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  • 1. Ahtiainen, Heini
    et al.
    Artell, Janne
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hasselström, Linus
    Håkansson, Cecilia
    Baltic Sea nutrient reductions - What should we aim for?2014In: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 145, 9-23 p.Article in journal (Refereed)
    Abstract [en]

    Nutrient load reductions are needed to improve the state of the Baltic Sea, but it is still under debate how they should be implemented. In this paper, we use data from an environmental valuation study conducted in all nine Baltic Sea states to investigate public preferences of relevance to three of the involved decision-dimensions: First, the roles of nitrogen versus phosphorus reductions causing different eutrophication effects; second, the role of time the - lag between actions to reduce nutrient loads and perceived improvements; and third; the spatial dimension and the roles of actions targeting the coastal and open sea environment and different sub-basins. Our findings indicate that respondents view and value the Baltic Sea environment as a whole, and are not focussed only on their local sea area, or a particular aspect of water quality. We argue that public preferences concerning these three perspectives should be one of the factors guiding marine policy. This requires considering the entire range of eutrophication effects, in coastal and open sea areas, and including long-term and short-term measures.

  • 2. Andersson, Agneta
    et al.
    Meier, H. E. Markus
    Ripszam, Matyas
    Rowe, Owen
    Wikner, Johan
    Haglund, Peter
    Eilola, Kari
    Legrand, Catherine
    Figueroa, Daniela
    Paczkowska, Joanna
    Lindehoff, Elin
    Tysklind, Mats
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Projected future climate change and Baltic Sea ecosystem management2015In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, S345-S356 p.Article in journal (Refereed)
    Abstract [en]

    Climate change is likely to have large effects on the Baltic Sea ecosystem. Simulations indicate 2-4 degrees C warming and 50-80 % decrease in ice cover by 2100. Precipitation may increase similar to 30 % in the north, causing increased land runoff of allochthonous organic matter (AOM) and organic pollutants and decreased salinity. Coupled physical-biogeochemical models indicate that, in the south, bottom-water anoxia may spread, reducing cod recruitment and increasing sediment phosphorus release, thus promoting cyanobacterial blooms. In the north, heterotrophic bacteria will be favored by AOM, while phytoplankton production may be reduced. Extra trophic levels in the food web may increase energy losses and consequently reduce fish production. Future management of the Baltic Sea must consider the effects of climate change on the ecosystem dynamics and functions, as well as the effects of anthropogenic nutrient and pollutant load. Monitoring should have a holistic approach, encompassing both autotrophic (phytoplankton) and heterotrophic (e.g., bacterial) processes.

  • 3.
    Blenckner, Thorsten
    et al.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Österblom, Henrik
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Larsson, Per
    Andersson, Agneta
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Baltic Sea ecosystem-based management under climate change: Synthesis and future challenges2015In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, 507-515 p.Article in journal (Refereed)
    Abstract [en]

    Ecosystem-based management (EBM) has emerged as the generally agreed strategy for managing ecosystems, with humans as integral parts of the managed system. Human activities have substantial effects on marine ecosystems, through overfishing, eutrophication, toxic pollution, habitat destruction, and climate change. It is important to advance the scientific knowledge of the cumulative, integrative, and interacting effects of these diverse activities, to support effective implementation of EBM. Based on contributions to this special issue of AMBIO, we synthesize the scientific findings into four components: pollution and legal frameworks, ecosystem processes, scale-dependent effects, and innovative tools and methods. We conclude with challenges for the future, and identify the next steps needed for successful implementation of EBM in general and specifically for the Baltic Sea.

  • 4.
    Blomqvist, Sven
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ekeroth, Nils
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hall, Per
    Long over-due improvement of box corer samplingManuscript (preprint) (Other academic)
  • 5.
    Blomqvist, Sven
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ekeroth, Nils
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hall, Per O. J.
    Long overdue improvement of box corer sampling2015In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 538, 13-21 p.Article in journal (Refereed)
    Abstract [en]

    An improved, large double-jawed box corer, intended primarily for sampling of soft sediments on continental margins and in large lakes, is described. The device performs reliably when entering the sediment and enclosing the sample, during withdrawal and hoisting on board the ship and also when detaching the collected sediment sample. It offers the following advantages: (1) robust design, (2) minimally impeded flow of water through the box chamber during lowering and (3) an efficient closure mechanism. It is furnished with a supporting stand, a transparent liner and an accessory anti-slosh baffle for insertion in the liner as the corer is set down on the ship's deck. In situ video records and turbidity measurements from field trials, as well as visual inspection of the core and supernatant water after retrieval, show that the device collects minimally disturbed sediment when properly and carefully operated. This contrasts with the bulky United States Naval Electronics Laboratory (USNEL) Spade Corer in which water flow through the box chamber during lowering is impeded, causing a bow-wave ahead of the corer that displaces surficial sediment. In addition, the USNEL's single-spade closing mechanism deforms the sediment sample severely and can even cause loss of sediment. Our new box corer performs much better, making it suitable for quantitative benthic sampling.

