INTRODUCTION
The archipelagos of the Azores, Madeira and the Canaries form the so-called Macaronesian region in the eastern Atlantic Ocean (Figure 1). They act as a bridge favouring faunistic exchange between the western and eastern Atlantic basins (e.g. González, Reference González1995; Santos et al., Reference Santos, Porteiro and Barreiro1997; Brito et al., Reference Brito, Pascual, Falcón, Sancho and González2002; Wirtz et al., Reference Wirtz, Araújo and Southward2006).
The Macaronesian region—archipelagos of the Azores, Madeira and the Canaries.
Islands have featured strongly in the development of evolutionary and ecological ideas from the earliest formal studies (see Hawkins et al., Reference Hawkins, Corte-Real, Pannacciulli, Weber and Bishop2000). The sea is generally viewed as homogeneous areas, being interconnected via ocean currents and broad scale dispersal mechanisms of the biota. Isolated islands are playing an important role in allopatric speciation of many species of gastropods and barnacles (e.g. Kay & Palumbi, Reference Kay and Palumbi1987; Hawkins et al., Reference Hawkins, Corte-Real, Pannacciulli, Weber and Bishop2000). Macaronesia is a superb natural laboratory to understand speciation in intertidal organisms. During glaciation, it is likely that many temperate species retreated to north-west Africa and the Canaries, from which refuge they may have subsequently expanded outwards and northwards, including into the Mediterranean Sea (Hawkins et al., Reference Hawkins, Corte-Real, Pannacciulli, Weber and Bishop2000; Brito et al., Reference Brito, Pascual, Falcón, Sancho and González2002). The biological performance of species close to their biogeographical boundaries is of critical interest in a period of rapid climate change and can inform predictions of future patterns of distribution (Herbert et al., Reference Herbert, Southward, Clarke, Sheader and Hawkins2009).
The volcanic characteristics of the Canary Islands are manifest by the absence of wide insular shelves, with a bottom depth of 180–200 m near the coast. The Canary archipelago is situated relatively close to the continents of Africa and Europe, but separated from them by great depths (Figure 1). The Canary Islands are also under the influence of the subtropical gyre of the eastern central Atlantic, which would facilitate the transport of marine organism larvae to the archipelago from the American, European and north-west African coasts (e.g. Aguilera et al., Reference Aguilera, Brito, Castilla, Díaz, Fernández-Palacios, Rodríguez, Sabaté and Sánchez1994). The littoral biota of the Canaries is dominated by tropical/subtropical east Atlantic species, followed by Atlantic–Mediterranean and amphi-Atlantic species (González, Reference González1995; Brito et al., Reference Brito, Lozano, Falcón, Rodríguez, Mena, Llinás, González and Rueda1996). The poverty of Guinean (tropical and subtropical) species on the Canary coasts may be the result of the absence of a consistent current flow from the south, and the thermal barrier created by the Cape Blanc upwelling cell (e.g. Mittelstaedt, Reference Mittelstaedt1983).
Recent studies about the hydrography, composition and horizontal distribution of a larval fish community between the Canary Islands and the African coast have found a strong mesoscale oceanographic activity. This mesoscale distribution of larvae has been described in filaments of the upwelling system from the African coast reaching the south-east of this archipelago (Rodríguez et al., Reference Rodríguez, Barton, Hernández-León and Arístegui2004; Bécognée et al., Reference Bécognée, Moyano, Almeida, Rodríguez, Fraile-Nuez, Hernández-Guerra and Hernández-León2009), and suggests specific retention mechanisms for the larvae of neritic invertebrate populations (including barnacles) around the oceanic islands of the Canaries (Landeira et al., Reference Landeira, Lozano-Soldevilla, Hernández-León and Barton2009, Reference Landeira, Lozano-Soldevilla, Hernández-León and Barton2010). These studies have proved that short-lived larvae from Africa are arriving to the Canary Islands transported by the currents or upwelling filaments, since a quasi-permanent flow of this type of organisms has been registered. Although some cypris larvae might be able to reach the Canaries and even to settle on their coast, a part of them might not be able to develop a stable reproductive population because of one or several adverse environmental conditions, like temperature of seawater, food availability, etc.
Also, the Canary Islands are geographically located on a very important maritime route and ships have long been recognized as a major vector for the introduction of non-native and encrusting organisms. Many yacht marinas are located at the Canary Islands, and some of them are frequently organizing races and cruises to Madeira and the Caribbean Sea with the participation of thousands of recreational boats.
Geomorphological, geographical and oceanographic particularities of the Canaries could explain the great diversity in the biogeographic patterns of the biota inhabiting this area. These physical and biodiversity characteristics, together with the climatic condition of the Canary Islands—a temperate–subtropical area—compared to the surrounding region highlight the uniqueness and oceanographic connectivity of the Canary Islands to the surrounding waters.
Professor A.J. Southward, being fascinated by the intrinsic interest of the islands and particularly interested in the bridging role of the Macaronesian islands in the distribution of marine species, first studied the Azorean barnacles (Southward, Reference Southward1998) followed by the Madeiran barnacles (Wirtz et al., Reference Wirtz, Araújo and Southward2006). He then started to identify some specimens of Cirripedia of the Canary Islands in the collections of the Instituto Canario de Ciencias Marinas, before his death in 2007.
