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  • 1.
    Albertsson, Jan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Trophic interactions involving mysid shrimps (Mysidacea) in the near-bottom habitat in the Baltic Sea2004In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 38, no 3, p. 457-469Article in journal (Refereed)
    Abstract [en]

    In a six month mesocosm tank experiment, hypotheses were tested concerning the role of benthopelagic mysid shrimps (Mysidacea) in the near-bottom food web of the Bothnian Sea, in the northern Baltic Sea. The first hypothesis tested was that the mysids interact, through predation, with benthic deposit-feeding Monoporeia affinis amphipods. A second hypothesis tested was that the sediment type is important for the overwintering success of the mysids. Changes in abundance and mass were recorded for M. affinis and mysids when separate and when coexisting, in two sediment types differing in organic content (food level); soft muddy clay (rich) and fine sand (poor). Despite the fact that newborn M. affinis offspring, a plausible target for predation by mysids, were present in substantial numbers in the tanks, no consistent evidence for any interaction between these taxa was found. The biomass of mysids was slightly higher in the muddy clay than in the sand tanks, and the mechanism behind this substrate effect is discussed. A third hypothesis, that the mysids interact with near-bottom zooplankton, was investigated. The tanks were continually supplied with in situ near-bottom sea-water containing a seminatural assemblage of near-bottom plankton. As a result of mysid predation, tanks with mysids had lower abundance and biomass of cyclopoid copepods than tanks without mysids. Thus, the major interaction found was predation on near-bottom zooplankton by mysids and it is suggested that this interaction could potentially be an important food link, especially during periods with low food availability in the pelagic system.

  • 2.
    Andersson, A.
    et al.
    Marine Ecology, Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden, Umeå Marine Sciences Centre, SE-910 20 Hörnefors, Sweden.
    Samuelsson, Kristina
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Medical Microbiology .
    Haecky, P.
    Umeå Marine Sciences Centre, SE-910 20 Hörnefors, Sweden, Botanical Institute, University of Copenhagen, Oster Farimagsgade 2D, DK-1353 Copenhagen K, Denmark.
    Albertsson, J.
    Umeå Marine Sciences Centre, SE-910 20 Hörnefors, Sweden.
    Changes in the pelagic microbial food web due to artificial eutrophication2006In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 40, no 3, p. 299-313Article in journal (Refereed)
    Abstract [en]

    The effect of nutrient enrichment on the structure and carbon flow in the pelagic microbial food web was studied in mesocosm experiments using seawater from the northern Baltic Sea. The experiments included food webs of at least four trophic levels, (1) phytoplankton-bacteria, (2) flagellates, (3) ciliates and (4) mesozooplankton. In the enriched treatments high autotrophic growth rates were observed, followed by increased heterotrophic production. The largest growth increase was due to heterotrophic bacteria, indicating that the heterotrophic microbial food web was promoted. This was further supported by increased growth of heterotrophic flagellates and ciliates in the high nutrient treatments. The phytoplankton peak in the middle of the experiments was mainly due to an autotrophic nanoflagellate, Pyramimonas sp. At the end of the experiment, the proportion of heterotrophic organisms was higher in the nutrient enriched than in the nutrient-poor treatment, indicating increased predation control of primary producers. The proportion of potentially mixotrophic plankton, prymnesiophyceans, chrysophyceans and dinophyceans, were significantly higher in the nutrient-poor treatment. Furthermore, the results indicated that the food web efficiency, defined as mesozooplankton production per basal production (primary production + bacterial production - sedimentation), decreased with increasing nutrient status, possibly due to increasing loss processes in the food web. This could be explained by promotion of the heterotrophic microbial food web, causing more trophic levels and respiration steps in the food web. © Springer Science+Business Media B.V. 2006.

