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  • 101.
    De La Torre-Castro, Maricela
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Eklöf, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rönnbäck, Patrik
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Botany.
    Seagrass importance in food provisioning services: fish stomach content as a link between seagrass meadows and local fisheries2008In: Western Indian Ocean journal of marine science, ISSN 0856-860X, Vol. 7, no 1, p. 95-110Article in journal (Refereed)
    Abstract [en]

    The links between ecosystem processes and functions and ecosystem services (i.e. the humanbenefits from those) are elusive. In this paper, the food provisioning service of seagrass meadows isoperationalized through the study of the stomach contents of 13 important commercial fish species inChwaka Bay, Zanzibar. Using local fishers’ knowledge on bait, scientific knowledge about the structureof the meadows (associated flora and fauna), stomach content analysis and multivariate statistics, the foodprovisioning service associated with seagrasses and its importance for fish (as important diet component)and for humans (in small-scale artisanal fisheries) are described. The study presents the food items for 13commercial fish species identified at the lowest possible taxonomical level and compares with previousliterature findings. In addition, differences in stomach contents of Siganus sutor and Leptoscarus vaigiensiscaught with both drag-nets and dema basket traps are investigated in order to explore bait presence andindirectly evaluate fishers’ knowledge on bait preference. The results show that most of the items consumedby commercial fishes are associated with seagrass beds and that there are clear indicators that the baittraditionally used seems to be effective. The paper elaborates on the consideration of seagrass ecosystemsin a holistic perspective, the difficulties in valuation of ecosystem services and finally the crucial importanceof these aspects for human well-being and sustainability in coastal communities of the Western IndianOcean.

  • 102.
    De la Torre-Castro, Maricela
    et al.
    Stockholm University, Stockholm Resilience Centre. Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lindström, Lars
    Stockholm University, Faculty of Social Sciences, Department of Political Science.
    Fishing institutions: Addressing regulative, normative and cultural-cognitive elements to enhance fisheries management2010In: Marine Policy, ISSN 0308-597X, E-ISSN 1872-9460, Vol. 34, no 1, p. 77-84Article in journal (Refereed)
    Abstract [en]

    Institutional approaches in natural resource management in general and in fisheries in particular seldom address cultural aspects or social institutions like kinship. In this study, a broad institutional approach is used to investigate the institutionalization of small-scale fisheries and seaweed farming in a seagrass dominated bay in Zanzibar. Regulative, normative and cultural-cognitive institutions and their rapid/slow moving properties are analyzed. The results show that dynamics of cooperation and conflict between different institutional elements and the balance of forces among actors are crucial to understand fisheries management dynamics. Regulations are, despite their importance, insufficient to promote sound management if they are not backed up by norms and cultural-cognitive institutions. Fisheries management would benefit by broadening the institutional perspective to increase the efficiency of management and to avoid blueprint solutions. The study shows that gaining knowledge about the wide institutional setting takes time but the investment is worth it in the long run.

  • 103.
    de la Torre-Castro, Maricela
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ochiewo, J
    Kithakeni Mbaga, T
    Pinault, M
    A framework for addressing socioeconomic and management aspects of sea cucumber resources in the western Indian Ocean2007In: Beche-de-mer-Information-Bulletin, Vol. 25, p. 22-28Article in journal (Refereed)
  • 104.
    Deutsch, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Naturresurshushållning.
    Gräslund, Sara
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Folke, Carl
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Troell, Max
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Huitric, Miriam
    Kautsky, Nils
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lebel, L
    Feeding aquaculture growth through globalization: exploitation of marine ecosystems for fishmeal2007In: Global Environmental Change, Vol. 17, p. 238-249Article in journal (Refereed)
  • 105.
    Didrikas, Tomas
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Effects of light intensity on activity and pelagic dispersion of fish: studies with a seabed-mounted echosounder2009In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 66, p. 388-395Article in journal (Refereed)
    Abstract [en]

    A seabed-mounted, upwards-pinging echosounder was used to study fish activity and pelagic dispersion in relation to fish size, light, and temperature. Four phases (day, dusk, night, dawn) in fish dispersion were distinguished over the diel cycle, and the swimming speed of fish varied among these phases. Notably, average swimming speed by day was twice as high as by night. For all phases combined, fish size, light intensity, and temperature explained 52% of the variability in swimming speed. When different phases were analysed separately, fish size was the most important variable by day, whereas light had the strongest effects on swimming speed in the evening. During the mornings, variability in swimming speed was best correlated with temperature, but by night all factors (fish size, light intensity, temperature) had similar effects on activity. These results have implications for fish bioenergetics models. Such models should account for seasonal, light-driven cycles in activity-induced respiration estimates, in particular when modelling populations at high latitudes.

  • 106.
    Diez, Beatriz
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Pedros-Alio, Carlos
    Anto, Meritxell
    Snoeijs, Pauline
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    High cyanobacterial nifh gene diversity in arctic seawater and sea ice brine2012In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229, Vol. 4, no 3, p. 360-366Article in journal (Refereed)
    Abstract [en]

    Although cyanobacterial diazotrophs are common in Arctic terrestrial and freshwater habitats, they have been assumed to be absent from Arctic marine habitats. We report here a high diversity of cyanobacterial nifH genes in Fram Strait and the Greenland Sea. The nifH gene encodes the iron protein of the nitrogenase enzyme complex, which is essential for biological N2 fixation. Using primers specific for nifH genes we uncovered communities of autotrophic and heterotrophic bacteria in sea ice brine and seawater between latitudes 65 and 81 degrees N. Cyanobacteria (Oscillatoriales and Chroococcales) with known marine planktonic and benthic distributions were distinguished, alongside a mix of metabolically versatile eubacteria (nifH Clusters I and III). Using primers selective for cyanobacterial nifH genes we identified filamentous non-heterocystous Trichodesmium-like and LPP (Leptolyngbya, Phormidium and Plectonema)-like Oscillatoriales, as well as Cyanothece-like Chroococcales in a brine sample from 81 degrees N. The occurrence of Trichodesmium-like cyanobacteria was further confirmed by sequences of the hetR gene of Trichodesmium. Microscopic examinations confirmed the presence of viable filamentous and unicellular cyanobacteria. Our results reveal the potential for microbial N2 fixation in the Arctic seas. However, it is still left to determine if these genes are also metabolically active before any biogeochemical importance of diazotrophy in the polar oceans can be assessed.

