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The North American bivalve mollusc Ensis directus (Conrad, 1843) (Bivalvia, Pharidae) is native to the Northwest Atlantic coasts from southern Labrador to northern Florida (Bousfield, 1960; Theroux and Wigley, 1983; Swennen et al., 1985; Abbott and Morris, 2001; Turgeon et al., 2009; Vierna et al., 2013). This species has been introduced outside its native range, with the first confirmed record from the German Bight in 1979 (Cosel et al., 1982). Thereafter, a subsequent secondary range expansion took place, and the species is presently known to occur from Spain to Norway, including the UK (e.g. Mühlenhardt- Siegel et al., 1983; Essink, 1985, 1986; Kerckhof and Dumoulin; 1987, Luczak et al., 1993; Rasmussen, 1996; Brattegard and Holthe, 1997; Eno et al., 1997; Severijns, 2000, 2002, 2004; Wolff, 2005; Dauvin et al., 2007; Houziaux et al., 2011; Arias and Anadon, 2012; Dannheim and Rumohr, 2012; Witbaard et al., 2013) and in the western Baltic (Gürs et al., 1993). The most recent expansion was to the Bay of Biscay (Arias and Anadon, 2012) from where it may be expected to spread further. E. directus has all the characteristics of a successful “r” strategist invader, including high reproductive capacity, short generation time, and rapid growth. Its expansion is principally due to natural dispersal. It usually occurs in clusters and has wide environmental tolerances (Dannheim and Rumohr, 2012). Moreover, its native predators (e.g. the snail Polinices heros and the nemertean Cerebratulus lacteus) are absent in Europe (Cosel, 2009). Although E. directus is common in its native range, it is more abundant in its introduced range. Further, its exceptional colonization success in Europe is likely related to its use of underutilized tidal habitats that are characterized by exposure to physical disturbance as a consequence of wave action and strong tidal currents. It appears that E. directus is one of the few larger benthic invertebrates able to tolerate the unstable sands in the tidal zone (Dekker and Beukema, 2012). Although there is high annual variability in E. directus densities, the species has become a prominent component of the macrobenthos in shallow subtidal sands in Europe. This review describes the current status of the species outside its native range.

Here we study the effects of fishing trawl gear on the seabed and benthic organisms. A BACI-design experiment was used to examine the effects of a traditional beam trawl gear and the pulse trawl gear. The pulse trawl gear is gaining popularity amongst Dutch fishers in recent years due to reduced fuel costs and good sole catches.The research was carried out in the northern part of the Dutch Voordelta (southern North Sea coastal zone area, 15 – 22m deep, sandy habitat) in June 2013. In this experimental area, fishing disturbance was considered to be low so interference with the experiment was minimalized. Within the experimental area 3 sub-areas (150m x 1000m) were established for the BACI experiment: 1) a pulse trawl area; 2) a beam trawl area; 3) a reference area. The pulse and beam trawl areas of the BACI experiment were trawled by a commercial vessel (pulse) and a research vessel (beam) for one day. Before trawling, the areas were sampled with a multibeam, a sediment profile imaging (SPI) camera and a benthic sledge. The same sampling was carried out after the trawling, as well as boxcore sampling.

International audience; The North Sea Benthos Project 2000 was initiated as a follow-up to the 1986 ICES North Sea Benthos Survey with the major aim to identify changes in the macrofauna species distribution and community structure in the North Sea and their likely causesThe results showed that the large-scale spatial distribution of macrofauna communities in the North Sea hardly changed between 1986 and 2000, with the main divisions at the 50 m and 100 m depth contours. Water temperature and salinity as well as wave exposure, tidal stress and primary production were influential environmental factors on a large (North Sea-wide) spatial scale. The increase in abundance and regional changes in distribution of various species with a southern distribution in the North Sea in 2000 were largely associated with an increase in sea surface temperature, primary production and, thus, food supply. This can be most likely related to the North Sea hydro-climate change in the late 1980s influenced by the variability in the North Atlantic Oscillation (NAO). Only one cold-temperate species decreased in abundance in 2000 at most of the stations. Indications for newly established populations of offshore non-native species were not found. Differences in macrofauna community structure on localised spatial scales were predominantly found north of the 50 m depth contour off the British coast along the Flamborough Head Front towards the Dogger Bank, off the coast of Jutland and at the Frisian Front. These changes were most likely attributed to stronger frontal systems in 2000 caused by the increased inflow of Atlantic water masses in relation to the hydro-climate change in the late 1980s.

