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  • 1. Aljetlawi, A A
    et al.
    Albertsson, Jan
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Leonardsson, K
    Effect of food and sediment pre-treatment in experiments with a deposit-feeding amphipod, Monoporeia affinis2000In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 249, no 2, p. 263-280Article in journal (Refereed)
    Abstract [en]

    We experimentally investigated the effects of different pre-treatments of the sediment, and the effect of daily addition of fresh phytoplankton, on the growth and survival of 1-year-old (1 +) individuals of the deposit feeder Monoporeia affinis (Amphipoda). We used three different types of sieved sediment: pre-frozen muddy clay, non-pre-frozen muddy clay, and fine sand. The muddy clay contained phytoplankton originating from the surface sediment sampled in the field during the late spring bloom. No phytoplankton was initially present in sand. The experiment lasted for 18 days. M. affinis responded to the daily phytoplankton addition by increasing growth. Phytoplankton addition had no significant effects on the survival of M. affinis. Upon phytoplankton addition, the sandy and non-frozen muddy clay gave similar growth and survival responses. In contrast, the pre-frozen sediment resulted in significantly lower growth and survival. The growth was negative in all treatments without phytoplankton. Thus, the high initial chlorophyll content in the muddy clay was not of sufficient quality or concentration to allow a positive growth response in M. affinis. The growth of M. affinis was significantly correlated with the reduction of the chlorophyll. Our results indicated that M. affinis is capable of assimilating settled phytoplankton with no, or only a few days' time delay. (C) 2000 Elsevier Science BN: All rights reserved.

  • 2.
    Lefébure, Robert
    et al.
    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).
    Larsson, S.
    Umeå University, Faculty of Science and Technology, Umeå Marine Sciences Centre (UMF).
    Byström, Pär
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Temperature and size-dependent attack rates of the three-spined stickleback (Gasterosteus aculeatus): are sticklebacks in the Baltic Sea resource-limited?2014In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 451, p. 82-90Article in journal (Refereed)
    Abstract [en]

    The three-spined stickleback Gasterosteus aculeatus is a small omnivorous fish, widely distributed in the northern hemisphere. In the Baltic Sea, recently observed increases in their population densities have been attributed to declines of piscivorous predators. Concurrent with this predator release, an alternative hypothesis is that past and present consumption rates and resource limitation thresholds may have contributed to the recent increases in stickleback abundance. To evaluate this hypothesis, we estimated the size- and temperature-dependent attack rate and the critical resource density (CRD) of three-spined sticklebacks. We incorporated laboratory results with time series of zooplankton abundance to estimate historical trends in degrees of resource limitation in sticklebacks and evaluate if increases in individual consumption rates could be a plausible mechanism facilitating the suggested population increase. Attack rates increased with body size and temperature in laboratory experiments. Estimated CRD increased with size but decreased with temperature, suggesting that stickleback scope for individual and population growth might increase at temperatures above 15 degrees C. Our results further suggest that sticklebacks have been living closer to maximum consumption capacity in the coastal areas of the Bothnian Sea (BS) and Bothnian Bay (BB). Moreover, decreasing levels of resource limitation in the corresponding off-shore zones may have facilitated increases in stickleback densities for these areas. However, in the coastal zones of the Baltic proper (BP), resource levels have declined and are approaching the CRD, suggesting that stickleback populations in BP may not increase further. The decrease in CRD with temperature implies that increasing summer temperatures will increase the scope of individual and population growth in the three-spined stickleback and may favor the three-spined stickleback's competitive ability over other species under a warmer climate. (C) 2013 Elsevier B.V. All rights reserved.

