Santos S.,Netherlands Institute for Sea Research |
Aarts G.,Netherlands Institute for Sea Research |
Aarts G.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
Luttikhuizen P.C.,Netherlands Institute for Sea Research |
And 4 more authors.
Marine Ecology Progress Series | Year: 2012
The development and maintenance of spatial patterns and the way they affect the dynamics of populations and ecosystems is a key issue in ecology. Since each individual and each species experiences the environment on a unique range of scales, it is vital to determine the spatial scales across which organisms interact with each other and the structuring influence of their environments, which can be achieved by analyzing species' distribution patterns. Here, the spatial variation in the distribution of Scrobicularia plana is described for 4 intertidal areas along the species' distributional range. Spatial autocorrelation correlograms based on Moran's coefficient reveal that while the Trondheim (Norway) population was randomly distributed, at Minho (Portugal), the Westerschelde, and the Wadden Sea (both in The Netherlands) populations were aggregated. Patch diameter varied from 150 to 1250 m, in Minho and Westerschelde, respectively; while in the Wadden Sea, patches of 4 to 10 km were detected. Comparisons of spatial patterns with those of other co-occurring bivalve species (Abra tenuis, Cerastoderma edule, and Macoma balthica) revealed that S. plana's distribution was generally patchier. The distribution of S. plana was correlated with sediment type at Westerschelde and Trondheim, but not Minho. The observed differences in distribution patterns and their correlation with environmental factors reveal that spatial patterns of S. plana are site-specific rather than species-specific. © Inter-Research 2012.
van Walraven L.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
van Walraven L.,University of Groningen |
Mollet F.M.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
van Damme C.J.G.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
And 2 more authors.
Journal of Sea Research | Year: 2010
Changes in the onset of sexual maturation, reproductive investment and growth of North Sea plaice are studied between three periods: 1900s, 1980s and 2000s. Probabilistic maturation reaction norms of both males and females, describing the probability of becoming mature conditional on age and size, shifted towards smaller sizes and younger ages, indicating a fisheries-induced evolutionary change. A higher rate of change was observed during the past 20 years, which may be related to higher temperature conditions. Reproductive investment was estimated from the decrease in lipid, protein, dry weight content and condition factor of the whole body between pre- and post-spawning adults. Reproductive investment expressed as the energy loss over the spawning period increased with body size from 19% at 20 cm to 30% at 40 cm in males and from 35% at 30 cm to 48% at 50 cm in females. No change in reproductive investment could be detected between the 1980s and the 2000s. Von Bertalanffy (VB) growth parameters showed a decrease in L∞ the asymptotic size and an increase in K, the velocity to reach L∞, in both males and females. The changes in VB growth are consistent with an increase in energy acquisition and reproductive investment. The observed changes in maturation, reproductive investment and growth are consistent with fisheries-induced evolution, but the changes in reproductive investment and growth need further investigation to disentangle the role of phenotypic plasticity. © 2009 Elsevier B.V. All rights reserved.
PubMed | University Utrecht, Scientific Institute of Public Health WIV ISP, University of Veterinary Medicine Hannover, University of Liège and 6 more.
Type: | Journal: Veterinary parasitology | Year: 2016
The occurrence of the zoonotic protozoan parasite Toxoplasma gondii in marine mammals remains a poorly understood phenomenon. In this study, samples from 589 marine mammal species and 34 European otters (Lutra lutra), stranded on the coasts of Scotland, Belgium, France, The Netherlands and Germany, were tested for the presence of T. gondii. Brain samples were analysed by polymerase chain reaction (PCR) for detection of parasite DNA. Blood and muscle fluid samples were tested for specific antibodies using a modified agglutination test (MAT), a commercial multi-species enzyme-linked immunosorbent assay (ELISA) and an immunofluorescence assay (IFA). Out of 193 animals tested by PCR, only two harbour porpoise (Phocoena phocoena) cerebrum samples, obtained from animals stranded on the Dutch coast, tested positive. The serological results showed a wide variation depending on the test used. Using a cut-off value of 1/40 dilution in MAT, 141 out of 292 animals (41%) were positive. Using IFA, 30 out of 244 tested samples (12%) were positive at a 1/50 dilution. The commercial ELISA yielded 7% positives with a cut-off of the sample-to-positive (S/P) ratio50; and 12% when the cut-off was set at S/P ratio20. The high number of positives in MAT may be an overestimation due to the high degree of haemolysis of the samples and/or the presence of lipids. The ELISA results could be an underestimation due to the use of a multispecies conjugate. Our results confirm the presence of T. gondii in marine mammals in The Netherlands and show exposure to the parasite in both the North Sea and the Eastern Atlantic Ocean. We also highlight the limitations of the tests used to diagnose T. gondii in stranded marine mammals.
Hufnagl M.,University of Hamburg |
Peck M.A.,University of Hamburg |
Nash R.D.M.,Norwegian Institute of Marine Research |
Pohlmann T.,University of Hamburg |
And 2 more authors.
