition will ultimately result in the exclusion of the pooreroadapted species fromthatnichei.e.onespecies populationwilldeclineastheothers grows:thisis Gause sprincipalofcompetitiveexclusion. The potential niche a species could occupy in the absence of betteroadapted competitorisknownasitsfundamentalniche.asinterspecificcompetitionisone of the more important factors determining the lower vertical distribution limit on theshore,thiswouldseemtosuggestthatspeciesoccupyingthehighershorecould potentially live further down. This has been observed in field experiments where scientists removed a species from the rock and observed the expansion of a competingspecies zoneasitpopulatesthenewlyclearedareainthelowershore. Predation on the rocky shore has a similar effect. The high shore may act as a relativelysafepreyrefuge,wheremobilemarinepredatorslikeseastarsandwhelks either cannot tolerate the harsher environmental conditions during exposure, or haveverylimitedfeedingopportunitiesduetotheshorterperiodsofsubmergence inthehighshorewhenthepredatorsareactive. 10

17 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Evidencefrom cageexclusion experimentshasshownthatifpredatorsarekeptout ofthelowershoreusingcagesovertherockthatallowpreyspeciestosettle,butare toosmalltoadmitpredators,thenthepreyspeciesareabletosettleandpopulate thelowershore. The effects of interspecific competition and predation therefore act to limit the spatial niche that many rocky shore organisms can occupy; this means that the actualor realised niche of the species are often smaller than their potential or fundamentalniches 4.However,oneoutcomeofthisisthatmanyspeciesareableto coexist on the shore and no single species tends to dominate. To illustrate these concepts, let us look at an example. Figure 7 represents the distribution of three interactingspeciesthatoccupytwoadjacentzonesonthemidshore. The barnacles and the oysters compete for living space on the rock. At the end of theirplanktoniclarvalstagesbothspeciescementthemselvestoabarepatchonthe rock and remain there for the rest of their lives. Barnacles and oysters are both filterofeeders. They have different structural adaptations for extracting their planktonicfoodfromthewater.thebarnacleusesfeatherymodifiedlegstocomb thewaterforfoodparticles.oysters(andotherbivalveslikemussels)haverowsof ciliaontheirgillsthatcreatefeedingcurrentstodrawwaterandplanktonintothe gills which are mucus lined to trap food. Although both species reduce their metabolicrateduringexposuretoconserveenergyandreduceoxygendemandand waste buildoup, the barnacles can open their shell valves to take some air into the shell during exposure which enables them to continue respiring at low tide. Barnacleshaveahighertolerancetoaerialexposurethanoystersandcanwithstand beinguncoveredbythetideforlongerperiods. The third species is a predatory whelk that feeds on both the barnacles and the oysters when submerged by the tide. Just before exposure by the falling tide, the whelk will seek a damp, shaded crevice in or under the rock. It secretes sticky mucus on to the base of its foot for attachment to the rock surface. A tough, waterproof pad on the foot called an operculum seals the snail into its shell and it remainsinactiveuntilitisresubmergedbytherisingtide. IntheexampleinFigure7,therealisedspatialnicheofthebarnaclespecieshasbeen determined by the barnacles tolerance for aerial exposure, the presence of the competingrockoysters,andbypredationfromthelinedwhelks.intheabsenceof the oysters and whelks it is likely that the barnacles distribution would increase downtheshore.however,itisunlikelytoincreaseuptheshoreasthebarnaclesis likely to be living at its upper tolerance limit for some limiting abiotic factor associated with the long periods of aerial exposure. Therefore, the barnacles fundamental spatial niche is wider than the one it is forced to occupy, but only in termsofthelowerdistributionlimit. 4 Interspecificcompetitionforresourcesotherthanlivingspacecanlimitaspecies distributionand thereforereducethesizeofitsrealisednichee.g.foodavailabilityandperiodsofactivity. 11

18 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology UpperLimit Huntingtimedecreases Actualrange Oyster srange Potentialverticalrange LowerLimit 1.7 Acornbarnacle Austrominiusmodestus ADAPTATIONSTOLIFEINTHEINTERTIDALZONE: COPINGWITHSTRESS Theorganismslivingintherockyintertidalzonearealmostallmarineinoriginbut haveadapted 5 tocopewiththedemandsofspendingpartoftheirdayuncoveredby the sea. Many of the adaptations that have evolved in intertidal organisms to survivetohelpthemcopewith,avoidorminimisestressesassociatedwithperiods ofaerialexposure.ofallofthewidelyvaryingabioticfactors,heatanddesiccation are probably the most important in setting the upper limits of intertidal species distributionontherockyshore Heatanddesiccation Rockoyster Ostreachilensis Linedwhelk Buccinulum linea Figure7Theeffectsoftolerance,predationandinterspecificcompetitionontheupperand lowerverticaldistributionlimitsofacornbarnacles(austrominiusmodestus). Even in cold, temperate environments like southern New Zealand, the air temperaturecanreachover30 Cinsummer.However,itisnotjustthemaximum temperature that is important, but the temperature variation. Seasonal variations overayearcanaccountforairtemperaturesbetween30 CandO5 Catsealevelin 5 Thishasoccurredovermanygenerationsastheyhaveevolvedbynaturalselection. 12

19 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Dunedin. Monthly variations may be equally dramatic: in March 2012 the highest recordedairtemperatureininvercargillinsouthernnewzealandwas24.3 Cwhile the lowest was 1.5 C (Deep South Weather, 2012). Daily variations in air temperature of 20 C between day and night are not uncommon in New Zealand. However, drastic changes in temperature can occur much more rapidly if the influencesofthetide,timeofdayandseatemperatureareconsideredtogether.for instance, during a midday low tide, an organism s body temperature can rise from the temperature of the seawater to well above that of the air temperature, a differenceofupto25 C(Helmuth,1998).Theorganism sbodytemperaturecould thenrapidlydropbackdowntothatoftheseawaterwhenitisreoimmersedbythe risingtide(seefigure8),butonaclearnightjustafewhourslater,itcandecreaseto severaldegreesbelowairtemperatureduringthenextlowtide. BodyTemperature Immersionbyrisingtide TimeofDay(hr) Figure8ChangesinbodytemperatureoftheintertidalmusselMytilus californianusoverpartofatidalcycleduringthesummer.modified fromhelmuth(1998). Intertidalorganismsareectothermicwhichmeansthattheylackanyphysiological mechanisms to generate body heat. As a result, their body temperature is greatly affected by their environment. This is particularly true for small organisms that havealowbodymassandthereforearelativelylowheatcapacity. Physiology involves the biochemical reactions and processes that occur within an organismtomaintainlife.forevery10 Cincreaseinbodytemperature,therateofa biochemicalreactionisapproximatelydoubled,andforevery10 Cdecreasetherate ishalved.henceanorganismthatexperiencesatemperaturechangeof20 Cwould experience a fourfold change in metabolic rates e.g. their respiration rate would increasebyfourtimesandsotheirrateofglucoseuse,oxygendemandandcarbon dioxide production would increase accordingly; a marine organism exposed to the aircannotfeedorcarryoutgasexchangewithseawater,sonormalratesofaerobic respirationcannotbesustained. 13