The monographs on Cirripedia by Darwin (Reference Darwin1851, Reference Darwin1854), and the account of barnacles of tropical West Africa by Stubbings (Reference Stubbings1967), do not include any record for the Canary Islands. The three most frequent species (Chthamalus stellatus, Pollicipes cornucopia and Balanus sp.) were included in the preliminary catalogue of the benthic fauna from the Canaries (Barquín-Diez et al., Reference Barquín-Diez, Moreno Batet, Pérez-Dionis and In Bacallado1983). Apart from several popular science books (Brito et al., Reference Brito, Cruz, Moreno, Pérez and Bacallado1984; Pérez & Moreno, Reference Pérez and Moreno1991; Franquet & Brito, Reference Franquet and Brito1995; Espino et al., Reference Espino, Boyra, Tuya and Haroun2006) and one non-annotated preliminary check-list (Haroun et al., Reference Haroun, Herrera, Domínguez, Moro, Martín, Garrido and Izquierdo2003), there have been no scientific studies devoted to the Canarian Cirripedia to date.
This is the first account of the intertidal, shallow-water and oceanic thoracian barnacles from the Canaries. It includes notes on their distribution and ecology, based on the authors' collections and the invaluable identification work conducted by the late A.J. Southward.
MATERIALS AND METHODS
This report is based on material collected by hand, snorkel- and SCUBA-diving from shore, shallow depths and ship hulls by the authors and their collaborators, with material collected during cruises or project surveys. Additional preserved material has been included, whenever relevant for depth-range or ecological information. Species reported from all these sources are listed in Table 1, which also lists the shallow-water species found in Madeira and the Azores. A scale map of the Canary Islands with the localities of capture of the specimens studied is provided in Figure 2.
Collection locations of barnacles studied around the Canary Islands.
Shallow-water/oceanic barnacle species (Cirripedia: Thoracica) occurring in the Canaries, Madeira and the Azores.
Depth-range and geographical distribution taken mainly from Southward (Reference Southward1998, Reference Southward, Crothers and Hayward2008), Young (Reference Young1998, Reference Young2001).
All reference samples and part of the additional material were identified by A.J. Southward at the Laboratory of the Marine Biological Association of the United Kingdom (MBA) in Plymouth. The remaining additional samples, mainly replicates of the reference material, were checked and identified at the Instituto Canario de Ciencias Marinas (ICCM) in Gran Canaria. The nomenclature and synonyms still in use follow Southward (Reference Southward, Crothers and Hayward2008). Voucher specimens have been deposited in the collections of the ICCM. All measurements (in mm ± 0.1) follow Young (Reference Young2001) and Southward (Reference Southward, Crothers and Hayward2008). Abbreviations are as follows: cl, capitular length; tl, total length; and rc, rostro-carinal diameter.
RESULTS
See Southward (Reference Southward, Crothers and Hayward2008) for families, genera and species' descriptions.
MATERIAL EXAMINED
Thirteen specimens found attached to a loggerhead turtle Caretta caretta (ICCM-345) and floating buoys (ICCM-326, 392) in Gran Canaria and La Palma islands. Size-range: tl (cl) 6.5 (4.0) to 55.9 (40.7) mm. Additional material from La Palma includes one extremely large barnacle measuring 108.8 (55.1) mm.
DISTRIBUTION
Cosmopolitan, including the Azores (Southward, Reference Southward1998), Madeira (Wirtz et al., Reference Wirtz, Araújo and Southward2006) and the Canaries (Pérez & Moreno, Reference Pérez and Moreno1991).
REMARKS
This is the most common pedunculate on the Canary coasts, where it usually attains 8 cm in length, living attached to any floating object such as wood, ropes, buoys, ship hulls or sea turtles.
MATERIAL EXAMINED
Two subadult specimens, tl (cl) 16.2 (11.8) to 23.7 (17.1) mm, and several juveniles, off Gran Canaria, surface, found on a loggerhead turtle Caretta caretta (ICCM-336).
DISTRIBUTION
Circumtropical, including the Azores (Southward, Reference Southward1998).
REMARKS
This is the first record of the species for the Canary Islands. It does truly belong to the Canarian fauna. In the past L. hilli was misidentified as L. anatifera.
MATERIAL EXAMINED
Many specimens, tl (cl) 1.8 (1.2) to 3.0 (2.0) mm, off La Palma, surface, hand-collected from a floating plastic bucket (ICCM-389). Additional material was collected on one dead Spirula spirula off Tenerife (Figure 3).
Many Lepas pectinata attached to a Spirula spirula (top left); two living recently settled barnacles (bottom right); broken valves of a cypris larvae and of the peduncle of a newly metamorphosed (bottom left); cypris larvae just attached to Spirula (top right).
DISTRIBUTION
Circumtropical, including the Azores (Southward, Reference Southward1998) and the Canaries (Pérez & Moreno, Reference Pérez and Moreno1991).
