Papers by Jan Vanaverbeke
PLoS ONE, 2014
Impact assessments of offshore wind farm installations and operations on the marine fauna are per... more Impact assessments of offshore wind farm installations and operations on the marine fauna are performed in many countries. Yet, only limited quantitative data on the physiological impact of impulsive sounds on (juvenile) fishes during pile driving of offshore wind farm foundations are available. Our current knowledge on fish injury and mortality due to pile driving is mainly based on laboratory experiments, in which high-intensity pile driving sounds are generated inside acoustic chambers. To validate these lab results, an in situ field experiment was carried out on board of a pile driving vessel. Juvenile European sea bass (Dicentrarchus labrax) of 68 and 115 days post hatching were exposed to pile-driving sounds as close as 45 m from the actual pile driving activity. Fish were exposed to strikes with a sound exposure level between 181 and 188 dB re 1 mPa 2 .s. The number of strikes ranged from 1739 to 3067, resulting in a cumulative sound exposure level between 215 and 222 dB re 1 mPa 2 .s. Control treatments consisted of fish not exposed to pile driving sounds. No differences in immediate mortality were found between exposed and control fish groups. Also no differences were noted in the delayed mortality up to 14 days after exposure between both groups. Our in situ experiments largely confirm the mortality results of the lab experiments found in other studies. the supplemental files uploaded together with this revision. The exception is (line 233-236) ''the energy needed per strike was positively correlated with the penetration depth, which means that the type of sediment layers that have to be penetrated forms a key factor in terms of energy requirements (Spearman's rank correlation coefficient 0.94 (C8); 0.90 (B3); 0.94 (G7); 0.92 (G8)).'' This data is obtained from a third party, Northwind and the request to publish the hammer logs data of the four monopiles underlying our finding was formally declined. Northwind stated that ''This data is project specific and contains confidential information with regard to the installation methodology, the impact and the soil conditions. A third party may, upon request, be granted access to the data of the hammer logs, provided that (i) its request is sufficiently motivated (fulfillment of this criteria lies in Northwind's sole discretion) and (ii) that an NDA in the form and conditions imposed by Northwind is executed between parties. All such requests may be directed to [email protected].
We investigated the temporal variation of pelagic and benthic food sources in the diet of two mar... more We investigated the temporal variation of pelagic and benthic food sources in the diet of two marine polychaetes: a macrobenthic omnivore (Nephtys hombergii) and a suspension-deposit feeder (Lanice conchilega) by means of fatty acid (FA) biomarkers and compound-specific stable isotope analysis (CSIA). FA biomarkers in the suspended particulate matter roughly mirrored phytoplankton dynamics in the water column, consisting of a small diatom dominance early spring, succeeded by a mass Phaeocystis peak followed by a mixed diatom-dinoflagellate bloom. Deposition and subsequent bacterial degradation of the phytoplankton bloom were also reflected in sediment FA biomarkers. The main distinction in FA biomarker concentration within macrobenthic tissue was observed at the species level (48% of variation), the diet of L. conchilega consisting of bacteria and diatoms and that of N. hombergii also of diatoms, but including more dinoflagellates and invertebrates. Temporal variation explained 17%: the two species retained more bacterial and Phaeocystis markers before the bloom, while they accumulated more poly-unsaturated FA after the bloom. CSIA revealed increased accumulation or biosynthesis of poly-unsaturated FA from the suspended matter in L. conchilega upon bloom deposition, which is probably related to energy storage for gametogenesis. In contrast, bloomdependent accumulation or biosynthesis of FA was not detected in N. hombergii, probably because of its reliance on invertebrate prey.
The role of a dominant macrobenthic polychaete, Scolelepis squamata, in the colonisation of defau... more The role of a dominant macrobenthic polychaete, Scolelepis squamata, in the colonisation of defaunated tropical sediments by sandy-beach nematodes was investigated and compared with a previous colonisation experiment carried out on a temperate sandy beach. Experimental cylinders, equipped with lateral windows allowing infaunal colonisation, were filled with defaunated sediment containing two treatments, with and without S. squamata. These cylinders were inserted into microcosms containing sediment with indigenous meiofauna collected from the field. The treatments were incubated in the laboratory at ambient temperature and salinity for 7, 14 and 21 days. The nematode assemblages in both treatments did not differ in composition between treatments and from the natural assemblages, suggesting that all the species were equally able to colonise the experimental cores. The presence of the polychaete did not affect the development of the nematode community composition, in contrast to the results from a previous temperate-beach experiment. However, our results did not indicate whether the difference in results was caused by the different behaviour of the polychaete specimens, or by the different composition and response of the present nematode community.