20 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology High temperatures also disrupt the organisation, stability and structure of delicate molecules in cells, such as membrane lipids, enzymes, DNA and RNA. For many importantbiologicalmolecules,functionisdependentonstructure,soanychangein structuremaycausealossoffunction. Intertidal organisms can slowly adjust to longoterm seasonal variations, but not to veryshortotermchangesoverthecourseofhours:thereforetheyneedtowithstand thisshortotermvariationbytoleratingit,avoidingitorreducingitseffects. Mostintertidalorganismsliveataleveloftheshorethatisveryclosetotheirupper thermal tolerance limit i.e. close to the point where the high environmental temperatures would be fatal. But how can some species live higher on the shore than others where they experience not only higher temperatures, but a greater rangeofenvironmentaltemperatures? Many intertidal species are eurythermal: they can tolerate much higher environmentaltemperaturesthantheirnonointertidalrelatives.theirphysiological processeshaveadaptedtofunctionathighertemperatures.figure9showshowthe upper lethal limit of temperature of five different species of porcelain or halfocrab varieswiththeirverticalpositionontheshoreateachoffourdifferentregionsinthe western Pacific Ocean. The differences in the upper thermal tolerance limit of the closelyrelatedcrabscanberelatedtoboththeirverticalpositionontheshoreand theirclimateinrelationtotheirlatitude(distancefromtheequator). Intertidalspeciesalsohaveamuchwidertemperaturetolerancerangethansubtidal species. In controlled laboratory incubation experiments by Somero (2002), the bodytemperatureofsomerockyshoreinvertebrateshasbeenshowntovarybyup to25 Cwithnoharmfuleffects.Theseorganisms bodysystemsarewelladaptedto changing conditions and they have evolved physiological mechanisms to tolerate a widerangeofbodytemperatures 6. Individual organisms can adjust their physiologies to short term changes over periods of days or weeks by a process calledacclimatisation. The properties of their body systems may alter to resist the influence of the environmental change. A good example of acclimatisation is a process called homeoviscous adaptation ( homeoo = same; viscous = opposite of fluid/runny) in cell membranes. As temperaturedecreases,membranesbecomemoreviscous 7,andastemperaturesrise membranes fluidity increases. Fluidity is an important physical property of a cell membraneandcanaffectcriticalmembranefunctions.forinstance,mitochondrial cellmembranesarethesiteofthemajorityofatpproductioninaerobicrespiration. Any changes to the fluidity of mitochondrial membranes will alter their structure andreduceatpproduction.theeffectontheorganismisareductioninrespiratory rateandthereforemetabolism. 6 Thesespeciesareknownasthermoconformersastheirbodytemperature conformsto andchanges withtheenvironmentaltemperature. 7 Trythisathome:observehowcookingoilbecomesrunnier(lessviscous)inafryingpanasitgets hotter. 14

21 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology LT50( C) Equator Maximumverticalshore position Figure 9 Upper limits of thermal tolerance for intertidal crabs, Petrolisthes spp. Each symbol represents a different species of the genus Petrolisthes i.e.eachopencircleisa speciesofcrabfromcalifornia.lt 50isthetemperatureatwhich50%ofthecrabsstudied diedduringtheincubationexperimenti.e.theaveragelethallimit.(stillman,2002). In laboratory experiements, American intertidal species such as Californian blue mussels (Mytilus californianus), abalone (Haliotis spp. 8 ) and rock oysters (Crassostrea virginica) can change the lipid content of their cell membranes to counter changes in its fluidity caused by temperature changes(cited by Rais and Stillman, 2010); these intertidal animals can respond by inserting more or less cholesterolandsaturatedfatsintotheircellmembraneswhichhelpthemembranes toremainfluidor runny despitebodytemperaturechanges. Because intertidal organisms are ectothermic, they cannot regulate their body temperaturebyphysiologicalmeans.however,nonophysiologicaladaptationshave evolvedinintertidalorganismsthathelpthemtocopewithextremeenvironmental temperatures by reducing heat gain and promoting heat loss. Additionally, physiological adaptations have evolved that protect or repair the cellular damage causedatextremelyhighbodytemperatures. A physiological adaptation to potentially damaging high environmental temperatures is the production of heat shock proteins during periods of thermal stress. The proteins function is to help maintain metabolic function by stabilising and repairing important enzymes and protecting them from heat damage. These proteinshaveevolvedinmanyintertidalmolluscssuchasmussels,limpets,topshells and periwinkles to help them tolerate high temperatures in the exposed upper shore. 8 NewZealandpauabelongtothegenusHaliotiswhichareknownasabaloneinAustraliaandthe USA. 15

22 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Figure 10 (Tomanek and Somero, 2000) shows the heat stress response of four differentspeciesofcloselyrelatedmarinesnailsofthetegulagenus 9. Productionofhsp70 Environmentaltemperature ( C) Figure10Productionofheatshockproteinhsp70marksthe start of the thermal stress zone in American subtidal and intertidaltopshells,tegulaspp.(somero,2000). The snails were incubated at different temperatures and the amount of heat shock protein (hsp70) in their body tissues was measured. T. rugosa is a subtropical species,whereastheothersaretemperatespecies.twospecies,t.funebralisandt. rugosaliveintheintertidalzone,whereastheothertwospeciesaresubtidal.the function of hsp70 is to repair and stabilise important metabolic enzymes in the snail stissues.itisonlyproducedatbodytemperaturesthatcausethermalstress. Atthepointwheretheproductionofhsp70fallstozero,theanimalhasexceededits thermaltoleranceandhasdied. The graph shows that the intertidal species experience thermal stress at higher temperatures than the subtidal species; this implies that their tolerance range for temperatureisbroader(above12 Catleast).Thegraphalsoshowsthattheheat shock response occurs over a much wider temperature range in the intertidal species.thissuggeststhatthetemperaturerangeofthestresszoneoftheintertidal speciesiswiderthanthatofthesubtidalspeciesi.e.theycanmanageawiderrange oftemperaturesthroughtheproductionoftheheatshockprotein. 9 TegulaarefoundinNorthAmericaareknownastopshells.TheyareecologicallysimilartoourNZ topshells,dilomaspp.andneritaspp. 16

