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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. Source

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. Source

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. Source

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. Source

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. Source

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