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  • 2020-2024  (26)
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  • 1
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    Juvenile Atlantic herring (Clupea harengus) use a time-compensated sun compass for orientation (2022)
    The Company of Biologists
    In:  EPIC3Journal of Experimental Biology, The Company of Biologists, 225(18), pp. jeb244607-, ISSN: 0022-0949
    Details
    Publication Date: 2023-10-12
    Description: Atlantic herring (Clupea harengus), an ecologically and economically important species in the northern hemisphere, shows pronounced seasonal migratory behaviour. To follow distinctive migration patterns over hundreds of kilometers between feeding, overwintering and spawning grounds, they are probably guided by orientation mechanisms. We tested whether juvenile spring-spawning Atlantic herring, caught in the western Baltic, use a sun compass for orientation just before they start leaving their hatching area. Fish were randomly divided into two groups, one of them clock-shifted 6 h backwards, to investigate whether they shift their orientation direction accordingly. Individual fish were placed in a circular bowl and their orientation was tested multiple times with the sun as a sole visual orientational cue. Our results show for the first time that juvenile Atlantic herring use a time-compensated sun compass during their migration. Their swimming direction was impaired, but still present, even when the sky was very cloudy, indicating additional orientation capabilities.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
    Format: application/pdf
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    PAPER (OA)
  • 2
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    Differential gene expression patterns related to lipid metabolism in response to ocean acidification in larvae and juveniles of Atlantic cod (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Highlights: • Larvae upregulate genes associated with fatty acid and glycogen synthesis under moderate ocean acidification (OA) • Larvae under high levels of OA fail to regulate • Dysfunctional metabolism and stress associated with pathologies in internal organs • Lack of differential gene regulation and stress response in juveniles correspond to a higher resilience to OA stress Elevated environmental carbon dioxide (pCO2) levels have been found to cause organ damage in the early life stages of different commercial fish species, including Atlantic cod (Gadus morhua). To illuminate the underlying mechanisms causing pathologies in the intestines, the kidney, the pancreas and the liver in response to elevated pCO2, we examined related gene expression patterns in Atlantic cod reared for two months under three different pCO2 regimes: 380 μatm (control), 1800 μatm (medium) and 4200 μatm (high). We extracted RNA from whole fish sampled during the larval (32 dph) and early juvenile stage (46 dph) for relative expression analysis of 18 different genes related to essential metabolic pathways. At 32 dph, larvae subjected to the medium treatment displayed an up-regulation of genes mainly associated with fatty acid and glycogen synthesis (GYS2, 6PGL, ACoA, CPTA1, FAS and PPAR1b). Larvae exposed to the high pCO2 treatment upregulated fewer but similar genes (6PGL, ACoA and PPAR1b,). These data suggest stress-induced alterations in the lipid and fatty acid metabolism and a disrupted lipid homeostasis in larvae, providing a mechanistic link to the findings of lipid droplet overload in the liver and organ pathologies. At 46 dph, no significant differences in gene expression were detected, confirming a higher resilience of juveniles in comparison to larvae when exposed to elevated pCO2 up to 4200 μatm.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Growth and nutritional condition of anchovy larvae on the west and southeast coasts of South Africa (2020)
    Inter Research
    Details
    Publication Date: 2023-02-08
    Description: Cape anchovy Engraulis encrasicolus is an ecologically and economically important pelagic fish species occurring along the coast of South Africa. A recent eastward shift in Cape anchovy distribution indicates that environmental conditions are becoming more favorable for the species on the east coast. This shift is particularly important in the sheltered Algoa Bay region, a nursery area for fish larvae. However, the relatively low productivity of the Agulhas Current Large Marine Ecosystem on the eastern coast of South Africa may result in an anchovy population in poorer nutritional condition and with slower growth rates than the west coast population. Using otolith and nucleic acid analyses, the growth rates of anchovy larvae from the western and southeastern coasts of South Africa were compared. The otolith analysis results indicated that, at any given age, individual growth rates for anchovy larvae were higher on the southeast coast than on the west coast. The RNA:DNA values also indicated that instantaneous growth rates of anchovy larvae were higher in Algoa Bay than on the west coast. At the time of sampling, chlorophyll and zooplankton productivity were higher at sampling sites in Algoa Bay than sites on the west coast, potentially due to favorable oceanographic features in the bay. As such, the results suggest that Algoa Bay is a suitable and potentially favorable nursery area for the early stages of anchovy, highlighting the importance of separate management of the southeast coast region in a changing world.