23 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Heat gain can be minimised by having a relatively large body size compared to specieslowerintheintertidal.thisresultsinalowsurfaceareatovolumeratioand so the surface available for heating is kept relatively small.arelativelylargebody size also means thatthereis more body tissue to heat up which therefore takes longer for any significant temperao ture rise to happen. This phenomenon can be seen in periwinkles (Austrolittorina sp.) and snakeskin chitons (Sypharochiton pelliserpentis) wherelargerindividuals tend to be distributed higher up theshoreastheycantolerate longer exposure to higher temperaturesduringlowtide. Dark colours absorb solar radiation and so lead to heat gain. Barnacles have light coloured shell plates and the Figure11Ridgesonthelimpets shellsincreasesurface areaforradiatingheatandthereforeincreasecooling. blue banded periwinkle Austrolittorina antipodum has white stripes that reflect radiationandreduceheating.theraysoflimpetshellsalsohelpthereoradiationof heatbyprovidingagreatersurfaceareaforcooling(figure11). Manyterrestrialorganismsuseevaporativecoolingtokeeptheirbodytemperature belowitstolerancelimit.forwatertoevaporate,heatenergymustbetransferred from a tissue which creates a cooling effect. Unfortunately for marine organisms, cooling by evaporation causes water loss which can lead to desiccation stress and subsequentdeath.however,someanimalscandrawonareservoirof extra water for cooling above that which is required for survival. Barnacles hold extra water withinthemantlecavityoftheirshellplateswhichcanbeusedforcoolingwithout causing dehydration. Chitons and limpets settle into a home scar : a specially created depression or cup in the rock that the animal has created and returns to before being uncovered by the falling the tide. This home scar may contain a reservoirofwaterthattheanimalcanuseforevaporativecooling. As temperature increases, evaporation rate increases and with it, the threat of desiccationordryingout.intertidalorganismshavebecomeadaptedtowithstand desiccationeitherbyminimisingwaterlossorbybeingabletotoleratedehydration forlimitedperiods. Animalsthatshowbehaviouraladaptationsusuallyhaveaninternalbodyclockthat issynchronisedwiththetidalcycle;inthisway,theyareabletoeffectivelypredict thefallingtideandensurethattheyactinsufficienttimetoreducewaterlossbefore theyareuncovered.mobileanimalsdothisbychangingtheirpositionontheshore 17

24 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology andseekingshelter,whereassessileanimalstimetheiractivityperiodstocoincide withsubmergenceandeffectively clamup duringexposure. Many shelled animals can tightly close their shell valves to create a high humidity environmentwithintheirshellswhichhelpstoreducewaterloss,forexamplemany marine snails, barnacles and mussels seal small amounts of seawater inside their shells when uncovered by the falling tide. Soft bodied anemones retract their delicate tentacles and withdraw inside their mucusocovered body, reducing their exposedsurfacearea. Behavioural adaptations in mobile intertidal animals to reduce water loss by evaporation include by avoidance behaviour or seeking areas of high humidity. Manyanimalslikeshorecrabsandchitonsburythemselvesbeneathloosesediments orclingtothemoistundersideofrocks.chitonsrespondtobothlightandgravity and tend to move downward towards dark crevices when exposed to the air, behavioursknownasphototaxisandgeotaxis. Limpetsscrapesmallbodysizeddepressionsintherock(oftenontheshadedside) calledhomescarswhichtheycanretreattoasthetidefalls;theylinethescarswith mucuswhichhelpstosealtheminandreducewaterloss. Topshellsandperiwinkles(Figure12)clustertogetherinlargenumbersincrevices orontheshadedsideofrocksorboulderstoincreaselocalhumidityandreducethe humiditygradient,therebyreducingtherateofevaporation. Figure12BlueVbandedperiwinkles(Austrolittorinaantipodum)shelteringincrevicesinthe rockontheuppershoreduringaerialexposure.thecrevicescreateshadedmicrohabitats withhigherhumiditythanthesurroundingrocksurfacewhich,togetherwiththeclumping behaviour,andmucuspadsecretedbythesnail,reducesdesiccation. 18

25 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Intertidal organisms have also evolved structural adaptations to reduce water loss that complement their behaviours. Purple shore crabs (Hemigrapsus sexdentatus) haveaveryhightolerancetoaerialexposurethankstoawaxy,waterproofcovering ontheircarapacecalledachitinouscuticle.thesecrabshaveapermeablesectionof theirlegsthroughwhichtheycarryoutgasexchange.thisregionisnotcoveredby the waterproof cuticle (which would prevent gas exchange) and so represents a potential source of water loss. However, the crabs can tightly fold this portion of their legs up into their carapace and maintain a high local humidity and reduce desiccation. Mostmarinesnailssecretewaterymucusaroundtheirshellopeningswhichformsa protective layer of gelatinous slime, a physiological response to aerial exposure. Periwinklesusethissamemucuspadtoattachtorockswhenthetideisout 10 ;they also have very small gills that reduce the evaporative surface. Topshells, catseyes periwinkles and whelks also have a thick, horny pad on their foot called an operculumthatsealstheshellopeningbehindthesnail. Some organisms have evolved very high tolerances to desiccation stress. Periwinklesthatliveinthehighestlevelsoftheshorecansurvivethelossofupto 70% of their water content and are capable of rapidly reohydrating when reo submerged by the rising tide. Many types of seaweed are also capable of withstandingseveredehydrationforshortperiodsandveryrapidrehydration.the highestzonedseaweedsontheshoreareverytolerantofextremedehydration,with species like sealettuce (Ulva sp.) and Neptune s Necklace(Hormosira banksii) capableoflosingover90%oftheirwatercontentbetweentidalcycles. Therateofphotosynthesisinseaweedsdecreasesasdesiccationincreasesand,like animals,manyintertidaltypesofseaweedpossessadaptationstoreducewaterloss. Manyseaweedssuchaskelpssecreteaslimycoveringcalledmucilage 11 whichhelps themreducewaterloss.theshapeoftheseaweedsfronds( leaves )andthegrowth formofthealgaeisalsoimportant.liketerrestrialcacti,thefleshysacsofneptune s Necklace,gummyweed(Splachnidiumrugosum)andothersacOlikealgaestorewater so that photosynthesis can continue; their rounded shape also provides a low surface area to volume ratio so that evaporation rate is low. Coralline algae often growinathickturfwhichhelpstoretainwaterandsokeepthelocalhumidityhigh Osmoticorsalinitystress Intertidal organisms experience stress due to changes in the salinity of their environment. This stress is known as salinity or osmotic stress and can cause changes in the water or salt content of their body tissues. If the salinity of the environmentisgreaterthanthesalinityofthebodytissuesoftheorganism,thenthe organismwilltendtolosewaterbyosmosisandmaygainsaltsbydiffusion.ifthe salinity of the environment is lower than the salinity of the body tissues, the organismwouldgainwaterandlosesalts.onlywhenthesalinityofthebodytissues 10 Italsoactsasaninsulatingpadtoreduceheattransfertoandfromtherock. 11 Themucilageofsomebrownseaweedslikekelpcontainsasugarcalledagarosewhichbindswater andisextractedtomakeaagargel. 19

