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Mysterieuze zachte blauwe balletjes met een diameter van ongeveer 1,5 cm. Ik vind ze regelmatig in de vloedlijn, soms meerdere samen. Andere strandwandelaars vinden ze ook. Iedereen reageert verbaasd als ze horen waar de balletjes vandaan komen.

Biofouling and introduced species are one of the causes of a changing biodiversity in the marine environment. In this talk I will address the topic of hull fouling and introduced species i.e. species introduced by human activities beyond their native range into new areas. In their new habitat such species pose a threat to native biodiversity because they may alter local communities, and have unwanted economic effects. Hence the introduction of non-indigenous species is recognized as a major threat to the marine environment, and, for example tackled in EU legislation such as the MSFD.Shipping, with ballast water and hull fouling, is an important vector for species introductions into the marine environment and since the dawn of maritime transport hull fouling has remained an everlasting nuisance, not only because it reduces the ships' speed and clogs intakes and pipes, it also impacts marine biodiversity, for, as biofouling, species are transported all over the world's oceans and introduced into areas beyond their natural distribution.While ballast water is being tackled in various legislations and regulations, hull fouling remains an important cause of introductions, especially since the ban of the very effective anti-fouling agent TBT (Tributyltin). During the past decades the chances for species to survive their journey and ultimately to colonise areas beyond their natural distribution has greatly increased, because maritime transport has become increasingly faster and more intense. Moreover, the permanent establishment of migrants is aided by the growing availability of artificial hard substrata in coastal areas and climate change. Barnacles (Cirripedia), probably the most common fouling organisms, are a good illustration of the ongoing changes as many species have nowadays established populations far beyond their original distribution.

Marine methylotrophs play a key role in the global carbon cycle by metabolizing reduced one-carbon compounds that are found in high concentrations in marine environments. Genome, physiology and diversity studies have been greatly facilitated by the numerous model organisms brought into culture. However, the availability of marine representatives remains poor. Here, we report the isolation of four novel species from North Sea sediment enrichments closely related to the Alphaproteobacterium Methyloceanibacter caenitepidi. Each of the newly isolated Methyloceanibacter species exhibited a clear genome sequence divergence which was reflected in physiological differences. Notably one strain R-67174 was capable of oxidizing methane as sole source of carbon and energy using solely a soluble methane monooxygenase and represents the first marine Alphaproteobacterial methanotroph brought into culture. Differences in maximum cell density of >1.5 orders of magnitude were observed. Furthermore, three strains were capable of producing nitrous oxide from nitrate. Together, these findings highlight the metabolic and physiologic variability within closely related Methyloceanibacter species and provide a new understanding of the physiological basis of marine methylotrophy.

Offshore wind farms, like other artificial structures in the marine environment, are hypothesised to favour introduced species and as such pose a threat to the native fauna. However, this has so far never been investigated for offshore wind farms. In this study, we investigated introduced species on Belgian offshore wind farms with particular interest in (1) the position of introduced species on offshore wind farms in relation to other hard substrata in the Belgian part of the North Sea (BPNS), (2) the distribution of introduced species in the subtidal versus intertidal zone and (3) the potential of offshore wind farms for future flourishment of the introduced species. Therefore we compared different hard substratum communities, both natural and man-made, on the relative importance of introduced species in the subtidal and intertidal communities.

n order to support the prioritisation of invasive alien species for future risk assessments, a horizon scanning methodology for the Europe was developed and implemented. The outcome was a list of 95 species, including all taxa (except microorganisms) within marine, terrestrial and freshwater environments, considered as very high or high priority for risk assessment.

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.

Between August 9th and October 27th the Dutch and Belgian beaches (Southern Bight of the North Sea) witnessed an unusual stranding of Aequorea spp. The northernmost sighting came from the Dutch Wadden Island of Ameland (9 September and 19 October), de southernmost from Raversijde, Belgium (18 August and 9 September). Strandings of Aequorea are infrequent and were often reported as A. vitrina. Unfortunately in the past, the distinction between A. forskalea and A. vitrina had not always been made and moreover identification of beached specimens is often not possible anymore due to decomposition of the animals. However during the recent stranding, surprisingly most individuals proved to be A. forskalea, until then considered as a rare species in the southern North Sea. Additionally, the recent sightings of Aequorea are validated and listed as well as all older sightings from Belgium and the Netherlands known to the authors.