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Factors influencing the spatial and temporal distribution of microplastics at the sea surface – A year-long monitoring case study from the urban Kiel Fjord, southwest Baltic Sea (2020)
    Elsevier
    Details
    Publication Date: 2023-02-08
    Description: Highlights: • Microplastic abundance was overall low and not related to environmental parameters. • High microplastic loads were found on few occasions after rainfall and snowmelt. • Microplastics were mainly hard fragments of PE and PP in various colours. • Microplastic contamination from the wastewater treatment plant was the lowest. • Stormwater drains are important source of microplastics into the marine environment. Abstract: Microplastics are ubiquitous to most marine environments worldwide, and their management has become one of the major challenges facing stakeholders. Here we monitored monthly, between March 2018 and March 2019, the abundance of microplastics (0.3–18.2 mm) at the sea surface within the Kiel Fjord, southwest Baltic Sea. Microplastics were sampled at eight locations, inside and outside the fjord, near potential source of microplastics, such as the outlets of storm drains or the Kiel-Bülk wastewater treatment plant, the Schwentine River mouth and the entrance of the Kiel Canal. Weather (wind, precipitations) and seawater (salinity, temperature) parameters were compared to the spatiotemporal distribution of the microplastics. We found an overall stable, and low (0.04 particles/m3), microplastic load within the Kiel Fjord compared to other urban areas worldwide with comparable population densities. No relationship was found between the microplastic abundance and the environmental factors, but the few samples that yielded unusually high amount of microplastics were all preceded by rainfall and snow/ice melt. During such events, vast amounts of water, potentially contaminated with microplastics, were released into the fjord via the storm drainage system. The microplastic abundances at the wastewater plant outflow were among the lowest of our survey, likely thanks to an efficient filtering system. The results of this study highlight the importance to repeat microplastic samplings over time and space to determine with confidence baseline microplastic abundance and to detect unusual acute contamination, especially during snow and ice melting. Overall, the microplastic abundance within the Kiel Fjord was low, probably thanks to efficient waste management on land. However, improvements are still needed to filter millimetre-sized particles within the storm drainage system, which is likely a major source of microplastics into the marine environment.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Pilot study to investigate the effect of long-term exposure to high pCO2 on adult cod (Gadus morhua) otolith morphology and calcium carbonate deposition (2021)
    Springer
    Details
    Publication Date: 2024-02-07
    Description: To date the study of ocean acidification on fish otolith formation has been mainly focused on larval and juvenile stages. In the present pilot study, wild-captured adult Atlantic cod (Gadus morhua) were exposed to two different levels of pCO2, 422µatm (ambient, low pCO2) or 1091µatm (high pCO2), for a period of 30 weeks (from mid-October to early April 2014–2015) in order to study the effects on otolith size, shape and CaCO3 crystallization amongst other biological parameters. We found that otoliths from cod exposed to high pCO2 were slightly smaller (− 3.4% in length; − 3.3% in perimeter), rounder (− 2.9% circularity and + 4% roundness) but heavier (+ 5%) than the low pCO2 group. Interestingly, there were different effects in males and females; for instance, male cods exposed to high pCO2 exhibited significant changes in circularity (− 3%) and roundness (+ 4%) compared to the low pCO2 males, but without significant changes on otolith dimensions, while females exposed to high pCO2 had smaller otoliths as shown for length (− 5.6%), width (− 2%), perimeter (− 3.5%) and area (− 4.8%). Furthermore, while the majority of the otoliths analysed showed normal aragonite deposition, 10% of fish exposed to 1091µatm of pCO2 had an abnormal accretion of calcite, suggesting a shift on calcium carbonate polymorph crystallization in some individuals under high pCO2 conditions. Our preliminary results indicate that high levels of pCO2 in adult Atlantic cod might affect otolith growth in a gender-specific way. Our findings reveal that otoliths from adult cod are affected by ocean acidification, and we believe that the present study will prompt further research into this currently under-explored area.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Impaired larval development at low salinities could limit the spread of the non-native crab Hemigrapsus takanoi in the Baltic Sea (2021)
