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  • 1.
    Arrhenius, Fredrik
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Feeding ecology of Baltic Sea herring (Clupea harengus L.): field and model studies of a dominant zooplanktivor1995Doctoral thesis, comprehensive summary (Other academic)
  • 2.
    Axenrot, Thomas
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Pelagic Fish Distribution and Dynamics in Coastal Areas in the Baltic Sea Proper2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Pelagic fish distribution and diel behaviour patterns were studied in coastal areas in the north-western Baltic Sea Proper to understand more about how fish distribution and behaviour might affect planning and analyses of results of hydroacoustic surveys (Papers I and II). The vertical distribution of fish at night from spring to autumn showed seasonal and annual trends that could be explained by predictable and consistent seasonal changes, e.g., in temperature and stratification. Horizontal fish distributions did not show any trends probably owing to a lack of such seasonal characteristics. The observed vertical fish distribution over the diel cycle showed that hydroacoustic surveys at night were to be preferred over daytime surveys. At night, fish did not school and were generally less aggregated resulting in less variable hydroacoustic backscattering values and a higher percentage of single echo detections. By starting the surveys one hour after sunset and stopping one hour before sunrise, confusion between day- and nighttime behaviour in fish could be avoided. At night, fish occupied mid-water layers to a higher extent than surface and bottom layers, which was beneficial for the quality of the hydroacoustic data, particularly with respect to the hydroacoustic blind and dead zones (i.e. surface and bottom, respectively).

    To quantify seasonal changes in pelagic fish abundance, densities and size distributions, nighttime hydroacoustic surveys were done every second week from spring through autumn in 2000 and 2001 (Paper III). There was a drastic increase in fish abundance and densities that started in early July and peaked in mid-August in both years. Analyses of the hydroacoustic data in relation to gillnet and trawl catches showed that the increase was caused mainly by young-of-the-year (YOY) herring. This age class is commonly not well represented in catches using traditional sampling methods like gillnets and trawling. Consequently, hydroacoustic data that have high precision and accuracy may improve quantitative estimates and our understanding of the biology in coastal nursery areas.

    Baltic herring spawn in coastal areas and the density of metamorphosed YOY individuals may provide an early estimate of year-class strength. By analysing the relationship between parameters known to affect recruitment success and year-class strength in age 2 herring (YCS) a model that predicted herring recruitment was developed (Paper IV). The model explained 93 % of the variation in the number of age 2 herring over the period 1985-2000 and included the parameters YOY densities, climate (North Atlantic Oscillation index) and spawning stock biomass (SSB). Thus YCS could be predicted two years earlier than today and three years before entering the fishery. Up to the present, three new years (2001-2003) have become available for testing the model. For one of these years the predicted YCS was notably different from the assessed YCS. The reason for this is not fully understood, but for all three years SSB was outside the range used in the original model. Including the three new years into the data series resulted in a poorer explanation of the observed recruitment variation (55 %). A comparison of the standardized regression coefficients of both models showed increased significance for the parameter YOY (from 0.47 to 0.61).

  • 3.
    Axenrot, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Didrikas, Tomas
    Danielsson, Charlotte
    Hansson, Sture
    Diel patterns in pelagic fish behaviour and distribution observed from a stationary, bottom- mounted and upward-facing transducer2004In: ICES Journal of Marine Science, ISSN 1054-3139, Vol. 61, no 7, p. 1100-1104Article in journal (Refereed)
  • 4. Axenrot, Thomas
    et al.
    Didrikas, Tomas
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Danielsson, Charlotte
    Hansson, Sture
    Diel patterns in pelagic fish behaviour and distribution observed from a stationary, bottom-mounted, and upward-facing transducer2004In: ICES Journal of Marine Science, ISSN 1054-3139, Vol. 61, no 7, p. 1100-1104Article in journal (Refereed)
  • 5.
    Axenrot, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Predicting herring recruitment from young-of-the-year fish densities, spawning stock biomass, and climate2003In: Limnology and Oceanography, ISSN 0024-3590, Vol. 48, no 4, p. 1716-1720Article in journal (Refereed)
  • 6.
    Axenrot, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Seasonal dynamics in pelagic fish abundance in a Baltic Sea coastal area2004In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, Vol. 60, no 4, p. 541-547Article in journal (Refereed)
  • 7.
    Barron, Jennie
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Dry spell mitigation to upgrade semi-arid rainfed agriculture: Water harvesting and soil nutrient management for smallholder maize cultivation in Machakos, Kenya2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Improvements in on-farm water and soil fertility management through water harvesting may prove key to up-grade smallholder farming systems in dry sub-humid and semi-arid sub-Sahara Africa (SSA). The currently experienced yield levels are usually less than 1 t ha-1, i.e., 3-5 times lower than potential levels obtained by commercial farmers and researchers for similar agro-hydrological conditions. The low yield levels are ascribed to the poor crop water availability due to variable rainfall, losses in on-farm water balance and inherently low soil nutrient levels. To meet an increased food demand with less use of water and land in the region, requires farming systems that provide more yields per water unit and/or land area in the future. This thesis presents the results of a project on water harvesting system aiming to upgrade currently practised water management for maize (Zea mays, L.) in semi-arid SSA. The objectives were to a) quantify dry spell occurrence and potential impact in currently practised small-holder grain production systems, b) test agro-hydrological viability and compare maize yields in an on-farm experiment using combinations supplemental irrigation (SI) and fertilizers for maize, and c) estimate long-term changes in water balance and grain yields of a system with SI compared to farmers currently practised in-situ water harvesting. Water balance changes and crop growth were simulated in a 20-year perspective with models MAIZE1&2.

