[email protected]

The molluscs of the intertidal algal turf in the Azores

Los moluscos del cesped algal intermareale en Azores

Sergio P. AVI LA* , **, Ana C. SANTOS*, Ana M. PENTEADO*, Ana M. RODRIGUES*, Ines QUINTINO* and Maria Ines MACHADO*

Recibido e/ 25- VIII-2004. Aceptado eI J-IV-2005

ABSTRACT The molluscan fauna of the high intertidal algal turf on the island of Pico (Azores) was studied in order to complement existing descriptions of the intertidal biota on these islands. A tOlal of 15,275 specimens belonging 10 19 species were found. Five species, Ihe gas tropods Alvania mediolittoralis Gofas, 1989, Omalogyra alomus (Philippi, 1841), Pisinna glabrala (Megerle von MLihlfeld, 1824) and Skeneopsis planorbis (Fabricius 0., 1780), and the bivalve Lasaea adansoni (Gmelin, 1791), account for 98% of the total number of specimens, P. glabrala itself being responsible for 46% of all specimens. In places where patellid limpets are absent, Ihe algal turf extends higher in the interlidal zone. In such places, three very abundant molluscan species characterize molluscan assemblages in the algal turf: Lasaea adansoni, Skeneopsis planorbis and Pisinna glabrala. Lasaeo adansoni and Skeneopsis planorbis virtually disappear in Ihe transition from algal lurf to algal fronds, Ihe only (very) abundant species being P. glabrala and, wilh less imporlance, Omalogyra alomus and Sinezona cingu/ala (Cosio O. G., 1861).

RESUMEN Se estudia 10 fauna malacol6gica del cesped algal del intermareal superior en 10 isla de Pico (Azores), con el fin de complemenlar los Irabajos yo existenles sobre 10 biota inler· mareal de estas islas. Se encontraron un total de 15275 ejemplares de 19 especies dislin tas. Cinco, los gaster6podos Alvania medio/ittoralis Gofas, 1989, Omalogyra alomus (Philippi, 1841), Pisinna glabrala (Meg erie von MLihlfeld, 1824) y Skeneopsis planorbis (Fabricius 0., 1780), y el bivalvo Lasaea adansoni (Gmelin, 1791), suman el 98% del total de ejemplares, de elias P. glabrata representa 01 46%. En aquellos lugares donde esl6n ausentes los patelidos, las algas se eXlienden hasta nive les superiores en el intermareal. En estas zonas hay tres especies de moluscos que carac terizan las asociaciones malacol6gicas algales: Lasaea adansoni, Skeneopsis planorbis y Pisinna glabrala. Lasaea adansoni y Skeneopsis planorbis desaparecen en 10 transici6n entre el cesped algal y 10 zona de algas frondosas. La unica especie abundante aqui es P. glabrala, y en menor medida Omalogyra alomus y Sinezona cingu/ala (Cosio O. G., 1861).

KEY\VORDS: micromolluscs, intercidal, algal turf, Azores. PALABRAS CLAVE: micromoluscos, intermareal, cesped algal, Azores.

* Deparramento de Biologia, Universiclade dos A~ores, Rua da Mile de Deus, PT-9500 Ponta Delgada, A~ores, Porrugal. ** CIRt'\J (Cenrro de Invesriga~ilo de Recursos Narumis), Deparramenro de Biologia, Universidade dos A~ores, PT 9500 Ponta Delgada - A~ores. E-mail: [email protected]