  • 3.
    Meunier, Cedric Leo
    et al.
    Alfred-Wegener-Institut für Polar- und Meeresforschung, Biologische Anstalt Helgoland, Germany.
    Schulz, Karoline
    Alfred-Wegener-Institut für Polar- und Meeresforschung, Biologische Anstalt Helgoland, Germany.
    Boersma, Maarten
    Alfred-Wegener-Institut für Polar- und Meeresforschung, Biologische Anstalt Helgoland, Germany.
    Malzahn, Arne Michael
    Alfred-Wegener-Institut für Polar- und Meeresforschung, Biologische Anstalt Helgoland, Germany ; Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research, Institute for Coastal Research, Geesthacht, Germany.
    Impact of swimming behaviour and nutrient limitation on predator-prey interactions in pelagic microbial food webs2013In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 446, p. 29-35Article in journal (Refereed)
    Abstract [en]

    Heterotrophic dinoflagellates are motile protozoans, important consumers of phytoplankton in aquatic environments. Motility is a main advantage for predators during grazing activities, but can also serve as defence mechanisms against being grazed. Thus, numerous microalgal species are also motile. We hypothesise that the nutrient status of an organism affects its swimming speed and especially that nutrient limitation has a negative impact on cell motility. Such altered motility of both predator and prey should influence feeding success of grazers. We tested those hypotheses by investigating the impact of nutrient (phosphorus) limitation on motility of two algal species, Rhodomonas sauna and Teleaulax sp., and the heterotrophic dinoflagellate Oxyrrhis marina and examined how differences in prey swimming speed affect grazing of O. marina. We show that nutrient limitation had a strong impact, reducing algal swimming speed and escape success and in turn significantly influencing food uptake of O. marina which was maximal for intermediate prey swimming speed. We also tested the importance of algal behaviour on O. marina selective feeding and observed that Teleaulax sp. presented an escape behaviour, which appeared to be an effective defence mechanism against grazing of O. marina. While this study has focused on the trophic interactions between two algal species and one dinoflagellate, the impact of nutrient limitation and escape strategy on feeding success of the predator is likely to be found in the whole range of plankton trophic interactions.

  • 4. Richardson, Katherine
    et al.
    Samuelsson, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hällgren, Jan-Erik
    The relationship between photosynthesis measured by C-14 incorporation and by uptake of inorganic carbon in unicellular algae1984In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 81, no 3, p. 241-250Article in journal (Refereed)
    Abstract [en]

    The traditional 14C method of estimating photosynthetic rates was compared with net photo-synthesis in two species of unicellular algae. Net photosynthesis was defined as the disappearance of inorganic carbon from the algal medium and was determined using a described infra-red gas analyser (IRGA) technique. For Amphidinium carterae Hulbert, the 14C method always led to lower calculated rates of photosynthesis than the IRGA technique. This difference was, on average, ≈100%. For Scenedesmusobliquus (Turpin) Kützing, the 14C method could lead to over-estimates, good agreement with, or underestimates of net photosynthesis. Although the under-estimates were only of the order of 15%, the over-estimates were in some cases > 100%. There is some indication that respiration rate is an important factor in the relationship between photosynthetic rates calculated by the two methods for this organism.

  • 5. Vehmaa, Anu
    et al.
    Larsson, Peder
    Vidoudez, Charles
    Pohnert, Georg
    Reinikainen, Marko
    Engstrom-Ost, Jonna
    How will increased dinoflagellate:diatom ratios affect copepod egg production?: - A case study from the Baltic Sea2011In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 401, no 1-2, p. 134-140Article in journal (Refereed)
    Abstract [en]

    Mild winters are modifying the plankton spring bloom composition so that diatoms are decreasing and dinoflagellates increasing. We used two common spring bloom phytoplankton species, a diatom and a dinoflagellate to study the effects of changing bloom composition on the reproduction of the calanoid copepod Acartia bifilosa Giesbrecht, a dominant species in the northern Baltic Sea. Egg production was significantly higher when copepods were fed with Scrippsiella hangoei (Schiller) Larsen dinoflagellates or a mixture of Scrippsiella and Skeletonema marinoi Sarno and Zingone diatoms than when they were provided with Skeletonema only. This effect was observed despite the fact that the Skeletonema strain did not produce polyunsaturated aldehydes (PUAs) and its nutritional quality was high according to polyunsaturated fatty acid (PUFAs) and sterol measurements, and moderate according to mineral (C:N and C:P) measurements. When offered mixtures of Skeletonema and Scrippsiella, copepods ingested both, even when the other one was rare. This indicates potential positive effect of multispecies diets not verified in this study. Here we show that increasing dinoflagellate:diatom ratio might have a positive effect on copepod reproduction. (C) 2011 Elsevier B.V. All rights reserved.

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