Journal of Sea Research | Year: 2013
We explored the hypothesis that spawning ground locations of North Sea plaice reflect the locations of nursery grounds using drift scenarios based on a baroclinic, shallow-water circulation model (HAMSOM). The transport of pelagic eggs and larvae was simulated each year from 1975 to 2006 using in situ forcing, temperature-dependent development and stage-specific behaviour of eggs and larvae. This long-term simulation period also allowed us to explore climate effects. A release position was considered a potential and suitable spawning site if larvae from that area reached coastal nurseries after the onset of metamorphosis. In general, larvae were transported in an anti-clockwise direction and settled in nurseries that were relatively close to the release positions. Spawning locations that were offshore were poorly connected to nursery grounds while those closer to the shore had higher connectivity. Simulated suitable spawning locations broadly agreed with the main centres of egg production (English Channel, Southern Bight, German Bight), except for the known spawning grounds south of Dogger Bank. Over the 31-year simulation period, positive and negative trends in transport success were found for the western and eastern parts of the North Sea, respectively. Changes in the west (Flamborough Head) were mainly due to changes in water circulation patterns whereas those in the east (northern German Bight) were induced by changes in both currents and water temperature. The implications of these findings, and the significant correlation between changes in drift and recruitment, suggest that climate-driven changes in the suitability of nursery grounds will directly affect the distribution and productivity of plaice in the North Sea. © 2012 Elsevier B.V.
Wijnhoven S.,Netherlands Institute of Ecology |
Escaravage V.,Netherlands Institute of Ecology |
Herman P.M.J.,Netherlands Institute of Ecology |
Smaal A.C.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
Hummel H.,Netherlands Institute of Ecology
Marine Ecology | Year: 2011
To study the possible environmental impact of hydraulic cockle-dredging on macrobenthic communities and the environment, a fishing experiment was executed on a tidal mudflat in the Oosterschelde (SW Netherlands) according to a BACI (before-after-control-impact) design. Following the characterization of the initial situation, a part of the mudflat was commercially fished, after which dredged and undredged areas were compared on the basis of macrofauna descriptors and sediment constitution approximately 2months (short term) and 1year (mid-long term) after fishing. Whereas a clear reduction of the larger Cerastoderma edule cockles (>23mm) in the fished areas was found, no effect of dredging on total macrofauna densities or median grain size was observed. No negative effect of fishing on total macrofauna biomass was found; in contrast, an increase of the biomass of the non-target species almost compensated for the loss in weight due to the extraction of the larger cockles. No significant effect of dredging on species diversity, richness or evenness was found in the short or mid-long term, these descriptors tending to have increased rather than decreased in the dredged plots after 1year. The selective fishing for larger cockles reduced the average cockle size, but 1year after fishing the average size had returned to the initial values in the dredged area. However, compared to the control area, the average size might still be reduced, as the size of the cockles in the control area also increased during the year. Local environmental conditions, with their specific macrobenthic communities, seem to be crucial for the type of effects and the impact of dredging. It is therefore of eminent importance to follow a research design with pre-defined environmental conditions, rather than a comparison of different areas that are open or closed to fisheries. The present study based on a BACI approach indicates that mechanical cockle fisheries had no overall negative impact in our study area. © 2011 Blackwell Verlag GmbH.
Hufnagl M.,Institute for Hydrobiology and Fishery Science |
Temming A.,Institute for Hydrobiology and Fishery Science |
Siegel V.,Johann Heinrich Von Thunen Institute |
Tulp I.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
Bolle L.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies
ICES Journal of Marine Science | Year: 2010
Total mortality (Z, year-1) of southern North Sea brown shrimp (Crangon crangon) was determined as Z = θK, based on the von Bertalanffy length-growth constant (K, year-1) and θ derived from length-based methods. Mortality estimates were based on length frequency distributions obtained from four long-term dataseries (1955-2006): German Demersal Young Fish Survey, Dutch Demersal Fish Survey, and two German Bycatch series (Büsum and East Frisia). Four methods to estimate θ and L∞ were evaluated. Highest total mortality (Z = 8 year-1) was estimated for the early 1990s, and the lowest (Z = 4 year-1) for the 1960s. Accounting for these differences, a median Z rather than mean values was calculated for the whole series, and the value ranged from 5.74 (Ssentongo and Larkin method), through 5.65 (Beverton and Holt method) and 5.64 (Jones and Zalinge method), to 5.35 (length-converted catch curves). Over the whole period, an increase in θ and a decrease in the proportion of shrimps >60 mm in the catch was observed, whereas asymptotic length L∞ remained constant (at 79.3 mm total length). © 2009 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.
