From sessile to vagile: Understanding the importance of epifauna to assess the environmental impacts of coastal defence structures

Ocean sprawl is leading to the introduction of multiple artificial structures into the marine environment. However, the biota on these novel habitats differ from that on natural hard substrates. Amphipods, despite their ecological importance, are usually overlooked when comparing benthic assemblages on artificial and natural hard substrates. So as to assess the effects of artificial structures on amphipod assemblage and to identify the main factors involved, the amphipod assemblage structure was studied in five different substrates (seawalls, cubes, acropods, rip-raps and natural rock). Abiotic measurements of each substrate (complexity, rock composition, and age) were related to the ecological patterns. Complexity measurements seemed to affect the amphipod community structure, highlighting the need to consider physical complexity in eco-engineering actions. Amphipod assemblages were also affected by the secondary substrate (sessile biota), suggesting that artificial structures are indirectly shaping amphipod assemblages by firstly shaping the sessile biota. Future research should study the same secondary substrates across different artificial structures to separate the direct effects (caused by the artificial structures) from the indirect effects (caused by the sessile biota). [Display omitted] •Amphipod assemblages differed among substrate types.•Coastal structures shaped amphipod assemblages through direct and indirect effects.•Physical features seemed to affect the development of amphipod assemblages.•The sessile community was also determinant in the assemblage's structure.