Annual dynamics of bivalve populations in muddy bottoms of the Ensenada de Baiona (Galicia, NW Iberian Peninsula)

2007·6.9 MB·English

by  Valeria Veloso

©SociedadEspañoladeMalacología Iberus,25 (2): 19-28,2007
Annual dynamics ofbivalvepopulations in muddybottoms
NW
ofthe Ensenadade Baiona (Galicia, Iberian Península)
Dinámicaanualdelaspoblacionesdebivalvosdelosfondosfangosos
NO
delaEnsenadadeBaiona (Galicia, PenínsulaIbérica)
ValeriaVELOSO1,JuanMOREIRA23-4*andJesúsS.TRONCOSO2
Recibidoel10-XI-2006.Aceptadoel9-V-2007
ABSTRACT
ThebivalvesAbranítida, Loripes¡acteusand Thyasiraflexuosaarecommon ¡nhabitantsof
muddysedimentsintheGalicianrías(NWSpain).Abundance, recruitmentandgrowthof
these specieswerestudied from May 1N9W96toMay 1997 in the Ensenada de Baiona, a
small ¡nlet¡ntheRíadeVigo,Galicia, Spain. Specimenswerecollected inashallow
subtidal sitewith muddysediments. Growth and life span wereestimated from length-fre-
quencydata by means ofstatistical packages based on von Bertalanffy's equation. The
studied populationsshowed marked seasonalvariations in numberswith onlyone period
ofrecruitment. Thyasiraflexuosashowedgreatermaximal abundancesthan in otherGali-
cian rías, apartfrom the Ría deCoruña. The population of L. lacteuswas mainlycom-
posedofsmallindividuáisandthelongevityofA. nítidawasgreaterthaninotheráreas.
RESUMEN
LosbivalvosAbranítida, LoripeslacteusyThyasiraflexuosasonespeciescomunesenfon-
dosfangososdelasríasgallegas(NoroestedeEspaña). Ladinámicaanual, reclutamiento
ycrecimientodeestasespeciesfueestudiadodesdeMayode 1996aMayode 1997en
la Ensenada de Baiona (Ría deVigo). Losejemplares estudiados fueron recolectados en
unfondofangosoa 2 m deprofundidad. Elcrecimientoylongevidadfueronestimadosa
partirdedatosdefrequencia detallaspormediodepaquetesestadísticosbasadosenel
modelodecrecimientoyecuacióndevon Bertalanffy. Laspoblacionesestudiadasmostra-
ron unas marcadasvariacionesestacionalesen númerodeindividuosyun único período
de reclutamiento anual. Las máximas densidades de T flexuosafueron mayores que las
registradasen la mayoría de las ríasgallegas, salvoen la Ría deCoruña. La población
deL. lacteusestuvocompuestaprincipalmenteporindividuosjuvenilesmientrasquelalon-
gevidaddeA. nítidafuemayorqueenotrasáreas.
KEYWORDS:bivalves,softbottoms,dynamics,growth,EnsenadadeBaiona,rías,AtlanticOcean.
PALABRASCLAVE:bivalvos,fondosblandos,dinámica,crecimiento,EnsenadadeBaiona,rías,OcéanoAdántico.
1LaboratoriodeDinámicadePopulacóesMarinhas,DepartamentodeCienciasNaturais,UniversidadedoRio
deJaneiro(UNIRIO),Av.Pasteur458,Sala411,Urca,CEP22290-240,RiodeJaneiro,Brazil.
2DepartamentodeEcoloxíaeBioloxíaAnimal,FacultadedeCiencias,CampusdeLagoas-Marcosendes/n,
UniversidadedeVigo,E-36310Vigo,Spain.
3EstacióndeBioloxíaMarinadaGrana,UniversidadedeSantiagodeCompostela,CasadoHórreo,Rúada
Ribeira1,E-15590,AGrana,Ferrol,Spain.