  • 107. Domis, Lisette N. De Senerpont
    et al.
    Elser, James J.
    Gsell, Alena S.
    Huszar, Vera L. M.
    Ibelings, Bas W.
    Jeppesen, Erik
    Kosten, Sarian
    Mooij, Wolf M.
    Roland, Fabio
    Sommer, Ulrich
    Van Donk, Ellen
    Winder, Monika
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lurling, Miquel
    Plankton dynamics under different climatic conditions in space and time2013In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 58, no 3, p. 463-482Article, review/survey (Refereed)
    Abstract [en]

    1.Different components of the climate system have been shown to affect temporal dynamics in natural plankton communities on scales varying from days to years. The seasonal dynamics in temperate lake plankton communities, with emphasis on both physical and biological forcing factors, were captured in the 1980s in a conceptual framework, the Plankton Ecology Group (PEG) model. 2.Taking the PEG model as our starting point, we discuss anticipated changes in seasonal and long-term plankton dynamics and extend this model to other climate regions, particularly polar and tropical latitudes. Based on our improved post-PEG understanding of plankton dynamics, we also evaluate the role of microbial plankton, parasites and fish in governing plankton dynamics and distribution. 3.In polar lakes, there is usually just a single peak in plankton biomass in summer. Lengthening of the growing season under warmer conditions may lead to higher and more prolonged phytoplankton productivity. Climate-induced increases in nutrient loading in these oligotrophic waters may contribute to higher phytoplankton biomass and subsequent higher zooplankton and fish productivity. 4.In temperate lakes, a seasonal pattern with two plankton biomass peaks in spring and summer can shift to one with a single but longer and larger biomass peak as nutrient loading increases, with associated higher populations of zooplanktivorous fish. Climate change will exacerbate these trends by increasing nutrient loading through increased internal nutrient inputs (due to warming) and increased catchment inputs (in the case of more precipitation). 5.In tropical systems, temporal variability in precipitation can be an important driver of the seasonal development of plankton. Increases in precipitation intensity may reset the seasonal dynamics of plankton communities and favour species adapted to highly variable environments. The existing intense predation by fish on larger zooplankters may increase further, resulting in a perennially low zooplankton biomass. 6.Bacteria were not included in the original PEG model. Seasonally, bacteria vary less than the phytoplankton but often follow its patterns, particularly in colder lakes. In warmer lakes, and with future warming, a greater influx of allochthonous carbon may obscure this pattern. 7.Our analyses indicate that the consequences of climate change for plankton dynamics are, to a large extent, system specific, depending on characteristics such as food-web structure and nutrient loading. Indirect effects through nutrient loading may be more important than direct effects of temperature increase, especially for phytoplankton. However, with warming a general picture emerges of increases in bacterivory, greater cyanobacterial dominance and smaller-bodied zooplankton that are more heavily impacted by fish predation.

  • 108. Donadi, Serena
    et al.
    van der Heide, Tjisse
    van der Zee, Els M.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Systems Ecology. University of Gothenburg, Sweden; University of Groningen, The Netherlands.
    van de Koppel, Johan
    Weerman, Ellen J.
    Piersma, Theunis
    Olff, Han
    Eriksson, Britas Klemens
    Cross-habitat interactions among bivalve species control community structure on intertidal flats2013In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 94, no 2, p. 489-498Article in journal (Refereed)
    Abstract [en]

    Increasing evidence shows that spatial interactions between sedentary organisms can structure communities and promote landscape complexity in many ecosystems. Here we tested the hypothesis that reef-forming mussels (Mytilus edulis L.), a dominant intertidal ecosystem engineer in the Wadden Sea, promote abundances of the burrowing bivalve Cerastoderma edule L. (cockle) in neighboring habitats at relatively long distances coastward from mussel beds. Field surveys within and around three mussel beds showed a peak in cockle densities at 50-100 m toward the coast from the mussel bed, while cockle abundances elsewhere in the study area were very low. Field transplantation of cockles showed higher survival of young cockles (2-3 years old) and increased spat fall coastward of the mussel bed compared to within the bed and to areas without mussels, whereas growth decreased within and coastward of the mussel bed. Our measurements suggest that the observed spatial patterns in cockle numbers resulted from (1) inhibition effects by the mussels close to the beds due to preemptive algal depletion and deteriorated sediment conditions and (2) facilitation effects by the mussels farther away from the beds due to reduction of wave energy. Our results imply that these spatial, scale-dependent interactions between reef-forming ecosystem engineers and surrounding communities of sedentary benthic organisms can be an important determinant of the large-scale community structure in intertidal ecosystems. Understanding this interplay between neighboring communities of sedentary species is therefore essential for effective conservation and restoration of soft-bottom intertidal communities.

  • 109.
    Downing, Andrea S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    van Nes, Egbert H.
    van de Wolfshaar, Karen E.
    Scheffer, Marten
    Mooij, Wolf M.
    Effects of resources and mortality on the growth and reproduction of Nile perch in Lake Victoria2013In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 58, no 4, p. 828-840Article in journal (Refereed)
    Abstract [en]

    1. A collapse of Nile perch stocks of Lake Victoria could affect up to 30million people. Furthermore, changes in Nile perch population size-structure and stocks make the threat of collapse imminent. However, whether eutrophication or fishing will be the bane of Nile perch is still debated. 2. Here, we attempt to unravel how changes in food resources, a side effect of eutrophication, and fishing mortality determine fish population growth and size structures. We parameterised a physiologically structured model to Nile perch, analysed the influence of ontogenetic diet shifts and relative resource abundances on existence boundaries of Nile perch and described the populations on either side of these boundaries. 3. Our results showed that ignoring ontogenetic diet shifts can lead to over-estimating the maximum sustainable mortality of a fish population. Size distributions can be indicators of processes driving population dynamics. However, the vulnerability of stocks to fishing mortality is dependent on its environment and is not always reflected in size distributions. 4. We suggest that the ecosystem, instead of populations, should be used to monitor long-term effects of human impact.

