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Peters J.,University of Hamburg | Peters J.,University of Bremen | Diekmann R.,University of Hamburg | Diekmann R.,Thunen Institute for Fisheries Ecology | And 2 more authors.
Marine Ecology Progress Series | Year: 2015

Sprat Sprattus sprattus larvae were used as model organisms to evaluate whether larval lipids reflect in situ feeding conditions and can thus identify match-mismatch situations. In detail, we determined larval lipid content, growth rates based on RNA:DNA ratios, and fatty acid (FA) composition during the spawning season in the Central Baltic Sea, and evaluated these in light of feeding, mortality and recruitment (which were determined in parallel within the project 'GLOBEC Germany'). Based on the opposing trend of RNA:DNA and lipid content, as well as on previous observations, we hypothesized that lipid content and current feeding conditions are largely uncoupled in the early life stages of sprat due to reduced lipid anabolism. However, lipids still provide information in several ways: (1) segmented generalised linear models proved to be a suitable tool for identifying phases of lipid catabolism during development, with the slope reflecting size-specific environmental starvation pressure. This method detected a previously identified mismatch situation with suitable prey in the early spawning season, which increased mortality of larger larvae. (2) Estimated starvation resistance, a proxy that accounts for temperature-and sizedependent metabolism, reflected the likelihood of near future starvation of individual larvae. (3) Principal component analyses on FAs identified monthly differences in diet composition. Biomarkers indicated a dinoflagellate and/or microbial loop based carbon flux to the larvae. (4) Regression analyses revealed lower docosahexaenoic acid (DHA) levels in spring, but no obvious effect on growth. Food quality was generally high, and its impact on larval survival was less evident than that of prey size suitability. © 2015 Inter-Research. Source

Wysujack K.,Thunen Institute for Fisheries Ecology | Dorow M.,Institute for Fisheries | Ubl C.,Institute for Fisheries
Journal of Coastal Conservation | Year: 2014

Recruitment of the European eel is in decline since three decades. So far, the reasons of the decline have not been fully understood. Beside other factors, infection with the exotic swimbladder parasite Anguillicoloides crassus has been discussed as a threat to the species. In the present study monitoring results for A. crassus in eels from North German waters are presented. Between 1996 and 2011, the swimbladders of 17,219 eels from eight freshwater and coastal water areas were analyzed. Prevalence, abundance of parasites, infection intensity and severity of the damage to the swimbladder were recorded by visual inspection. In the freshwaters the prevalence was in the range of 65-83 %, whereas significantly lower values were found in the brackish waters. The differences were less clear for infection intensity but significantly lower values were found in the outermost location in the Baltic Sea. Mean damage to the swimbladders was highest in eels from the Rivers Weser and Elbe and lowest in the Baltic coastal waters. Prevalence and damage degree were stable in all waters except for two rivers, where a decreasing trend in infection intensity was found. © 2013 Springer Science+Business Media Dordrecht. Source

Peck N.,Senckenberg Institute | Peters J.,University of Hamburg | Diekmann R.,University of Hamburg | Diekmann R.,Thunen Institute for Fisheries Ecology | And 2 more authors.
Journal of Plankton Research | Year: 2014

The euryhaline, eurytherm copepod Acartia tonsa plays a key role in many marine food webs as a grazer on phytoplankton and as prey species for commercially important planktivorous fishes. The different populations of this cosmopolitan species experience a wide range of environmental conditions. This study aims to elucidate the response of A. tonsa to changes in multiple environmental factors. The effects of temperature (T), salinity (S) and the interaction of both variables on recruitment processes were investigated to show potential influences of changes in environmental conditions on its life cycle and population dynamics. Estuarine conditions appeared to be optimal for reproduction, despite the marine origin of the population. Interactive effects of T X S were more pronounced when the population was exposed for a longer period of time to constant laboratory conditions. Potential resting eggs were identified based on morphology and hatching characteristics, and were mainly produced at high S and low T. Our results emphasize the importance of investigating the combined effects of different physical factors to gain a better understanding of potential changes in population dynamics resulting from climate-induced changes in key environmental factors. © The Author 2014. Source

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