4DepartamentodeBioloxíaAnimal&InstitutodeAcuicultura, UniversidadedeSantiagodeCompostela,
CampusSur,E-15782,SantiagodeCompostela,Spain.
*Correspondingauthor:[email protected]
19
Iberas,25 (2),2007
INTRODUCTION Despitetheexistingwealthofinfor-
mation on the soft-bottom fauna of
Marine benthic assemblages in manyGalician"rías",littleisknownof
shallow subtidal soft-bottoms are fre- the distribution and dynamics of the
quentlycomposedofalargenumberof subtidal soft-bottom fauna from the
species, someofwhichmayshowfluc- Ensenada de Baiona (Anadón, 1980).
tuations of their populations through Thisinletislocatedatthemouthofthe
time(Rees, 1983).Thedistributionand Ría de Vigo and its soft bottoms are
temporal dynamics of soft-bottom mostlysandy(Alejo,Austin,Francés
faunasmaybeconditionedbyanumber AND VlLAS, 1999; MOREIRA, QUINTAS
ofabioticfactorsandbioticinteractions andTroncoso,2005).Overthelast30
(Rhoads and Young, 1970; Gray, years, adepositionoflargeamountsof
1981).Variationsofthesefactorsatdif- silt/clay has been detected in the
ferentspatialandtemporalscalesmay shallowsedimentsaroundtheharbour
transíate into variations in density of ofBaionaduetothechangeindynamics
speciesandcompositionofassemblages. oflocalcurrentsaftertheconstructionof
Thestudyofthesepatternsofvariation ajettyinthe 1970s (AlejoandVilas,
is therefore crucial when determining 1987). An "Abra alba community" is
conditions and quality of marine presentinthesemuddysedimentsand
benthosandformanagementofbiodi- isdominatedbyseveralspeciesofpoly-
versityandnaturalresources(Kelaher chaetesandbivalves (Moreiraetal.,
andColé,2005). 2005,2006).Amongthem, thebivalves
TheGalicianríasareacomplexand Abranítida(Müller, 1776),Loripeslacteus
uniquekindofestuarinesystemswith (Linnaeus, 1758) and Thyasiraflexuosa
highprimaryproductivity(Tenoreet (Montagu, 1803)arenumericallydomi-
al., 1995) and great economic and nant species (Moreira et al., 2005).
socialimportancebecauseofthepres- Bivalves are a key component of the
enceoffisheriesand diverseshellfish structureofsoft-bottombenthicassem-
resources (Figueiras, Labarta and blages (Peterson and Andre, 1980;
Fernández,2002).Inaddition,therías WlDDICOMBE AND AUSTEN, 1999), the
have a large variety of sediments dietofanumberofdemersalfishofeco-
inhabited by a diverse benthic fauna nomic interest (Dauvin, 1985; Brey,
(Cadée, 1968; López-Jamar and Arntz,PaulyandRumohr, 1990)and
Mejuto, 1985; Garmendia, Sánchez- may serve as indicators of the condi-
MataandMora,1998).Insomerías,a tionsofmarinebottoms(Stirling,1975;
number of human activities, such as Bresler, Bissinger, Abelson, Dizer,
the culture of bivalves on rafts, the Sturm, Kratke, Fishelson and
construction ofharbour facilities and Hansen,1999).
the disposal of sewage, have already This study describes the temporal
induced large alterations in composi- dynamicsoftheaforementioneddomi-
tion of benthic assemblages through nantbivalvesduringaone-yearperiod
organic enrichment and changes in from a muddy site in the harbour of
sedimentary composition (López- Baiona. For instance, T. flexuosa is
Jamar, 1978; López-Jamar and knowntobeadominantspecieswhen
Mejuto,1985).Thesedisturbancesmay recolonizingmuddysedimentsandthus
alsoaffectthevariabilityofindividual it can be expected to have a higher
populations of benthic organisms growth rate when compared to other
(Underwood, 1992). Therefore, in bivalves. Growth and longevity were
ordertoidentifytheimpactofanthro- also estimated for those species and
pogenic disturbances on the marine comparedwiththoseofotherpopula-
benthos it is necessary to study the tions.Thisworkispartofalargerbase-
distribution and natural spatio- linestudyonthebenthicassemblagesin
temporal variations of the benthic subtidalsoftsedimentsoftheEnsenada
infauna. deBaiona.