Lately, across-shore zonation has been found to be more important in structuring the nematode com... more Lately, across-shore zonation has been found to be more important in structuring the nematode community of a tropical macrotidal sandy beach than microhabitat heterogeneity. To evaluate whether this zonation pattern applies to a temperate beach, a macrotidal ridge-and-runnels sandy beach in the North Sea was studied. We investigated whether a similar zonation occurs in sandbar and runnel microhabitats, and whether the runnels harbour a different community from the subtidal. Our results indicate that nematode communities from runnel and sandbar habitats are significantly different. In addition, horizontal zonation patterns for nematode communities differ between both habitats. Nematode assemblages from sandbars are divided to lower, middle and upper beach while upper and middle runnels cluster together. The subtidal and upper runnels showed dissimilar nematode assemblages, although runnels showed the same dominant species (Daptonema normandicum), which increases its abundance towards the upper runnels. This study illustrates the importance of microhabitat heterogeneity, which resulted in different zonation patterns across the sandy beach examined. The divergent zonation between sandbars and runnels in the macrotidal temperate sandy beach, compared with the pattern observed for a subtropical sandy beach with similar morphodynamics, indicates that generalizations about nematode distribution patterns should be made with caution.
1. Biodiversity conservation often focuses on threatened or rare species. While this structural a... more 1. Biodiversity conservation often focuses on threatened or rare species. While this structural asset of biodiversity is indeed important, the functional diversity aspect has to be considered as an even more important criterion for marine management and conservation. This paper explores the use of functionally important ecosystem engineers in North Sea management approaches.
Two offshore w ind farm s became fu n ctio n a l in the Belgian part o f the North Sea during 200... more Two offshore w ind farm s became fu n ctio n a l in the Belgian part o f the North Sea during 2009 and 2010 on respectively the T ho rnto nb a nk (C-Power) and the Bligh Bank (Belwind). D uring the past five years, a m on itoring program m e has been carried o ut to determ ine the baseline situation on the soft-sedim ent m acrobenthos in these areas, to ge th er w ith any p rim ary im pacts th a t could have arisen during and after co nstruction. D uring the firs t and second years a fte r im plem entation o f the turbines no large-scale im pacts were detected on the m acrobenthos (Reubens e t al., 2009;. Therefore, a small scale sam pling strategy was carried o ut during 2010 to detect any impacts around the fifth gra vity based tu rb in e on the Thorntonbank. M acrobenthic com m unities can be h ighly dependent o f sedim entological characteristics such as median grain size and organic m atter content (Pearson and Rosenberg, 1978;. The increased epifaunal com m unities co lo nizing the hard substrates (turbines) could produce organic enriched sediments, possibly m odifying the soft-sedim ent m acrobenthic com m unities (Kerckhof e t al., 2010). Sediment samples were taken along fo u r gradients, tw o parallel and tw o perpendicular to the currents. Samples at one and seven metres from the scour protection systems (boulders) were taken during June and September 2010 by divers. Samples fu rth e r away fro m the boulders (1 5, 25, 50, 100, 200m ) were taken d urin g Septem ber 2010 using a Van Veen grab on a small research vessel. To detect organic enrichm ent in the sedim ents several elem ents were analysed such as to ta l organic matter, chlo ro p hyll a and fa tty acid concentrations. The m acrobenthos was identified to species level and th e ir subsequent biomass was determ ined. First results show a s h ift from Nephtys cirrosa com m unities to a dom inance in C orophium acherusicum and Lanice conchilega at the closest samples to the boulders. These results show the im portance o f a small-scale m o n itoring strategy to determ ine the effects o f w ind tu rb ine s on the soft-sedim ent m acrobenthos. Any im pact detected at small-scale can be extrapolated to a possible large-scale impact. Since fu tu re plans have been made to construct additional w ind farm s in the Belgian part o f the North Sea it is very im p o rta n t to understand the possible changes th a t could occur in the marine environm ent.
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Papers by Jan Vanaverbeke