Local scale environmental gradients within harbours induce strong community and physiological shifts on hard artificial substratesInvasion Ecology

Christophe Lejeusne¹, Robin Gauff², Simon Rondeau³, Olivier Bohner³, Stéphane Loisel³, Jérôme Coudret³, Stéphane Greff¹, Dominique Davoult³

¹Aix Marseille Univ, Avignon Universite ́, CNRS, IRD, IMBE, UMR CNRS 7263 - IRD 237, Station Marine d’Endoume, France - ²University of Padova, Italy - ³Sorbonne University, Roscoff Biological Station, France

Coastal areas, characterized by high biodiversity and major ecosystem services, are at the heart of environmental issues, concentrating all the challenges linked to global change (urbanization, urban and industrial pollutions, introductions of non-indigenous species (NIS), heat-waves). Because over 80% of world trade is now passing along maritime routes, maritime harbours, which are interfaces between urban and marine environments, now crystallize major coastal issues and problems. Harbour infrastructures provide artificial substrata, colonized by fauna and flora. They do, however, not substitute natural ecosystems because their environmental forcings and biotic composition differ from natural habitats. A particularity of harbours is the high diversity and abundance, or even dominance, of NIS. Harbours and other man-made structures greatly favour biofouling and are thus hotspots for invasions, constituting potential entry points and distribution centres for NIS. Local disturbance and stress due to pollution may further contribute to their persistence in these habitats. The presence of strong environmental gradients within harbours may drive differential community assemblages at local scale (e.g. harbour entrance vs. inner parts) but may also induce some intra-specific physiological changes along these gradients. This might potentially indicate local adaptation. By combining field observations and yet in marine environments rarely employed experimental approaches like reciprocal transplant experiments, we studied such patterns in different harbours from the Mediterranean Sea and the English Channel. A particular focus was set on NIS. Our results showed that environmental gradients, particularly pollution gradients induce strong heterogeneity at local scale on a community- and intraspecies- level and tend to favour NIS.