| 1. |
- Austin, Åsa, 1988-
(author)
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Aquatic vegetation in coastal ecosystems : The role of biotic interactions and environmental change for ecosystem functions and resilience in the Baltic Sea
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Coastal ecosystems are among the most productive on Earth but subjected to many human pressures. In shallow coastal areas, aquatic vegetation constitutes foundation species that sustain secondary production and act as a nutrient filter, which may buffer human impacts. But little is known about how anthropogenic factors alter biotic interactions in aquatic vegetation, and how these changes affect ecosystem functions and resilience.The aim of this thesis was to investigate how natural and anthropogenic factors alter aquatic vegetation communities and biotic interactions, and how these in turn affect ecosystem functions and resilience to common stressors. Shallow coastal bays in the Baltic Sea were used as model system. A large field survey was conducted to investigate effects of natural and anthropogenic gradients, including bay topographic openness and nutrient runoff, on vegetation communities and ecosystem functions. Results suggest that high vegetation cover can improve water clarity, whereas sediment-driven turbidity can negatively affect vegetation by decreasing the light penetration of the water (Paper I). This dual relationship indicates the potential for two alternative, self-sustaining states in shallow bays; with or without vegetation.Using data from the same survey I investigated the influence of species richness and cover of rooted aquatic vegetation and drift wrack (Fucus vesiculosus), for ecosystem multifunctionality (MF) (Paper II). MF was estimated as the mean of four variables used as proxies for key functions; large predatory fish recruitment, grazer biomass, inverted ‘nuisance’ algal biomass and water clarity. MF was highest when the two functionally different vegetation types (rooted and drifting) co-occurred at high covers, and high species richness increased multifunctionality by increasing rooted vegetation cover.To understand in greater detail if and how interactions within and between vegetation species mediate the effects of environmental change, I conducted two experiments. First, a cage experiment to test if intraspecific plant facilitation may buffer effects of altered top-down and bottom-up control (Paper III), then a mesocosm experiment to test if shading alters interspecific interactions between three common plant species (Paper IV). The cage experiment showed that high shoot density of a common plant (Myriophyllum spicatum) increased individual shoot performance, but only when subjected to both fertilization and large predatory fish exclusion (Paper III). The mesocosm experiment showed that individual species’ traits had stronger effect than shading on interspecific competition and community yield (Paper IV).In conclusion, my thesis shows that single and multiple ecosystem functions benefit from high vegetation cover, with direct and indirect effects of diversity, but are sensitive to anthropogenic stressors (Papers I, II). Further, shading alters biotic interactions among vegetation species in a eutrophic coastal ecosystem by increasing the competitive advantage of dominant species (Paper IV), while intraspecific facilitation increases resilience to interacting stressors (Paper III). Together, the results highlight the need for ecosystem-based management where efforts to reduce anthropogenic influence (e.g. by nutrient reduction and fishing restrictions) are combined with improved protection and restoration of the ecologically and economically valuable aquatic vegetation communities.
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| 2. |
- Austin, Åsa N., et al.
(author)
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Relationships between aquatic vegetation and water turbidity : A field survey across seasons and spatial scales
- 2017
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 12:8
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Journal article (peer-reviewed)abstract
- Field surveys often show that high water turbidity limits cover of aquatic vegetation, while many small-scale experiments show that vegetation can reduce turbidity by decreasing water flow, stabilizing sediments, and competing with phytoplankton for nutrients. Here we bridged these two views by exploring the direction and strength of causal relationships between aquatic vegetation and turbidity across seasons (spring and late summer) and spatial scales (local and regional), using causal modeling based on data from a field survey along the central Swedish Baltic Sea coast. The two best-fitting regional-scale models both suggested that in spring, high cover of vegetation reduces water turbidity. In summer, the relationships differed between the two models; in the first model high vegetation cover reduced turbidity; while in the second model reduction of summer turbidity by high vegetation cover in spring had a positive effect on summer vegetation which suggests a positive feedback of vegetation on itself. Nitrogen load had a positive effect on turbidity in both seasons, which was comparable in strength to the effect of vegetation on turbidity. To assess whether the effect of vegetation was primarily caused by sediment stabilization or a reduction of phytoplankton, we also tested models where turbidity was replaced by phytoplankton fluorescence or sediment-driven turbidity. The best-fitting regional-scale models suggested that high sediment-driven turbidity in spring reduces vegetation cover in summer, which in turn has a negative effect on sediment-driven turbidity in summer, indicating a potential positive feedback of sediment-driven turbidity on itself. Using data at the local scale, few relationships were significant, likely due to the influence of unmeasured variables and/or spatial heterogeneity. In summary, causal modeling based on data from a large-scale field survey suggested that aquatic vegetation can reduce turbidity at regional scales, and that high vegetation cover vs. high sediment-driven turbidity may represent two self-enhancing, alternative states of shallow bay ecosystems.
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| 3. |
- Austin, Åsa N., 1988-, et al.
(author)
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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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In: Aquatic Botany. - : Elsevier BV. - 0304-3770 .- 1879-1522. ; 187
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Journal article (peer-reviewed)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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| 4. |
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| 5. |
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| 6. |
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| 7. |
- Bowes, Rachel E., et al.
(author)
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Landscape features control river's confluences water quality and tributary fish composition
- 2023
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In: Rivers Research and Applications. - : John Wiley & Sons. - 1535-1459 .- 1535-1467. ; 39:6, s. 1025-1036
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Journal article (peer-reviewed)abstract
- Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and differences in connectivity and land use influence dispersal, and consequently biodiversity patterns. We, therefore, measured variation in water chemistry and fish abundance and related these to a number of landscape characteristics (e.g., wetland, urban, wooded, and agricultural) in the River Klaralven and its 30 permanently flowing tributaries. We hypothesized that these environmental attributes would differ between tributary and main stem habitat and that these differences would be driven by landscape attributes including land use. We found considerable intertributary variation in temperature and nutrient levels, and between the tributaries and the main stem. Generally, water temperature was lower in the tributaries, whereas nutrient levels were higher in the tributaries. The lower water temperature has implications for coldwater fishes, and we found two fishes, burbot and lamprey, associated with coldwater tributaries. We also found an inverse relationship between water quality and anthropogenic land use. Protecting tributaries with low anthropogenic impact will likely become increasingly important with ongoing global warming as they can function as thermal refugia for coldwater fishes. Hence, this study underscores the need to evaluate water courses at regional scales to identify spatial refuges and ensure connectivity.
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| 8. |
- Carlson, Peter, et al.
