The molluscs of the intertidal algal turf in the Azores

2005·6.6 MB·English

by  Sdrgio P Avila

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SociedadEspañola deMalacología Iberus, 23 (1): 67-76, 2005
The molluscs ofthe intertidal algal turfin the Azores
Los moluscos del césped algal intermareale en Azores
Sergio P. ÁVILA*' **, Ana C. SANTOS*, Ana M. PENTEADO*, Ana M.
RODRIGUES*, Inés QUINTINO* and Maria Inés MACHADO*
Recibidoel25-VIII-2004.Aceptadoell-IV-2005
ABSTRACT
The molluscan fauna of the high ¡ntertidal algal turf on the ¡sland of Pico (Azores) was
studied ¡n order to complementexisting descriptions ofthe ¡ntertidal biota on these islands.
A total of 15,275 specimens belonging to 19 species were found. Five species, the gas-
tropods Alvania mediolittorolis Gofas, 1989, Omalogyra otomus (Philippi, 1841), Pis'mna
glabrata (Megerle von Mühlfeld, 1824) and Skeneopsis plonorbis (Fabricius O., 1780),
and the bivalve Lasaea adansoni (Gmelin, 1791), account for 98% of the total number of
specimens, P. glabrata itself being responsible for 46% ofall specimens.
In places where patellid limpets are absent, the algal turf extends higher in the ¡ntertidal
zone. In such places, three very abundant molluscan species characterize molluscan
assemblages in the algal turf: Lasaea adansoni, Skeneopsis planorbis and Pisinna
glabrata. Lasaea adansoni and Skeneopsis planorbis virtually disappear in the transition
from algal turf to algal fronds, the only (very) abundant species being P. glabrata and,
with less importance, Omalogyra atomus and Sinezona cingulata (Costa O. G., 1861).
RESUMEN
Se estudia la fauna malacológica del césped algal del intermareal superior en la isla de
Pico (Azores), con el fin de complementar los trabajos ya existentes sobre la biota inter-
mareal de estas islas. Se encontraron un total de 15275 ejemplares de 19 especies distin-
tas. Cinco, los gasterópodos Alvania mediolittoralis Gofas, 1989, Omalogyra atomus
(Philippi, 1841), Pisinna glabrata (Megerle von Mühlfeld, 1824) y Skeneopsis planorbis
(Fabricius O., 1780), y el bivalvo Lasaea adansoni (Gmelin, 1791), suman el 98% del
total de ejemplares, de ellas P. glabrata representa al 46%.
En aquellos lugares donde están ausentes los patélidos, las algas se extienden hasta nive-
les superiores en el intermareal. En estas zonas hay tres especies de moluscos que carac-
terizan las asociaciones malacológicas algales: Lasaea adansoni, Skeneopsis planorbis y
Pisinna glabrata. Lasaea adansoni y Skeneopsis planorbis desaparecen en la transición
entre el césped algal y la zona de algas frondosas. La única especie abundante aquí es P.
glabrata, y en menor medida Omalogyra atomus y Sinezona cingulata (Costa O. G.,
1861).
KEYWORDS: micromolluscs, intertidal, algal turf,Azores.
PALABRAS CLAVE: micromoluscos, intermareal, céspedalgal,Azores.
*DepartamentodeBiologia, UniversidadedosAcores, RúadaMáedeDeus, PT-9500 PontaDelgada,Acores,
Portugal.
**CIRN (CentrodeInvestigacaodeRecursosNaturais), DepartamentodeBiologia, UniversidadedosAcores,
PT9500PontaDelgada-Acores. E-mail: [email protected]
67
Iberus, 23 (1), 2005
INTRODUCTION differentiated by their species-composi-
tion and morphology. The higher part is
Locatedinthemiddleofthenorthern characterized by a "dense and short
Atlanticandthereforerelativelyisolated, tangle forming a mat, almostimpossible
the oceanic islands that form theAzores to sepárate into components" whereas
archipelago (36° 55' to 39° 45' N, 24° 45' the lowerpartis composed of frondose
to 31° 17' W) are a "live-laboratory" and larger algae. We followher designa-
where patterns and processes of disper- tion and restrict most of this study to
sión, colonization and speciation canbe theupperpartofthe "algalturf".
