Four Sargassaceae genus presenting high biomass in Brittany and\or in the South Pacific were chosen as models of this study. The aims of this works were i) to understand the chemical ecology of Sargassaceae in temperate and tropical environment, ii) to characterize specific chemomarkers from certain species and iii) to identify potential bioactive molecules. Then, a pluridisciplinary work was carry out with the study of the chemical ecology of Sargassaceae, in Brittany on one hand, with the study of the spatio-temporal variations of certain defense compounds of Sargassum muticum, Bifurcaria bifurcata and Cystoseira baccata associated with an ecological survey of these species and in the South Pacific on the other hand, with the study of these same defense compounds within Turbinaria sp. and Sargassum sp from various sites. At the same time, two chemotaxonomical studies were led. On the Turbinaria genera to identify one or several chemomarker(s) allowing discriminating T. ornata and T. conoides. And on the other hand, on B. bifurcata to understand the geographical distribution of the existing chemical types within this species. Then, to answer the third objective of this work, three biological activities were looked for first and foremost within the studied species: cytotoxicity, anti-inflammatory activity and neurotoxicity. The results allowed i) to highlight the impact of the environmental conditions on the biological and ecological variables studied to these species in temperate and tropical environments; ii) to identify the acid turbinaric as a chemomarker of T. conoides and to highlight the existence of ecotypes from B. bifurcata ; iii) to report the anti-phospholipase A2 activity of fatty acids stemming from tropical seaweeds and the antiradical and antioxidant activities of eleganolone isolated from B. bifurcata .