(author)
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Responses of macroinvertebrate communities to small dam removals: Implications for bioassessment and restoration
- 2018
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In: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 55, s. 1896-1907
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Research review (peer-reviewed)abstract
- 1. Small dam removals are increasing on a global scale; yet, general predictions of organism response to dam removal are constrained by heterogeneity of study designs, implementation strategies, geographies, and characteristics of dams and their removals.2. Macroinvertebrate data extracted from 29 studies including 34 small dam removals over a broad geographical range were re-analysed utilizing dam removal effect sizes (a quantified change from before to after removal). Effect sizes of 10 metrics of community structure were calculated to investigate the spatiotemporal extent of small dam removal effects and if responses differ with characteristics of the dam and environmental settings.3. We found that dam removal had initial negative effects on total macroinvertebrate density and Ephemeroptera, Plecoptera and Trichoptera (EPT) density, both downstream and upstream; however, recovery to pre-removal values was reached and exceeded after c. 15-20 months. Mean annual discharge, land use in the catchment and distance from the dam affected the magnitude and direction of responses of four community metrics: total density, EPT density, % EPT density and family biotic index.4. Synthesis and applications. Our study provides evidence that macroinvertebrate community recovery from dam removal is mediated by catchment characteristics and system size, which may correlate with sediment flushing efficiency. Negative impacts were observed in smaller systems or those with a high percentage of undisturbed catchment areas, conditions that may benefit from sediment management prior to dam removal. Significant responses in reaches upstream of the impoundment clearly indicate that caution be applied to interpretations of - response in sampling designs that utilize upstream sites for reference condition.
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| 9. |
- Donadi, Serena, et al.
(author)
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A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems
- 2017
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In: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 284:1859
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Journal article (peer-reviewed)abstract
- Trophic cascades occur in many ecosystems, but the factors regulating them are still elusive. We suggest that an overlooked factor is that trophic interactions (TIs) are often scale-dependent and possibly interact across spatial scales. To explore the role of spatial scale for trophic cascades, and particularly the occurrence of cross-scale interactions (CSIs), we collected and analysed food-web data from 139 stations across 32 bays in the Baltic Sea. We found evidence of a four-level trophic cascade linking TIs across two spatial scales: at bay scale, piscivores (perch and pike) controlled mesopredators (three-spined stickleback), which in turn negatively affected epifaunal grazers. At station scale (within bays), grazers on average suppressed epiphytic algae, and indirectly benefitted habitat-forming vegetation. Moreover, the direction and strength of the grazer-algae relationship at station scale depended on the piscivore biomass at bay scale, indicating a cross-scale interaction effect, potentially caused by a shift in grazer assemblage composition. In summary, the trophic cascade from piscivores to algae appears to involve TIs that occur at, but also interact across, different spatial scales. Considering scale-dependence in general, and CSIs in particular, could therefore enhance our understanding of trophic cascades.
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| 10. |
- Donadi, Serena, et al.
(author)
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Contrasting long-term trends in juvenile abundance of a widespread cold-water salmonid along a latitudinal gradient: effects of climate, stream size and migration strategy
- 2023
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In: Ecography. - : Wiley. - 0906-7590 .- 1600-0587.
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Journal article (peer-reviewed)abstract
- A changing climate reshapes the range distribution of many organisms, and species with relatively low thermal optima, like many salmonids, are increasingly expected to face local population extinctions at lower latitudes. Understanding where and how fast these changes are happening is of pivotal importance for successful mitigation and conservation efforts.We used an extensive electrofishing database to explore temporal trends of juveniles of brown trout Salmo trutta in 218 locations from 174 Swedish streams, over the last 30 years (1991-2020). We hypothesized that 1) declines in abundance have occurred predominately in the warmer, southern regions, while increases have occurred in the colder, northern regions, 2) larger stream sizes may partly offset negative effects of climate, and 3) migrating and resident populations are affected differently by a warming climate.We found that abundance of brown trout juveniles generally declined in warmer regions especially in smaller streams (<= 6 m wide), while the abundance increased in colder regions. In larger streams, negative effects of higher temperatures were seemingly buffered, as we found lower rates of decline or even positive trends. The rate of change (i.e. the slopes of the trends in abundance) was more pronounced towards the climate extremes, and was on average zero in regions with a normal annual air temperature (average temperature over 30 year period) around 5-6 degrees C. Warmer climate had stronger effects on migrating compared to resident populations, suggesting that climate-induced loss of stream connectivity could be an additional factor that hinders recruitment in anadromous populations in a changing climate.Considering predictions of increasing temperatures and frequency of summer droughts, management of cold-water salmonid populations should focus on conserving and restoring riparian vegetation, wetlands, climate and thermal refugia, and habitat integrity overall. Such measures may, however, not suffice for small streams at lower latitudes, unless hydrological connectivity is maintained.
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| 11. |
- Donadi, Serena, et al.
(author)
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Country-wide analysis of large wood as a driver of fish abundance in Swedish streams : Which species benefit and where?
- 2019
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In: Aquatic conservation. - : John Wiley & Sons. - 1052-7613 .- 1099-0755. ; 29:5, s. 706-716
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Journal article (peer-reviewed)abstract
- Rivers are heavily affected by human impacts that threaten many fish species. Among restoration measures, the addition of large wood (LW) in streams has been shown to increase fish abundance, yet which species benefit from LW, to what extent relative to other drivers, and which factors influence LW quantity is not clear, and these uncertainties limit our ability to use LW as an effective restoration measure. Here, a time series (from 1993 to 2016) of electrofishing data, including 3641 streams across Sweden, was used to investigate the beneficial effects of LW on the abundance of juvenile brown trout, Salmo trutta, juvenile Atlantic salmon, Salmo salar, and juvenile and adult sculpins, Cottus gobio and Cottus poecilopus, while accounting for other abiotic and biotic factors, and the drivers of LW abundance at a country-wide scale. Large wood benefitted brown trout, and the effects were greater with decreasing shaded stream surface. LW effects were comparable in magnitude to the positive effects of average annual air temperature and the negative effects of stream depth and predator abundance - factors where the influence was second only to the negative effects of stream width. LW did not benefit salmon abundance, which was correlated positively with stream width and negatively with altitude, nor did it benefit sculpin abundances, which mainly decreased with annual average air temperature and altitude. The quantity of LW strongly diminished with stream width, and, to a lesser extent, with stream depth, altitude, annual average air temperature, and forest age, whereas it increased with stream velocity, slope, and forest cover. The results suggest that LW can be used as an effective restoration tool for brown trout in shallow and narrow streams, especially in areas with little shade. Here, the addition of LW may help to alleviate the impacts of forest clearance and climate change.
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| 12. |
- Donadi, Serena, et al.