Since 1993 a large part of the Dutch coastal waters is monitored. Annual benthos inventories are carried out with different samplers. In principal, these surveys are designed for the assessments of the stocks of several commercial bivalve species. All species that are caught as bycatch in these surveys are counted, weighted and registered. This data is accumulated in the IMARES database. So far, little of this data has been used. This extensive survey data can used to answer various policyrelated or commercial research questions. Its analysis may help to evaluate the quality status of specific areas and the biological effects of human activities. This report provides an overview of the available data, listing the available species and showing examples of the distribution and/or population development of several species.

The American jackknife clam (Ensis directus), first detected in the German Bight of the North Sea in 1978, was observed for the first time in the Belgian sector in 1987. Since then, increasing numbers of specimens wash ashore every year, suggesting that the species forms large nearshore populations likely to significantly alter the local biological communities. A research project was started in 2009 to study this issue, extending the studied area to Dutch waters. On the one hand, the population dynamics will be investigated as well as its impact on the local fauna, making use of pre‐1987 macrobenthic datasets; using knowledge acquired since some years on benthos–sediment relationships in this area, optimum habitats for this alien species will tentatively be determined through a modelling exercise (“habitat suitability modelling”) and acoustic seabed mapping. On the other hand, the impact of altered composition of macrobenthic communities on populations of seabirds will be evaluated. These data will further allow us to evaluate the feasibility, sustainability, and ecological impact of a targeted Ensis fishery within Belgian waters, incorporating lessons learned from commercial vessels operating in the nearby Dutch waters. In this contribution, our preliminary results are presented and discussed.

The American jackknife clam (Ensis directus), first detected in the German Bight of the North Sea in 1978, was observed for the first time in the Belgian sector in 1987. Since then, increasing numbers of specimens wash ashore every year, suggesting that the species forms large nearshore populations likely to significantly alter the local biological communities. A research project was started in 2009 to study this issue, extending the studied area to Dutch waters. On the one hand, the population dynamics will be investigated as well as its impact on the local fauna, making use of pre-1987 macrobenthic datasets; using knowledge acquired since some years on benthos–sediment relationships in this area, optimum habitats for this alien species will tentatively be determined through a modelling exercise (“habitat suitability modelling”) and acoustic seabed mapping. On the other hand, the impact of altered composition of macrobenthic communities on populations of seabirds will be evaluated. These data will further allow us to evaluate the feasibility, sustainability, and ecological impact of a targeted Ensis fishery within Belgian waters, incorporating lessons learned from commercial vessels operating in the nearby Dutch waters. In this contribution, our preliminary results are presented and discussed.

This paper is chapter 5.2 of the ICES CRR “Structure and dynamics of the North Sea benthos” (ICES 2007) compiled by the ICES Study Group on the North Sea Benthos Project 2000. The North Sea Benthos Project 2000 (NSBP) was initiated as a follow-up to the earlier 1986 ICES North Sea Benthos Survey (NSBS). One major aim of the NSBP 2000 was to compare the outcome with that of the 1986 NSBS, in order to identify any significant changes in the community structure and their likely causes. In general, the spatial distribution of the macrofaunal communities in 2000 was rather similar to that in 1986. But changes were found within communities which were addressed to changes in the hydroclimate caused by changes in the North Atlantic Oscillation influencing changes in currents and sediment structure as well as food availability.