studiedandecological, evolutionaryand The aim of this study is to incorpó-
biogeographicaltheoriesbetested. rate the vertical distribution of micro-
Lajes do Pico, a small town located molluscs in the general zonationpattern
in the south coast of Pico island, Azores already described for the intertidal of
(Fig. 1), is one of the most interesting theAzores.
places in the littoral of the Azores,
because ofits very diverse marine fauna
and flora.Asa consequenceofanumber MATERIALAND METHODS
of biological studies (Azevedo, 1990,
Santos, 1992; Azevedo, Rodrigues, BetweenAugust 7 and 11, 1995, a 30
Mendizabal and Arruda, 1995; m long transect was examined on the
Morton, Britton and Martins, 1996, gently sloping rocky shore of Lajes do
1998; Ávila, 1998), this área was chosen Pico, near "Poca do Paño", in a moder-
as worthy of protection to conserve bio- ately exposed site (Fig. 1). The shore7
logical diversity; for a detailed review profile was drawn, following the spirit
seeÁvila, EliasandMedeiros (2000). leveling method (Emery, 1961; Hawkins
Rocky shores in the Azores are andJones, 1992)and allelevationswere
usually covered by an intricate mixture related to ChartDatum,Azores (CD),by
ofsmall-sized species ofalgae forming a using sea-level at the time of predicted
characteristic algal turf (Hawkins, low-tide. Tidal range in the Azores is
Burnay, Neto, Cunha and Martins, small (less than 2 m), for which reason
1990; Neto, 1992; Neto and Tittley, the transect location was carefully
1995). This turf is particularly effective chosen. The selected site presents a very
for a number of small animal species, gentle slope and, as a result, the transect
m
protecting them from wave exposure, was 30 long, a distance very seldom
excessive temperatures and desiccation found in Azoreanintertidal shores. This
(Azevedo, 1992). Chapman (1955) was procedure minimized problems derived
the first author to study the fauna asso- from the blurring effect that occurs in
ciated to this algal turf, mainly com- the zonation of organisms, when tran-
posed of Corallina spp. and he was sur- sects are made in sites with steeper
prised by the great abundance of mol- slopes.
luscs found in a sample of 10 x 10 cm, Five quadrats of25x25 cmwere col-
m
collected atFaialIsland. Azevedo (1992) lected at5, 10, 20, 25 and30 alongone
studied the molluscan species composi- transect (Fig. 2). The highly uniform
tion, abundance, diversity, seasonal species compositionofthe algal turfand
variationsandtheeffectofdifferencesin the large área used (25 x 25 cm instead
wave exposure on the high intertidal oftheusual 10x 10 cm) (Bullock, 1995)
algal turf of the Azores, on a temporal minimizes possible sampling problems
scale at Sao Miguel Island. He con- derived from a single transect without
cluded that floristic composition and replicates. After the littorinid zone that
m
biomass ofthe algal turfare fundamen- extended from to 15 along the tran-
tal for the molluscan communities in sect, and the barnacle zone (10-15 m), 3
thisparticularhabitat. quadrats of 25 x 25 cm were scraped
m
According to Neto (1992), the "algal from the "algal turf" at 20, 25 and 30
turf" is divided into two distinct zones, and the material collected (all of the
68
ÁVILAETAL.: The molluscs ofthe intertidal algal turfin theAzores
Corvo
Graciosa
Ro*S Azores Archipelago
" SaoJorge
P.co
Terceira
-
SaoMigue*
;.-''.;--x Vj JáSS f^V -'•""' i
Sí"Marta
Á
í 2000000
-.
/
v.
n.
Figure 1. Azores archipelago (top), Pico island (bottom, left) and detail oflocation ofPoca do
PañoatLajesdo Picovillage (Pico Island).