(author)
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Density-dependent positive feedbacks buffer aquatic plants from interactive effects of eutrophication and predator loss
- 2018
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In: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 99:11, s. 2515-2524
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Journal article (peer-reviewed)abstract
- Self-facilitation allows populations to persist under disturbance by ameliorating experienced stress. In coastal ecosystems, eutrophication and declines of large predatory fish are two common disturbances that can synergistically impact habitat-forming plants by benefitting ephemeral algae. In theory, density-dependent intraspecific plant facilitation could weaken such effects by ameliorating the amount of experienced stress. Here, we tested whether and how shoot density of a common aquatic plant (Myriophyllum spicatum) alters the response of individual plants to eutrophication and exclusion of large predatory fish, using a 12-week cage experiment in the field. Results showed that high plant density benefitted individual plant performance, but only when the two stressors were combined. Epiphytic algal biomass per plant more than doubled in cages that excluded large predatory fish, indicative of a trophic cascade. Moreover, in this treatment, individual shoot biomass, as well as number of branches, increased with density when nutrients were added, but decreased with density at ambient nutrient levels. In contrast, in open cages that large predatory fish could access, epiphytic algal biomass was low and individual plant biomass and number of branches were unaffected by plant density and eutrophication. Plant performance generally decreased under fertilization, suggesting stressful conditions. Together, these results suggest that intraspecific plant facilitation occurred only when large fish exclusion (causing high epiphyte load) was accompanied by fertilization, and that intraspecific competition instead prevailed when no nutrients were added. As coastal ecosystems are increasingly exposed to multiple and often interacting stressors such as eutrophication and declines of large predatory fish, maintaining high plant density is important for ecosystem-based management.
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| 13. |
- Donadi, Serena
(author)
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Facilitation by ecosystem engineers enhances nutrient effects in an intertidal system
- 2017
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In: Ecosphere. - : Wiley. - 2150-8925. ; 8
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Journal article (peer-reviewed)abstract
- Ecosystem engineering research has recently demonstrated the fundamental importance of non-trophic interactions for food-web structure. Particularly, by creating benign conditions in stressful environments, ecosystem engineers create hot beds of elevated levels of recruitment, growth, and survival of associated organisms; this should fuel food webs and promote production on the ecosystem scale. However, there is still limited empirical evidence of the influence of non-trophic interactions on the classical food-web processes that determine energy transfer, that is, consumer-resource interactions. On the basis of a biomanipulation experiment covering 600 m(2) of an intertidal flat, we show that ecosystem engineers influence resource uptake efficiency and the accumulation of algae following nutrient enrichment in a soft-sediment food web. Nutrient additions increased chlorophyll a concentrations in the sediment by 90%, but only in plots where we also introduced high densities (2000 per m(2)) of a burrowing bivalve, the common cockle Cerastoderma edule. The artificial cockle beds increased the nutrient uptake efficiency of the biofilm and promoted sediment accumulation, which suggests that the cockles facilitated the sediment-living algae by increasing sediment stability. This indicates that ecological interactions, rather than the availability of nutrients per se, set the limits for production in this coastal ecosystem. Our results emphasize the need to include facilitation theory and recognize that positive interactions between species are key to understand, manage, and restore ecosystems under human influence.
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| 14. |
- Donadi, Serena, et al.
(author)
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Interactive effects of land use, river regulation, and climate on a key recreational fishing species in temperate and boreal streams
- 2021
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In: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 66, s. 1901-1914
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Journal article (peer-reviewed)abstract
- Numerous anthropogenic stressors, including river regulation, excess loadings of nutrients and sediment, channelisation, as well as thermal and hydrological stressors driven by climate change impact riverine ecosystems worldwide. In a time when freshwater degradation and the rate of global warming are faster than ever, understanding the potential interactive effects of local and catchment-scale stressors with large-scale climatic conditions is essential to enhance our ability to plan effective conservation, restoration, and mitigation measures. In this study we analysed a dataset spanning the whole of Sweden using a space-for-time approach to investigate interactive effects of land use, river regulation, and climate on brown trout (Salmo trutta) abundance in streams. We found that in warmer regions trout populations were negatively affected in catchments with more intense river regulation by hydropower dams (i.e. >= 10 m(3)/km(2) total reservoir storage volume). In such catchments, a 7 degrees C warmer mean summer air temperature was associated with an average between 44% and 83% decline in trout abundance. In catchments with less intense river regulation, trout abundance instead increased moderately with increasing temperature. We also found that brown trout abundance declined with increasing areal extent of urban areas when found in combination with >= 20% agricultural land use. When agricultural land use reached maximum values (84%), brown trout abundance decreased from an average of 13 individuals per 100 m(2) in catchments with no urban areas to values <= 1 in catchments with >= 5% urban land use. Also, brown trout abundance declined with increasing agricultural land use in catchments with >= 3% urban land use. Our study brings innovative empirical evidence of interactive effects between river regulation, land use and climate on brown trout populations. From a management perspective our findings suggest that: (1) restoring natural flows (e.g. through dam removal) and riparian vegetation could mitigate adverse effects of climate change; and (2) restoration measures that minimise the effects of agriculture and urban land use (e.g. reduction of nutrient levels and restored riparian buffer zones) could help rehabilitate brown trout in catchments with high anthropogenic land use change. However, given the large observed variation between streams, we advise for bespoke management actions stemming from sound knowledge of local habitat conditions and target populations, whenever possible, using an ecosystem management-based approach.
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| 15. |
- Donadi, Serena, et al.
(author)
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Perch and pike recruitment in coastal bays limited by stickleback predation and environmental forcing
- 2020
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In: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 246
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Journal article (peer-reviewed)abstract
- Role reversal can shift fish communities from predator to prey dominance. In the Baltic Sea, the increase in abundance of the small-bodied three-spined stickleback (Gasterosteus aculeatus) has co-occurred with declines of coastal predatory fish, such as perch (Perca fluviatilis) and pike (Esox lucius) in many areas. Recent studies have pointed at predator-prey reversal as a possible mechanism explaining these trends, but conclusive evidence on the phenomenon or its relative importance compared to other drivers is at present open to question. In this study, we applied path analysis to quantify the potential role of stickleback in limiting the recruitment of perch and pike in enclosed bays (i.e. flads) along the Swedish and Finnish coasts. We constructed a causal network model based on vast field data combined with data from GIS and orthophotos, representing fish abundance, hydrographic factors, habitat-forming vegetation, anthropogenic disturbances and geomorphological factors. We found that stickleback abundance had as large effect on larval densities of perch and pike as environmental forcing, represented in our best models by the thermal regime of the flads. Larval densities decreased with stickleback abundance and increased with increasing summer cumulative temperature at a similar rate. Stickleback abundance, in turn, was strongly limited by flad openness, expressed as the number of flad openings to the sea, and increased with vascular plant cover (flad averages). Our study shows that predator-prey reversal could be a strong determinant of perch and pike larval survival, and suggests that the prevalence of more enclosed flads, which are less accessible to stickleback, may be crucial for recruitment of these piscivores. This implies that (1) in areas with, or prone to, increased stickleback abundance, habitat restoration and actions to conserve piscivore populations should primarily focus on more enclosed flads, and that (2) dredging and canalization to enhance boating in these areas could have detrimental effects on piscivore recruitment by decreasing water temperature and enhancing stickleback abundance, hence restricting larval growth and survival.
