Aquatic Invasions (2010) Volume 5, Supplement 1: S21-S25 This is an Open Access article; doi: 10.3391/ai.2010.5.S1.006 Open Access © 2010 The Author(s). Journal compilation © 2010 REABIC Aquatic Invasions Records The slipper limpet Crepidula fornicata Linnaeus, 1758 becomes established in Ireland Gavin McNeill1, Julia Nunn2* and Dan Minchin3 1Agri-Food and Biosciences Institute (AFBI), Fisheries and Aquatic Ecosystems Branch, AFESD, 18a, Newforge Lane, Belfast, BT9 5PX Northern Ireland 2National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, Co. Down, Ireland 3Marine Organism Investigations, Caragh, Marina Village, Ballina, Killaloe, Co Clare, Ireland E-mail: [email protected] (GM), [email protected] (JN), [email protected] (DM) * Corresponding author Received: 10 March 2010 / Accepted: 14 May 2010 / Published online: 28 May 2010 Abstract Chains and solitary individuals of the slipper limpet Crepidula fornicata were found, some with egg capsules, at several localities within Belfast Lough on the north-east coast of Ireland during 2009. The species is widely dispersed, being found on the lower shore to depths of 7 m attached to scallops, mussels and stones and so is considered to be established. Shell winter growth checks indicated a possible arrival in or before 2004. While there have been previous records of this invasive species in Ireland, this is the only known established population. Key words: slipper limpet, Crepidula, Belfast Lough, Ireland, alien, exotic Introduction numbers sufficient to alter habitat, change communities, and in some localities form the The snail, the slipper limpet Crepidula fornicata predominant composition of biomass. Over a Linnaeus, 1758, is native to the east coast of million tonnes of this species now exist in North America. It probably became established European waters (Quiniou and Blanchard 1987; in Europe in the late 1870s following imports of Sauriau et al. 1989). Its appearance in Ireland American oysters Crassostrea virginica (Gmelin, was predicted with imports of half-grown oysters 1791) to the south-east coast of Britain but was in the 1920s (Spicer 1923). While it’s occurrence first recognised in 1893 (Crouch 1895). From from Belfast Lough is referred to by Fretter and there it has spread to most of the Atlantic coast Graham (1981) and subsequently by Hayward of Europe ranging from Norway to Spain and Ryland (1995), the record was not (Richard et al. 2006), with some small recognised by Smith (1976). We know of no populations in the Mediterranean Sea (Parenzen confirmed records of this species in this lough 1939). It is well established in some inlets of the until those reported here. An erroneous record Bristol Channel (Seaward 1982). It has in recent for Belfast Lough from the late 1990s was decades spread northwards in Britain with relaid published on the NBN Gateway consignments of blue mussels Mytilus edulis http://data.nbn.org.uk before being corrected. We Linnaeus, 1758 to the Menai Strait in the Irish describe the relative abundance and distribution Sea in 2006, where there was an attempt to of the species in Belfast Lough. remove it (Countryside Council for Wales 2009). This species mainly occurs from low water to depths of ~20m (Blanchard 1997). Individuals Material and methods start out as wandering males and subsequently settle and become females. Additional males Collections were made by dredging (two foot cling to such females to form chains which may scallop dredge) in March 2009 during an be composed of up to a dozen individuals investigation by the Agri-Food and Biosciences (Fretter and Graham 1981). They can form vast Institute of all licensed aquaculture beds in S21 G. McNeill et al. Belfast Lough. Two specimens of Crepidula fornicata were identified from this survey. This find prompted a series of shore line surveys undertaken by walking stretches of the intertidal close to low water in Belfast Lough within one hour before and up to one hour after low water during March and May 2009, and April 2010. Intertidal visits were also made to a few sites in Carlingford Lough (May 2009) and Larne Lough (July 2009). A further eighteen stations were dredged over mussel aquaculture beds in Belfast Lough in April 2009. Figure 1. Low water occurrence of three Crepidula fornicata Specimens obtained were measured for specimens from Jordanstown, Belfast Lough (photo credit: longest straight (antero-posterior) length and JN). distance between observed distinct winter growth check marks, using callipers to the nearest tenth of a millimetre. The first 1mm of each shell from One living specimen attached to a stone, and a the apex was not included (pre-settlement recently vacated shell, were collected on the growth; Fretter and Graham 1981). Disturbance south shore of Belfast Lough at Craigavad and growth marks on the largest individuals were Seapark respectively in May 