The Pacific bryozoan, Smittoidea prolifica Osburn, 1952, is reported for the first time from the Northwest Atlantic coast. Colonies were discovered during routine benthic sampling of Casco Bay, Maine, encrusting mussel shells and barnacles. Aiming to compare specimens from native and introduced locations, uncertainties about the Pacific range of S. prolifica were resolved by re-examining specimens from Japan, southern Korea, the United States west coast, and Mexico. The occurrence of this species in Japan was confirmed but southern Korea specimens were found to be Smittoidea spinigera (Liu, 1990). Comparisons of biometrics among specimens from widely dispersed locations where S. prolifica is native and introduced showed significant trends in variation with most characters largest for California and smallest for Germany. Zooid width was largest for Maine specimens. Comparisons between oceans showed that Pacific and Atlantic specimens differed significantly in all measures except zooid length and orifice width. Low substrate specificity and broad range of temperatures and salinities in occupied habitats suggests the potential for successful introduction is high. Smittoidea prolifica was most likely introduced through commercial shipping from the North Sea where it is an established non-native species. This was the third non-indigenous species found in Casco Bay discovered within the same timeframe and which shared the same likely region of origin. This spike matched a rise in commercial shipping from the Northeast Atlantic to Portland, Maine, suggesting this seaport is shifting towards becoming a bioinvasion hotspot.

Species introduced into new areas often show a reduction in parasite and genetic diversity associated to the limited number of founding individuals. In this study, we compared microsatellite and parasite diversity in both native (lower Danube) and introduced populations of 4 Ponto-Caspian gobies, including those (1) introduced from within the same river system (middle Danube; Neogobius kessleri and N. melanostomus), and (2) introduced from a different river system (River Vistula; N. fluviatilis and N. gymnotrachelus). Microsatellite data confirmed the lower Danube as a source population for gobies introduced into the middle Danube. Both native and introduced (same river system) populations of N. kessleri and N. melanostomus had comparable parasite species richness and microsatellite diversity, possibly due to multiple and/or continual migration/introduction of new individuals and the acquisition of local parasites. Reduced parasite species richness and microsatellite diversity were observed in introduced (different river system) populations in the Vistula. A low number of colonists found for N. fluviatilis and N. gymnotrachelus in the Vistula potentially resulted in reduced introduction of parasite species. Insufficient adaptation of the introduced host to local parasite fauna, together with introduction into an historically different drainage system, may also have contributed to the reduced parasite fauna.

The invasive species Caulerpa racemosa var. cylindracea represents a serious threat to the diversity of benthic assemblages in the Mediterranean Sea. In the present study, a removal experiment was carried out to test whether, after 18 months of C. racemosa var. cylindracea exclusion, the macrophyte assemblage resembled a non-invaded assemblage. The results show that in the assemblage invaded by C. racemosa var. cylindracea the number of species, macrophyte cover, Shannon diversity and Pielou's evenness were lower than in the non-invaded assemblage. Erect perennial species were particularly affected and other introduced species were significantly reduced or completely excluded. After 18 months of removal/exclusion of C. racemosa var. cylindracea, only partial recovery of the macrophyte assemblage could be observed. Species numbers, total cover and erect perennial species cover were still significantly lower than in the non-invaded plots. However Shannon diversity and Pielou's evenness had reached comparable levels. In contrast to native macrophytes, the total cover of other introduced species reached a level comparable to the non-invaded plots. In summary, the present study revealed that after 18 months of C. racemosa var. cylindracea exclusion: (i) only partial recovery of the macrophyte assemblage occurred; and (ii) the development of other invasive species was favoured by the absence of C. racemosa var. cylindracea (Sisyphus effect).