  • 3. Andersson, Agneta
    et al.
    Samuelsson, Kristina
    Haecky, Pia
    Albertsson, Jan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Changes in the pelagic microbial food web due to artificial eutrophication2006In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 40, no 3, p. 299-313Article in journal (Refereed)
    Abstract [en]

    The effect of nutrient enrichment on the structure and carbon flow in the pelagic microbial food web was studied in mesocosm experiments using seawater from the northern Baltic Sea. The experiments included food webs of at least four trophic levels; (1) phytoplankton-bacteria, (2) flagellates, (3) ciliates and (4) mesozooplankton. In the enriched treatments high autotrophic growth rates were observed, followed by increased heterotrophic production. The largest growth increase was due to heterotrophic bacteria, indicating that the heterotrophic microbial food web was promoted. This was further supported by increased growth of heterotrophic flagellates and ciliates in the high nutrient treatments. The phytoplankton peak in the middle of the experiments was mainly due to an autotrophic nanoflagellate, Pyramimonas sp. At the end of the experiment, the proportion of heterotrophic organisms was higher in the nutrient enriched than in the nutrient-poor treatment, indicating increased predation control of primary producers. The proportion of potentially mixotrophic plankton, prymnesiophyceans, chrysophyceans and dinophyceans, were significantly higher in the nutrient-poor treatment. Furthermore, the results indicated that the food web efficiency, defined as mesozooplankton production per basal production (primary production + bacterial production - sedimentation), decreased with increasing nutrient status, possibly due to increasing loss processes in the food web. This could be explained by promotion of the heterotrophic microbial food web, causing more trophic levels and respiration steps in the food web.

  • 4.
    Dahlgren, Kristin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Eriksson Wiklund, Ann-Kristin
    Department of Applied Environmental Science, ITM, Stockholm University, 106 91 Stockholm, Sweden.
    Andersson, Agneta
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Influence of plankton structure and temperature on pelagic food web efficiency in a brackish water system2011In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 45, p. 307-323Article in journal (Refereed)
    Abstract [en]

    As part of one climate change scenario, water temperature as well as the ratio between heterotrophic and autotrophic production is expected to increase; the latter at least in higher latitudes. In order to test how this scenario would affect organisms, such as metazooplankton, at higher trophic levels and carbon transfer up the food chain, a mesocosm experiment was performed at two different temperatures; 5 and 10°C, with two food webs; one phytoplankton-based (NP; autotrophic) and one bacteria-based (CNP; heterotrophic).  The groups of pelagic organisms included in the mesocosms were bacteria, flagellates, ciliates, phytoplankton and metazooplankton. Metazooplankton production was observed to increase with temperature, but was not significantly affected by food web structure. A change in food web structure, i.e. increased heterotrophy, did however lead to decreased fatty acid content and lower individual weight of the metazooplankton. Food web efficiency (FWE), defined as metazooplankton production divided by basal production, increased with autotrophy and temperature: 5CNP (0.2%) < 10CNP (0.4%) < 5NP (1.2%) < 10NP (7.3%). Our results indicate that in the climate change scenario under consideration, the temperature will have a positive effect on FWE whereas the increase in heterotrophy will have a negative effect on FWE. Furthermore, the quality, in terms of fatty acid content and individual weight of the metazooplankton, will be reduced with possible negative effects on higher trophic levels.

  • 5. Dahlgren, Kristin
    et al.
    Wiklund, Ann-Kristin Eriksson
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Andersson, Agneta
    The influence of autotrophy, heterotrophy and temperature on pelagic food web efficiency in a brackish water system2011In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 45, no 3, p. 307-323Article in journal (Refereed)
    Abstract [en]

    Climate change has been suggested to lead to higher temperature and increased heterotrophy in aquatic systems. The aim of this study was to test how these two factors affect metazooplankton and food web efficiency (FWE was defined as metazooplankton production divided by basal production). We tested the following hypotheses: (1) that lower metazooplankton production and lower FWE would be found in a food web based on heterotrophic production (bacteria) relative to one based on autotrophic production (phytoplankton), since the former induces a larger number of trophic levels; (2) the metazooplankton in the heterotrophic food web would contain less essential fatty acids than those from the autotrophic food web; and (3) that higher temperature would lead to increased FWE. To test these hypotheses, a mesocosm experiment was established at two different temperatures (5 and 10A degrees C) with a dominance of either autotrophic (NP) or heterotrophic basal production (CNP). Metazooplankton production increased with temperature, but was not significantly affected by differences in basal production. However, increased heterotrophy did lead to decreased fatty acid content and lower individual weight in the zooplankton. FWE increased with autotrophy and temperature in the following order: 5CNP < 10CNP < 5NP < 10NP. Our results indicate that in the climate change scenario we considered, the temperature will have a positive effect on FWE, whereas the increase in heterotrophy will have a negative effect on FWE. Furthermore, the quality and individual weight of the metazooplankton will be reduced, with possible negative effects on higher trophic levels.