  • 110.
    Díaz, Eliecer R.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Erlandsson, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Westerbom, Mats
    Kraufvelin, Patrik
    Depth-related spatial patterns of sublittoral blue mussel beds and their associated macrofaunal diversity revealed by geostatistical analyses2015In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 540, p. 121-134Article in journal (Refereed)
    Abstract [en]

    The blue mussel Mytilus edulis is a foundation species with ecosystem engineering functions in the brackish, non-tidal Baltic Sea. In this study from the western Gulf of Finland, the relationship between the spatial patchiness of blue mussels and the diversity of associated macrofauna was examined across small scales (centimeters to meters) for the first time in subtidal habitats. It was demonstrated using geostatistical tools that blue mussel abundance and the diversity of associated macrofauna varied and interacted at 2 depths. Classic analyses (ANOVAs, correlations and multivariate techniques) detected no relationships between the abundance of blue mussels and their associated macrofaunal diversity, or differences in the abundance of mussels or the diversity of associated macrofauna between depths. Using semivariograms, differences in spatial heterogeneity between depths emerged: i.e. patchiness at 5 m and random patterns at 8 m depth. Cross-semivariograms detected negative spatial co-variation between blue mussel abundance and diversity of macrofauna at 5 m, but positive and neutral spatial relationships at 8 m depth. Combining the approaches suggested that high dislodgment of mussels in shallow environments causes this pattern. Dislodgement effects may be compensated for by increased turnover of small mussels in patches within mussel beds, which would result in reduced habitat space for associated macrofauna. On the basis of our results, it is suggested that patchiness of a foundation species is an ecological response, or result of a disturbance, that reduces the diversity of the associated macrofaunal community.

  • 111.
    Edlund, Anna
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ek, Karin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Breitholtz, Magnus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Antibiotic-Induced Change of Bacterial Communities Associated with the Copepod Nitocra spinipes2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 3, p. e33107-Article in journal (Refereed)
    Abstract [en]

    Environmental pressures, such as physical factors, diet and contaminants may affect interactions between microbial symbionts and their multicellular hosts. Despite obvious relevance, effects of antimicrobial contaminants on host-symbiont relations in non-target aquatic organisms are largely unknown. We show that exposure to antibiotics had negative effects on survival and juvenile development of the copepod Nitocra spinipes and caused significant alterations in copepod-associated bacterial communities. The significant positive correlations between indices of copepod development and bacterial diversity indicate that disruption of the microflora was likely to be an important factor behind retarded juvenile development in the experimental animals. Moreover, as evidenced by ribotype distribution in the bacterial clone libraries, the exposure to antibiotics caused a shift in dominance from Betaproteobacteria to Cardinium bacteria; the latter have been shown to cause reproductive manipulations in various terrestrial arthropods. Thus, in addition to providing evidence that the antibiotic-induced perturbation of the microbial community associates with reductions in fitness-related traits of the host, this study is the first record of a copepod serving as a host for endosymbiotic Cardinium. Taken together, our results suggest that (1) antimicrobial substances and possibly other stressors can affect micobiome and symbiont-mediated interactions in copepods and other hosts, and (2) Cardinium endosymbionts may occur in other copepods and affect reproduction of their hosts.

  • 112.
    Ehrenberg, Sigrid Z.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Diet of the sand goby in the Baltic sublittoral: composition and impact on benthic preyManuscript (Other academic)
  • 113.
    Ehrenberg, Sigrid Z.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    The invasive species Cercopagis pengoi (Cladocera) and Marenzelleria spp. (Polychaeta) as food for the indigenous Baltic sand goby, Pomatoschistus minutus (Pisces)Manuscript (Other academic)
  • 114.
    Ehrenberg, Sigrid Z.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    The neglected ecology of the sand goby: Abundance and feeding in the Baltic sublittoral2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    I investigated the ecology and population density of the sand goby, Pomatoschistus minutus, at sub-thermocline depth in the north-western Baltic proper. Most previous research on the sand goby, and the co-occurring closely related common goby, P. microps, has focused on their stay in shallow waters, while important parts of their life cycles have been largely neglected.

    Photography was used to assess goby population density and size distribution, a basis for estimations of the potential annual food consumption of the goby community. Diet analysis of the most abundant goby, the sand goby, was combined with the population censuses to estimate the contribution of different prey to the goby consumption. Both benthic and pelagic prey were consumed, including two non-indigenous species. The amphipod Monoporeia affinis was by far the most important prey for the overall consumption, while pelagic and benthic copepods, and naidid oligochaetes were important prey for sand gobies < 3.5 cm. Goby predation is likely to influence the populations of naidid oligochaetes and the amphipod M. affinis, as large parts of their production may be consumed.

    The potential goby consumption was calculated to be about 72 kJ m-2 yr-1, which corresponds to 14-60 % of the annual production on soft bottoms in the area. In a laboratory study of the sand goby activity, active swimming occurred preferentially at night and burying in the sediment mostly at day. Both behaviours may lead to underestimates in photographic censuses of up to 40 %. The goby community in the sublittoral links the benthic and pelagic sub-systems in the area by being able to remove a substantial amount of energy from the benthic production, by inclusion of pelagic prey, and by holding an intermediate position in the coastal marine food web of the Baltic Sea. Consequently, their role in the flow of energy, elements and substances, some potentially harmful, between the pelagic and benthic ecosystem should be further investigated.

  • 115.
    Ehrenberg, Sigrid Z.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ejdung, Gunilla
    Daily activity pattern of the sand goby, Pomatoschistus minutus (Pisces), at low light intensity2007In: Hydrobiologia, ISSN 0018-8158, Vol. 603, no 1, p. 129-137Article in journal (Refereed)
  • 116.
    Ehrenberg, Sigrid Z.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ejdung, Gunilla
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Daily activity pattern of the sand goby, Pomatoschistus minutus (Pisces), at low light intensity.2008In: HYDROBIOLOGIA, ISSN 0018-8158, Vol. 603, p. 129-137Article in journal (Refereed)
    Abstract [en]

    In autumn and winter, the sand goby (Pomatoschistus minutus) in the Baltic Sea is to a large extent found on soft bottoms deeper than the summer thermocline. Although P. minutus are numerous during a large part of the year in these areas, most studies on this species have been performed on very shallow bottoms. Here we study the activity of P. minutus in autumn using video recordings in the laboratory, under light (1.5-2 lux) and temperature conditions prevailing at ca. 30 m depth. We propose that the results can be used to evaluate in situ abundance censuses. P. minutus had the same nocturnal activity pattern in low light intensity as described for light intensities found in shallow water. The fish swim significantly more in darkness than in light, and bury in the sediment mainly at day. These behaviours, recorded in the absence of predators, are suggested to be adaptations to avoid predators.

