Since there is no local management for Marine Protected Areas (MPAs) to prevent the establishment of macroalgae non-indigenous species (NIS), successful efforts to contrast their spread probably should concentrate in the conservation of resistant habitats.

This study aimed to evaluate the role of depth and habitat in the spread of macroalgal non-indigenous species. Abundance of NIS macroalgae was compared over a one-year period across different substrates and depths within a Mediterranean MPA (Capo Carbonara, Sardinia). In addition, the ecological quality of macroalgal assemblages in relation to invasion was assessed through the Allien Biotic Index (ALEX).

The NIS macroalgae found in the MPA, Caulerpa cylindracea, Acrothamnion preisii, Womersleyella setacea and Falkenbergia sp., were overall quite low in abundance and, accordingly, the ALEX index had generally high values. The results show that the substrate, depth and time significantly affected NIS abundance; however, the lack of significant interannual variability suggested that the occurrence of these four NIS will no further expand in the MPA at the scale of habitat.

It is highlighted that the patterns of NIS abundance found suggest the importance of detailed sampling designs of monitoring taking into consideration different habitats and depths and using suitable sampling methods to assess NIS establishment and spread, such as those required by international directives.

Piazzi et al. (2021) Monitoring non-indigenous macroalgae in a Mediterranean MPA: Lessons from a short-temporal variability of pristine habitats invasion. Ocean and Coastal Management 207: 105608.