26 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology became equal to the salinity of the environment would there be no net change in water content. Changes in a cell s water content create physical stresses due to changes in cell volume and pressure which can lead to cell rupture or collapse. Chemicalstressescanalsooccurduetochangesintheavailabilityofwaterandthe concentrationofreactantsinthecellleadingtoreducedreactionrateortoxicity.if the organism does not counter these changes and regulate its water content (osmoregulation)withintolerablelevelsitwilldie. Asthetideebbs,surfacefilmsofseawaterontheexposedshorebecomemoresaline asfreshwaterevaporates.likewise,freshwaterevaporatingfromrockpoolsraises theirsalinity;thisisparticularlysignificantinthosesmallerpoolsintheuppershore thatareexposedtotheairforrelativelylongperiodsandloselargeamountsoftheir freshwaterbyevaporation.conversely,largeamountsofrainfallontheshoreatlow tide means that organisms experience very low salinity conditions and freshwater can accumulate in rock pools. Organisms in large rock pools will experience a slowerdecreaseinsalinitythanorganismsonorunderrocksthatarewashedwith freshrainwater. Unlike most estuarine organisms, few intertidal organisms are well adapted to toleratechangesinthesalinityoftheirbodytissues.mostintertidalspeciescannot control the salt content of their body; these types of organisms are called osmoconformers. Thesalinityoftheirtissuesisgenerallysimilartothatofnormalseawater(36ppt.); afterallthisistheenvironmentthattheyevolvedinandareadaptedto.however,as forheatstress,theycanlimittheeffectsofchangingenvironmentalsalinitiesintheir surroundingsbyeithertolerating,reducingoravoidingtheeffects.mobileanimals reducetheeffectsofchangingsalinitybyavoidingthestressandmovingintoamore suitablemicrohabitat. Structuraladaptationsthatreduceevaporationcanprovideprotectionagainstwater lossduetoosmosis;forexamplethethickwaterproofcuticlesofcrabsandbarnacles are effective barriers to water and salt movement. However, gas exchange structureslikegillsareveryvulnerabletoosmoticstress.gillsneedtohavealarge surface area and be permeable to oxygen and carbon dioxide for efficient respiration. These structures are kept moist and in almost continual contact with water. Whether water is trapped inside a shell as in mussels and barnacles, is presentassurfacewatercoatingthegillsofcrabs,orisbathingthegillsoffishina rockpool,thesalinitywillchangewithincreasingaerialexposure.thiscanchange thewaterandsaltcontentoftheorganism stissuespastitstolerancelimits. Physiologicaladaptationstoregulatethebodyfluid ssaltandwatercontenthelpto countersuchchangesandmaintainarelativelysteadysaltandfluidbalancethrough a process called osmoregulation. Many invertebrates actively excrete salts like sodium and chloride ions through their nephridia, gills, gut or antennal glands (Taylor and Andrew, 1988). Other organisms can reduce water movement by osmosis by matching the total salinity of their internal fluids to the environment through exchanging good ions and dissolved substances for sodium and chloride ions e.g. seaweeds use glycerol, sucrose and mannitol (Biebl, 1962); some 20

27 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology invertebratesuseaminoacids.inthisway,theorganismscanosmoregulateandso maintainastablewatercontentintheirtissues. Someorganismslikeperiwinkleshavesimplyevolvedphysiologiesthatarecapable of putting up with extreme salinity fluctuations and have a very wide passive tolerance range. This is also true of many intertidal algae that have a greater physiologicaltolerancerangethantheirsubtidalrelatives Respiratorystress With the exception of the highoshore pulmonate limpets 12, most intertidal animals rely directly on water for dissolved oxygen for aerobic respiration. Gas exchange structures like gills need to be moist to function, therefore during aerial exposure, intertidal animals need to maintain wet gill surfaces and avoid desiccation. Additionally, the concentration of dissolved oxygen in water decreases with increasing temperature, so small rockpools that experience the midday sun on the highshorearelikelytocontainfarlessoxygenthanlarger,moreshadedpoolsinthe lowershore,especiallyifthelowshorepoolsarenearthesplashzoneandaerated bybreakingwaves. Periwinklesliveattheveryupperlimitoftheintertidalzone.Theirgillsareadapted toefficientlyextractoxygenfromtheairduringexposureatlowtide.notonlyhave theirgillsdecreasedinsizetoreduceevaporativewaterloss,buttheliningoftheir gillcavitieshasaveryrichbloodsupplythatcanexchangegaseswiththemoistair surroundingthemucusolinedshellopening,likeasimplelung. Intermsofbehaviouraladaptations,avoidanceofstressfulconditionsiscommonin mobile animals like crabs and chitons that can move wit the tide and stay submerged.sessilebarnaclesandlimpetsareabletostoreairbubblesinsidetheir gillcavitiesduringaerialexposureatlowtide.theairactsasanoxygenreservoir and keeps the water surrounding the gills enriched with oxygen. Topshells and whelksalsotrapwaterinthejellyolikemucusaroundtheedgeoftheirgillobearing mantlecavities.oxygenfromtheairdissolvesintothismoistlayerandcanthenbe extracted by the gills. However, even allowing for the limited ability of some intertidal organisms to extract some oxygen from the air during exposure, most of these marine animals cannot maintain a high respiratory demand when the tide is out. Their gas exchange organs are mainly adapted for extracting oxygen from seawater; prolonged activity during exposure will rapidly deplete oxygen in their tissuesandcarbondioxidewillaccumulate,loweringcellularph.themostcommon physiologicaladaptationistoreducetheoxygendemandandrateofcarbondioxide productionbyloweringthemetabolic(andthereforerespiration)rate,andfuelling essential life processes by anaerobicrespiration;thelacticacidbuildupisthen reversedduringreosubmergenceasthetiderises. 12 ThisgroupofhighOshoremolluscsarenotthoughttobecloselyrelatedtothecommonshore limpets,buthaveevolvedfromarelativelyrecentterrestrialancestorlikethelandsnails.they possessapseudoolungratherthangillsthatenablesthemtocarryoutgasexchangeintheairand haveadaptedtothesaltyconditionsontheuppershore.theirresemblancetothetruemarine limpetsisaneatexampleofconvergentevolution:wheredistantlyrelatedspecieshavebeen shaped bynaturalselectioninthesameway,bythesameenvironmentalpressuresintheirsimilarniches. 21

