Recreational Boating as a vector of spread of alien species around the Mediterranean

Many stressors, such as climate change, overfishing, pollution and biological invasions, are currently devastating marine domain. Despite species being passively transported to new marine ecosystems since the onset of boat travel, invasion biology is relatively new field of science. Recreational boating as a major vector in the transport of non-indigenous species (NIS) has largely been overlooked until very recently, mostly because of the perceived effectiveness of antifouling coatings on boat-hulls. The role of recreational boating in facilitating marine bioinvasions urgently necessitated a proper evaluation, especially in the Mediterranean Sea which hosts 2/3 of global charter boat traffic and is also the global hotspot for alien species. This study addresses this shortfall by completing the first-ever Mediterranean basin-wide study investigating the influence of recreational boats in the transfer of NIS from biofouling both in marinas and from boat-hulls. First, a thorough investigation of NIS was conducted in 34 marinas across the Mediterranean (spanning from Spain to Turkey), targeting benthic macroinvertebrates. All marinas were found to host NIS, ranging from 2 to 27 per marina. This first output of this research provides a massive update of new NIS records and updated species distributions for the Mediterranean, and presents three new species in the Mediterranean basin, 51 new NIS country records and 20 new subregional records, which can now be fed into models and databases to gain a better comprehension of the scale of NIS colonizing marina habitats. Next, boat owners/captains were surveyed on their vessel characteristics including hull-cleaning and painting history along with their recent travel itinerary. Subsequently, biological samples of the biofouling were collected from approximately 600 of the same boat-hulls whose captains had already completed the survey, in order to search for correlations between the findings of the two. After the biofouling samples were identified, it was realized that almost 75% of sampled fouled vessels were found to host at least 1 NIS, while quite a few boats hosted as many as 8 NIS. It was also found that recreational vessels visiting new marinas sometimes carry NIS not yet present neither in that marina nor in the country in which they are visiting, thus providing ample evidence of recreational boating supplying new NIS to marinas. The results of this large-scale Mediterranean marina assessment were combined with other existing data on NIS in Italian marinas for a total sample size of 50 marinas, which were then used to feed multivariate statistical tests aimed at identifying which abiotic factors mainly contribute to NIS presence amongst marinas. The results revealed that NIS distributions in Mediterranean marinas are largely shaped by environmental factors which are found to be associated with the native ranges for species such as temperature, salinity, and biogeographical region and climate type. Proximity to the Suez Canal has a strong influence on NIS distributions, confirming that this particular pathway has a unique and prevailing influence particularly in the Eastern Mediterranean. Rather surprisingly, some factors that we thought to be relevant in determining NIS presence, were not found to be significant contributors affecting NIS similarities between communities. These marina factors included marine area, presence of shipyard presence of and total pontoon length and marina opening size (enclosement ratio). The results presented within this thesis, adding to those surveyed from around the world, form a robust case that recreational boating provides an extremely important pathway in facilitating the primary NIS introduction events and their associated secondary spread to other coastal areas as ‘stepping stone’ habitats. These results indicate that the recreational boating vector requires urgent management to reduce the scale of future invasions.

Mentre in passato la distribuzione delle specie marine era limitata da barriere geografiche, l'attuale globalizzazione ha fatto sì che queste vengano infrante, e che quindi siano i fattori climatici a controllare la distribuzione di molte specie. L'aumento globale dei viaggi e commerci marittimi ha facilitato infatti il trasporto di specie aliene per lunghi tragitti. Alcuni elementi chiave, quali il cambiamento climatico, l'aumentata frequenza dei trasporti, la creazione di corridoi artificiali e la mancanza di regolazioni sul biofouling hanno comportato un aumento delle invasioni biologiche marine negli ultimi decenni. È urgente effettuare una valutazione del ruolo della navigazione da diporto nel facilitare le invasioni biologiche, specialmente nel Mediterraneo che da solo ospita circa i 2/3 del traffico da diporto globale, e inoltre è il mare più affetto da invasioni biologiche. La presente tesi affronta questo problema, e rappresenta il primo studio a scala dell'intero bacino Mediterraneo che investiga il ruolo della navigazione ricreativa nel trasferimento di specie non-indigene tramite il vettore biofouling, analizzando sia le marine turistiche, sia le imbarcazioni. Una campagna di campionamento finalizzata a determinare se le marine turistiche rappresentano effettivamente "punti caldi" di introduzione di specie non-indigene è stata condotta in 34 marine, dalla Spagna alla Turchia, focalizzandosi sulle comunità di macroinvertebrati. Contestualmente, circa 600 diportisti sono stati intervistati sulle caratteristiche della loro imbarcazione, le abitudini di pulizia e verniciatura dello scafo, nonché il loro itinerario dell'ultimo anno. Da queste imbarcazioni sono stati inoltre raccolti anche campioni di biofouling, al fine di esplorare la correlazione tra abitudini di utilizzo del natante e presenza di specie non-indigene. I risultati di questa indagine a scala Mediterranea sono stati integrati con risultati di altre ricerche pregresse, condotte con simili modalità in marine turistiche italiane: la base dati che ne è risultata include l'elenco di NIS marine presenti in 50 marine del Mediterraneo. Questi dati sono stati analizzati con approccio statistico multivariato, al fine di identificare i fattori abiotici che contribuiscono maggiormente alla ricchezza in specie aliene nelle marine, e alla similarità nella composizione in NIS tra marine diverse.