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Water2022,14,3187.https://doi.org/10.3390/w14193187www.mdpi.com/journal/water
Article
EffectofSeawaterandSurface‐SedimentVariablesonEpipelic
DiatomDiversityandAbundanceintheCoastalAreaofNegeri
Sembilan,Malaysia
AhmedAwadhSas
1,2
,SuNyunPauSuriyanti
1,3
,SimonKumarDas
1,3
andZaidiCheCob
1,3,
*
1
DepartmentofEarthSciencesandEnvironment,FacultyofScienceandTechnology,
UniversitiKebangsaanMalaysia,Bangi43600,Malaysia
2
DepartmentofMarineBiology,FacultyofEnvironmentalScienceandMarineBiology,
HadhramoutUniversity,MukallaP.O.Box50512,Yemen
3
MarineEcosystemResearchCenter(EKOMAR),FacultyofScienceandTechnology,
UniversitiKebangsaanMalaysia,Bangi43600,Malaysia
*Correspondence:zdcc@ukm.edu.my
Abstract:Benthicdiatomsareimportantcomponentsofmarineshallow‐waterhabitatsthatmay
affectprimaryproduction,stabilizesediment,andproduceextracellularpolymericsubstances.Ben‐
thicdiatomsareusefulforestimatingthetrophicstatusofmarineecosystems.Inthisstudy,we
investigatedthediversityandabundanceofbenthicdiatomstointegratethesedatawiththephys‐
icochemicalcharacteristicsofshallowcoastalareasinNegeriSembilan.Atotalof39speciesofepi‐
pelicdiatomswereextractedbyremovingorganicmatterfromsedimentsthatweredominatedby
pennatediatoms.ResultsshowedthatDiploneiscrabro,Eunotogrammalaevis,Actinoptychussp.,and
Cocconeisplacentulaweretheimportantspeciesinthearea.Theabundancevariedbetween1.85×10
3
and3.43×10
3
cells/g,andthediversityindexfluctuatedbetween2.13and2.58.Theabundancehad
significantpositivecorrelationswithseawatersurfacetemperature(SST)buthadnegativecorrela‐
tionswithpHandNH
3
.ThediversityontheotherendwaspositivelycorrelatedwithSSTbutneg‐
ativelycorrelatedwithtotalsuspendedsolidsandSiO
2
.Principalcomponentanalysis(PCA)
demonstratedthattheabundanceofD
.
crabro,E.laevis,andActinoptychussp
.
canbeattributedto
highlevelsofNO₂
–
,NH
3
,andtotaldissolvedsolids.PCAalsoshowedpositivecorrelationsofC
.
placentulawithNO
3–
andSiO
2
butnegativeoneswithPO
4−3
andpH.Theepipelicdiatomcommunity
showedhighdiversitywithhighvariationsthroughoutthestudyarea.
Keywords:benthicdiatom;species;pennate;variations;NegeriSembilan
1.Introduction
Coastalareasarehighlyproductiveregionsoftheocean,withhighcontributions
fromplanktonicandbenthicprimaryproduction.Althoughcoastalareasandestuaries
constitutelessthan10%oftheocean,theycontributeupto30%oftheocean’sprimary
production[1,2].Theyserveasimportantnurserygroundsforfishlarvae,habitatsfor
benthicorganisms,andfeedinggroundsformanymarineanimals[3].Coastalareasare
alsotheepicenterofhumansettlementandactivities,wherealmostthree‐quartersofthe
world’shumanpopulationresides.Consequently,anunprecedentedincreaseinnutrients
andotherenvironmentalissuesassociatedwithcoastaldevelopmenthasoccurred[4].
Problemssuchasnutrientover‐enrichmentandeutrophicationofestuarineandcoastal
ecosystemsarecommonandaccelerating[4].
Diatoms(ClassBacillariophyceae)constitutethemainmassofmarinephytoplankton
andhaveaworldwidedistribution,withrecentestimatesrangingfrom12,000to30,000
species,contributingaround20%ofthetotalphytoplanktonprimaryproduction[5,6].
Citation:Sas,A.A.;Suriyanti,S.N.P.;
Das,S.K.;Cob,Z.C.Effectof
SeawaterandSurface‐Sediment
VariablesonEpipelicDiatom
DiversityandAbundanceinthe
CoastalAreaofNegeriSembilan,
Malaysia.Water2022,14,3187.
https://doi.org/10.3390/w14193187
AcademicEditor:LiudmilaS.