REMARKS
This species is a winter breeder (Southward, Reference Southward, Crothers and Hayward2008), which is confirmed by our observations of living recently settled individuals and cyprids in late February (Figure 3).
MATERIAL EXAMINED
Seventeen specimens, tl (cl) 8.6 (6.3) to 13.0 (9.7) mm, plus three juveniles, Gran Canaria and El Hierro, found on loggerhead turtles Caretta caretta, and on a mooring at 20–25 m depth (ICCM-335, 398). One additional specimen was observed in Gran Canaria on a mooring at 5 m.
DISTRIBUTION
It is known worldwide, including the Azores, on ships, whales and other floating objects (Southward, Reference Southward, Crothers and Hayward2008).
REMARKS
This is the first record of the species for the Canary Islands.
Synonyms: Mitella pollicipes, Pollicipes pollicipes.
MATERIAL EXAMINED
One specimen, tl (cl) 53.5 (28.1) mm, Fuerteventura, 0–1 m (ICCM-360). It was first reported from the Canary Islands by Barquín-Diez et al. (Reference Barquín-Diez, Moreno Batet, Pérez-Dionis and In Bacallado1983; as Pollicipes cornucopia).
DISTRIBUTION
A north-east Atlantic species, including the Canaries (Barquín-Diez et al., 1983). Not found in the Azores (Southward, Reference Southward1998) or Madeira (Wirtz et al., Reference Wirtz, Araújo and Southward2006).
REMARKS
In the Canaries, this species occurs as scattered colonies in the north and west sectors of the islands, but is common in certain localities of the easternmost islands, Lanzarote and Fuerteventura, especially on the west coast of the latter (Franquet & Brito, Reference Franquet and Brito1995). It inhabits the low-water mark on rocky coasts in highly wave-exposed areas, mainly on vertical faces and in crevices. It usually occurs as a pinecone- or raceme-shaped cluster of several barnacles, up to 100 mm in length.
MATERIAL EXAMINED
Four specimens, rc 0.4–0.6 mm, La Palma, 10 m, found on the walls of a cave (one of them on a specimen of Megabalanus tulipiformis) (ICCM-397). One additional specimen, Alegranza islet, Lanzarote, 38 m, attached to a M. tulipiformis, collected by SCUBA-diving, deposited at the Laboratory of the MBA.
DISTRIBUTION
A Mediterranean and north-east Atlantic species, including the Azores (Southward, Reference Southward1998), Madeira (Wirtz et al., Reference Wirtz, Araújo and Southward2006) and the Canaries (Pérez & Moreno, Reference Pérez and Moreno1991).
REMARKS
The citation of Verruca stroemia (O.F. Müller, 1776) by Gruvel (Reference Gruvel1902, Reference Gruvel1920) for the Azores was probably based on a mistaken identification, because this species has a boreo-Arctic distribution (the White Sea to the Algarve, Portugal) living from extreme low water to 500 m (Southward, Reference Southward1998, Reference Southward, Crothers and Hayward2008). In the Mediterranean, in southern Spain, the Azores and Madeira, the genus is represented by V. spengleri (depth-range: 0–130 m) (Southward, Reference Southward1998, Reference Southward, Crothers and Hayward2008). The original description of V. spengleri is based on specimens from Madeira (Museu Municipal do Funchal), where it is common in dark places from low-water level downwards, e.g. under stones and on the walls of caves (Wirtz et al., Reference Wirtz, Araújo and Southward2006). The citation of V. stroemia for the Canaries by Pérez & Moreno (Reference Pérez and Moreno1991) is very probably erroneous and based on V. spengleri specimens.
MATERIAL EXAMINED
One colony, rc 3.0–6.0 mm, Lanzarote, 0–1 m. Two additional specimens ranging rc 2.1–4.3 mm (ICCM-331), attached to a Pollicipes pollicipes specimen from north-west Africa were used as comparative material.
DISTRIBUTION
A north-east Atlantic species. Known from British and Irish coasts to at least Senegal (Southward, Reference Southward, Crothers and Hayward2008). This species is absent from the Azorean and Madeiran coasts (Southward, Reference Southward1998, Reference Southward, Crothers and Hayward2008; Wirtz et al., Reference Wirtz, Araújo and Southward2006). For more details on its distribution-range, see Southward (Reference Southward, Crothers and Hayward2008).
REMARKS
Chthamalus montagui was first reported from the Canary Islands by Crisp et al. (Reference Crisp, Southward and Southward1981) based on examples from the east coast of Puerto del Carmen, Lanzarote, one of the nearest islands to the African mainland, where the species is present. We have searched intensively for this species on the shores of the Canary Islands, but only encountered it at the previously cited locality at Lanzarote, where it apparently occurs in areas sheltered from wave action. The fact that it is an uncommon species in the Canaries suggests that it does not have a breeding population capable of extending its distribution at present.