  • 6.
    Degerman, Erik
    et al.
    Swedish university of agricultural sciences, Sweden.
    Tamario, Carl
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Watz, Johan
    Karlstad University, Sweden.
    Nilsson, P. Anders
    Karlstad University, Sweden;Lund University, Sweden.
    Calles, Olle
    Karlstad University, Sweden.
    Occurrence and habitat use of European eel (Anguilla anguilla) in running waters: lessons for improved monitoring, habitat restoration and stocking2019In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 53, no 4, p. 639-650Article in journal (Refereed)
    Abstract [en]

    To improve the management of the European eel (Anguilla anguilla) in freshwater, it is essential to define important lotic habitats. Electrofishing data from 289 wadeable, hard-bottom sites in 69 Swedish coastal rivers and streams, originally surveyed for salmonid monitoring, were used to evaluate the effects of sampling- and habitat-related factors on eel occurrence. Probability of eel occurrence, as influenced by sampling procedure (sampled area, number of consecutive runs and ambient water temperature) and habitat characteristics (size of catchment, dominating bottom substrate, shade, water velocity, mean depth), was evaluated for small (total length <= 150 mm) and large (>150 mm) yellow eels. Data were analysed in a mixed presence/absence generalized linear model with dispersal (distance to mouth from sampled site), habitat and sampling-related variables as covariates. The two models explained variation in occurrence to 81.5% for small eel and 76.2% for large eel. Probability of eel occurrence decreased with distance from the river mouth, and increased with sampled area, number of runs, water temperature, coarser substrate and size of river. We suggest that future eel habitat restoration should focus on lower reaches of larger rivers with suitable coarse bottom habitats. Stocking of young eel should be carried out in comparable accessible habitats in the upper reaches where eel densities are low. The results also strongly indicate that eel may be sampled together with young salmonids with DC electrofishing in wadeable habitats.

  • 7.
    Degerman, Erik
    et al.
    Swedish University of Agricultural sciences.
    Tamario, Carl
    Linnaeus University.
    Watz, Johan
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Nilsson, Per Anders
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013). Lund University.
    Calles, Olle
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Environmental and Life Sciences (from 2013).
    Occurrence and habitat use of European eel (Anguilla anguilla) in running waters: lessons for improved monitoring, habitat restoration and stocking2019In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 53, no 4, p. 639-650Article in journal (Refereed)
    Abstract [en]

    To improve the management of the Europeaneel (Anguilla anguilla) in freshwater, it isessential to define important lotic habitats. Electrofishingdata from 289 wadeable, hard-bottom sites in 69Swedish coastal rivers and streams, originally surveyedfor salmonid monitoring, were used to evaluatethe effects of sampling- and habitat-related factors oneel occurrence. Probability of eel occurrence, asinfluenced by sampling procedure (sampled area,number of consecutive runs and ambient watertemperature) and habitat characteristics (size ofcatchment, dominating bottom substrate, shade, watervelocity, mean depth), was evaluated for small (totallength B 150 mm) and large ([150 mm) yelloweels. Data were analysed in a mixed presence/absencegeneralized linear model with dispersal (distance tomouth from sampled site), habitat and samplingrelatedvariables as covariates. The two modelsexplained variation in occurrence to 81.5% for smalleel and 76.2% for large eel. Probability of eeloccurrence decreased with distance from the rivermouth, and increased with sampled area, number ofruns, water temperature, coarser substrate and size ofriver. We suggest that future eel habitat restorationshould focus on lower reaches of larger rivers withsuitable coarse bottom habitats. Stocking of young eelshould be carried out in comparable accessible habitatsin the upper reaches where eel densities are low.The results also strongly indicate that eel may besampled together with young salmonids with DCelectrofishing in wadeable habitats.