Shirokova
Received:29August2022
Accepted:7October2022
Published:10October2022
Publisher’sNote:MDPIstaysneu‐
tralwithregardtojurisdictional
claimsinpublishedmapsandinstitu‐
tionalaffiliations.
Copyright:©2022bytheauthors.Li‐
censeeMDPI,Basel,Switzerland.
Thisarticleisanopenaccessarticle
distributedunderthetermsandcon‐
ditionsoftheCreativeCommonsAt‐
tribution(CCBY)license(https://cre‐
ativecommons.org/licenses/by/4.0/).
Water2022,14,31872of13
Diatomsinestuariesorshallowmarinesystemscanbeclassifiedintotwogroups,namely
thebenthicandpelagicgroups.Theformercanberesuspendedintothewatercolumnby
turbulence[7].Epipelicdiatomsoftendominatethemicrophytobenthos,whichisim‐
portantfortheprimaryproductivityofthebenthiczone[8].Theirdiversityandcomposi‐
tioncanbeinfluencedbywide‐rangingenvironmentalvariables[9,10],andtheirgrowth
formsshowadistinctdistributionamongintertidalhabitatscharacterizedbydifferent
typesofsediment[11,12].
Physicochemicalvariablessuchaswatertemperature,salinity,nutrients,pH,and
DOareamongthemostimportantfactorscontrollingphytoplanktongrowth,diversity,
andproductioninmarineenvironments[13,14].Epipelicdiatomsprovidemanybenefits
inthecoastalarea,suchasbeingasourceofprimaryproductionandthemainfoodsource
formicroherbivores.Theycanalsobeusedforbiologicalmonitoringbecausetheylieat
thebaseofaquaticfoodwebsandareamongthefirstrapidresponsetotheenvironmental
stressoforganisms[10,15].Despitetheirubiquityandfunctionalimportance,thespatial
andtemporalpatternsoftheabundanceanddiversityofepipelicdiatomgroupsare
poorlyunderstood.InMalaysia,thetaxonomiccompositionofintertidalepipelicdiatom
communitiesremainsrelativelyunknown.Conversely,thephytoplanktontaxonomyof
Malaysiahasbeenstudiedindetailovertheyears[16].Previousstudiesonphytoplankton
intheMalaccaStraitshavebeenconductedbyseveralauthors[16–25].Theyhaveshown
thatdiatomsarehighlydominantinplanktonandcontributeasmainactorsinthepelagic
realms.Diatomsmayalsobethedominantgroupinthebenthicarea,butthisaspecthas
rarelybeenreportedwithintheMalaccaStraitareas.Benthicdiatomsareindeedavery
importantcomponentofcoastalandestuarinesystemsandrepresentakeycomponentin
theprimaryproductionofthesecoastalhabitats.Theyareresponsibleforupto30%of
carbonfixationofthoseecosystems,sotheyaresuppliersoforganiccompoundstograzers
todepositfeeder’saquaticorganisms,includingmacro‐andmeiofauna.Accordingly,the
currentresearchaimstofillthegapsandcontributestotheknowledgeofepipelicdiatom
diversityandabundanceincoastalhabitats,aswellastoevaluatetheroleofphysico‐
chemicalvariablesinaffectingtheepipeliccommunitycompositionintheintertidalzone
ofthePortDicksonCoastofNegeriSembilan,MalaccaStraitsarea,Malaysia.
2.MaterialsandMethods
2.1.StudyArea
ThestudyareawaslocatedwithinthecoastalareaofPortDickson,inNegeriSembi‐
lan,Malaysia.Thecoastisabout54kmlongandfacestheStraitsofMalacca.Fieldsam‐
plingswereconductedinDecember2019,duringlow‐tideperiods.Surfacesedimentsam‐
pleswerecollectedfromsixsamplingstations(denotedasSt.1toSt.6)locatedwithinthe
intertidalzones,withfivereplicatesamplesateachstation.Thesefivesampleswerecol‐
lectedfromeachsiteandcompositedintoonehomogeneoussamplerepresentingthesta‐
tion(Figure1).TheepipelicdiatomsweresampledusingaPVCcoreof8.4cmdiameter,
andsamplingwasperformedonthesameday,withatimedifferenceoflessthanhalfan
hourbetweenstations.Thetop1cmlayerofwetandexposedsurfacesedimentsatthe
edgeoftheseawaterwascollected.Thesedimentscontainingepipelicdiatomswere
placedinablackpolythenebagandmaintainedindarknessinarefrigeratoruntilpro‐
cessinginthelaboratory[26].