67 IberttS, 23 0), 2005

INTRODUCTION differentiated by their species-composi tion and morphology. The higher part is Located in the middle of the northern characterized by a "dense and short Atlantic and therefore relatively isolated, tangle forming a mat, almost impossible the oceanic islands that form the Azores to separate into components" whereas archipelago (36° 55' to 39° 45' N, 24° 45' the lower part is composed of frondose to 31° 17' W) are a "live-laboratory" and larger algae. We follow her designa where patterns and processes of disper tion and restrict most of this study to sion, colonization and speciation can be the upper part of the "algal turf". studied and ecological, evolutionary and The aim of this study is to incorpo biogeographical theories be tested. rate the vertical distribution of micro Lajes do Pico, a small town located molluscs in the general zonation pattern in the south coast of Pico island, Azores alread y described for the intertidal of (Fig. 1), is one of the most interesting the Azores. places in the littoral of the Azores, because of its very diverse marine faw1a and flora. As a consequence of a number MATERIAL AND METHODS of biological studies (AZEVEDO, 1990, SANTOS, 1992; AZEVEDO, RODRIGUES, Between August 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; AVILA, 1998), this area was chosen Pico, near "Po<;a do Pano", in a moder as worthy of protection to conserve bio ately exposed site (Fig. 1). The shore' logical diversity; for a detailed review profile was drawn, following the spirit see AVILA, ELIAS AND MEDEIROS (2000). leveling method (EMERY, 1961; HAWKlNS Rocky shores in the Azores are AND JONES, 1992) and all elevations were usually covered by an intricate mixture related to Chart Datum, Azores (CD), by of small-sized species of algae 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 TlTTLEY, 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 protecting them from wave exposure, was 30 m long, a distance very seldom excessive temperatures and desiccation found in Azorean intertidal 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 of 25 x 25 cm were col collected at Faial Island. AZEVEDO (1992) lected at 5,10,20,25 and 30 m along one studied the molluscan species composi transect (Fig. 2). The highly uniform tion, abundance, diversity, seasonal species composition of the algal turf and variations and the effect of differences in the large area used (25 x 25 cm instead wave exposure on the high intertidal of the usual 10 x 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 biomass of the algal turf are fundamen extended from 0 to 15 m along the tran tal for the molluscan communities in sect, and the barnacle zone (10-15 m), 3 this particular habitat. quadrats of 25 x 25 cm were scraped According to NETO (1992), the "algal from the "algal turf" at 20, 25 and 30 m turf" is divided into two distinct zones, and the material collected (all of the

68 AVlLA ET AL.: The molluscs of (he imertidal algal turf in (he Azores

Azores Archipelago

Figure I. Azores archipelago (wp), Pica island (borwrn, lefr) and derail of locarion of Po<;a do Pano ar Lajes do Pica village (Pica Island). Figura I. Archipielago de las Azores (arriba), isla de Pico (abajo, izquierda) y detalle de Ia localizaci6n de Pora do Pano y Ia lJilla de Lajes do Pico (isla de Pico). algae and contained sediment) put into determined for each quadrat, after labelled bags. In the laboratory, this drying for 48 hours at 60°C. Abundance material was washed several times and of molluscs was expressed as density 2 the animals removed from the algae. (n/m ) as well as nl100 g ADW (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 database.

69 [bentS, 23 0), 2005

2,7 Melarhaphe neritoides ~ Chthamalus stellatus 2,4 T T

iIOOI\ Algal rurf ] 2,1 Littorina striata o J,8 U 1---/------HWST " 1,5 ;>o -g 1,2 -fn 0,9 'v 1: 0,6 0,3 +------1------"'" LWST

0+------,------,-----,------,-----,,-----, o 5 10 15 20 25 30 Disrance (m) Figure 2. Transecr performed ar POya do Pano (Lajes do Pico, Pico island) and venical disrriburion of rocky shore organisms. HWST: mean high warer level ar spring rides; LWST: mean low warer level ar spring rides. Figura 2. Transecto realizado en Po~a do Pano (Lajes do Pico, isla de Pico) y distribuci6n vertical de organismos de costa rocosa. HWST nivel medio superior del agua en mareas de primavera: LWST nivel medio inferior del agtta en mareas de primavera.