  • 117.
    Ehrenberg, Sigrid Z.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Elmgren, Ragnar
    Sublittoral abundance and food consumption of Baltic gobies2005In: Journal of Fish Biology, ISSN 0022-1112, Vol. 67, no 4, p. 1083-1093Article in journal (Refereed)
  • 118.
    Ejdung, Gunilla
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Byren, Lars
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Wiklund, Ann-Kristin
    Department of Applied Environmental Science (ITM).
    Sundelin, Brita
    Department of Applied Environmental Science (ITM).
    Uptake of diatoms in Baltic Sea macrozoobenthos during short-term exposure to severe and moderate hypoxia.2008In: Aquatic Biology, ISSN 1864-7790, Vol. 3, no 1, p. 89-99Article in journal (Refereed)
    Abstract [en]

    he effect of severe and moderate hypoxia on food uptake of benthic macrofauna was studied in the laboratory. The hypothesis was that low oxygen concentrations negatively affect feeding at oxygen levels that have little effect on the studied animals' survival. The bivalve Macoma balthica, the priapulid Halicryptus spinulosus, the amphipods Monoporeia affinis (subadult & juvenile) and Pontoporeia femorata (subadult) were offered the C-14-labelled diatom Skeletonema costatum in 0.8 to 10.6 mg O-2 l(-1). Feeding was measured as radioactivity uptake. Subadult amphipods were studied one species at a time (single) or together (mixed). Feeding changed in all amphipods at the lowest oxygen concentrations, but no effect was found for M. balthica and H. spinulosus. At the lowest concentration (0.8 mg O-2 l(-1)) feeding by subadult M affinis (single) was only 17% of the full oxygen saturation (10.6 mg O-2 l(-1)), and, at 1.6 mg O-2 l(-1), 14% of the feeding at 8.9 mg O-2 l(-1). Juvenile M affinis consumed more labelled algae at 3 Mg O-2 l(-1) than at higher oxygen concentrations. M balthica feeding was not affected. Little radioactivity uptake was registered for H. spinulosus at any oxygen concentration, showing that H. spinulosus is not a surface deposit feeder. The amphipods were the most sensitive to week-long oxygen deficiency. Survival decreased significantly in the lowest oxygen concentrations (0.8; 1.6 mg O-2 l(-1)). Of the subadult M. affinis 15 and 65%, respectively, survived, compared with 0 and 58% for P. femorata. Juvenile M. affinis mortality was high in all oxygen concentrations, whereas most M balthica and H. spinulosus survived.

  • 119.
    Ejdung, Gunilla
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Flach, Elsina
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Byrén, Lars
    Stocksunds Hamn, Marina Iäroverket.
    Hummel, Herman
    Netherlands Inst Ecol, Ctr Estuarine & Marine Ecol.
    Predation by crustaceans on native and non-native Baltic clams2009In: Aquatic biology, ISSN 1864-7790, Vol. 6, p. 15-24Article in journal (Refereed)
    Abstract [en]

    We studied the effect of crustacean predators on native/non-native Macoma balthica bivalves in aquarium experiments. North Sea M balthica (NS Macoma) were recently observed in the southern Baltic Sea. They differ genetically and in terms of morphology, behaviour and evolutionary history from Baltic Sea M balthica (BS Macoma), and this may affect predation pressure and community structure. We hypothesised that predators consume more of the prey they co-exist with. NS Macoma and BS Macoma were exposed to crustacean predators common in the North Sea (Carcinus maenas and Crangon crangon) and in the Baltic Sea (C. crangon and Saduria entomon). Contrary to our hypotheses, the North Sea predators ate more BS Macoma, and S. entomon ate more NS Macoma. The crush-limited C. maenas preyed more on globular BS Macoma, whereas S. entomon, which do not crush but pry open the bivalve shell, ate more NS Macoma, which have a lighter (thus probably thinner) shell than BS Macoma. When NS and BS Macoma were offered together, BS Crangon ate more NS Macoma. We also studied BS Crangon consumption of M. balthica to assess whether sizes offered fall within the size spectrum that C. crangon can eat. Small (20 to 40 mm long), medium (40 to 50 mm) and large (50 to 60 mm) C. crangon especially ate small M. balthica. Differences in shape, size and meat/shell weight ratio between the BS and NS Macoma partly explained the differences in the susceptibility to predation by native and non-native predators.

  • 120.
    Ekeroth, Nils
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    On benthic fluxes of phosphorus in the Baltic Sea proper – drivers and estimates2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This Thesis focuses on the exchange of phosphorus (P) across the sediment–water interface in the Baltic Sea proper, with particular attention to the influence of bioturbating macrofauna and benthic redox conditions. Benthic P fluxes have major influence on P availability in the water column, which in turn regulates growth conditions for dinitrogen fixating cyanobacteria in the Baltic proper. Presently, a very large area of bottom sediment is overlain by oxygen depleted bottom water and is therefore devoid of aerobic organisms.

    In paper I, anoxic sediment from the Western Gotland Basin was oxygenated and exposed to bioturbation by three macrofauna species in a laboratory experiment. The experimental design allowed for detailed studies of how bioturbating animals influence the P fluxes on a species-specific level. All species (Monoporeia affinis, Mysis mixta, and Macoma balthica) mobilised dissolved organic P from the bottom sediment to the supernatant water. Also, particulate P was released by the two former species. None of these P fractions showed any mobility in control sections of the aquarium system. These animal-dependent P fluxes are a previously largely overlooked but potentially significant source of bioavailable P in coastal marine areas, such as the Baltic Sea.

    In paper II, we estimate a contemporary reflux of 146 kton dissolved inorganic P (DIP) from bottom sediments in the Baltic proper. This estimate is based on data from a large number of in situ benthic flux measurements using benthic chamber landers along a depth gradient in the Eastern Gotland Basin. DIP effluxes increased with increasing water depth, and decreasing bottom water oxygen concentrations. Bottom water anoxia was identified as a major driver for the mobilisation of DIP from bottom sediments. During such conditions, the DIP efflux was well correlated to carbon oxidation rate, while on oxic bottoms DIP fluxes were low irrespectively of the carbon oxidation rate. Our data support the hypothesis of a positive feedback loop of self-amplifying eutrophication in the Baltic Sea. Thus, both nutrient emission cuts and active mitigation actions to strengthen sedimentary P sinks are warranted for effective remediation of eutrophication in the Baltic Sea.

