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Le succès de recrutement de la moule bleue : influence de la qualité de la ressource trophique

Abstract : The rate of settlement-metamorphosis is one of the determinant factors for the recruitment success, and thus the populations' renewal, in benthic marine invertebrates with bentho-pelagic life-cycle. Related to the abundance and behavior of peri-metamorphic stages (competent larvae and post-larvae), the settlement rate is regulated by the interaction of multiple endo- and exogenous factors. Pre-required for the vital functioning of heterotrophic organisms, the trophic resource is an important exogenous biotic factor as it affects their physiological conditions. Its influence on recruitment is often considered in a quantitative point of view whereas laboratory researches certify the importance of its lipid quality. In such context, the main objective of the present study is to evaluate the influence of the trophic resource quality on the recruitment success, using the blue mussel (Mytilus edulis, L 1758) as biological model. The research concentrated on the potential food resources available for the peri-metamorphic stages, such as the plankton and the biofilm. A particular emphasis is given to polyunsaturated (PUFA) and essential fatty acids (EFA), which are largely recognized to be indispensable for aquatic organisms. Moreover, studies dealing with recruitment show a bentho-pelagic decoupling between larvae and recruits, an important spatio-temporal variability of the settlement, and settlement peak synchronization. Even if larval availability and behavior are often incriminated factors, origins of such phenomenon still remain uncertain. Thus, the present study proposes to provide additional response elements by producing a fine analysis of the spatio-temporal variability during the larval ontogeny. Three principal research axes constitute the project where we define the settlement as the process by which individuals associate to the substrate, and the recruitment as the number of individuals present at a time t of the benthic life: i) Considering the Cushing " match/mismatch " theory, we hypothesize that EFA concentration in the food influence the success of both settlement and recruitment. We simultaneously monitored the larval development and the trophic conditions during two successive reproductive seasons (2007 and 2008); ii) Considering biofilm as potential trophic resource, we hypothesize that the settlement rate increases with the biofilm age and its EFA content. We conditioned and performed a fine characterization of biofilms in order to test their influence on mussels' settlement success; iii) Considering the important role of behavior and physiological conditions in peri-metamorphic stages, we hypothesized an important microscale spatial variability, a bentho-pelagic decoupling, and a physiological advantage during the settlement peak. We monitored the larval development in several sites, and also the lipid quality of post-larvae and of their trophic resources. Our results highlight the predominant control of phytoplanktonic communities on the blue mussel recruitment success via two innovative processes: i) the match/mismatch with the planktonic lipid quality, and ii) the trophic settlement trigger (TST). Nutritional role of PUFA/EFA seems to be important for the recruitment of the year, but their concentration in benthic and pelagic compartments seems not to insofar as affect behavior and physiology of young mussels during the season. The latest seems to strongly respond to variations in autotrophic picoplankton (picoeukaryotes, < 2 μm) abundance within both compartments. Finally, our results show a bentho-pelagic coupling between larvae and recruits, and suggest for the first time that decoupling depends on the two typical behavioral traits of bivalves: the metamorphosis delay and the bysso-pelagic drifting. This research provides new lines of thinking about the benthic invertebrates ecology and highlights the need to consider planktonic compartment, and behavior during the larval and post-larval ontogeny when working on the population dynamics in the field. A special emphasis should be given to the trophic resources lipid quality and taxonomical composition, and the separation of the different developmental stages appears necessary to understand populations dynamic. The notion of TST constitute the major point of the study as it would rely on a cue independent from the prospected habitat that would synchronize the settlement behavior, whatever substratum quality and/or individual historic life.
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Submitted on : Friday, August 31, 2012 - 5:24:18 PM
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  • HAL Id : tel-00726985, version 1


Nicolas Toupoint. Le succès de recrutement de la moule bleue : influence de la qualité de la ressource trophique. Ecologie, Environnement. Université du Québec à Rimouski, 2012. Français. ⟨tel-00726985⟩



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