Metabarcoding identifies macroalgal composition as a driver of benthic invertebrate assemblages in restored habitats

Large brown macroalgal forests support diverse communities of associated invertebrates. However, human activities have led to their degradation, replacing the original macroalgal assemblages with less-complex habitats and altering the associated invertebrate communities. To counteract this, restoration actions are currently being performed aiming at their recovery. Here, we used metabarcoding of the COI gene to describe the invertebrate community of a 10-year restored macroalgal forest dominated by Gongolaria barbata. This invertebrate assemblage was compared with an assemblage adjacent to the restoration site where G. barbata is absent, and two healthy assemblages also dominated by G. barbata, used as references. Results showed that arthropods, molluscs, and annelids were the most abundant groups. Specific MOTUs representing sponge and ascidian species were exclusively found in G. barbata assemblages, suggesting that the restoration particularly benefited some of these organisms. Crustaceans and molluscs, however, were similarly abundant across assemblages, including the one dominated by photophilous macroalgae (without G. barbata), thus indicating that these mobile groups may equally colonise these alternative habitats. The overall composition of the restored assemblage did not completely resemble references, suggesting that recovering all associated diversity is a complex process, most likely influenced by multiple factors that require further investigation.