  • 8.
    Hansen, Joakim
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Wikström, Sofia
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Axemar, Hanna
    Stockholm University, Faculty of Science, Department of Botany.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Botany.
    Distribution differences and active habitat choices of invertebrates between macrophytes of different morphological complexity2011In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 45, no 1, p. 11-22Article in journal (Refereed)
    Abstract [en]

    This study explores: (1) whether the abundance of macroinvertebrates differs between macrophytes differing in both morphological complexity and tolerance to nutrient enrichment; (2) whether the distribution of invertebrates between macrophytes is due to active habitat choice; and (3) whether invertebrates prefer structurally complex to simple macrophytes. Macroinvertebrate abundance was compared between two common soft-bottom plants in the Baltic Sea that are tolerant to eutrophication, Myriophyllum spicatum and Potamogeton pectinatus, and one common plant that is sensitive to eutrophication, Chara baltica. Both field sampling and habitat choice experiments were conducted. We recorded higher total macroinvertebrate abundance on the structurally complex M. spicatum than on the more simply structured P. pectinatus and C. baltica, but found no difference in macroinvertebrate abundance between P. pectinatus and C. baltica. In accordance with the field results, our experiment indicated that the crustacean Gammarus oceanicus actively chose M. spicatum over the other macrophytes. Besides, we found that G. oceanicus actively preferred complex to simply structured artificial plants, indicating that the animal distribution was at least partly driven by differences in morphological complexity between plant species. In contrast, the gastropod Theodoxus fluviatilis did not make an active habitat choice between the plants. Our findings suggest that human-induced changes in vegetation composition can affect the faunal community. Increased abundance of structurally complex macrophytes, for example, M. spicatum, can result in increased abundance of macroinvertebrates, particularly mobile arthropods that may actively choose a more structurally complex macrophyte.

  • 9. Hansson, L-A
    et al.
    Brodersen, Jakob
    Chapman, Ben
    Ekvall, M
    Hargeby, A
    Hulthén, K
    Nicolle, A
    Nilsson, P. Anders
    Lund University.
    Skov, C
    Brönmark, C
    A lake as a microcosm: Reflections on developments in aquatic ecology2013In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 47, p. 125-135Article in journal (Refereed)
    Abstract [en]

    In the present study, we aim at relating Forbes' remarkable paper on "The lake as a microcosm", published 125 years ago, to the present status of knowledge in our own research group. Hence, we relate the observations Forbes made to our own microcosm, Lake Krankesjon in southern Sweden, that has been intensively studied by several research groups for more than three decades. Specifically, we focus on the question: Have we made any significant progress or did Forbes and colleagues blaze the trail through the unknown wilderness and we are mainly paving that intellectual road? We conclude that lakes are more isolated than many other biomes, but have, indeed, many extensions, for example, input from the catchment, fishing and fish migration. We also conclude that irrespective of whether lakes should be viewed as microcosms or not, the paper by Forbes has been exceptionally influential and still is, especially since it touches upon almost all aspects of the lake ecosystem, from individual behaviour to food web interactions and environmental issues. Therefore, there is no doubt that even if 125 years have passed, Forbes' paper still is a source of inspiration and deserves to be read. Hence, although aquatic ecology has made considerable progress over the latest century, Forbes might be viewed as one of the major pioneers and visionary scientists of limnology.

  • 10.
    Hylander, Samuel
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Hansson, Lars-Anders
    Unds universitet.
    Vertical distribution and pigmentation of Antarctic zooplankton determined by a blend of UV radiation, predation and food availability2013In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 47, no 4, p. 467-480Article in journal (Refereed)
    Abstract [en]