RESULTS species, the gastropods Ornalogyra atomus (Philippi, 1841), Skeneopsis planorbis Zonation: The "littoral fringe" is (Fabricius 0.,1780), Alvania mediolittoralis bound at the top by a littorinid zone that Gofas, 1989 and Pisinna glabrata (Megerle extends for 15 m along the transect, with von MUhlfeld, 1824) (=P. punctulum) and a vertical range of l.7 m, between 0.9 m the bivalve Lasaea adansoni (Gmelin, and 2.6 m above chart datum. This is fol 1791), account for 98% of the total num lowed by a barnacle zone (Chthamalus ber of specimens, P. glabrata itself being stellatus (Poli)) with an extension of about responsible for 46% of all specimens 5 m along the transect (between 10 and (Table I). No molluscs were collected in 15 m), free of molluscs and with a vertical the middle of the barnacle zone. In range of about 0.5 m (Fig. 2). After this, quadrats 3 and 4, located at 20 and 25 m an algal turf, dorrLinated by Corallina offic in the transect, three species dominated: ina lis L., covers the rocky substrate L. adansoni, S. planorbis and P. glabratl7 entirely. No limpets were found in this (Table II). In the lowermost quadrat, lo zone, nor molluscs that were common cated at LWST, P. glabrata was clearly the elsewhere, like Stramonita haemastoma most abundant species, representing (Linnaeus, 1766) or Mitra cornea Lamarck, about 90% of all specimens in that 1811 (HAWKINS, CORTE-REAL, PANNACCI quadrat. Species density and number of ULU, WEBER AND BISHOP, 2000). Immedi specimens/l00g ADW (algal dry weight) ately after LWST (mean low water level generally decreased towards 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 fayalensis Dautzenberg, 1889) (Figs. 3, 4). mades, in Cremades et Perez-Cirera replace the coralline turf. Molluscs: A total of 15,275 specimens DISCUSSION belonging to 19 species were found in the intertidal algal turf at "Po<;a do Pano n The site studied broadly conforms to (Lajes do Pico) (Table I and Fig. 5). Five the zonation pattern described from the

70 AVlLA ET AL.: The molluscs of the intertidal algal turf in rhe Azores

Table I. Specific composirion of rhe molluscan fauna inhabiring rhe inrerridal algal rurf and roral number of specimens collecred in each quadrar. Quadrars 1-5 collecred ar, respecrively, 5, 10, 20, 25 and 30 In along rransecr (see Figure 2 for furrher derails). Tab/.a /. Composicion especifica de /.a fiuma de moluscos del cesped algal intermareal y numero total de ejemplares recogido en cada cuadrante. Cuadrantes l-5 obtenidos a 5, lO, 20, 25 Y 30 malo /.argo del transecto, respectivamente (ver la Figura 2 para mtis detalles).

Taxa \ Quadrats Total % Alvania mediolittoralis Golas, 1989 0 0 40 325 22 387 2.5 Bittium latreillii (Payraudeau, 1826) 0 0 0 1 6 7 0.0 Bothryphallus ovummuscae (Golas, 1990) 0 0 1 0 0 1 0.0 Cardita calyculata (Linnaeus, 1758) 0 0 36 47 6 89 0.6 Cingula trifasciata (Adams J., 1798) 0 0 1 0 0 1 0.0 Gregariella semigranata (Reeve, 1858) 0 0 0 1 0 1 0.0 (= Trichomusculus semigranatus (Reeve, 1858)) lasaea adansoni (Gmelin, 1791) 0 0 1,811 2,417 1 4,229 27.7 littorina striata King and Broderip, 1832 2 6 0 0 0 8 0.1 Manlonia unifasciata Dautzenberg, 1889 0 0 0 0 1 1 0.0 Melarhaphe neritoides (Linnaeus, 1758) 5 3 0 0 0 8 0.1 Odostamia sp. 0 0 0 3 0 3 0.0 Omalogyra atomus (Philippi, 1841) 0 0 96 35 156 287 1.9 Pisinna glabrata (Megerle von Muhlleld, 1824) 0 0 1,149 4,309 1535 6,993 45.8 Rissaella cf. diaphana (Alder, 1848) 0 0 3 0 0 3 0.0 Runcina cf. adriatica Thompson, 1980 0 0 0 20 0 20 0.1 Setia subvaricosa Galas, 1990 0 0 0 0 25 25 0.2 Selia sp. 0 0 0 2 12 14 0.1 Sinelona cingulata (Costa O. G., 1861) 0 0 2 6 78 86 0.6 Skeneopsis planorbis (0. Fabricius, 1780) 0 0 1,107 2,003 2 3,112 20.4 Total 4,246 9,169 1,844 15,275 100.0

