Ecosystem vulnerability to alien and invasive species: a case study on marine habitats along the Italian coast

1. Spread of alien species (AS) is a serious threat to marine habitats and analysis of principal descriptors of theiroccurrence is pivotal to set reliable conservation strategies.2. In order to assess the susceptibility of marine habitats to biological invasions, a dataset was gathered of theoccurrence of 3899 species from 29 phyla, taken from 93 marine sites located along the Italian coast in theperiod 2000-2012.3. In total, 61 AS belonging to 11 phyla have been recorded. Invertebrates were the most represented (63%).Alien species were found in all the habitats examined (EUNIS, level 2), although they showed highestabundance in benthic habitats. Most of the AS were associated with a single EUNIS habitat, while some ofthem were present in more than one habitat. Trans-habitat occurrence suggests the potential invasiveness of AS.4. According to statistical analysis, AS recorded could have been more numerous, since some of the marinehabitats seemed to be still unsaturated. The model that best describes the spread of AS takes account of bothnative species richness (Rn) and EUNIS habitat type as explanatory variables. The number of observed AS wasdirectly related to Rn and it was highest in rocky circalittoral and infralittoral habitats.5. The results of this macro-ecological study focus on the importance of performing large-scale studies, sinceadopting ecosystem approaches to marine invasion management seems especially fruitful.6. The results, moreover, highlight the importance of AS monitoring of different habitats, from thosesubjected to anthropogenic pressure, historically considered to be hubs of introduction of AS, to the mostbiologically rich and diverse marine habitats. Indeed, it is necessary to set monitoring strategies to detect theintroduction, the distribution and persistence of AS over time. These recommendations are especiallysignificant in the light of the strategic plans currently under formulation in Mediterranean countries withregard to AS monitoring.