  • 6. Cloern, James E.
    et al.
    Abreu, Paulo C.
    Carstensen, Jacob
    Chauvaud, Laurent
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Grall, Jacques
    Greening, Holly
    Johansson, John Olov Roger
    Kahru, Mati
    Sherwood, Edward T.
    Xu, Jie
    Yin, Kedong
    Human activities and climate variability drive fast-paced change across the world's estuarine-coastal ecosystems2016In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 22, no 2, 513-529 p.Article, review/survey (Refereed)
    Abstract [en]

    Time series of environmental measurements are essential for detecting, measuring and understanding changes in the Earth system and its biological communities. Observational series have accumulated over the past 2-5 decades from measurements across the world's estuaries, bays, lagoons, inland seas and shelf waters influenced by runoff. We synthesize information contained in these time series to develop a global view of changes occurring in marine systems influenced by connectivity to land. Our review is organized around four themes: (i) human activities as drivers of change; (ii) variability of the climate system as a driver of change; (iii) successes, disappointments and challenges of managing change at the sea-land interface; and (iv) discoveries made from observations over time. Multidecadal time series reveal that many of the world's estuarine-coastal ecosystems are in a continuing state of change, and the pace of change is faster than we could have imagined a decade ago. Some have been transformed into novel ecosystems with habitats, biogeochemistry and biological communities outside the natural range of variability. Change takes many forms including linear and nonlinear trends, abrupt state changes and oscillations. The challenge of managing change is daunting in the coastal zone where diverse human pressures are concentrated and intersect with different responses to climate variability over land and over ocean basins. The pace of change in estuarine-coastal ecosystems will likely accelerate as the human population and economies continue to grow and as global climate change accelerates. Wise stewardship of the resources upon which we depend is critically dependent upon a continuing flow of information from observations to measure, understand and anticipate future changes along the world's coastlines.

  • 7.
    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, 432-432 p.Article in journal (Other (popular science, discussion, etc.))
  • 8. Franzen, Frida
    et al.
    Kinell, Gerda
    Walve, Jakob
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Soderqvist, Tore
    Participatory Social-Ecological Modeling in Eutrophication Management: the Case of Himmerfjarden, Sweden2011In: Ecology & society, ISSN 1708-3087, E-ISSN 1708-3087, Vol. 16, no 4, 27- p.Article in journal (Refereed)
    Abstract [en]

    Stakeholder participation is increasingly seen as central in natural resource management. It is also required by the European Union Water Framework Directive, which identifies three levels of participation; information, consultation, and active involvement. In this paper we discuss the active involvement of stakeholders, using our experience from a case study in the Himmerfjarden region, which is a coastal area southwest of Stockholm, Sweden. Our study used the systems approach proposed by the European Union research project called Science and Policy Integration for Coastal System Assessment (SPICOSA), in which local stakeholders and a study site team constructed an integrated simulation model of a crucial coastal management issue. In this case the issue was nitrogen enrichment. We showed how stakeholder participation in the modeling process helped identify interesting and currently relevant management scenarios, and how the modeling process facilitated communication of the likely ecological, economic, and social effects of these scenarios to the stakeholders. In addition, stakeholders also reported social gains in terms of network building. We managed to actively involve local stakeholders in water issues, and the research process clearly strengthened the social capital in the Himmerfjarden region, and created a basis for future collaboration regarding water management. Our experience indicates that the approach we tried is a useful tool for promoting active stakeholder involvement in water management projects. Also, the results of our science and policy integration approach indicated that the study site team assumed a leadership role, which is a commonly recognized factor in successful natural resource management.