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| 16. |
- Donadi, Serena, et al.
(author)
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The body-size structure of macrobenthos changes predictably along gradients of hydrodynamic stress and organic enrichment
- 2015
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In: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 162:3, s. 675-685
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Journal article (peer-reviewed)abstract
- Body size is related to an extensive number of species traits and ecological processes and has therefore been suggested as an effective metric to assess community changes and ecosystem's state. However, the applicability of body size as an ecological indicator in benthic environments has been hindered by the poor knowledge of the factors influencing the size spectra of organisms. By applying biological trait analysis (BTA) and generalized linear models to a species dataset collected in the German Wadden Sea (53A degrees 41'14'' N, 7A degrees 14'19'' E) between 1999 and 2012, we show that the size structure of the macrobenthic community changes predictably along environmental gradients. Specifically, body size increases with increasing current-induced shear stress and sediment organic matter content. In addition, the presence of oyster-mussel reefs in one of the sampling stations enhanced the survival of species belonging to the smallest size categories in habitats with high hydrodynamic energy. This was probably due to the local sheltering effects, which together with biodeposition also increased organic matter in the sediment, likely favoring large deposit feeders as well. Our results suggest that body size can be a useful trait for estimating effects of anthropogenic stressors, such as organic enrichment or alteration of hydrodynamic regime and could therefore be effectively included in current monitoring programs of intertidal macrobenthic communities.
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| 17. |
- Donadi, Serena
(author)
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The interactive role of predation, competition and habitat conditions in structuring an intertidal bivalve population
- 2020
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In: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 523
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Journal article (peer-reviewed)abstract
- Habitat characteristics, predation and competition are known to interactively drive population dynamics. Highly complex habitats, for example, may reduce predation and competition, allowing more individuals living together in a certain area. However, the strength and direction of such interactions can differ strongly and are context dependent. Furthermore, as habitat characteristics are rapidly changing due to anthropogenic impacts, it becomes increasingly important to understand such interactions. Here, we studied the interactive effects of predation and competition on common cockle (Cerastoderma edule) recruitment, growth and survival under different habitat characteristics in the Wadden Sea, one of the world's largest intertidal ecosystems. In a predator-exclosure experiment, we manipulated cockle densities (100 vs. 1000 individuals m(-2)) and shorebird predation at two sites differing in habitat characteristics, namely at the wake of a blue mussel bed (Mytilus edulis) and at an adjacent sandy site. We found that recruitment was higher in the mussel-modified habitat, most likely due to reduction of hydrodynamic stress. Although bird predation strongly reduced recruit density, the combined effects still yielded more recruitment at the vicinity of the mussel bed compared to the sandy area. Furthermore, we found that high cockle densities combined with high densities of other potential prey (i.e. mussels) at the mussel-modified site, mitigated predation effects for adult cockles. Apart from these positive effects on adults, mussel-modified habitat reduced cockle growth, most likely by reducing hydrodynamics in the wake of the mussel bed and by increasing inter-specific competition for food. Our study experimentally underpins the importance of habitat characteristics, competition and predation in interactively structuring intertidal communities.
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| 18. |
- Eklöf, Johan, 1978-, et al.
(author)
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Habitat-Mediated Facilitation and Counteracting Ecosystem Engineering Interactively Influence Ecosystem Responses to Disturbance
- 2011
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203.
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Journal article (peer-reviewed)abstract
- Recovery of an ecosystem following disturbance can be severely hampered or even shift altogether when a point disturbance exceeds a certain spatial threshold. Such scale-dependent dynamics may be caused by preemptive competition, but may also result from diminished self-facilitation due to weakened ecosystem engineering. Moreover, disturbance can facilitate colonization by engineering species that alter abiotic conditions in ways that exacerbate stress on the original species. Consequently, establishment of such counteracting engineers might reduce the spatial threshold for the disturbance, by effectively slowing recovery and increasing the risk for ecosystem shifts to alternative states. We tested these predictions in an intertidal mudflat characterized by a two-state mosaic of hummocks (humps exposed during low tide) dominated by the sediment-stabilizing seagrass Zostera noltii) and hollows (low-tide waterlogged depressions dominated by the bioturbating lugworm Arenicola marina). In contrast to expectations, seagrass recolonized both natural and experimental clearings via lateral expansion and seemed unaffected by both clearing size and lugworm addition. Near the end of the growth season, however, an additional disturbance (most likely waterfowl grazing and/or strong hydrodynamics) selectively impacted recolonizing seagrass in the largest (1 m2) clearings (regardless of lugworm addition), and in those medium (0.25 m2) clearings where lugworms had been added nearly five months earlier. Further analyses showed that the risk for the disturbance increased with hollow size, with a threshold of 0.24 m2. Hollows of that size were caused by seagrass removal alone in the largest clearings, and by a weaker seagrass removal effect exacerbated by lugworm bioturbation in the medium clearings. Consequently, a sufficiently large disturbance increased the vulnerability of recolonizing seagrass to additional disturbance by weakening seagrass engineering effects (sediment stabilization). Meanwhile, the counteracting ecosystem engineering (lugworm bioturbation) reduced that threshold size. Therefore, scale-dependent interactions between habitat-mediated facilitation, competition and disturbance seem to maintain the spatial two-state mosaic in this ecosystem.
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| 19. |
- Eklöf, Johan S., et al.
(author)
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A spatial regime shift from predator to prey dominance in a large coastal ecosystem
- 2020
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In: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Journal article (peer-reviewed)abstract
- Regime shifts in ecosystem structure and processes are typically studied from a temporal perspective. Yet, theory predicts that in large ecosystems with environmental gradients, shifts should start locally and gradually spread through space. Here we empirically document a spatially propagating shift in the trophic structure of a large aquatic ecosystem, from dominance of large predatory fish (perch, pike) to the small prey fish, the three-spined stickleback. Fish surveys in 486 shallow bays along the 1200 km western Baltic Sea coast during 1979–2017 show that the shift started in wave-exposed archipelago areas near the open sea, but gradually spread towards the wave-sheltered mainland coast. Ecosystem surveys in 32 bays in 2014 show that stickleback predation on juvenile predators (predator–prey reversal) generates a feedback mechanism that appears to reinforce the shift. In summary, managers must account for spatial heterogeneity and dispersal to better predict, detect and confront regime shifts within large ecosystems.
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| 20. |
- Eklöf, Johan, et al.