    Inter Research
    Details
    Publication Date: 2024-02-07
    Description: The Asian shore crab Hemigrapsus takanoi, native to the northwest Pacific Ocean, was recently discovered in Kiel Fjord (southwestern Baltic Sea). In laboratory experiments, we tested the salinity tolerance of H. takanoi across 8 levels (0 to 35) and across 3 life history stages (larvae, juveniles and adults) to assess its potential to invade the brackish Baltic Sea. Larval development at different salinities was monitored from hatching to the megalopa stage, while survival and feeding of juveniles and adults were assessed over 17 d. Larvae of H. takanoi were able to complete their development to megalopa at salinities 〉= 20 and the time needed after hatch to reach this stage did not differ between salinities of 20, 25, 30 and 35. At a salinity of 15, larvae still reached the last zoea stage (zoea V), but development to the megalopa stage was not completed. All juveniles and adults survived at salinities from 5 to 35. Feeding rates of juveniles increased with increasing salinity across the entire salinity range. However, feeding rates of adults reached their maximum between salinities of 15 and 35. Our results indicate that both juveniles and adults of H. takanoi are euryhaline and can tolerate a wide range of salinities, at least for the time period tested (2 wk). However, larval development was impaired at salinities lower than 20, which may prevent the spread of H. takanoi into the Baltic Proper.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Ocean Acidification Alters the Predator – Prey Relationship Between Hydrozoa and Fish Larvae (2022)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: Anthropogenic CO2 emissions cause a drop in seawater pH and shift the inorganic carbon speciation. Collectively, the term ocean acidification (OA) summarizes these changes. Few studies have examined OA effects on predatory plankton, e.g. Hydrozoa and fish larvae as well as their interaction in complex natural communities. Because Hydrozoa can seriously compete with and prey on other higher-level predators such as fish, changes in their abundances may have significant consequences for marine food webs and ecosystem services. To investigate the interaction between Hydrozoa and fish larvae influenced by OA, we enclosed a natural plankton community in Raunefjord, Norway, for 53 days in eight ≈ 58 m³ pelagic mesocosms. CO2 levels in four mesocosms were increased to ≈ 2000 µatm pCO2, whereas the other four served as untreated controls. We studied OA-induced changes at the top of the food web by following ≈2000 larvae of Atlantic herring (Clupea harengus) hatched inside each mesocosm during the first week of the experiment, and a Hydrozoa population that had already established inside the mesocosms. Under OA, we detected 20% higher abundance of hydromedusae staged jellyfish, but 25% lower biomass. At the same time, survival rates of Atlantic herring larvae were higher under OA (control pCO2: 0.1%, high pCO2: 1.7%) in the final phase of the study. These results indicate that a decrease in predation pressure shortly after hatch likely shaped higher herring larvae survival, when hydromedusae abundance was lower in the OA treatment compared to control conditions. We conclude that indirect food-web mediated OA effects drove the observed changes in the Hydrozoa – fish relationship, based on significant changes in the phyto-, micro-, and mesoplankton community under high pCO2. Ultimately, the observed immediate consequences of these changes for fish larvae survival and the balance of the Hydrozoa – fish larvae predator – prey relationship has important implications for the functioning of oceanic food webs.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: archive