2009. used to back-calculate an estimate of earlier Two specimens in a chain attached to a large years of its likely existence in Belfast Lough. mature Mytilus edulis were found offshore in Belfast Lough in August 2009 (4m). In February 2009, there was a report from The Results Netherlands of C. fornicata in mussels origi- nating from Carlingford Lough. Yet despite two Two live specimens of Crepidula fornicata were dredge surveys carried out in May 2009 by found attached to live scallops Pecten maximus NIEA, in collaboration with the Marine Institute, (Linnaeus, 1758) collected from 4m on 4th Loughs Agency and the mussel aquaculture March 2009 in Belfast Lough (Annex 1). A industry and a second undertaken by AFBI, there further 18 living and 3 fresh dead shells were was no indication of its presence, suggesting a collected from the shore at Jordanstown on the case of sample contamination. No specimens north side of Belfast Lough also in March 2009. were found during searches on the north shore of These were attached to stones and shell (Figure Carlingford Lough (May 2009) or at selected 1). Two contained egg capsules (35+). A single shores in Larne Lough (July 2009). specimen was collected at Fisherman’s Quay In all sixty living C. fornicata, with chains of shore, north of Jordanstown (March 2009), and a up to three individuals, as well as six recently further 11 living attached to stones and shell and vacated shells were collected from Belfast Lough two recently vacated shells from the same area. in 2009 and early 2010 (Figure 2; Annex 1). Two specimens were found with egg capsules Four females with broods were observed. present under the shell (20+). A search at nearby The live specimens ranged in shell length Kilroot Power Station (north of this area) did not from 7.8 to 43.0 mm. Nineteen of these reveal any specimens. A further 15 specimens specimens (all collected in March 2009) were were observed during a revisit to Fisherman’s measured for winter (disturbance) growth Quay in April 2010. checks. There appeared to be up to five year Nine specimens of C. fornicata were collected classes, with four distinct disturbance rings, from three stations during a dredge survey of the indicating that the largest specimens measured mussel beds in Belfast Lough in April 2009 at (all from the intertidal) may have settled in early depths from 2-6m. Three of these were attached 2004 or late 2003. Growth for all classes to living Mytilus edulis; the remainder were averaged 9.7 and 8.6 mm for first and second attached to vacant shells and stones. This is an years respectively since settlement, which is area that is restocked with mussels from consistent with expected growth rates (Fretter elsewhere. and Graham 1981). S22 Establishment of Crepidula fornicata in Ireland Figure 2. Sites visited in Belfast Lough during the present study, showing records of Crepidula fornicata (see Annex 1 for localities). Discussion male specimens attached to oyster shells, were imported from France (Minchin et al. 1995). We show the occurrence of Crepidula fornicata Males were also found on such imports to from Belfast Lough. No shell or specimens were Dungarvan and Carlingford bays on the southern recovered in surveys in the nearby Carlingford and eastern coasts of Ireland respectively. The and Larne Loughs, where the Pacific oyster oysters were held in meshed bags on trestles. Crassostrea gigas is cultivated on trestles. Some months later the oysters were re-examined Although only a small number of individuals and no further specimens were found. It is likely were recovered in this study, their wide these had become crushed by the turning of distribution from the lower shore to depths of 6m oysters within the bags. and the presence of a brood in four individuals Other records of C. fornicata exist but no indicate that the species is established. living material is known to have survived Its first appearance in Ireland was with following these records. Some of the records pre- imports of half-grown American oysters (Sykes date the cold winter of 1962-63 (Crisp 1964), 1905) arriving in Ballinakill Bay on the west during which two populations reported initially coast of Ireland in wooden oyster barrels by Arnold (1960) from Kilmakillogue, Kenmare originally imported from Long Island Sound to Bay on the south-west coast of Ireland and from Britain. These were removed before the oysters Clew Bay on the west coast of Ireland (Minchin were laid on the shore. It is possible that living et al. 1995) may have died out. Both of these specimens may, in the early 1920s, have been sites were carefully examined in the 1970s and introduced by the same means to Carlingford the 1980s respectively and no shell material was Lough because six worn shells (of 18-38 mm found. There are other records of shells from the shell length) appear in the collections of the Irish coast.