Les processus d'invasions biologiques en milieu côtier marin : le cas de l'algue brune Undaria pinnatifida, cultivée et introduite à l'échelle mondiale

Abstract : Biological invasions are a major threat for coastal marine biodiversity. These processes have been considered as a latent ecological and evolutionary paradox: how a species may settle and even replace native species in an environment where it did not evolved? Facing this paradox, many hypotheses have been raised; among them the role played by human activities by increasing the propagule pressure as well as ecosystems’ perturbations. In this scientific context, this PhD work aimed at investigating the role played by human activities on the introduction success of one invasive species that spread rapidly (less than 30 years) all over the world, the Japanese kelp Undaria pinnatifida, a cultivated macro-alga in its native and introduced distribution range. Firstly, the sequence polymorphism of two mitochondrial spacers was investigated in 27 populations (524 individuals) sampled over the present-day distribution range of U. pinnatifida. Contrasted processes were evidenced in the different regions where the species has been introduced: in Australasia, recurrent introductions (likely due to maritime exchanges) from genetically differentiated sources were shown whereas in Europe, the primary introduction was likely to be due to intentional or accidental introduction in relation to aquaculture from sources genetically close. Based on 10 microsatellite loci, 26 European populations were then analyzed. The output of this analysis suggested that various dispersal vectors linked to human activities (like ship or cultures) enhanced the secondary expansion at the regional level within Europe. Such a process is explained by the occurrence of U. pinnatifida in various kind of habitats (marinas, rocky shores, cultures): A two-year study of the microsatellite genetic diversity within a bay of North Brittany showed that populations inhabiting habitats influenced by human activities (e.g. marinas) can act as a reservoir of migrants for some of the populations located in the wild although others may be self-sustained. The role played by marinas is even more important when considering the results of a four-years demographic survey showing the efficiency (in relation to the life-history traits) of the colonisation by U. pinnatifida on recruitment panels within two marinas. Altogether, the above mentioned results underline the major role played by trade activities and man-made habitats on both primary and secondary introductions, especially for those species that are sustainably interacting with human activities like aquaculture. Here, the limited natural ability of U. pinnatifida to disperse is balanced by its rapid development in habitats where dispersal vectors related to human activities promote its regional expansion. A long-term survey might help to examine the possibility for evolution of local adaptation in the different habitats colonized by this alga.
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Marie Voisin. Les processus d'invasions biologiques en milieu côtier marin : le cas de l'algue brune Undaria pinnatifida, cultivée et introduite à l'échelle mondiale. Ecosystèmes. Paris 6, 2007. Français. ⟨tel-01118270⟩

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