• numerical simulations
• larval dispersal
• free-fall speed
• connectivity
• benthic invertebrates
• rocky habitat

Connectivity has an important role for populations persistence in fragmented areas as it enables recolonization after local disturbance and compensate low local larval retention rates in sink populations. For most marine benthic invertebrates, which exhibit a complex bentho-pelagic life cycle, connectivity arises from dispersal during the pelagic larval phase.
In the seascape of the Gulf of Lion, rocky habitat is fragmented and separated by large sandy areas. Objective of this study is to quantify the potential connectivity among populations of sessile or sedentary benthic invertebrates inhabiting rocky habitat of the Gulf of Lion based on numerical simulations of larval dispersal, which integrate numerical simulations of ocean currents and larval traits affecting larval dispersal. To achieve this objective, the work is organized around three axis, forming the 3 chapters of the thesis.
In the first chapter, a review based on literature has been carried out collecting data on the traits affecting larval dispersal, mainly period and duration of spawning, Pelagic Larval Duration (PLD), larval size and larval motility behavior. The review includes all species building up the biodiversity of 4 hard-bottom assemblages of the Gulf of Lion. Each assemblage is designated according to the gorgonian (Octocorallia, Alcyonacea) which dominated the assemblage in terms of biomass: Paramuricea clavata (Plexauridae), Corallium rubrum (Coralliidae), Eunicella cavolinii (Gorgoniidae) and Eunicella singularis (Gorgoniidae). Gorgonians are of particular interest as they are among the main structural species of the Mediterranean hard-bottom communities due to their three-dimensional structures that create an habitat for small epifauna and refuge for several vagile species, determining the increase of the biodiversity of hard substrates. The inventory of existing knowledge clearly evidenced a lack of information about larval traits affecting larval dispersal (information available on less than 25 % of species) especially for the motility behavior.
The second chapter presents new data about experimental quantification of the free-fall speed of Eunicella singularis larvae, in order to increase the information on larval traits of a benthic species abundant in the rocky habitat of the Gulf of Lion. The free-fall speed was quantified using a particle tracking routine applied to video recordings of the passive motility behavior of Eunicella singularis larvae.
In the third chapter larval dispersal simulations in the Gulf of Lion were performed with a Lagrangian larva tracking model, integrating ocean currents and some larval traits, such as spawning areas, spawning period and Pelagic Larval Duration (PLD), according to the review made in chapter 1 for benthic invertebrate inhabiting rocky habitat (larval dispersal simulations are summarized in the form of connectivity matrices).
This thesis was carried out at the Laboratoire d'Ecogéochimie des Environnements Benthiques (LECOB, UMR 8222), at the Observatoire Océanologique de Banyuls sur Mer, which is a joint laboratory of the Université Pierre et Marie Curie (UPMC) and the Centre National de la Recherche Scientifique (CNRS).