MATERIAL EXAMINED
About one hundred specimens, rc 0.4–6.8 mm, Fuerteventura, Gran Canaria, La Palma, Tenerife, and La Gomera, 0–1 m, in general on rocks with or without algae but also on aquaculture sea cages (ICCM-343, 359, 361, 369, 384, 395-6). Twenty-nine additional specimens collected from La Gomera were identified by A.J. Southward and deposited in the MBA.
DISTRIBUTION
A north-east Atlantic species, known from the British Isles to north-west Africa and the Cape Verde Islands, including the Azores, Madeira and the Canaries; also reported from the Mediterranean Sea and the Black Sea (Southward, Reference Southward, Crothers and Hayward2008; Pannacciulli et al., Reference Pannacciulli, Manetti and Maltagliati2009).
REMARKS
In the Canaries, this abundant species (‘sacabocaos’ or ‘canutillos’) forms a wide yellowish band on the rocky level just on the top of the intertidal zone. The density of C. stellatus in this level increases with the degree of wave exposure (Brito et al., Reference Brito, Cruz, Moreno, Pérez and Bacallado1984). Individuals are small, and rarely attain more than 8 mm in diameter (Pérez & Moreno, Reference Pérez and Moreno1991).
MATERIAL EXAMINED
Two entire specimens, rc 6.1–7.2 mm, and four disarticulated ones, rc 6.3–7.0 mm, La Palma (Fuencaliente), 10–15 m, on rocks, collected by SCUBA-diving in December of 2008 (ICCM-374). Additional material (2 specimens, rc 5.5–6.0 mm) from Lanzarote (El Salado, La Graciosa) has been collected in November of 2010 from the intertidal zone at 0 m.
REMARKS
The specimens examined have a low conical shell (altitude up to 2.6 mm), dull brown-white coloured, not corroded; five individuals have smooth shell plates with smooth rounded edges, the remaining one is moderately ribbed with crenulated edges; shell orifice kite-shaped; scuto-tergal articulation placed 1/4 to 1/3 the distance from carina to rostrum, and forming an oblique angle when the two occludent angles are added together; scutum with relative long occludent edge and a straight tergal margin; adductor muscle insertion not clearly visible; tergum wide with slightly prominent spur, the lateral margin only slightly indented; depressor muscle crests, 3–4 (Figure 4). These morphological features clearly separate these individuals from the Chthamalus species known to occur on the Mediterranean, European and north-west African coasts. Chthamalus sp. from the Canaries seems to be, based on shell morphology, closely related to Chthamalus proteus Dando & Southward, Reference Dando and Southward1980, a western Atlantic and tropical eastern Pacific intertidal species (reaching about 1 cm diameter), which is arriving in Hawaiian harbours on the bottoms of ships (Dando & Southward, Reference Dando and Southward1980; Southward et al., Reference Southward, Burton, Coles, Dando, Defelice, Hoover, Parnell, Yamaguchi and Newman1998). Chthamalus proteus, a barnacle that arrived in the Hawaiian Islands ~30 years ago, is now the most abundant and widespread non-native barnacle in the intertidal zone on the island of Oahu; at an intertidal site on this island, the invasive barnacle settled in highest numbers on rough substrata, with a trend toward higher settlement on dark-coloured substrata (Zabin & Altieri, Reference Zabin and Altieri2007; Zabin, Reference Zabin2009). However, the dissection of one specimen from La Palma and another from Lanzarote has made evident their arthropodal characters which can provide, according to Southward & Newman (Reference Southward and Newman2003) and Southward (Reference Southward, Crothers and Hayward2008), a sound taxonomic basis. As a result, Chthamalus sp. found on the Canary coast belongs to the Southward & Newman 'malayensis' subgroup of the genus. They have conical spines on the inner side of the outer ramus of the first cirri and with basal guards present on complex setae on cirrus II, and the pecten of mandible show small teeth.
Chthamalus sp. Specimen with smooth shell plates (top). Specimen moderately ribbed (middle). External appearance of terga and scuta (bottom).
MATERIAL EXAMINED
Three specimens, rc 8.7–9.8 mm, Gran Canaria, on a loggerhead turtle Caretta caretta (ICCM-334).
DISTRIBUTION
Turtle barnacles are cosmopolitan in tropical and warm temperate seas, including now British and Irish waters (Southward, Reference Southward, Crothers and Hayward2008). Reported from the Irish Sea found on a leatherback turtle Dermochelys coriacea; apparently recently-settled juveniles, clustered at the basis of the flippers (Southward, Reference Southward, Crothers and Hayward2008).
REMARKS
According to Pérez & Moreno (Reference Pérez and Moreno1991), in the Canaries it is an occasional to rare species on sea turtles and other floating objects.
MATERIAL EXAMINED
Three specimens, tl 24.3–26.7 mm, Gran Canaria, on pectoral, dorsal and caudal fin of a short-finned pilot whale Globicephala macrorhynchus (ICCM-337).
DISTRIBUTION
Worldwide on cetaceans (Southward, Reference Southward, Crothers and Hayward2008).
REMARKS
This is the first record of the species for the Canary Islands.
MATERIAL EXAMINED
Two dead shells in a sponge, Petrosia ficiformis, rc 6.9–7.6 mm, La Gomera, 12 m (ICCM-328).