28 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology PART2:SURVEYINGTHEROCKYSHORE 2.1 INTRODUCTION:WHYSTUDYTHEROCKYINTERTIDALSHORE? NewZealandisacoastalnation.Ithasoneofthelargestcoastlinesrelativetoour landareaintheworld.ourcoastisunderpressurefrommanydifferentusers.the intertidalborderbetweenthesea(marine)andland(terrestrial)environmentsare susceptible to impacts from both the land and the sea including pollution; overfishing; mineral extraction and dredging; invasive pest species like Undaria seaweed;nutrientenrichmentandincreasedsedimentinriversfromrunooff;habitat loss and alteration; and the global effects of climate change that include rising sea level, increased air and sea temperatures, disrupted weather systems and ocean acidification. The intertidal border between the land and the sea is a productive and diverse habitat. It has a high biodiversity and is home to many slowomoving or sessile speciesthatarerelativelyeasilyquantifiedformonitoringchanges.collectingdata on species distribution, abundance, community structure and biodiversity will provideausefulbaselinefordetectinganyfuturechanges. 2.2 HOWTOCARRYOUTTHESHORESURVEY Theaimfortheclasswillbetoconstructatablethatshowsthemeandensityand distributionofintertidalorganismsfromtheupperlimitofthetide sinfluencetothe lowwatermark. Aclasswillsetup3O5randomlyplacedtransectsthatwillrunfromtheupperlimit ofthehightide sinfluence(thesplashzone)downtheshoretothewater sedgeat lowtide.eachgroupof3o4peoplewillberesponsibleforsurveyingonetransect. Alongeachtransecttherewillbe11samplingpoints.Atthesepointsaquadratwill beplacedtomeasuretheabundanceofall 13 oftheanimalsandplantsfoundthere. Thesamplingpointswillbeevenlyspacedalongthetransectatregularintervalsof 1/10 the total transect length. Each sampling point will correspond to a different tidalleveli.e.quadrat1(q1)willalwaysbeattheupperlimitofthehighshore;q5 willbethemidshoresample,andq11thelowestofthelowshoresamples(figure 13). Aseachgroupwillusethesamemethod,theirdatacanbepooled.Attheendofthe surveythepooleddatacanbeusedtocalculatethemeandensityateachshorelevel forallspeciesfoundinthesurvey. 13 Youshouldnotassumethatyouknowwhatthedominantorimportantspeciesinanintertidal communityarebeforeyousurveyitandchoosetocountonlythosespecies;avalidmethodfora communitysurveywouldcollectdataonallspeciesthatcanthenbeanalysedforpatternsthatmight suggestsignificantinteractionsbetweendifferentspecies. 22

29 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Usingastandardisedmethodmeansthatresultsfromdifferenttimesandplacescan becompared. T2 T1 Q1 T3 Upperlimitof highshore Q5 Midshorelevel Q9 Q10 Q11 Lowshorelevel Figure13Anexampleofasurveyarea(planformview)showingthreetransects,T1 3,eachwith 11quadrats(Q1 11)atregularintervalsof1/10ofeachtransect stotallength Whyisthequadratsamplingintervalalwaysonetenthofeachtransect s totallength? Mostshorelinesareirregularshapesanditisunlikelythatanytwotransectswillbe thesamelength.sometransectsmaylayonmoresteeplyslopingpartsoftheshore thanothers.tocalculateanaveragedensityforaspeciesataparticulartidallevel, data from different transects need to be pooled together O but how do you know whichquadratsareatapproximatelythesametidallevel?thequadratsatthevery topandbottomofthetransectwillbeequivalentasthehighandlowtidelevelsare easytofix.youcouldalsoassumethatthequadratsinthemiddleofeachtransect areatthesametidallevel atthemidtide.buthowcanyoumakesurethatquadrat 3ontransect1isatanequivalenttidalheightasquadrat3ontheothertransects? Thesolutionistoplacequadratsatthesamerelativedistancesalongtheirtransects; thesedistancesarefoundbydividingeachtransectintothesamenumberoflengths andplacingaquadratateachofthesepoints.thiswillenableyoutopoolquadrats atapproximatelyequivalenttidalheights.ashoreprofilediagramshouldalwaysbe drawnsothatanyexceptionallyhighorlowquadratscanbeideitifiedandanalysed 23

30 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology later. A convenient number to divide the transect by is 10. This will give 11 quadrats in total,whichwillprovidesufficientdatatoshowthepresenceofany patterninspeciesdistributionalongthetransect. 2.3 EQUIPMENTLIST Thefollowingisessentialequipment: Quadrat:0.5x0.5msquareframewitha totalareaof0.25m2 Transect:Measuringtape:30 50mplastic, reeled HBpencil A4hardcovernotebookorA4clipboardin aclearplasticbag NZRockyShoreGuide(Figure14) 14. Sunscreen,hat,waterandsensiblefootwear Figure14TheNZRockyShoreGuide Youmayalsofindthefollowingequipmentuseful: Thermometer:stainlesssteelprobe,O10 C 50 Crange Digitalcameraand30cmwhiteplasticrulerforscale Datarecordingsheet(see SurveyDataSheet,Appendix1) Tentpegsforsecuringeachendofyourtransect Handlensforidentifyingsmallorganisms Small plastic sandwich bags for collecting small samples of seaweed for preservingoridentificationafterthesurvey 2.4 SURVEYMETHOD 1. Aimtobeginsurveyingatlowtide.Arriveattheshoreatleast30minutesbefore lowtidesothatyouhavetimetomarkoutyoursurveyarea. 2. Measurethewidthofyoursurveyareaalongthehighshore,eitherbypacesor using a tape. Thetransectsshouldrundown the shore from the upper limit of the sea s influence where the splash zone ends. Finding this region can be difficult, but there are some indicator species that can be used e.g. littorinid or periwinklesnails(austrolittorinaantipoda)andencrustingmarinelichens.find the height where these organisms are no longer consistently found and let this representtheabsoluteupperlimitofthetide sinfluenceandthestartpointfor yourtransect. 14 FreedownloadforNorthernandSouthernregionsavailablefromthe Resources sectionofthe NewZealandMarineStudiesCentrewebsitehttp:// 24

