1. 2015
Intertidal variations in
populations of Hormosira Banksii
due to wave exposure
ABSTRACT
Intertidal areasprovide diversecommunities,andare influencedbymany
differentbioticandabioticfactors. Hormosira Banksiiisa dominantspecies
withinthese ecosystems,andhasa broad distributionthroughoutthe
temperate Australiana.We monitoredarange of factors(Percentage cover,
numberof individualsinpopulation,frondlength) of H.Banksiiin the intertidal
zone,samplingfromtwodistinctive areasof shelteredfromorexposedto
waves,withthe aimto determineif there isasignificantdifferencein
populations.We foundthatthere washighermeasuresof frondlengthand
abundance inshelteredareasincomparison toexposedareas,witha
significantdifference(p<0.05) recordedacross all three variables.These
resultsserve tohighlight H.Banksii’s abilitytoadapttomicroclimates,and
distinctivelyhighlight differencesinphysiologyandabundance between
sample populationsindifferentmicroclimates.
JACK DAVIS: 698625
Word Count:1870

2. Introduction
Intertidal rockymarine environmentsprovide ecologistswiththe opportunitytostudyspecies
distributionpatterns,andcanleadto a comprehensive understandingof environmentalprocesses.A
varietyof differentbiological andphysical processesinteract withcommunitiesof species
populationsresulting inquite distinctdistributionpatterns.Intertidal algae canbe effectedbya
myriadof differentprocesses,includingwave exposure,lightexposure andtemperature of the
water,and isimportantas intertidal algae are the largestprimary producersinthe intertidal
communitywiththeirbiomassdominatingecosystemsinturnprovidinghabitatandfoodfor
numerousaquaticspecies (Harvey,1860) (Taylor,2002). The effectof wave exposure isknowntobe
importantfornumerousaquaticorganisms (Underwood&Jernakoff,1984) (Westerbom&Jattu,
2006), but wasprovenby McKenzie,PrudenceandBellgrove(2009) to be an importantmechanism
inthe dispersal of fertile Hormosira Banksiitissue.
H. Banksii,also knownas‘Neptune’sNecklace’orby‘Necklace Seaweed’, isamonotypicbrownalga
native totemperate watersaroundthe Australianmainland,Tasmania,NorfolkIsland,LordHowe
IslandandNewZealand (Osborn,1948). The speciesinhabitsexposedrockplatformswithin
intertidal regions,andisknowntobe fertile all yearroundchieflydue toitsdioeciousnature. H.
Banksii isalsoextremelydroughttolerant,and itsphysiologyisknowntochange due todifferent
environmental factors (Harvey,1860).The effectof wave exposure hasbeenstudiedextensively,
and the physiologyof the planthasbeennotedtovarywhendependingonwave exposure (Osborn,
1948) (Taylor,2002) (McKenzie &Bellgrove,2009).However,the hasbeennosignificantresearch
conductedondetailingthe effectof wave exposure on Hormosira Banksii,andwhetherthere’sa
significantdifferencebetweenorganismsize andabundance betweenshelteredpopulationsin
comparisontospeciespopulationsexposedtowaves.
Method
Data for Hormosira Banksiiwas monitoredinthe fieldatPointGellibrandCoastal HeritagePark,
Victoria(37°52’ S,144°54’), in one site visitatthe endof winter(23rd
of August,2015). Withinthe
site data onorganismabundance andfrondlength wascollectedfromthe rockyintertidal zone
alongthe foreshore reserve,fromapproximately11am throughto 1pm as the tide receded(High
tide:8:22 am, Low tide;2:05 pm),withthe dayreachingan maximumtemperatureof 15.5 °C during
the day withSoutherlywindgustsof upto11 km/hour (Bureauof Meteorology,2015)
(WillyWeather,2015).Data was sampledattwo replicate sitesalongthe foreshorereserve,witha
significantdistancebetweeneach site.
To define the twomicroclimates,shelteredandexposed,itwasagreedthata shelteredarea
consistedof the presence of arock barrier(10 cm above or below the waterlevel) thatwasvisually
observedtodisturbthe movementof the wavesbetweenthe barrierandthe shore,withthe
exposedareabeing the rockbarrierandintothe PortPhilliparea. 24 replicateswere collectedfrom
the shelteredareas,usinga50cm by 50cm quadrat.Withinthe quadrat 3 differentfactorswere
recorded:abundance,numberof individualswithinthe quadratandfrondlength.Abundance was
recordedas the percentage of coverage,andestimatedbytwoindividualsunanimously. Frond
lengthwasrecordedbymeasuringfromthe holdfasttothe endof the longestfrondonthe organism
usinga clearplasticruler.Whilstmeasuringfrondlengthof individualswithinaquadratthe number
of individualsinthe quadratwere recorded. 135 individualreplicate measuresof frondlengthwere
collectedfrombothshelteredpopulationsand exposedpopulation,howevermore quadratdatahad
to be collectedfromexposedareastosample 135 individualswithinthe exposedpopulations.

