| 1. |
- Bergström, Ulf, et al.
(författare)
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Inför fler fiskefria områden för att skydda bestånd och ekosystem
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Fiskefria områden kan vara ett effektivt verktyg för att skydda både fisk- och kräftdjursbestånd och marina ekosystem. Men det är viktigt att områdena utformas på rätt sätt och är tillräckligt stora. Lektidsfredade områden kan vara enklare att driva igenom, men ger inte lika goda effekter.
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| 2. |
- Eklöf, Johan S., 1978-, et al.
(författare)
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Effects of seasonal spawning closures on pike (Esox lucius L.) and perch (Perca fluviatilis L.) catches and coastal food webs in the western Baltic Sea
- 2023
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 263
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Tidskriftsartikel (refereegranskat)abstract
- Marine protected areas have become one of the main tools in the battle to curb marine biodiversity loss and habitat degradation. Yet, implementation of permanent fishery closures has often generated resource user conflicts that ultimately undermine conservation goals. Here we assessed the influence of an alternative and often more accepted measure – seasonal fish spawning closures – on large predatory fish and coastal food webs in the western Baltic Sea (Sweden). In spring 2017, we conducted a multivariable field survey in 11 seasonal closures and 11 paired references areas open to fishing. In each area, pike was sampled through angling, and perch and mesopredators through gillnet surveys. To assess trophic cascades, we measured zooplankton abundance and loss of tethered gammarids from predation. Catches per unit effort of northern pike (Esox lucius) – the main target species in recreational fisheries – were ca. 2.5 times higher per unit effort in closures than reference areas; an effect that may be caused by higher abundance and/or higher catchability of pike in the absence of fishing. Catch and weight per unit effort of the more common predator European perch (Perca fluviatilus), and the mesopredators roach (Rutilus rutilus) and three-spined stickleback (Gasterosteus aculeatus) in survey nets were, however, unaffected by closures. Moreover, a previously hypothesized trophic cascade from perch to zooplankton via three-spined stickleback was supported by the analyses, but appeared independent of closures. Yet, predation risk for tethered gammarid amphipods (a prey of stickleback and an important grazer on macroalgae) was three times higher in fished areas than in closures; a cascading closure effect that may potentially be caused by small predatory fish being less active in protected areas to avoid pike predation. Overall, our results suggest that spawning closures impact pike abundance and/or behavior and could help limit the effects of fishing, but that more research is needed to disentangle i) what mechanism(s) that underlie the protection effect on pike catches, ii) the apparently weaker closure impacts on other fish species, as well as iii) the potential for cascading effects on lower trophic levels. Therefore, new seasonal spawning closures should be implemented in addition to (and not instead of) much-needed permanent closures, which have well-known effects on the wider ecosystem.
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| 3. |
- Niemi, Niklas, et al.
(författare)
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Influence of reed beds (Phragmites australis) and submerged vegetation on pike (Esox lucius)
- 2023
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Ingår i: Fisheries Research. - : Elsevier BV. - 0165-7836 .- 1872-6763. ; 261
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Tidskriftsartikel (refereegranskat)abstract
- Eutrophication and reduced grazing have led to an expansion of the common reed (Phragmites australis) in archipelago areas in the Baltic Sea, while at the same time the composition of submerged vegetation has changed. Although reed is important as nursery habitat for many fish species, extensive emergent vegetation may reduce biodiversity and abundance of predatory fish. Pike (Esox lucius) is a predatory fish whose larvae and young-of-the-year find both food and shelter in reed but use different micro-habitats during different life-stages. Here we investigate the influence of reed and submerged vegetation on abundance and body size of adult pike during the spawning season. We predicted that coastal bays with extensive but heterogeneous reed beds with higher cover of submerged vegetation would have more and larger pike than bays with smaller, homogenous reed belts or with less submerged vegetation. To test these predictions, we estimated abundance and size-structure of adult pike from catches in angling fishing among 22 bays in the Stockholm archipelago at the Swedish Baltic Sea coast. Our analyses show that catches of adult pike were positively associated with both extensive reed beds and cover of rooted submerged vegetation. However, pike size was not correlated with any vegetation variable, but instead increased with wave exposure and bay area. Our study suggests that reed beds and submerged vegetation are important for adult pike during the spawning season, and even the most extensive reed beds had no evident negative effect on pike populations. We could not see any clear relationship between emergent reed habitat and cover of submerged vegetation among the studied bays, and conclude that to maintain pike population during the spawning season it is important that coastal bays have sufficient amounts of both reed beds and rooted submerged vegetation.
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| 4. |
- Austin, Åsa N., 1988-, et al.
