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  • 1.
    Ahlbeck, Ida
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hjerne, Olle
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Evaluating fish diet analysis methods by individual-based modelling2012In: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533, Vol. 69, no 7, p. 1184-1201Article in journal (Refereed)
    Abstract [en]

    Knowledge of diet compositions is important in ecological research. There are many methods available and numerous aspects of diet composition. Here we used modelling to evaluate how well different diet analysis methods describe the true diet of fish, expressed in mass percentages. The methods studied were both basic methods (frequency of occurrence, dominance, numeric, mass, points) and composite indices (Index of Relative Importance, Comparative Feeding Index). Analyses were based on both averaged stomach content of individual fish and on pooled content from several fish. Prey preference, prey size, and evacuation rate influenced the performance of the diet analysis methods. The basic methods performed better than composite indices. Mass and points methods produced diet compositions most similar to the true diet and were also most robust, indicating that these methods should be used to describe energetic-nutritional sources of fish.

  • 2.
    Ahlbeck, Ida
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hjerne, Olle
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Evaluation of diet analysis methods by individual based modellingIn: Canadian Journal of Fisheries and Aquatic Sciences, ISSN 0706-652X, E-ISSN 1205-7533Article in journal (Refereed)
  • 3.
    Ahlbeck, Ida
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Karlöf, Oliver
    Sedentarity in Eurasian perch (Perca fluviatilis) in a coastal Baltic Sea areaIn: Ecology of Freshwater Fish, ISSN 0906-6691, E-ISSN 1600-0633Article in journal (Refereed)
  • 4.
    Bergendahl, I. Ahlbeck
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Holliland, Per Benjamin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Karlöf, Oliver
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Feeding range of age 1+year Eurasian perch Perca fluviatilis in the Baltic Sea2017In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 90, no 5, p. 2060-2072Article in journal (Refereed)
    Abstract [en]

    Using the widespread Eurasian perch Perca fluviatilis as a model organism, feeding ranges were investigated using stable-isotope ratios (N-15 and C-13) and body condition. Differences were found between closely located sampling sites in a littoral area without obvious migration barriers, indicating that individual fish had small feeding ranges. Body condition differences between sampled stations were consistent over 4 years. Such sedentary behaviour is important to consider in, e.g. fisheries management and environmental monitoring, as local catch regulations may be meaningful or geographic stability in sampling locations may reduce noise in data.

  • 5. Bonsdorff, Erik
    et al.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Varning för fiskepolitik à la Jönssonligan2007In: Svenskt Fiske, Vol. 1, p. 38-39Article in journal (Other (popular science, discussion, etc.))
  • 6.
    Ek, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Karlson, Agnes M. L.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Garbaras, Andrius
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Stable Isotope Composition in Daphnia Is Modulated by Growth, Temperature, and Toxic Exposure: Implications for Trophic Magnification Factor Assessment2015In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, no 11, p. 6934-6942Article in journal (Refereed)
    Abstract [en]

    The potential for using stable isotope analysis in risk assessment of environmental contaminants is crucially dependent on the predictability of the trophic transfer of isotopes in food webs. The relationship between contaminant levels and trophic position of consumers is widely used to assess biomagnification properties of various pollutants by establishing trophic magnification factors (TMF). However, contaminant-induced variability of the isotopic composition in biota is poorly understood. Here, we investigated effects of toxic exposure on delta N-15 and delta C-13 values in a consumer, with a main hypothesis that these effects would be largely mediated via growth rate and metabolic turnover of the test animals. The cladoceran Daphnia magna was used in two experiments that were conducted to manipulate growth and body condition (assayed as C:N ratio) by food availability and temperature (Experiment 1) and by toxic exposure to the pesticide lindane (Experiment 2). We found a significant negative effect of growth rate and a positive effect of temperature on the consumer-diet discrimination factor for delta N-15 and delta C-13, with no effects on the C:N ratio (Experiment 1). In lindane-exposed daphnids, a significant growth inhibition was observed, with concomitant increase in metabolic costs and significantly elevated size-specific delta N-15 and delta C-13 values. Moreover, a significantly higher incorporation of carbon relative to nitrogen, yet a concomitant decrease in C:N ratio was observed in the exposed animals. Together, these results have methodological implications for determining trophic positions and TMF in polluted environments, where elevated delta N-15 values would translate into overestimated trophic positions and underestimated TMF. Furthermore, altered delta C-13 values may lead to erroneous food-chain assignment of the consumer in question.