20
VELOSOETAL.:AnnualdynamicsofbivalvepopulationsinmuddybottomsofGalicia
MATERIALANDMETHODS and Pauly, 1996), that assumes a von
Bertalanffyequationforgeneralgrowth,
Sampling and laboratory procedures: modified for seasonality (Pauly and
Thestudiedsite(42°07'19"N,8o50'45" Gaschütz, 1979). Although various
W)wasselectedasbeingrepresentative models have been proposed for the
ofthe"Abraalbacommunity"presentin descriptionofindividualbody-growth
themuddysedimentsoftheEnsenada (Richards,1959;Pauly,1980;Schnute,
deBaiona.Thesiteisatadepthof2m 1981), the von Bertalanffy model
andthe sedimentis mostlymuddy (> (1938) hasbeen the mostwidelyused
50% silt/clay). Five replicate samples forinvertebratesandfishes(Luckhurst,
werecollectedbymeansofaVanVeen Dean and Reichert, 2000; Laudien,
grab (0.056 m2) at monthly intervals BreyandArntz,2003).ThevonBerta-
between May 1996 to May 1997. This lanffyequationwasthereforeusedfor
grab penetrates about 15 cm into the thiswork[Lt=L-{l-e[-K(t"to)+{CK/2n)"»{2n
sediment.Totalsampledárea(0.28m2) (t-ts))]j^whereLtislength(mm)attimet,
was larger than that of other works Looisthemaximaltheoreticlengththat
sdteuvdoiteeddhetroet(hee.g.s,a0m.1e75bimv2alfovreTshpyeacsiiersa ntihteelsyp,eKcieisstwhoeuilndtrirnesaicchgirfoitwtlihveradtiend(ecfuir--
flexuosainLópez-Jamar,Gonzálezand vature parameter), C is a constant for
Mejuto,1987;0.175m2forAbranítidain theamplitudeofoscillationinseasonal
0F.r2a0nmc2efsocrhLorainpedslLacótpeeusz-inJaCmuarrr,as1a99n1d; gthreowitniht,iatlopiosiangteofatsezaesroonlaelngostchi,llaantdiontsiins
Mthorroau,gha1909.65).mmSammepslhesanwdefriexedsiinev4e%d trealtaitoinoonftothtis=e0q.uTahtieognrpaprhoidcuaclesreaprceusrevne-
formaldehyde. Molluscs were sorted thatisevaluatedthroughthegoodness-
from the sediment and counted. The of-fitindexRn(Gayaniloetal., 1996).
lengthoftheanterior-posterioraxisof Thegrowthindex(=phi-primeindex,
the shellwas measuredto thenearest wasusedtomeasurethegrowthper-
0.1 mm with vernier caliper for the <fJ)o')rmance of the species (Pauly and
largerspecimensandwithaneyepiece Munro, 1984).Thisindexidentifiesthe
micrometer for the smaller. Sediment distortedestimatesofthegrowthpara-
samplesweretakenmonthlytomeasure meters because there is a recognized
particle size composition, carbonates trendoftheELEFANroutinetounder-
andtotalorganicmatter.Mediangrain estimateKandoverestimateLoo(Isaac,
size(Q50)andsortcoefficient(So)were 1990). Winter point (WP) is also pro-
also determined for each sample. vided,i.e.thepointoflowestgrowthin
Content of carbonates (%) was esti- theyear,expressedasadecimalfraction
matedbyatreatmentofthesamplewith oftheyear.