    Selection pressure induced by simultaneously occurring environmental threats is a major evolutionary driver for organisms in terrestrial, as well as in aquatic ecosystems. For example, protection against ultraviolet radiation (UVR) and predation include both morphological and behavioral components. Here we address those selective pressures on zooplankton by performing a latitudinal monitoring, combined with mechanistic experiments in the Antarctic Southern Ocean, where the UVR-threat is extremely high. We assessed vertical distributions of zooplankton along the Antarctic coast showing that animals were most abundant at 20-80 m and tended to avoid the surface at sites with clear water. UVR-threat disappeared at between 9 and 15 m at sites with low and high water transparency, respectively. Light levels were, however, sufficient for visual fish predation down to approximately 19 and 37 m, respectively. The few zooplankton that were present in surface waters had high levels of non-pigmented UVR-protective compounds (mycosporine-like amino acids) compared to deeper dwelling zooplankton. Overall they had low levels of red pigmented UVR-protective compounds (carotenoids), suggesting high predation on pigmented individuals. In a complementary laboratory study we showed that levels of UVR-protective compounds increased considerably when zooplankton were exposed to UVR in the absence of predator cues. The recently developed transparency-regulator hypothesis predicts that UVR avoidance is an important driver to diel vertical migration in transparent waters, such as in Antarctica. We, however, conclude that copepods resided well below the level where UVR had diminished to very low levels and that predator avoidance or food availability are more likely drivers of zooplankton vertical depth distribution in transparent marine systems.

  • 11.
    Hylander, Samuel
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Hansson, Lars-Anders
    Unds universitet.
    Vertical distribution and pigmentation of Antarctic zooplankton determined by a blend of UV radiation, predation and food availability2013In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 47, no 4, p. 467-480Article in journal (Refereed)
    Abstract [en]

    Selection pressure induced by simultaneously occurring environmental threats is a major evolutionary driver for organisms in terrestrial, as well as in aquatic ecosystems. For example, protection against ultraviolet radiation (UVR) and predation include both morphological and behavioral components. Here we address those selective pressures on zooplankton by performing a latitudinal monitoring, combined with mechanistic experiments in the Antarctic Southern Ocean, where the UVR-threat is extremely high. We assessed vertical distributions of zooplankton along the Antarctic coast showing that animals were most abundant at 20-80 m and tended to avoid the surface at sites with clear water. UVR-threat disappeared at between 9 and 15 m at sites with low and high water transparency, respectively. Light levels were, however, sufficient for visual fish predation down to approximately 19 and 37 m, respectively. The few zooplankton that were present in surface waters had high levels of non-pigmented UVR-protective compounds (mycosporine-like amino acids) compared to deeper dwelling zooplankton. Overall they had low levels of red pigmented UVR-protective compounds (carotenoids), suggesting high predation on pigmented individuals. In a complementary laboratory study we showed that levels of UVR-protective compounds increased considerably when zooplankton were exposed to UVR in the absence of predator cues. The recently developed transparency-regulator hypothesis predicts that UVR avoidance is an important driver to diel vertical migration in transparent waters, such as in Antarctica. We, however, conclude that copepods resided well below the level where UVR had diminished to very low levels and that predator avoidance or food availability are more likely drivers of zooplankton vertical depth distribution in transparent marine systems.

  • 12. Janssen, Annette B. G.
    et al.
    Arhonditsis, George B.
    Beusen, Arthur
    Bolding, Karsten
    Bruce, Louise
    Bruggeman, Jorn
    Couture, Raoul-Marie
    Downing, Andrea S.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Elliott, J. Alex
    Frassl, Marieke A.
    Gal, Gideon
    Gerla, Daan J.
    Hipsey, Matthew R.
    Hu, Fenjuan
    Ives, Stephen C.
    Janse, Jan H.
    Jeppesen, Erik
    Joehnk, Klaus D.
    Kneis, David
    Kong, Xiangzhen
    Kuiper, Jan J.
    Lehmann, Moritz K.
    Lemmen, Carsten
    Oezkundakci, Deniz
    Petzoldt, Thomas
    Rinke, Karsten
    Robson, Barbara J.
    Sachse, Rene
    Schep, Sebastiaan A.
    Schmid, Martin
    Scholten, Huub
    Teurlincx, Sven
    Trolle, Dennis
    Troost, Tineke A.
    Van Dam, Anne A.
    Van Gerven, Luuk P. A.
    Weijerman, Mariska
    Wells, Scott A.
    Mooij, Wolf M.
    Exploring, exploiting and evolving diversity of aquatic ecosystem models: a community perspective2015In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 49, no 4, p. 513-548Article in journal (Refereed)
    Abstract [en]

