The southern limit of distribution of Patella vulgata

2007·11.5 MB·English

by  Joao Paulo Cabral

.
©SociedadEspañoladeMalacología Iberus, 25 (1): 57-75, 2007
The southern limit ofdistribution ofPatella vulgata
Ellímite surde distribución dePatella vulgata
JoáoPauloCABRAL*1 andJoséSIMÓES**
Recibidoel20-XI-2006.Aceptadoel23-IV-2007
ABSTRACT
SamplesofPatellavulgatawerecollected along the Portuguesecontinental and thesouth-
ern Spanish coast. Specimens were ¡dentified using shell and radula characteristics.
Patella vulgatawas abundantatsites north ofthe river Douro whereas, to the south, its
abundance decreased markedly. Patella vulgata was not observed at Portinho da
Arrábida; however, nearCapeSaoVicente, atPonta Ruiva andTelheiro, thespecieswas
again abundant. Passing Cape Sao Vicente, the species became scarce. The lastsignifi-
cantpopulationwasobservedatIngrina,andthelastspecimenatRocha. Itwasproposed
thatthesesitesconstitutethe presentdaylimitofdistribution ofP. vulgata, replacing Ode-
ceixe, reported intheliteraturefiftyyearsago.ThedistributionofP. vulgataisnotasimple
function of the máximum or mínimum seawater surface temperature, but appears to
depend directlyon the temperature in May, the species being absentwhen the tempera-
tureishigherthan ca. 18°C.
Two hypotheseswereformulated toexplain the influenceofseawatertemperature in May
onthedistributionofP. vulgata:
1 Inhibition ofthe beginning ofgametogenesis dueto high temperature stress during the
resting period.
2. Death ofthe spatdue to high temperature stress, with concomitantfailure ofthe settle-
mentofnewgenerationsonthesubstrates. Inaddition,theabsenceofupwellingwaters in
the eastern part ofthe Algarve coastcould hinder the larval stage of P. vulgata, and
severe competition with Patella intermediaand Patella ulyssiponensiscould preventthe
establishmentofthosefew individuáisofthespatthatsurvived. Tonel, Mareta, Martinhal,
Barranco and Ingrina sites are candidates to be used as reference points to followfuture
changesinseawatersurfacetemperature.
RESUMEN
MuestrasdePatellavulgatafueron recogidasa lolargodelacostacontinental Portuguesa
ydelacostasurdeEspaña. Losejemplaresfueron identificadosutilizandolascaracterísti-
cas de la rádula yde la concha. P. vulgataes abundanteen las localidades al norte del
río Duero. Hacia el sur, la abundancia disminuye acusadamente. No se observó P. vul-
gataen Portinho da Arrábida pero, cerca de Cabo San Vicente, en Ponta Ruiva yTel-
heiro, la especie se vio nuevamente en abundancia. Pasando el Cabo San Vicente, la
especievuelvea serescasa. La última población significativa fueobservada en Ingrina,y
el últimoejemplaren Rocha. Se proponequeéstaslocalidadesconstituyen actualmenteel
límitesurdeladistribucióndeP vulgata, ensubstitucióndeOdeceixe, indicadoen la bib-
liografía hacecincuentaaños. LadistribucióndeP vulgatanoesunafunciónsimpledela
*UniversityofOporto,CenterofMarineandEnvironmentalResearch(CIIMAR)andFacultyofSciences.Rúa
doCampoAlegre,1191,4150-181Porto,Portugal.E-mail:[email protected]
**CasadoGrandeSul,CerroGordo,8400-550CarvoeiroLGA,Portugal.
Authorforcorrespondence.
57
Iberus,25 (1),2007
temperatura máxima o mínima del agua de mar, sinoque parecedependerdirectamente
de la temperatura del agua en Mayo. La especie no aparece cuando la temperatura
sobrepasa ca. 18°C.