  • 9. Hopkins, Tom S.
    et al.
    Bailly, Denis
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Glegg, Gillian
    Sandberg, Audun
    Stottrup, Josianne G.
    A Systems Approach Framework for the Transition to Sustainable Development: Potential Value Based on Coastal Experiments2012In: Ecology & society, ISSN 1708-3087, E-ISSN 1708-3087, Vol. 17, no 3, 39- p.Article in journal (Refereed)
    Abstract [en]

    This article explores the value of the Systems Approach Framework (SAF) as a tool for the transition to sustainable development in coastal zone systems, based on 18 study sites in Europe, where the SAF was developed and tested. The knowledge gained from these experiments concerns the practical aspects of (a) governance in terms of policy effectiveness, (b) sustainability science in terms of applying transdisciplinary science to social-ecological problems, and (c) simulation analysis in terms of quantifying dysfunctions in complex systems. This new knowledge can help broaden our perspectives on how research can be changed to better serve society. The infusion of systems thinking into research and policy making leads to a preference for multi-issue instead of single-issue studies, an expansion from static to dynamic indicators, an understanding of the boundaries between system-dependent and system-independent problems, and the inclusion of non-market evaluations. It also develops a real partnership among research, management, and stakeholders to establish a quantitative basis for collaborative decision making. Furthermore, the article argues that the transition to sustainable development for coastal systems requires consideration of the scale interdependency from individual to global and recognition of the probable global reorganizational emergence of scale-free networks that could cooperate to maximize the integrated sustainability among them.

  • 10.
    Kahru, Mati
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of California San Diego, USA.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Multidecadal time series of satellite-detected accumulations of cyanobacteria in the Baltic Sea2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, no 13, 3619-3633 p.Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria, primarily of the species Nodularia spumigena, form extensive surface accumulations in the Baltic Sea in July and August, ranging from diffuse flakes to dense surface scums. The area of these accumulations can reach similar to 200 000 km(2). We describe the compilation of a 35-year-long time series (1979-2013) of cyanobacteria surface accumulations in the Baltic Sea using multiple satellite sensors. This appears to be one of the longest satellite-based time series in biological oceanography. The satellite algorithm is based on remote sensing reflectance of the water in the red band, a measure of turbidity. Validation of the satellite algorithm using horizontal transects from a ship of opportunity showed the strongest relationship with phycocyanin fluorescence (an indicator of cyanobacteria), followed by turbidity and then by chlorophyll a fluorescence. The areal fraction with cyanobacteria accumulations (FCA) and the total accumulated area affected (TA) were used to characterize the intensity and extent of the accumulations. The fraction with cyanobacteria accumulations was calculated as the ratio of the number of detected accumulations to the number of cloud-free sea-surface views per pixel during the season (July-August). The total accumulated area affected was calculated by adding the area of pixels where accumulations were detected at least once during the season. The fraction with cyanobacteria accumulations and TA were correlated (R-2 = 0.55) and both showed large interannual and decadal-scale variations. The average FCA was significantly higher for the second half of the time series (13.8 %, 1997-2013) than for the first half (8.6 %, 1979-1996). However, that does not seem to represent a long-term trend but decadal-scale oscillations. Cyanobacteria accumulations were common in the 1970s and early 1980s (FCA between 11-17 %), but rare (FCA below 4 %) during 1985-1990; they increased again starting in 1991 and particularly in 1999, reaching maxima in FCA (similar to 25 %) and TA (similar to 210 000 km(2)) in 2005 and 2008. After 2008, FCA declined to more moderate levels (6-17 %). The timing of the accumulations has become earlier in the season, at a mean rate of 0.6 days per year, resulting in approximately 20 days advancement during the study period. The interannual variations in FCA are positively correlated with the concentration of chlorophyll a during July-August sampled at the depth of similar to 5 m by a ship of opportunity, but interannual variations in FCA are more pronounced as the coefficient of variation is over 5 times higher.

  • 11. Kahru, Mati
    et al.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Savchuk, Oleg P.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre, Baltic Nest Institute.
    Changing seasonality of the Baltic Sea2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 4, 1009-1018 p.Article in journal (Refereed)
    Abstract [en]

    Changes in the phenology of physical and ecological variables associated with climate change are likely to have significant effect on many aspects of the Baltic ecosystem. We apply a set of phenological indicators to multiple environmental variables measured by satellite sensors for 17-36 years to detect possible changes in the seasonality in the Baltic Sea environment. We detect significant temporal changes, such as earlier start of the summer season and prolongation of the productive season, in several variables ranging from basic physical drivers to ecological status indicators. While increasing trends in the absolute values of variables like sea-surface temperature (SST), diffuse attenuation of light (Ked490) and satellite-detected chlorophyll concentration (CHL) are detectable, the corresponding changes in their seasonal cycles are more dramatic. For example, the cumulative sum of 30 000 W m(-2) of surface incoming short-wave irradiance (SIS) was reached 23 days earlier in 2014 compared to the beginning of the time series in 1983. The period of the year with SST of at least 17 degrees C has almost doubled (from 29 days in 1982 to 56 days in 2014), and the period with Ked490 over 0.4 m(1) has increased from about 60 days in 1998 to 240 days in 2013 -i.e., quadrupled. The period with satellite-estimated CHL of at least 3 mg m(-3) has doubled from approximately 110 days in 1998 to 220 days in 2013. While the timing of both the phytoplankton spring and summer blooms have advanced, the annual CHL maximum that in the 1980s corresponded to the spring diatom bloom in May has now shifted to the summer cyanobacteria bloom in July.

