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Pathways of introduction of marine alien species in Europe and the Mediterranean - a possible undermined role of marine litter

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In recent assessments of pathways of introduction of alien marine species in European seas, shipping, corridors (Suez canal and inland corridors), aquaculture, and aquarium trade have been identified as the most important (in decreasing order). In theMediterranean Sea, the same pathways have been identified as the main ones, with the Suez Canal being the most important. The role of marine litter as a vector of introduction or secondary spread of alien species in the Mediterranean has not been considered and studied so far. Primary introductions of alien species in the Mediterranean Sea by rafting on floating litter through the Suez Canal or the Gibraltar strait could have occurred. Furthermore, the huge amounts of floating plastic in the Mediterranean offer increased opportunities for many alien species to further spread in the Basin. Thirteen established aliens in the Mediterranean are known to be able to colonize floating litter. Furthermore, as inferred from their life cycle and traits, more than 80% of the known alien species in the Mediterranean could potentially use litter for further expanding their range (after their initial introduction).
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... hitchhikers on mollusc shells; Naylor et al., 2001;Lee and Gordon, 2006;Mckindsey et al., 2007;Davidson et al., 2015;Cottier-Cook et al., 2016). According to current research, aquaculture is the second most important pathway of marine alien species introduction to European Seas, and a largely underestimated role of marine litter in such introductions is suggested (Katsanevakis et al., 2013;Katsanevakis and Crocetta, 2014). ...
... Although rafting may not be regarded as an important way of dispersal for non-native biota, the availability of rafting vectors has about doubled with the use of plastics (Barnes, 2002). In a recent review, Katsanevakis and Crocetta (2014) suggest that > 80% of invasive species in the Mediterranean might be able to raft on floating litter, while 13 of such species have already been found rafting on floating litter. It is now known that biota can not only attach to artificial objects, but also multiply and survive long time periods and distances on it (Winston et al., 1997;Hoeksema et al., 2012;Holmes et al., 2015). ...
... For this reason, the marine litter plays an important role in the primary introduction and diffusion of alien species. Both primary introduction and secondary diffusion of already introduced alien species have been understudied in the European Seas (Zenetos et al., 2012;Katsanevakis et al., 2013;Galil et al., 2014;Katsanevakis and Crocetta, 2014;Nunes et al., 2014). To date, only one research was conducted on macrozoobenthic communities associated with benthic marine litter in Italian waters (Crocetta et al., 2020) and data about the specific composition of litter-associated fauna appear to be fragmentary, hence underestimated. ...
... The discovery of 6 NIS confirms that marine litter can act as a vector for the introduction and spread of some alien species (Zenetos et al., 2012;Katsanevakis et al., 2013;Galil et al., 2014;Nunes et al., 2014;Katsanevakis and Crocetta, 2014). The fact that some non-indigenous individuals such as M. gigas and the polychaetes H. elegans and H. dirampha were dead at the time of sample processing in the laboratory lead us to hypothesize that litter colonization occurred far away from the sampling area, possibly near the port of Civitavecchia. ...
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... In addition, also P. oceanica and Zostera tasmanica G. Martens ex Ascherson were found on floating plastics (Aliani and Molcard, 2003;Astudillo et al., 2009). Katsanevakis and Crocetta (2014) and Rech et al. (2016) underlined how floating marine litter is a potentially important vector of primary introduction or of secondary spread of alien species; however, the impact of floating litter on biological invasion is difficult to assess and compare with other vectors, like shipping and mariculture. ...
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