(author)
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Size matters : relationships between body size and body mass of common coastal, aquatic invertebrates in the Baltic Sea
- 2017
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In: PeerJ. - : PeerJ. - 2167-8359. ; 5
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Journal article (peer-reviewed)abstract
- Background. Organism biomass is one of the most important variables in ecological studies, making biomass estimations one of the most common laboratory tasks. Biomass of small macroinvertebrates is usually estimated as dry mass or ash-free dry mass (hereafter `DM' vs. 'AFDM') per sample; a laborious and time consuming process, that often can be speeded up using easily measured and reliable proxy variables like body size or wet (fresh) mass. Another common way of estimating AFDM (one of the most accurate but also time-consuming estimates of biologically active tissue mass) is the use of AFDM/DM ratios as conversion factors. So far, however, these ratios typically ignore the possibility that the relative mass of biologically active vs. non-active support tissue (e.g., protective exoskeleton or shell)-and therefore, also AFDM/DM ratios-may change with body size, as previously shown for taxa like spiders, vertebrates and trees.Methods. We collected aquatic, epibenthic macroinvertebrates (>1 mm) in 32 shallow bays along a 360 km stretch of the Swedish coast along the Baltic Sea; one of the largest brackish water bodies on Earth. We then estimated statistical relationships between the body size (length or height in mm), body dry mass and ash-free dry mass for 14 of the most common taxa; five gastropods, three bivalves, three crustaceans and three insect larvae. Finally, we statistically estimated the potential influence of body size on the AFDM/DM ratio per taxon.Results. For most taxa, non-linear regression models describing the power relationship between body size and (i)DM and (ii) AFDM fit the data well (as indicated by low SE and high R-2). Moreover, for more than half of the taxa studied (including the vast majority of the shelled molluscs), body size had a negative influence on organism AFDM/DM ratios.Discussion. The good fit of the modelled power relationships suggests that the constants reported here can be used to quickly estimate organism dry-and ash-free dry mass based on body size, thereby freeing up considerable work resources. However, the considerable differences in constants between taxa emphasize the need for tax on specific relationships, and the potential dangers associated with ignoring body size. The negative influence of body size on the AFDM/DM ratio found in a majority of the molluscs could be caused by increasingly thicker shells with organism age, and/or spawning-induced loss of biologically active tissue in adults. Consequently, future studies utilizing AFDM/DM (and presumably also AFDM/wet mass) ratios should carefully assess the potential influence of body size to ensure more reliable estimates of organism body mass.
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| 21. |
- Engel, Friederike G., et al.
(author)
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Mussel beds are biological power stations on intertidal flats
- 2017
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In: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 0272-7714 .- 1096-0015. ; 191, s. 21-27
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Journal article (peer-reviewed)abstract
- Intertidal flats are highly productive areas that support large numbers of invertebrates, fish, and birds. Benthic diatoms are essential for the function of tidal flats. They fuel the benthic food web by forming a thin photosynthesizing compartment in the top-layer of the sediment that stretches over the vast sediment flats during low tide. However, the abundance and function of the diatom film is not homogenously distributed. Recently, we have realized the importance of bivalve reefs for structuring intertidal ecosystems; by creating structures on the intertidal flats they provide habitat, reduce hydrodynamic stress and modify the surrounding sediment conditions, which promote the abundance of associated organisms. Accordingly, field studies show that high chlorophyll a concentration in the sediment co-vary with the presence of mussel beds. Here we present conclusive evidence by a manipulative experiment that mussels increase the local biomass of benthic microalgae; and relate this to increasing biomass of microalgae as well as productivity of the biofilm across a nearby mussel bed. Our results show that the ecosystem engineering properties of mussel beds transform them into hot spots for primary production on tidal flats, highlighting the importance of biological control of sedimentary systems.
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| 22. |
- Eriksson, Britas Klemens, et al.
(author)
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Habitat segregation of plate phenotypes in a rapidly expanding population of three-spined stickleback
- 2021
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In: Ecosphere. - : Wiley. - 2150-8925 .- 2150-8925. ; 12:6
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Journal article (peer-reviewed)abstract
- Declines of large predatory fish due to overexploitation are restructuring food webs across the globe. It is now becoming evident that restoring these altered food webs requires addressing not only ecological processes, but evolutionary ones as well, because human-induced rapid evolution may in turn affect ecological dynamics. We studied the potential for niche differentiation between different plate armor phenotypes in a rapidly expanding population of a small prey fish, the three-spined stickleback (Gasterosteus aculeatus). In the central Baltic Sea, three-spined stickleback abundance has increased dramatically during the past decades. The increase in this typical mesopredator has restructured near-shore food webs, increased filamentous algal blooms, and threatens coastal biodiversity. Time-series data covering 22 years show that the increase coincides with a decline in the number of juvenile perch (Perca fluviatilis), the most abundant predator of stickleback along the coast. We investigated the distribution of different stickleback plate armor phenotypes depending on latitude, environmental conditions, predator and prey abundances, nutrients, and benthic production; and described the stomach content of the stickleback phenotypes using metabarcoding. We found two distinct lateral armor plate phenotypes of stickleback, incompletely and completely plated. The proportion of incompletely plated individuals increased with increasing benthic production and decreasing abundances of adult perch. Metabarcoding showed that the stomach content of the completely plated individuals more often contained invertebrate herbivores (amphipods) than the incompletely plated ones. Since armor plates are defense structures favored by natural selection in the presence of fish predators, the phenotype distribution suggests that a novel low-predation regime favors stickleback with less armor. Our results suggest that morphological differentiation of the three-spined stickleback has the potential to affect food web dynamics and influence the persistence and resilience of the stickleback take-over in the Baltic Sea.
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| 23. |
- Hansen, Joakim P., et al.
(author)
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Recreational boating degrades vegetation important for fish recruitment
- 2019
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In: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 48:6, s. 539-551
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Journal article (peer-reviewed)abstract
- Recreational boating increases globally and associated moorings are often placed in vegetated habitats important for fish recruitment. Meanwhile, assessments of the effects of boating on vegetation, and potential effects on associated fish assemblages are rare. Here, we analysed (i) the effect of small-boat marinas on vegetation structure, and (ii) juvenile fish abundance in relation to vegetation cover in shallow wave-sheltered coastal inlets. We found marinas to have lower vegetation cover and height, and a different species composition, compared to control inlets. This effect became stronger with increasing berth density. Moreover, there was a clear positive relationship between vegetation cover and fish abundance. We conclude that recreational boating and related moorings are associated with reduced cover of aquatic vegetation constituting important habitats for juvenile fish. We therefore recommend that coastal constructions and associated boating should be allocated to more disturbance tolerant environments (e.g. naturally wave-exposed shores), thereby minimizing negative environmental impacts.
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| 24. |
- Näslund, Joacim, et al.