hydrochloric acid. Content of total
organicmatter(%)wasestimatedfrom
theweightlossoncombustiónat450°C RESULTS
for 4 hours. Analyses of correlation
throughSpearmancoefficientweredone Environmental parameters: Sediment
toassesstherelationshipsbetweenthe was mainly composed of silt/clay (<
densitiesofthebivalvesandtheenvi- 0.063mm;75.2±4.6%,mean±SD)and
ronmentalvariables. veryfine sand (0.125-0.063 mm; 17.0 ±
Populationparameters:Forestimates 2.7%). Median grain size ranged from
of growth parameters, the analysis of 0.031 mmto0.040mmwithanannual
the length-frequency distribution meanof0.035±0.003mm.Selectionof
methodwasused, throughtheroutine thesedimentrangedfrommodérateto
ELEFANI(ElectronicLengthFrequency poor.Contentoftotalorganicmatterwas
Analysis; Pauly, 1987) from the high(10.0±1.7%)andcontentofcarbon-
program FISAT (FAO-ICLARM Stock ateswaslow(8.7±0.9%).Temperatureof
Assessment Tools; Gayanilo, Sparre waterneartothesedimentrangedfrom
21
Iberas,25 (2),2007
Abranítida
Loripeslacteus
Thyasiraflexuosa
M J J A S O N D J
1996 1997
Figure1.Monthlyvariationsindensity(ind.m"2)oíAbranítida,LoripeslacteusandThyasiraflexu-
osaatthestudysiteintheEnsenadadeBaiona.
Figura1. Variacionesmensualesdeladensidad(ind. m'2)deAbranitida,LoripeslacteusyThyasira
flexuosaenelfondoestudiadoenlaEnsenadadeBaiona.
11.0°C inJanuary to 19.5°C inAugust throughoutthestudy.Largeanimáis(>
with anannualmeanof 15.5±2.65°C. 10mm)werescarcelyfoundthroughthe
Salinityshowedanannualmeanof33.6± year(<6%).
1.8%owithminimalvaluéinDecember DensitiesofThyasiraflexuosawere
(30.P0o%pou)laantidomnaxaibumnadlanicneJ:ulyDe(n3s5.i3t%ioe)s. of bexettrweemeenly7vaarnidabl1e15(0Figi.nd1.),mos2ciwlliatthinag
Av±ib1dr2ua4áinisintmdi.da2m,vwa2irt(ih±edSaEm)f.ornoTtmhhel11ygrtmeoeata4e0nr0oafibnu2dn0i-7- hSmieogpnhtteehsmtlbyneurmmeabanednrsJoafwneu6ra6er9yr±-eAc4po2rri3ld.iendIdni.nJmuAnue2g-.uJTsuhtle-y
dances were recorded in August-Sep- this species was almost absent from
tember,NovemberandFebruary-March samples.Recruitmentoccurredonceayear
whilethesmallestnumberswerefound duringspringwiththelargestnumbersof
fromMaytoJuly1996(Fig. 1).Recruit- smallindividuáis(<2mm)foundinApril
mentoccurred onceayearinsummer 1997(Fig.2).Alargeproportionofthepop-
accordingtothelargernumberofjuve- ulationconsistedofanimáisbetween3
niles (<4mm)foundinsamplesfrom and6mm(80%)whilelargeanimáis(7to
A18ugmusmti(Fnigl.en2)g.thL,arcgoempinrdiisveidduáliess,s1t6hatno 9mmN)umwbeerresscoafrcTef(l4e%x)u.osaandL. lacteus
3%ofthepopulation. were positively correlated with total
NumbersofLoripeslacteusfluctuated contentofsand(p<0.05)whiledensity
between and 1018 ind. m~2, with a of A. nitida was positively correlated
monthly mean of 268 ± 319 ind. nr2. withcontentofveryfinesand(p<0.05).