Dos hipótesissehan formulado paraexplicarla influencia de la temperatura delagua de
maren ladistribucióndeP vulgata:
1. Inhibición del desarrollo de la ganada, causado por stress de altas temperaturas
duranteel periododereposoenel iniciodelproceso.
2. Muerte de los juveniles, causado por stressde altas temperaturas, con el subsiguiente
fracaso del establecimiento de nuevas generaciones en el substrato. Adicionalmente, la
ausencia de upwellingen la costa oriental delAlgarve puede perjudicarel estadio larval
de P. vulgatay la competencia severa con Patella intermediay Patella ulyssiponensis
puede evitar el establecimiento de los pocos juveniles que hubieran podido sobrevivir.
Tonel, Mareta, Martinhal, Barranco y Ingrina parecen localidades idóneas para ser uti-
lizadas como puntos de referencia al objeto de seguir futuras alteraciones en la temper-
aturadelaguademar.
KEYWORDS:Patellavulgata;AVHRR,SST,limpets.
PALABRASCLAVE:Patellavulgata;AVHRR,SST,lapas.
INTRODUCTION
Mappingthegeographicaldistribu- andcoastalenvironmentshavechanged
tionofamollusc,speciallyitsboundary substantially, seawater temperature is
limits,isimportant,sinceitgivesinfor- rising.Thesefactorsmighthavechanged
mationaboutecologicalconditionsthat the distribution ofP. vulgata since the
allowgoodgrowthandreproductionof 1950s.Thereisatpresentaconsiderable
individuáis,butalsoaboutconditionsthat amountofdetaileddataonenvironmen-
arenotfavorableforthespecies'survival. talvariables, suchasatmosphericand
ContinentalPortugal,attheconflu- seawatertemperatures.Wearenowina
ence between the Atlantic and the betterpositiontoformúlatehypothesis
Mediterranean,displaysarichinterplay onfactorsinvolvedinthesouthernlimit
betweenthenorthernandsouthernflora ofdistribution ofthis northernPatella
andfaunaofEurope. Indeed,thepres- species. The aimsofthis investigation
ence,onourrockyshores,offourPatella werethereforetwofold.Firstly,todeter-
species, one northern (Patella vulgata mine,indetail,thepresentdaysouthern
Linné1758),twosouthern{Patellarustica limitofdistributionofP. vulgata,updat-
Linné 1758 and Patella ulyssiponensis ing the information of Fisher-Piette
Gmelin1791),andonewithaninterme- andGaillard(1959),andcomplement-
diare character (Patella intermedia ing the recent studies ofBoavenlura
Murray in Knapp 1857) (Christiaens, (2000),Boavenlura,Ré,Fonsecaand
1973;CLEMAM,2002),attestandillus- Hawkins (2002a) and Sanlos (2000).
tratethisconvergenceofinfluences. Secondly, to explain or formúlate
The paper by Fisher-Piette and hypothesisonthemainfactorsinvolved
Gaillard(1959)onthedistributionof indeterminingthesouthernlimitofdis-
limpetsalongtheIberianandMoroccan tributionofP.vulgata.
coasts established Odeceixe, on the
southwestcoastofcontinentalPortugal,
asthesouthernlimitofdistributionofP. MATERIALANDMETHODS
vulgata.Almosthalfacenturyafterthis
work, we felt that it was worth and Samplingwascarriedoutalongthe
opportunetore-analyzetheissueofthe Portuguesecontinentalcoast,fromthe
southern limit of this species. Marine farnorthern to the far southernrocky
58
CabralANDSlMÓES:ThesouthernlimitofdistributionofPatellavulgata
44.0
•
Abundant
• Notmuchabundant
• Scarce
Veryscarce 43.0
O
Absent
-42.0
41.0
39.0
-38.0
36.0
-9.3 -8.8 -8.3 -7.8 -7.3 -6.8 -6.3
Figure 1.LocalizationofsamplingsitesontriePortuguesecontinentalcoast(#1 -#35)andinthe
Huelvaregión(#36-#37).AbundanceofPatellavulgataateachsamplingsite.