(author)
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Considerations needed for analysing data from the Swedish Electrofishing RegiSter (SERS), with special reference to the RivFishTIME database of long-term riverine surveys
- 2023
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In: Fauna Norvegica. - 1502-4873 .- 1891-5396. ; 42, s. 47-51
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Journal article (peer-reviewed)abstract
- The published database RivFishTIME (Comte et al. 2021, Global Ecology and Biogeography, doi: 10.1111/geb.13210) includes a large section of time-series data on fish abundance in Swedish rivers from the Swedish Electrofishing RegiSter, SERS. Knowledge about the limitations of the source data are important when extracting and analyzing data and with this brief note we provide some details that may be helpful for interpreting the Swedish time-series. The note highlights the importance of linking vital metadata to extracted focal data when constructing new databases, especially concerning time series data from monitoring programs conducted in non-randomly selected sites with human environmental impacts. Many of the SERS data come from rivers that have been affected by human impact, e.g. liming to mitigate environmental acidification and hydropower dams, since before monitoring was initiated. Data in SERS are also biased towards shallow salmonid habitats, due to the configuration of Swedish monitoring programs. Hence, data from many rivers are not representative of their fish biodiversity in general. This information is vital for appropriate interpretation of fish biodiversity trends. For RivFishTIME analyses considerations are important since Swedish data constitutes a large proportion of the database. We also provide background information about SERS and references to other Swedish databases containing complementary information. Finally, we provide contact information of the SERS database curators, who can assist prospective analysts with data extraction from SERS.
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| 25. |
- Sandin, Leonard, et al.
(author)
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Sötvatten – förvaltning och restaurering med förändrat klimat : Slutrapport från projektet FRESHREST (Sötvattenslandskapet – förvaltning och restaurering i förändrat klimat)
- 2020
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Reports (other academic/artistic)abstract
- Limniska ekosystem förväntas drabbas hårt av klimatförändringar. Ett förändrat klimat kommer att påverka sötvattensekosystem genom höjda luft- och vattentemperaturer, förändrade flöden och nederbörd. Klimatförändringarna kan också förstärka effekterna av annan mänsklig påverkan såsom t ex övergödning. Ett ekosystem under stress har samtidigt ofta en försämrad motståndskraft (resiliens) mot andra störningar. Redan idag används flera förebyggande åtgärder och restaureringsmetoder för att motverka effekter av klimatförändringar. Det råder dock ofta osäkerhet kring restaureringsmetodernas effektivitet och dessutom är metoderna i många fall platsspecifika.Projektets mål var att sammanfatta kunskapsläget när det gäller klimatförändringar och dess påverkan på limniska ekosystem. Mer specifikt försökte vi att (1) identifiera nyckelbiotoper och arter som är i behov av skydd, (2) utvärdera effekter av klimatförändringar på limniska ekosystem utsatta för multipla stressorer (flera typer av påverkan som samtidigt påverkar ett ekosystem) och (3) bedöma den ekologiska effektiviteten i nuvarande (och möjligen framtida) restaureringsåtgärder i sötvatten.Sverige är ett av världens sjö- och vattendragsrikaste länder i förhållande till ytan. Landets sjöar utgör ca 9 % av den totala landarealen och det finns ca 50 000 mil älvar, åar och bäckar som i ett gigantiskt kapillärnätverk förenar grundvatten, sjöar och våtmarker med havet. Ekosystem i sötvatten har utsatts och utsätts framgent för många typer av mänsklig påverkan vars kumulativa effekter kan försämra systemets förmåga att klara av miljöförändringar. Nu är uppvärmningshastigheten snabbare än någonsin, men förståelsen för potentiella synergistiska effekter av lokala påverkansfaktorer (till exempel dämning, förändrad markanvändning, näringsläckage) och klimat är fortfarande mycket begränsad. Detta försämrar vår förmåga att planera och anpassa effektiva åtgärder för bevarande och restaurering i sötvattensekosystem.Vi använde data från 283 svenska vattendrag för att undersöka möjliga kumulativa effekter av markanvändning, dämningar och klimat på abundans hos öring. Vi fann att ett varmare klimat ger en negativ inverkan på öringpopulationer i avrinningsområden med högre grad av vattenreglering där en uppvärmning på 6 °C resulterar i att abundansen av öring minskar med i genomsnitt 75 %. I avrinningsområden utan eller med lägre grad av vattenreglering ökade istället abundansen av öring något med ett varmare klimat. Jordbruk och urban markanvändning hade en synergistisk negativ effekt på öring. Abundansen av öring minskade i avrinningsområden med en högre andel urban miljö men bara i avrinningsområden som också hade en hög andel jordbruksmark (≥ 20 %). Resultatet tyder på att 1) minskad vattenreglering i form av dämning skulle kunna minska de negativa effekterna av klimatförändringar för öring och 2) restaureringsåtgärder som reducerar effekter från jordbruket skulle underlätta rehabiliteringen av öring i avrinningsområden med urbana miljöer.Vi genomförde också en litteraturstudie för att undersöka klimatförändringens effekter på sötvattensekosystem. Förändringar i fysiska och till viss del kemiska parametrar, var mer förutsägbara än de mer komplexa biologiska förändringarna. Högre temperaturer resulterar i mindre isbildning (inklusive minskande glaciärer) och snötäcke, samt en minskning av vårflödet – vilket är en viktig komponent i naturliga boreala sötvattensekosystem. En allmän uppvärmning av vattnet bör främja ökningen och spridningen av varmvattenarter samt spridningen av invasiva arter (inkl. parasiter, vilka ofta gynnas av varmare vatten) medan man kan förvänta sig en minskning av kallvattenarter. Många av effekterna kopplade till uppvärmning beräknas orsaka fysiska eller kemiska förändringar, vilka i sin tur påverkar ekologiska processer i sötvattensekosystemens näringsväv. Ur mänskligt perspektiv går de flesta förutspådda förändringarna från mer till mindre eftersträvansvärda tillstånd.Restaurering innebär att återskapa eller återföra ekosystemets abiotiska eller biotiska komponenter till dess