How does the connectivity between populations mediate range limits of marine invertebrates? A case study of larval dispersal between the Bay of Biscay and the English Channel (North-East Atlantic)

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Ayata, Sakina-Dorothée | Lazure, Pascal | Thiébaut, Éric

Edité par CCSD ; PERGAMON-ELSEVIER SCIENCE LTD ; Elsevier -

International audience. For many marine species, larval dispersal plays a crucial role in population persistence, re-colonization of disturbed areas, and distribution of species range limits through the control of population connectivity. Along the French Atlantic coast (NE Atlantic), a biogeographical transition zone has been reported between temperate and cold-temperate marine faunal assemblages. Hydrodynamics in this area are highly complex and variable including numerous mesoscale features (e.g. river plumes, fronts, upwellings, low salinity lenses), which could constrain larval transport and connectivity. In this context, the aim of this study was to assess how hydrodynamic conditions and biological traits influence larval transport and contribute to population connectivity along the biogeographical transition zone between the Bay of Biscay and the English Channel. A coupled bio-physical individual-based model was used at a regional scale to track larval trajectories under realistic hydroclimatic conditions (tides, river run-offs, and meteorological conditions) and for some common life-history traits. Larval particles were released monthly from February to August for the years 2001 to 2005, from 16 spawning populations corresponding to the main bays and estuaries of the study area. Two planktonic larval durations (2 vs. 4 weeks) and three vertical distributions (no swimming behaviour, diel vertical migration, and ontogenic vertical migration) were considered. Dispersal kernels were described by 17 parameters and analysed in a multivariate approach to calculate connectivity matrices and indices. The main factors responsible for the variability of the dispersal kernels were the spawning month in relation to the seasonal variations in river run-offs and wind conditions, the planktonic larval duration, the spawning population location, and the larval behaviour. No significant inter-annual variability was observed. Self-retention rates were high and larval exchanges occurred mainly within the main hydrodynamical areas: the western English Channel, the Southern Brittany, and the Central Bay of Biscay. Connectivity between the English Channel and the Bay of Biscay populations was low and occurred only under particular hydroclimatic conditions (i.e. high river run-off and strong SW winds) and for some biological traits (i.e. long planktonic larval duration). (C) 2010 Elsevier Ltd. All rights reserved.

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