Search

To monitor the impact on birds following the construction of two offshore wind farms in the Belgian part of the North Sea, a twofold strategy was followed. Monthly ship-based seabird surveys allowed for a detailed displacement effect assessment, while radar research aimed at studying avoidance behaviour and barrier effects. Both methods provided input data for collision risk modelling in order to assess bird collision rates. Three years after the completion of the wind farm at the Bligh Bank, it showed that northern gannet, common guillemot and razorbill avoid the wind farm, while numbers of lesser black-backed and herring gull increased significantly. Collision risk modelling learned that gulls in particular are at risk of colliding with the turbine blades, with up to 2.4 bird strikes per turbine per year.

The elusive and highly mobile harbour porpoise is the most abundant cetacean in Belgian waters, seasonally reaching average densities of more than 2 animals/km². Operational wind farms may affect the porpoise habitat in various negative and positive ways, such as through the introduction of possibly deterrent noise or the introduction of artificial substrates with associated porpoise prey fish. Porpoises show concentration areas in Belgium, none of which being linked to the wind farms so far. Because of the spatial resolution being too low, aerial surveys will need to be complemented with targeted passive acoustic monitoring in the future.

The harbour porpoise Phocoena phocoena is currently the most abundant marine mammal in Belgian waters. Large-scale changes in the distribution of this top predator in the North Sea have occurred during the last decades, possibly caused by changes in food availability. An analysis of the strandings database 1970-2011, containing data on 737 harbour porpoises, revealed that throughout the year two peaks in strandings occurred: one in spring, for an important part caused by the strandings of animals incidentally bycaught in fishing gear, and a second one during summer. Most of the stranded animals were juveniles, with a higher percentage of males than females. As could be expected, bycaught animals were on average heavier than equally sized naturally died animals, and they had a thicker blubber layer. In naturally died animals the blubber layer was thicker in winter than in summer, illustrating the insulating function of the blubber layer besides its function as an energy storage.We investigated the stomach content of 64 harbour porpoises washed ashore or bycaught in Belgium between 1997 and 2011. Ten of the stomachs were empty. Fish contributed to most of the prey remains. In total we found the remains of 19 fish species belonging to 10 families. The numerically most important prey items in juveniles were gobies (Gobiidae). Reconstructing the original weight of the prey items revealed that gobies constituted the most important prey by weight, but that larger sandeels (Ammodytidae) and to a lesser extent gadoids (Gadidae) were also important. In adults the majority of prey items were gobies and sandeels, but the reconstructed weight of the stomach content revealed that sandeels and gadoids constituted by far the most important prey. Surprisingly, clupeids (Clupeidae) did not contribute much to the diet, although the return of the harbour porpoise is often linked to an increase in herring Clupea harengu stocks in the southern North Sea. Also no twaite shad Alosa fallax were found, although this diadromic fish is common again in the area. A small number of smelt Osmerus eperlanus was found in some of the recently stranded harbour porpoises. Smelt is a diadromic fish of which densities are increasing from very low levels. The fact that juvenile harbour porpoises had apparently fed on large quantities of small bottom fish may help to explain why they were more prone to bycatch than adults. The analysis revealed that a gradual shift occurs in the feeding habits of harbour porpoises while becoming adults: from small benthic fish towards larger fish taken from the water column.

The impact of pile driving on marine mammals is one of the major environmental concerns in offshore wind farm (OWF) construction. We assessed the impact of pile driving for the construction of the C-Power OWF (Thorntonbank, Belgian waters) on the spatial and temporal distribution of harbour porpoises during the season in which they occur in a high density in Belgian waters. We combined data collected by passive acoustic monitoring (PAM) devices, moored inside and outside the project area, with standardised aerial surveys covering the Belgian part of the North Sea. The combination and integration of both techniques proved very useful as PAM results in low spatial but high temporal resolution data, while aerial surveys have a complementary low temporal but high spatial resolution. At the end of March 2011, just before construction activities started, aerial surveys yielded an estimate of 2.5 harbour porpoises/km2. Density estimates in mid April 2011, after the start of the co. Although a decreasing density in Belgian waters towards the end of April should be considered as normal (cf. seasonal migration), changes in the spatial distribution between pre-and post-piling suggested harbour porpoise disturbance. This pattern was further explored with PAM, which indeed showed a clear fine-scale match between acoustic harbour porpoise detections and piling activities. Immediately upon the start of piling activities, harbour porpoise detections at a few km from the piling site fell to virtually zero. After the cessation of piling it took hours to days before new detections were made at this location. Aerial surveys allowed quantifying the distance over which an apparent impact occurred at around 22 km, with a repopulation of part of the area observed after one day with no piling.

