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| 2. |
- Ghinter, Leopold, et al.
(författare)
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Microbial functional structure and stable isotopic variation of leptocephali across three current zones in the western South Pacific
- 2020
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 182
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Tidskriftsartikel (refereegranskat)abstract
- The ecology of leptocephali remains poorly known but they appear to feed on marine snow that can vary spatially and temporally according to the food web dynamics. This study provided new information about the position of leptocephali within the functional structure of microbial plankton and other food web components of the western South Pacific (WSP) region at a large geographic scale including the New Caledonia, Fiji, and Samoa islands. The hydrographic structure varied with latitude, and nutrient levels were generally low but somewhat variable. Stable isotopic signatures were examined in relation to the 3 current zones of the eastward flowing South Equatorial Countercurrent (SECC; north), the westward South Equatorial Current (SEC; mid-latitudes), and the eastward South Tropical Countercurrent (STCC; south), and all zones were found to be primarily based on a heterotrophic planktonic functioning that were co-limited by inorganic nitrogen and phosphorus, with biomasses of planktonic groups varying with depth. Isotopic signatures of leptocephali were compared to the signatures of other mesozoplankton, micronekton, and Trichodesmium components of the food web, and in relation to the signatures of particulate organic matter (POM) that varied among the 3 collection depths. The isotopic signatures of six taxa of leptocephali, other taxonomic groups and POM showed interesting variability according to latitude and among some stations. The presence of Trichodesmium at the surface in the STCC zone influenced the isotopic signatures of POM and thus the signatures of leptocephali. The signatures of leptocephali were therefore linked with the overall food web and were consistent with the larvae feeding on marine snow components of POM. The two apparent groups of leptocephali with different isotopic signatures that have also been observed in other oceanic areas may be explained by feeding behavior at different depths or on different types of marine snow.
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| 3. |
- Kahma, T., et al.
(författare)
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Food-web comparisons between two shallow vegetated habitat types in the Baltic Sea
- 2021
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Ingår i: Marine Environmental Research. - : Elsevier BV. - 0141-1136 .- 1879-0291. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- Coastal vegetated habitats maintain highly diverse communities, where the contribution of macrophyte production is significant for macroinvertebrate primary consumers. In the brackish-waters of the Baltic Sea, the taxonomical diversity of different macrophytes includes both marine and limnic species. To study the basal food-web differences of two key vegetated habitat types, either dominated by a perennial brown macroalgae (Fucus vesiculosus) or by angiosperm plants, 13C and 15N compositions of different primary producers and macroinvertebrate consumers were examined, and their diets were estimated by Bayesian mixing models. Carbon isotope diversity of primary producers was high especially in the hard-bottom Fucus-dominated habitats, which was also reflected in a larger consumer isotope niche. However, consumer isotope niche among sites was similar within the same habitat type. Our models indicated that the perennial macrophyte dietary median contribution was about 25% for deposit feeders and omnivores in both habitat types, while epigrazers preferred filamentous algae (30–60%). The niche positions of the abundant clams L. balthica, M. arenaria and C. glaucum differed between the two habitats, but they showed only small (<10% units) differences in their macrophyte dietary contributions. The isotopic compositions of the dominating primary producer assemblage reflected significantly in the isotope niche structure of the associated primary consumers.
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| 4. |
- Källberg Normark, Lydia, et al.
(författare)
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Isotopic niche size variability in an ecosystem engineer along a disturbance gradient in a South African lagoon
- 2022
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Ingår i: Marine Environmental Research. - : Elsevier BV. - 0141-1136 .- 1879-0291. ; 173
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Tidskriftsartikel (refereegranskat)abstract
- A key challenge for natural resource management is how to detect effects of environmental stress on individuals and populations before declines in abundance occur. Variability in carbon and nitrogen isotope composition (δ13C and δ15N) among consumers can provide information on the population trophic niche and how it may change in response to environmental stress. We measured δ13C and δ15N values in primary producers and in an ecosystem engineer, the bioturbating sandprawn Kraussillichirus kraussi, in Langebaan Lagoon, South Africa, along a human disturbance gradient. Diet partitioning mixing models were coupled with isotope niche analyses and individual body condition data to investigate shifts in resource utilisation and diet plasticity from minimally to highly disturbed sites. The δ15N values of seagrass, Zostera capensis indicated a nutrient gradient, with the highest δ15N values at highly disturbed sites indicating either anthropogenic or marine nitrogen inputs. A decreasing δ15N signal with distance from human disturbance/mouth of lagoon was however not evident for sandprawns nor their presumed dietary sources (phytoplankton, microphytobenthos or sediment organic matter), likely because of faster isotope turnover time compared to seagrass and/or differential fractionation for sandprawns among the sites. Sandprawn isotope niche sizes varied among sites, with no trend along the disturbance gradient. The smallest niche coincided with uniform feeding on microphytobenthos according to mixing models. On an individual level, deviating isotope values from population means were correlated to better body condition, suggesting that a divergent feeding strategy is beneficial. Our results support a generalist feeding behavior of the sandprawns with no evidence of reduced physiological status at the site with most human disturbance.