    Dry spell analyses showed that potentially yield-limiting dry spells occur at least 75% of seasons for 2 locations in semi-arid East Africa during a 20-year period. Dry spell occurrence was more frequent for crop cultivated on soil with low water-holding capacity than on high water-holding capacity. The analysis indicated large on-farm water losses as deep percolation and run-off during seasons despite seasonal crop water deficits. An on-farm experiment was set up during 1998-2001 in Machakos district, semi-arid Kenya. Surface run-off was collected and stored in a 300m3 earth dam. Gravity-fed supplemental irrigation was carried out to a maize field downstream of the dam. Combinations of no irrigation (NI), SI and 3 levels of N fertilizers (0, 30, 80 kg N ha-1) were applied. Over 5 seasons with rainfall ranging from 200 to 550 mm, the crop with SI and low nitrogen fertilizer gave 40% higher yields (**) than the farmers’ conventional in-situ water harvesting system. Adding only SI or only low nitrogen did not result in significantly different yields. Accounting for actual ability of a storage system and SI to mitigate dry spells, it was estimated that a farmer would make economic returns (after deduction of household consumption) between year 2-7 after investment in dam construction depending on dam sealant and labour cost used.

    Simulating maize growth and site water balance in a system of maize with SI increased annual grain yield with 35 % as a result of timely applications of SI. Field water balance changes in actual evapotranspiration (ETa) and deep percolation were insignificant with SI, although the absolute amount of ETa increased with 30 mm y-1 for crop with SI compared to NI. The dam water balance showed 30% productive outtake as SI of harvested water. Large losses due to seepage and spill-flow occurred from the dam. Water productivity (WP, of ETa) for maize with SI was on average 1 796 m3 per ton grain, and for maize without SI 2 254 m3 per ton grain, i.e, a decerase of WP with 25%. The water harvesting system for supplemental irrigation of maize was shown to be both biophysically and economically viable. However, adoption by farmers will depend on other factors, including investment capacity, know-how and legislative possibilities. Viability of increased water harvesting implementation in a catchment scale needs to be assessed so that other down-stream uses of water remains uncompromised.

  • 8.
    Barron, Jennie
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Okwach, G
    Run-off water harvesting for dry spell mitigation in maize (Zea mays L.): results from on-farm research in semi-arid Kenya2005In: Agricultural Water Management, ISSN 0378-3774, E-ISSN 1873-2283, Vol. 74, no 1, p. 1-21Article in journal (Refereed)
    Abstract [en]

    Maize (Zea mays L.) yields obtained by small-holder farmers in semi-arid zones in sub-Sahara Africa (SSA) are often less than half of potential yields. Water deficit during critical crop growth stages together with low nutrient input interacts to reduce yields. Collection of surface run-off, which could be used as supplemental irrigation may prove beneficial in improving current small-holder farming system in SSA. This paper presents the results of an on-farm study of the effects of supplemental irrigation (SI) on maize yield in semi-arid Kenya. Surface run-off from a catchment of 2.7 ha was harvested in a hand-dug earth dam of 300 m2. The water was supplied by gravity to mitigate dry spells in fertilized (SI30, SI80 kg N ha−1) and non-fertilized (SI0 kg N ha−1) maize. Treatments of SI were compared to non-irrigated treatments (NI80, NI30, NI0 kg N ha−1). Rainfall varied, during the five seasons of study, from 196 to 564 mm. The volume of water harvested in the dam ranged between 1% and 4% of seasonal rainfall. The outtake for supplemental irrigation varied between 20 and 240 mm per season. Seepage losses accounted for 11 to 74% of harvested dam water. Lowest maize yields were in NI0, representing farmers’ current practise. SI with fertilizer increased yields compared to non-irrigated and fertilised treatments (NI30, NI80) for low rainfall seasons (<300 mm). High rainfall seasons (>300 mm) resulted in no yield increase for SI compared to NI. Mean seasonal grain yield for SI and fertilizer (30 or 80 kg N ha−1) of 1796 kg ha−1 was significantly higher (P < 0.001) than NI0 kg N ha−1 of 1319 kg ha−1, and higher than SI0 kg N ha−1 and NI30 kg N ha−1 (P < 0.01). Lowest average rain and irrigation water use efficiency (RUE, kg grain mm−1 ha−1) was for NI0 with RUE = 2.1, and highest for SI30 with RUE = 4.1. Water harvesting of surface run-off added as SI resulted in improved maize yields as a result of dry spell mitigation, but only in combination with N fertilizer. To upgrade on-farm water management in semi-arid SSA, the results suggest that supplemental irrigation combined with fertilizer may reduce the currently existing yield gap in small-holder farming systems.