Water2022,14,31873of13
Figure1.StudyarealocatedalongthePortDicksoncoast,Malaysia,stretchingfromSungaiSepang
inthenorthtoTanjungTuaninthesouth.Circlesindicatethesamplingstations.
2.2.EpipelicDiatomExtractionandCounting
Epipelicdiatomswerecollectedandextractedaccordingtothemethoddescribedby
[27,28].Around1gofwetweightofsurfacesedimentwasheatedat70°Cwith30%hy‐
drogenperoxide(H2O2)and10%HClinawaterbathuntilallorganicmatterandcar‐
bonatesweredigested.Thesedimentwassubsequentlywashedwithdeionizedwaterand
lefttosettletoremovetheacids.Around0.5mLofcleanedsamplewastransferredtoa
coverslipandairdriedonawarmhotplate.Threepreparedslidesfromeachsamplewere
countedfortheepipelicspecies,resultinginthreereplicateabundanceestimates.
Countingandidentificationwereconductedunderacompoundlightmicroscope
(LeicaDM1000LED,Wetzlar,Germany)withacounterchamber(Sedgwick‐Rafter,Grat‐
iculesOpticsLimited,Cambridge,UK).Identificationwasbasedonpreviousdescriptions
[26,29–31].EpipelicdiatomdiversityandrichnesswerecalculatedusingtheShannon–
Wienerindex[32]andMargalef’sindex[33].
2.3.EnvironmentalParameters
Surfaceseawatertemperature(SST),surfaceseawatersalinity(SSS),dissolvedoxy‐
gen(DO),electricalconductivity(EC),totaldissolvedsolids(TDS),andpHweremeas‐
uredinsituwithahandheldGPSAquameter(AP700,Bath,UK).Around3Lofseawater
sampleswerecollectedinaplasticcontainerfromtheintertidalzoneandimmediately
keptinacoolconditionbeforetransportingbacktothelaboratoryfornutrientanalysis.
Nitrate(NO3−),nitrite(NO2−),ammonia(NH3),silica(SiO2),andphosphate(PO43−)were
analyzedusingaHACHDR2010spectrophotometer(HACHCompany,Loveland,CO,
USA).Totalsuspendedsolid(TSS)concentrationsweredeterminedbyapreviouslyde‐
scribedmethod[34].Forchlorophyll‐aanalysis,theseawatersampleswerepassed
throughaGF/Ffilterpaper(WhatmanGF/F‐F4‐4700,Maidstone,UK),whichwasthen
coveredwithaluminumfoilandplacedinadeepfreezer(HaierDW‐40L262,Qingdao,
Shandong,China)indarknessat−20°Cuntilextractionwith10mLof90%acetone[35].
Chlorophyll‐awasdeterminedwithaspectrophotometer(ShimadzuUV/VISmini‐1240,
Kyoto,Japan).ResultswerecomparedwiththeMalaysianMarineWaterQualityStand‐
ards(MMWQS)publishedbytheDepartmentofEnvironment,Malaysia[36].Sediment
Water2022,14,31874of13
organicmatter(OM)wasestimatedbythepercentagelossonignitiontechniqueasde‐
scribedby[37].Ahalf‐gramofwetsedimentwasovendriedfor~24hat90°C(Memmert
universalovenUN30,Büchenbach,Baden‐Württemberg,Germany)toaconstantweight.
Theremainingdrysedimentwasthencombustedinamufflefurnace(Daihanscientific
co.ltd.,Gangwon,SouthKorea))at550°Cfor4hforcompleteignitionoftheOM.After
ignition,thesedimentsampleswerecooledinadesiccator,andtheweightloss(%dry
weight)wasdetermined.
2.4.DataAnalysis
Statisticaldataanalysis(Pearsoncorrelationcoefficient)wasperformedusingSPSS
20.0(IBM,Armonk,NY,USA).Tocharacterizephysicochemicalvariablesandtheirinflu‐
enceonepipelicdiatomsinthestudystations,principalcomponentanalysis(PCA)was
performedusingadatasetof14seawaterparametersandepipelicdiatomabundancedata
inthestudyarea.
