MEPS 276:147-159 (2004)  -  doi:10.3354/meps276147

Invasion of the eastern Bay of Biscay by the nassariid gastropod Cyclope neritea: origin and effects on resident fauna

Guy Bachelet1,*, Benoît Simon-Bouhet2,3, Céline Desclaux1, Pascale Garcia-Meunier2, Guillaume Mairesse1, Xavier de Montaudouin1, Hélène Raigné1, Karine Randriambao1, Pierre-Guy Sauriau4, Frédérique Viard3

1Laboratoire d¹Océanographie Biologique, UMR 5805 CNRS-Université Bordeaux 1, Station Marine d¹Arcachon, 2 rue du Professeur Jolyet, 33120 Arcachon, France
2Laboratoire de Biologie et Environnement Marins, EA 3168, Université de La Rochelle, 17000 La Rochelle, France
3Evolution et Génétique des Populations Marines, UMR 7127 CNRS, Station Biologique de Roscoff, BP 74, 29682 Roscoff cedex, France
4Centre de Recherche sur les Ecosystèmes Marins et Aquacoles, UMR 10 CNRS-IFREMER, Place du Séminaire, BP 5, 17137 L¹Houmeau, France

Abstract: The distribution area of the nassariid gastropod Cyclope neritea (L.) includes the Mediterranean and the Black Sea, as well as the Atlantic coasts of the southern Iberian Peninsula. The species has spread north to the eastern Bay of Biscay (Arcachon Bay in 1976, Marennes-Oléron area and Morbihan Gulf in 1983-84). This spread might be explained either by (1) a natural spread favoured by environmental changes (e.g. an increase of temperature) or (2) a sudden range expansion due to the introduction of individuals from distant native populations. Molecular genetic analyses based on mitochondrial markers suggest that the present C. neritea population in Arcachon Bay has been introduced, probably unintentionally with oyster transfers, from several source populations, genetically similar to the populations analysed in this study, i.e. those in the western Mediterranean and in south Portugal. Within its new distribution area, C. neritea could potentially compete with the autochthonous nassariid Nassarius reticulatus, both species being scavengers. Although C. neritea tends to occur mainly in relatively clean sands in the intertidal and N. reticulatus in subtidal, organic rich sediments, the habitats of both species partially overlap. Laboratory experiments showed that in still water conditions C. neritea was more active and reached carrion faster than N. reticulatus, thereby having a competitive advantage over the latter; flow conditions ( ~1 cm s-1) appeared to stimulate the activity of N. reticulatus. Analysis of parasite load in both species in Arcachon Bay indicated that N. reticulatus was more heavily parasitized by digenean trematodes than C. neritea. This suggests that the spread and population dynamics of C. neritea along the French Atlantic coast has been favoured by the lack of parasites. Altogether, recurrent introduction, competitive ability and lack of heavy parasitic load might explain the successful settlement of C. neritea along the French Atlantic coast.

KEY WORDS: Introduced species · Scavenging gastropods · Population genetics · Interspecific competition · Behaviour · Parasites

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