DISTRIBUTION AND REMARKS
In the east Atlantic Ocean it was only known from Madeira, where it lives embedded in sponges in the sublittoral zone, around 12 m depth (Wirtz et al., Reference Wirtz, Araújo and Southward2006). Around Madeira this species seems to replace Acasta spongites Polli, 1795 (Southward, Reference Southward, Crothers and Hayward2008). This is the first record of the species for the Canary Islands.
MATERIAL EXAMINED
Sixty-one specimens, rc 2.2–12.9 mm, Gran Canaria, Lanzarote, La Palma, and Tenerife, 0–50 m, on rocks, concrete modules, floating buoys and bottom traps, also as a fouling species and as overgrowth on other balanids (ICCM-327, 340, 347, 352, 355, 357, 362, 377, 382, 388, 391).
DISTRIBUTION
Widely distributed in all tropical/subtropical seas. In the eastern Atlantic it ranges from Belgium down to South Africa (Southward, Reference Southward, Crothers and Hayward2008). It has been reported several times on the Azores coasts from 0 to 54 m depth (Southward, Reference Southward1998), and as the most common shallow subtidal barnacle in Madeira (Wirtz et al., Reference Wirtz, Araújo and Southward2006).
REMARKS
This species is sometimes recorded from intertidal situations, but is more common in the sublittoral down to 100 m depth and also it is well-known as a member of the fouling community on ships (Southward, Reference Southward1998, Reference Southward, Crothers and Hayward2008). Although it is now the most abundant Balanus on the Canary Islands, we have not found any documented record of this species for this archipelago, apart from the check-list by Haroun et al. (Reference Haroun, Herrera, Domínguez, Moro, Martín, Garrido and Izquierdo2003). In the Canaries, it settles on floating objects, on rocky bottoms covered by algae, and on the Diadema barren grounds, it is very common down to around 50 m depth. Therefore, our reference material, based on many samples collected from 0 to 23 m depth, should be considered as the first record for the Canaries. This species has the usual planktotrophic larva, and like C. stellatus, is evidently able to maintain an abundant population among the islands (Southward, Reference Southward1998).
Synonym: Balanus amphitrite amphitrite.
MATERIAL EXAMINED
Ten specimens, rc 7.9–16.7 mm, Gran Canaria, Tenerife, and La Palma, 0–2 m, in mixed colony (fouling) together with three other balanids, on a ship hull, and on dikes (ICCM-351, 379, 394).
DISTRIBUTION
It is a very common fouling species, now widely distributed intertidally and sublittorally in all tropical seas. In the eastern Atlantic it ranges from Britain and The Netherlands down to southern Portugal, and from many Mediterranean locations (Southward, Reference Southward, Crothers and Hayward2008).
REMARKS
Several colonies of scattered individuals of different size-classes observed at Charca de Maspalomas, south of Gran Canaria, 0.5–2 m, which is a coastal brackish pool receiving freshwater.
Synonym: Balanus perforatus.
MATERIAL EXAMINED
One specimen, rc 18.1 mm, port of Santa Cruz de Tenerife, 0–1 m, on a jetty from a yacht marina (ICCM-380). This is the first record of the species for the Canary Islands.
DISTRIBUTION
An eastern Atlantic warm water species, known from Britain and The Netherlands down to the Spanish Atlantic coast into the Mediterranean and southward down to Luanda. The species has not yet reached Ireland or Scotland (Southward, Reference Southward, Crothers and Hayward2008).
REMARKS
Its distribution pattern seems to be similar to that of C. montagui, and the short distance between the Canaries and the African mainland may have permitted its penetration into the islands. It is normally intertidal and when abundant occupies the lower half of the intertidal zone, but sometimes extends into the sublittoral as deep as 40 m (Herbert et al., Reference Herbert, Hawkins, Sheader and Southward2003). Despite its capacity to occur sublittorally and settle on floating objects, this species is absent on both Madeira (Wirtz et al., Reference Wirtz, Araújo and Southward2006) and the Azores (Southward, Reference Southward1998).
MATERIAL EXAMINED
About sixty specimens, rc 6.9–41.0 mm, Fuerteventura, Gran Canaria, La Gomera, Tenerife, El Hierro and La Palma, 0–22 m, on rocks, dead shells, concrete modules, jetties, floating buoys, aquaculture sea cages, bottom traps, and as a fouling species together with other balanids (ICCM-327, 342, 350, 354, 358, 364, 371–3, 375–6, 378, 383, 385, 390). Barnacle samples taken from an archaeological site (‘conchero’) were sent by the first author to A.J.S., who identified them as M. azoricus (ICCM-387). This dumping place for shells (mainly from Patella) and bones, probably dated from over 800 years ago, is located at Jinámar, Gran Canaria.
DISTRIBUTION
This is an eastern warm-temperate and tropical Atlantic species (Southward, Reference Southward, Crothers and Hayward2008). Apart from the Canaries, it is now only known on the Azores, Madeira (Wirtz et al., Reference Wirtz, Araújo and Southward2006; Southward, Reference Southward, Crothers and Hayward2008) and St Helena, inhabiting from 0 to 40 m depth (Southward, Reference Southward1998).