Figura 1. ArchipiélagodelasAzores (arriba), isladePico (abajo, izquierda)ydetalledela localización
dePocadoPañoylavilladeLajesdoPico (isladePico).
algae and contained sediment) put into determined for each quadrat, after
labelled bags. In the laboratory, this dryingfor48hours at60 °C. Abundance
material was washed several times and of molluscs was expressed as density
ADW
the animáis removed from the algae. (n/m2) as well as n/100 g (algal
Samples were then labelled and pre- dry weight), where n is the number of
served in 70% ethanol. The live-col- specimens of the ith species in a
lected molluscs were sorted, identified quadrate.
and counted under a binocular dissect- Species authorities and synonymy of
ing microscope. Dominant algae were mollusc species follow the CLEMAM
identified and algal dry weight (g) was datábase.
69
Iberus, 23 (1), 2005
^
2,7 y y Melarhapheneritoides ' $ Chthamalusstellatus
2,4H
12,1 *m Algal turf
Littorinastriata
HWST
LWST
5 10
Distance (m)
Figure 2.Transectperformedat Pocado Paño (Lajes do Pico, Pico island) andvertical distribution
ofrocky shore organisms. HWST: mean high water level at spring tides; LWST: mean lowwater
levelatspringtides.
Figura 2. Transecto realizado en Poca do Paño (Lajes do Pico, isla dePico)y distribución verticalde
organismosdecostarocosa. HWST: nivelmediosuperiordelaguaen mareasdeprimavera:LWST: nivel
medioinferiordelaguaen mareasdeprimavera.
RESULTS species, thegastropodsOmalogyraatomus
(Philippi, 1841), Skeneopsis planorbis
Zonation: The "littoral fringe" is (FabriciusO., 1780),Alvaniamediolittoralis
bound atthe topby alittorinidzone that Gofas, 1989andPisinnaglabrata (Megerle
m
extends for 15 along the transect, with vonMühlfeld, 1824) (=P. punctulum) and
m
a vertical range of 1.7 m, between 0.9 the bivalve Lasaea adansoni (Gmelin,
m
and2.6 above chartdatum. Thisisfol- 1791), account for 98% ofthe total num-
lowed by a barnacle zone (Chthamalus ber of specimens, P. glabrata itselfbeing
stellatus(Poli))withanextensiónofabout responsible for 46% of all specimens
5 m along the transect (between 10 and (Table I). No molluscs were collected in
15m),freeofmolluscsandwithavertical the middle of the barnacle zone. In
m m
range of about 0.5 (Fig. 2). After this, quadrats 3 and4, located at 20 and 25
analgalturf, dominatedbyCorallinaoffic- in the transect, three species dominated:
inalis L., covers the rocky substrate L. adansoni, S. planorbis and P. glabrata
entirely. No limpets were found in this (Table II). In the lowermost quadrat, lo-
zone, ñor molluscs that were common cated atLWST, P.glabrata was clearlythe
elsewhere, like Stramonita haemastoma most abundant species, representing
(Linnaeus, 1766)orMitracorneaLamarck, about 90% of all specimens in that
1811 (Hawkins, Corte-Real, Pannacci- quadrat. Species density and number of
ulli, Weberand Bishop, 2000). Immedi- specimens/lOOgADW(algaldryweight)
ately after LWST (mean low water level generally decreasedtowards LWST, with
at spring tides), frondose algae (mainly the exception of O. atomus and Sinezona
Pterocladiella capillacea (S.G. Gmelin) and cingulata (Costa O. G., 1861) (=Schismope
Enteromorpha muscoides (Clem.) Cre- fayalensisDautzenberg, 1889)(Figs.3,4).
mades, in Cremades et Perez-Cirera
replacethecorallineturf.
Molluscs: Atotal of 15,275 specimens DISCUSSION
belongingto19specieswerefoundinthe
intertidal algal turf at 'Toga do Paño" Thesitestudied broadlyconformsto
(Lajes do Pico) (Table I and Fig. 5). Five the zonationpattern described from the
70
) )
ÁVILAETAL.: The molluscs ofthe intertidal algal turfin theAzores
Table I. Specific composition ofthe molluscan fauna inhabiting the intertidal algal turfand total
number ofspecimens collected in each quadrat. Quadrats 1-5 collected at, respectively, 5, 10, 20,
m
25 and30 alongtransect (seeFigure2 forfurtherdetails).