  • 7. Euclide, Peter T.
    et al.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Stockwell, Jason D.
    Partial diel vertical migration in an omnivorous macroinvertebrate, Mysis diluviana2017In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 787, no 1, p. 387-396Article in journal (Refereed)
    Abstract [en]

    Partial migration, whereby only a portion of a population migrates, has just recently received attention in aquatic systems. Partial diel vertical migration (DVM) has received even less attention but could significantly influence our understanding of trophic interactions and nutrient movement in open water systems. Recent work in the Baltic Sea shows differences in isotope composition between benthic and pelagic Mysis salemaai sampled at night, suggesting that partial DVM may be fixed at the individual level. Historic observations of North American M. diluviana suggest partial DVMin this species, but this behavior has largely been ignored in the literature. We used length, occurrence of gravid females, and body delta C-13, delta N-15, delta S-34, and C:N ratio as markers to test for differences among adult M. diluviana collected from benthic and pelagic habitats at night in Lake Champlain, USA. We found differences in body length and occurrence of gravid females between pelagic- and benthic-caught M. diluviana and differences in C: N between pelagic-and benthic-caught non-gravid individuals, consistent with life stage and body condition hypotheses for partial migration. Partial DVM of M. diluviana could have significant impacts on population assessments which could bias food web models used in basic research and management.

  • 8.
    Gorokhova, Elena
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Höglander, Helena
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Andersen, Christian Marc
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Stable isotopes show food web changes after invasion by the predatory cladoceran Cercopagis pengoi in a Baltic Sea bay2005In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 143, no 2, p. 251-259Article in journal (Refereed)
    Abstract [en]

    Cercopagis pengoi, a recent invader to the Baltic Sea and the Laurentian Great Lakes, is a potential competitor with fish for zooplankton prey. We used stable C and N isotope ratios to elucidate trophic relationships between C. pengoi, zooplankton (microzooplankton, 90–200 m, mostly copepod nauplii and rotifers; mesozooplankton, >200 m, mostly copepods), and zooplanktivorous fish (herring, size range 5–15 cm and sprat, 9–11 cm) in a coastal area of the northern Baltic Sea. The isotope ratios in C. pengoi and fish were much higher than those of zooplankton, showing general trends of enrichment with trophic level. Young-of-the-year (YOY) herring had a significantly higher 15N/14N ratio than C. pengoi, suggesting of a trophic linkage between the two species. To evaluate the possible relative importance of different food sources for C. pengoi and YOY herring, two-source isotope-mixing models for N were used, with micro- and mesozooplankton as prey for C. pengoi and mesozooplankton and C. pengoi as prey for YOY herring. These models indicate that mesozooplankton was the major food source of both species. However, microzooplankton may be important prey for young stages of C. pengoi. Comparative analyses of the herring trophic position before and after the invasion by C. pengoi showed a trophic level shift from 2.6 to 3.4, indicating substantial alterations in the food web structure. Our findings contribute to a growing body of evidence, showing that C. pengoi can modify food webs and trophic interactions in invaded ecosystems.

  • 9. Gorska, N
    et al.
    Cieslik, L
    Didrikas, Tomas
    Stockholm University, Faculty of Science, Department of Systems Ecology. Marin ekologi.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology. marin ekologi.
    On acoustic backscattering by Baltic zooplankton2007In: Hydroacoustics, Vol. 10, p. 55-68Article in journal (Refereed)
  • 10.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Comments to Heikinheimo et al. (2014) - On recruitment in Baltic Sea pikeperch2016In: Fisheries Research, ISSN 0165-7836, E-ISSN 1872-6763, Vol. 179, p. 351-351Article in journal (Refereed)
  • 11.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gösforskning i svenska Himmerfjärden.2008In: Fiskeritidskrift för Finland, Vol. 4/2008Article in journal (Other (popular science, discussion, etc.))
  • 12.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Reply to response from Outi Heikinheimo and Timo J. Marjomaki on my comment on Heikinheimo et al., 2014: Spawning stock-recruitment relationship in pikeperch Sander lucioperca (L.) in the Baltic Sea, with temperature as an environmental effect2016In: Fisheries Research, ISSN 0165-7836, E-ISSN 1872-6763, Vol. 183, p. 482-482Article in journal (Refereed)
  • 13.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Vad har hänt med fiskbestånden i Östersjön?2008In: Fiskets kollaps utanför Nordamerika - vad kan Sverige och Europa lära?, 2008Chapter in book (Other (popular science, discussion, etc.))
  • 14.
    Hansson, Sture
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergström, Ulf
    Bonsdorff, Erik
    Härkönen, Tero
    Jepsen, Niels
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lundström, Karl
    Lunneryd, Sven-Gunnar
    Ovegård, Maria
    Salmi, Juhani
    Sendek, Dmitry
    Vetemaa, Markus
    Competition for the fish - fish extraction from the Baltic Sea by humans, aquatic mammals, and birds2018In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 75, no 3, p. 999-1008Article in journal (Refereed)
    Abstract [en]