  • 9.
    Barron, Jennie
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rockström, J
    Gichuki, F
    Rainwater management for dry spell mitigation in semi-arid Kenya1999In: East African Agriculture and Forestry Journal, Vol. 65, no 1, p. 57-69Article in journal (Refereed)
  • 10.
    Barron, Jennie
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rockström, J
    Gichuki, F
    Hatibu, N
    Dry spell analysis and maize yields for two semi-arid locations in East Africa2003In: Agricultural and Forest Meteorology, ISSN 0168-1923, Vol. 117, no 1-2, p. 23-37Article in journal (Refereed)
  • 11.
    Barron, Jennie
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rockström, J
    Stroosnijder, L
    Modelling on-farm water balance effects of water harvesting system for Zea mays in semi-arid KenyaManuscript (Other academic)
  • 12.
    Barron, Jennie
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rockström, Johan
    Stockholm University, Stockholm Resilience Centre, Stockholm Environment Institute.
    Fox, P
    Risk analysis and economic viability of water harvesting for supplemental irrigation in the Semi-arids2005In: Agricultural Systems, ISSN 0308-521X, E-ISSN 1873-2267, Vol. 83, no 3, p. 231-250Article in journal (Refereed)
    Abstract [en]

    Food insecurity affects a large portion of the population in sub-Saharan Africa (SSA). To meet future food requirements current rainfed farming systems need to upgrade yield output. One way is to improve water and fertiliser management in crop production. But adaptation among farmers will depend on perceived risk reduction of harvest failure as well as economic benefit for the household. Here, we present risk analysis and economical benefit estimates of a water harvesting (WH) system for supplemental irrigation (SI). Focus of the analysis is on reducing investment risk to improve self-sufficiency in staple food production. The analysis is based on data from two on-farm experimental sites with SI for cereals in currently practised smallholder farming system in semi-arid Burkina Faso and Kenya, respectively. The WH system enables for both SI of staple crop (sorghum and maize) and a fully irrigated off-season cash crop (tomatoes). Different investment scenarios are presented in a matrix of four reservoir sealants combined with three labour opportunity costs. It is shown that the WH system is labour intensive but risk-reducing investment at the two locations. The current cultivation practices do not attain food self-sufficiency in farm households. WH with SI resulted in a net profit of 151–626 USD year−1 ha−1 for the Burkina case and 109–477 USD year−1 ha−1 for the Kenya case depending on labour opportunity cost, compared to −83 to 15 USD year−1 ha−1 for the Burkina case and 40–130 USD year−1 ha−1 for the Kenyan case for current farming practices. Opportunity cost represents 0–66% of the investment cost in an SI system depending on type of sealant. The most economical strategy under local labour conditions was obtained using thin plastic sheeting as reservoir sealant. This resulted in a net profit of 390 and 73 USD year−1 ha−1 for the Burkina Faso and Kenyan respective site after household consumption was deducted. The analysis suggests a strong mutual dependence between investment in WH for SI and input of fertiliser. The WH system is only economically viable if combined with improved soil fertility management, but the investment in fertiliser inputs may only be viable in the long term when combined with SI.

  • 13.
    Blidberg, Eva
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ecotoxicological studies on giant clams (Tridacnidae): Environmental problems and future concerns2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Giant clams (Tridacnidae; Bivalvia) are described as important framework builders on coral reefs in the Indo-Pacific region. They are phototrophic as they are associated with primary producing zooxanthellae. Populations are low due to over-exploitation and most species are now endangered in many areas. Also the general degradation of coral reef habitats and marine pollution related disturbances are threatening local giant clam populations. The aim of my thesis is to provide information of physiological and ecological requirements of giant clams to improve the management of these species.

    By using mainly physiological methods and lethality tests, the responses to anthropogenic stress and natural disturbance were studied. In Paper I, the effect of elevated temperature was tested for in three different species of clams in order to rank the relative sensitivity. Using the end-point production to respiration ratio (Pg/R), we concluded Hippopus hippopus to be the most sensitive species. Paper II compares two different methods measuring copper stress on the photosynthetic efficiency. It was evident that fluorescence measurements and whole animal physiology gave different results. In Paper III Tridacna gigas were transplanted to sites with increased turbidity due to human activities during 6 months. Clearly, the actual growth rate decreased compared to a “clean” site. The clams from turbid waters on the other hand developed a somewhat higher tolerance to copper exposure. Tridacna gigas larvae were exposed to a combination of copper and low salinity in Paper IV, and it was shown that reduced salinity increases mortality, and synergistic effects were obvious. In Paper V and Paper VI effects of oil pollution on juveniles and larvae were studied. Juvenile clams displayed a reduction in the Energy Balance Equation due to reduced filter feeding and absorption efficiency. The larval stage had low tolerance to benzo[a]pyrene, and there was a negative trend in settlement success.

    Overall, the studies acknowledge harmful effects of pollutants found in tropical coastal areas. The importance of taking this into account when discussing the future of wild giant clams is indisputable.