Thisspeciesshowedsmallvariationsin L.lacteuswasnegativelycorrelatedwith
densitybetweenlatespringandautumn contentofsilt/clay(p<0.05).
with a strong increase in numbers Growth and Ufespan: Table I shows
duringwinter-earlyspring(Fig. 1)due the growth parameters of von Berta-
torecruitmentofjuveniles(<4mm;Fig. lanffy's curve for the three studied
2). The population was mainly com- species.Loripeslacteusshowsthebetter
posedofsmallanimáis(<5mm,>75%) performance, reaching a larger body
22
VELOSOETAL.:AnnualdynamicsofbivalvepopulationsinmuddybottomsofGalicia
n=35 :289
n=62
pfl.MX
n=0 a= 11
n=22
n=37 n=300
n=9
n=35
November 20
o
40- n=45 n=21
December 20
n=35 n=286 i=301
11
n=39
n=138 n=227
J^ n=222 [i=245
n=45 n=19 n=69
5 10 15 5 10 15 2 4 6
Length(mm) Length(mm) Length(mm)
Figure2.Length-frequencydistributionofbivalvesatthestudysiteintheEnsenadadeBaiona.A,
Abranítida;B,Loripeslacteus;C, Thyasiraflexuosa.Numberofindividuáismeasured(n)aregiven
foreachsamplingdate.
Figura2. DistribucióndefrecuenciasdetallasdebivalvosenelfondoestudiadoenlaEnsenadade
Baiona.A,Abranitida;B,Loripeslacteus;C,Thyasiraflexuosa.Seindicaelnúmerodeindividuos
medidos(n)encadafechademuestreo.
23
Iberus,25 (2),2007
TableI.Growth,mortalityandlifespanestimatesforAbranítida,Loripeslacteusand Thyasiraflex-
uosaatthestudysiteintheEnsenadadeBaiona.
TablaI. Crecimiento,estimasdemortalidadylongevidadparaAbranítida,Loripeslacteus^Thyasira
flexuosaenelfondoestudiadodelaEnsenadadeBaiona.
¿oo(mm) fíyear1 WP Rn 0' í™*(mm) í/mr(years)
A.nítida 19.5 0.26 0.1 0.2 0.154 2.0 17.5 8.8
Llocteus 21.9 0.31 0.3 0.4 0.150 2.2 20.0 4.9
lflexuosa 12.9 0.40 0.1 0.2 0.156 1.8 9.3 3.2
sizeinlesstimethantheotherspecies, increasesindensitiesfollowedbydra-
as indicated by the valúes of £'. Esti- matic declines (Buchanan, Kingston
mates of growth indicated small sea- andSheader,1974;Josefson,1982).
sonaloscillations(0.1-0.3)forthethree In the Ría de Coruña, recruitment
species.ThecalculatedWPindicateda beginsinOctoberandendsinMaywith
decreasedgrowthrateinlatewinterfor peaksinJanuary-February(Francesch
Abranítidaand Thyasiraflexuosa(WP= and López-Jamar, 1991) while in the
0.2x12=2.4,February-March)andin Ensenada de Baiona it occurs in late
springforL.lacteus(WP=0.4x12=4.8, summer.Josefson(1982)pointsoutthat
April-May). The estimated life span recruitment may occur from late
(fmax)washigherforA.nítidathanforL. summertoautumnalthoughtheactual
lacteus and T.flexuosa (8.8yearsvs4.9 periodsmaybevariable. Furthermore,
and3.2years,respectively). successofrecruitmentmaydependon
thesizeofadultpopulationsandthose
ofother competitors, such as deposit-
DISCUSSION feedingpolychaetes,whichmayingest
newspatorcompeteforfood(Josefson,
Abranítida 1981,1982).
