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  • 1.
    Donadi, Serena
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Swedish University of Agricultural Sciences (SLU), Sweden.
    Austin, Åsa N.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergström, U.
    Eriksson, B. K.
    Hansen, Joakim P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Jacobson, P.
    Sundblad, G.
    van Regteren, M.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    A cross-scale trophic cascade from large predatory fish to algae in coastal ecosystems2017In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 284, no 1859, article id 20170045Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Donadi, Serena
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Hanse-Wissenschaftkolleg - Institute for Advanced Study, Germany.
    Eriksson, Britas Klemens
    Lettmann, Karsten Alexander
    Hodapp, Dorothee
    Wolff, Joerg-Olaf
    Hillebrand, Helmut
    The body-size structure of macrobenthos changes predictably along gradients of hydrodynamic stress and organic enrichment2015In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 162, no 3, p. 675-685Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Donadi, Serena
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences, Sweden; University of Groningen, The Netherlands.
    Nilsson Austin, Åsa
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Svartgren, Evira
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eriksson, Britas Klemens
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Hansen, J. P.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Density-dependent positive feedbacks buffer aquatic plants from interactive effects of eutrophication and predator loss2018In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 99, no 11, p. 2515-2524Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Eklöf, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Austin, Åsa
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergström, Ulf
    Donadi, Serena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Eriksson, Britas D. H. K.
    Hansen, Joakim
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Sundblad, Göran
    Size matters: relationships between body size and body mass of common coastal, aquatic invertebrates in the Baltic Sea2017In: PeerJ, ISSN 2167-8359, E-ISSN 2167-8359, Vol. 5Article in journal (Refereed)
    Abstract [en]

    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.

  • 5. Engel, Friederike G.
    et al.
    Alegria, Javier
    Andriana, Rosyta
    Donadi, Serena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gusmao, Joao B.
    van Leeuwe, Maria A.
    Matthiessen, Birte
    Eriksson, Britas Klemens
    Mussel beds are biological power stations on intertidal flats2017In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 191, p. 21-27Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Hansen, Joakim P.
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Sundblad, Göran
    Bergström, Ulf
    N. Austin, Åsa
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Donadi, Serena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish University of Agricultural Sciences (SLU), Sweden.
    Eriksson, Britas Klemens
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Recreational boating degrades vegetation important for fish recruitment2018In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Nilsson Austin, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hansen, Joakim P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Donadi, Serena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Relationships between aquatic vegetation and water turbidity: A field survey across seasons and spatial scales2017In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 12, no 8, article id e0181419Article in journal (Refereed)
    Abstract [en]

    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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