    Here, we present a community perspective on how to explore, exploit and evolve the diversity in aquatic ecosystem models. These models play an important role in understanding the functioning of aquatic ecosystems, filling in observation gaps and developing effective strategies for water quality management. In this spirit, numerous models have been developed since the 1970s. We set off to explore model diversity by making an inventory among 42 aquatic ecosystem modellers, by categorizing the resulting set of models and by analysing them for diversity. We then focus on how to exploit model diversity by comparing and combining different aspects of existing models. Finally, we discuss how model diversity came about in the past and could evolve in the future. Throughout our study, we use analogies from biodiversity research to analyse and interpret model diversity. We recommend to make models publicly available through open-source policies, to standardize documentation and technical implementation of models, and to compare models through ensemble modelling and interdisciplinary approaches. We end with our perspective on how the field of aquatic ecosystem modelling might develop in the next 5-10 years. To strive for clarity and to improve readability for non-modellers, we include a glossary.

  • 13.
    Leberfinger, Karolina
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Bohman, Irene
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Grass, mosses, algae or leaves? Food preference among shredders from open-canopy streams2010In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 44, no 1, p. 195-203Article in journal (Refereed)
    Abstract [en]

    Shredder feeding is a vital process in making decomposition products available to biota in streams. To investigate which food sources shredders in open-canopy streams exploit, we conducted a feeding preference experiment with the invertebrate detritivores Limnephilus bipunctatus and Nemoura sp., which are commonly found in open-canopy streams on the Swedish island of A-land in the southern Baltic Sea. Leaves of birch, Swedish whitebeam, and shrubby cinquefoil; dead and fresh grass; water moss; and algae were offered to the shredders in multi- and single treatments. We hypothesized that food with high nutritional value would be preferred. Both taxa preferred leaves of shrubby cinquefoil, a bush common in the riparian zone of A-land streams; additionally Nemoura sp. also chose algae. Dead grass, the most abundant food source in the streams during the whole year, was the least consumed food type. The fresh food types had highest nutritional value, measured as carbon to nitrogen content. Therefore, food quality could not alone explain the preference of shrubby cinquefoil. However, among the detritus type offered, shrubby cinquefoil had the highest nutritional value. Shrubby cinquefoil may constitute one important energy source to these open-canopy stream ecosystems and may be essential in maintaining an abundant shredder community in these streams. Thus, the results of this study indicate that detrital resources are indeed important in open-canopy stream systems.

  • 14.
    Nilsson, Jonas
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Engkvist, Roland
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Persson, Lars-Eric
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Long-term decline and recent recovery of Fucus populations along the rocky shores of southeast Sweden, Baltic Sea2004In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 38, no 4, p. 587-598Article in journal (Refereed)
    Abstract [en]

    The Fucus populations on rocky shores along 300 km of the coastal waters of southeast Sweden in the Baltic proper have been studied since 1984 at a number of fixed sites as part of monitoring programmes. This paper describes changes in distribution and abundance of F. vesiculosus and F. serratus during the period 1984–2001. Sheltered sites showed a consistent temporal and spatial pattern of Fucus spp. distribution over a coastline of 300 kilometres. The depth penetration and abundance of Fucus spp. increased during the 1980s. Around 1990 the development reversed as a consequence of grazing and in 1997 many sites were almost devoid of Fucus spp. Since 1998 both abundance and depth penetration have increased again, possibly as a result of local measures against eutrophication. Exposed sites, on the other hand, lost their Fucus populations at the beginning of the 1990s, and they have not recovered. Extended field studies lead us to deduce that the fixed sites referred to above were representative of the Fucus populations in the area investigated. Major declines, both at sheltered and exposed sites, are attributed to grazing by the isopod Idotea baltica. The populations of I. baltica may have been favoured by the continuing eutrophication of the Baltic, a series of mild winters in the 1990s, and a contemporary decline in some potential predators.