REMARKS
Both on the Azores and Madeira, it forms bands just below low tide on exposed rocky shores (Wirtz et al., Reference Wirtz, Araújo and Southward2006). In the Canaries, it is a common species more abundant in the eastern islands, Lanzarote and Fuerteventura (Franquet & Brito, Reference Franquet and Brito1995, as M. tintinabulum [sic]), which are closer to the African coasts, living from the mid-water mark to 5 m depth on rocky coasts in highly wave-exposed areas. It usually occurs in aggregates of several barnacles, up to 70 mm in height.
MATERIAL EXAMINED
Twenty-five specimens, rc 5.5–32.2 mm, Lanzarote, Gran Canaria, Tenerife, and La Palma, 0–22 m, on rocks, concrete modules, dead shells, bottom traps, as well as on a L. anatifera attached to a floating buoy, and as a fouling species together with other balanids (ICCM-325, 341, 346, 353, 356, 370, 386, 393).
DISTRIBUTION
A fouling species occurring in the eastern Atlantic, now known from the French Bay of Biscay down to the western Mediterranean, and southward down to Angola (Southward, Reference Southward, Crothers and Hayward2008). Reported from the Canaries (Pérez & Moreno, Reference Pérez and Moreno1991), Madeira (Wirtz et al., Reference Wirtz, Araújo and Southward2006; Southward, Reference Southward, Crothers and Hayward2008), but absent in the Azores (Southward, Reference Southward1998).
REMARKS
In the Canary Islands, the species has been reported to inhabit closely associated with coralliferous bottoms between 10 and 100 m of depth, frequently attached to dead branches of the tree coral Dendrophyllia ramea (Pérez & Moreno, Reference Pérez and Moreno1991). Previously reported at 25–250 m depth, our findings enlarge its bathymetric range to surface level.
DISCUSSION
The barnacles listed in the present paper constitute the first scientific account on the thoracic Cirripedia of the Canary Islands, including the intertidal, shallow-water and oceanic species on animals (commensal or epizoic barnacles) and other floating objects from surface to about 150 m depth. Seventeen species, belonging to 7 families, 4 suborders and 2 orders are listed in this annotated catalogue, and seven of them recorded for the first time for the Canaries herein: Lepas hilli, Conchoderma virgatum, Xenobalanus globicipitis, Chthamalus sp., Acasta cyathus, Balanus trigonus and Perforatus perforatus. However, the Canaries have not yet been fully surveyed for this ecologically important group. The Canarian deep-sea forms should be catalogued in the near future, in order to have a complete check-list of the Cirripedia for the area and to better understand their ecological role and the mechanisms of colonization.
The shallow-water/oceanic barnacle species known to occur in the Canaries, Madeira and the Azores are systematically listed in Table 1, with information on depth- ranges, first citations and recent references, and geographical distribution pattern.
Adult Lepas hilli and Lepas pectinata are pelagic forms; moreover, L. hilli is occasionally transported on ships' hulls and on sea turtles (this paper). Balanus trigonus can occur to considerable depths (100 m depth), so this species might not need so many emerged island stepping stones to spread as do the purely intertidal form on the Canary coasts. Balanus trigonus appears to be most abundant on Diadema barren grounds, probably due to the intensity of grazing activity of the herbivorous Diadema aff. antillarum.
There is some confusion over the species of barnacles occurring on turtles (Southward, Reference Southward, Crothers and Hayward2008). Chelonibia caretta (Spengler, 1790) was reported for Madeira and the Azores (Southward, Reference Southward1998; Wirtz et al., Reference Wirtz, Araújo and Southward2006), meanwhile Chelonibia testudinaria was cited for the Canaries (Pérez & Moreno Reference Pérez and Moreno1991; this paper). This fact may reflect a latitudinal substitution of this epizoic barnacle.
The species of Megabalanus can also be carried by ships, so caution is needed when they are classed as endemics; the reported occurrence of Megabalanus azoricus at St Helena and from ships suggests a wider distribution (Southward, Reference Southward1998, Reference Southward, Crothers and Hayward2008). In fact, Megabalanus is a group of related species that had evolved in different parts of the world, but have since been distributed on ships, even before Darwin (Reference Darwin1854) looked at them, so their geographical entity has been confused. Megabalanus azoricus is the species that occurs along the South European/North African coasts including the island archipelagos, and is also found on ships in the region—especially research ships that spend lots of time travelling slowly. Megabalanus azoricus is different from the Caribbean species, Megabalanus antillensis Newman & Ross, 1976, while true Megabalanus tintinnabulum (Linnaeus, 1758) is a Far Eastern species. In the Canaries, the species occurring is certainly M. azoricus, in addition to Megabalanus tulipiformis, which is quite different morphologically and occurs as far north as the southern Bay of Biscay (observations by A.J.S.).
