a b s t r a c tAn inventory in the Dutch-German-Danish Wadden Sea revealed a total of 66 nonnative (alien) taxa including 17 tentative cryptogenics in the brackish-marine macrobenthos until 2010, which is close to average compared with similar inventories from other coasts. Although the Wadden Sea is known for the largest sedimentary tidal flats in the world, most aliens encountered were fouling at harbor walls, pontoons in marinas, at hard structures for coastal defense but also in epibenthic mussel and oyster beds. Recent qualitative rapid assessments focusing on port localities have substantially improved knowledge on introduced species in the Wadden Sea. Nonnative species have pervaded algal and invertebrate communities, and the guild of suspension feeders became particularly strengthened by aliens which took advantage of a recent phase with relatively warm years. Most alien species were not directly introduced into the Wadden Sea but have spread secondarily from adjacent coasts with more active harbors or shellfish cultures. We suggest that aliens which have already established in the Wadden Sea ecosystem should be tolerated to avoid ongoing manipulations in eco-evolutionary developments in this protected nature area. Mitigation of the advancing tide of invasive aliens should focus on vector control (shipping and open aquacultures) as well as on early detection with attempts of eradication during the initial phase of invasions on a scale of the entire European Atlantic coast of which the Wadden Sea ecosystem is an integral part.

Living conditions for macrofauna on flood delta shoals are determined by surf, strong currents and sediment mobility. Thus, a unique assemblage of invertebrate species colonize these far off-shore, low intertidal flats. We here describe the macrobenthic fauna of emerging shoals in the Wadden Sea between the islands of RSm5 and Sylt. Besides ubiquitous macroinvertebrates of the intertidal zone and species which attain their main distribution in the subtidal zone, the flood delta shoals are characterized by organisms adapted to live in these highly unstable sediments, like the polychaetes Spio martinensis, Streptosyllis websteri, Magelona mirabilis, Psammodrilus balanoglossoides, the pericarid crustaceans Cumopsis goodsiri, Tanaissus lilljeborgi, Bathyporeia sarsi and a few others. Average abundance (1440 m -2 of ind > 1 re_m) and biomass (12.9 g AFDW m -2) were low compared to other intertidal habitats in the Wadden Sea. Biomass was dominated by largesized individuals of the lugworm Arenicola marina. The U-shaped burrows of these polychaetes were inhabited by high numbers of Urothoe poseidonis. Maximum densities of these amphipods occurred in the deepest parts of the burrows. Sampling at approximately monthly intervals revealed no apparent seasonality of U. poseidonis abundance. Together with small Capitella capitata, these amphipods constitute a deep-dwelling component of the macrofauna associated with lugworms, which is separated from all other macrofauna living at the sediment surface. As a response to rising sea level and increasing tidal ranges, we expect the unstable sandy shoals, inhabited by numerous Spio martinensis and Urothoe poseidonis, to expand within the Wadden Sea at the cost of stable sandy flats with abundant macrofauna.

We report the isolation of an empty spiracles class homeodomain-containing gene, Cn-ems, from the hydrozoan Hydractinia symbiolongicarpus, the first gene of this class characterized in a lower metazoan. Cn-ems was found to be expressed in the head of gastrozooids, specifically in endodermal epithelial cells of the taeniolae of the hypostome. Cn-ems is not expressed in gonozooids, which lack taeniolae. Experimental conversion of the posterior region of the planula larva into head structures up-regulates expression of the gene. These findings establish that the association of ems-class genes with head structures preceded the evolution of bilateral symmetry.

Florence, was a brilliant Italian zoologist and ethologist, and one of the most well-known and active experts on alien aquatic species. Since her masters degree in Biology (1979) and her PhD in Animal Biology (Ethology) (1987), both obtained at the University of Florence, Francesca studied the behaviour and ecology of aquatic animals. Initially, most of her research concerned social recognition in crustaceans: she was particularly renowned for her studies on hermit crabs and crayfish, her principal model organisms.Then, from the 1990's onwards she worked in the field of invasion biology, her main interest until her death. Francesca devoted herself with enthusiasm and energy, not only to the problem of the invasive red swamp crayfish Procambarus clarkii, by revealing several aspects of its behavioral ecology, and by developing with her collaborators different methods for its control, but she gradually became an international expert on crayfish and more generally on aquatic alien species. In all aspects of her life, she was constantly driven by a continuous curiosity, thirst for knowledge and a will to face challenges; this was expressed by exploring and frequently opening new research fields. And she transmitted her drive and passion to the many students she supervised. One of the last papers with her contribution is published in this issue of Aquatic Invasions by Vera Gonçalves, her Portuguese PhD student working on the interaction between Procambarus clarkii and the zebra mussel Dreissena polymorpha, an issue of recent increasing interest in Francesca's team.

With globally growing aquaculture activities, the co-introduction of parasites alongside large-scale movements of commercial species poses an increasing risk for marine ecosystems. Here, we present the first record of the shell-boring polychaete Polydora websteri Hartman in Loosanoff and Engle, 1943 in invasive Pacific oysters Crassostrea (Magallana) gigas (Thunberg, 1793) in the European Atlantic Ocean. In October 2014, mud blisters in the shells of wild Pacific oysters and specimens of a spionid polychaete were observed in close proximity to a commercial oyster farm at the island of Sylt (Germany) in the European Wadden Sea. Subsequent investigations indicated that these blisters only occurred near the farm and that no other mollusc species were affected. Morphological and molecular analysis identified the polychaete as Polydora websteri, a species that nowadays widely occurs around the globe, but likely is native to the Asian Pacific. Later sampling activities detected P. websteri also at other locations around Sylt as well as in the Dutch part of the Wadden Sea at the island of Texel. The number of polychaetes in the oysters was, however, relatively low and mostly below 10 individuals per oyster. Together, this evidence suggests that P. websteri is currently extending its range. As the introduction of P. websteri may have severe ecological and economic implications, this study aims to alert others to look for P. websteri at Western European coasts within farmed or wild Pacific oysters to further document its spread.

Based on the past 150 years of research and ongoing time-series observations we give a comprehensive overview of marine species composition around the island of Sylt in the eastern North Sea. A total of 2758 species is listed according to the categories microplankton (591 species), zooplankton (137), nekton (118), benthic microflora (158), benthic macroflora (125), benthic micro-and meiofauna (1204), benthic macrofauna (509), birds and mammals (91), and neobiota (39). Plants account for a third of the species, most (85%) of them are microscopic Chromista. Among animals, 60% of the species are micro-and meiofauna though this faunal component is still insufficiently known. These figures are similar to records from the southern North Sea and therefore may by typical for temperate climate sedimentary coastal areas. A comparison with the total of marine species suggests that the small benthic fauna may be severely understudied over most of the world. Analysis of global change depends on sound baseline data and species inventories like this can assist in the detection of biodiversity changes. They emphasise rare species and the full range of local habitats while time-series measurements usually rely on a few selected habitats and biotic components to generate a very general picture of the state of an ecosystem.

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