    Seals and fish-eating birds have increased in the Baltic Sea and there is concern that they compete with fisheries. Using data from around year 2010, we compare consumption of different fish species by seals and birds to the catch in the commercial and recreational fishery. When applicable this is done at the geographical resolution of ICES subdivisions. Predation by birds and mammals likely has limited impact on the populations of the commercially most important species (herring, sprat, and cod). In the central and southern Baltic, seals and birds consume about as much flatfish as is caught by the fishery and competition is possible. Birds and seals consume 2-3 times as much coastal fish as is caught in the fishery. Many of these species are important to the fishery (e. g. perch and whitefish) and competition between wildlife and the fishery is likely, at least locally. Estimated wildlife consumption of pike, sea trout and pikeperch varies among ICES subdivisions and the degree of competition for these species may differ among areas. Competition between wildlife and fisheries need to be addressed in basic ecosystem research, management and conservation. This requires improved quantitative data on wildlife diets, abundances and fish production.

  • 15.
    Hansson, Sture
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Dippner, Joachim W.
    Larsson, Ulf
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Climate effects on zooplankton biomasses in a coastal Baltic Sea area2010In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 15, no 3, p. 370-374Article in journal (Refereed)
    Abstract [en]

    To evaluate if climate influence zooplankton densities and dynamics in a coastal Baltic Sea area, we performed statistical analyses of two 12-13-year-long data series. The winter (December March) North Atlantic Oscillation index (NAO) was used as the independent variable and monthly biomasses of seven groups of zooplankton as the dependent variables. Most of the statistically significant correlations were obtained for the spring-early-summer period and they all indicate higher zooplankton biomasses after winters with high NAO values (mild winters). This supports results from other Baltic Sea studies, indicating that winter/spring climate is important to the early summer zooplankton community.

  • 16.
    Hansson, Sture
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. marin ekologi.
    Hjerne, Olle
    Stockholm University, Faculty of Science, Department of Systems Ecology. marin ekologi.
    Harvey, C
    Kitchell, JF
    Cox, SP
    Essington, TE
    Managing Baltic Sea fisheries under contrasting production and predation regimes: ecosystem model analyses2007In: Ambio, Vol. 36, no 2-3, p. 259-265Article in journal (Refereed)
  • 17.
    Hansson, Sture
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergström, Ulf
    Bonsdorff, Erik
    Jepsen, Niels
    Lundström, Karl
    Lunneryd, Sven-Gunnar
    Ovegård, Maria
    Salmi, Juhani
    Sendek, Dmitry
    Vetemaa, Markus
    Response to comments by Heikinheimo et al. (in press) on Hansson et al. (2018): competition for the fish—fish extraction from the Baltic Sea by humans, aquatic mammals, and birds2018In: ICES Journal of Marine Science, ISSN 1054-3139, E-ISSN 1095-9289, Vol. 75, no 5, p. 1837-1839Article in journal (Refereed)
    Abstract [en]

    As discussions and debates are crucial to science, we appreciate the comments by Heikinheimo et al. (in press) on our article on competition for Baltic Sea fish resources between fishery and wildlife. We cannot see that the comments by Heikinheimo et al. changes the general conclusion derived in our original article—that there are cases of competition between wildlife and fisheries in the Baltic Sea, although not for all species and not to the same extent everywhere. Our responses are structured in the same order as the comments by Heikinheimo et al.