naturliga eller ursprungliga tillstånd. I Sverige spenderade centrala myndigheter ca 491 miljoner SEK specifikt på restaurering av vattenmiljöer under perioden 1995–2011 och den totala restaureringsbudgeten uppgick till cirka 1 miljard SEK. Mer än 75% av medlen gick till restaurering av vattendrag och våtmarker. Nästan hälften av programmen för vattendragsrestaurering fokuserar på enskilda arter av fisk, mollusker och kräftor. I svenska sjöar har fysiska restaureringsåtgärder haft fokus på att höja vattennivån i tidigare sänkta sjöar, ekologiskt anpassa vattennivån i reglerade sjöar, sedimentmuddra övergödda sjöar, restaurera strandzonen på olika sätt, ta bort dämmen i sjöutlopp och ersätta dem med stentrösklar som håller vattennivå i rätt läge. I vattendrag har mycket av restaureringsåtgärderna fokuserat på återställande av vegetationen i kantzonen, habitatförbättringar i vattendraget, dammrivningar, omstrukturering av vattendragsfåran, fiskpassagelösningar, flödesförändringar och återkoppling av vattendraget till svämplanet. Många av dessa åtgärder kommer att fortsatt rekommenderas i ett förändrat klimat.Kostnaden för att skapa ökad konnektivitet vid samtliga kraftverksdammar i Sverige har uppskattats till 18 miljarder SEK. En tidigare beräkning för att åtgärda bristande kontinuitet landade på upp till 2,2 miljarder SEK för vattendrag och 0,35–0,74 miljarder SEK för sjöar, totalt nästan 3 miljarder SEK vilket förmodligen är i underkant. Nödvändiga åtgärder för att uppnå gynnsam bevarandestatus för sötvattensnaturtyper (enligt art- och habitatdirektivets definitioner), uppskattas till cirka 1 miljard SEK och 2,2 miljarder SEK, för områden innanför respektive utanför Natura2000. För vägtrummor och omläggning av vägar uppgår åtgärdsuppskattningen till 208 miljoner SEK, men kan uppgå till 1 miljard SEK när det gäller allmänna vägar. Tidigare har behovet för omläggning av vägtrummor vid skogsbilvägar uppskattats till 2–4 miljarder SEK och järnvägstrummor till 2–4 miljarder SEK.Eftersom det är svårt att förutsäga var och i vilken utsträckning klimatförändringar kommer att påverka sötvattensekosystem, är det en stor utmaning att förutsäga dess effekter på nuvarande och framtida planerade restaureringsåtgärder. Det är dock möjligt att förvänta sig ett antal generella och mer specifika klimatrelaterade förändringar vid planering av restaureringsåtgärder. Vi undersökte sex vanliga restaureringsåtgärder kopplade till fysiskt påverkade vattendrag och hittade 25 relevanta artiklar inom detta ämne. I de publicerade artiklar som var kopplade till klimatförändring förväntades åtgärder som dammrivning och återskapande av naturliga flödesregimer bli allt viktigare i ett föränderligt klimat. Rinnande vatten som är fritt från hinder (dammar) eller med mer naturliga flödesregimer kommer sannolikt behöva färre restaureringsåtgärder i framtiden för att bibehålla viktiga funktioner och biodiversitet. Ett restaurerat system i balans kan kanske till och mer förhindra eller motverka kolonisation av invasiva arter.Det finns många exempel på dåliga eller icke-fungerande faunapassager i vattendrag. Framtidens klimat kommer att sätta stor press på passage-effektiviteten då extremväder och nederbörd kommer att öka med efterföljande förändringar i flödesregim. Den potentiella positiva effekten av habitat- eller lekplatsrestaurering ser något begränsad ut i ett framtida förändrat klimat. Det finns många vetenskapliga studier som påpekar vikten av landbaserade restaureringsåtgärder (t ex restaurering av strandzonen och våtmarker) i ett förändrat klimat.Vi ger nio rekommendationer för hur framtida restaurering i sötvatten bör ta hänsyn till ett förändrat klimat: (1) Förbättra kunskapen om vilka sötvattensresurser vi har i Sverige och hur de kommer påverkas av ett ändrat klimat, (2) Använd en holistisk syn i restaureringsarbetet, (3) Beakta möjliga klimateffekter i planeringsfasen, (4) Identifiera, restaurera och skydda kallvattenrefugier, (5) Åtgärda vandringshinder, (6) Behåll och ge vattnet plats i landskapet, (7) Integrera land- och vattenbaserad förvaltning, (8) Justera restaureringsmålen så att de är förenliga med framtida klimat och (9) Öka satsningen på utvärdering av genomförda åtgärder.Denna kunskapsöversikt över förändrat klimat på sötvattensrestaurering visar att det finns många kunskapsluckor. Många frågor skulle behöva besvaras genom fortsatt forskning, men vi vill särskilt peka ut forskningsbehov inom följande områden: (1) Identifiering av kallvattensrefugier i vattenlandskapet, (2) Kumulativa stresseffekter och dess påverkan på sötvattensekosystem, (3) Utvärdering av biologiska effekter i ett förändrat klimat och (4) Koppling mellan konnektivitet och restaureringsåtgärder.
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| 26. |
- Tamario, Carl, et al.
(author)
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Nature-like fishways as compensatory lotic habitats
- 2018
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In: River Research and Applications. - : Wiley. - 1535-1459 .- 1535-1467. ; 34, s. 253-261
-
Journal article (peer-reviewed)abstract
- Damming of rivers disrupts migration of fish and results in lotic habitats being both scarcer and spaced further apart, ultimately affecting riverine fish communities. Nature-like fishways are often designed as bypass channels, constructed with natural materials that reroute part of the water around weirs and dams, restoring longitudinal connectivity as well as forming nature-mimicking habitats. We evaluated the potential of such bypasses to function as compensatory lotic habitats by comparing fish fauna in 23 bypasses to adjacent lotic stream habitats in a same-river pairwise design. Bypasses were narrower, shallower, and less shaded than adjacent stream habitats, but very few significant differences could be detected in the fish communities, indicating the potential of such nature-like fishways to constitute compensatory lotic habitats for fish. Analyses also indicated how bypass design may be altered to favour or disfavour certain target species. Generally, narrower and shallower bypasses with high gradient favoured brown trout (Salmo trutta), whereas European eel (Anguilla anguilla) were more abundant at sites with lower gradient. Finally, to increase the impact of these compensatory habitats on running water ecosystems, we suggest that the size of bypasses should be maximized in areas where natural stream habitats have been lost.
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| 27. |
- Widén, Åsa, et al.
