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Raab K.,Wageningen University | Nagelkerke L.A.J.,Wageningen University | Rijnsdorp A.D.,Wageningen University | Temming A.,Institute For Hydrobiologie Und Fischereiwissenschaft
Journal of Sea Research | Year: 2011

The diet of anchovy (Engraulis encrasicolus) in the North and Baltic Seas was studied using stomach analysis from four sampling events in different areas. Zooplanktivory was confirmed; the most frequent prey items (in over 40% of stomachs) were copepods, malacostracan larvae and fish larvae. In the Baltic Sea, Paracalanus spp. and Pseudocalanus spp. were important in relative terms; in the German Bight, Temora spp. dominated the stomach contents. Relative abundances of prey items varied with area more than absolute abundance or presence absence of items. Moreover, the level of resolution of prey categories influenced which prey categories were considered to be most important in driving variability in stomach content. Anchovy diet is broad across the seasons, years and areas sampled, suggesting that it is not a specialist feeder in the North Sea. The similarity of diet between anchovy and other clupeids, as well as anchovy consumption of larval fish, makes the new increased anchovy population a potential intraguild predator of commercial species like herring. © 2010 Elsevier B.V.

Raab K.,Wageningen University | Nagelkerke L.A.J.,Wageningen University | Rijnsdorp A.D.,Wageningen University | Temming A.,Institute For Hydrobiologie Und Fischereiwissenschaft
Marine Ecology Progress Series | Year: 2012

European anchovy Engraulis encrasicolus increased its abundance and distribution in the North Sea during the mid-1990s and may consume similar zooplankton to and/or compete with other occupants of the North Sea like herring Clupea harengus and sprat Sprattus sprattus. The diets of adult anchovy, sprat and juvenile herring of comparable sizes, sampled close in time and space, were compared to understand how the 3 species prey on zooplankton and establish whether their diets overlap or not. Anchovy was found to be more generalist, consuming a higher diversity of prey items. Herring was more specialized, with low diversity of food items. Sprat was intermediate between anchovy and herring. The dietary overlap between anchovy and sprat was highest, followed by herring and sprat before anchovy and herring. The mean weight of stomach contents did not differ between species. We conclude that of the 3 species, anchovy is likely to be the least affected by changing plankton communities. © Inter-Research 2012.

Elliott M.,University of Hull | Borja A.,Tecnalia | McQuatters-Gollop A.,Sir Alister Hardy Foundation for Ocean Science | Mazik K.,University of Hull | And 4 more authors.
Marine Pollution Bulletin | Year: 2015

The EU Marine Strategy Framework Directive (MSFD) requires that Good Environmental Status (GEnS), is achieved for European seas by 2020. These may deviate from GEnS, its 11 Descriptors, targets and baselines, due to endogenic managed pressures (from activities within an area) and externally due to exogenic unmanaged pressures (e.g. climate change). Conceptual models detail the likely or perceived changes expected on marine biodiversity and GEnS Descriptors in the light of climate change. We emphasise that marine management has to accommodate '. shifting baselines' caused by climate change particularly during GEnS monitoring, assessment and management and '. unbounded boundaries' given the migration and dispersal of highly-mobile species. We suggest climate change may prevent GEnS being met, but Member States may rebut legal challenges by claiming that this is outside its control, force majeure or due to 'natural causes' (Article 14 of the MSFD). The analysis is relevant to management of other global seas. © 2015 Elsevier Ltd.

Acheampong E.,Institute For Hydrobiologie Und Fischereiwissenschaft | Nielsen M.H.,Technical University of Denmark | Mitra A.,University of Swansea | St. John M.A.,Technical University of Denmark
Ecological Modelling | Year: 2012

Ultimately, the structure and functioning of marine ecosystems is defined by the transfer of autotrophic production to higher trophic levels and selective consumption of these autotrophs by predators. Hence, feeding regulation via modification of grazing and food incorporation by predators is critical for understanding and predicting the dynamics of ecosystems. In marine ecosystem and biogeochemical models, feeding regulation by consumers is assumed to be mainly dictated by food quality (Q), which is determined using food quality modules (FQMs) that mimic a consumers' ability to anticipate fitness consequences for feeding on specific prey items. Current FQMs are based on frameworks that a priori identify specific food components, usually nitrogen (N), and/or phosphorus, as limiting. This negates the importance of consumer physiology, and ignores biochemical constrains on the limiting role of chemical elements in animal production. To help address these problems, we propose a new adaptive approach that bases Q on consumers' capacity for food uptake and metabolic physiology. Uniquely, it (i) has separate pathways for the utilisation of carbon (C) associated with proteins, lipids and carbohydrates, (ii) considers stage-specific structural biochemical requirement of animals, and (iii) does not treat consumers' structural demand for carbon as a " unitary requirement" but discriminates among the required biochemical forms of carbon. The approach is applicable to all heterotrophs. In the example given here the model has been configured to represent the calanoid copepod Acartia tonsa. Consistent with experimental observation, but unlike previous models, our model predicts the relationship between Q and food C:N to be unimodal with a maximum Q only at the threshold C:N for biomass production. Results suggest that prey C:N ratios may be irrelevant for food quality due to macromolecular biochemical constrains on the utilisation of chemical elements. This result emphasizes the importance of biochemical substances in animal nutrition and production as well as the necessity of developing food quality models able to adapt to the biochemical needs of the consumer. © 2011 Elsevier B.V.

Acheampong E.,Institute For Hydrobiologie Und Fischereiwissenschaft | Campbell R.W.,Prince William Sound Science Center | Diekmann A.B.S.,Institute For Hydrobiologie Und Fischereiwissenschaft | John M.A.St.,Institute For Hydrobiologie Und Fischereiwissenschaft
Marine Ecology Progress Series | Year: 2011

Food availability has been linked to changes in the biochemical composition of zooplankton eggs. However, a number of species are capable of resource storage and are thereby able to use accumulated reserves for reproduction during periods of poor food conditions. Conversely, in species such as Acartia tonsa with limited storage capacities, there can be a strong dependence of egg composition on ambient food conditions. The aim of this study was to determine the effect of food availability on the carbohydrate, protein and fatty acid composition of A. tonsa females and their eggs after being fed with different concentrations of the cryptophyte Rhodomonas baltica. During the experiments, no significant differences in the biochemical composition of females were observed, although egg protein composition was higher in food-limited females. We propose that the production of protein-rich eggs by food-limited copepods is a reproductive strategy for ensuring the survival of offspring during poor feeding conditions. In terms of their relative biochemical makeup, there were no significant differences between both adults and eggs of A. tonsa and their prey R. baltica. However, these biochemical similarities did not influence egg production. Rather, higher biochemical similarities were observed between R. baltica and eggs when females were food limited. These findings suggest that food-limited females may moderate the cost of reproduction by producing eggs without much modification tothe substrates they ingest. © Inter-Research 2011.

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