Offshore wind farms generate underwater noise during construction, operation and decommissioning. Different foundation designs are in use for offshore wind farms. Steel monopiles, jackets made of four steel pinpiles and gravity-based foundations are applied in the Belgian part of the North Sea. Both monopiles and jacket pinpiles are hammered into the bottom and as such excessive noise is generated during their installation. This paper aims at comparing the emitted underwater noise generated during the piling activities of two wind farms, each using a different type of pile foundation: steel monopiles were used in the Belwind wind farm (Bligh Bank), while jacket pinpiles were chosen for the C-Power project (phases 2 and 3) on the Thorntonbank. Underwater noise was measured from a rigid hull inflatable boat at various distances from the pile driving location during the installation of steel monopiles and pinpiles. Analysis focused on the quantification of the discontinuous impulsive pile driving-generated underwater noise. Zero to peak sound pressure level (Lz-p), unweighted sound exposure level (SEL), cumulative SEL and 1/3 octave spectra were computed in order to quantify and compare the underwater noise. Lz-p and SEL were normalized to 750 m distance from the piling location. Piling of the monopiles generated a Lz-p between 179 and 194 dB re 1µPa. Although piling of the smaller pinpiles was expected to be less noisy, no significant differences with monopiling could be demonstrated (pinpiling Lz-p: 172-189 dB re 1 µPa). Similarly, also SEL, varying between 145 and 168 dB re 1 µPa2s, exerted no statistical difference between mono- and pinpiling and furthermore near identical spectra were measured for both types of piling. The rather wide variability within and broad overlap between both types of piling can possibly be attributed to the (small scale) differences in bottom type as well as in the setup used. However, the radius of discomfort in the harbour porpoise Phocoena phocoena was estimated at 30 km and 19 km for monopiles and pinpiles, respectively. Furthermore, the pinpiling (four pinpiles per foundation) took about 2.5 times more time than the monopiling and will as such have a prolonged impact onto the marine fauna. When standardised to megawatt installed (3 MW turbines on the monopiles and 6 MW turbines on the jacket foundations) both types of piling will score about equally.

In this contribution, the species composition and ecological succession of the biofouling on the subtidal zone (circa littoral) of selected foundations of two offshore wind farms in the Belgian part of the North Sea, the C-Power farm on the Thorntonbank and the Belwind farm on the Bligh Bank, are studied through time. As observed in many other studies, the colonization of the bare substratum has been very fast in the two studied wind farms. No less than 50% of the total species pool (41 taxa out of 78 taxa) was shared between both wind farms and both wind farms were dominated by the amphipod Jassa herdmani with up to 90000 ind./m2 (i.e. about 70% of the enumerable fauna). Other dominant species in both wind farms comprised the starfish Asterias rubens and the amphipod Stenothoe valida. The first year of the succession also showed a highly similar trajectory, with particularly mobile species, e.g. J. herdmani and Corophium acherusicum displaying a typical summer – winter oscillation pattern in both wind farms. This similarity was however less obvious for the sessile species such as Pomatoceros triqueter and Clytia hemisphaerica, and seemed to strongly diverge after the first year. The concrete gravity based foundations (GBFs) at the Thorntonbank hosted more species than the steel monopiles at the Bligh Bank (70 taxa versus 49 species). The presence of some coastal, soft sediment species such as the bivalves Abra alba and Mysella (Kurtiella) bidentata, only in the C-Power farm, further contributed to the dissimilarity between both wind farms. The biofouling on both wind farms exhibits direct influence by the same pool of species originating from the surrounding artificial and natural hard substrata. As for shipwrecks, specific features of the studied structures such as verticality, substratum composition or lower depths may explain specific patterns of taxonomic composition such as an impoverished sessile epifauna compared to the surrounding natural hard substrata. Predatory activities are an important factor controlling the succession of sessile species on the substratum. The high degree of patchiness suggests that the colonization process is still ongoing and the mature state, the Metridium senile biotope, characteristic for this type of substrata in the North Sea is not fully reached yet. Apart from the slipper limpet Crepidula fornicata, no introduced species have been observed thus far in the permanently submerged part of the wind turbine foundations. This observation contrasts with the intertidal and splash zone, where many introduced species were present in the biofouling community.

pouting; acoustic telemetry; dummy transmitter; survival rate

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.