3. Replicatesof the quadratswere randomlytakenfromboththe shelteredandexposedareas,
howeverreplicateswereonlytakenfrom H.Banksiihabitat,predominatelyrockyseafloorswhere it
attachesto.
Results
Figure 1 presentsthe meannumberof individualplantscountedwithin asample populationat
eithersite.There isasignificantdifference(p value <0.05) betweenthe numberof individual
organismswithinthe populationata shelteredsite incomparisonto apopulationwithinan exposed
site,withonaverage there beingapproximately4more organismswithina H. Banksiipopulation
withinashelteredsite than atan exposedsite. Figure 2indicates thatH. Banksiihas a significantly
higherpercentage coverwithinashelteredsite (mean=35.6, n=24, SE = 4.875) than at an exposed
site (mean= 14.67, n = 24, SE = 2.51, df = 23, p value < 0.05; Fig.2), whereas percentage coverwas
≈21% inshelteredpopulations.Thesetwovariablesboth indicate thatwithinashelteredsitethere is
a higherabundance of H. Banksii.No otherspecies were observedateitherthe shelteredorexposed
site,leavingthe percentage notcoveredby H.Banksiiseafloor.
Figure 1: Mean (± Standard Error) number of individuals, sampled from in exposed and sheltered areas. N = 24
7.25
3
0
1
2
3
4
5
6
7
8
9
Sheltered Exposed
Numberofindividuals
Sample Area
Qty

4. Figure 3 displaysthe mean(±s.e.) frondlengthwithinpopulationsateithershelteredorexposed
sites.Frondlength withinpopulationsatshelteredsitesare significantlydifferent(n= 135, df = 134,
p value < 0.05) fromlengthsinexposedpopulations. The frondlengthforshelteredpopulations
(mean= 18.5, n = 135, SE = 0.55) ison average significantlyhigherthan exposedpopulations(mean=
10.42, n = 135, SE = 0.62, df = 134, p < 0.05).
Figure 3: Mean (± SE) frond length at sheltered and exposed sites. N = 135
Discussion
Data from Figures1, 2 and 3 prove that there’sasignificantdifferencein Hormosira Banksii
individualspecimensandspeciespopulationsdependingonwhetherthey’re shelteredbyarock
barrieror exposedtowaves.Figure 1and 2 suggestthatshelteredpopulationsare more abundant
35.58333333
14.66666667
0
5
10
15
20
25
30
35
40
45
Sheltered Exposed
PercentageCover(%)
Sample Area
Abundance
18.52222222
10.42222222
0
5
10
15
20
25
Sheltered Exposed
FrondLength(cm)
Sample Area
Frond Length
Figure 2: Mean (± SE.) percentage cover of populations in both exposed and sheltered
microclimates. N = 24