31 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology 3. Generate up to 5 random numbers 15 between0andthewidthofyoursurvey area.eachofthesenumbersisastartingpointforyourtransectinthehighshore andthelocationofyourhighestshorequadrat,q1. 4. Holdthemeasuringtapeatthehighestsamplingpoint(Q1)forthetransectatthe highshoreregionandrunoutthemeasuringtapedowntheshoretothewater s edgetoformalinethatisapproximatelyperpendiculartotheshoreline;thisis yourtransectline.walkwiththetapeonyourlefthandside thiswillhelpyou towalktotherightofthetransectandavoidtramplingyoursurveyarea. 5. Measure the total length of the transect. Divide this number by 10 to find the samplingdistancebetweenquadratsalongthetransect. 6. The first quadrat to sample is in the low shore at the water s edge. This is numbered Q11 onthesurveysheet.placethequadratontothesubstratewith the top left corner of the quadrat s outer edge on the sampling point on the transect(whenfacinguptheshoretowardsthehightidezone). 16 Thisquadratis sampledfirst. Alwaysfacetheseawhilecountingsoyoucanwatchforlargewaves 7. Startinginthetopleftcorner,systematicallysearchtheentirehabitatwithinthe quadrat and record the abundance of all macroscopic organisms. Here are someguidelinestohelpyourecordabundance: Recordabundancesforoverlyingcanopyspeciesfirst. The canopy species can then be lifted or moved aside to record abundances of the understorey species living beneath them. Remember to look inside crevices and under rocksandweed. Animals should be recorded using a tally to produce a total count or frequency. Seaweedsshouldberecordedaspercentagecover. For small, encrusting animals that form colonies (such as ascidians, bryozoansandsponges)and/orcover a large area (such as barnacles and little black mussels) you can either count the individual colonies, or treat themlikeseaweedsandrecordtheirpercentagecover. Whereananimal sabundanceismuchgreaterthan100(e.g.specieslikehorn snails,bluebandedperiwinklesandbarnacles),youcandoaroughcountin one part of the quadrat and multiply this up (extrapolate) to represent the wholequadrat. 15 Randomnumberscanbegeneratedusingastandardscientificcalculator,iGenerateRandom NumbersiPhone/iPod App oronlineathttp:// 16 Samplingstartsatthelowshoreandworksuptheshorewiththeincomingtidefollowingbehind. 25

32 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology If a relatively large organism is directly beneath or touching the quadrat frame,thenyouneedtocountitdifferently.onlycounttheorganismifmore thanhalfoftheorganismisinsidethequadrat. Whenyouhavefinishedsearchingthequadratremembertoreplaceany rockstotheiroriginalorientationandposition. 8. Record the substrate type in the quadrat. The underlying or base substrate is recordedaseitherrock,cobble,mixed(looseassortedstones)orpoolofwater. 9. If you have time, photograph the quadrat from above for visual reference. Includethequadrat,transectandsitenumber,anda30cmwhiteplasticrulerfor scaleineachphotograph. 10. Recordenvironmentalinformationaboutthesite.Thiscouldinclude: GPScoordinatesormapgridreference Airandseatemperature. Aspect.Thisisthecompassdirectiontheshorefacese.g.northfacing. Exposurelevel.Thisisameasureofhowexposedtheshoreistowindand waveactione.g.sheltered,veryexposed,etc. Shoregradientorslope.Thiscanbeestimatedbymeasuringthedropdown theshorein1horizontalmetre.foramoreaccuratemeasurement,thiscan bedoneseveraltimesalongtheentirelengthofthetransectandaveragedfor asteadilyslopingshore,orusedtohelpcreateashoreprofilediagramwhere theshoreslopechanges. 14cmdropover100cmhorizontal=14%slope 14cm Significantfeatures:theseareanyfeaturesthatyouthinkmightinfluencethe survey area e.g. large boulders, storm water drain outfall, stream or creek outlet,grazinganimals,rockfall,wreckageorrubbish,pipeline,etc. Photographs, video or sketched profile diagrams of the survey area so that youorsomeoneelsecanlocateyoursamplingareaagainlater. 26

33 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology PART3:ABRIEFGUIDETOSEASHORESURVEYS 3.1 INTRODUCTION Aneffective,validbiologicalsurveyshouldhavesixkeyfeatures;itshouldbe: Randomised Samplesshouldbetakenfromareasthathavebeenselected atrandomtoavoidanybiasinthesurveyresults Representative Gives results that describe the full range of important featuresofthewholestatisticalpopulation 17 beingsurveyed Repeatable Canbecarriedoutagaininsuchawaythattheresultswould be very similar if the population being surveyed had not changed Reliable Results should be accurate (closetotherealvalueinthe biggerpopulation)withlittlevariabilityduetosurveyerrors, allowing you andothers tohaveconfidenceinany conclusionsyoudrawfromthem Realistic Doesn t measure everything in the population surveyor makesthebestuseofthelimitedtimeandresourcesavailable bymeasuringenough Responsible Doing the survey does not significantly damage or alter the environmentorstatisticalpopulationbeingsurveyed 3.2 TRANSECTS A transect is a line along which the distribution and abundance of different organismsaresurveyedandenvironmentalvariablesaremeasured. Atransectisusuallyplacedrunningalonganenvironmentalgradienttoshowifand how organisms distributions and environmental variables change along that gradient. 17 Anoteontheword population.thiswordhasdifferentmeaningsdependingonwhetheryouarea biologistorastatistician.inbiology,apopulationisagroupofindividualsofthesamespeciesliving inaspecificareathatarecapableofinterbreedingandsharethesamegenepool.instatistics,a populationisanygroupfromwhichasampleistaken.unfortunately,asamarineecologist,youare bothabiologistandastatisticiansohowshouldweusethewordhere?wewillusetheterm populationinthebiologicalsensei.e. thepopulationofhalfocrabs,andonlyusethetermstatistical populationifweneedtotalkaboutthesurveystatistics. 27