  • 14.
    Blidberg, Eva
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Effects of copper and decreased salinity on survival rate and development of Tridacna gigas larvae2004In: Marine Environmental Research, ISSN 0141-1136, Vol. 58, p. 793-797Article in journal (Refereed)
  • 15.
    Blidberg, Eva
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Elfwing, Tina
    Plantman, Peter
    Tedengren, Michael
    Water temperature influences on physiological behaviour in three species of giant clams (Tridacnidae)2002In: Proceedings 9th International Coral Reef Symposium, Bali 23-27 October 2000, Vol. 1, p. 561-565Article in journal (Refereed)
  • 16.
    Blidberg, Eva
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Tedengren, Michael
    Effects of petroleum on bioenergetics and DNA integrity in the giant clam Hippopus hippopusIn: Aquatic Toxicology, ISSN 0166-445XArticle in journal (Refereed)
  • 17.
    Blidberg, Eva
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Tedengren, Michael
    Survival and development in giant clam larvae (Tridacna gigas) exposed to benzo[a]pyreneManuscript (Other academic)
  • 18.
    Bodin, Örjan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    A network perspective on ecosystems, societies and natural resource management2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis employs a network perspective in studying ecosystems and natural resource management. It explores the structural characteristics of social and/or ecological networks and their implications on societies’ and ecosystems’ ability to adapt to change and to cope with disturbances while still maintaining essential functions and structures (i.e. resilience).

    Paper I introduces terminology from the network sciences and puts these into the context of ecology and natural resource management. Paper II and III focus on habitat fragmentation and how it affects an agricultural landscape in southern Madagascar. Two ecosystem services were addressed: (1) crop pollination by bees, and (2) seed dispersal by ring-tailed lemurs. It is shown that the fraction of the studied landscape presently covered by both crop pollination and seed dispersal is surprisingly high, but that further removal of the smallest habitat patches in the study area could have a severe negative impact on the landscape’s capacity to support these ecosystem services.

    In Papers IV and V, the network approach is used to study social networks and the impact they may have on the management of natural resources. In Paper IV it is found that social networks of low- to moderate link densities (among managers) significantly increase the probability for relatively high and stable utility returns whereas high link densities cause occasional large-scale ecological crises between periods of stable and excessively high utility returns. In Paper V, social networks of a rural fishing community in eastern Africa were analyzed. The results indicate that patterns of communication partly explain the distribution of ecological knowledge among villagers, and that gear type used by small-scale coastal fishermen strongly correlates with their patterns of communication. The results also show that groups most central in the network, and hence potentially most influential, are dominated by one type of fishermen.

  • 19. Bodin, Örjan
    et al.
    Crona, Beatrice
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Community-based management of natural resources – the role of social capital and leadership in a rural fishing communityManuscript (Other academic)
  • 20.
    Bodin, Örjan
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Norberg, Jon
    A network approach for analyzing spatially structured populations in fragmented landscapesManuscript (Other academic)
  • 21.
    Bodin, Örjan
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Norberg, Jon
    Information network topologies for enhanced local adaptive management2005In: Environmental Management, ISSN 0364-152X, Vol. 35, no 2, p. 175-193Article in journal (Refereed)
  • 22.
    Bodin, Örjan
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Tengö, Maria
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Norman, Anna
    Stockholm University, Stockholm Resilience Centre.
    Lundberg, Jakob
    Elmqvist, Thomas
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    The value of small size: loss of forest patches and ecological thresholds in southern Madagascar2006In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 16, no 2, p. 440-451Article in journal (Refereed)
    Abstract [en]

    Many services generated by forest ecosystems provide essential support for human well-being. However, the vulnerability of these services to environmental change such as forest fragmentation are still poorly understood. We present spatial modeling of the generation of ecosystem services in a human-dominated landscape where forest habitat patches, protected by local taboos, are located in a matrix of cultivated land in southern Madagascar. Two ecosystem services dependent on the forest habitats were addressed: (1) crop pollination services by wild and semidomesticated bees (Apoidea), essential for local crop production of, for example, beans, and (2) seed dispersal services based on the presence of ring-tailed lemurs (Lemur catta). We studied the vulnerability of these ecosystem services to a plausible scenario of successive destruction of the smallest habitat patches. Our results indicate that, in spite of the fragmented nature of the landscape, the fraction of the landscape presently covered by both crop pollination and seed dispersal services is surprisingly high. It seems that the taboo system, though indirectly and unintentionally, contributes to upholding the generation of these services by protecting the forest patches. Both services are, however, predicted to be very vulnerable to the successive removal of small patches. For crop pollination, the rate of decrease in cover was significant even when only the smallest habitat patches were removed. The capacity for seed dispersal across the landscape displayed several thresholds with habitat patch removal. Our results suggest that, in order to maintain capacity for seed dispersal across the landscape and crop pollination cover in southern Androy, the geographical location of the remaining forest patches is more crucial than their size. We argue that in heavily fragmented production landscapes, small forest patches should increasingly be viewed as essential for maintaining ecosystem services, such as agricultural production, and also should be considered in the ongoing process of tripling the area of protected habitats in Madagascar.