Abra nítida has typically been Data on the growth of Abra nítida
recorded from muddy bottoms (Gle- fromotheráreas are scarce (Josefson,
marec, 1964;Mora, 1982).Thisspecies 1982; Francesch and López-Jamar,
acts primarily as a deposit-feeder 1991). Inthe Ensenada de Baiona, life
(Wikander,1980)andcontributestothe spanandmaximallengthweregreater
reworkingofsedimentthroughlocomo- thanthosefoundintheRíadeCoruña
tionandfeeding(RhoadsandYoung, insimilarbottoms(8.77yearsand 17.5
1970). Monthly densities in the Ense- mmvs3.9yearsand 14.3mm, respec-
nada de Baiona were similar to those tively). Longevityinestablishedadult
foundbyFranceschandLópez-Jamar populationsofA. nítidamaybecondi-
(1991)inmuddybottomsfromtheRía tioned by predation of boring gas-
de Coruña (46-480 ind. m2). In our tropods such as naticids (Josefson,
study,maximaldensitieswererecorded 1982) and therefore longevity may be
in late summer-autumn and early greaterintheabsenceofstrongpreda-
spring while in other áreas maximal tion. For soft sediments deeper than
densities occured during spring- those studied at the Ensenada de
summer (Josefson, 1982; Francesch Baiona, Josefson (1982) recorded
andLópez-Jamar, 1991;López-Jamar, growthratesof10mmfor1to1.5years
Francesch,DorríoandParra, 1995). after recruitment. Growth may,
Because of the high variability in however,varybetweenyearsandsites
numbersofitspopulations,A.nítidahas atdifferentdepthsfromyeartoyearand
beenconsideredasavolatileandoppor- is strongly dependentonintraspecific
tunisticspecies,whichmayshowgreat competition for food when there are
24
VELOSOETAL.\AnnualdynamicsofbivalvepopulationsinmuddybottomsofGalicia
largepopulationsofadults (Josefson, recorded between January and April.
1982).Thus,differencesingrowthrates No recruitment was detected during
betweenpopulationsmaybetheresult summer and autumn. Curras and
of differences in the size-structure of Mora (1996) suggest that macroalgal
thesepopulations. growth on the surface of sediment
duringsummermaypreventsuccessful
Loripeslacteus recruitment. Macroalgal blooms are
Loripeslacteusisacommonbivalve known to affect the physico-chemical
infinesand,muddysandandmudand featuresofthesediment-waterinterface
canalsobefoundinpollutedsediments and the underlying sediments and
(Cadée, 1968;Guerra-García,Corzo thereforeaffecttheinfauna(Raffaelli,
andGarcía-Gómez,2003).Thisspecies Raven and Poole, 1998), although
mayinhabitreducedsedimentsandhar- these effects may differ between taxa
bours chemoautotrophic sulphur-oxi- (Lopes,PardalandMarques,2000).In
dizingbacteriawithinitsgills(Johnson ourcase,thepresenceofulvaceanalgae
andFernandez,2001).IntheGalician during July (personal observation)
"rías", L. lacteus is a characteristic could have had a negative effect on
species from softsediments colonized summerrecruitmentofL. lacteus,henee
byseagrassessuchasZosteramarinaL. thesmallnumbersofjuvenilesduring
and Z. noltii Hornem. (Curras and thefollowingmonths.
Mora, 1996;Olabarría,Urgorriand
Troncoso,1998).However,intheEnse- Thyasiraflexuosa
nadadeBaiona,L.lacteushasonlybeen IntheGalicianrías, Thyasiraflexuosa
foundinmuddysediments(Moreiraet is a common species in muddy sedi-
al.,2005). ments with a high contení of organic
ThepopulationsrudiedintheEnse- matter (López-Jamar and Mejuto,
nadadeBaionawasmainlycomposed 1985; López-Jamar and Parra, 1997;
ofjuvenileanimáis.CurrasandMora Olabarríaetal., 1998)andcanbethe
(1996)recordeddifferencesinsize-class numericallydominantbivalve(López-
structurebetweensedimentsofdifferent Jamaretal., 1987; López-Jamarand
granulometry. Thus, larger animáis Parra, 1997). This species is also
foundinsandymudwithZosteranoltii present in sandybottoms although in
throughouttheyearmeasuredbetween smallernumbers (López-Jamaretal.,
7 and 11 mm, while populations in 1995;López-JamarandParra,1997).T.
muddysandwithZosteramarinawere flexuosa may show large increases in
dominated by animáis smaller than 5 numbersaftereventssuchasoilspills
mm (Curras and Mora, 1996). The and other anthropogenic disturbances
scarcepresenceofadultsinthemuddy oceurringinharbour áreaswhenthey
sedimentssrudiedheremight,however, arefollowedbyperiodsofrecruitment
beduetomigrationofadultstoother (Dauvin, 1982; López-Jamar et al.,
sediments. Furthermore, Guerra- 1987;López-JamarandMejuto, 1988).