3.Results
3.1.EnvironmentalConditions
Thespatialvariationsinphysicochemicalvariablesalongthecoastalareaaresum‐
marizedinFigures2and3.Ingeneral,temperaturevariationsinthecoastalwatersofthe
PortDicksoncoastaresmall,rangingfrom(28.73±0.26)°CinSt.3to(31.19±0.28)°Cin
St.5.However,thevariationsinSSSlevelsarehigh,rangingfrom(20.20±0.26)pptinSt.3
to(27.33±0.35)pptinSt.5.ThepHrangedfrom7.72±0.30inSt.1to8.34±0.38inSt.2,and
theDOrangedfrom(6.72±0.33)mg/LinSt.5to(7.74±0.30)mg/LinSt.1.TheECwas
relativelyconsistent,rangingfrom(26,220.67±27.08)μS/cminSt.1to(30,853.75±18.6)
μS/cminSt.6.TheTDSalsoshowedhighvariations,rangingfrom(18,532.67±13.7)mg/L
inSt.6to(19,420.33±15.31)mg/LinSt.4,whereastheTSSfluctuatedbetween(45.4±0.83)
mg/LinSt.4and(77.91±0.95)mg/LinSt.1.ThesedimentOMvariedbetween21.00±0.8%
and25.85±0.49%,withmaximumvaluesinSt.6andminimuminSt.2(Figure2).
0
5
10
15
20
25
30
26
27
28
29
30
31
32
St.1 St.2 St.3 St.4 St.5 St.6
SST (°C)
SST SSS
Stations
SSS (ppt)
0
2
4
6
8
10
0
2
4
6
8
St.1 St.2 St.3 St.4 St.5 St.6
PH
pH DO
Stations
DO (mg/L)
Water2022,14,31875of13
Figure2.Variationsinseawaterparameters(mean±SD)alongthestudyarea:seawatersurface
temperature(SST)andsalinity(SSS);pHanddissolvedoxygen(DO);electricalconductivity(EC)
andtotaldissolvesolid(TDS);andtotalsuspendedsediment(TSS)andorganicmatter(OM).
Amongthenutrients,NO
3–
rangedfrom(0.018±0.0014)mg/LinSt.5to(0.033±
0.0007)mg/LinSt.3.TheNO
2–
concentrationswererelativelylower,rangingfrom(0.002
±0.0006and±0.0012)mg/LinSt.5andSt.6,to(0.01±0.007)mg/LinSt.2.NH
3
rangedfrom
(0.38±0.021)mg/LinSt.6to(0.53±0.014)mg/LinSt.3,whichwasmuchhigherthanthe
nitrate+nitritelevels.PO
4−3
concentrationswerenotaspronouncedastheammonia,with
thehighestconcentrationrecordedinSt.5(0.21±0.011)mg/LandthelowestinSt.2(0.04
±0.002)mg/L.SiO
2
rangedfrom(0.08±0.011)mg/Lto(0.11±0.014and±0.012)mg/L,with
thelowestconcentrationsinSt.
1
andhighestinSt.2and
St.5.Therangeofconcentration
forChl‐ainthesixstationswasfrom0.10±0.028mg/Lto0.13±0.021mg/L,withthe
highestconcentrationrecordedatSt.6andthelowestatSt.5(Figure3).
Figure3.Variationsinseawaternutrients(mean±SD)alongthePortDicksoncoasts,Malaysia:
nitrate(NO
3–
)andnitrite(NO
2–
);ammonia(NH
3
)andphosphate(PO
4−3
);andchlorophyll‐a(Chl‐a)
andsilica(SiO
2
).
18,000.00
18,500.00
19,000.00
19,500.00
20,000.00
22,000.00
24,000.00
26,000.00
28,000.00
30,000.00
32,000.00
St.1 St.2 St.3 St.4 St.5 St.6
EC TDS
Stations
EC ( μS/cm)
TDS (mg/L)
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.000
0.010
0.020
0.030
0.040
St.1 St.2 St.3 St.4 St.5 St.6
NO₃⁻ NO₂⁻
NO₃⁻ (mg/L)
NO₂⁻ (mg/L)
Stations
Water2022,14,31876of13
3.2.DynamicsofEpipelicDiatoms
Atotalof39epipelicdiatomspecieswerecollectedandidentified,andthepennate
diatoms(78%atSt.5)weremoredominantthanthecentricones(47%atSt.1)(Figure4a).