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| 5. |
- Liénart, Camilla, et al.
(författare)
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A sprinkling of gold dust : Pine pollen as a carbon source in Baltic Sea coastal food webs
- 2022
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 67:1, s. 53-65
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Tidskriftsartikel (refereegranskat)abstract
- Allochthonous subsidies to marine ecosystems have mainly focused on biogeochemical cycles, but there has also been recent interest in how terrestrial carbon (C) influences marine food webs. In the Baltic Sea, pine (Pinus sylvestris) pollen is found in large amounts in shallow bays in early summer. Pollen is a significant C-source in freshwater ecosystems and may also be important in coastal food webs. We examined the consumption of pollen and autochthonous resources by benthic invertebrates in shallow bays of the Baltic Sea. We used stable isotopes to estimate diets and reconstructed consumer-resource networks (food webs) for grazers and particulate organic matter (POM)-feeders to compare how these different guilds used pollen. We found that P. sylvestris pollen was consumed in small amounts by a variety of animals and in some cases made up a sizeable proportion of invertebrates' diets. However, invertebrates generally depended less on pollen than other resources. The degree of pollen consumption was related to feeding traits, with generalist invertebrate grazers consuming more pollen (> 10% of diet) than the more specialist POM-feeders (< 5% of diet contributed by pollen). POM-feeders may consume additional microbially-degraded pollen which was not identifiable in our model. We suggest that pollen is a small but substantial allochthonous C-source in shallow bay food webs of the Baltic Sea, with the potential to affect the dynamics of these ecosystems.
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| 6. |
- Liénart, Camilla, et al.
(författare)
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Diet quality determines blue mussel physiological status : A long-term experimental multi-biomarker approach
- 2023
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 563
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Tidskriftsartikel (refereegranskat)abstract
- Cyanobacterial blooms have increased worldwide and decreases in spring blooms of diatoms in temperate aquatic ecosystems are increasingly reported. Whether such shifts in the food base positively or negatively affect primary consumer's physiological status, growth, and more broadly, ecosystem functioning, is poorly known. Here, we test how a widespread filter-feeding blue mussel from the genus Mytilus reacts to diatoms, filamenous non-toxic cyanobacteria and a mixture of the two in a 50 day feeding experiment and compare with mussels in the field. We use a multi-tracer approach to assess mussels' nutritional and physiological status. Diatoms had highest relative proportions of the essential fatty acids 20:5ω3 (EPA) and 22:6ω3 (DHA), but cyanobacteria had a high relative proportion of polyunsaturated FAs (PUFAs) especially 18:3ω3, a precursor of ω3 FAs. Bulk and amino-acid-δ15N demonstrated assimilation of cyanobacterial N or diatom N by the mussels, while fatty acid (FA) composition and δ13C-FA analyses demonstrated assimilation of C and FAs from diatoms. Still, C and N from both food sources were utilized when mussels were fed the mix and condition index, scope for growth (SFG; measure of energy status) and the elemental N:P ratio of mussels where higher in mussels fed cyanobacteria only, indicating better growth status in this treatment. It seems like mussels fed cyanobacteria, a food with low proportions of essential FAs compared to diatoms, were able to cover the dietary requirements through FA biosynthesis from precursor FAs. The FA composition and δ15N-results from mussels fed cyanobacteria agreed well with seasonal field measurements of mussels. Our study provides the first feeding experiment investigating how blue mussels utilize N from cyanobacteria and shows the rather positive response to this type of food. Our results suggest that imbalances in the biochemical composition of diet of consumers can be overcome through biosynthesis of essential FAs. In the context of climate change with shifting biogeochemical baselines, it is crucial to understand the biological effects of such changes in the quality of the production base.
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| 7. |
- Liénart, Camilla, et al.