5. (meanpercentage cover[%± SE] = 35.6 ± 4.875, numberof specimen[#individuals±SE] ≈ 7 ± 0.75)
than exposedpopulations(meanpercentagecover[% ±SE] = 14.7 ± 2.5, numberof specimen[#
individuals±SE] ≈ 3 ± 0.4), whilstfigure 3 suggestsfrondlengthin shelteredpopulations (mean=
18.5, n = 135, SE = 0.55) issignificantlylongerthaninexposedpopulations (mean=10.42, n = 135,
SE = 0.62, df = 134, p < 0.05). H. Banksiirequiresarock platformforthe holdfasttoattach to,which
createsa fundamental niche inwhichthe speciescangrow in (Harvey,1860) (McKenzie &Bellgrove,
2009) (Osborn,1948) (Taylor,2002).
Thisfundamental niche wasalso,however,the realisedniche forthe speciesasthere wasobserved
competitionfromanyotherspeciesof intertidal algae. Thiscould be explainedif H.Banksiihad
colonisedasite withlittle tonocompetitionfromotherspeciesdue the effectof predationfrom
aquaticlife suchas fish speciesorinvertbrae grazers,as HBanksii has nosignificantpredators,or
poor recruitmentforsessile marinespeciesdue tostagantsedimentof rocksurfaces (Taylor,
2002)(Osborn,1948) (Underwood&Jernakoff,1984) (Westerbom&Jattu,2006). Taylor(2002)
foundthat H. Banksiiwas more abundantat wave protectedorshelteredsites,corelatingwiththe
data displayedin Figures1and 2. However, H.Banksii’abundance insheltered,intertidal rockyareas
couldalsobe attributtedtothe species resiliance todesication,asthe species’possessesinternal
waterreserveswhichrenderthe organismmore orless‘droughtresistant’ (Osborn,1948).This
internal waterreserve,coupledwithdioeciousnature,annual fertilityandlackof signicant
predators, couldpotentiallyallow H.Banksiito colonise intertidalareaoutside of otherspecies
realisedniches. Thiswouldalso corelatewiththe proposedinverse relationshipbetweenpredation
and speciescompetitioninintertidal areas,which ismostprominentin midandhighlevelsof the
intertidal area(Lubchenco&Menge,1978).
H. Banksii populations inexposedregionswere consistenlysmaller,withfewerindividualsina
sample population,smallerpercentage coveredforapopulationsample andsmallerfrondlength
measurements.Consideringthe niche H.Banksiirequirestogrow,smallercoverage sizesfrom
quadrat samplingmayreflectthe limitedavailibilityforthe holdfastof the organismtoattachto,
whilstthe lowcountof individaulorganismscouldbe attributedto H.Banksii’s tendenceytodisplay
a weakattachmentstrength,incomparisontootherintertidal algea (McKenzie &Bellgrove,2009).
The weakattachmentstrengthcouldexplainthe higherpercentagecovervs.numberof individuals
ina sampledpopulation,asthe organismstill needsthe frondcellstofunctionbutthereforemust
grow themina more spread,compact mannerthanthe organismsprotectedfromwave exposure.
Thismay alsobe due to the observeduniquecapabilitiesof the genecticof the organism, as H.
Banksii frondsare regularlybreakdislodgefromthe holdfastwhilstitremainsattachedtothe parent
rock, allowingunimpededvegative regeneration (Underwood&Jernakoff,1984).This,coupledwith
the organismsabilitytoregenerate adamagedholdfast,appearstobe an evolutionaryadaptionto
survivinginthisaparticularniche and hence the breakpointandfore describedregenative
capabilitiesare adaptionsthatallowthe speciestothrive inanexposedareaandfurthercolonise
the area throughtide drivenlongdistance dispersal mechanisms (McKenzie &Bellgrove,2009)
(Osborn,1948) (Underwood&Jernakoff,1984).
The sample populationsfrom shelteredandexposedareasdemosntrate significantdifferences
betweenthe twopoulations.However,the twodifferentpopulationsare andisplayof localised
adaptionstoenvironmental conditionswithsignificantspeculationfromearlydocumentersof the
spciesasto whetherthese localisedadaptionsare differentspecies,assummedupfirstbyHarvey
(1860) : “Whoeverhasseenandcarefullystudiedthisplantonit’snative coastswillfullyagree with
me inr educingtoone specieswiththe several synonymsenumerated……The differencesinsize and
shape of the vesiclesseemtoresultmerelyfrom local causes;eitherfromthe depthof the waterat

6. whichthe specimenwasgrown,orfromexposure tothe opensea,or shelterinenclosedharbours…
…Intermediate formsbetweenall the varieitiesmaybe readilyfound”.The speciesabilitytoadaptto
numerousenvironmental conditionsindicatesthat H.Banksii isboth a strongcompetitorinit’s
natural habitat. To betterformconclusionsabout H.Banksii’sinshelteredandexposedareas,and
understandthe ecological driversbehindthesedifferences, more comprehensive biodiversity
surveysshouldbe conducted tobetterunderstandgrazerssuchasgastropodsonthe communityas
well asa surveyof the percentage of niche requirementsinthe shelteredandexposedareas. This
studyservestohighlightthe difference betweenabundanceandphysiologyin H.Banksiisample
populationswithinshelteredandexposedareas.
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