  • 18.
    Holliland, Per B.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ahlbeck, Ida
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Westlund, Erica
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Ontogenetic and seasonal changes in diel vertical migration amplitude of the calanoid copepods Eurytemora affinis and Acartia spp. in a coastal area of the northern Baltic Proper2012In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 34, no 4, p. 298-307Article in journal (Refereed)
    Abstract [en]

    We studied diel vertical migration (DVM) of the six copepodite stages of two of the most abundant crustacean zooplankton in the Baltic Sea, the calanoid copepods Eurytemora affinis and Acartia spp. The study was conducted monthly from May through October in a bay in the northwestern Baltic proper. Fish biomass, phytoplankton abundance and temperature were obtained in conjunction with the zooplankton sampling. Both copepod species performed DVM. With the exception of females, all E. affinis copepodite stages performed migrations of over 10 m with only a slight increase with the copepodite stage. Adult female E. affinis remained at depth with only slight upward movement at night. In Acartia spp., DVM amplitude increased with stage and size, suggesting an ontogenetic shift in behaviour; although they had a less pronounced DVM than E. affinis. Although DVM amplitude increased with size, indicative of visual predation, fish biomass did not correlate with the amplitude of DVM. However, fish were present throughout the study period. We surmise that these ontogenetic shifts in behaviour are due to size increase and therefore visibility to predators and that the difference in DVM between the species may well be a result of physiological differences and reproductive strategy.

  • 19. Jensen, O. P.
    et al.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Didrikas, T.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Stockwell, J. D.
    Hrabik, T. R.
    Axenrot, T.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Kitchell, J. F.
    Foraging, bioenergetic and predation constraints on diel vertical migration: field observations and modelling of reverse migration by young-of-the-year herring Clupea harengus2011In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 78, no 2, p. 449-465Article in journal (Refereed)
    Abstract [en]

    Diel vertical migration (DVM) of young-of-the-year (YOY) herring Clupea harengus and one of their major predators, pikeperch Sander lucioperca, was examined using bottom-mounted hydroacoustics in Himmerfjarden, a brackish bay of the Baltic Sea, in summer. In contrast to previous studies on DVM of C. harengus aggregated across size and age classes, YOY C. harengus showed a reverse DVM trajectory, deeper at night and, on average, shallower during the day. This pattern was observed consistently on five acoustic sampling occasions in 3 years and was corroborated by two out of three trawl surveys. Large acoustic targets (target strength >-33 dB, probably piscivorous S. lucioperca > 45 cm) showed a classic DVM trajectory, shallow at night and deeper during the day. Variability in YOY C. harengus vertical distribution peaked at dawn and dusk, and their vertical distribution at midday was distinctly bimodal. This reverse DVM pattern was consistent with bioenergetic model predictions for YOY C. harengus which have rapid gut evacuation rates and do not feed at night. Reverse DVM also resulted in low spatial overlap with predators.

  • 20.
    Nielsen, Jens M.
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Reutervik, Katja L.
    Winder, Monika
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Amino acid stable isotope discrimination in diverse aquatic food chains2015Manuscript (preprint) (Other academic)
  • 21.
    Ogonowski, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Andersson, Kristoffer
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    A weight and temperature dependent model of respiration in Praunus flexuosus (Crustacea, Mysidacea)2012In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 34, no 7, p. 642-645Article in journal (Refereed)
    Abstract [en]

    The mysid shrimp Praunus flexuosus is common in littoral habitats in the Baltic Sea and other marine areas, but its bioenergetic characteristics have not been studied. We present the first model of its routine respiration rate as a function of size and a natural temperature range. The model explained 87% of the variance in respiration, indicating that it could be useful in a larger modeling framework. Specific respiration rates and temperature dependence were consistent with previous reports for this and other littoral mysids at low-to-moderate temperatures. Respiration at higher temperatures was lower, indicating that previous reports may have been biased by residual SDA (specific dynamic action) effects. Increased respiration due to SDA was detectable over a longer period than previously reported, ∼30 h.