  • 15.
    Nilsson, Jonas
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Malm, Torleif
    Stockholm University.
    Engkvist, Roland
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Interaction between isopod grazing and wave action: a structuring force in macroalgal communities in the southern Baltic Sea2004In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 38, no 3, p. 403-413Article in journal (Refereed)
    Abstract [en]

    The macroalgal belt in the southern Baltic Sea may be partly structured by the interaction of physical and biological factors. A field study, spanning the 1990s, describes a rapid decline of the Fucus spp. stands along the wave-exposed Swedish southeast coast. During this period, a relative dominance of Fucus vesiculosus L. shifted to a relative dominance of Fucus serratus L. The decline of F. vesiculosus coincided with observations of large numbers of the grazing isopods Idotea baltica (Pallas) and Idotea granulosa Rathke, or with field observations of frequent grazing marks on Fucus fronds. I. baltica, but not I. granulosa, tended to aggregate in the declining Fucus spp. stands, indicating a strong preference for Fucus spp. In a mesocosm experiment I. baltica, when given a choice, grazed both Fucus species at weak water motion. At strong water motion grazing was concentrated on F. vesiculosus. It is hypothesized that one of the reasons I. baltica preferred F. vesiculosus to F. serratus at strong water motion may have been differences in habitat quality, like width of thallus, influencing the ability to cling to the plant. Smaller thallus, as in F. vesiculosus, thus is the preferred habitat for grazing of I. blatica. We postulate that the existence of F. serratus in the area may be favoured by strong wave action and moderate but not strong grazing by I. baltica, relaxing the interspecific competition from F. vesiculosus.

  • 16.
    Penning, W.E.
    et al.
    Deltares, Delft.
    Dudley, B.
    CEH, Edinburgh.
    Mjelde, M.
    NIVA, Oslo.
    Hellsten, S.
    University of Oulu.
    Hanganu, J.
    DDNI, Tulcea.
    Kolada, A.
    Institute for Environmental Protection, Warszawa.
    Berg, M. Van Den
    Rijkswaterstaat RIZA, Lelystad.
    Poikane, S.
    Joint Research Centre, Ispra.
    Phillips, G.
    University of Stirling.
    Ecke, Frauke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Using aquatic macrophyte community indices to define the ecological status of European lakes2008In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 42, no 2, p. 253-264Article in journal (Refereed)
    Abstract [en]

    Defining the overall ecological status of lakes according to the Water Framework Directive (WFD) is to be partially based on the species composition of the aquatic macrophyte community. We tested three assessment methods to define the ecological status of the macrophyte community in response to a eutrophication pressure as reflected by total phosphorus concentrations in lake water. An absolute species richness, a trophic index (TI) and a lake trophic ranking (LTR) method were tested at Europe-wide, regional and national scales as well as by alkalinity category, using data from 1,147 lakes from 12 European states. Total phosphorus data were used to represent the trophic status of individual samples and were plotted against the calculated TI and LTR values. Additionally, the LTR method was tested in some individual lakes with a relatively long time series of monitoring data. The TI correlated well with total P in the Northern European lake types, whereas the relationship in the Central European lake types was less clear. The relationship between total P and light extinction is often very good in the Northern European lake types compared to the Central European lake types. This can be one of the reasons for a better agreement between the indices and eutrophication pressure in the Northern European lake types. The response of individual lakes to changes in the abiotic environment was sometimes represented incorrectly by the indices used, which is a cause of concern for the use of single indices in status assessments in practice.

  • 17.
    Penning, W.E.
    et al.
    Deltares, Delft.
    Mjelde, M.
    NIVA, Oslo.
    Dudley, B.
    CEH, Edinburgh.
    Hellsten, S.
    SYKE, University of Oulu.
    Hanganu, F.
    DDNI, Tulcea.
    Kolada, A.
    Institute for Environmental Protection, Warszawa.
    Berg, M. Van Den
    Rijkswaterstaat RIZA, Lelystad.
    Poikane, S.
    Joint Research Centre, Ispra.
    Phillips, G.
    Environment Agency for England and Wales, Reading.
    Willby, N.
    University of Stirling.
    Ecke, Frauke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Classifying aquatic macrophytes as indicators of eutrophication in European lakes2008In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 42, no 2, p. 237-251Article in journal (Refereed)
    Abstract [en]