TablaI. Composición específica de lafaunade moluscosdelcéspedalgalintermarealy número totalde
ejemplaresrecogido en cadacuadrante. Cuadrantes 1-5obtenidosa5, 10, 20, 25y30m a lo largo del
transecto, respectivamente(verlaFigura2para másdetalles).
Taxa\Quadrats 1 2 3 4 5 Total %
AlvaniomediolittofolisGofas, 1989 40 325 22 387 2.5
Bittiumlotreitti(Payraudeau, 1826) 1 6 7 0.0
Botbryphallusovummuscae(Gofas, 1990) 1 1 0.0
Coditocalyculata(Linnaeus, 1758) 36 47 6 89 0.6
Cingulatrtfasciato(AdamsJ., 1798) 1 1 0.0
Gregariellosemigranata(Reeve, 1858) 1 1 0.0
(= Trichomusculussemigronotus(Reeve, 1858))
Lasaeaadansoni(Gmelin, 1791) 1,811 2,417 1 4,229 27.7
LittorinostriataKingandBroderip, 1832 2 6 8 0.1
MonzoniounifosciotaDautzenberg, 1889 1 1 0.0
Melarhapbeneritoides(Linnaeus, 1758) 5 3 8 0.1
Odostomiosp. 3 3 0.0
Omologyraatomus(Philippi, 1841 96 35 156 287 1.9
Pisinnaglabrata(MegerlevonMühlfeld, 1824) 1,149 4,309 1535 6,993 45.8
Rissoellaá. diapbana(Alder, 1848) 3 3 0.0
Runtinocf. adñaticaThompson, 1980 20 20 0.1
SetiasubvaricosaGofas, 1990 25 25 0.2
Se/yosp. 2 12 14 0.1
Sinezonocingulato(Costa0.G., 1861 2 6 78 86 0.6
Skeneopsisplanorbis(0. Fabricius, 1780) 1,107 2,003 2 3,112 20.4
Total 7 9 4,246 9,169 1,844 15,275 100.0
rocky shores oftheAzores by Hawkins human overexploitation (Hawkins et
etal. (1990)(Caloura,SaoMiguelIsland) al., 1990;Hawkinsetal.,2000),thealgal
andNetoandAzevedo(1990)forFlores turf, usually coralline dominated by
Island (seealsoNeto, 1992, andMorton Corallina, Jania, Amphiroa or Haliptylon
etal., 1998). These authors divided the spp. directly attached to the rocky sub-
vertical zonation of the organisms into strate (Netoand Tittley, 1995) extends
three main zones: an upper one, the higher in the intertidal zone, a situation
splash and sprayzone, dominatedbylit- alsoencounteredbyNeto(1992). Insuch
torinids, lichens and ephemeral (sea- places oftheAzoreanrocky shores, three
sonal) algae; a middle zone located very abundant micromolluscan species
between HWST (mean high water level characterize and further define the algal
at spring tides) and LWST (mean low turflocated in the intertidal zone: Lasaea
water level at spring tides), occupied by adansoni, Skeneopsis planorbis and Pisinna
filter-feedingbarnaclesinitsupperlevéis glabrata. In the transition from algal turf
andby the algal turfin the lower levéis; to algal fronds, Lasaea adansoni and Ske-
and the lowermost zone, characterized neopsis planorbis virtually disappear, the
bythe appearanceofalgalfronds. Tothis only (very) abundant species being P.
scheme, we may add now the vertical glabrata and, withless importance, Omol-
distributionofothermolluscsbesidesthe ogyraatomusandSinezonacingulata.
littorinids. In places where patellid Mostofthespeciesfoundintheinter-
limpets are absent, possibly due to tidal algal turf at Lajes do Pico do not
71
) ) )
Iberas, 23 (1), 2005
Table II. Density (n/m2) and number ofspecimens per 100 g algal dryweight (n/lOOgADW) of
themolluscan faunainhabitingthe intertidalalgal turfatLajes do Pico. Forlocation ofquadrats 1,
2, 3, 4and 5, pleasereferto Figure2.
