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  • 1.
    Baltar, Federico
    et al.
    Univ Las Palmas Gran Canaria, Fac Ciencias Mar, Las Palmas Gran Canaria 35017, Spain.
    Arístegui, Javier
    Gasol, Josep M.
    Sintes, Eva
    Herndl, Gerhard J.
    Evidence of prokaryotic metabolism on suspended particulate organic matter in the dark waters of the (sub)tropical North Atlantic2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 1, p. 182-193Article in journal (Refereed)
    Abstract [en]

    The distribution of prokaryotic abundance (PA), respiratory activity (ETS), heterotrophic production (PHP), and suspended particulate (POM) and dissolved (DOM) organic matter was determined in the meso- and bathypelagic waters of the (sub) tropical North Atlantic. PA decreased by one order of magnitude from the lower euphotic zone to the bathypelagic waters, while ETS decreased by two and PHP by three orders of magnitude. On a section following the Mid-Atlantic Ridge from 35 degrees N to 5 degrees N, ETS below 1000-m depth increased southwards up to three-fold. This latitudinal gradient in the deep waters was paralleled by a six-fold increase in Particulate Organic Carbon (POC), whereas no trend was apparent in the DOM distribution. Significant correlations between POM and ETS were obtained in the water masses between 1000-m and 3000-m depth, the Antarctic Intermediate Water and the North East Atlantic Deep Water. A strong imbalance in the dark ocean was found between prokaryotic carbon demand (estimated through two different approaches) and the carbon sinking flux derived from sediment-trap records corrected with Th-230. The imbalance was greater when deeper in the water column, suggesting that the suspended carbon pool must account for most of the carbon deficit. Our results, together with other recent findings discussed in this paper, indicate that microbial life in the dark ocean is likely more dependent on slowly sinking or buoyant, laterally advected suspended particles than hitherto assumed. 

  • 2. Blackburn, N.
    et al.
    Azam, F.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Spatially explicit simulations of a microbial food web.1997In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 42, p. 613-622Article in journal (Refereed)
  • 3. Boras, Julia
    et al.
    Sala, Montse M.
    Baltar, Federico
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Arístegui, Javier
    Duarte, Carlos M.
    Vaqué, D.
    Effect of viruses and protists on bacteria in eddies of the Canary Current region (subtropical Northeast Atlantic).2010In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 55, no 2, p. 885-898Article in journal (Refereed)
    Abstract [en]

    The effect of oceanic eddies on microbial processes, with emphasis on bacterial losses due to protists and phages, was examined in the Canary Current region (subtropical northeast Atlantic) through the water column (down to 1000 m) during August 2006. Sampling stations were located in cyclonic and anticyclonic eddies, as well as in regions situated outside the influence of the eddy field (far-field stations). In the euphotic zone, in cyclonic eddies losses of bacteria due to viruses and protists were from 25.6% to 69.8%, and from not detected to 46.8% of bacterial production (BP) d(-1), respectively. In anticyclonic eddies, these values ranged from 20.6% to 90.2% of BP d(-1) for viruses, and from 8.0% to 79.4% of BP d(-1) for protists. At far-field stations, losses of bacteria ranged from 48.7% to 66.9% for viruses, and from not detected to 44.8% for protists. In addition, covering all stations and depths (from the epipelagic to the bathypelagic layer), bacterial losses due to viruses were significantly higher than losses by protists, and did not differ significantly among depths except for the stations situated in anticyclonic eddies, where they were significantly higher in the epipelagic layer. Lysogenic infection was more frequent at anticyclonic stations, where the highest pressure of protists on bacteria was observed. Because of the importance of viral activity, we suggest that lysis products from bacteria may be a source of regenerated nutrients in the surface of the oligotrophic ocean, in addition to the input of nutrients upwelled by eddies.

  • 4.
    Brüsin, Martin
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Svensson, P. Andreas
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Hylander, Samuel
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Individual changes in zooplankton pigmentation in relation to ultraviolet radiation and predator cues2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, no 4, p. 1337-1344Article in journal (Refereed)
    Abstract [en]