34 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology The word transect literally means to cut across (trans across; sect cut). In zonationstudies,thetransectisusuallyplacedperpendicular(atarightangle)to thedirectionofthezonessothatit cutsacross thedifferentcommunitiesallowing changes in abundance to be measured and related to the change in the environmentalgradient. Inanintertidalrockyshoresurvey,transectsareusuallyrunfromthetopofthehigh tidezonetothewater sedgeatlowtide(figure15).thisgivesacompletepictureof changesinthecommunityfromhightolowtide. Several transects are used across the width of the shore so that arepresentative picture of the whole survey area is obtained. The start position of the transects withinthesamplingareashouldberandomlyselected.samplingthenoccursalong thelengthofthetransectbetweenthetopofthehightidezoneandthelowwater markatregularintervalsusingquadrats. Figure15Maindirectionoftheenvironmentalgradientsontherocky intertidalshore. 28

35 3.3 QUADRATS EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Aquadratissimplyacountingaidthatisusedtomeasuretheabundanceofsessile (stationeryorfixedinplace)andsloworpoorlymotileorganismsinasamplefrom abiggercommunity.ithasafixedshape,aknownareaandisusuallyfourosided. The quadrat most commonly used in rocky shore intertidalstudiesisa0.25m 2 squareframequadrat. Thishassidesthatare0.5minlength.However,on a very short, steep shore a rectangular letterbox shapedquadratcanbeused(figure17(c)). The frame of the quadrat is usually made of aluminium,woodorrigidplastictubing.itmaybeof the string frame type (Figure 17(a)) or a simple squareopentype(figure17(b)).ideally,oneofthe 4cornersismarkedtoalengthof0.1mtocreatea 0.01m 2 area(markedx)forsubsampling. Onacobbleorbouldershoreanopenframequadrat ispreferableasitallowsthesurveyortoliftupand Figure16Openframequadrat. examinerocksinsidethequadrat(figure16). Markingthequadratfromthecornerswithalternating10cmlongblackedgeswith blackpaint/markerisusefulforscalingobjectsizesandanalysingphotographs. 0.1 x 0.1m 0.5m 17(a) 17(b) (c) 1.0m Figure17Typesof0.25m 2 quadrat:(a)squarestringframe(b)basic (c)letterboxforsamplingovershortverticaldistancesonsteepshores 29

36 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Ecologists use quadrat samples to estimate the distribution and density of organismsinaparticularhabitat. Althoughquadratscanbeanyshape,theyareusuallysquare.Thisisusefulbecause they can be easily divided into smaller, regular sized areas to count very small, abundant organisms that occur in very high numbers in the quadrat (measuring abundanceusingasmallerareawithinthequadratsampleiscalledsubsampling). For example, in the quadrat below (Figure 18) there are thousands of blue periwinkles(austrolittorinaantipodum)insidethe0.25m 2.However,thenumberof periwinkles inside one of the smaller 0.1 m x 0.1 m squares can be counted more easily.thisrepresentsasubsampleofthefullquadrat. Figure18Showinghowtomeasureabundanceofsmallorganismsusingsubsampling (Thereare59inthe0.01m 2 subsample.thiswouldgiveancalculatedpopulationdensityof 59x100per1m 2 =5900individuals/m 2.) If larger organisms are present in low numbers, square quadrats can be easily flipped along their edges and placed next to each other to create a larger sized samplei.e.fourquadratsof0.25m 2 canbeplacedtogetheraroundasinglepointto makeonelargersquarequadratwithanareaof1m 2. Anumberofimportantfactorsneedtobeconsideredwhenusingquadratsincluding thenumber,placementandsizeofthequadrats Number Themorequadratsyouhave,thebiggeryoursampleisandthemorereliableyour sample calculation of the true population parameter (e.g. density or vertical distributionontheshore)willbe.itfollowsthatthebestnumberofquadratswould beenoughquadratstocompletelycoveryourseashorethisiscalleda census and isnotpracticalasthereisnotenoughtimetocounteverything.fortunately,thereis no need a survey is a method of estimating a statistical population parameter using measurements of smaller samples taken from within that statistical 30

37 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology population.somesimplestatistics,canbecalculatedthatallowecologiststopredict the accuracy of their sampling i.e. how close your surveyed value is to the actual populationvalue.whatyoutendtofindisthatthelargerthesampleyoutake,the closer your survey sample gets to the actual statistical population value; in theory, your value is the same as the actual value when you have sampled the entire habitat 18. Itisbettertouseseveralquadratsratherthanjustonelargeone.Eventhoughthe total area sampled might be the same, using several quadrats in different places helpstocreateamorerepresentativepictureofthewholesurveysite.theanimals andplantsontherockshoretendtobedistributedquiteunevenlyin patches ;ifyou tryandbuildapictureofthesurveysitefromjustonequadratyouwilleitherunder or overestimate an organism s abundance depending on whether your quadrat is placedonorbetweenoneofthepatches. Inthefollowingexample,theeffectofusingone1m 2 quadratiscomparedtousing fourrandomlyplaced0.25m 2 quadratstosamplealimpetpopulationfromasmall regionoftheshore(notethatthelimpetsarenottoscale). Figure19Samplingalimpetpopulationusingonequadrat.Theresult wouldbeverydifferentifthequadratwereplacedinpositionaorb. Theareaoftheshore(insidethedashedborder)is6m 2.Thereare24limpetsin total. Therefore the actual population density of limpets in this area is 24/6 = 4 limpets/m Thisrarelyhappensaseventhebestsurveyorsoverlooksomeorganismsintheirsampleor miscountthem.thesearenormalsamplingerrorsandcanbereducedandquantified,butnever eliminated seethesectiononaccuracy,validityandreliability. 31