rocky shores of the Azores by HAWKINS human overexploitation (HAWKINS ET ET AL. (1990) (Caloura, Sao Miguel Island) AL., 1990; HAWKINS IT AL., 2000), the algal and N ETO AND AZEVEDO (1990) for Flores turf, usually coralline dominated by Island (see also NETO, 1992, and MORTON Coraliina, Jania, Amphiroa or Haliptylon ET AL., 1998). These authors divided the spp. directly attached to the rocky sub vertical zonation of the organisms into strate (NETO AND TITTLEY, 1995) extends three main zones: an upper one, the higher in the intertidal zone, a situation splash and spray zone, dominated by lit also encountered by NETO (1992). In such torinids, lichens and ephemeral (sea places of the Azorean rocky 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 turf located in the intertidal zone: Lasaea water level at spring tides), occupied by adansoni, Skeneopsis planorbis and Pisinna filter-feeding barnacles in its upper levels glabrata. In the transition from algal turf and by the algal turf in the lower levels; to algal fronds, Lasaea adansoni and Ske and the lowermost zone, characterized neopsis planorbis virtually disappear, the by the appearance of algal fronds. To this only (very) abundant species being P. scheme, we may add now the vertical glabrata and, with less importance, Omal distribution of other molluscs besides the ogyra atomlls and Sinezona cingulata. littorinids. In places where patellid Most of the species found in the inter limpets are absent, possibly due to tidal algal turf at Lajes do Pi co do not

71 IbmtS, 23 (1), 2005

2 Table II. Densiry (n/m ) and number of specimens per 100 g algal dry weight (n/IOOg ADW) of tne molluscan fauna inhabiting tne intertidal algal turf at Lajes do Pico. For location of quadrats 1, 2,3,4 and 5, please refer to Figure 2. Tabla I/. Densida (nlni) y mimero de ejemplares pOI' 100 g de peso seco de algas (nl100g ADW) de Ia founa de moluscos del cesped algal intermareal en Lajes do Pico. Para la localizaci6n de /os cuadranets 1 a 5, vel' Ia Figura 2.

Density (n/m 2) n/100g ADW Taxa \ Quadrats 2 3 3 4 A/vania medio/ittora/is Gofas, 1989 0 0 640 5,2 352 208 618 57 Bittium /otreillii (Payraudeau, 1826) 0 0 0 16 96 0 2 16 Bothryphollus ovummuswe (Gofas, 1990) 0 0 16 0 0 5 0 0 Cardita w/yw/ata (Linnaeus, 1758) 0 0 576 752 96 188 89 16 Cingu/a trifasciata (Adams J., 1798) 0 0 16 0 0 5 0 0 Rissoello d diaphana (Alder, 1848) 0 0 48 0 0 16 0 0 Lasoea adansoni (Gmelin, 1791) 0 0 28,976 38,672 16 9,432 4,595 3 Littorina striata King and Broderip, 1832 32 96 0 0 0 0 0 0 Manzonia unifasdata Daulzenberg, 1889 0 0 0 0 16 0 0 3 Me/orhophe neritaides (Linnaeus, 1758) 80 48 0 0 0 0 0 0 Oma/ogyra atomus (Philippi, 1841) 0 0 1,536 560 2,496 500 67 407 Pisinna g/abrata (Megerle von MOhlfeld, 1824) 0 0 18,384 68,944 24,560 5,984 8,192 4,008 Runeina d adrialica Thompson, 1980 0 0 0 320 0 0 38 0 Selia subvariwsa Gofas, 1990 0 0 0 0 400 0 0 65 Selia sp. 0 0 0 32 192 0 4 31 Sinezona cingu/ata (Costa O. G., 1861) 0 0 32 96 1,248 10 11 204 Skeneopsis p/anarbis (0. Fabricius, 1780) 0 0 17,712 32,048 32 5,7 66 3,808 5 Gregariella semigranata (Reeve, 1858) 0 0 0 16 0 0 2 0 (= Triehamusw/us semigranatus (Reeve, 1858))

2 Table III. Maximum densities (n/m ) recorded for the Azores. I: Feteira, Faial Island; 2: Piscina de 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: I1heu de Vila Franca, Sao Miguel Island; 8: "Po~a da Barra", Lajes do Pico, Pico Island, intertidal, sheltered; 9: "Po<;:a do Pano", Lajes do Pico, Pico Island, intertidal, moderately exposed. 2 Tabla /I/. Densidades maximas (nlm ) encontraclas en las Azores. 1: Feteira, isla de Faial; 2: Piscina de Santa Cruz, isla de Flores, protegido; 3: Ponta Delgada, isla de Flores, expuesto; 4: Ca/oura, isla de Sao lvliguel, intermareal, protegido; 5: Caloura, isla de Sao lvliguel, intermareal, expuesto; 6· Calollra, isla de Sao Miguel, infralitoral, protegido; 7: IIMu de Vi/a Franca, isla de Sao Miguel; 8: "Po[a cia Barra'; Lajes do Pico, isla de Pico, intermareal, protegido; 9: "Po[a do Pano'; Lajes do Pico, isla de Pico, inter mareal, moderadamente expuesto.