  • 121.
    Ekeroth, Nils
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lindström, Magnus
    Blomqvist, Sven
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hall, Per
    Recolonisation by macrobenthos mobilises organic phosphorus from reoxidised Baltic Sea sediments2012In: Aquatic geochemistry, ISSN 1380-6165, E-ISSN 1573-1421, Vol. 18, no 6, p. 499-513Article in journal (Refereed)
    Abstract [en]

    In recent decades, eutrophication has increased the extent of hypoxic and anoxic conditions in many coastal marine environments. In such conditions, the nutrient flux across the sediment–water interface is a key process controlling the biogeochemical dynamics, and thereby the level and character of biological production. In some areas, management attempts to drive the ecosystem towards phosphorus (P) limitation, which calls for reliable knowledge on the mechanisms controlling P-cycling. We report a well-controlled laboratory experiment on benthic fluxes of P, when shifting from a state of hypoxic and azoic sediments to oxic and zoic bottom conditions. Adding any of three types of macrobenthic fauna (mysid shrimp, pontoporeid amphipod and tellinid clam) to oxygenated aquarium sections resulted in benthic P fluxes that differed consistently from the azoic control sections. All species caused liberation of dissolved organically bound P (DOP) from the sediment, in contrast to the azoic systems. The shrimp and the amphipod also resuspended the sediment, which resulted in a release of P bound to particles (>0.45 μm). Dissolved inorganic phosphate (DIP) was released during hypoxic conditions, but was taken up after oxygenation, irrespective of the presence or absence of bottom fauna. In the presence of fauna, the uptake of DIP roughly equalled the release of DOP, suggesting that the benthic efflux of DOP following oxygenation and bottom fauna (re)colonisation might be considerable. This is an hitherto overlooked animal-controlled nutrient flux, which is missing from coastal marine P budgets.

  • 122.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Anthropogenic Disturbances and Shifts in Tropical Seagrass Ecosystems2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Seagrasses constitute the basis for diverse and productive ecosystems worldwide. In East Africa, they provide important ecosystem services (e.g. fisheries) but are potentially threatened by increasing resource use and lack of enforced management regulations. The major aim of this PhD thesis was to investigate effects of anthropogenic distur-bances, primarily seaweed farming and coastal fishery, in East African seagrass beds. Seaweed farming, often depicted as a sustainable form of aquaculture, had short- and long-term effects on seagrass growth and abundance that cascaded up through the food web to the level of fishery catches. The coastal fishery, a major subsistence activity in the region, can by removing urchin predators indirectly increase densities of the sea urchin Tripneustes gratilla, which has overgrazed seagrasses in several areas. A study using simulated grazing showed that high magnitude leaf removal – typical of grazing urchins – affected seagrasses more than low magnitude removal, typical of fish grazing. Different responses in two co-occurring seagrass species furthermore indicate that high seagrass diversity in tropical seagrass beds could buffer overgrazing effects in the long run. Finally, a literature synthesis suggests that anthropogenic disturbances could drive shifts in seagrass ecosystems to an array of alternative regimes dominated by other or-ganisms (macroalgae, bivalves, burrowing shrimp, polychaetes, etc.). The formation of novel feedback mechanisms makes these regimes resilient to disturbances like seagrass recovery and transplantation projects. Overall, this suggests that resource use activities linked to seagrasses can have large-scale implications if the scale exceeds critical levels. This emphasizes the need for holistic and adaptive management at the seascape level, specifically involving improved techniques for seaweed farming and fisheries, protection of keystone species, and ecosystem-based management approaches.

  • 123.
    Eklöf, Johan S.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Vad kostar den grillade fisken och glassen egentligen?2008In: Forskning, Vol. 5, p. 53-Article in journal (Other (popular science, discussion, etc.))
  • 124.
    Eklöf, Johan S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Alsterberg, Christian
    Havenhand, Jonathan N.
    Sundbäck, Kristina
    Wood, Hannah L.
    Gamfeldt, Lars
    Experimental climate change weakens the insurance effect of biodiversity2012In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 15, no 8, p. 864-872Article in journal (Refereed)
    Abstract [en]

    Ecosystems are simultaneously affected by biodiversity loss and climate change, but we know little about how these factors interact. We predicted that climate warming and CO 2-enrichment should strengthen trophic cascades by reducing the relative efficiency of predation-resistant herbivores, if herbivore consumption rate trades off with predation resistance. This weakens the insurance effect of herbivore diversity. We tested this prediction using experimental ocean warming and acidification in seagrass mesocosms. Meta-analyses of published experiments first indicated that consumption rate trades off with predation resistance. The experiment then showed that three common herbivores together controlled macroalgae and facilitated seagrass dominance, regardless of climate change. When the predation-vulnerable herbivore was excluded in normal conditions, the two resistant herbivores maintained top-down control. Under warming, however, increased algal growth outstripped control by herbivores and the system became algal-dominated. Consequently, climate change can reduce the relative efficiency of resistant herbivores and weaken the insurance effect of biodiversity.

  • 125.
    Eklöf, Johan S
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    de la Torre-Castro, Maricela
    Seagrass loss and feedback mechanisms: multiple regimes in seagrass ecosystemsManuscript (Other academic)
  • 126.
    Eklöf, Johan S
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    de la Torre-Castro, Maricela
    Adelsköld, Lisa
    Kautsky, Nils
    Jiddawi, Narriman S
    Differences in macrofaunal and seagrass assemblages in seagrass beds with and without seaweed farms2005In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, Vol. 63, no 3, p. 385-396Article in journal (Refereed)
  • 127.
    Eklöf, Johan S
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    de la Torre-Castro, Maricela
    Nilsson, Camilla
    Rönnbäck, Patrik
    How do seaweed farms influence fishery catches in a seagrass-dominated setting in Chwaka Bay, Zanzibar?2006In: Aquatic Living Resources, ISSN 0990-7440, Vol. 19, no 2, p. 137-147Article in journal (Refereed)
  • 128.
    Eklöf, Johan S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Fröcklin, Sara
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lindvall, Annika
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Stadlinger, Nadja
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Kimathi, Alex
    Uku, Jacqueline N.
    McClanahan, Tim R.
    How effective are MPAs? Predation control and ‘spill-in effects’ in seagrass–coral reef lagoons under contrasting fishery management.2009In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 384, p. 83-96Article in journal (Refereed)
  • 129.
    Eklöf, Johan S
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Fröcklin, Sara
    Stadlinger, Nadja
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Dahlberg, Annika
    Uku, Jacqueline N
    Kimathi, Alex
    McClanahan, Tim R
    Fishing, trophic cascades, and overgrazing of Kenyan seagrass bedsManuscript (Other academic)
  • 130.
    Eklöf, Johan S
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gullström, Martin
    Björk, Mats
    Asplund, Maria
    Dahlgren, Annika
    Hammar, Linus
    Öhman, Marcus C
    Physical responses of two co-occurring seagrasses to different grazing regimesManuscript (Other academic)
  • 131.
    Eklöf, Johan S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Moksnes, Per-Olav
    Göteborgs universitet.
    Baden, Susanne
    Göteborgs universitet.
    Sjögräsängar - hotade av både övergödning och fiske?2009In: Havsutsikt, no 1, p. 10-11Article in journal (Other (popular science, discussion, etc.))
  • 132.
    Eklöf, Johan S
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Henriksson, Rebecka
    Kautsky, Nils
    Effects of tropical open-water seaweed farming on seagrass ecosystem structure and function2006In: Marine Ecology Progress Series, ISSN 0171-8630, Vol. 325, p. 73-84Article in journal (Refereed)
  • 133.
    Eklöf, Johan S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    McMahon, Kathryn
    Lavery, Paul S.
    Effects of multiple disturbances in seagrass meadows: shading decreases resilience to grazing.2009In: Marine and Freshwater Research, ISSN 1323-1650, E-ISSN 1448-6059, Vol. 60, p. 1317-1327Article in journal (Refereed)
  • 134.
    Eklöf, J.S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    de la Torre-Castro, M.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Zoology.
    Uku, J.
    Muthiga, N.
    Lyimo, T.
    Bandeira, S.O.
    Sea urchin overgrazing of seagrasses: A review of current knowledge on causes, consequences and management2008In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 79, no 4, p. 569-580Article in journal (Refereed)
    Abstract [en]

