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Bolte S.,Evolutionary Ecology of Marine Fishes | Fuentes V.,CSIC - Institute of Marine Sciences | Haslob H.,Thunen Institute of Sea Fisheries | Huwer B.,Technical University of Denmark | And 6 more authors.
Marine Ecology Progress Series | Year: 2013

Repeated invasions of European waters by the ctenophore Mnemiopsis leidyi offer a unique opportunity to study population dynamics and dispersal in gelatinous zooplankton. Here we followed population establishment in 2 recently invaded areas, the North and Baltic Seas, and analysed changes in population structure during a 3 yr interval using 7 highly polymorphic microsatellites comprising 191 alleles. A second goal was to reconstruct routes of recent invasive range expansion into the Mediterranean Sea. During the study period (2008 to 2010), populations in the North Sea and Western Baltic Sea maintained their allelic composition with virtually unchanged levels of genetic diversity and between-population differentiation, demonstrating limited gene flow between the 2 regions and successful reproduction in both areas. In contrast, at the eastern distribution limit in the central Baltic (Bornholm Basin), the same measures fluctuated between years and genetic diversity decreased from 2008 to 2010. In concordance with prior ecological observations, this supports the view that M. leidyi in the central Baltic is a sink population. In the area of recent range expansion (Mediterranean Sea), we observed high population differentiation: pairwise differentiation (FST ) values between sites in Spain, France and Israel were significant and between 0.04 and 0.16. Despite this differentiation, Bayesian clustering and phylogeographic analysis support the hypothesis that all Mediterranean M. leidyi result from a secondary introduction originating from the Black Sea. Our study contributes to growing evidence that multiple invasions of the same species can vary in their degree of genetic diversity and demonstrates how genetic markers can help to resolve whether gelatinous plankton species form self-sustaining populations © 2013 Inter-Research.

Knebelsberger T.,Senckenberg Institute | Landi M.,University of Minho | Neumann H.,Senckenberg Institute | Kloppmann M.,Thunen Institute of Sea Fisheries | And 6 more authors.
Molecular Ecology Resources | Year: 2014

Valid fish species identification is an essential step both for fundamental science and fisheries management. The traditional identification is mainly based on external morphological diagnostic characters, leading to inconsistent results in many cases. Here, we provide a sequence reference library based on mitochondrial cytochrome c oxidase subunit I (COI) for a valid identification of 93 North Atlantic fish species originating from the North Sea and adjacent waters, including many commercially exploited species. Neighbour-joining analysis based on K2P genetic distances formed nonoverlapping clusters for all species with a ≥99% bootstrap support each. Identification was successful for 100% of the species as the minimum genetic distance to the nearest neighbour always exceeded the maximum intraspecific distance. A barcoding gap was apparent for the whole data set. Within-species distances ranged from 0 to 2.35%, while interspecific distances varied between 3.15 and 28.09%. Distances between congeners were on average 51-fold higher than those within species. The validation of the sequence library by applying BOLDs barcode index number (BIN) analysis tool and a ranking system demonstrated high taxonomic reliability of the DNA barcodes for 85% of the investigated fish species. Thus, the sequence library presented here can be confidently used as a benchmark for identification of at least two-thirds of the typical fish species recorded for the North Sea. © 2014 John Wiley & Sons Ltd.

Groger J.P.,Thunen Institute of Sea Fisheries | Groger J.P.,University of Rostock | Hinrichsen H.-H.,Leibniz Institute of Marine Science | Polte P.,Leibniz Institute for Baltic Sea Research
PLoS ONE | Year: 2014