Chapman, 1955 Neto and Azevedo, 1990 Azevedo, 1991 Bullock, 1995 Avila, 1998 This work A/vania medio/ittora/is 64 (2) 14 (4) 54,400 (7) 160 (8) 5,200 (9) Lasaea adansoni 12,200 (1) 17,888 (3) 724 (4) 1,674,400 (7) 1,088 (8) 38,672 (9) Om%gyra atomus 68,046 (6) 16 (8) 2,496 (9) Pisinna g/abrata 5,975 (4) 104,100 (7) 32 (8) 68,944 (9) Skeneopsis planorbis 2,000 (1) 4,304 (5) 129,400 (7) 16 (8) 32,048 (9)

72 AVlLA ET AL.: The molluscs of the intertidal algal turf in the Azores

Table IV. Geographical ranges of rhe mosr abundant molluscan species inhabiring rhe intenidal algal turf ar Lajes do Pico (see AVILA, 2000 and references rherein). np: non-plankro[[ophic rype of development (ir includes direcr development and lecirhorrophic development); br: brooding. Tabla IV. DistribucZ6n geogrdfica de las especies de moluscos mds abundantes en eI cesped algal interma real de Lajes do Pico (vel' A VILA, 2000 Y las referencias alii citad.as). np: desarrollo no planctotr6fico (incluyendo desarrollos directo y Iecitotr6fico); br: desarrollo planctotr6fico.

Species Type of development Geographical range Alvania medialittaralis np Azores, Madeira Omalagyra alamus np Scandinavia, British Isles, Boy of Biscay, Partugal, Mediterranean, Azares, Madeira, Canary Islands, Cope Verde and Ascension Island Skeneapsis planorbis np Scandinavia, Brinsh Isles, Boy of Biscay, Portugal, Mediterranean, Azares, Madeira, Canary Islands and Caribbean Pisinna glabrala np Azores, Canary Islands and Mediterranean lasaea adansani br Scandinavia, British Isles, Boy of Biscay, Portugal, Mediterranean, Azares, Madeira, Canary Islands, Cope Verde, Ascension Island, Saint Helena and Caribbean

extend their distribution to the sublit Omalogyra atomus, Pisinna glabrata and toral. A VILA (2003) has established the Skeneopsis planorbis collected in 51 molluscan vertical distribution between 3 quadrats (50 x 50 cm) between 3 and 30 and 30 m depths for the Azorean rocky m depth, was only 73 individuals, corre shores covered by algal fronds. He found sponding to about 0.20% of all specimens that the endemic rissoids Alvania angioyi collected (A VILA, 2003). The only species van Aartsen, 1982, Manzonia unifasciata that apparently extends its vertical distri (Dautzenberg, 1889) and Rissoa guernei bution from the lower levels of the inter Dautzenberg, 1889, the also endemic tidal algal turf down to the shallow sub trochid Gibbula delgadensis Nordsieck, littoral algal fronds (2-3 m depth) is the 1982, the Macaronesian Anachis avaroides minute Omalogyra atomus, which is the Nordsieck, 1975 and the small bivalve most abundant species at 2-3 m depth Parvicardium vroomi van Aartsen, throughout the year (AZEVEDO, 1991). Menkhorst and Gittenberger, 1984 were However, this species is very uncommon only abw1dant in shallow water (3 to 5-6 at greater depths (AVILA, 2003). The m), whereas Alvania 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 of those found by other 1826), Tricolia pullus azorica (Dautzenberg, authors for other islands of the archipel 1889) and Jujubinus pseudogravinae Nord ago, being intermediate between the very sieck, 1973 were fOLmd in large numbers high densities found by BULLOCK (1995) along the whole depth-range, albeit in a very sheltered place (liheu de Vila slightly more abundant in the lower Franca, Sao Miguel Island) and the densi levels (AVILA, 2003). Thus, as expected ties found by NETO AND AZEVEDO (1990) because of the different spatial architec and AZEVEDO (1991) (see Table III). ture of algae, there is a marked difference 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 boulders and not in algal turf. abundant molluscan species of the algal It is noteworthy that 4 out of the 5 turf is present in high numbers in algal most abLmdant molluscan species in the fronds. The total number of specimens of intertidal of the Azores (the minute Ske Alvania mediolittoralis, Lasaea adansoni, neopsis planorbis and Omalogyra atom us,