A substantial expansion of offshore wind farms in the North Sea has been planned, inducing a growing interest in the effects of these artificial habitats on the marine environment. Numerous researches have been done to consider the possible effects of wind farms. However, to date little research investigated actual effects on the ichthyofauna.This study provides the first insights into the use of the artificial hard substrates by Trisopterus luscus (pouting) at the Thorntonbank wind farm in the Belgian part of the North Sea.Scuba diving operated visual surveys around one wind turbine revealed a distinctly higher pouting population size and biomass (i.e. 22 000 individuals yielding a total biomass of 2700 kg) as compared to the population size present at the soft sediments surrounding the wind turbines. Stomach content analyses further demonstrated the dietary preference for prey species that lived on the turbines (i.e. Jassa herdmani and Pisidia longicornis). Yet, the present study clearly demonstrates that wind turbines built at sea may attract fish populations considerably, possibly related to the enhanced provision of resident food items on the turbines.

The harbour porpoise Phocoena phocoena is currently common in the Belgian part of the North Sea (BPNS), after decades of virtual absence. This article describes the results of aerial surveys to assess its distribution and density in Belgian waters, in concert with the first results of tests with passive acoustic monitoring devices (Porpoise Detectors - PoDs), and a basic analysis of strandings. The strandings data over four decades clearly demonstrate an increase of harbour porpoises in the BPNS, with only few stranded animals between 1970 and 1997 (0 to 6 per year), increasing numbers between 1998 and 2004 (8 to 40 per year), and even higher numbers between 2005 and 2009 (62 to 94 per year). The combined results of aerial surveys, strandings monitoring and tests with passive acoustic monitoring reveal a seasonal pattern, with harbour porpoises being abundant from February to April, and more scarce from May to January. Average densities in 2008 and 2009, as estimated by aerial monitoring covering most of the BPNS (with the exclusion of the nearshore 5 km strip), ranged from 0.05 animals per km2, or in total less than 200 animals in an area equivalent to the BPNS in August 2009, to 1.01 animals per km2, or in total almost 3,700 animals in an area equivalent to the BPNS during April 2008. In the first quarter of the year porpoises occur throughout the BPNS, including territorial waters (12 mile zone), whereas they are restricted to more offshore and northerly waters later in the year. Erratic invasions in the BPNS however blur general seasonal spatio temporal patterns, which complicates our understanding of spatial distribution and migration.

The collection of the barnacle Chirona (Striatobalanus) amaryllis (Darwin 1954) (Crustacea, Cirripedia) from the hull of a ship that had been operating for five months in the Gulf of Guinea and off Sierra Leone triggered a closer investigation of the cirriped fauna of the West African coast. Both C. amaryllis and Megabalanus coccopoma can now be added to the list of successful invasions in tropical West African waters. This discovery, as well as the circumstances of the findings, necessitates an update of the invertebrate faunal inventory of tropical West African marine waters.Keywords: Chirona amaryllis, Cirripedia, invasive aquatic species, Megabalanus coccopoma, tropical West AfricaAfrican Journal of Marine Science 2010, 32(2): 265–268

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 focuses on the importance of biophysical interactions on short-term and long-term sediment dynamics. Therefore, various biological (macrobenthos, photopigments, colloidal EPS) and physical parameters (grain size, water content, sediment stability, bed level) were determined (bi)monthly in nine sampling plots on the IJzermonding tidal flat (Belgium, 51°08'N, 2°44'E) during three consecutive years (July 2005–June 2008). Results showed that sediment stability varied on the short timescale and was directly influenced by biota, while bed level varied mainly on the long-term due to interannual variability. The short-term dynamic relationships between mud content, water content, fucoxanthin and macrobenthos density resulted in a seasonal mud deposition and erosion cycle, and directly influenced sediment stability. Moreover, macrobenthos was proven to be the most important parameter determining sediment stability. On the long-term, a shift was observed from high fucoxanthin/chla concentration, high mud content and zero to moderate densities of Corophium volutator towards low fucoxanthin/chl a and mud content and high Corophium densities, which resulted in a transition from net accretion to net erosion. However, most measured variables proved to be poor predictors for these long-term bed level changes, indicating that external physical forces, such as waves and storminess, probably were the most important factors triggering long-term sediment dynamics. Nevertheless, biota indirectly influenced bed level changes by mediating short-term changes in sediment stability, thereby influencing the erodability of the sediment. The macrobenthos, and especially the mud shrimp Corophium, was suggested as the (indirect) driving destabilising factor for the sampling plots in the IIzermonding when considering the long-term evolution.

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.