    Aquatic macrophytes are one of the biological quality elements in the Water Framework Directive (WFD) for which status assessments must be defined. We tested two methods to classify macrophyte species and their response to eutrophication pressure: one based on percentiles of occurrence along a phosphorous gradient and another based on trophic ranking of species using Canonical Correspondence Analyses in the ranking procedure. The methods were tested at Europe-wide, regional and national scale as well as by alkalinity category, using 1,147 lakes from 12 European states. The grouping of species as sensitive, tolerant or indifferent to eutrophication was evaluated for some taxa, such as the sensitive Chara spp. and the large isoetids, by analysing the (non-linear) response curve along a phosphorous gradient. These thresholds revealed in these response curves can be used to set boundaries among different ecological status classes. In total 48 taxa out of 114 taxa were classified identically regardless of dataset or classification method. These taxa can be considered the most consistent and reliable indicators of sensitivity or tolerance to eutrophication at European scale. Although the general response of well known indicator species seems to hold, there are many species that were evaluated differently according to the database selection and classification methods. This hampers a Europe-wide comparison of classified species lists as used for the status assessment within the WFD implementation process.

  • 18.
    Persson, Anders
    et al.
    Department of Ecology, Limnology, Lund University, Lund, Sweden.
    Svensson, Jonas M.
    Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS), Environmental Science, Wetland Research Centre.
    Vertical distribution of benthic community responses to fish predators, and effects on algae and suspended material2006In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 40, no 1, p. 85-95Article in journal (Refereed)
    Abstract [en]

    The vertical positioning of benthic invertebrates should be a trade-off between the risky, but productive, sediment surface and the safer, but physiologically harsher, conditions deeper down in the sediment. This is because the foraging efficiency of benthic fish decreases with sediment depth, whereas the sediment surface is generally better oxygenated and has a higher resource quality than lower layers. We studied how two benthic fish predators, bream (Abramis brama) and ruffe (Gymnocephalus cernuus), affected the community composition and vertical distribution of benthos, and their indirect effects on algae and suspended material, in field enclosures. Whereas bream had significant effects on the density, composition and distribution of the benthos, ruffe had no such effects. The total benthos biomass in bream treatments was an-order of magnitude lower in the upper sediment layer (0-1 cm) and three times lower in the middle layer (1-3 cm) than in the controls, whereas there were no significant effects in the deepest layer (3-10 cm). Bivalves persisted in the deepest layer although their density was reduced in shallow sediment, whereas gastropods faced the risk of local extinction in the presence of bream. As indirect effects, small-bodied cladocerans, phytoplankton, periphyton and both organic and inorganic suspended material were higher in the bream treatments. We conclude that the impact of bream diminished substantially with increasing sediment depth, enabling invertebrates to survive in the sediment and to persist in the presence of bream. However, there were no indications of any group adjusting their vertical position behaviourally as a response to predation threat.

  • 19.
    Weyhenmeyer, Gesa A.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Evolution, Limnology.
    Do warmer winters change variability patterns of physical and chemical lake conditions in Sweden?2009In: Aquatic Ecology, ISSN 1386-2588, E-ISSN 1573-5125, Vol. 43, no 3, p. 653-659Article in journal (Refereed)
    Abstract [en]

    In this study, the effect of a warmer winter climate on variability patterns of physical and chemical lake conditions was examined by using monthly air temperature data from 72 meteorological Swedish sites, ice breakup data from 77 Swedish lakes and monthly data of 17 water chemical variables from 11 nutrient-poor Swedish reference lakes during 1988–2005. The results showed significantly increasing variations of lake ice breakup dates and nitrate concentrations over Sweden along with increasing winter air temperatures. Variability patterns of other water chemical variables were not affected by warmer winters. Nitrate concentrations increased their variability in spring and early summer not only between lakes but also within lakes, which was attributed to a climate-induced increase in spring nitrate concentrations in particular in southern Sweden, while summer nitrate concentrations remained rather constant and low all over Sweden (median 10 μg l−1). Since nitrate concentrations play an important role for primary production, highly varying concentrations will be a challenge for biota to adapt.

1 - 19 of 19
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