  • 12. Kahru, Matti
    et al.
    Savchuk, Oleg
    Stockholm University, Faculty of Science, Department of Systems Ecology. marin ekologi.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology. marin ekologi.
    Satellite measurements of cyanobacterial bloom frequency in the Baltic Sea: interannual and spatial variability2007In: Marine Ecology Progress Series, Vol. 343, 15-23 p.Article in journal (Refereed)
  • 13.
    Karlson, Agnes M. L.
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Duberg, Jon
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Motwani, Nisha H.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hogfors, Hedvig
    Klawonn, Isabell
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ploug, Helle
    Barthel Svedén, Jennie
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Garbaras, Andrius
    Sundelin, Brita
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hajdu, Susanna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Larsson, Ulf
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs2015In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, 413-426 p.Article in journal (Refereed)
    Abstract [en]

    Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N-2 allows cyanobacteria to circumvent the general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for the food web. However, the fate of the nitrogen fixed by cyanobacteria remains unresolved, as does its importance for secondary production in the Baltic Sea. Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial nitrogen is efficiently assimilated and transferred in Baltic food webs via two major pathways: directly by grazing on fresh or decaying cyanobacteria and indirectly through the uptake by other phytoplankton and microbes of bioavailable nitrogen exuded from cyanobacterial cells. This information is an essential step toward guiding nutrient management to minimize noxious blooms without overly reducing secondary production, and ultimately most probably fish production in the Baltic Sea.

  • 14.
    Karlson, Agnes M. L.
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Do deposit-feeders compete? Isotopic niche analysis of an invasion in a species-poor system2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, 9715Article in journal (Refereed)
    Abstract [en]

    Successful establishment of invasive species is often related to the existence of vacant niches. Competition occurs when invaders use the same limiting resources as members of the recipient community, which will be reflected in some overlap of their trophic niches. The concept of isotopic niche has been used to study trophic niche partitioning among species. Here, we present a two-year field study comparing isotopic niches of the deposit-feeding community in a naturally species-poor system. The isotopic niche analyses showed no overlap between a recent polychaete invader and any of the native species suggesting that it has occupied a vacant niche. Its narrow isotopic niche suggests specialized feeding, however, the high delta N-15 values compared to natives are most likely due to isotope fractionation effects related to nitrogen recycling and a mismatch between biological stoichiometry of the polychaete and the sediment nitrogen content. Notably, highly overlapping isotopic niches were inferred for the native species, which is surprising in a food-limited system. Therefore, our results demonstrate that invaders may broaden the community trophic diversity and enhance resource utilization, but also raise questions about the congruence between trophic and isotopic niche concepts and call for careful examination of assumptions underlying isotopic niche interpretation.

  • 15.
    Karlson, Agnes M. L.
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Nitrogen Fixed by Cyanobacteria Is Utilized by Deposit-Feeders2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 8, e104460- p.Article in journal (Refereed)
    Abstract [en]

    Benthic communities below the photic zone depend for food on allochthonous organic matter derived from seasonal phytoplankton blooms. In the Baltic Sea, the spring diatom bloom is considered the most important input of organic matter, whereas the contribution of the summer bloom dominated by diazotrophic cyanobacteria is less understood. The possible increase in cyanobacteria blooms as a consequence of eutrophication and climate change calls for evaluation of cyanobacteria effects on benthic community functioning and productivity. Here, we examine utilization of cyanobacterial nitrogen by deposit-feeding benthic macrofauna following a cyanobacteria bloom at three stations during two consecutive years and link these changes to isotopic niche and variations in body condition (assayed as C:N ratio) of the animals. Since nitrogen-fixing cyanobacteria have delta N-15 close to -2 parts per thousand, we expected the delta N-15 in the deposit-feeders to decrease after the bloom if their assimilation of cyanobacteria-derived nitrogen was substantial. We also expected the settled cyanobacteria with their associated microheterotrophic community and relatively high nitrogen content to increase the isotopic niche area, trophic diversity and dietary divergence between individuals (estimated as the nearest neighbour distance) in the benthic fauna after the bloom. The three surface-feeding species (Monoporeia affinis, Macoma balthica and Marenzelleria arctia) showed significantly lower delta N-15 values after the bloom, while the sub-surface feeder Pontoporeia femorata did not. The effect of the bloom on isotopic niche varied greatly between stations; populations which increased niche area after the bloom had better body condition than populations with reduced niche, regardless of species. Thus, cyanobacterial nitrogen is efficiently integrated into the benthic food webs in the Baltic, with likely consequences for their functioning, secondary production, transfer efficiency, trophic interactions, and intra- and interspecific competition.