Theoveralldiatomabundancerangedfrom(1.85×103±0.09cells/g)inSt.3to(3.43×103±
0.18cells/g)inSt.6(Figure4b).TheShannon–Wienerdiversityindex(H’)wasrelatively
high,rangingfrom2.13inSt.1to2.58inSt.4,whereastheMargalef’srichnessindexranged
from1.32inSt.2to2.08inSt.5.
Figure4.Epipelicdiatompopulationparametersalongthestudyarea.(a):Percentagecontribution
ofpennatediatomandcentricdiatom;(b):Abundance,diversity(Shannon–Wienerindex)andrich‐
ness(Margalef’sindex).
Thepercentagecompositionofdiatomspeciesrecordedateachstationissumma‐
rizedinTable1.CocconeisplacentulaandEolimnaminimawerethemostcommonspecies,
with67%occurrence.Notably,eachstationwasdominatedbydifferentspecies,whereC.
placentulawasdominantinSt.1(41%),DiploneiscrabroinSt.2(24%),Eunotogrammalaevis
inSt.3(34%),Actinoptychussp.inSt.4(15%),Amphorasp.inSt.5(28%),andCoscinodiscus
sp.inSt.6(15%)(Table1andFigure5).Theseresultsindicatedhighspatialvariationsin
epipelicdistributionalongthestations.
Water2022,14,31877of13
Table1.Listofepipelicdiatomsspeciespredominance(%)atthesamplingstationsalongPortDick‐
soncoast,Malaysia.Occurrence(%Pr):0–20(sporadically,S);21–40(rarely,R);41–60(commonly,
C);61–80(frequently,F);and81–100(highlyfrequently,H).
St.1St.2St.3St.4St.5St.6%PrClass
A
ctinoptychussp.
9
3
15 50
C
A
.undulates
(J.W.Bailey)Ralfs,1861.
3
3
5
50
C
A
mphoraarenariaDonkin,1858.13
8
4
50
C
A
mphorasp.
2
5
2850
C
A
uliscuselegansAuliscuselegansvar.californica
(GrunowinSchmidtetal.)Rattray,1888.
4
5
8
50
C
Caloneissp.
8
3
33
R
Campylodiscussp.
7
3
6
50
C
CocconeisplacentulaEhrenberg,1838.4114
5
1
67
F
C.radiatusEhrenberg,1840. 1217
X
C.gigasvar.praetexta(Janisch)Hustedt,1930.
7
9
11 50
C
Coscinodiscussp.
6
1533
R
CyclotellastriataGrunowinVanHeurck,1882.
6
8
1350
C
DiploneiscrabroEhrenberg,1854
.
24
5
2
50
C
Diploneisobliqua(Brun)Hustedt,1937
.
1117
X
EunotogrammalaevisGrunow,1883. 34
5
6
50
C
Eolimnaminima(Grunow)Lange‐Bertalot&
W.Schiller,1997.
5
6
8
7
67
F
Gyrosigmaeximium(Thwaites)Boyer,1927.
3
6
33
R
Lyrellaclavata
(
Gregory)D.G.Mann,1990.10 17
X
Lyrellasp.
5
2
33
R
M
astogloiaangulataLewis,1861.
5
6
4
50
C
M
elosirasp.
3
3
1150
C
Naviculasp. 4 17
X
N.longa(Gregory)RalfsexPritchard,1861.
9
17
X
N
.peregrine 4 4 33
R
Nitzschia
sigma
(Hantzsch)Grunow,1878.
7
17
X
Odontellasp. 51033
R
O.mobiliensis(J.W.Bailey)Grunow,1884. 3 17
X
Paraliasulcate(Ehrenberg)Cleve,1873.
5
1
33
R
Petroneisgranulate(Bailey)D.G.Mann,1990.
4
8
1
50
C
Pinnulariasp. 717
X
P.aestuariiCleve,1895.317
X
Pleurosigmasp.10
4
33
R
P.naviculaceumBrébisson,1854
4
4
17
X
p
seudo‐nitzschiasp.
2
17
X
Surirellasp. 7 17
X
S.fastuosa(Ehrenberg)Ehrenberg,1843. 6 17
X
S.spiralisKützing,1844
2
17
X
Thalassiosirasp.