  • 23. Bodin, Örjan
    et al.
    Tengö, Maria
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Norman, Anna
    Lundberg, Jakob
    Elmqvist, Thomas
    The value of small size: loss of forest patches and threshold effects on ecosystem services in southern MadagascarManuscript (Other academic)
  • 24. Bradshaw, Clare
    et al.
    Kumblad, Linda
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Larsson, Anna
    Remobilisation of buried radionuclides from anoxic sediments by bioturbationManuscript (Other academic)
  • 25.
    Byrén, Lars
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Comparing rate and depth of feeding in benthic deposit-feeders: a test on two amphipods, Monoporeia affinis (Lindström) and Pontoporeia femorata Kröyer2002In: Journal of Experimental Marine Biology and Ecology, no 281, p. 109-121Article in journal (Refereed)
  • 26.
    Byrén, Lars
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Deposit-feeding in benthic macrofauna: Tracer studies from the Baltic Sea2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A low content of organic matter, which is largely refractory in nature, is characteristic of most sediments, meaning that aquatic deposit-feeders live on a very poor food source. The food is derived mainly from sedimenting phytodetritus, and in temperate waters like the Baltic Sea, from seasonal phytoplankton blooms. Deposit-feeders are either bulk-feeders, or selective feeders, which preferentially ingest the more organic-rich particles in the sediment, including phytodetritus, microbes and meiofauna.

    The soft-bottom benthos of the Baltic Sea has low species biodiversity and is dominated by a few macrobenthic species, among which the most numerous are the two deposit-feeding amphipods Monoporeia affinis and Pontoporeia femorata, and the bivalve Macoma balthica. This thesis is based on laboratory experiments on the feeding of these three species, and on the priapulid Halicryptus spinulosus.

    Feeding by benthic animals is often difficult to observe, but can be effectively studied by the use of tracers. Here we used the radioactive isotope 14C to label food items and to trace the organic matter uptake in the animals, while the stable isotopes 13C and 15N were used to follow feeding on aged organic matter in the sediment.

    The abundance of M. balthica and the amphipods tends to be negatively correlated, i.e., fewer bivalves are found at sites with dense populations of amphipods, with the known explanation that newly settled M. balthica spat are killed by the amphipods. Whether the postlarvae are just accidentally killed, or also ingested after being killed was tested by labelling the postlarvae with 14C and Rhodamine B. Both tracer techniques gave similar evidence for predation on and ingestion of postlarval bivalves. We calculated that this predation was likely to supply less than one percent of the daily carbon requirement for M. affinis, but might nevertheless be an important factor limiting recruitment of M. balthica.

    The two amphipods M. affinis and P. femorata are partly vertically segregated in the sediment, but whether they also feed at different depths was unknown. By adding fresh 14C-labelled algae either on the sediment surface or mixed into the sediment, we were able to distinguish surface from subsurface feeding. We found M. affinis and P. femorata to be surface and subsurface deposit-feeders, respectively.

    Whether the amphipods also feed on old organic matter, was studied by adding fresh 14C-labelled algae on the sediment surface, and using aged, one-year-old 13C- and 15N-labelled sediment as deep sediment. Ingestion of old organic matter, traced by the stable isotopes, differed between the two species, with a higher uptake for P. femorata, suggesting that P. femorata utilises the older, deeper-buried organic matter to a greater extent.

    Feeding studies with juveniles of both M. affinis and P. femorata had not been done previously. In an experiment with the same procedure and treatments as for the adults, juveniles of both amphipod species were found to have similar feeding strategies. They fed on both fresh and old sediment, with no partitioning of food resources, making them likely to be competitors for the same food resource.

    Oxygen deficiency has become more wide-spread in the Baltic Sea proper in the last half-century, and upwards of 70 000km2 are now devoid of macrofauna, even though part of that area does not have oxygen concentrations low enough to directly kill the macrofauna. We made week-long experiments on the rate of feeding on 14C-labelled diatoms spread on the sediment surface in different oxygen concentrations for both the amphipod species, M. balthica and H. spinulosus. The amphipods were the most sensitive to oxygen deficiency and showed reduced feeding and lower survival at low oxygen concentrations. M. balthica showed reduced feeding at the lowest oxygen concentration, but no mortality increase. The survival of H. spinulosus was unaffected, but it did not feed, showing that it is not a surface deposit-feeder. We conclude that low oxygen concentrations that are not directly lethal, but reduce food intake, may lead to starvation and death in the longer term.

  • 27.
    Byrén, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ejdung, Gunilla
    Elmgren, Ragnar
    The use of sedimentary organic matter by two deposit-feeding amphipods, studied using three isotopic tracersManuscript (Other academic)
  • 28.
    Chopin,, T.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Buschmann,, A.H.
    Halling,, C.
    Troell,, M.
    Kautsky,, N.
    Neori,, A.
    Kraemer, G.P.
    Zertuche-González, J.A.
    Yarish, C.
    Neefus, C.
    Integrating seaweeds into marine aquaculture systems: a key toward sustainability2001In: Journal of Phyclolgy, Vol. 37, p. 975-986Article in journal (Refereed)
  • 29. Colding, J
    et al.
    Lundberg, Jakob
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lundberg, S
    Urban golf courses sustain wetland biodiversityArticle in journal (Refereed)
  • 30. Colding, J
    et al.
    Lundberg, Jakob
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Olsson, P
    Tengö, M
    Folke, C
    Elmqvist, T
    The role of culturally maintained habitats for supporting biodiversityManuscript (Other academic)
  • 31.
    Colding, Johan
    et al.
    Stockholm University, Stockholm Resilience Centre.
    Lundberg, Jakob
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Folke, Carl
    Stockholm University, Stockholm Resilience Centre.
    Incorporating Green-Area User Groups in Urban Ecosystem Management2006In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 35, no 5, p. 237-244Article in journal (Refereed)
  • 32.
    Crona, Beatrice
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Of Mangroves and Middlemen: A study of social and ecological linkages in a coastal community2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis studies some of the links between the social and ecological components in a coastal Social-Ecological System (SES) of East Africa to gain insight into factors affecting natural resource management at a community level. It does so by assessing the return of ecosystem goods and services in restored mangroves through both ecological and socio-economic measurements, and by empirically studying variations and diversity in content of local ecological knowledge among resource users, its relation to valuation of ecosystem goods and services and its distribution across a social network.