38 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Firstwecanseeaneffectofsamplingwithasinglelargequadratof1m 2 area(figure 19).IfthequadratisplacedatAthenthedensitywouldbe11/m 2 whichistoohigh. IfthequadratwereplacedatB,thenthedensitywouldbeonly1limpet/m 2 whichis toolow. So even though the total area sampled is the same, the results are very differentandneitherisveryaccurate. Hereisanalternativeusingfourrandomlyplaced0.25m 2 quadrats(figure20).the total area sampled is the same as the 1 m 2 quadrat(4x0.25m 2 =1m 2 ). The populationdensityisthesumofthenumberoflimpetsinthefourquadrats: =4limpets/m 2 whichismuchclosertotheactualdensityofthelimpets.note that the quadrats that are empty are important in gaining an accurate value of the densityestimateastheyhelptoshowthepatchydistributionofthelimpetsintheir habitat Placement Figure20SamplingalimpetpopulationusingfourrandomlyVplaced quadrats. An important assumption of any survey is that it is representative of the larger populationbeingstudied.thismeansthatnofeatureofthepopulationisunderor overorepresented in the results. It is important to randomise the location of the samples in the habitat to avoid your survey being biased. Bias is when there is a tendencytochooseorselectsomethingthatcaninfluenceresults.insurveying,this may be selecting the position of a quadrat on the shore to include an interesting feature, or clump of organisms or even toavoid having to count a large clump of tinyorganismsthiscouldleadtoanestimatethatisinaccurateandmaynotreflect thetruenatureofthesitebeingsurveyed.iforganismsoccurinclumps,thespace between them is just as important as the clumps themselves and needs to be includedinthesurvey;iftherealenvironmentispatchy,avalidsurveyshouldshow this. 32

39 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Letuslookatourlimpetexampleagain.Ifthepositionofthequadratswaschosen, thenwemightbetemptedtoplacethequadratsinareaswherethelimpetsare,and avoidtheareaswheretheyarenot(figure21).wecanseethatthiswouldleadtoa large overestimate of their actual abundance in this habitat: = 14 limpets/m 2 comparedtoanactualdensityof4limpets/m 2. Figure21Showingtheimportanceofselectingrandomsitestopositionthequadrats. But in this habitat, just like on the rocky shore, the limpets are not distributed evenly;theyarerandomlydispersedinpatchesthroughoutthesurveyarea.sofor oursamplestoaccuratelydescribetherealhabitatweneedtorepresenttheareasin thehabitatwithoutanylimpets thespacebetweenthelimpetsisjustasimportant astheclumps;andthebestwaytorepresenttheentirehabitatisbynotchoosing wherethequadratsareplacedbutpositioningthemrandomly Size Thesizeofaquadratisveryimportant.Alotofstudyhasbeendoneonthe best sizeofquadrattouse.avalidquadratsizedependsonwhatisbeingcounted.for intertidalrockyshoreorganisms,aquadratwithanareaof0.25m 2 isoftenusedand suitableforestimatingabundanceformostorganisms.iflargermotileanimalslike seastars, urchins or kelp plants are present then a larger sample is required. This canbeaslargeasyoutimeandresourcesallow. How do you know that the quadrat area is big enough? You can plot a species accumulation curve (Figure 22). This is done by first recording the number of species in a small quadrat, then counting the number of new species found as the 33

40 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology sizeofthequadratisincreased.thenumberofnewspeciesfoundasaddedtothe number found in the smaller quadrat and a cumulative or running total is calculated.asthecumulativenumberofspeciesbeginstoleveloff,youcanpredict whattheoptimumquadratsizewillbe.inthediagrambelow,theoptimumquadrat sizewouldbearoundpointxwherethemajorityofthepredictednumberofspecies willbefoundforareasonablecountingeffort. Cumulativenumberofspecies Plateau= likelymaximum numberofspecies X Quadratarea Figure22SpeciesVaccumulationcurveshowingtheeffectofincreasingsamplesize onthenumberofspeciesrecorded. Increasingthesizeofthequadratbeyondthispointisonlylikelytoproduceasmall increaseinthenumberofspeciesyetwouldrequirealotmorecountingeffortsois probablynotworthit. 34

41 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology PART4:THETIDES Theeffectofthetidesisthattheheightoftidalseaschangesinaregular,predictable cycle. Themoonandthesuncreateagravitationalpullonthewateroftheworld sseasand oceansandcreateatidalforce.althoughthesunhasmoremassthanthemoon,the sunismuchfurtherawayfromtheearthanditstidalforceisonlyabouthalfthatof themoon. Thesegravitationalforcescreatea bulge ofwaterontheearth ssurfaceinthe directionofthepull.becausetheearthisspinning,anothercorrespondingbulgeis created on the opposite side of the Earth where the gravitation attraction by the moon is less and by soocalled centrifugal force. These two bulges correspond to increasedsealevelsthatwecallhightides. Onaslopinglandmass,theincreaseinheightofseawateroverapointcorresponds tothefloodtidewesaythetideis comingin.aswepassthroughthebulgingtidal sea,thewaterleveldropsandweexperienceanebbtideasthewater goesout. AstheEarthrotatestowardtheEast,thetwobulgesofwaterseemtotravelaround theearthacrossthesurfacetowardsthewest butastheearthrotatesitmoves beneaththebulges. 35

42 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology It takes one solar day (24 hours) for a complete rotation of the Earth on its axis. ThereforeapointontheEarth ssurfacewouldbeexpectedtopassbeneathabulge ofseawatertwiceaday,givingtwohightidesperdaythatwere12hoursapart. 36

43 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Butthemoonismovingtoo.Ittakes28daystocompleteoneorbitaroundtheEarth. Asthemoonmoves,itdelaysthetidalcycleeachdayby1/28 th of24hoursor51 minutes.thismeansthatthetimebetweentwohightidesisnot12hours,but12 hours51minutese.g.ifthefirsthightideonday1wasat09:00,thefirsthightideon day2wouldbeapproximately09:51. 37

44 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology When the moon and the sun are aligned in the same plane as the Earth, their gravitational forces are added together to create an extraolarge tidal bulge on the Earth ssurface.asmorewaterispulledintothesebulges,thetroughsinbetween containlesswaterandsocorrespondtoextralowtides.theselargetidesarecalled SpringTidesandoccurtwiceamonthduringnewmoonandfullmoon. 38

45 EcologyoftheNewZealandRockyShoreCommunity: AResourceforNCEALevel2Biology Whenthesunandmoonareatrightanglesduringthequartermoonphases,the smallerbulgeofthesunisaddedtothelowtidecreatedbythemoon.thisresultsin alowerhightideandahigherlowtide.thesetidesarecalledneaptidesandoccur everytwoweeksbetweenthespringtides. 39