Since the 1980s, Pollicipes pollicipes (‘percebe’ or ‘patacabra’) and M. azoricus (‘claca’) are much appreciated as food and commercially collected by hand from the coasts of Lanzarote and Fuerteventura (Franquet & Brito, Reference Franquet and Brito1995). No information on this activity is currently available, but we suspect that these resources are over-exploited in these islands of the Canary archipelago due to an excessive uncontrolled harvesting.
A particular problem is: how did the warm-water European barnacles, Chthamalus group and Perforatus perforatus, reach the islands? Because the occurrence of other Chthamalus species are based on mistaken identifications (Southward, Reference Southward, Crothers and Hayward2008), only Chthamalus stellatus is found on the Azores and Madeira. However, in the Canaries there is also a small population of C. montagui (far less abundant than C. stellatus) on the east coast of Lanzarote, one of the nearest islands to the African mainland (see Crisp et al., Reference Crisp, Southward and Southward1981). Sousa et al. (Reference Sousa, Cruz and Castro2000) studied the patterns of distribution and abundance of these co-occurring Chthamalus barnacles on the south-west coast of Portugal. Chthamalus montagui was significantly more abundant than C. stellatus in both degrees of wave action (on headlands and not) and at all tidal levels (low, mid and upper). Chthamalus montagui was more abundant at mid tide-level, while C. stellatus was more abundant on headlands. Small-scale variability (between sites) of abundance of each species was detected, while differences on a larger scale (between shores) were not significant. O'Riordan et al. (Reference O'Riordan, Arenas, Arrontes, Castro, Cruz, Delany, Martínez, Fernández, Hawkins, McGrath, Myers, Oliveros, Pannacciulli, Power, Relini, Rico and Silva2004) examined the spatial variation in the recruitment (cyprids and metamorphs) of C. montagui and C. stellatus over five locations at Ireland, Spain, Portugal and Italy. They found significant differences among shores in each location. The recruitment period of both species varied with location, with recruitment beginning earlier further south. In general, recruitment of C. montagui and C. stellatus was recorded in 8 months in north-west Spain and north-east Italy, while only in 7 months in south-west Ireland. Recruitment of C. montagui occurred in 10 months in south-west Portugal, but no recruits of C. stellatus were found. In all locations there was at least one distinct peak of recruitment.
Herbert et al. (Reference Herbert, Southward, Sheader and Hawkins2007) re-surveyed the influence of recruitment and temperature on distribution of C. montagui and C. stellatus in the central English Channel from 1994 to 2004, a decade of exceptionally high sea temperatures, and found range extensions on both sides of the Channel compared to the 1950s and 1970s. Highest recruitment occurred during the warmest years. A high degree of similarity of annual recruitment within coastal cells was found, suggesting that local processes (hydrographic barriers and substratum) are also important. Herbert et al. (Reference Herbert, Southward, Clarke, Sheader and Hawkins2009) have recently proposed that reductions in larval supply of C. montagui on the south coast of England caused by complex regional hydrography and suboptimal habitat quality, not caused by any gradient in adult biological performance (reproduction, growth, survival), is most likely responsible for a steep gradient in recruitment as the border (geographical boundary) is approached, although possible limitations in larval performance cannot be totally discounted.
Within the context of this paper the point is that in Morocco and Western Sahara the dominant species is C. montagui, but its larvae hardly spread to the Canaries and when they do they obviously do not maintain an extensive population. It should be noted that cirripeds have a number of ‘bottlenecks’ in their ability to colonize new habitats. First, the majority of them are cross-fertilizing hermaphrodites, and individuals have to be fairly close together to breed. Thus, successful colonization by these species demands a dense initial settlement. A second bottleneck is the length of larval life. Exceptionally, a few species such as Chthamalus species can self-fertilize (Wirtz et al., Reference Wirtz, Araújo and Southward2006). Chthamalus stellatus has the usual pelagic larval phases, has a comparatively long planktonic life and is evidently able to maintain an abundant population among the islands of the Macaronesian group (Southward, Reference Southward1998). Species with full planktotrophic development through six naupliar stages may live from several days to a few weeks in the plankton, depending on temperature (Wirtz et al., Reference Wirtz, Araújo and Southward2006). Pannacciulli et al. (Reference Pannacciulli, Manetti and Maltagliati2009) have found that the among-samples genetic diversity in the Azorean archipelago suggested extensive connectivity in C. stellatus (see Tesseropora atlantica in Discussion for further information).
Most Chthamalus species do not settle on ships and are not fouling organisms but C. proteus can settle and grow on ships, so this is why it might be able to reach the Canary Islands from Brazil or the Caribbean (E.C. Southward, personal communication). If this is C. proteus it must be a recent introduction and worth investigating, and looking for it around yacht marinas.
Perforatus perforatus has failed to reach Ireland, and is certainly not found on the Azores (Southward, Reference Southward1998) or Madeira (Wirtz et al., Reference Wirtz, Araújo and Southward2006). Despite its capacity to occur sublittorally to 40 m depth and settle on floating objects, this species is absent on both oceanic archipelagos confirming that it is unable to cross sea barriers (Crisp & Southward, Reference Crisp and Southward1953). Its distribution pattern, quite similar to that C. montagui, and the short distance (100 km) between the Canaries and the African mainland may have permitted its penetration into these islands, as far as Tenerife in the central group within this archipelago, but only one specimen has been found.