  • 22.
    Ogonowski, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Duberg, Jon
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Behavioral, Ecological and Genetic Differentiation in an Open Environment-A Study of a Mysid Population in the Baltic Sea2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 3, p. e57210-Article in journal (Refereed)
    Abstract [en]

    Diel vertical migration (DVM) is often assumed to encompass an entire population. However, bimodal nighttime vertical distributions have been observed in various taxa. Mysid shrimp populations also display this pattern with one group concentrated in the pelagia and the other near the bottom. This may indicate alternative migratory strategies, resembling the seasonal partial migrations seen in birds, fishes and amphibians, where only a subset of the population migrates. To assess the persistence of these alternative strategies, we analyzed the nitrogen and carbon stable isotope signatures (as proxies for diet), biochemical indices (as proxies for growth condition), and genetic population divergence in the Baltic mysid Mysis salemaai collected at night in the pelagia and close to the bottom. Stable isotope signatures were significantly different between migrants (pelagic samples) and residents (benthic samples), indicating persistent diet differences, with pelagic mysids having a more uniform and carnivorous diet. Sequencing of the mitochondrial cytochrome subunit I (COI) gene showed genetic differentiation attributable to geographic location but not between benthic and pelagic groups. Divergent migration strategies were however supported by significantly lower gene flow between benthic populations indicating that these groups have a lower predisposition for horizontal migrations compared to pelagic ones. Different migration strategies did not convey measurable growth benefits as pelagic and benthic mysids had similar growth condition indices. Thus, the combination of ecological, biochemical and genetic markers indicate that this partial migration may be a plastic behavioral trait that yields equal growth benefits.

  • 23.
    Ogonowski, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Duberg, Jon
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Persistent lack of diel vertical migration in a pelagic mysid population: a case of partial migrationManuscript (preprint) (Other academic)
  • 24.
    Ogonowski, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Duberg, Jon
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Status and vertical size distributions of a pelagic mysid community in the northern Baltic proper2012In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 18, no 1, p. 1-18Article in journal (Refereed)
    Abstract [en]

    We report on abundance, biomass, trophic position and vertical size distribution of pelagic mysids (Mysis mixta, Mysis relicta/salemaai, Neomysis integer) in a coastal Baltic Proper area. As compared with the situation in this area in the 1980s, the formerly dominating M. mixta has declined and the total mysid biomass decreased by 50%. Neomysis integer now constitutes the bulk of the mysids. Stable isotopes indicate that they feed on a lower trophic level than Mysis spp., and M. relicta appears more carnivorous than M. mixta. For N. integer, size increases with depth and decreases with in situ light. This was not found for Mysis spp., probably due to their narrow size span and smaller sample size than for N. integer. In N. integer, in situ light explained the size variation with depth better than temperature, indicating that this variation is a response to predation rather than size-related thermal preference.

  • 25. O'Malley, Brian P.
    et al.
    Dillon, Rebecca A.
    Paddock, Robert W.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Stockwell, Jason D.
    An underwater video system to assess abundance and behavior of epibenthic Mysis2018In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, Vol. 16, no 12, p. 868-880Article in journal (Refereed)
    Abstract [en]

    The application of remote video technologies can provide alternative views of in situ behavior and distribution of aquatic organisms that might be missed with traditional net‐based techniques. We describe a remote benthic video camera system designed to quantify epibenthic density of the macroinvertebrate Mysis diluviana. We deployed the camera multiple times during the day and night at a 60‐m depth site in Lake Champlain and quantified Mysis density from the footage using basic methods and readily available software. Density estimates from the video were on average 43 times higher than concurrent estimates from benthic sled tows, suggesting sleds may be inefficient at sampling mysids. Deployment caused initial scattering of individuals, resulting in low densities immediately after deployment that slowly increased. On some occasions, Mysis densities on video fluctuated greatly over several hours, consistent with organisms that have a patchy distribution on the lake bottom. The camera system provided novel insights on behavior and distribution of Mysis on benthic habitats, demonstrating potential for use as a tool to study partial diel vertical migration and predator–prey interactions.