    Taking its starting point in a study of the return of ecological functions in restored mangroves (Paper I) the main results of the thesis are presented in three sections. The ecological perspective, showing restored mangroves as nursery grounds for juvenile shrimp communities, is complemented by findings from interviews with local user groups revealing a range of ecosystem goods and services associated with natural and replanted forests (Paper II). The thesis moves on to show heterogeneity in local ecological knowledge held by groups of resource users (Paper III) and how this can be correlated with structure of the social network for transferring such information and knowledge (Paper IV). This network structure is elaborated upon in the third and final section to look at the role it might play for community social capital and for structurally well positioned individuals to access such capital and initiate collective action for natural resource management (Paper V). The role played by social capital in shaping the informal institution represented by middlemen in the study area is also touched upon as is the function of middlemen in linking social and ecological dynamics of the coupled Social Ecological System (Paper VI). Finally, the implications of these findings are discussed in the context of natural resource management with focus on co-management and community involvement.

  • 33.
    Crona, Beatrice
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Supporting and enhancing development of heterogeneous ecological knowledge among resource users in a Kenyan seascape2006In: Ecology and Society, ISSN 1708-3087, Vol. 11, no 1, p. 32-Article in journal (Refereed)
  • 34. Crona, Beatrice
    et al.
    Bodin, Örjan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    WHAT you know is WHO you know? – communication patterns among resource users as a prerequisite for co-management2006In: Ecology & society, ISSN 1708-3087, E-ISSN 1708-3087, Vol. 11, no 2, p. Aricle nr 7-Article in journal (Refereed)
    Abstract [en]

    The social networks is one factor determining the flow of information within communities and as such may be important in determining successful implementation of community based management. We mapped the social network used for communication of knowledge and information related to natural resource extraction among villagers in a coastal seascape in Kenya. We further identified subgroups and examined their interrelations while measuring to what extent personal attributes such as occupation can explain observed group structure. Finally, we compared the local ecological knowledge held by villagers of different occupations with the structure of the communication network to map how well this structure can explain distribution of ecological knowledge among them. Results show that communication occurs primarily between fishermen who use the same gear type, which may inhibit exchange of ecological knowledge within the community. This may partly explain why the community has been unsuccessful in regulating resource extraction, especially since potentially influential groups of nonfishermen have a limited communication with the various fisher groups. Analysis of network structure also shows that groups most central, and hence potentially most influential, are dominated in numbers by migrant deep sea fishermen, hypothetically less motivated to initiate collective action for resource management. Hence, we conclude that a lack of collective action to remedy an unsustainable situation may be attributed to various different but distinct aspects of the specific structure of the social network.

  • 35.
    Crona, Beatrice
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Bodin, Örjan
    WHAT you know is WHO you know? Communication patterns among resource users as a prerequisite for co-management2006In: Ecology and Society, ISSN 1708-3087, Vol. 11, no 1Article in journal (Refereed)
  • 36.
    Crona, Beatrice
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Nyström, Magnus
    Mogensen, Jens
    Folke, Carl
    Middlemen as critical links in Social-Ecological Systems: An example from fishing communities in Eastern AfricaManuscript (Other academic)
  • 37.
    Crona, Beatrice
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rönnbäck, Patrik
    Utilization of replanted mangroves by postlarval and juvenile shrimps in Gazi Bay, Kenya2005In: Estuarine Coastal and Shelf Science, ISSN 0272-7714, Vol. 65, no 3, p. 535-544Article in journal (Refereed)
  • 38.
    Crépin, Ann-Sophie
    et al.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. Royal Swedish Academy of Science, Beijer Institute of Ecological Economics, Sweden.
    Norberg, Jon
    Stockholm University, Faculty of Science, Department of Systems Ecology. Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Folke, Carl
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. Royal Swedish Academy of Science, Beijer Institute of Ecological Economics, Sweden.
    Kautsky, Nils
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Troell, Max
    Stockholm University, Faculty of Science, Stockholm Resilience Centre. Royal Swedish Academy of Science, Beijer Institute of Ecological Economics, Sweden.
    Social-ecological systems as complex adaptive systems: modeling and policy implications2013In: Environment and Development Economics, ISSN 1355-770X, E-ISSN 1469-4395, Vol. 18, no 2, p. 111-132Article in journal (Refereed)
    Abstract [en]

    Systems linking people and nature, known as social-ecological systems, are increasingly understood as complex adaptive systems. Essential features of these complex adaptive systems – such as nonlinear feedbacks, strategic interactions, individual and spatial heterogeneity, and varying time scales – pose substantial challenges for modeling. However, ignoring these characteristics can distort our picture of how these systems work, causing policies to be less effective or even counterproductive. In this paper we present recent developments in modeling social-ecological systems, illustrate some of these challenges with examples related to coral reefs and grasslands, and identify the implications for economic and policy analysis.