    Copepods are common crustaceans in aquatic systems and one of the most important producers of carotenoidastaxanthin pigments, which can enhance the animals’ resistance against potentially damaging ultraviolet radiation (UVR), but at the same time, increases the risk of fish predation. Previous studies have demonstrated that copepods have different pigmentation levels matching the current threat level in terms of UVR and fish occurrence. However, these other studies have quantified population-levels changes in pigmentation, making it difficult to disentangle the role of individual phenotypic colour changes from that of selection.We quantified carotenoid-based pigmentation with colorimetric methods, which enabled us to track changes within individual copepods. Two species of copepods, Diaptomus castor and Eudiaptomus gracilis, were exposed to high and low UVR and fish cues in a factorial design. L*a*b* colour values (CIE; CommissionInternational de l’Eclairage) were extracted from digital photographs of each copepod and used as proxies for carotenoid concentration. Our results showed that individual copepods significantly changed their pigmentation in response to both UVR and fish cues within a period of 2 weeks. However, the responses differed between sexes and between adults and juveniles. UVR effects were present in all life-stages whereas fish effects were only detected in juveniles, with largest responses in D. castor. This confirms that carotenoid pigmentation is a phenotypically plastic trait, and highlights that strategies for trading off risks of UVR and predation differ between males and females as well as between life-stages.

  • 5.
    Ekvall, Mikael T.
    et al.
    Lund University.
    Hylander, Samuel
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Walles, Tim
    Lund University.
    Yang, Xi
    Lund University.
    Hansson, Lars-Anders
    Lund University.
    Diel vertical migration, size distribution and photoprotection in zooplankton as response to UV-A radiation2015In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, no 6, p. 2048-2058Article in journal (Refereed)
    Abstract [en]

    The transparency regulator hypothesis (TRH) proposes that ultraviolet radiation (UVR) is a main driving force behind diel vertical migration (DVM) of zooplankton in clearwater systems. While previous studies have mainly studied DVM in relation to the TRH on a spatial scale across systems we here focus on long-term trends in a single system in order to assess if UVR explains observed patterns in DVM. We show that the strength of DVM in Daphnia is to a large extent explained by UVR and we demonstrate a tipping point at which the UVR intensity drastically affects the strength of DVM in Daphnia. In contrast, the strength of DVM could not be explained by the level of UVR among calanoid copepods. The amount of photoprotective compounds did not differ between zooplankton found at different depths indicating that zooplankton do not change their vertical position in relation to the amount of accumulated photoprotective compounds. In addition, we show that both Daphnia and calanoid copepods display patterns of size structured migration.

  • 6.
    Fridolfsson, Emil
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Lindehoff, Elin
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Legrand, Catherine
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Hylander, Samuel
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Thiamin (vitamin B1) content in phytoplankton and zooplankton in the presence of filamentous cyanobacteria2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, no 6, p. 2423-2435Article in journal (Refereed)
    Abstract [en]

    Top predators in several aquatic food webs regularly display elevated reproductive failure, caused by thiamin(vitamin B1)deficiency. The reasons for these low-thiamin levels are not understood and information about the transfer of thiamin from the producers (bacteria and phytoplankton) to higher trophic levels is limited. One main concern is whether cyanobacterial blooms could negatively affect thiamin transfer in aquatic systems. Laboratory experiments with Baltic Sea plankton communities and single phytoplankton species were used to study the effect of filamentous cyanobacteria on the transfer of thiamin from phytoplankton to zooplankton. Experiments showed that the thiamin content in copepods was reduced when exposed to elevated levels of cyanobacteria, although filamentous cyanobacteria had higher levels of thiamin than any other analyzed phytoplankton species. Filamentous cyanobacteria also had a negative effect on copepod egg production despite high concentrations of non-cyanobacterial food. Phytoplankton species composition affected overall thiamin concentration with relatively more thiamin available for transfer when the relative abundance of Dinophyceae was higher. Finally, phytoplankton thiamin levels were lower when copepods were abundant, indicating that grazers affect thiamin levels in phytoplankton community, likely by selective feeding. Overall, high levels of thiamin in phytoplankton communities are not reflected in the copepod community. We conclude that presence of filamentous cyanobacteria during summer potentially reduces the transfer of thiamin to higher trophic levels by negatively affecting phytoplankton and copepod thiamin content as well as copepod reproduction, thereby lowering the absolute capacity of the food web to transfer thiamin through copepods to higher trophic levels.