Figura1.Localizacióndelaslocalidadesdemuestreoenlacostacontinentalportuguesa(#1-#35)yen
lacostadelaregióndeHuelva (#36-#37).AbundanciadePatellavulgataencadalocalidadde
muestreo.
shores. Inaddition,threebeacheswith tionandlocalizationofallstudiedsites
rockysubstratesinthesoutherncoastof is presented in Figure 1 and Table I.
Portugal (the pontoon ofVila Real de Only beaches accessible by walking
SantoAntonio)andSpain(thecollapsed were examined. Rockyzonesbetween
towersofTorredelOroandTorredela beachesonlyaccessiblebyboatwerenot
Higuera)wereexamined.Theidentifica- surveyed.
59
Iberus,25 (1),2007
Observations were carried out by Inordertocorrelatethedistribution
walking along the beach, generally of P. vulgata with environmental vari-
starting 1 hour before and ending 1 ables,apreliminarysearchwascarried
hourafterthelowesttide.Allecological out in reference literature - oceano-
nicheswereexamined,fromthosefully graphic atlases (Maillard, 1986;
exposed to wave action to protected OceanographicAtlasoftheNorth
sites, andfromsunnyto damp, shady Atlantic Ocean; World Ocean
sites,includingcaves(particularlyabun- Atlas)and PortugueseMetereological
dantontheAlgarvecoast).Aprelimi- Instituteon-linepublications(IM,2006),
nary identification of P. vulgata speci- focusingontheregiónbetweenBrittany
menswascarriedoutinthefieldusing (France)andHuelva (southernAtlantic
conchologicalcharacters.Representative Spain),andexaminingthemostimpor-
P. vulgata specimens of all sizes and tantcandidatevariables:coastalairtem-
fromallshorelevéiswerethencollected, perature; air temperature and relative
transportedtothelaboratoryandfrozen humidity at ocean surface; seawater
untilanalysis.Specimenswereanalyzed surfacetemperature (SST);salinity,dis-
forshell and radula characteristics. In solved oxygen, alkali-chloride coeffi-
the laboratory, the animáis were cientandphosphatesoftheseawater.
immersedforafewminutesinboiling SSTalongtheAtlanticcoastbetween
watertosepáratetheshellfromthesoft Brittany and Huelvawasexaminedin
part.Theradulawasremovedfromthe detail. Threedifferentsourcesofinfor-
visceralmassbydissection,immersed mationwereused.
in household bleach to remove 1. Shore SST data provided by the
mucilaginous substances, andwashed Portuguese Metereology Institute,
indistilledwater.Externalandinfernal Lisbon.Thesetemperaturesweremea-
shellsurfaceswereexaminedandtheir sured every day, at 9 am local time,
characteristics recorded. After air- directly from the seashore, in shallow
drying,theradulawasobservedusinga water. On the Portuguese continental
binocularmicroscope.Themorphology coast,dataareavailablefromsevensites
ofthepluricuspidteethwasobservedin (CapeSantaMaria,CapeSantaMarta,
detailwith80xfinalmagnification.The Forte do Cávalo, Leixóes, Peniche,
final identification of specimens was Rocha and Sines), as means of the
basedoncharacteristicsoftheshelland period 1981-2000 (Carvalho and
radula, by comparison with data Soares,2001).
reportedintheliterature(Fisher-Piette, 2. NearshoreSSTdataprovidedby
1934, 1935; Fisher-Piette and Gail- thePortugueseHydrographicInstitute
lard, 1959;Evans, 1947, 1953; Rolan, (Lisbon) and the Spanish Puertos del
1993;RolanandOtero-Schmitt,1996) Estado. Thesetemperaturesweremea-
andinpreviouspublications (Cabral, suredatregularintervals(usuallyevery
2003, 2005). Thegreatmajorityofpre- hour),inbuoyslocatednearthecoast,
liminaryidentificationswereconfirmed and are displayed as monthly means.