  • 39.
    de la Torre-Castro, Maricela
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Beyond regulations in fisheries management: the dilemmas of the "beach recorders" Bwana Dikos in Zanzibar, TanzaniaManuscript (Other academic)
  • 40.
    de la Torre-Castro, Maricela
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Humans and Seagrasses in East Africa: A social-ecological systems approach2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The present study is one of the first attempts to analyze the societal importance of seagrasses (marine flowering plants) from a Natural Resource Management perspective, using a social-ecological systems (SES) approach. The interdisciplinary study takes place in East Africa (Western Indian Ocean, WIO) and includes in-depth studies in Chwaka Bay, Zanzibar, Tanzania. Natural and social sciences methods were used. The results are presented in six articles, showing that seagrass ecosystems are rich in seagrass species (13) and form an important part of the SES within the tropical seascape of the WIO. Seagrasses provide livelihoods opportunities and basic animal protein, in from of seagrass associated fish e.g. Siganidae and Scaridae. Research, management and education initiatives are, however, nearly non-existent. In Chwaka Bay, the goods and ecosystem services associated with the meadows and also appreciated by locals were fishing and collection grounds as well as substrate for seaweed cultivation. Seagrasses are used as medicines and fertilizers and associated with different beliefs and values. Dema (basket trap) fishery showed clear links to seagrass beds and provided the highest gross income per capita of all economic activities. All showing that the meadows provide social-ecological resilience. Drag-net fishery seems to damage the meadows. Two ecological studies show that artisanal seaweed farming of red algae, mainly done by women and pictured as sustainable in the WIO, has a thinning effect on seagrass beds, reduces associated macrofauna, affects sediments, changes fish catch composition and reduces diversity. Furthermore, it has a negative effect on i.a. women’s health. The two last papers are institutional analyses of the human-seagrass relationship. A broad approach was used to analyze regulative, normative and cultural-cognitive institutions. Cooperation and conflict take place between different institutions, interacting with their slow or fast moving characteristics, and are thus fundamental in directing the system into sustainable/unsustainable paths. Ecological knowledge was heterogeneous and situated. Due to the abundance of resources and high internal control, the SES seems to be entangled in a rigidity trap with the risk of falling into a poverty trap. Regulations were found insufficient to understand SES dynamics. “Well” designed organizational structures for management were found insufficient for “good” institutional performance. The dynamics between individuals embedded in different social and cultural structures showed to be crucial. Bwana Dikos, monitoring officials, placed in villages or landing sites in Zanzibar experienced four dilemmas – kinship, loyalty, poverty and control – which decrease efficiency and affect resilience. Mismatches between institutions themselves, and between institutions and cognitive capacities were identified. Some important practical implications are the need to include seagrass meadows in management and educational plans, addressing a seascape perspective, livelihood diversification, subsistence value, impacts, social-ecological resilience, and a broad institutional approach.

  • 41.
    de la Torre-Castro, Maricela
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Lindström, Lars
    Fishing for institutions: the institutionalization of the social-ecological web in Chwaka Bay, ZanzibarManuscript (Other academic)
  • 42.
    de la Torre-Castro, Maricela
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rönnbäck, Patrik
    Links between humans and seagrasses: an example from tropical East Africa2004In: Ocean & Coastal Management, ISSN 0964-5691, Vol. 47, p. 361-387Article in journal (Refereed)
  • 43.
    Deutsch, L
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Björklund, J
    Made in Sweden ? : Re-defining the Swedish animal production systemArticle in journal (Refereed)
  • 44.
    Deutsch, L
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Folke, C
    Skånberg, K
    The critical natural capital of ecosystem performance as insurance for human well-being2003In: Ecological Economics , Vol. 44, p. 205-217Article in journal (Refereed)
  • 45.
    Deutsch, L
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gräslund, S
    Folke, C
    Troell, M
    Huitric, M
    Kautsky, N
    Lebel, L
    Feeding aquaculture growth through globalization: exploitation of marine ecosystems for fishmealManuscript (Other academic)
  • 46.
    Deutsch, L
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Jansson, Å
    Troell, M
    Rönnbäck, P
    Folke, C
    Kautsky, N
    The "ecological footprint": communicating human dependence on nature's work2000In: Ecological Economics , Vol. 32, p. 351-355Article in journal (Refereed)
  • 47.
    Deutsch, Lisa
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Global trade, food production and ecosystem support: Making the interactions visible2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Modern food production is a complex, globalized system in which what we eat and how it is produced are increasingly disconnected. This thesis examines some of the ways in which global trade has changed the mix of inputs to food and feed, and how this affects food security and our perceptions of sustainability. One useful indicator of the ecological impact of trade in food and feed products is the Appropriated Ecosystem Areas (ArEAs), which estimates the terrestrial and aquatic areas needed to produce all the inputs to particular products.