3
8
8
50
C
Triceratiumsp. 1317
X
Water2022,14,31878of13
Figure5.Scanningelectronmicrographsofthemostcommonspeciesindifferentstations:(A)Dip‐
loneiscrabro,(B)Cocconeisplacentula,(C)Actinoptychussp.,
(D)Eunotogrammalaevis,(E)Amphorasp.,
and
(F)Coscinodiscussp.
Thecorrelationsbetweentheepipelicdiatom’sabundanceanddiversityagainstvar‐
iousenvironmentalparametersarepresentedinTable2.Significantpositivecorrelations
existedbetweenabundanceofepipelicdiatomtaxaagainstSSTandTSS(p<0.05),and
significantnegativecorrelationsexistedamongtheabundanceoftheepipelicdiatomcom‐
munityandpHandNH
3
(p<0.05).Meanwhile,theepipelicdiversityshowedasignificant
negativecorrelationwithTSSandSiO
2
andasignificantpositivecorrelationwithSST(p<
0.05).FurtheranalysisusingPCAshowedeigenvaluesof6.20and2.80,respectively,
whichexplained79.83%ofthevariance(Figure6).TheabundanceofD.crabro,Actinop‐
tychussp.,andE.laevisinSt.2,St.4,andSt.3werepositivelycorrelatedwithNO
2–
,DO,
NH
3
,andTDSandnegativelycorrelatedwithOMandSSS.Amphorasp.inSt.5wasposi‐
tivelycorrelatedwithSST,EC,Chl‐a,PO
4−3
,andpHbutnegativelycorrelatedwithSiO
2
,
NO
3−
,andTSS.Coscinodiscussp
.
inSt.6waspositivelycorrelatedwithSSSandOM.
Table2.Pearson’scorrelationcoefficient(randpvalue)ofepipelicdiatomabundance(cells/g)and
diversity(H’)againstsignificantphysicochemicalvariablesatPortDicksoncoast.Asterisk(*)indi‐
catessignificanceat0.05level(2‐tailed).Parameterswithnosignificantcorrelationswereexcluded.
Physicochemical
Variables
AbundancesofEpipelicDiatom
Communities(cells/g)
DiversityofEpipelicDiatom
Communities(H’)
rpValuerpValue
SST(°C)0.630.03*0.580.04*
pH−0.580.04*0.430.16
TSS(mg/L)0.530.08*−0.85<0.01*
NH₃(mg/L)−0.670.02*0.070.83
SiO2(mg/L)0.360.25−0.630.03*
Chl‐a(mg/L)0.74<0.01*−0.110.73
Water2022,14,31879of13
Figure6.Principalcomponentanalysisordinationsofthedominantepipelicdiatomspeciesand
physiochemicalvariablesmeasuredatsixstationsalongthePortDicksoncoasts,Malaysia.
4.Discussion
4.1.EnvironmentalConditions
Physicochemicalvariablesweremeasuredtodeterminethecoastal‐waterqualitypa‐
rametersthatmayaffecttheepipelicdiatomdistributioninthedifferentstudystations.
TheSSTvalueswererelativelyhighandstable,withameanvalueof30.36°C±0.89°C,
whichisthestandardfortropicalcoastalwaters[38].Increasingtemperaturecanleadto
changesinthedistributionpatternsofbenthicdiatoms[39].Thisphenomenonwasfound
inthecurrentstudy,wherethehighestnumberofepipelicspecieswasrecordedatSt.5
withthehighesttemperatures,whereastheoppositewasatSt.3.Conversely,theSSSlev‐
elsshowedawiderange,whichwasalsonormalfornearshorecoastalwaters.SSSgener‐
allydidnotshowanyeffectonepipelicabundanceasitwasnotamongthecriticalparam‐
etersdeterminingthedistributionofabundanceofepipelicspecies[40].
pHisanimportantfactoraffectingtheproliferationofaquaticorganisms,andin‐
creasingordecreasingpHmayaffectphytoplanktongrowth[41].ThepHvaluesrecorded
inthesestudiesrangedfromneutraltoalkaline(mean=8.07±0.21),whichwerewithin
theMMWQS[36].TheDOvalueswererelativelyhigh,withameanvalueof6.95±0.74
mg/L,similartoapreviousstudy[42].VariabilityintheDOlevelsnearthecoastlinecan
beattributedtodifferentriveroutflowsalongthestudyarea.