  • 16.
    Karlson, Agnes M. L.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Nascimento, Francisco J. A.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Näslund, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Higher diversity of deposit-feeding macrofauna enhances phytodetritus processing2010In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 91, no 5, 1414-1423 p.Article in journal (Refereed)
    Abstract [en]

    The link between biodiversity and ecosystem functioning is an important question that remains unresolved, particularly in marine systems, in which cycling of organic matter by benthic organisms is of global significance. Direct observations of specific resource use by each species in single- and multispecies communities, as quantified by stable isotopes, facilitates a mechanistic understanding of the importance of each species for ecosystem functioning. We tested the effects of altered biodiversity (species richness) of deposit-feeding macrofauna on incorporation and burial of phytodetritus in combinations of three species representing natural communities found in the sediments of the species-poor Baltic Sea. The three species, two amphipods and a bivalve, had different rates of incorporation and burial and different needs for carbon (C) and nitrogen (N). The amphipods exhibited clear resource partitioning in sympatry, as a result of vertical separation in the sediment and consequent differential use of food. Communities of several species incorporated more C and N than expected from the respective single-species treatments, due to higher incorporation by surface feeders in multispecies treatments. Community incorporation of N in the most diverse treatment even exceeded N incorporation by a single-species treatment of the best-performing species, showing transgressive over-yielding. This over-yielding was primarily due to positive complementarity in all treatments. Diverse soft bottoms are also likely to be more productive in the long run, as species-specific traits (subsurface feeding) preserve fresh phytodetritus by burying it to depths in the sediment at which the mineralization rate is low. The more diverse sediment communities showed more efficient trophic transfer of phytodetritus, a finding of general significance for understanding biological processes driving the transformation of nutrients and energy in benthic ecosystems.

  • 17.
    Karlson, Agnes M. L.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Nascimento, Francisco J. A.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Sanna, Suikkanen
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Benthic fauna affects recruitment from sediments of the harmful cyano­bacterium Nodularia spumigena 2012In: Harmful Algae, ISSN 1568-9883, E-ISSN 1878-1470, Vol. 20, 126-131 p.Article in journal (Refereed)
    Abstract [en]

    Physical disturbance and feeding by macrofauna in the sediment can potentially affect bloom initiation of phytoplankton species that have benthic stages in their life cycle. In this experimental study, we investigated how different species of macrozoobenthos can affect the recruitment of Nodularia spumigena from the sediment to the water column. N. spumigena is a toxic, nitrogen-fixing filamentous cyanobacterium, which forms large summer blooms in the Baltic Sea. Benthic recruitment from resting stages (akinetes) and vegetative cells deposited on the seafloor have long been suspected to initiate the blooms. We found that, depending on species-specific traits, deposit-feeding macrofauna (an amphipod, Monoporeia affinis, a bivalve, Macoma balthica and an invasive polychaete, Marenzelleria cf. arctia) has the potential to either reduce or facilitate recruitment of this cyanobacterium. Shorter filament length in treatments with fauna than in the treatment without indicates feeding on or mechanical destruction of N. spumigena by the animals. Our results show the importance of an often overlooked aspect of phytoplankton bloom initiation, the role of macrozoobenthos.

  • 18.
    Karlson, Agnes M. L.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Näslund, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ryden, Sara Blomgren
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Polychaete invader enhances resource utilization in a species-poor system2011In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 166, no 4, 1055-1065 p.Article in journal (Refereed)
    Abstract [en]