TablaII. Densida (n/m2)y número deejemplarespor 100gdepesoseco dealgas (n/WOgADW) dela
faunademoluscosdelcéspedalgalintermarealenLajesdoPico. Paralalocalizacióndeloscuadranets 1
a5, verlaFigura2.
Density(n/m2) n/lOOgADW
Taxa\Quadrats 1 2 3 4 5 3 4 5
AlvoniomediolittoralisGofas, 1989 640 5,2 352 208 618 57
Bittiumlatreillü(Payraudeau, 1826) 16 96 2 16
Bothryphallusovummuscae(Gofas, 1990) 16 5
Corditacolyculota(Ünnaeus, 1758) 576 752 96 188 89 16
Cingulotrifasciata(AdamsJ., 1798) 16 5
Pissoellacf.diaphona(Alder, 1848) 48 16
Losoeoadansoni(Gmelin, 1791 28,976 38,672 16 9,432 4,595 3
üttorinastríotaKingandBroderip, 1832 32 96
ManzoniaunifosciotoDoutzenberg, 1889 16 3
Melarbapbeneritoides(Ünnaeus, 1758) 80 48
Omalogyraotomus(Philippi, 1841 1,536 560 2,496 500 67 407
Pisinnoglabrata(MegerlevonMühlfeld, 1824) 18,384 68,944 24,560 5,984 8,192 4,008
Runcinacf.adrioticoThompson, 1980 320 38
SetiasubvaricosaGofas, 1990 400 65
Setiosp. 32 192 4 31
Sinezonocingulata(Costa0.G., 1861 32 96 1,248 10 11 204
Skeneopsisplanorbis(0.Fabricius, 1780) 17,712 32,048 32 5,766 3,808 5
Cregariellasemigranata(Reeve, 1858) 16 2
(= Trichomusculussemigronotus(Reeve, 1858))
Table III. Máximum densities (n/m2) recordedfortheAzores. 1: Feteira, Faial Island; 2: Piscinade
Santa Cruz, Flores Island, sheltered; 3: Ponta Delgada, Flores Island, exposed; 4: Caloura, Sao
Miguel Island, intertidal, sheltered; 5: Caloura, Sao Miguel Island, intertidal, exposed; 6: Caloura,
Sao Miguel Island, infralittoral, sheltered; 7: Ilhéu deVila Franca, Sao Miguel Island; 8: "Poca da
Barra", Lajes do Pico, Pico Island, intertidal, sheltered; 9: "Poca do Paño", Lajes do Pico, Pico
Island, intertidal, moderatelyexposed.
TablaIII. Densidadesmáximas (n/m2) encontradasen lasAzores. 1:Feteira, isladeFaial;2:Piscinade
Santa Cruz, isladeFlores,protegido;3:PontaDelgada, isladeFlores, expuesto;4: Caloura, isladeSao
Miguel, intermareal,protegido; 5: Caloura, isla deSaoMiguel, intermareal, expuesto; 6: Caloura, isla
deSaoMiguel, infralitoral,protegido; 7: Ilhéude VilaFranca, isladeSaoMiguel; 8: "PocadaBarra"
LajesdoPico, isladePico, intermareal,protegido;9: "PocadoPaño", LajesdoPico, isladePico, inter-
mareal, moderadamenteexpuesto.
Chapman, 1955 NetoandAzevedo, 1990 Azevedo, 1991 Bullock, 1995 Ávila, 1998 Thiswork
Alvaniamediolirtoralis 64(2) 14(4) 54,400 (7) 160(8) 5,200 (9)
Lasaeaadansoni 12,200(1) ',888 (3) 724 (4) 1,674,400(7) 1,088(8) 38,672 (9)
Omalogyraotomus 68,046 (6) 16(8) 2,496 (9)
Pisinnaglobrata 5,975 (4) 104,100(7) 32(8) 68,944 (9)
Skeneopsisplanorbis 2,000(1) 4,304 (5) 129,400(7) 16(8) 32,048 (9)
72
ÁVILAETAL.: The molluscs ofthe intertidal algal turfin the Azores
Table IV. Geographical ranges ofthe most abundant molluscan species inhabiting the intertidal
algal turfat Lajes do Pico (see ÁVILA, 2000 and references therein). np: non-planktotrophic type
ofdevelopment (itincludesdirectdevelopmentandlecithotrophicdevelopment); br: brooding.