afterexaminingtheradula. Theabun- For the Portuguese continental coast,
danceofP. vulgatawasthenestimated data are available from three buoys
foreachsamplingsiteusingthefollow- (Faro,LeixóesandSines),butspanning
ingclassification: 1.Abundant,ifmany verydifferentperiods:
individuáis were present, and evenly -Faro,from2000to2004,withmost
distributed. 2. Not very abundant, if yearscomplete
more than 25 individuáis were - Leixóes, from 1998 to 2004, but
observed,butthesewerenotregularly mostyearswereincomplete.
distributed.3.Scarce,ifonly5-25speci- -Sines,from1996to2004,withmost
menswerefoundinthesurvey.4.Very yearscomplete.
scarce, ifless than 5 individuáis were Therawinformationwaspurchased
observed.5.Absent,ifnospecimenwas fromtheHydrographicInstitute.Forthe
observed. SpanishAtlantic coast, data are avail-
60
CABRALANDSlMÓES:Thesouthern limitofdistributionoíPatellai
TableI. Identificationofsamplingsites. Máximum shell length ofPatellavulgataandnumberof
analyzedspecimenscollectedateachsamplingsite.
TablaI. Identificacióndelaslocalidadesdemuestreo. Extensiónlongitudinalmáximadelaconchay
númerodeejemplaresdePatellavulgatarecogidosencadalocalidad.
# Identification Coordinates:W/N Máximumshelllength Numberofspecimens NearAVHRR#
1 ínsua -8.8740 41.8701 49.7 365 -1
2 Moledo -8.8702 41.8452 39.7 49 +1
3 Arda -8.8756 41.7818 41.9 46 +2
4 Afife -8.8754 41.7798 39.7 42 +2
5 Agucadoura/AVero-Mar -8.7821 41.4319 49.4 366 +14
6 FigueiradaFoz -8.9060 40.1773 41.1 6 +62
7 SaoMartinhodoPorto -9.1369 39.5159 42.9 21 +85
8 Baleal -9.3382 39.3742 41.2 16 +88
9 Ericeira -9.4182 38.9648 38.9 33 +100
10 SaoJoaodoEstoril -9.3722 38.6940 49.6 27 +113
11 Oeiras -9.3240 38.6773 45.9 18 +114
12 PortinhodaArrábida -8.9715 38.4840 Notfound +126
13 Odeceixe -8.7944 37.4478 43.5 15 +167
14 Amoreira -8.8434 37.3553 42.2 18 +171
15 MonteClérigo -8.8521 37.3423 47.9 27 +171
16 Bordeira -8.8987 37.2022 45.3 41 +177
17 Amado -8.9036 37.1682 45.0 56 +177
18 PontaRuiva -8.9672 37.0691 52.3 62 +182
19 Telheiro -8.9781 37.0478 49.5 15 +182
20 Tonel -8.9471 37.0082 55.9 8 +187
21 Mareta -8.9383 37.0065 47.4 8 +187
22 Martinhal -8.9266 37.0166 41.8 10 +188
23 BarrancodoBenacoitao -8.8937 37.0421 56.6 10 +188
24 Ingrina -8.8778 37.0477 44.7 25 +188
25 Zavial -8.8705 37.0477 Notfound +189
26 Salema -8.8233 37.0661 43.6 4 +190
27 Luz -8.7250 37.0879 22.9 1 +192
28 Lagos-DonaAna -8.6679 37.0932 Notfound +194
29 TresIrmaos -8.5763 37.1199 Notfound +195
30 Rocha -8.5410 37.1182 32.2 2 +196
31 Carvoeiro-ValedeCentianes -8.4503 37.0911 Notfound +199
32 Marinha -8.4109 37.0912 Notfound +199
33 ArmacaodePera -8.3534 37.1019 Notfound +200
34 Olhosd'Água -8.1912 37.0905 Notfound +205
35 VilaRealdeSantoAntonio -7.4092 37.1770 Notfound +222
36 TorredelOro -6.7349 37.0941 Notfound +237
37 TorredelaHiguera -6.5623 37.0071 Notfound +241
ablefromtwobuoys(BilbaoandGijón), Resolution Radiometer) on board the
for March to November, 2004, and NOAA series polar orbiting satellites.