García et al. (2003) point out that IntheEnsenadadeBaiona,thedistribu-
larger individuáis of Loripes lacteus in tion of this bivalve was restricted to
similarsedimentstendtoappeardeeper muddy sediments (Moreira et al.,
intothesediment(>10cmdepth)and 2005). Here, maximal densities were
therefore these animáis could onlybe largerthaninothermuddysediments
sampledmoreaccuratelywithdevices with high organic content from other
thatpenétratedeeperintothesediment. Galicianrías,excepttheRíadeCoruña
Loripes lacteus may recruit twice a (López-JamarandParra,1997).López-
year,inlatewinter-springandsummer- Jamarand Parra (1997) suggest that
autumn (Massé and Guerin, 1978; thegreatermeandensitiesintheRíade
Curras and Mora, 1996; Johnson, Coruñaincomparisontootherríasmay
FernandezandPergent,2002). Here, beduetothe greaterwatercontentof
the largestnumbers ofjuveniles were sedimentinthelatter.Therefore,muddy
25
Iberus,25 (2),2007
sediments of greater fluidity and less Baiona were similar to those found by
stablethanthosepresentintheRíade López-Jamaretal.(1987)fromtheRía
CortinawouldbelessfavourableforT. deCoruñaalthoughgrowthrateandlife
flexuosa (López-Jamar and Parra, spanwereslightlygreaterinourstudy
1997).Inourstudy,numbersofT.flexu- (K,0.4vs0.28-0.37;Uax,3.2vs3years).
osashowedapositivecorrelationwith ThissuggeststhatThyasiraflexuosamay
contentofsandalthoughsedimentwas showgreatergrowthratesduringrecolo-
mainlycomposedofsilt/claythrough- nizationofdisturbedsedimentscoinci-
outtheyear.Thus,thepresenceofsand, dentwithperiodsofrecruitment(López-
even in small amounts, may improve JamaretAL.,1987).Posteriorinterannual
thestabilityofsedimentsandtherefore variationsingrowthofthesepopulations
favourthepresenceofT.flexuosa. maybetheresultofintraspecificcompe-
IntheRíadeCoruña, Thyasiraflexu- titionfollowinggreatincreaseinnum-
osaspawnsinJanuaryandFebruaryand bers(López-Jamaretal.,1987).
recruitsduringspring(López-Jamaret
al.,1987),withpeaksbetweenApriland
May(López-JamarandMejuto, 1988). ACKNOWLEDGEMENTS
mm
Juveniles between 0.7 and 1.3
appearbytheendofwinterwithpeaks The authors want to express their
ofabundanceinMayandJune(López- gratitudetoF.J. Cristobo, C. Olabarría
JamarandParra,1997).Thesamesitu- and P. Reboreda for theirhelp during
aciónhasbeenobservedforthepopula- fieldworkandtoS.Brillantwhokindly
tionintheEnsenadadeBaiona,which revisedtheEnglishversiónofthemanu-
alsoshowedonlyoneperiodofrecruit- script.CommentsfromS.Gofasandone
ment during the year. Ibanez and anonymousrefereehavecontributedto
Dauvin(1988)recordedpeaksofabun- improvethemanuscript.Thispaperhas
dance in autumn for muddy sands in partiallybeensupportedbytheproject
theBayofMorlaix,althoughthesemay PHB2002-0045-PC of the Dirección
alsooccurinspringandsummer. GeneraldeUniversidadesdelMiniste-
Growthparametersestimated from riodeEducaciónyCiencia(Spain)and
the population in the Ensenada de CAPESagency(Brazil).
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