Climate forcing in complex ecosystems can have profound implications for ecosystem sustainability and may thus challenge a precautionary ecosystem management. Climatic influences documented to affect various ecological functions on a global scale, may themselves be observed on quantitative or qualitative scales including regime shifts in complex marine ecosystems. This study investigates the potential climatic impact on the reproduction success of spring-spawning herring (Clupea harengus) in the Western Baltic Sea (WBSS herring). To test for climate effects on reproduction success, the regionally determined and scientifically well-documented spawning grounds of WBSS herring represent an ideal model system. Climate effects on herring reproduction were investigated using two global indices of atmospheric variability and sea surface temperature, represented by the North Atlantic Oscillation (NAO) and the Atlantic Multi-decadal Oscillation (AMO), respectively, and the Baltic Sea Index (BSI) which is a regional-scale atmospheric index for the Baltic Sea. Moreover, we combined a traditional approach with modern time series analysis based on a recruitment model connecting parental population components with reproduction success. Generalized transfer functions (ARIMAX models) allowed evaluating the dynamic nature of exogenous climate processes interacting with the endogenous recruitment process. Using different model selection criteria our results reveal that in contrast to NAO and AMO, the BSI shows a significant positive but delayed signal on the annual dynamics of herring recruitment. The westward influence of the Siberian high is considered strongly suppressing the influence of the NAO in this area leading to a higher explanatory power of the BSI reflecting the atmospheric pressure regime on a North-South transect between Oslo, Norway and Szczecin, Poland. We suggest incorporating climate-induced effects into stock and risk assessments and management strategies as part of the EU ecosystem approach to support sustainable herring fisheries in the Western Baltic Sea. © 2014 Grö ger et al.

Bernreuther M.,University of Hamburg | Bernreuther M.,Thunen Institute of Sea Fisheries | Schmidt J.,Leibniz Institute of Marine Science | Schmidt J.,University of Kiel | And 3 more authors.
Marine Ecology Progress Series | Year: 2013

Prey selectivity of Baltic herring Clupea harengus and sprat Sprattus sprattus was studied in the Bornholm Basin, Baltic Sea, in June 2001. A total of 165 sprat stomachs (10 to 15 cm total length, TL) and 214 herring stomachs (12 to 30 cm TL) were analysed. The diel vertical distribution of zooplankton prey was analysed by multi-net samples; clupeid distributions were estimated by hydroacoustic measurements. These measurements enabled us to describe the diel feeding rhythm and to estimate vertically resolved selectivity indices for the 2 most important zooplanktivores in the Baltic Sea. Diet composition of herring and sprat were similar (mainly copepods and cladocerans), resulting in strong competition. Possibly to reduce this competition, both species were partly specializing on certain prey species (sprat: Podon spp.; herring: Evadne nordmanni and Temora longicornis) and copepodite stages (sprat: adult [C6] males of Pseudocalanus acuspes; herring: C6 females of P. acuspes). Sprat and, to some extent, herring exhibited a marked shift in prey preference between day and night. Sprat mainly selected T. longicornis during the day and Podon spp. during the night, while herring mainly selected T. longicornis during the day and E. nordmanni during parts of the night. A comparison of the field stomach contents with the estimated gastric evacuation predicted by parameters based on laboratory experiments indicated that sprat fed during the night, while herring did not or only to a minor extent. Comparison of our zooplankton sampling scheme with commonly used sampling designs revealed that investigations which consider both time and stage are needed to fully understand the feeding selectivity dynamics of herring and sprat in the Baltic Sea. However, the objective of a selectivity study should determine the most appropriate zooplankton sampling scheme. © Inter-Research 2013 · www.int-res.com.

Neumann V.,Technical University of Denmark | Koster F.W.,Technical University of Denmark | Schaber M.,Thunen Institute of Sea Fisheries | Eero M.,Technical University of Denmark
ICES Journal of Marine Science | Year: 2014

Cod (Gadus morhua) recruitment in the eastern Baltic Sea is influenced by predation on early life stages by sprat (Sprattus sprattus) and herring (Clupea harengus), which is considered as one of the mechanisms preventing cod recovery in the 1990s. In the light of improved cod recruitment in the second half of the 2000s, new analyses of stomach content of sprat and herring were conducted, to elucidate the contribution of changes in predation pressure on cod recruitment. Comparison of stomach contents of sprat and herring in 2004-2008 with data from the 1990s showed a similar diet composition in the two periods; however, changes were found in the ichthyoplankton abundance and composition in the diet, indicating reduced predation pressure on cod eggs in the most recent period. The abundance of cod eggs in the field, availability of other prey, and horizontal and vertical overlap between predator and prey were investigated as potential factors influencing cod egg predation. © International Council for the Exploration of the Sea 2014. All rights reserved.

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