Meiofaunal colonization potential in barren grounds: new cues for habitat rehabilitation

Anthropogenic pressures have a prominent role in fostering regime shifts, which, in turn, induce negative consequences like habitat and biodiversity loss. In the Mediterranean Sea, hard-bottom ecosystems dominated by macroalgal forests formed by Cystoseira sensu lato may switch to less-productive barren grounds. Ecological restoration is increasingly acknowledged as the most effective strategy to reverse the biodiversity loss, together with conservation, fostered by resilience of marine ecosystems once the pressures are mitigated. Meiofauna have been studied both for assessing the loss of biodiversity and ecosystem functioning in barren grounds and the success of restoration intervention of Cystoseira s.l. forests. Here, we tested the possibility for meiofauna to colonize barren grounds, once they have a suitable habitat, simulating a possible habitat rehabilitation intervention (i.e., the presence of a substrate to settle, mimicking the three-dimensional structure of Cystoseira s.l. as substrate for associated biodiversity). We used artificial substrates to assess the potential capability of meiofauna to colonize macroalgal forests and barren grounds, comparing meiofaunal assemblages in the artificial substrates with those retrieved from benthos, in both habitats. Significant higher abundance, richness of higher taxa and different taxonomic composition were observed in macroalgal forests than barren grounds. Moreover, high abundance and richness of taxa were observed in artificial substrates in barren grounds. This suggests that meiofaunal diversity can be recovered once the habitat is rehabilitated, also in degraded barren grounds. Complementary actions, as reintroducing the habitat-forming species in combination with artificial substrates for benthic components, can augment the restoration success and shorten ecosystem recovery.