downloaded from the Puertos del The AVHRR measures emitted and
Estadosite(www.puertos.es). reflected radiation in two visible and
3. Nearshore SST data estimated three infrared channels. SSTestimates
fromtheAVHRR(AdvancedVeryHigh usetheinfraredchannelsinformation,
61
Iberus,25 (1),2007
calibrated with in situ determinations Cávalo, Leixóes, Peniche, Rocha and
measured using moored and drifting Sines,pixels+211, +112, +123, +21,+90,
buoys (Smith, Vázquez, Tran and +196and+114,respectively,and forthe
Sumagaysay, 1996). AVHRRmeasures buoysofFaro,Leixóes,Sines,Bilbaoand
theocean's «skin» temperature, corre- Gijón,pixels,+211,+18,+145,-169and-
spondingto theuppermostmillimeter 111,respectively. Thesethreesourcesof
oftheocean(Smithetal., 1996). Buoys informationontheSSThaveadvantages
measurethetemperatureoftheunderly- andlimitations. Shoreandbuoysdata
ingmixedlayer,theocean's«bulk»tem- wereavailableonlyatafewsitesalong
perature(Smithetal.,1996).Theocean theexaminedcoast,andwereparticu-
skin temperature can be as much as larly scarce in the Portuguese and
0.7°Ccoolerthanthebulktemperature, Spanishsoutherncoast.Bothsourcesare
duetoevaporationorradiativecooling expectedtobeaccurate,sincedetermi-
(Smith et al., 1996). However, since nationswerecarriedoutwithmeasur-
AVHRR measurements are calibrated inginstruments.Shoredataweredeter-
usingbuoys' determinations, thefinal minedonthebeach(onlyonceaday),
estimateresemblesmorecloselyabulk butbuoyswerenearthecoast(several
temperatureestimatethanaskintem- readingsperday).AVHRRdataarecon-
peratureestimate (Smithetal., 1996). tinuousalongthestudiedcoast,butthe
Data were downloaded from the valúes are estimates, with several
AVHRR Pathfinder v5 data set, at monthsmissingduetocloudcover,and
http://poet.jpl.nasa.gov, as monthly measuredpixelswerenearthecoast,not
means, from 1985 to 2004, withnight- ontheshore.
timeretrieval.Eachpixelcorrespondsto Inordertocorrelatethedistribution
a square with a 4 km side. Data were ofP.vulgatawiththegeologyofthePor-
firstdownloadedinsetscorresponding tuguesecontinentalcoast,therocksof
to squares with Io longitude x Io lati- thesamplingsiteswereidentifiedusing
tude. The closest, or the two pixels referenceliterature (CartaGeológica
closer to the coastwere then selected, dePortugal).
and the other valúes discarded. This Totestiftheslopeandinterceptof
procedure resulted in 350 SST pixels the regression lines were significantly
alongthenorthernFrenchandSpanish different from one and zero, respec-
coast,and243SSTpixelsalongthePor- tively,theprocedureofZar(1984)was
tuguese and southern Spanish coasts used.Significancelevelwassetat0.05.
(Fig.2).Twosetsofdatawerebuilt.One
set,withmeanmáximum(August)and
meanminimum(February)SSTforthe RESULTS
period 1984-2004,alongtheentiresetof
pixels (-350to+243).Anotherset,with IDistribution,abundanceandsize
monthlymeansfortheyear2000,along ofP.vulgata
theBiscaycoast,andfromGaliciatothe P.vulgatashellsareshowninFigures
furthestpixel +243. One ofthe limita- 3 and 4, including the four specimens
tions of the AVHRR measurements is collected from the extreme far sitesof
cloud cover, which results in several Salema,LuzandRocha(Figs.3,4,H-K).
