title: Do settlement dynamics influence competitive interactions between an alien tunicate and its native congener?
abstract: Variation in density of early stages, that is, larvae and juveniles, is a major determinant of the distribution and abundance of the adult population of most marine invertebrates. These early stages thus play a key role in competitive interactions, and, more specifically, in invasion dynamics when biologically similar native and non-native species (NNS) come into contact in the same habitat. We examined the settlement dynamics and settlement rate of two important members of the fouling community that are common on human-made infrastructures around the world:Ciona robusta(formerly known asCiona intestinalistype A) andC. intestinalis(formerly known asC. intestinalistype B). In the western English Channel, the two species live in close syntopy following the recent introduction ofC. robustain the native European range ofC. intestinalis. Using settlement panels replaced monthly over 2 years in four marinas (including one studied over 4 years) and species-diagnostic molecular markers to distinguish between juveniles of both species (N= 1,650), we documented similar settlement dynamics of both species, with two settlement periods within a calendar year. With one exception, settlement times were highly similar in the congeners. Although the NNS showed lower settlement density than that of the native congener, its juvenile recruitment was high during the second settlement period that occurs after the warm season, a pattern also observed in adult populations. Altogether, our results suggest that species' settlement dynamics do not lead to the dominance of one species over the other through space monopolization. In addition, we showed that changes over time are more pronounced in the NNS than in the native species. This is possibly due to a higher sensitivity of the NNS to changes of environmental factors such as temperature and salinity. Environmental changes may thus eventually modify the strength of competitive interactions between the two species as well as species dominance.
authors.affiliation: Sorbonne Universités UPMC Univ Paris 6 Station Biologique de Roscoff 29680 Roscoff France; CNRS UMR 7144 Adaptation et Diversité en Milieu Marin Equipe DIVCO Station Biologique de Roscoff 29680 Roscoff France.
authors.forename: Sarah
authors.initials: S
authors.lastname: Bouchemousse
authors.affiliation: Sorbonne Universités UPMC Univ Paris 6 Station Biologique de Roscoff 29680 Roscoff France; CNRS FR2424 Station Biologique de Roscoff 29680 Roscoff France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Lévêque
authors.affiliation: Sorbonne Universités UPMC Univ Paris 6 Station Biologique de Roscoff 29680 Roscoff France; CNRS UMR 7144 Adaptation et Diversité en Milieu Marin Equipe DIVCO Station Biologique de Roscoff 29680 Roscoff France.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Viard
keywords: Ciona spp.; congeneric species; long‐term coexistence; marine invaders; settlement