(författare)
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Stronger effect of individual species’ traits than shading on aquatic plant community productivity and interspecific competition
- 2023
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Ingår i: Aquatic Botany. - : Elsevier BV. - 0304-3770 .- 1879-1522. ; 187
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Tidskriftsartikel (refereegranskat)abstract
- Competition is one of the major factors structuring plant communities. Species with similar traits generally compete more intensely and have more similar yield than functionally dissimilar species, which often respond differently to environmental change. Little is known about how the interacting species’ traits influence the effect of environmental change on interspecific competition. However, theory predicts that environmental change should lead to more asymmetric competition, by favouring the species best adapted to the particular environmental change. Here we used a mesocosm experiment with three common aquatic plant species from the Baltic Sea (Northern Europe), to test how community productivity and competition asymmetry were affected by functional dissimilarity, individual species’ traits and a common stressor: shading. Competition asymmetry was defined as the absolute difference in reductions in yield relative to monocultures of two interacting species. Community productivity decreased and competition asymmetry increased with functional dissimilarity of the interacting species, possibly explained by the traits of the superior species, which had higher specific leaf area, maximum canopy height and primary production rate than the subordinate species. Community productivity was not affected by shading, contrary to our expectation, while competition asymmetry was higher in shaded than ambient conditions. Individual species yield depended on species identity and species combination. Only the shortest species was negatively affected by shading. Thus, by favouring tall-growing species, shading can alter interspecific competition. Together, these findings suggest that non-random species loss following environmental change can be caused by competitive exclusion, in addition to a direct effect of abiotic filtering.
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| 5. |
- Hansen, Joakim P., 1978-
(författare)
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Benthic vegetation in shallow inlets of the Baltic Sea : Analysis of human influences and proposal of a method for assessment of ecological status
- 2012
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Rapport (refereegranskat)abstract
- The European Union Water Framework Directive (WFD) has a general objective that all European waters should attain good ecological status by 2015. Shallow wave-protected inlets with soft-sediment bottoms are common environments along the Swedish and Finnish Baltic Sea coastlines. However, there is no suitable method for assessing the ecological status of this biotope. The current assessment methods based on macrovegetation for coastal waters in Sweden and Finland are mainly designed for hard-bottom biotopes and function poorly for shallow soft bottoms. The aim of this study was to analyse the effects of human activities on submerged macrovegetation in shallow inlets along the Swedish and Finnish Baltic Sea coasts, and to develop a method for assessment of environmental status for the inlets.The results of the study showed that the proportion of disturbance-sensitive species decreased with increasing total phosphorus concentration and boating activity. In addition, macrophyte cover was lower in inlets with high, as compared to low, boating pressure. Natural environmental factors were found to be very important for explaining variation in the macrophyte community. However, a large part of the variation was unexplained in the models tested, and should be examined further.Based on the results, an assessment method for classification of environmental status was developed. The method uses a macrophyte index based on a cover proportion of sensitive to tolerant species, as well as the mean cover of all species combined. The two macrophyte responses are expressed as ecological quality ratios relative to a reference condition. Specific threshold values were developed to classify the environmental status on a five-point scale, from high to good, moderate, poor, and bad status. The method suggested can be used as a complement to the existing methods that are applied to deeper areas. The method is applicable to individual inlets and may also be suitable to larger water areas according to divisions in the WFD. It does, however, need further development and independent testing before application.
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| 6. |
- Joakim P., Hansen, 1978-
(författare)
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Effects of shore-level displacement on the ecology of Baltic Sea bays
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents the up to date understanding of changes in ecological structure of small Baltic Sea bays following shore-level displacement and isolation of bays from the sea. It was producedas a part of the biosphere research programme, which has a strong emphasis on the characterization of properties and processes affecting the fate of potentially released radionuclides from the suggested repository of nuclear waste in the bedrock of the Forsmark area. The report has a focus on ecology and gives a description of input data, methodology and results on changes in flora and fauna communities, as well as some abiotic factors, with topographic isolation of bays from the sea. It is intended to describe the properties and conditions at the Forsmark site and to give information essential for demonstrating site specific understanding of processes and properties linked to a sea-to-lake succession. Long-term landscape development in the Forsmark area is dependent on two main and partly interdependent factors; shore-level displacement and climate variations. These two factors in combination strongly affect a number of processes, which in turn influence the development of ecosystems. Some examples of such processes are erosion and sedimentation, primary production and decomposition of organic matter. In this work focus has been to report changes in the structure and biomass of flora and fauna communities, which affect primary production, and influence the processes of decomposition of organic matter and sedimentation. A section of the study also deals with the biological processes of primary production, autotrophic carbon uptake and influence of allochtonous energy. The study is part of a description of the Forsmark ecosystem succession during a glacial cycle, which is one of the main objectives of the biosphere modelling at the Swedish Nuclear Fuel and Waste Management Company (SKB). The biomass of macrofauna was found to decrease with increasing isolation of bays. The changes in the macrofauna community also reflected the animals ability to re-colonize an unstable habitat, where slow colonizers with passively dispersed larvae were almost absent from the most isolated bays. Fast colonizers – particularly the ones with flying adults (insects) – were however found inhigher proportions in isolated bays. Contrary to the macrofauna and flora, the zooplankton and juvenile fish increased in biomass with increasing bay isolation. This study describes a significant change in ecological properties of Baltic Sea bays with shore-level displacement. This change affects ecosystem processes which may be of importance for the fate of potentially released radionuclides to the biosphere.
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