    Ecosystem consequences of biodiversity change are often studied from a species loss perspective, while the effects of invasive species on ecosystem functions are rarely quantified. In this experimental study, we used isotope tracers to measure the incorporation and burial of carbon and nitrogen from a simulated spring phytoplankton bloom by communities of one to four species of deposit-feeding macrofauna found in the species-poor Baltic Sea. The recently invading polychaete Marenzelleria arctia, which has spread throughout the Baltic Sea, grows more rapidly than the native species Monoporeia affinis, Pontoporeia femorata (both amphipods) and Macoma balthica (a bivalve), resulting in higher biomass increase (biomass production) in treatments including the polychaete. Marenzelleria incorporated and buried bloom material at rates similar to the native species. Multi-species treatments generally had higher isotope incorporation, indicative of utilization of bloom material, than expected from monoculture yields of the respective species. The mechanism behind this observed over-yielding was mainly niche complementarity in utilization of the bloom input, and was more evident in communities including the invader. In contrast, multi-species treatments had generally lower biomass increase than expected. This contrasting pattern suggests that there is little overlap in resource use of freshly deposited bloom material between Marenzelleria and the native species but it is likely that interference competition acts to dampen resulting community biomass. In conclusion, an invasive species can enhance incorporation and burial of organic matter from settled phytoplankton blooms, two processes fundamental for marine productivity.

  • 19.
    Karlson, Agnes
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Nascimento, Francisco
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Incorporation and burial of carbon from settling cyanobacterial blooms by deposit-feeding macrofauna2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, 2754-2758 p.Article in journal (Refereed)
    Abstract [en]

    Summer blooms of filamentous, nitrogen-fixing cyanobacteria are typical of the Baltic Sea, and recent findings indicate that cyanobacteria may be an important food source for the benthos below the euphotic zone. In a 2-week laboratory experiment, we measured incorporation of cyanobacterial carbon by the deposit-feeding amphipod Monoporeia affinis when exposed to 14C-radiolabeled, natural blooms of cyanobacteria dominated by either the toxic Nodularia spumigena or non-toxic Aphanizomenon sp. Carbon from both cyanobacterial blooms was used, with greater incorporation from Aphanizomenon-dominated bloom material than from N. spumigena, indicating that the latter is less suitable as food. However, neither cyanobacterium supported significant amphipod growth. Also, less cyanobacterial carbon was mixed down in the sediment in the N. spumigena treatment, indicating lower bioturbation activity in this treatment. Long-term effects on feeding and survival remain to be studied, especially for the toxic N. spumigena.

  • 20.
    Larsson, Ulf
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Nyberg, Svante
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Zakrisson, Anna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hajdu, Susanna
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Walve, Jakob
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Rolff, Carl
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Baltic Sea phytoplankton: Long-term variability of major groups and primary production in spring and summer related to nutrients and temperatureManuscript (preprint) (Other academic)
  • 21.
    Nascimento, F.J.A.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Karlson, A.M.L.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, R.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Settling blooms of filamentous cyanobacteria as food for meiofauna assemblages.2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 6, 2636-2643 p.Article in journal (Refereed)
    Abstract [en]

    Summer blooms of filamentous nitrogen-fixing cyanobacteria in the Baltic Sea are normally dominated by Aphanizomenon sp. and the toxin-producing Nodularia spumigena. In a 2-week laboratory experiment, we followed the uptake by representative benthic meiofauna species of C-14-labeled organic carbon from blooms, each dominated by one of these cyanobacteria. Natural bloom material was collected and labeled by incubation with (NaHCO3)-C-14. Uptake of cyanobacterial carbon was recorded for the major meiofauna taxa living in the first-centimeter layer, namely ostracods, harpacticoids, and nematodes. The uptake rates were within the range found for diatoms in other studies, indicating that cyanobacteria may be an important food resource for the meiobenthos. The uptake of cyanobacterial carbon varied significantly among species, even within the same class. The ostracod Candona neglecta showed the highest uptake values, whereas two other ostracod species took up very little of the label. There was no significant difference in utilization of carbon from Aphanizomenon sp. and N. spumigena and no reduction in the abundance of the meiofaunal taxa analyzed compared to unexposed controls, indicating that Baltic meiofaunal assemblages in general experience no mortality when exposed to settled cyanobacteria, even the hepatotoxic N. spumigena.

  • 22.
    Nascimento, Francisco J. A.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Karlson, Agnes M. L.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Näslund, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Diversity of larger consumers enhances interference competition effects on smaller competitors2011In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 166, no 2, 337-347 p.Article in journal (Refereed)
    Abstract [en]

    Competition between large and small species for the same food is common in a number of ecosystems including aquatic ones. How diversity of larger consumers affects the access of smaller competitors to a limiting resource is not well understood. We tested experimentally how species richness (0-3 spp.) of benthic deposit-feeding macrofauna changes meiofaunal ostracods' incorporation of fresh organic matter from a stable-isotope-labeled cyanobacterial bloom, using fauna from the species-poor Baltic Sea. Presence of macrofauna mostly decreased meiofaunal incorporation of bloom material, depending on the macrofauna species present. As expected, the species identity of macrofauna influenced the incorporation of organic matter by meiofauna. Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon. With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments. Field data from the Baltic Sea showed a negative correlation between macrofauna diversity and meiofaunal ostracod abundance, as expected from the experimental results. We argue that this is caused by interference competition, due to spatial niche differentiation between macrofauna species reducing the sediment volume in which ostracods can feed undisturbed by larger competitors. Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.