(author)
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Sveriges torrfåror : geografi, naturvärden och metoder för miljöförbättringar
- 2022
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Reports (other academic/artistic)abstract
- Syftet med projektet var att ta fram metoder för att underlätta beslut om minimitappning och andra miljöförbättringsåtgärder för torrfåror, d.v.s. vattendragssträckor där vatten letts bort via kanaler eller tunnlar för att passera genom vattenkraftverks turbiner. Ibland sker även överledning från ett vattendrag till ett annat för att på så sätt öka produktionen av vattenkraft i vissa kraftverksanläggningar. Detta lämnar den ursprungliga fåran helt eller delvis torrlagd under stora delar av året. Vi har i denna rapport valt att använda begreppet ”torrfåror” för att indikera att det mest utmärkande draget är den reducerade vattenföringen. Många av dessa sträckor var ursprungligen forsar, och ekosystem och arter knutna till forsar har blivit sällsynta. Vi kartlade förekomsten av torrfåror i Sverige, och totalt identifierades och verifierades 972 torrfåror i en databas. 366 av dessa är belägna i Götaland, 323 i Svealand och 283 i Norrland. Den absoluta majoriteten av Sveriges torrfåror saknar bestämmelser om minimitappning. För de 622 torrfåror där vi hittat uppgifter om vattenföring, saknar 481 (77%) en tilldömd minimitappning. De 137 torrfårorna med minimitappning hade i genomsnitt en medelminimitappning på årsbasis på endast 3,6% av den naturliga årsmedelvattenföringen. I 63% av torrfårorna med minimitappning var denna lika med eller mindre än 5% av den naturliga årsmedelvattenföringen, och 48% var flödet lika med eller mindre än 0,5 m3/s. Analyser av fiskfaunan baserat på elfiskedata visar att torrfåror hade i genomsnitt lägre andel fiskar som hör till typiskt sett strömlevande arter och lägre total fiskabundans jämfört med av vattenkraft opåverkade referenslokaler. Torrfåror med minimitappning hade bättre status vad gäller fiskfaunan än de utan minimitappning vad gäller andel strömlevande arter, total fiskabundans och artrikedom av fisk. Andel individer av strömlevande fiskarter, total fiskabundans och fiskartrikedom ökade med ökande minimitappning i torrfårorna, men sambanden var icke-linjära och planade ut med ökande minimitappning. Torrfårornas medellutning var relativt hög (3,6%), och de representerar till övervägande del strömmande och forsande miljöer som helt eller delvis har torrlagts. Torrfårorna var i genomsnitt 1317 m, medan medianlängden endast var 319 m. De korta (50-100 m) och mycket korta (<50 m) torrfårorna var framför allt belägna i södra Sverige, medan långa (1-10 km) och mycket långa (>10 km) var vanligare i Norrlands inland. Majoriteten av torrfårorna i Sverige låg i vattendragens nedströmsdelar, i vattendragsordning 1 eller 2 räknat från mynningen. Miljöförbättringsåtgärder av olika slag, som mer naturliga vattenflöden, fiskvägar eller biotopvårdande åtgärder, har utförts vid 10% av torrfårorna sedan 1970. Av de 574 torrfåror där överensstämmelsen med vattenförekomster i VISS var god var 434 klassade som naturliga och 140 som kraftigt modifierade. I det senare fallet var den ekologiska potentialen enligt Vattendirektivet alltid klassificerad som måttlig eller sämre. Av de 434 som definierades som naturliga vattenförekomster hade de flesta givits måttlig ekologisk status. De största problemen i vattenförekomster som helt eller delvis motsvarar torrfåror är brister i konnektivitet och att den hydrologiska regimen är förändrad. Våra resultat visar att kortare torrfåror, som bara omfattar en del av en vattenförekomst, ofta förbises vid statusklassningen enligt Vattendirektivet, och att torrfåran ges samma ekologisk status som vattenförekomsten i stort. För att kunna välja ut vilka torrfåror som ska restaureras och genomföra restaureringsprojekt i torrfåror är fungerande samverkansprocess mellan berörda parter (t.ex. verksamhetsutövare, myndigheter, konsulter och ideella organisationer) viktig för att underlätta vägen från kartläggning till genomförande. Vi presenterar aspekter som underlättar, och kompetenser som behövs hos för att processen ska bli lyckosam. För att underlätta genomförandet av miljöförbättringsåtgärder i torrfåror presenterar vi ett metodiskt och strukturerat arbetssätt som ger en komplett kartläggning av torrfåran samt dess omgivande dämningsområden med biflöden, som leder fram till analyser av påverkansgraden, brister jämfört med opåverkade ekosystem, och åtgärdsbehov. Behov av åtgärder grundar sig på vilken restaureringspotential som finns baserat på förhållanden innan reglering och opåverkade referenslokaler. När man summerar naturvärden ger det en bild av vad som är möjligt att göra och vad som kan åstadkommas inom rimliga gränser med tanke på vattenkraftsproduktion. Målet är att detektera för vattenkraftsproduktion kostnadseffektiva och i det långa perspektivet resursanpassade åtgärder som gynnar ekosystemet och bevarar eller ökar naturvärdena. Som en grund för att kunna bestämma nivå på minimitappning presenterar vi en lista på vilka flöden eller aspekter av en naturlig flödesregim som krävs för att uppnå olika naturvärden (ökad biologisk mångfald av naturligt förekommande arter på en vattendragssträcka) eller ekosystemfunktioner. Denna kan hjälpa att bedöma vilka aspekter av naturliga flödesregimer som behövs för att erhålla önskade naturvärden, eller omvänt, att kunna ge en prognos för vilka naturvärden som kan förväntas vid en viss flödesregim, allt fokuserat på torrfåror. Vi presenterar också en metodik för att inventera torrfåror med kvantitativa metoder som bygger på att med hjälp av stickprov skatta hur mycket det finns av olika strukturer. Syftet med inventeringen är att kvantifiera strukturer i och kring vattendraget som kan vara viktiga för en bedömning av potentialen för att återskapa naturvärden (både akvatiska och i strandmiljön) vid olika möjliga flöden i torrfåror. Det finns flera fördelar med att ha en sådan samplingdesign (istället för kvalitativa metoder) i studier av ekologiska restaureringsprojekt. Det möjliggör att skatta t.ex. medelvärdet eller storleken på variabler som är av intresse, vare sig det är ytan av ett vegetationsbälte, mängden död ved eller fraktioner av sediment i fåran. Det kanske viktigaste skälet att göra det är att det möjliggör kvantitativ utvärdering av miljöförbättringsåtgärder, och avgöra om åtgärder har haft avsedd effekt. Miljödomar bör utformas för att vara långsiktigt hållbara för torrfårans ekosystem, d.v.s. vara relevanta under flera decennier trots att elsystemet och klimatet förändras. Få föreslagna åtgärder gällande torrfåror har genomförts praktiskt och att utreda genom uppföljning och belägga huruvida genomförda åtgärder faktiskt gett miljönytta är essentiellt. Uppföljning förutsätter att en vetenskaplig förstudie har genomförts (naturvärde, nuläge, påverkans- och bristanalys). Om det finns förstudier så finns goda förutsättningar att utvärdera effekterna, om tillräckligt lång tid efter restaurering har gått för att åtminstone initial ekologisk respons ska ha skett. Sammanfattningsvis konstaterar vi att de allra flesta torrfåror saknar minimitappning eller andra åtgärder för att förbättra den biologiska mångfalden och vattendragsekosystemen, men att det finns stöd för att sådana åtgärder är effektiva. Vår förhoppning är att de metoder vi presenterar ska underlätta beslut och genomförande av miljöförbättringsåtgärder i torrfåror.
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