  • 7. Havskum, H.
    et al.
    Thingstad, T.F.
    Scharek, R.
    Peters, F.
    Berdalet, E.
    Sala, M.M.
    Alcarazd, M.
    Bangsholt, J.C.
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Perez, M.
    Dolan, J.R.
    Silicate and labile DOC interfere in structuring the microbial food web via algal-bacterial competition for mineral nutrients: Results of a mesocosm experiment.2003In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 48, p. 129-140Article in journal (Refereed)
  • 8.
    Hylander, Samuel
    et al.
    Lunds universitet.
    Boeing, Wiebke J.
    Graneli, Wilhelm
    Karlsson, Jan
    von Einem, Jessica
    Gutseit, Kelly
    Hansson, Lars-Anders
    Complementary UV protective compounds in zooplankton2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 6, p. 1883-1893Article in journal (Refereed)
    Abstract [en]

    Zooplankton accumulate several groups of photoprotective compounds to shield against damaging ultraviolet radiation (UV). One of these groups, the carotenoids, makes the animals more conspicuous to visually hunting predators, whereas others, such as the mycosporine-like amino acids (MAAs) may not. The blend of photoprotective compounds is therefore important for the UV defense but also for the ability to escape predation through crypsis. Here we assess laboratory and field data from different latitudes to examine how UV, predation threat, and pigment availability ( in food) affects the mixture of UV-protective compounds in copepods. Overall, the blend of MAAs and carotenoids was partly explained by the availability of MAAs in the food, the UV-threat, and the presence of predators. Copepods upregulated their MAA content when UV threat was increasing (i.e., if MAAs were abundant in food), and in field data this accumulation only occurred at high levels of predation threat. If MAAs were scarce, copepods instead compensated with higher carotenoid accumulation. However, when there was a high predation threat this carotenoid compensatory effect was disadvantageous, and low concentrations of both MAAs and carotenoids at high UV-threat resulted in lower reproduction. In all, these results showed that carotenoids and MAAs are complementary substances, i.e., one is high when the other is low, and copepods are, hence, able to adjust their blend of different UV-protective compounds to optimize their defenses to the threats of UV and predation. These defense systems may buffer against direct food-web interactions and help the zooplankton to survive in environments with high UV threat.

  • 9.
    Hylander, Samuel
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Kiørboe, Thomas
    Tech Univ Denmark, Denmark.
    Snoeijs, Pauline
    Stockholm University.
    Sommaruga, Ruben
    Univ Innsbruck, Austria.
    Nielsen, Torkel Gissel
    Tech Univ Denmark, Denmark;Greenland Inst Nat Resources, Greenland.
    Concentrations of sunscreens and antioxidant pigments in Arctic Calanus spp. in relation to ice cover, ultraviolet radiation, and the phytoplankton spring bloom2015In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, p. 2197-2206Article in journal (Refereed)
    Abstract [en]

    Arctic zooplankton ascend to shallow depths during spring to graze on the yearly occurring phytoplankton bloom. However, in surface waters they are exposed to detrimental ultraviolet radiation (UVR) levels. Here, we quantified concentrations of substances known to have UVR-protective functions, namely mycosporine-like amino acids (MAAs) and the carotenoid astaxanthin, from March to May in Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus. Ice cover was 100% in the beginning of March, started to break up during April and was gone by the end of May. UVR-exposure in the water column was tightly linked to the ice conditions and water UVR-transparency was up to 6 m (depth where 1% radiation remains). Concentrations of MAAs in C. finmarchicus and C. glacialis increased sharply during ice break-up and peaked concurrently with maximum chlorophyll a (Chl a) levels. MAA-concentrations in C. hyperboreus increased later in accordance with its later arrival to the surface. The concentration of astaxanthin increased in all three species over time but there was no synchrony with ice conditions or the phytoplankton bloom. Even though only the upper 6 m of the water column was affected by UV-radiation, MAAs in the copepods were tightly correlated to the UV-threat. Hence, changes in ice cover are projected to have a large impact on the UVR-exposure of zooplankton emphasizing the importance of the timing of zooplankton ascent from deep waters in relation to the phytoplankton bloom and the ice break-up.

  • 10.
    Hylander, Samuel
    et al.
    Lunds universitet.
    Larsson, Niklas
    Lunds universitet.
    Hansson, Lars-Anders
    Lunds universitet.
    Zooplankton vertical migration and plasticity of pigmentation arising from simultaneous UV and predation threats2009In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 54, no 2, p. 483-491Article in journal (Refereed)
    Abstract [en]

    We assessed how zooplankton (copepods) handle the simultaneous threats of predators and ultraviolet (UV) radiation and whether they respond with changes in pigmentation, vertical migration, or both. We found weak vertical migration among copepods in response to UV stress, and this response was not apparently influenced by predation risk. Exposure to high levels of UV radiation caused copepods to retain pigments in the absence of a predation threat. When exposed to predation threat, they reduced their pigmentation regardless of UV level. Thus, they ranked predation as a threat more severe than UV radiation. Reducing the protective pigment level in response to predation in a situation in which UV radiation is high may, however, lead to higher mortality.