    Sea urchins are one of the most common seagrass macro-grazers in contemporary seagrass systems. Occasionally their grazing rates exceed seagrass growth rates, a phenomenon sometimes referred to as overgrazing. Because of a reported increasing frequency of overgrazing events, concomitant with loss of seagrass-associated ecosystem services, it has been suggested that overgrazing is one of the key threats to tropical and subtropical seagrasses. In light of this, we review the current knowledge on causes, consequences. and management of sea urchin overgrazing of seagrasses. Initially we argue that the definition of overgrazing must include scale and impairment of ecosystem services, since this is the de facto definition used in the literature, and will highlight the potential societal costs of seagrass overgrazing. A review of 16 identified cases suggests that urchin overgrazing is a global phenomenon, ranging from temperate to tropical coastal waters and involving at least 11 seagrass and 7 urchin species. Even though most overgrazing events Seem to affect areas of <0.5 km(2), and recovery often occurs within a few years, overgrazing can have a range of large, long-term indirect effects such as loss of associated fauna and decreased sediment stabilization. A range of drivers behind overgrazing have been suggested, including bottom-up (nutrient enrichment). top-down (reduced predation control due to e.g. overfishing), "side-in" mechanisms (e.g. changes in water temperature) and natural population fluctuations. Based on recent studies, there seems to be fairly strong support for the top-down and bottom-up hypotheses. However, many potential drivers often co-occur and interact, especially in areas with high anthropogenic pressure, suggesting that multiple disturbances-by simultaneously reducing predation control, increasing urchin recruitment and reducing the resistance of seagrasses-could pave the way for overgrazing. In management, the most common response to overgrazing has been to remove urchins, but limited knowledge of direct and indirect effects makes it difficult to assess the applicability and sustainability of this method. Based on the wide knowledge gaps, which severely limits management, we suggest that future research should focus on (1) identification and quantification of ecosystem and societal scale effects of overgrazing; (2) assessment of the relative importance and interactions of different drivers; and (3) development of a holistic proactive and reactive long-term management agenda.

  • 135.
    Eklöf, J.S.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gullström, Martin
    Department of Zoology. Ekologi.
    Björk, Mats
    Department of Botany.
    Asplund, M.E.
    Hammar, L.
    Dahlgren, A.
    Öhman, Marcus
    Department of Zoology. Ekologi.
    The importance of grazing intensity and frequency for physiological responses of the tropical seagrass Thalassia hemprichii2008In: Aquatic botany, Vol. 89, p. 337-340Article in journal (Refereed)
    Abstract [en]

    Seagrass grazing is an intrinsic disturbance in primarily tropical and subtropical areas. While there is a general parabolic response in seagrass growth to grazing intensity, there is less knowledge on the role of grazing frequency, as well as potential interactions between grazing intensity and frequency. This study experimentally investigated physiological responses in Thalassia hemprichii to simulated (leaf cutting) grazing regimes with different intensities (25% vs. 75%) and frequencies (I times vs. 3 times) over 35 days in Chwaka Bay (Zanzibar, Tanzania). The results showed that the two high-intensity treatments (75% removal) had 37-41% lower growth rate than the low-intensity/low-frequency treatment, and rhizome sugar and starch content were both affected in a similar way. A 36% lower starch content in the simulated low-intensity/high-frequency regime (25% x 3) compared to the one of low-intensity/low-frequency (25% x I) also shows an interaction between grazing intensity and frequency. This suggests that high-intensity (and to some extent frequency) grazing regimes, in comparison to low-intensity regimes, could negatively affect T. hemprichii growth, energy reserves, and thereby the ability to deal with additional stress like light limitation or grazing.

  • 136.
    Elmgren, Ragnar
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Kumblad, Linda
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Emil, Rydin
    Baltic2020 Foundation.
    Wulff, Fredrik V.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Political backing to save the Baltic sea2012In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 487, p. 432-432Article in journal (Other (popular science, discussion, etc.))
  • 137.
    Elmqvist, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Alfsen, C.
    Colding, J.
    Urban Systems2008In: Encyclopedia of ecology, Elsevier, Oxford , 2008, p. 3665-3672Chapter in book (Refereed)
  • 138.
    Elmqvist, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Pyykönen, Markku
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Tengö, Maria
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rakotondrasoa, F
    Rabakonandrianina, E
    Radimilahy, C
    Patterns of loss and regeneration of tropical dry forest in Madagascar: The social institutional context2007In: Plos One, Vol. 2, no 5, p. e402-Article in journal (Refereed)
  • 139.
    Elmqvist, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Tengö, M
    Spontaneous regeneration of tropical dry forest in Madagascar2010In: Reforesting landscapes: linking pattern and process / [ed] Nagendra H and Southworth J, Dordrecht: Springer, 2010Chapter in book (Other academic)
  • 140.
    Enfors, Elin
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Traps and Transformation. Water System Innovations in Dryland Environments2007Licentiate thesis, monograph (Other academic)
  • 141.
    Enfors, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre.
    Barron, Jennie
    Stockholm University, Stockholm Resilience Centre, Stockholm Environment Institute.
    Makurira, Hodson
    University of Zimbabwe.
    Rockström, Johan
    Stockholm University, Stockholm Resilience Centre, Stockholm Environment Institute.
    Tumbo, Siza
    Sokoine University of Agriuclture.
    Yield and soil system changes from conservation tillage in dryland farming: A case study from North Eastern Tanzania2011In: Agricultural Water Management, ISSN 0378-3774, E-ISSN 1873-2283, Vol. 98, no 11, p. 1687-1695Article in journal (Refereed)
    Abstract [en]