  • 26. O'Malley, Brian P.
    et al.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Stockwell, Jason D.
    Evidence for a size-structured explanation of partial diel vertical migration in mysids2018In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 40, no 1, p. 66-76Article in journal (Refereed)
    Abstract [en]

    Mysids are known for benthic-pelagic diel vertical migration (DVM), where the population is benthic by day and pelagic by night. However, historical and recent observations in members of the Mysis relicta complex suggests populations exhibit partial DVM, with some remaining benthic at night. We used pelagic net and benthic sled tows to assess diel habitat use by Mysis diluviana at two stations (60 and 100 m deep) in Lake Champlain, USA, during June-November 2015. At both stations, mysids were on the bottom both day and night, but the extent of pelagic habitat use by Mysis varied by site depth. At 60-m, pelagic densities were an order of magnitude lower during the day compared to at night, indicative of benthic-pelagic DVM. Contrary to expectations, we found no diel difference between pelagic and benthic sled density estimates at 100-m, suggesting an equal number of Mysis are benthic day and night, and an equal number are pelagic-day and night at deeper sites. Mean body length of benthic-caught mysids was greater than pelagic-caught individuals, a pattern that was evident both day and night at 100-m. Our findings indicate Mysis partial DVM is common across seasons and influenced by body size and depth.

  • 27.
    Sjöberg, Niklas B.
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology. Swedish Board of Fisheries, Institute of Freshwater Research, Sweden.
    Petersson, Erik
    Wickström, Håkan
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Effects of the swimbladder parasite Anguillicola crassus on the migration of European silver eels Anguilla anguilla in the Baltic Sea2009In: Journal of Fish Biology, ISSN 0022-1112, E-ISSN 1095-8649, Vol. 74, no 9, p. 2158-2170Article in journal (Refereed)
    Abstract [en]

    In a mark–recapture study in 2006, migrating European Anguilla anguilla silver eels were caught,tagged and released in the Baltic Sea and recaptures in commercial pound nets examined for possibleeffects on migration of infection with the swimbladder parasite Anguillicola crassus. The overallrecapture rate was 36%. The prevalence of infection was lowest at the northernmost sampling site.There were no significant differences between infected and uninfected A. anguilla in conditionindices, body fat content and estimated migration speeds. Parasite infection intensity levels weresignificantly negatively correlated with times and distances covered between release and recapture,but did not correlate with migration speed. It appears that more heavily infected A. anguilla wererelatively more vulnerable to recapture in pound nets. It is hypothesized that parasite-induced damageto the swimbladder inhibited vertical migrations and infected A. anguilla tended to migrate inshallower coastal waters, relatively close to the shore.

  • 28. Webster, Clare N.
    et al.
    Hansson, Sture
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Didrikas, Tomas
    Gorokhova, Elena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Peltonen, Heikki
    Brierley, Andrew S.
    Lehtiniemi, Maiju
    Stuck between a rock and a hard place: zooplankton vertical distribution and hypoxia in the Gulf of Finland, Baltic Sea2015In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 162, no 7, p. 1429-1440Article in journal (Refereed)
    Abstract [en]

    Zooplankton often migrate vertically to deeper dark water during the day to avoid visual predators such as fish, a process which can strengthen benthic-pelagic coupling. In the Gulf of Finland, Baltic Sea, a pronounced hypoxic layer develops when there is an inflow of anoxic bottom water from the Central Baltic Sea, which could be a barrier for vertical migrants. Here, we report an acoustic study of the distributions of crustacean zooplankton (mysid shrimp and the copepod Limnocalanus macrurus), gelatinous zooplankton (Aurelia aurita) and fish. Zooplankton trawl nets were used to ground-truth acoustic data. Vertical profiles of oxygen concentration were taken, and the physiological impact of hypoxia on mysids was investigated using biochemical assays. We hypothesised that the vertical distribution of zooplankton and fish would be significantly affected by vertical heterogeneity of oxygen concentrations because anoxia and hypoxia are known to affect physiology and swimming behaviour. In addition, we hypothesised that mysids present in areas with hypoxia would exhibit a preparatory antioxidant response, protecting them from oxidative damage during migrations. The acoustic data showed peaks of crustacean zooplankton biomass in hypoxic (< 2 mL L-1) and low oxygen (2-4 mL L-1) concentrations (depth > 75 m), whereas fish shoals and A. aurita medusae were found in normoxic (5-6 mL L-1) upper water layers (< 40 m), with individual fish in deeper water excepting that rule. Mysid shrimp from areas with hypoxia had significantly enhanced antioxidant potential compared with conspecifics from areas with no hypoxia and had no significant indications of oxidative damage. We conclude that mysids can protect themselves from oxidative damage, enabling them to inhabit hypoxic water. Our data suggest that hypoxic and low oxygen zones (up to 4 mL L-1) may provide some zooplankton species with a refuge from visual predators such as fish.

  • 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, p. 877-889Article 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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