TablaIV.Distribucióngeográficadelasespeciesdemoluscosmásabundantesen elcéspedalgalinterma-
realde Lajes do Pico (verÁVILA, 2000y las referencias allícitadas), np: desarrollo noplanctotrófico
(incluyendodesarrollosdirectoylecitotrófico); br:desarrolloplanctotrófico.
Species Typeofdevelopment Geographicalrange
Alvoniomediolittoralis np Azores,Madeira
Omalogyraatomus np Scandinavia,BritishIsles,BayofBiscay,Portugal,Mediterráneas
Azores,Madeira,CanaryIslands,CapeVerdeandAscensión
Skeneopsisplanorbis np Scandinavia,BritishIsles,BayofBiscay, Portugal,Mediterranean,
Azores,Madeira,CanaryIslandsandCaribbean
Pisinnaglabrota np Azores,CanaryIslandsandMediterranean
Lasoeaodansoni br Scandinavia,BritishIsles,BayofBiscay, Portugal,Mediterranean,
Azores,Madeira,CanaryIslands,CapeVerde,AscensiónIsland
SaintHelenaandCaribbean
extend their distribution to the sublit- Omalogyra atomus, Pisinna glabrata and
toral. Ávila (2003) has established the Skeneopsis planorbis collected in 51
molluscanverticaldistributionbetween3 quadrats (50 x 50 cm) between 3 and 30
m m
and 30 depths for the Azorean rocky depth, was only73individuáis, corre-
shorescoveredbyalgalfronds. Hefound spondingtoabout0.20% ofallspecimens
that the endemic rissoids Alvania angioyi collected (Ávila, 2003). The only species
van Aartsen, 1982, Manzonia unifasciata thatapparentlyextendsitsverticaldistri-
(Dautzenberg, 1889) and Rissoa guernei bution from the lowerlevéis ofthe inter-
Dautzenberg, 1889, the also endemic tidal algal turfdown to the shallow sub-
m
trochid Gibbula delgadensis Nordsieck, littoral algal fronds (2-3 depth) is the
1982, the MacaronesianAnachis avaroides minute Omalogyra atomus, which is the
m
Nordsieck, 1975 and the small bivalve most abundant species at 2-3 depth
Parvicardium vroomi van Aartsen, throughout the year (Azevedo, 1991).
Menkhorst and Gittenberger, 1984 were However, this speciesisveryuncommon
only abundantin shallow water (3 to 5-6 at greater depths (Ávila, 2003). The
m), whereasAlvania sleursi (Amati, 1987) abundances of the algal-turf associated
was especially abundant below 20 m molluscan fauna found at Lajes do Pico
depth. Bittium latreillii (Payraudeau, are in the range ofthose found by other
1826), Tricoliapullusazorica(Dautzenberg, authors for other islands ofthe archipel-
1889) andJujubinus pseudogravinae Nord- ago,beingintermedíatebetweenthevery
sieck, 1973were foundinlarge numbers high densities found by Bullock (1995)
along the whole depth-range, albeit in a very sheltered place (Ilhéu de Vila
slightly more abundant in the lower Franca,SaoMiguelIsland)andthedensi-
levéis (Ávila, 2003). Thus, as expected ties foundby NetoandAzevedo (1990)
because of the different spatial architec- andAzevedo(1991)(seeTableIII).
tureofalgae, thereisamarkeddifference Some species found in the quadrats
between the molluscan species composi- are accidental (e.g. Botryphallus and
tion of the algal turf and that present in Cingula) which live under intertidal
algal fronds. In fact, none of the most bouldersand notinalgalturf.