    Yield levels in smallholder farming systems in semi-arid sub-Saharan Africa are generally low. Water shortage in the root zone during critical crop development stages is a fundamental constraining factor. While there is ample evidence to show that conservation tillage can promote soil health, it has recently been suggested that the main benefit in semi-arid farming systems may in fact be an in situ water harvesting effect. In this paper we present the result from an on-farm conservation tillage experiment (combining ripping with mulch and manure application) that was carried out in northeastern Tanzania from 2005 to 2008, testing this hypothesis. Special attention was given to the effects on the water retention properties of the soil. The tested conservation treatment only had a clear yield increasing effect during one of the six experimental seasons (maize grain yields increased by 41%, and biomass by 65%), and this was a season that received exceptional amounts of rainfall (549 mm). While the other seasons provided mixed results, there seemed to be an increasing yield gap between the conservation tillage treatment and the control towards the end of the experiment. Regarding soil system changes, small but significant effects on chemical and microbiological properties, but not on physical properties, were observed. This raises questions about the suggested water harvesting effect and its potential to contribute to stabilized yield levels under semi-arid conditions. We conclude that, at least in a shorter time perspective, the tested type of conservation tillage seems to boost productivity during already good seasons, rather than stabilize harvests during poor rainfall seasons. Highlighting the challenges involved in upgrading these farming systems, we discuss the potential contribution of conservation tillage towards improved water availability in the crop root zone in a longer-term perspective.

  • 142.
    Enfors, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gordon, Line
    Analysing resilience in dryland agro-ecosystems: A case study of the Makanya catchment in Tanzania over the past 50 years2007In: Land Degradation and Development, ISSN 1085-3278, E-ISSN 1099-145X, Vol. 18, no 6, p. 680-696Article in journal (Refereed)
  • 143.
    Enfors, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gordon, Line
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, interfaculty units, Stockholm Resilience Centre.
    Dealing with drought: The challenge of using water system technologies to break dryland poverty traps2008In: Global environmental change, ISSN 0959-3780 , Vol. 18, no 4, p. 607-616Article in journal (Refereed)
    Abstract [en]

    We explore strategies among farmers in semi-arid Tanzania to cope with drought, and investigate if access to a local supplemental irrigation system (the Ndiva system) can improve coping capacity. Results show high dependency on local ecosystem services when harvests fail, and indicate that farmers commonly exhaust asset holdings during droughts. Ndiva access did not have any direct effects on coping capacity, but seemed to have some indirect effects. Drawing on our findings we discuss the complexity of escaping persistent dryland poverty, and outline the circumstances under which small-scale water system technologies, such as Ndiva irrigation, may help.

  • 144.
    Enfors, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gordon, Line
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre.
    Peterson, Garry
    Stockholm University, Stockholm Resilience Centre. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bossio, Deborah
    Making investments in dryland development work: participatory scenario planning in the Makanya catchment, Tanzania2008In: Ecology and society, ISSN 1708-3087 , Vol. 13, no 2, p. 42-Article in journal (Refereed)
  • 145.
    Engqvist, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Döös, Kristofer
    Department of Meteorology.
    Andrejev, O
    Modeling water exchange and contaminant transport through a Baltic coastal region2006In: Ambio, ISSN 0044-7447, Vol. 35, no 8, p. 435-447Article in journal (Refereed)
  • 146.
    Engqvist, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Stenström, Petter
    Royal Inst Technol, Dept Land & Water Resources Engn.
    Flow regimes and long-term water exchange of the Himmerfjärden estuary.2009In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 83, no 2, p. 159-174Article in journal (Refereed)
    Abstract [en]

    A numerical model of processes determining the water exchange encountered in Baltic coastal archipelagos is calibrated and validated against salinity and temperature field data spanning two decades with approximately bi-weekly resolution assessed in the Himmerfjarden estuary. This area is resolved into 17 basins interconnected by 38 individual straits of varying geometrical properties using GIS-based methods. All formulations of the strait exchange flows are free from parameters that need calibration and permit computations of the flow through a strait contraction with or without a coincident sill under a flow classification scheme, of which the first one (a) consists of two groups of multiple layers including aspirated layers from levels beneath the sill crest. The other regimes are as follows. (b) Pure barotropic flow; (c) rotationally controlled flow and (d) plug-flow, which serves as resort solution for flow situations that cannot be solved with (a) and also for computation of the barotropic part of the total flow. For long canals where friction effects act to reduce the flow, a fifth exchange regime is used. The vertical mixing formulation is based on energy balances between supplied wind energy and its work against buoyancy forces. The values of semi-empirical parameters involved in the mixing scheme have been established by calibration against measured data of the first decade period. A statistical evaluation is performed comparing the model results with the measurements of the second decade.It is found that the accuracy of the model is yet limited by the poor temporal resolution in the boundary and the thermal forcing. The overall accuracy of this approach is found to be comparable to earlier model studies in the same area. Since the exchange flows are now based on first principles and are applied to four times more basins, it seems that this more articulated model approach can confidently be applied to more complex archipelago areas.

