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Exotic species are a growing global ecological threat; however, their overall effects are insufficiently understood. While some exotic species are implicated in many species extinctions, others can provide benefits to the recipient communities. Here, we performed a meta-analysis to quantify and synthesize the ecological effects of 76 exotic marine species (about 6% of the listed exotics) on ten variables in marine communities. These species caused an overall significant, but modest in magnitude (as indicated by a mean effect size of g < 0.2), decrease in ecological variables. Marine primary producers and predators were the most disruptive trophic groups of the exotic species. Approximately 10% (that is, 2 out of 19) of the exotic species assessed in at least three independent studies had significant impacts on native species. Separating the innocuous from the disruptive exotic species provides a basis for triage efforts to control the marine exotic species that have the most impact, thereby helping to meet Aichi Biodiversity Target 9 of the Convention on Biological Diversity., This research was supported by King Abdullah University of Science and Technology (KAUST) through baseline funding to C.M.D., by Horizon 2020 Framework Programme (EU Framework Programme for Research and Innovation H2020) (grant no. 659246) to S.B., by the Ministry of Economy and Competitiveness, Agencia Estatal de Investigación (Spanish Agencia Estatal de Investigación) (grant no. FJCI – 2016 – 30728) to S.B., by the Ministry of Economy and Competitiveness, Agencia Estatal de Investigación (Spanish Agencia Estatal de Investigación) (grant no. CGL 2015 – 71809 – P) to N.M., J.S.-G. and S.B., and by the ARC Centre of Excellence for Coral Reef Studies (grant no. CE 140100020) to J.M.P.

Caulerpa cylindracea (Sonder), among the most successful marine bio-invaders on a global scale, poses severe threats to biodiversity. However, the effects of this seaweed on the quantity and the biochemical composition of sedimentary organic matter are still poorly known. Since the whole set of sedimentary features affects the availability of substrates for benthic microbial communities, we: i) investigated the biochemical composition of sediments colonized and not-colonized by C. cylindracea, and ii) compared the metabolic patterns of the microbial communities associated with C. cylindracea and in the sediments colonized and not-colonized by the seaweed. Our results show that C. cylindracea can influence the quantity and biochemical composition of sedimentary organic matter (OM), and that microbial populations associated with colonized sediments do have specific metabolic patterns and degradation capacities. Caulerpa cylindracea can also influence the metabolic patterns of the microbial community specifically adapted to degrade compounds released by the seaweed itself, with possible consequences on C cycling.

I - Introduction Caulerpa racemosa est une macrophyte originaire du sud-ouest de l'Australie et dont l'aire de répartition actuelle est préoccupante, vue sa présence dans les mers tropicales et tempérées chaudes. Elle est décrite dans la littérature avec de nombreuses variétés et formes différentes qui pourraient en fait masquer plusieurs espèces distinctes (M. VERLAQUE et al., 2000). La forme Caulerpa racemosa, considérée comme envahissante par de nombreux auteurs (M. VERLAQUE et al., 2003, ...