ThevalueofTSSinthisstudycanbecategorizedasunderClassIIIoftheMMWQS
[36].St.1hadhigherTSSthantheotherstations,mostlikelyowingtoitsproximitytothe
SepangRiver.Tidalfluctuations,winddirections,windspeeds,andriveroutflowswere
amongthemajorfactorsregulatingthespatialandtemporalvariationsofTSS[43,44].
Othercoastalfeaturessuchasnearbymangrovesandcoastalvegetations,aswellasthe
amountofOMincoastalwaters,mayalsoaffecttheTSS.ThehighestOMwasrecorded
atSt.6followedbySt.1,whereSt.6waslocatedinfrontofthemangroves,whereasSt.1
waslocatedclosetotheestuary.Studieshaveshownthatmangrovesoilsmaysupply
Water2022,14,318710of13
significantamountsofOMwithhighpercentagesoforganiccarbontonearbycoastalwa‐
ters[45,46].
Nutrientconcentrationssignificantlyimpactphytoplanktonoccurrenceandabun‐
danceastheydrawinsignificantamountsofnutrientsfromtheecosystem[41,47].How‐
ever,thepresentstudyshowedlowvariabilitiesintheconcentrationofnutrientssuchas
NO3−,NO2−,NH3−,PO43−,andSiO2throughoutthestations.Nevertheless,highammonium
concentrationswererecorded,asalsoreportedby[48],indicatingahighlevelofpollution
inthestudyarea.Furthermore,Ref.[42]reportedahighlevelofpollutioninthePort
Dicksoncoasts,andtheseareashaveevenbeensuggestedtobeunhealthyforhumanac‐
tivities.
SiO2andChl‐aalsosignificantlyaffectedtheabundanceofepipelicdiatomassem‐
blagesanddiversity.TheSiO2concentrationswerelowatSt.1,St.3,St.4,andSt.6,butthey
wererelativelyhigheratSt.2andSt.5.Conversely,Chl‐awasrelativelysimilarbetween
stations,rangingfrom0.10mg/Lto0.13mg/L.Chlorophyllisanindicatorofbiomassvar‐
iabilityandphytoplanktongrowth,anditsconcentrationmaybegreatlyinfluencedby
nutrients[7,49].
4.2.DynamicsofEpipelicDiatoms
Theabundanceofepipelicdiatomrecordedthroughoutthestationswasconsidered
asrelativelylow,whichcanprobablybeattributedtothedifferentspatialvariables,the
highlevelofpollution,andthepoorsedimentcondition.Thisfindingmayhaveastrong
impactondiatomsgrowingonthesedimentsurface[50].Eachdifferentgroupofnutrient
concentrationswascharacterizedbyadifferentbenthicdiatomcomposition.Therelative
abundancesofbenthicdiatomformschangedinresponsetominorinputsofnutrients
[51].TheinputofOMalsocausedtheadditionofsuspendedsolidsandthedeoxygenation
ofwater.Nevertheless,pennateandcentricdiatomswerewellpresentedinallstations.
Thecompositionofcentricdiatomswassignificantlylower,whichwasnormalbecause
mostofthemwereplanktonthatadaptedtomoveupwardstowardthesedimentsurface
undermoderatelightintensitiesandmigrateddeeperintothesedimentindarknessand
underveryhighlightintensities[52].Indeed,thehigherratioofpennatetocentricforms
iscommoninthecoastalbenthicdiatomscommunityandhasbeenpreviouslyreported
elsewhere[53].
Theabundanceanddiversityofepipelicdiatomsshoweddifferentcorrelationswith
variousphysicochemicalfactors.Increaseinseawatertemperatureusuallyledtohigher
metabolicactivity,therebyincreasingthebenthicalgalbiomass[54,55].Furthermore,OM
isimportantincontrollingdiatomcommunitiesandtheirnutritivevalues[26,56].Previ‐
ousstudieshaveindicatedthatvariationsinOMcontentplayanimportantroleinthe
diversityofbenthicdiatomcommunities,whereincreasingdiatomdiversitynormallyco‐
incideswithhigherOMcontentinthesediment[57].