Oxynaspis celata Darwin, Reference Darwin1851 (Lepadomorpha: Oxynaspidae) was originally recorded for the Madeira archipelago and is presently reported from there on bushes of the black coral Antipathella wollastoni (Gray, 1857), from 35 m downwards (Wirtz et al., Reference Wirtz, Araújo and Southward2006). However, no specimens have been found to date around the Canary Islands.
Megatrema anglicum (Sowerby, 1823) (synonyms: Pyrgoma anglicum and Boscia anglicum) (Balanomorpha: Pyrgomatidae) has been recorded for the Madeira archipelago (Darwin, Reference Darwin1854; Wirtz et al., Reference Wirtz, Araújo and Southward2006). Its vertical distribution extends from low water mark to 80 m, and it lives singly or with several others, spaced around the rim of a living solitary coral. It has been reported from Brittany, the Mediterranean, Madeira and the Cape Verde Islands (Southward, Reference Southward, Crothers and Hayward2008). However, apart from a non-documented citation of this species in the Canaries in the check-list by Haroun et al. (Reference Haroun, Herrera, Domínguez, Moro, Martín, Garrido and Izquierdo2003), no specimens have been found by us around the Canary Islands.
A particular problem is posed by the relict barnacle Tesseropora atlantica Newman & Ross, 1976 (Balanomorpha: Tetraclitidae) found so far only in Bermuda, the Azores (Southward, Reference Southward1998), St Paul's Rocks and recently in Madeira where living individuals have been recorded (Wirtz et al., Reference Wirtz, Araújo and Southward2006). According to Hawkins et al. (Reference Hawkins, Corte-Real, Pannacciulli, Weber and Bishop2000), the Mediterranean/Atlantic interface, which includes Macaronesia, has clearly generated considerable differentiation of populations leading to allopatric speciation, including the generation of some endemic species. Greater differentiation has occurred in limpets with their shorter length of larval life (Patella spp., 1–2 weeks) than in barnacles (Chthamalus spp., 3–6 weeks). The Azores (and possibly Madeira) is also a refuge for at least one Tethyan relict species (T. atlantica) which may also have endemic status (Hawkins et al., Reference Hawkins, Corte-Real, Pannacciulli, Weber and Bishop2000). It has never been found on the shores of the continents on the eastern side of the Atlantic (Wirtz et al., Reference Wirtz, Araújo and Southward2006). In Madeira, as in the Azores, it grows very low down in the intertidal zone, where it is wetted by waves, but where it is also sheltered from sunlight; typically it is on the undersides of boulders or in crevices (Wirtz et al., Reference Wirtz, Araújo and Southward2006; observations by A.J.S.). A final bottleneck in the spread of this species is that adults incubate their lecithotrophic larvae to the cypris stage before release, thus restricting larval dispersal to a few days or else requiring some unknown vector (Wirtz et al., Reference Wirtz, Araújo and Southward2006). How does it reach isolated islands? Within this context, Pannacciulli et al. (Reference Pannacciulli, Manetti and Maltagliati2009) compared the genetic structure of C. stellatus and T. atlantica in the Azores; the two barnacles differ as regards life cycle: the former conducting pelagic life for about 22 days, the latter for only 24 hours. Their results were consistent with expectations based on species life history and corroborate the importance of pelagic stages in determining the degree of genetic structuring in benthic marine invertebrates. These authors have found that the among-samples genetic diversity in the Azorean archipelago suggested isolation.
Despite the apparent absence of Oxynaspis celata, Megatrema anglicum and Tesseropora atlantica on the Canary Islands coasts, we cannot dismiss the possibility of finding them on this archipelago in view of their current geographical distribution and ecological requirements.
Thus, it seems that the majority of barnacle species apparently have difficulty reaching the Atlantic islands from the European or African mainland. It is necessary to postulate ‘rafting’ on floating objects, transport on larger animals (sea turtles, marine mammals, etc.), or the existence of island ‘stepping stones’ now vanished. There is also the possibility that remote dispersal by fouling on ships has taken place since maritime trade with the Atlantic islands began ~600 years ago (Southward, Reference Southward1998; Wirtz et al., Reference Wirtz, Araújo and Southward2006). Another point is that, if global warming continues, some tropical species might arrive and colonize on the Canary coast, in particular some chthamalid and balanid species coming from the eastern tropical Atlantic, for instance from the Cape Verde Islands.
ACKNOWLEDGEMENTS
This paper is in memory of Professor Dr Alan James Southward. His wife and lifelong science collaborator, Dr Eve C. Southward, encouraged us in the writing of this paper which has been revised by her. We would like to thank our colleagues Dr Santiago Hernández-León, Pascual Calabuig, Leopoldo Moro and Kilian Toledo for helping us in this investigation. Thanks are due to the personnel of the ICCM department of Biología Pesquera and Silvia Díaz (RMB La Palma) for skilful technical assistance. This research received no specific grant from any funding agency, commercial or not-for-profit sectors.