There is a worldwide concern about the expansion of non-indigenous species because they may threaten local biodiversity as some of them may successfully outcompete native species. We report on the presence of two introduced mud worm species, Boccardia proboscidea and Boccardiella hamata, in the southern North Sea, where the former species has been discovered on groynes along the Belgian coast and both species were detected among Pacific oysters Crassostrea gigas in the south-western Dutch delta. Boccardia proboscidea is native to the North Pacific and was first detected in Europe along the Spanish Basque coast in 1996. Our record is the third for European waters and the first for the North Sea. Although B. proboscidea occurs in limited numbers and in ephemeral habitats along the Belgian coast, the species probably has established a permanent population, since it has been reported repeatedly after its first discovery in January 2011. Boccardiella hamata is native to the Atlantic and Gulf coasts of North America. This species has never been recorded from Europe before.Our research demonstrates that in under-studied habitats, such as man-made hard substrata, even well-established populations of newly introduced species may stay undetected. Due to a lack of monitoring of these particular habitats and insufficient knowledge about introduced biota, introduced species may pass unnoticed or may be overlooked for several years. A dedicated monitoring will be necessary to detect introduced species in an early stage. In view of the upcoming Marine Strategy Framework Directive requirements such monitoring will be inevitable.

We detail the discovery of recently established immigrant populations and beached material of the encrusting bryozoan Fenestrulina delicia from the Atlantic coasts of Europe. This species of unknown origin is highly invasive and, in contrast to most other introduced bryozoans spreads along offshore natural and artificial hard substrates, rather than hopping from one marina to another. Part of the material, collected in situ, was found on empty shells at locations well known for their aquaculture of oysters and mussels. This suggests that the import of shellfish could be the vector of primary introduction. Beached material suggests that floating plastic debris might be a vector of transport for secondary introduction. The base of offshore wind turbines forms a supplementary substrate in the sandy southern North Sea and probably provides stepping stones for this exotic species.

Integrated monitoring of the effects of aggregate extraction is needed to reach Good Environmental Status of the marine environment by 2020 (European Marine Strategy Framework Directive (MSFD); 2008/56/EC). This requires increased process and system knowledge that incorporates both natural and human-induced variability. Additionally, when exploitation is within or near Habitat Directive Areas, appropriate assessments are needed of all stressors (92/43/EEC). Recently, new extraction activities started in a far offshore sandbank area in the Belgian part of the North Sea, just north of a Habitat Directive Area. Therefore, a dedicated monitoring programme was set-up, with focus on assessing changes in seafloor integrity and hydrographic conditions, two descriptors that define Good Environmental Status.Since extraction started in 2012, monitoring results are short-term and relate to: (1) natural variability; (2) sediment plume formation and deposition, differentiating between small and large trailing suction hopper dredgers; (3) far–field impacts, with focus on the nearby Habitat Directive Area, where ecologically valuable gravel beds occur. New insights were revealed on the three levels, though most striking was enrichment of fines in the coarse permeable sands of the gravel area. No direct relationship could yet be made between the intensive extractions and the mud enrichment, though MSFD requires further monitoring of the gravel beds, since favourable colonization and growth of epifauna is critical for the maintenance and increase of biodiversity in the Belgian part of the North Sea.

Since the installation of the wind farm foundations and associated scour protection in an area previously characterized by soft bottom sediments, the number of hard substrate associated fish and benthic species has increased markedly. At the level of a single turbine footprint a nearly 4000-fold increase in autumn biomass was observed, whereas at the level of the entire wind farm a 14-fold increase was observed. Further development of the entire Belgian wind energy zone may increase benthic biomass by as much as 3% of the current estimated benthic biomass in the Belgian part of the North Sea.