  • 23.
    Nascimento, Francisco
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Näslund, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Meiofauna enhances organic matter mineralization in soft sediment ecosystems2010Manuscript (preprint) (Other academic)
    Abstract [en]

    Organic matter mineralization in soft sediments is a key process mediated by benthic fauna and bacteria that is crucial for sustaining primary production in aquatic systems. Few studies have examined the effect of meiofauna on the degradation of labile organic matter in soft sediments. Here we investigated the influence of meiofauna on the benthic decomposition of a radiolabelled diatom bloom by measuring the production of 14CO2 in a laboratory microcosm. Mineralization of the diatom bloom material was significantly enhanced when meiofauna was present in higher abundances, with cumulative mineralization values after 17 days being on average 50% greater in the treatment with high meiofauna abundance compared to sediments with low meiofauna abundance. Our experiment shows that meiofauna can enhance the mineralization of organic matter, probably by stimulating the activity of sediment bacterial community, indicating that positive biological interactions such as facilitation from meiofauna are important for ecosystem processes in soft sediments.

  • 24.
    Rolff, Carl
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. marin ekologi.
    Almesjö, Lisa
    Stockholm University, Faculty of Science, Department of Systems Ecology. marin ekologi.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology. marin ekologi.
    Nitrogen fixation and the abundance of the diazotrophic cyanobacterium Aphanizomenon sp. in the Baltic Proper2007In: Marine Ecology Progress Series, Vol. 332, 107-118 p.Article in journal (Refereed)
  • 25.
    Rolff, Carl
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Voss, M.
    Deposition of nitrogen and phosphorus on the Baltic Sea: Seasonal patterns and nitrogen isotope composition.2008In: Biogeosciences, Vol. 5, 1657-1667 p.Article in journal (Refereed)
  • 26.
    Savage, Candida
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Leavitt, Peter R.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Effects of land use, urbanization, and climate variability on coastal eutrophication in the Baltic Sea2010In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 55, no 3, 1033-1046 p.Article in journal (Refereed)
    Abstract [en]

    Sedimentary records of organic matter inputs (stable nitrogen isotopes [delta N-15], nitrogen [N], and carbon [C] content), phytoplankton abundance (pigments, stable carbon isotopes [delta C-13]), and community composition (pigments) were used to reconstruct the history and pathway to water-quality degradation in a Swedish Baltic coastal bay. Changes in nutrient sources and cycling began in the 1800s, but eutrophication intensified only after the 1950s, coincident with intensified agricultural practices. Specifically, sedimentary N and C content doubled, delta 13C increased, and concentrations of pigments indicative of total algal biomass (beta-carotene, Chlorophyll a), diatoms (fucoxanthin, diatoxanthin), chlorophytes (lutein-zeaxanthin, Chlorophyll b), and cyanobacteria (canthaxanthin) increased significantly after 1950. Enhanced algal abundance was most strongly related to total N influx and secondly to total P influx. In particular, historical change in algae was related to agricultural N influx and only weakly to agricultural P. In recent decades, wastewater N influx has further stimulated algal biomass, particularly diatoms. In contrast, colonial cyanobacteria were more correlated to total P than total N inputs. Variance-partitioning analysis explained 60% of the changes in algal abundance and community composition since 1880, with diffuse and point nutrients jointly explaining 36% of the long-term change in algal biomass. Climate variability has become more important as a factor influencing coastal eutrophication in recent decades, explaining 14% of the variance in the algal data since 1975. Both urban and agricultural sources of nutrients have degraded water quality, illustrating the need for cooperation between stakeholders at regional levels to achieve ""good ecological status'' in the Baltic coastal environment.