absences of estimates, especially in Shellshadanellipsoidal,slightlyeccen-
winter months. For the calculation of tricbase.Shellconicitywasvariable,but
máximum and minimum means, only shellswereusuallyneitherveryfíatñor
pixelswithmorethan50%determina- very tall. The margin ofthe shell was
tions were used. For comparison entirelyorslightlyindented.Theexter-
betweenshoreorbuoysSSTdetermina- nal surface was smooth at the apex,
tions,andAVHRRSSTestimates,those withspaceddiscreetribsbelow. Shells
pixels closest to the shores or buoys fromhighshorelevéiswereusuallybare
werechosen,andwerefor,CapeSanta (Figs.3,4,A-C),butthosefrommidand
Maria, Cape Santa Marta, Forte do low shore levéis were completely
62
CABRALANDSlMÓES:ThesouthernlimitofdistributionofPatellavulgata
AVHRR# Coastalsite
-350 Brest
-340 Audierne
-335 Guilvinec
-325 Concarneau
48,0
-315 Lorient
-300 Vannes
-288 Saint-Brévin-les-Pins
-285 Pornic
-278 Saint-Jean-de-Monts
-271 LesSablesd'Olonne
-264 LaRochelle
-260 Rocherfort
-249 Soulac-sur-Mer
-231 Andemos-les-Bains
-204 Biarritz
AVHRR# Coastalsite
-200 Hendaye
-172 Bilbao
-154 Santander
-111 Gijón
-81 Castropol
-62 Cariño
-48 ACoruña
-24 Fisterra
-7 Vigo
1 VilaPraiadeÁncora
4 VianadoCastelo
23 Porto
62 CaboMondego
83 Nazaré
106 CabodaRoca
121 CaboEspichel
144 Sines
184 CabodeSaoVicente
202 Albufeira
211 CabodeSantaMaria
222 VilaRealdeSantoAntonio
242 Matalascañas
Figure 2. Localization oftheAVHRRpixels used to estímate nearshore SST, from Brittany
(France)toHuelva(Spain).RepresentativemainlandcoastalsitesneartheAVHRRpixelsaredis-
placed.
Figura2. LocalizacióndelospixelsAVHRRutilizadosparaestimarlaSSTcercadelacosta, desde
Bretaña(Francia)hastaHuelva(España). Semuestranlocalidadesrepresentativasdelacostacercade
lospixelsAVHRR.
63
Iberus,25 (1),2007
•••
Figure3. RepresentativeshellsofspecimensofPatellavulgatafoundalongthePortugueseconti-
nentalcoast.A-C,fromEriceira;D,fromSaoMartinhodoPorto;E,fromFigueiradaFoz;F,from
PontaRuiva; G, fromIngrina; H,fromSalema; I,fromLuz;J-K, fromRocha.A-C,specimens
fromhighshorelevéis.D-K,specimensfrommid-lowshorelevéis.
Figura3. ConchasrepresentativasdeejemplaresdePatellavulgataencontradosenlacostacontinental
dePortugal.A-C,delaEriceira;D,deSaoMartinhodoPorto;E,deFigueiradaFoz;F,delaPonta
Ruiva;G,deIngrina;H,deSalema;I,deLuz;J-K,delaRocha.A-C,ejemplaresdenivelesaltosdela
playa.D-K,ejemplaresdenivelesmediosybajosdelaplaya.
covered with algae (Figs. 3, 4, D-K). totallyyellow(Fig.4C)ordark(Fig.4D).
