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A good understanding of the mechanisms and magnitude of the impact of invasive alien species on ecosystem services and biodiversity is a prerequisite for the efficient prioritisation of actions to prevent new invasions or for developing mitigation measures. In this review, we identified alien marine species that have a high impact on ecosystem services and biodiversity in European seas, classified the mechanisms of impact, commented on the methods applied for assessing the impact and the related inferential strength, and reported on gaps in available information. Furthermore, we have proposed an updated inventory of 87 marine species in Europe, representing 13 phyla, which have a documented high impact on ecosystem services or biodiversity.Food provision was the ecosystem service that was impacted by the greatest number of alien species (in terms of both positive and negative impacts). Following food provision, the ecosystem services that were negatively affected by the highest number of alien species were ocean nourishment, recreation and tourism, and lifecycle maintenance, while the ecosystem services that were most often positively impacted were cognitive benefits, water purification, and climate regulation. In many cases, marine aliens were found to impact keystone/protected species and habitats. Thirty percent of the assessed species had an impact on entire ecosystem processes or wider ecosystem functioning, more often in a negative fashion. Forty-nine of the assessed species were reported as being ecosystem engineers, which fundamentally modify, create, or define habitats by altering their physical or chemical properties.The positive impacts of alien species are probably underestimated, as there is often a perception bias against alien species. Among the species herein assessed as high-impact species, 17 had only negative and 7 only positive impacts; for the majority (63 species), both negative and positive impacts were reported; the overall balance was often unknown. Although there is no doubt that invasive species have modified marine ecosystems, evidence for most of the reported impacts is weak, as it is based on expert judgement or dubious correlations, while only 13% of the reported impacts were inferred via manipulative or natural experiments. A need for stronger inference is evident, to improve our knowledge base of marine biological invasions and better inform environmental managers.

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Examination of the hydroid fauna of the Canadian Pacific coast in the collections of the Royal Ontario Museum collected between 1934 and 1985 indicates that the genus Sertularella Gray, 1848 from the infralittoral zone in the region remains poorly enumerated. The present study shows that several European or northeast Atlantic hydroid species, Sertularella conica Allman, 1877, Sertularella rugosa (Linnaeus, 1758), Sertularella tenella Alder, 1856, Sertularella polyzonias (Linnaeus, 1758), and Sertularella fusiformis (Hincks, 1861) have been incorrectly reported from the west coast of North America and suggests that assumptions of cosmopolitanism of some species require verification by continuing refinement of regional species-level taxonomy. Four new species, Sertularella cervicula, S. coronata, S. sacciformis, and S. pacifica are recognized and described in this paper. Sertularella gigantea Hincks, 1874 is recognized for the first time from the Pacific coast of North America.

We show that the high seas are colonized by a diverse array of coastal species, which survive and reproduce in the open ocean, contributing strongly to its floating community composition. Analysis of rafting plastic debris in the eastern North Pacific Subtropical Gyre revealed 37 coastal invertebrate taxa, largely of Western Pacific origin, exceeding pelagic taxa richness by threefold. Coastal taxa, including diverse taxonomic groups and life history traits, occurred on 70.5% of debris items. Most coastal taxa possessed either direct development or asexual reproduction, possibly facilitating long-term persistence on rafts. Our results suggest that the historical lack of available substrate limited the colonization of the open ocean by coastal species, rather than physiological or ecological constraints as previously assumed. It appears that coastal species persist now in the open ocean as a substantial component of a neopelagic community sustained by the vast and expanding sea of plastic debris.

Insects are usually considered to be excluded from the marine environment. A small number of species, however, are considered to be marine, due to spending some portion of their life cycle in salt water. We use natural history collection specimens, in-field observations, and molecular analysis to generate new locale records and natural history data for seven insect species. All seven species are associated with barnacles (Balanomorpha: Balanidae, Chthamalidae) along the Pacific coast of Canada, the United States of America, or Japan. Use of DNA barcode analysis confirms the monophyly of three species of Oedoparena (Diptera: Dryomyzidae). Natural history collection specimens expand the geographical range and illuminate the phenology of Oedoparena spp. In-field observations record direct associations between three species of Thalassosmittia (Diptera: Chironomidae), Diaulota densissima (Casey) (Coleoptera: Staphylinidae), and intertidal barnacles from various locations in British Columbia, Canada. Barnacle host associations and microhabitat preferences are proposed for all species. A new definition of what constitutes a marine insect is offered.

An account is given of the names of families, genera, and species of hydroids established by C.M. Fraser of Canada, excluding those from Allan Hancock Pacific Expeditions and the Allan Hancock Caribbean Sea Expedition. The names of four families, 11 genera, and 101 species are attributed to him in this work, complementing those of another two genera and 164 species described by Fraser in various Allan Hancock publications. Information is provided on type localities of his new species, on locations and kinds of type material in existence, where known, and on the current taxonomic status of families, genera, and species described by him in works reviewed herein. Two replacement names (Thuiaria geniculata Fraser, 1918a and Salacia fraseri Calder, 1991) exist for Thuiaria distans Fraser, 1914a (not Thuiaria distans Allman, 1877). The widely overlooked senior synonym, T. geniculata, is recognized as the valid name of the species. Diphasia alta nom. nov. is proposed as a new replacement name for the permanently invalid junior primary homonym Diphasia robusta Fraser, 1943a (not D. attenuata robusta Billard, 1924). In addition, Cryptolaria crassa nom. nov. is proposed as a new replacement name for the junior secondary homonym Cryptolaria rigida (Fraser, 1948) [not C. rigida (Fraser, 1940a)]. Lectotypes have been designated for 47 of the species to establish objective standards for application of their names. Corymorpha adventitia Fraser, 1941b, from the Pacific coast of Panama, is assigned to Ralpharia Watson, 1980, as R. adventitia. No type specimens are known to exist for seven of the species considered, including one holotype (of Hebella eximia Fraser, 1944a) missing from its bottle. Particular attention has been paid to dating and chronology of the 51 publications of Fraser covered in this work. Earlier bibliographic errors are corrected, most notably establishing that the book Distribution and relationship in American hydroids was published in early 1947 rather than 1946 as per the title page.