Skoczynska E.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
Leonards P.,VU University Amsterdam |
De Boer J.,VU University Amsterdam
Analytical Methods | Year: 2013
Alkylated polycyclic aromatic hydrocarbons (alkyl-PAHs) are ubiquitously present in the environment and they are recognized as a toxicologically hazardous group. The biggest obstacle in the assessment of environmental risks of alkyl-PAHs is identification and quantification; the complete (chromatographic) separation of alkylated homologues is difficult if not impossible. Therefore, alkyl-PAHs are usually identified as a group of isomers with the same degree of alkylation and quantified as one group using one chromatographic response factor. In this study we demonstrate that the relative response factors of twenty-three methylated PAHs with the same molecular weight of 242 (six methyl-chrysenes, twelve benz[a]anthracenes and five benzo[c]phenanthrenes) range from 0.1 for 12-methylbenz[a]anthracene and 4-methylbenzo[c]phenanthrene to 1.7 for 6-methylbenz[a]anthracene. Quantification of methylated PAHs with equal molecular weights as a group using the same relative response factor can thus overestimate or underestimate their concentrations and, therefore, the toxicological risk of an environmental sample. A two-dimensional gas chromatography method was developed with which fourteen methylated PAHs (Mw = 242) could be separated. Twelve of them were identified and quantified in Elbe River sediment. © 2013 The Royal Society of Chemistry.
Van Der Veer H.W.,Netherlands Institute for Sea Research |
Koot J.,Netherlands Institute for Sea Research |
Aarts G.,Netherlands Institute for Sea Research |
Aarts G.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
And 6 more authors.
Marine Ecology Progress Series | Year: 2011
Since 1975, juvenile flatfish (plaice and flounder) populations have been monitored at the Balgzand intertidal and, based on this data series (1975-2007), the interannual patterns in predation pressure were quantified. Temporal patterns in abundance have changed greatly, especially for plaice. Up to the early 1980s, 3 year classes (0-, I- and II-group) were present and growing up in the area, but from the late 1980s onwards, densities of the I- and II-group plaice dropped from a few hundred individuals per 1000 m 2 to levels close to zero. It appears that the Balgzand intertidal has lost its nursery function for I- and II-group plaice, although feeding conditions have remained the same or even slightly increased since the late 1970s. The absence of I- and II-group flatfish in the intertidal cannot be explained at present; however, processes operating offshore are most likely involved. As a consequence, the annual predation pressure by juvenile flatfish upon the intertidal macrozoobenthos dropped by 94%, declining from an average of approximately 5 to 0-25 g ash free dry mass m -2. Such a decline in top-down predation may not only have directly influenced the macrozoobenthic community, but may also have indirectly affected food availability and accessibility for other top predators (e.g. shorebirds). © Inter-Research 2011.
Rusina T.P.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
Korytar P.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
de Boer J.,VU University Amsterdam
International Journal of Environmental Analytical Chemistry | Year: 2011
Four quantification methods for short-chain chlorinated paraffins (SCCPs) or polychlorinated alkanes (PCAs) using gas chromatography electron capture negative ionisation low resolution mass spectrometry (GC-ECNI-LRMS) were investigated. The method based on visual comparison of congener group patterns of external standards used for quantification and fish samples was very sensitive for the choice of the quantification standard. Two other methods used the existing relation of the response factors with the chlorine content of SCCP mixtures for quantification. Results from the three methods above deviated from nominal values less than 20%. This was ~50% when individual PCA standards were applied for quantification of SCCPs. The deviation is probably caused by the fact that only C10 carbon chain length standards with 5-9 chlorine atoms could be used. However, quantification using individual PCA standards is a promising method provided more standards will become commercially available. The clear advantage is that the standards are defined, which makes quantification comparable between different laboratories. Application of all four quantification methods to the analysis of four different fish samples gave results that agreed with the median values within ±40%. © 2011 Taylor & Francis.
de Boer J.,VU University Amsterdam |
Dao Q.T.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
van Leeuwen S.P.J.,VU University Amsterdam |
Kotterman M.J.J.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies |
Schobben J.H.M.,Wageningen IMAResearch Institute for Marine Resources and Ecosystem Studies
Environmental Pollution | Year: 2010
Because of their excellent properties as a biomonitor, yellow eels (Anguilla anguilla) have been used for time-trend monitoring of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and tetrabrominated diphenylether (tetra-BDE). The program has now lasted for thirty years and has delivered valuable information on trends and spatial differences of these compounds in the delta of the rivers Rhine and Meuse and other Dutch canals, rivers and lakes. Specific local PCB, HCH and dieldrin contaminations were identified. Temporal trends show a slow decrease of PCB concentrations since 1977. Eels from the rivers Rhine and Meuse still exceed present European maximum residue limits for dioxin-like PCBs. Apart from some exceptions, OCP and tetra-BDE concentrations have also decreased, and more than those of PCBs. Fat contents of eel have decreased from an average of 21 to ca. 13%. This decrease in fat contents, coincides with the strong reduction of the European eel stock. © 2010 Elsevier Ltd. All rights reserved.