    The method is introduced in Paper I and used to calculate and track changes in imported subsidies to Swedish agriculture over the period 1962-1994. In 1994, Swedish consumers needed agricultural areas outside their national borders to satisfy more than a third of their food consumption needs. The method is then applied to Swedish meat production in Paper II to show that the term “Made in Sweden” is often a misnomer. In 1999, almost 80% of manufactured feed for Swedish pigs, cattle and chickens was dependent on imported inputs, mainly from Europe, Southeast Asia and South America. Paper III examines ecosystem subsidies to intensive aquaculture in two nations: shrimp production in Thailand and salmon production in Norway. In both countries, aquaculture was shown to rely increasingly on imported subsidies. The rapid expansion of aquaculture turned these countries from fishmeal net exporters to fishmeal net importers, increasingly using inputs from the Southeastern Pacific Ocean.

    As the examined agricultural and aquacultural production systems became globalized, levels of dependence on other nations’ ecosystems, the number of external supply sources, and the distance to these sources steadily increased. Dependence on other nations is not problematic, as long as we are able to acknowledge these links and sustainably manage resources both at home and abroad. However, ecosystem subsidies are seldom recognized or made explicit in national policy or economic accounts. Economic systems are generally not designed to receive feedbacks when the status of remote ecosystems changes, much less to respond in an ecologically sensitive manner. Papers IV and V discuss the problem of “masking” of the true environmental costs of production for trade. One of our conclusions is that, while the ArEAs approach is a useful tool for illuminating environmentally-based subsidies in the policy arena, it does not reflect all of the costs. Current agricultural and aquacultural production methods have generated substantial increases in production levels, but if policy continues to support the focus on yield and production increases alone, taking the work of ecosystems for granted, vulnerability can result. Thus, a challenge is to develop a set of complementary tools that can be used in economic accounting at national and international scales that address ecosystem support and performance.

    We conclude that future resilience in food production systems will require more explicit links between consumers and the work of supporting ecosystems, locally and in other regions of the world, and that food security planning will require active management of the capacity of all involved ecosystems to sustain food production.

  • 48.
    Didrikas, Tomas
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Distribution and activity of pelagic fish - acoustic studies in the Baltic Sea2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Fisheries agencies around the Baltic Sea use hydroacoustics to assess stock sizes of herring and sprat. These assessments rely on the assumption that the acoustic properties of Baltic clupeids are the same as North Sea herring. This may lead to biased results, as system-specific differences in salinity and fish fat content may influence acoustic target strength. The acoustic properties of the Baltic clupeids were explored and a new relationship between target strength and fish length was developed (paper I). The intercept of this new relationship is 3.4 dB higher than normally used by the agencies. Applying this new relationship would reduce the acoustic stock biomass estimates by approximately 50%.

    Diel variation in the vertical distribution of fish may influence acoustic abundance estimates. Fish body posture may influence target strength and if fish concentrate near the surface or bottom this may affect detectability by an echo sounder. A seabed-mounted, upward pinging echo sounder was used to study diel variation in vertical distribution, acoustic size distribution and abundance of fish (Paper II). Differences between day and night were substantial and it was concluded that night time acoustics are to be preferred, at least in our study area. The seabed-mounted echo sounder was also used to study fish swimming activity and vertical distribution in relation to light intensity and water temperature (paper III). Four phases of fish distribution were distinguished over the diel cycle (day, night, dawn and dusk). Acoustic tracking was used to estimate the swimming speed of individual fish. The speed varied among the diel periods and the greatest difference was observed between day and night with twice as high swimming speed during the day. Regression models were developed to investigate the effects of fish size and environmental factors (water temperature, light intensity at the sea surface and in situ, measured at the depth of the fish) on swimming speed. Fish size, light intensities and temperature were all significant variables in the models, with fish size being generally most important. These results have clear implications for fish bioenergetics models. Such models should account for seasonal, light-driven cycles in the activity-induced respiration estimates, in particular when modelling populations at high latitudes.

    Vertical and horizontal fish distributions were studied from spring through autumn during two consecutive years (paper IV). The seasonal dynamics in vertical distribution patterns were consistent between years. Prior to thermocline formation, fish of all sizes concentrated near surface where water temperatures were higher than in the underlying water mass. During the summer period of pronounced thermal stratification, larger fish were found deeper than small individuals (including young-of-the-year fish), which remained close to the surface. In the autumn, when the thermal stratification diminished, the small fish moved somewhat deeper while larger individuals dispersed throughout the water column. Fish showed clear horizontal patchiness, but horizontal distributions were not significantly related to wind directions.

  • 49. Didrikas, Tomas
    et al.
    Axenrot, Thomas
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Pelagic fish distribution in relation to water temperature and wind direction; a study in a Baltic Sea coastal bay Manuscript (Other academic)
  • 50.
    Didrikas, Tomas
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Axenrot, Thomas
    Hansson, Sture
    Pelagic fish distribution in relation to water temperature and wind direction: a study in a Baltic Sea coastal bayManuscript (Other academic)
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