  • 27.
    Svedén, Jennie B.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Walve, Jakob
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Larsson, Ulf
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The bloom of nitrogen-fixing cyanobacteria in the northern Baltic Proper stimulates summer production2016In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 163, 102-112 p.Article in journal (Refereed)
    Abstract [en]

    In the northern Baltic Sea Proper, total nitrogen (TN) increases during the summer bloom of filamentous heterocystous cyanobacteria. To follow the fate of the nitrogen they fix, we studied several N fractions during the bloom. We measured cyanobacterial biomass, TN, particulate organic N (PON, two size fractions), dissolved organic N (DON), and PON sedimentation in two areas in 2011. TN increased mainly due to increasing PON, but also to DON. Cyanobacteria contributed about 20% of the PON increase and ~ 10% of the TN increase. About half the PON changes (increase, then decrease) could be explained by the sum of cyanobacteria, other autotrophs (> 2 μm) and zooplankton, indicating that the bloom stimulates primary and secondary production. TN decreased after the bloom mainly due to declining PON > 10 μm, but sedimentation rates did not increase and could explain little of the post-bloom N-loss. There was little settling of undecomposed cyanobacteria.

    The seasonal development of Aphanizomenon sp. and N pools was similar among stations and areas. For Nodularia spumigena between-station variability increased once patchy surface accumulations developed. A brief Dolichospermum spp. bloom indicated that sampling frequency may be more important than spatial resolution for capturing dynamics of this bloom.

  • 28. Zhang, J.
    et al.
    Gilbert, D.
    Gooday, A. J.
    Levin, L.
    Naqvi, S. W. A.
    Middelburg, J. J.
    Scranton, M.
    Ekau, W.
    Pena, A.
    Dewitte, B.
    Oguz, T.
    Monteiro, P. M. S.
    Urban, E.
    Rabalais, N. N.
    Ittekkot, V.
    Kemp, W. M.
    Ulloa, O.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Escobar-Briones, E.
    Van der Plas, A. K.
    Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development2010In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, no 5, 1443-1467 p.Article in journal (Refereed)
    Abstract [en]

    Hypoxia has become a world-wide phenomenon in the global coastal ocean and causes a deterioration of the structure and function of ecosystems. Based on the collective contributions of members of SCOR Working Group #128, the present study provides an overview of the major aspects of coastal hypoxia in different biogeochemical provinces, including estuaries, coastal waters, upwelling areas, fjords and semi-enclosed basins, with various external forcings, ecosystem responses, feedbacks and potential impact on the sustainability of the fishery and economics. The obvious external forcings include freshwater runoff and other factors contributing to stratification, organic matter and nutrient loadings, as well as exchange between coastal and open ocean water masses. Their different interactions set up mechanisms that drive the system towards hypoxia. Coastal systems also vary in their relative susceptibility to hypoxia depending on their physical and geographic settings. It is understood that coastal hypoxia has a profound impact on the sustainability of ecosystems, which can be seen, for example, by the change in the food-web structure and system function; other influences include compression and loss of habitat, as well as changes in organism life cycles and reproduction. In most cases, the ecosystem responds to the low dissolved oxygen in non-linear ways with pronounced feedbacks to other compartments of the Earth System, including those that affect human society. Our knowledge and previous experiences illustrate that there is a need to develop new observational tools and models to support integrated research of biogeochemical dynamics and ecosystem behavior that will improve confidence in remediation management strategies for coastal hypoxia.

  • 29.
    Österblom, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Larsson, Ulf
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hjerne, Olle
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Wulff, Fredrik
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre.
    Elmgren, Ragnar
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Folke, Carl
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Stockholm Resilience Centre.
    Human-induced trophic cascades and ecological regime shifts in the Baltic Sea2007In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 10, no 6, 877-889 p.Article in journal (Refereed)
    Abstract [en]

    The ecosystems of coastal and enclosed seas are under increasing anthropogenic pressure worldwide, with Chesapeake Bay, the Gulf of Mexico and the Black and Baltic Seas as well known examples. We use an ecosystem model (Ecopath with Ecosim, EwE) to show that reduced top-down control (seal predation) and increased bottom-up forcing (eutrophication) can largely explain the historical dynamics of the main fish stocks (cod, herring and sprat) in the Baltic Sea between 1900 and 1980. Based on these results and the historical fish stock development we identify two major ecological transitions. A shift from seal to cod domination was caused by a virtual elimination of marine mammals followed by a shift from an oligotrophic to a eutrophic state. A third shift from cod to clupeid domination in the late 1980s has previously been explained by overfishing of cod and climatic changes. We propose that the shift from an oligotrophic to a eutrophic state represents a true regime shift with a stabilizing mechanism for a hysteresis phenomenon. There are also mechanisms that could stabilize the shift from a cod to clupeid dominated ecosystem, but there are no indications that the ecosystem has been pushed that far yet. We argue that the shifts in the Baltic Sea are a consequence of human impacts, although variations in climate may have influenced their timing, magnitude and persistence.

1 - 29 of 29
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