Silicawasfoundtobenegativelycorrelatedwithepipelicdiversity,whichmaybe
duetotheintensiveuptakebysomegrouporspecies.Previousstudieshaveshownthat
thesilicarequirementofepipelicdiatomnegativelyaffectsthesilicabalanceinthemarine
ecosystem[58].Nitrogenoussubstancesareimportantnutrientsforprimaryproductivity.
However,Ref.[59]reportedthatdiatomsprefernitratebutdonotrespondwelltoammo‐
nium.Nevertheless,otherstudieshaveshownthatammoniumisamorereadilyassimi‐
latedsourceofnitrogencompoundsinmarineepipelicdiatoms,anditisthemostim‐
portantfactordeterminingthesourcesoftheepipeliccommunitystructure[40,60].This
phenomenonmayresultinashiftintheircommunitycomposition,whichexplainsthe
negativecorrelationofammoniawiththeabundanceofepipelicdiatom.
Withinthestudyarea,C.placentulawasoneofthemostabundantandextensively
distributedspecies.ThisfindingagreedwithotherstudiesthatalsoreportedCocconeissp.
asthedominantbenthicspeciesassociatedwithepiphyticorepipelichabitats[9,61].Coc‐
coneisspp.alsocontributedasthemostabundantbenthicmicroalgae(at58%)insediments
collectedfromMukaHeadJetty,Penang,Malaysia[20].
Water2022,14,318711of13
PCAdemonstratedthatthepositivecorrelationforD.crabro,E.laevis,andActinop‐
tychussp.instationsSt.2,St.3,andSt.4canbeattributedtothehighconcentrationsofNO2–
,NH3,andTDSattherespectivestations.PCAalsoshowedpositivecorrelationsofC.
placentulawithNO3−andSiO2butnegativecorrelationswithPO43−andpH.Previousstud‐
ieshavereportedthatnutrientconcentrationandpHplayimportantrolesinthemorpho‐
logicalstructureandpore‐holesizedistributionofC.placentula [62,63].Theratioofsilica
compositionwas30.71%inCoscinodiscusspp.[64],whichmayexplainthenegativecorre‐
lationbetweenCoscinodiscusspp.andSiO2atSt.6(Figure6).
5.Conclusions
Highspatialvariationsinepipelicdistributionwereobservedalongthestudysta‐
tions.SST,TSS,TDS,NO2−,NH3,OM,andSiO2,wereconsideredasthemostinfluential
physicochemicalvariablesonepipelicdiatomdiversity,abundance,anddistributionin
thestudyarea.Coconeisplacentula,D.crabro,E.laevis,Actinoptychussp.,Amphorasp.,and
Coscinodiscussp.werethemostabundanttaxainthestudyarea.Theyshowedstrongcor‐
relationswithSST,TSS,SiO2,OM,NH₃,NO₂⁻,pH,Chl‐a,andTDS.Thisstudywasthe
firsttodescribetheepipelicdiatomdiversityanddistributioninMalaysiancoastalwaters,
whichmayserveasabaselineformorestudiesonepipelicdiatomdynamicsinthefuture.
AuthorContributions:Conceptualization,A.A.S.,S.N.P.S.,Z.C.C.;methodology,A.A.S.,S.N.P.S.,
Z.C.C.;investigation,A.A.S.,S.N.P.S.,Z.C.C.,S.K.D.;writing—originaldraftpreparation,A.A.S.,
S.N.P.S.,Z.C.C.;writing—reviewandediting,A.A.S.,S.N.P.S.,Z.C.C.andS.K.D.;supervision,
Z.C.C.,S.N.P.S.&S.K.D.;fundingacquisition,Z.C.C.Allauthorshavereadandagreedtothepub‐
lishedversionofthemanuscript.
Funding:ThisworkwasfundedbyUKMresearchfundthroughGUP‐2021‐049toZ.C.C.
InstitutionalReviewBoardStatement:Notapplicable.
InformedConsentStatement:Notapplicable.
DataAvailabilityStatement:Notapplicable.
Acknowledgments:WesincerelythankAmirandZuhaimifromtheMarineScienceProgram,Uni‐
versitiKebangsaanMalaysia(UKM)fortheirdedicatedeffortsinsamplecollectionandanalysis.
Wealsothanktheanonymousreviewersfortheirveryusefulcomments.
ConflictsofInterest:Theauthorsherebydeclarenoconflictofinterest.
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