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Analysis of reproductive traits reveals complex population dynamics on a small geographical scale in Atlantic herring (2023)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: Atlantic herring (Clupea harengus) has a complex population structure and displays a variety of reproductive strategies. Differences in reproductive strategies among herring populations are linked to their time of spawning, as well as to their reproductive investment which can be an indicator for migratory vs. stationary behavior. These differences are reflected in the number of oocytes (fecundity) and the size of the oocytes prior spawning. We studied potential mixing of herring with different reproductive strategies during the spring spawning season on a coastal spawning ground. It has been hypothesized that both spring and autumn spawning herring co-occur on this specific spawning ground. Therefore, we investigated the reproductive traits oocyte size, fecundity, fertilization success as well as length of the hatching larvae during the spring spawning season from February to April. We used a set of 11 single nucleotide polymorphism markers (SNPs), which are associated with spawning season, to genetically identify autumn and spring spawning herring. Reproductive traits were investigated separately within these genetically distinct spawning types. Furthermore, we used multivariate analyses to identify groups with potentially different reproductive strategies within the genetic spring spawners. Our results indicate that mixing between ripe spring and autumn spawners occurs on the spawning ground during spring, with ripe autumn spawners being generally smaller but having larger oocytes than spring spawners. Within spring spawners, we found large variability in reproductive traits. A following multivariate cluster analysis indicated two groups with different reproductive investment. Comparisons with other herring populations along the Norwegian coastline suggest that the high variability can be explained by the co-occurrence of groups with different reproductive investments potentially resulting from stationary or migratory behavior. Fertilization success and the length of the hatching larvae decreased with progression of the spawning season, with strong inter-individual variation, supporting our findings. Incorporating such complex population dynamics into management strategies of this species will be essential to build its future population resilience.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Effects of changing environmental conditions on plastic ingestion and feeding ecology of a benthopelagic fish (Gadus morhua) in the Southwest Baltic Sea (2022)
    Elsevier
    Details
    Publication Date: 2024-02-07
    Description: Highlights: • Microplastics were found both at the surface and at depth within the Baltic Sea. • Microplastic ingestion occurred within both G. morhua and S. sprattus. • Major inflows of water into the Baltic Sea altered G. morhua feeding patterns. • Increase in pelagic feeding in G. morhua increased ingestion of microplastics. This study documents how the abundance of microplastics (〈5 mm) in the Atlantic cod, Gadus morhua, relates to the changes of the fish diet during years with contrasting levels of anoxia for example following years of low or high major Baltic inflows (MBI). A MultiNet Maxi trawl and CTD were deployed annually to collect microplastic samples alongside oxygen, temperature, and salinity conditions. Microplastics were homogenously distributed both within the water column and across years. Gadus morhua diet shifted from dominantly benthic invertebrates (61 %) under oxygenated conditions to dominantly Sprattus sprattus (81 %) under anoxic conditions. The proportion of G. morhua with microplastics in their digestive tract increased when they fed on pelagic fish (38 %) versus on benthic invertebrates (15 %). The proportion of S. sprattus which ingested microplastics (~18 %) did not vary. As anoxia at depth is expected to increase due to climate change, microplastic ingestion by G. morhua will potentially increase.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Juvenile Atlantic herring (Clupea harengus) use a time-compensated sun compass for orientation (2022)
    The Company of Biologists
    Details
    Publication Date: 2024-02-07
    Description: Atlantic herring (Clupea harengus), an ecologically and economically important species in the northern hemisphere, shows pronounced seasonal migratory behaviour. To follow distinctive migration patterns over hundreds of kilometers between feeding, overwintering and spawning grounds, they are probably guided by orientation mechanisms. We tested whether juvenile spring-spawning Atlantic herring, caught in the western Baltic, use a sun compass for orientation just before they start leaving their hatching area. Fish were randomly divided into two groups, one of them clock-shifted 6 h backwards, to investigate whether they shift their orientation direction accordingly. Individual fish were placed in a circular bowl and their orientation was tested multiple times with the sun as a sole visual orientational cue. Our results show for the first time that juvenile Atlantic herring use a time-compensated sun compass during their migration. Their swimming direction was impaired, but still present, even when the sky was very cloudy, indicating additional orientation capabilities.
    Type: Article , PeerReviewed
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    OceanRep: Article in a Scientific Journal - peer-reviewed
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