  • 147. Engström-Öst, Jonna
    et al.
    Hogfors, Hedvig
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    De Stasio, Bart
    Vehmaa, Anu
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Toxin-producing cyanobacterium Nodularia spumigena, potential competitors and grazers: testing mechanisms of reciprocal interactions2011In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 62, no 1, p. 39-48Article in journal (Refereed)
    Abstract [en]

    Interactions among toxic cyanobacteria, sympatric algae and planktivorous grazers are key processes governing plankton dynamics and cyanobacterial blooms. We studied interactions between the cyanobacterium Nodularia spumigena and microalgae (Rhodomonas salina and Tetraselmis suecica) as well as effects of zooplankton (copepod Eurytemora affinis) grazing on these interactions. N. spumigena was incubated without algae or with algae at different concentrations and with or without copepods. Following similar to 24 h incubation, we assayed changes in N. spumigena and algae abundance, concentration of intracellular (IC) and dissolved nodularin (toxin produced by N. spumigena) and quantity of Nodularia DNA in copepod guts (as a proxy for grazing pressure on the cyanobacterium). In the presence of algae, IC nodularin levels increased in a concentration-dependent manner; however, when copepods were present in the mixtures of algae and cyanobacterium, this increase was significantly less. The presence of T. suecica negatively affected the growth rate of N. spumigena, whereas the presence of the cyanobacterium strongly impeded growth of R. salina, but not of T. suecica. The IC nodularin quota correlated negatively with growth of R. salina, implicating the toxin's involvement in the observed growth suppression of the eukaryotic alga. Copepods actively ingested N. spumigena, even when the alternative food was plentiful, and neither N. spumigena quantity nor its toxin concentrations influenced copepod feeding rates and survival. These findings suggest complex allelopathic interactions between the autotrophs, whereas mesozooplankton grazers have an indirect negative effect on the nodularin concentrations by suppressing the competitors. These findings underscore the need to study ecologically important interactions among toxic cyanobacteria, sympatric algae and grazers, if we are to understand mechanisms regulating cyanobacterial blooms.

  • 148.
    Ericson, Hanna
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Thorsen, Gunnar
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Kumblad, Linda
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Physiological effects of diclofenac, ibuprofen and propranolol on Baltic Sea blue mussels2010In: Aquatic Toxicology, ISSN 0166-445X, E-ISSN 1879-1514, Vol. 99, no 2, p. 223-231Article in journal (Refereed)
    Abstract [en]

    Pharmaceuticals are constantly dispersed into the environment and little is known of the effects on non-target organisms. This is an issue of growing concern. In this study, Baltic Sea blue mussels, Mytilus edulis trossulus, were exposed to diclofenac, ibuprofen and propranolol, three pharmaceuticals that are produced and sold in large quantities and have a widespread occurrence in aquatic environments. The mussels were exposed to pharmaceuticals in concentrations ranging from 1 to 10,000 mu g l(-1). The pharmaceuticals were added both separately and in combination. Mussels exposed to high concentrations of pharmaceuticals showed a clear response compared to controls. Firstly, they had a significantly lower scope for growth, which indicates that the organisms had a smaller part of their energy available for normal metabolism, and secondly, they had lower byssus strength and lower abundance of byssus threads, resulting in reduced ability to attach to the underlying substrate. Mussels exposed to lower concentrations showed tendencies of the same results. The concentration of diclofenac and propranolol was quantified in the mussels using both liquid chromatography coupled to mass spectrometry (LC-MS). The measurements showed a significantly higher concentration in the organisms as compared to the water the mussels were exposed to; the uptake reached concentrations two orders of magnitudes higher than found in sewage treatment plant effluents. This study showed that common pharmaceuticals are taken up and negatively affect the physiology of a non-target species at levels of two to three orders of magnitudes higher than found in sewage treatment plant effluents.

  • 149.
    Eriksson, Britas Klemens
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ljunggren, Lars
    Swedish Board Fisheries.
    Sandström, Alfred
    Swedish Board Fisheries.
    Johansson, Gustav
    Fdn Uppland.
    Mattila, Johanna
    Åbo Akad Univ.
    Rubach, Anja
    Univ Cologne.
    Råberg, Sonja
    Stockholm University, Faculty of Science, Department of Botany.
    Snickars, Martin
    Åbo Akad Univ.
    Declines in predatory fish promote bloom-forming macroalgae.2009In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 19, no 8, p. 1975-1988Article in journal (Refereed)
    Abstract [en]

    In the Baltic Sea, increased dominance of ephemeral and bloom-forming algae is presently attributed to increased nutrient loads. Simultaneously, coastal predatory fish are in strong decline. Using field data from nine areas covering a 700-km coastline, we examined whether formation of macroalgal blooms could be linked to the composition of the fish community. We then tested whether predator or nutrient availability could explain the field patterns in two small-scale field experiments, by comparing joint effects on algal net production from nutrient enrichment with agricultural fertilizer and exclusion of larger predatory fish with cages. We also manipulated the presence of invertebrate grazers.

    The abundance of piscivorous fish had a strong negative correlation with the large-scale distribution of bloom-forming macroalgae. Areas with depleted top-predator communities displayed massive increases in their prey, small-bodied fish, and high covers of ephemeral algae. Combining the results from the two experiments showed that excluding larger piscivorous fish: (1) increased the abundance of small-bodied predatory fish; (2) changed the size distribution of the dominating grazers, decreasing the smaller gastropod scrapers; and (3) increased the net production of ephemeral macroalgae. Effects of removing top predators and nutrient enrichment were similar and additive, together increasing the abundance of ephemeral algae many times. Predator effects depended on invertebrate grazers; in the absence of invertebrates there were no significant effects of predator exclusion on algal production. Our results provide strong support for regional declines of larger predatory fish in the Baltic Sea promoting algal production by decreasing invertebrate grazer control. This highlights the importance of trophic interactions for ecosystem responses to eutrophication. The view emerges that to achieve management goals for water quality we need to consider the interplay between top-down and bottom-up processes in future ecosystem management of marine resources.

  • 150. Eriksson, Britas Klemens
    et al.
    Sieben, Katrin
    Eklöf, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ljunggren, Lars
    Olsson, Jens
    Casini, Michele
    Bergström, Ulf
    Effects of Altered Offshore Food Webs on Coastal Ecosystems Emphasize the Need for Cross-Ecosystem Management2011In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 40, no 7, p. 786-797Article, review/survey (Refereed)
    Abstract [en]

    By mainly targeting larger predatory fish, commercial fisheries have indirectly promoted rapid increases in densities of their prey; smaller predatory fish like sprat, stickleback and gobies. This process, known as mesopredator release, has effectively transformed many marine offshore basins into mesopredator-dominated ecosystems. In this article, we discuss recent indications of trophic cascades on the Atlantic and Baltic coasts of Sweden, where increased abundances of mesopredatory fish are linked to increased nearshore production and biomass of ephemeral algae. Based on synthesis of monitoring data, we suggest that offshore exploitation of larger predatory fish has contributed to the increase in mesopredator fish also along the coasts, with indirect negative effects on important benthic habitats and coastal water quality. The results emphasize the need to rebuild offshore and coastal populations of larger predatory fish to levels where they regain their control over lower trophic levels and important links between offshore and coastal systems are restored.

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