(författare)
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Long‐term changes in trophic ecology of blue mussels in a rapidly changing ecosystem
- 2021
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 66:3, s. 694-710
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Tidskriftsartikel (refereegranskat)abstract
- Ocean climate change strongly affects organisms and ecosystems, and the causes, consequences, and underlying mechanisms need to be documented. In the Baltic Sea, a marginal sea under severe eutrophication stress, a longer productive season, and changes in the phytoplankton community over the last few decades have likely impacted diet and condition of keystone species, from individual to population level. This study uses stable isotopes (δ13C, δ15N, and derived isotope niche metrics) to trace energy and nutrient flows in archived samples of blue mussel (Mytilus edulis trossulus) spanning 24 yr (1993–2016). We test if long-term changes in isotope and elemental composition in mussels, as well as population abundance and biomass, can be explained by changes in abiotic and biotic variables, using partial least square regressions and structural equation modeling. We found decreasing trends in δ13C and δ15N as well as in mean size and total biomass of mussels, but no unidirectional changes in their stoichiometry or condition index. Changes in isotope composition were best explained by nitrogen-fixing cyanobacteria, by increased terrestrial organic carbon from land runoff (reflecting precipitation) and by decreases in dissolved inorganic nitrogen (indicative of successful eutrophication mitigation) and in biomass of a mixotrophic ciliate species. The trophic niche (assessed from isotope niche) was included as the best predictor for both mussel body condition and the observed decline in their total biomass. This study reveals that altered trophic relationships from climate-induced changes in the productivity base may strongly impact keystone species, with potential knock-on effects on ecosystem functions.
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| 8. |
- Liénart, Camilla, et al.
(författare)
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Spatio-temporal variation in stable isotope and elemental composition of key-species reflect environmental changes in the Baltic Sea
- 2022
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 157:2, s. 149-170
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Tidskriftsartikel (refereegranskat)abstract
- Carbon and nitrogen stable isotope ratios are increasingly used to study long-term change in food web structure and nutrient cycling. We retrospectively analyse elemental composition (C, N and P) and stable isotopes (δ13C, δ15N) in archived monitoring samples of two important taxa from the bottom of the food web; the filamentous ephemeral macroalgae Cladophora spp. and the blue mussel Mytilus edulis trossulus from three contrasting regions in the Baltic Sea (coastal Bothnian Sea and Baltic Proper, open sea central Baltic). The aim is to statistically link the observed spatial and interannual (8–24 years’ time-series) variability in elemental and isotope baselines with their biomass trends and to the oceanographic monitoring data reflecting the ongoing environmental changes (i.e., eutrophication and climate) in this system. We find clear differences in isotope baselines between the two major Baltic Sea basins. However, the temporal variation in Mytilus δ13C was similar among regions and, at the open sea station, mussels and algae δ13C also correlated over time, likely reflecting a global (Suess) effect, whereas δ15N of both taxa varied with local and regional dissolved nitrogen concentrations in water. δ15N in source amino acids allowed detection of diazotrophic N in Mytilus, which was masked in bulk δ15N. Finally, Cladophora N:P reflected regional nutrient levels in the water while P%, which differed for both taxa, was linked to food quality for Mytilus. This study highlights the potential of a multi-taxa and multi-stable isotope approach to understand nutrient dynamics and monitor long-term environmental changes.
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| 9. |
- Åkermark, Cedric, et al.
(författare)
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Long-term decrease in Baltic Sea blue mussel shell length
- 2022
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 276
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Tidskriftsartikel (refereegranskat)abstract
- Multi-decadal monitoring data and archived biological samples make the rapidly changing Baltic Sea an ideal system for quantifying alterations in ecosystem function. The Baltic Sea blue mussel (Mytilus edulis trossulus) acts as a keystone species by providing food and habitat for other species, and through its filtering activity clearing the water and promoting organic matter and nutrient cycling between benthic and pelagic ecosystems. A decrease in biomass of blue mussels along with altered environmental conditions has been observed in the northern Baltic Sea over a 24-year period (1993–2016), but the size distribution of the mussels was unknown. The present study focuses on retrospective measurements of the individual shell lengths of these archived blue mussels. The mean shell length was found to be significantly lower at the end of the time series than in the beginning (11.1–11.5 mm for the years 1993–1996 compared to 10.3–10.9 mm during 2012–2015), with the proportion of larger mussels decreasing in the population. This 6% decrease in shell length translated into a significantly lower (16%) mean filtration capacity at the end of the time series compared to the beginning, influencing the ecosystem services blue mussels provide.
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