| 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. |
- Hansen, Joakim, 1978-, et al.
(författare)
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Distribution differences and active habitat choices of invertebrates between macrophytes of different morphological complexity
- 2011
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Ingår i: Aquatic Ecology. - : Springer Science and Business Media LLC. - 1386-2588 .- 1573-5125. ; 45:1, s. 11-22
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Tidskriftsartikel (refereegranskat)abstract
- This study explores: (1) whether the abundance of macroinvertebrates differs between macrophytes differing in both morphological complexity and tolerance to nutrient enrichment; (2) whether the distribution of invertebrates between macrophytes is due to active habitat choice; and (3) whether invertebrates prefer structurally complex to simple macrophytes. Macroinvertebrate abundance was compared between two common soft-bottom plants in the Baltic Sea that are tolerant to eutrophication, Myriophyllum spicatum and Potamogeton pectinatus, and one common plant that is sensitive to eutrophication, Chara baltica. Both field sampling and habitat choice experiments were conducted. We recorded higher total macroinvertebrate abundance on the structurally complex M. spicatum than on the more simply structured P. pectinatus and C. baltica, but found no difference in macroinvertebrate abundance between P. pectinatus and C. baltica. In accordance with the field results, our experiment indicated that the crustacean Gammarus oceanicus actively chose M. spicatum over the other macrophytes. Besides, we found that G. oceanicus actively preferred complex to simply structured artificial plants, indicating that the animal distribution was at least partly driven by differences in morphological complexity between plant species. In contrast, the gastropod Theodoxus fluviatilis did not make an active habitat choice between the plants. Our findings suggest that human-induced changes in vegetation composition can affect the faunal community. Increased abundance of structurally complex macrophytes, for example, M. spicatum, can result in increased abundance of macroinvertebrates, particularly mobile arthropods that may actively choose a more structurally complex macrophyte.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- Hansen, Joakim, 1978-
(författare)
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Effects of morphometric isolation and vegetation on the macroinvertebrate community in shallow Baltic Sea land-uplift bays
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Shallow sheltered Baltic Sea bays are ecologically important habitats that harbour a unique vegetation community and constitute vital reproduction areas for many coastal fish species. Knowledge about the invertebrate community in these bays is, however, limited. This thesis examines the macroinvertebrate community in shallow sheltered Baltic Sea bays and how it is affected by: (1) the natural morphometric isolation of bays from the sea due to post-glacial land uplift; and (2) differences in vegetation types. The invertebrate biomass and number of taxa was found to decrease with increased bay isolation. The taxon composition changed from dominance by bivalves and gastropods in open bays to a community composed of a larger proportion of insects in isolated bays. Stable isotope analysis indicated epiphytes and periphyton as the major energy resources for most of the examined consumers, but the relative importance of these in relation to larger plants decreased for some consumers with increased bay isolation. A comparison of invertebrate abundance between plants revealed a close relationship with morphological complexity of the plants. More complexly structured plants had higher invertebrate abundance than plants with simpler morphology. The results suggest that management of these coastal habitats should be dynamic and take into consideration the natural change in invertebrate community resulting from the slow bay isolation process. In addition, the results imply that changes in the aquatic vegetation due to anthropogenic influences could induce changes in the invertebrate community as the plant habitat structure is altered. A changed invertebrate community may in turn affect higher trophic levels since invertebrates are important food for many fish and waterfowl species.
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| 7. |
- Hansen, Joakim, 1978-, et al.
(författare)
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Effects of plant morphology on small-scale distribution of invertebrates
- 2010
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Ingår i: Marine Biology. - : Springer. - 0025-3162 .- 1432-1793. ; 157:10, s. 2143-2155
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Tidskriftsartikel (refereegranskat)abstract
- Habitat structure influences organism communities by mediating interactions between individuals and species, affecting abundance and species richness. We examined whether variations in the morphology of soft-bottom plants affect their function as habitat and whether complex structured plants support higher macroinvertebrate abundance and species richness. Three Baltic Sea plant species were studied, together with artificial plants resembling each species. In a field collection, we found higher invertebrate abundance on the morphologically more complex plants Myriophyllum spicatum and Chara baltica than on the structurally simpler plant Potamogeton perfoliatus. In a colonization experiment, we found the highest invertebrate abundance on artificial M. spicatum but found no difference between natural plants. Invertebrate taxon richness displayed no consistent relationship with plant structural complexity. The results imply that plant morphology influences small-scale invertebrate distribution, partly supporting the hypothesis that structurally complex plants harbour higher invertebrate abundance.
