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The European Union lacks a comprehensive framework to address the threats posed by the introduction and spread of marine non-indigenous species (NIS). Current efforts are fragmented and suffer substantial gaps in coverage. In this paper we identify and discuss issues relating to the assessment of spatial and temporal patterns of introductions in European Seas (ES), based on a scientifically validated information system of aquatic non-indigenous and cryptogenic species, AquaNIS. While recognizing the limitations of the existing data, we extract information that can be used to assess the relative risk of introductions for different taxonomic groups, geographic regions and likely vectors. The dataset comprises 879 multicellular NIS. We applied a country-based approach to assess patterns of NIS richness in ES, and identify the principal introduction routes and vectors, the most widespread NIS and their spatial and temporal spread patterns. Between 1970 and 2013, the number of recorded NIS has grown by 86, 173 and 204% in the Baltic, Western European margin and the Mediterranean, respectively; 52 of the 879 NIS were recorded in 10 or more countries, and 25 NIS first recorded in European seas since 1990 have since been reported in five or more countries. Our results highlight the ever-rising role of shipping (commercial and recreational) as a vector for the widespread and recently spread NIS. The Suez Canal, a corridor unique to the Mediterranean, is responsible for the increased introduction of new thermophilic NIS into this warming sea. The 2020 goal of the EU Biodiversity Strategy concerning marine Invasive Alien Species may not be fully attainable. The setting of a new target date should be accompanied by scientifically robust, sensible and pragmatic plans to minimize introductions of marine NIS and to study those present.

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Biological invasions in marine environment are the lesser known aspect of global change. However, recent events which occurred in the Mediterranean Sea demonstrate that they represent a serious ecological and economical menace leading to biodiversity loss, ecosystem unbalancing, fishery and tourism impairment. In this paper we review marine bioinvasions using examples taken from the Mediterranean/Black Sea region. Particular attention is given to the environmental status of the receiving area as a fundamental pre-requisite for the colonisation success of alien species. The spread of the tropical algae belonging to the genus Caulerpa in the northwestern basin of the Mediterranean Sea has been facilitated by pre-existing conditions of instability of the Posidonia oceanica endemic ecosystem in relation to stress of both natural and anthropogenic origin. Human interventions caused long-term modification in the Black Sea environment, preparing a fertile ground for mass bioinvasion of aquatic nuisance species which, in some cases, altered the original equilibrium of the entire basin. Finally, the Venice lagoon is presented as the third example of an environment subjected to high propagule pressure and anthropogenic forcing and bearing the higher "diversity" of non-indigenous species compared to the other Mediterranean lagoons. Stressed environments are easily colonised by alien species; understanding the links between human and natural disturbance and massive development of non-indigenous species will help prevent marine bioinvasions, that are already favoured by global oceanic trade.

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A number of authors have demonstrated that heavy metal concentrations in intestinal Helminths are higher than those found in the tissues of their final hosts. In this work, Pb and Cr concentrations in the Acanthocephalan Acanthocephalus anguillae were measured by means of electrothermal atomic absorption spectrometry. The metal concentrations measured in the whole body of Acanthocephalans were compared to those in the liver of their fish hosts (Leuciscus cephalus) sampled in the Lambro river (Northern Italy). The results show higher concentrations of Pb and Cr in the parasites, respectively approximately 200 times and approximately 60 times higher than that of the host liver. These results corroborate the usefulness of parasites in the monitoring of biologically available metal concentrations in aquatic ecosystems that are non severely polluted.

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The distribution of two acanthocephalan species (Pomphorhynchus laevisAcanthocephalus anguillae) in the chub (Leuciscus cephalus) was studied in four river reaches characterized by different levels of pollution: the River Ticino near Abbiategrasso (unpolluted), the Naviglio Grande Canal, in Milano (slightly polluted), the River Lambro near Merone village (polluted) and the River Lambro near Monza (severely polluted).Pomphorhynchus laevis was restricted to the unpolluted and the slightly polluted sites, while the intensity of A. anguillae increased proportionally to water pollution. These differences were partially explained by the variation in abundance of their intermediate hosts (Echinogammarus stammeri for P. laevisAsellus aquaticus for A. anguillae). Data on the occurrence of P. laevis and A. anguillae showed a significant negative binomial frequency distribution, suggesting their tendency to be aggregated within the host populations of L. cephalus.