Almostallshellshadasilveryheadscar, Themostnotoriousandconstantchar-
intheinterior.Afewspecimensshowed acteristicsofP. vulgata shellswerethe
a whitish-silver head scar. Below the smoothexternalsurfaceattheapexand
headscar,mostspecimenshadalternat- thesilveryinteriorheadscar.Noconsis-
ing dark and orange/yellow/green tentmorphologicaltrendwasobserved
rays,butafewspecimenswerealmost inspecimensfromnorthtosouth,and
64
CABRALANDSlMÓES:ThesouthernlimitofdistributionofPatellavulgata
Figure4.InteriorofshellsshowninFigure3.Samelocalities,
Figura4.InteriordelasconchasdelaFigura3.Mismas
no peculiar characteristics were constantcharacteristicoftheradulawas
observedinspecimenscollectedatthe apointedextensiónontheoutersideof
extremesitesofSalema,LuzandRocha. cusp3. Thesizeofthispointedexten-
Themorphologyofpluricuspidteethin siónvariedbetweenspecimens,andina
the radula was similar to the types few,wasveryreduced,butwasalways
reportedintheliterature(Fisher-Piette, present, including in specimens col-
1934, 1935; Fisher-Piette and Gail- lected at the extreme sites of Salema,
lard, 1959; Evans, 1953; Hawkins, LuzandRocha.
Watson, Hill, Harding, Kyriakides, TheabundanceofP. vulgatashowed
HUTCHINSON AND NORTON, 1989; agenerallydecreasingtrendfromnorth-
Cabral,2003).Themostnotoriousand ern to southern sites, till Cape Sao
65
Iberus,25 (1),2007
CabodeSantaMaría
PraiadaRocha
SSTdeterminationinsituintheshore(°C)
Figure5. RelationshipbetweennearshoreSSTestimatedfromAVHRR(means 1985-2004) and
shoreSSTmeasuredbyinstruments(means 1981-2000).Insert,resultsfortestingiftheslopeand
interceptweresignificandydifferentfrom1and0,respectively.
Figura5. RelaciónentrelaSSTcercadelacostaestimadaporAVHRR(media1985-2004)ylaSST
medidaporinstrumentos(media 1981-2000). Enrecuadro, resultadosparatestarsilapendientey
ordenadasonsignificativamentediferentesde1y0,respectivamente.
Vicente, and then from western to reportedintheliterature(Cabral,2003,
eastern sites (Fig. 1). However, this 2005).Notrendinradularrelativesize
patternwasnotregular.P. vulgatawas wasobservedfromnortherntosouthern
abundant at sites north of the river sites.
Douro. To the south, abundance
decreasedpronouncedly,butnearCape II Patterns ofSSTvariationalong
SaoVicente,atPontaRuivaandTelheiro the French, Spanish and Portuguese
(#18and#19),P. vulgatawasabundant. coasts
P vulgatawasnotobservedatPortinho Apreliminarysearchcarriedoutin
da Arrábida (#12). Passing Cape Sao referenceliteraturerevealedthatforthe
Vicente,thespeciesbecamescarce,and regiónconsideredbetweenBritannyand
the last significant population was at Huelva, out of all possible variables,
Ingrina(#24).Thespecieswasobserved only two exhibited a clear trend from
even to the east, at Salema, Luz and northtosouthtillCapeSaoVicente,and
Rocha, but only very few specimens thenfromwesttoeast-theairtempera-
wereobserved. turealongthecoastandoceansurface,
Máximumshellsizevariedbetween andtheseasurfacetemperature(SST).
sites (Table I), and no trend was The relative humidity ofair at the
observed from northern to southern oceansurfacedisplayednosignificant
sites. Even at the far extreme site of trendinthisregión.Salinityofseawater
Salema (#26), shells reached consider- atthesurfacedecreasedslightlyalong
abledimensions.OnlyatLuzandRocha theBrittanycoast,BayofBiscay,andthe
(#27and#30),shellsweresmall,butnot northernandcentralPortuguesecoast
minute.Thereforetherewasnocorrela- due to the outputoffreshwater from
tionbetweenabundanceandmáximum largerivers inthese regions,butfrom
sizeofP. vulgataalongthePortuguese thesoutherncoastofPortugaltosouth-
continental coast. The relative size of ernSpain,watersalinitywasconstant.
radulatoshelllengthwasusuallyinthe Dissolved oxygenand the alkali-chlo-
range1.5-2.0.Similarvalúeshavebeen ridecoefficientwereconstantbetween
66