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| 8. |
- 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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| 9. |
- Hansen, Joakim, 1978-, et al.
(författare)
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Taxon composition and food-web structure in a morphometric gradient of Baltic Sea land-uplift bays
- 2012
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Ingår i: Boreal environment research. - 1239-6095 .- 1797-2469. ; 17:1, s. 1-20
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Tidskriftsartikel (refereegranskat)abstract
- Shallow Baltic Sea bays undergo a process of morphometric isolation from the sea due to post-glacial land uplift. Recent studies have documented that both flora and fauna communities change along this gradient. Changes in taxon composition may in turn alter feeding ecology and trophic relationships. In addition, the relative importance of carbon from terrestrial sources may increase with bay isolation. In accordance with previous studies, we found a change in the community composition of both flora and fauna with bay isolation. Results of stable isotope analysis (δ13C, δ15N) suggested that epiphytes and periphyton are the major carbon sources for most benthic primary consumers, but that their importance in relation to angiosperms and charophytes decreased with bay isolation. The results also indicated that filter feeders utilize terrestrially derived carbon, but its importance could not be critically related to bay isolation. Trophic positions of the consumers were similar across the bay isolation gradient.
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| 10. |
- Hansen, Joakim, 1978-
(författare)
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Uppföljning av bottenvegetation i grunda Östersjövikar : Varians- och precisionsanalyser av data insamlade med visuella metoder genom snorkling
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Syftet med den här studien var att analysera variation i bottenvegetation i tid och rum, samt precision i insamlandet av data för att ge rekommendationer för uppföljning av grunda vikar i Östersjön (habitatdirektivets naturtyp laguner 1150, med undergrupperna 1153 och 1154). I studien har variation analyserats avseende skillnader på olika geografisk skala (vik, län, havsområde) samt inventeringsår. Analysen utfördes på data som samlats in i den här miljön i lite mer än ett decennium (2001–2014), där stickprovsmetoder med visuell observation i 50×50-cm prov längs transekter eller slumpvist placerade stationer á 10 m diameter tillämpats. De responsvariabler som studerades var antal arter, antal typiska arter, täckningsgrad, två index baserade på indikatorarter, samt andelen långskottsvegetation. Variationen i de undersökta variablerna var störst inom vikar och mellan vikar, medan den var liten mellan län och havsområden. Det var även en viss variation mellan år, men den var inte samstämmig mellan vikar de olika åren. Vegetationens täckningsgrad varierade mest medan antalet arter och indexet beräknat på antalet indikatorarter varierade minst. Baserat på resultaten föreslås för samtliga havsområden att minst 100 små inventerings-rutor (0,25 m2) eller 30 större stationer (79 m2) bör inventeras per vik för att få en god precision* i medelvärdesskattning av antal arter och täckningsgraden av bottenvegetation per vik. Detta motsvarar ungefär 8 arbetstimmar med den första metoden, respektive 20 arbetstimmar med den andra metoden (fördelat på två personer). Med en lägre provtagningsinsats om 70 små inventeringsrutor (ca 6 h) eller 12 stationer (8 h) per vik nås en lägre men acceptabel precision**. Vid uppföljning av antal arter, typiska arter, täckningsgrad, indikatorartsindexen och andel långskottsvegetation på havsområdesnivå krävs att minst 16 vikar undersöks för att nå en god precision* i norra Egentliga Östersjön. För kumulativt artantal krävs att minst 8 vikar per naturtypsundergrupp provtas eftersom antalet arter och artsammansättningen skiljer mellan naturtypsundergrupperna i det här havsområdet. Då variationen mellan vikar var större i södra Egentliga Östersjön och Bottniska viken än i norra Egentliga Östersjön krävs en provtagning av 20 till 30 vikar per havsområde för att nå en god precision* i medelvärdesskattningar av de undersökta responsvariablerna i de två förstnämnda havsområdena. Med 16 vikar per havsområde når man dock en lägre, men acceptabel, precisionsnivå**. För god precision avseende mellanårsvariation föreslås en provtagning om sex år för de undersökta uppföljningsvariablerna. Resultaten som redovisas i den här studien kompletterar de undersökningar som gjorts av variation i fiskyngelförekomst i samma typ av Östersjövikar och tillsammans kan studierna utgöra en grund för att utforma uppföljningsprogram av grunda vikar i Östersjön.
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