73 IberttS, 23 (1), 2005

100000 3

10000

q 1000 ----, C v A/vania mediolittoralis Q 100 - Cardita calyculata 10 -----.- Lasaea adansoni 20 25 30 --+-- Omafogyra atomus Distance (m) ...<:; ·~10000 --D- Pisinna glabrata ;l C -u --0-- Sinezona cingulata -;;; 1000 bJ) -;;; bJ) --I'r- Skeneopsis planorbis 0 100 0

v~ (L 10 ~ -D E 4 ::J Z 20 25 30 Distance (m) Figures 3, 4. Abundance of the molluscs collected in the algal turf at "Poya do Pano" (Lajes do 2 Pico, Pico island). 3: n/m ; 4: nil 00 g ADW ADW: algal dry weight. Figuras 3,4. Abundaneia de moluseos reeogidos en el cesped algal en "Po(,a do Pano" (Lajes do Pieo, isla 2 de Pico). 3: nlm ; 4: nl100 g ADW ADW peso seco de algas. the rissoid Alvania mediollitoralis and the adansoni, Skeneopsis planorbis and Pisinna anabathrid Pisinna glabrata) all have a glabrata. In the transition from algal turf non-planktotrophic type of develop to frondose algae, Lasaea adanSOl1i and ment (AVILA, 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 Omalogyra atomus and Sinezona cingulata. clearly is not the case (with the excep tion of A. mediolittoralis) (see Table IV). Perhaps the small size of these gastro ACKNOWLEDGEMENTS pod species is an advantage for disper sal, as well as their location in the inter We thank Manuel Campos Marques tidal, therefore having higher possibili and Rui Pedro Avila Marques for field ties of rafting. assistance. We are also grateful to Frias Martins for correcting the manuscript. Pedro "Bw?" Cerqueira and Ant6nio CONCLUSIONS Moniz (Se((;ao de Geografia do Departa mento de Biologia da Universidade dos In the studied algal turf located A~ores) are acknowledged for Figure l. between the barnacle zone (above) and The author also thanks the comments of the frondose algae (below), three species two anonymous referees. S.P. Avila was of molluscs are very common: Lasaea supported by grant SFRH/BD/5115/2001.

74 AVlLA ET AL.: The molluscs of the intertidal algal turf in the Azores

Figure 5. Common molluscs of rhe intertidal zone in rhe Azores. A: A/vtlllia /n ediolittoralis G ofas, 1989; B: Bothflphallus ovummuseM (Gofas, 1990); C: Mamwnia tmiflseiata Dautzenberg, 1889; D: Cingula trififSclata (Adams ]., 1798); E: Setia subllllricosa Gofas , 1990; F: Pisi/ma g/abrata (Megerle von Miihlfeld, 18 24); G: Bittilln/ lamiilii (Payraudeau, 18 26); H: Stramonita bal'mas· toma (Linnaeus, 1766) ; I. J: Skeneop,·is planorbis (0. Fabricius, 1780; K: Melarhaphe naitoides (I.innaeus, 1758); L, M: Ca rdita calyculattl (Linnaeus, 1758). Figu ra 5. Moluseos (o muncr en III Z()J/(/ intermaretll d~' lflS AZJJ/"o . A: Alvania mediolirtoralis Gofos, 1989; B: Bothrypball us ovummuscae (Gofos. 1990); C: Manzonia unifasciata Dautzen berg, 1889; D: Cingula rri fa sciat3 (Adams j., 1798); E: Setia subvaricosa Gofos, 1990; F: Pisinna glabrata (Meg!:r!/' vall M iihlfi:lrI, 1824); G: Bittium larreillii (PaYl71l1dt'IIU, 18 6); H: Stramonita haem3sroma (Lin f/fltIus. il66); 1, }: Skeneopsis planorbis (0. Fabricills, il80; K Melarhaphe neriroides (Lin lIa{'l/S, 1758); L, M: C ardita calyculata (Iil/nll/tw. 1758).

75 Ibmts, 23 (1), 2005

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