abundant molluscan species ofthe algal It is noteworthy that 4 out of the 5
turfis present inhigh numbers in algal most abundant molluscan species in the
fronds. Thetotalnumberofspecimensof intertidal of the Azores (the minute Ske-
Alvania mediolittoralis, Lasaea adansoni, neopsis planorbis and Omalogyra atomus,
73
Iberus, 23 (1), 2005
Alvaniamediolittoralis
Carditacalyculata
Lasaeaadansoni
Omalogyraatomus
Pisinnaglabrata
-e- Sinezonacingulata
Skeneopsisplanorbis
25
Distance (m)
Figures 3, 4. Abundance ofthe molluscs collected in the algal turfat "Poca do Paño" (Lajes do
Pico, Pico island). 3: n/m2; 4: n/100gADW.ADW: algaldryweight.
Figuras3, 4. Abundanciademoluscosrecogidosen elcéspedalgalen "PocadoPaño"(LajesdoPico, isla
dePico). 3:n/m2;4: ni'100gADW.ADW:pesosecodealgas.
the rissoid Alvania mediollitoralis and the adansoni, Skeneopsis planorbis and Pisinna
anabathrid Pisinna glabrata) all have a glabrata. Inthe transitionfrom algal turf
non-planktotrophic type of develop- to frondose algae, Lasaea adansoni and
ment (Ávila, 2000). This type of devel- Skeneopsis planorbis virtually disappear,
opment is usually associated with a the only (very) abundant species being
restricted geographical range (Schel- P. glabrata and, with less importance,
tema, 1978; Jablonski, 1986), which Omalogyraatomus and Sinezonacingulata.
clearly is not the case (with the excep-
tion of A. mediolittoralis) (see Table IV).
ACKNOWLEDGEMENTS
Perhaps the small size of these gastro-
pod species is an advantage for disper-
sal, aswell as their location in the inter- We thank Manuel Campos Marques
tidal, therefore having higher possibili- and Rui Pedro Ávila Marques for field
tiesofrafting. assistance. We are also grateful to Frias
Martins for correcting the manuscript.
Pedro "Bué" Cerqueira and Antonio
CONCLUSIONS Moniz (Seccao deGeografíadoDeparta-
mento de Biologia da Universidade dos
In the studied algal turf located Acores) are acknowledged for Figure 1.
between the barnacle zone (above) and The author also thanks the comments of
the frondóse algae (below), three species two anonymous referees. S.P. Ávila was
of molluscs are very common: Lasaea supportedbygrantSFRH/BD/5115/2001.
74
ÁVILAETAL.: The molluscs ofthe intertidal algal turfin theAzores
Figure 5. Common molluscs ofthe intertidal zone in theAzores. A:Alvania medioiittoralis Gofas,
1989; B: Bothryphallus ovummuscae (Gofas, 1990); C: Manzonia unifasciata Dautzenberg, 1889;
D: Cingula trifasciata (Adams J., 1798); E: Setia subvaricosa Gofas, 1990; F: Pisinnaglabrata
(Megerle von Mühlfeld, 1824); G: Bittium latreillii (Payraudeau, 1826); H: Stramonita haemas-
toma (Linnaeus, 1766); I, J: Skeneopsisplanorbis (O. Fabricius, 1780; K: Melarhaphe neritoides
(Linnaeus, 1758); L, M: Carditacalyculata (Linnaeus, 1758).
Figura 5. Moluscos comunes en la zona intermarealde lasAzores. A: Alvania mediolittoralis Gofas,
1989; B: Bothryphallus ovummuscae (Gofas, 1990); C: Manzonia unifasciata Dautzenberg, 1889;
D: Cingula trifasciata (AdamsJ., 1798); E: Setia subvaricosa Gofas, 1990; F: Pisinna glabrata
(MegerlevonMühlfeld, 1824); G: Bittium latreillii (Payraudeau, 1826);H: Stramonitahaemastoma
(Linnaeus, 1766); L,J: Skeneopsis planorbis (O. Fabricius, 1780; K: Melarhaphe neritoides (Lin-
naeus, 1758);L, M:Carditacalyculata (Linnaeus, 1758).
75
Iberus, 23 (1), 2005
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