  • 11.
    Koehler, Birgit
    et al.
    Uppsala University.
    Broman, Elias
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Uppsala University.
    Tranvik, Lars J.
    Uppsala University.
    Apparent quantum yield of photochemical dissolvedorganic carbon mineralization in lakes2016In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, no 6, p. 2207-2221Article in journal (Refereed)
    Abstract [en]

    Up to one tenth of the carbon dioxide (CO2) emissions from inland waters worldwide are directly inducedby the photochemical mineralization of dissolved organic matter (DOM). The photochemical production ofdissolved inorganic carbon (DIC) per photon absorbed by chromophoric DOM (CDOM) decreases exponentiallywith increasing irradiance wavelength, and is commonly described by an “apparent quantum yield”(AQY) spectrum. Although an essential model parameter to simulate photochemical mineralization the AQYremains poorly constrained. Here, the AQY of photochemical DIC production for 25 lakes located in boreal,polar, temperate, and tropical areas, including four saline lagoons, was measured. The wavelength-integratedAQY (300–500 nm; mol DIC mol CDOM-absorbed photons21) ranged from 0.05 in an Antarctic lake to 0.61in a humic boreal lake, averaging 0.2460.03 SE. AQY was positively linearly correlated with the absorptioncoefficient at 420 nm (a420) as a proxy for CDOM content (R2 of 0.64 at 300 nm and 0.26 at 400 nm), withspecific UV absorption coefficients as a proxy for DOM aromaticity (R2 of 0.56 at 300 nm and 0.38 at400 nm), and with the humification index (R2 of 0.41 at 300 nm and 0.42 at 400 nm). Hence, a considerablefraction of the AQY variability was explained by water optical properties in inland waters. The correlation ofAQY with a420 opens up the possibility to improve large-scale model estimates of sunlight-induced CO2 emissionsfrom inland waters based on water color information derived by satellite remote sensing.

  • 12.
    Lagergren, Ragnar
    et al.
    Zoologiska institutionen, Göteborgs universitet.
    Leberfinger, Karolina
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Stenson, Jan A. E.
    Zoologiska institutionen, Göteborgs universitet.
    Seasonal and ontogenetic variation in diel vertical migration of Chaoborus flavicans and its effect on depth-selection behavior of other zooplankton2008In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 53, no 3, p. 1083-1092Article in journal (Refereed)
  • 13.
    Lebret, Karen
    et al.
    Lund University.
    Fernandez, Maria Fernandez
    Hagman, Camilla H. C.
    Rengefors, Karin
    Hansson, Lars-Anders
    Grazing resistance allows bloom formation and may explain invasion success of Gonyostomum semen2012In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 57, no 3, p. 727-734Article in journal (Refereed)
    Abstract [en]

    The nuisance alga Gonyostomum semen (Raphidophyceae) has expanded in the Nordic countries during the last decades and can dominate lake phytoplankton communities almost completely. A possible explanation to its dominance could be limited grazing by zooplankton. We investigated the potential grazing pressure on G. semen using an experimental approach supported by field data. We determined the grazing rate by cladocerans, calanoid copepods, and Chaoborus larvae to determine which were able to feed on G. semen. Only the large cladoceran Daphnia magna was able to feed successfully on G. semen. The large cell size of G. semen was likely a limiting factor for the filtering apparatus of smaller cladocerans. The copepod Eudiaptomus gracilis did not graze on G. semen, although the mechanism behind this selective feeding is still unknown. In addition to the experimental study, we quantified the zooplankton and phytoplankton communities in 40 lakes to determine the composition and abundance of the zooplankton communities co-occurring with G. semen, suggesting that large cladoceran species were not present in lakes where G. semen occurred. Hence, the growth of G. semen is not significantly controlled by grazing in natural systems, which likely facilitates bloom formation and invasion success of G. semen.

  • 14.
    Lundgren, Veronica
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Granéli, Edna
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Grazer-induced defense in Phaeocystis globosa (Prymnesiophyceae): Influence of different nutrient conditions2010In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 55, no 5, p. 1965-1976Article in journal (Refereed)
    Abstract [en]

    We examined the combined effects of grazer infochemicals and nutrient status on colony development ofPhaeocystis globosa cultures grown under nitrogen and phosphorus (NP)–sufficient, P-deficient, and N-deficientconditions exposed to high and low Acartia spp. density filtrates. Changes in colony development relative tocontrols receiving no grazer signals were estimated. P. globosa colony development responded to grazerinfochemicals regardless of nutrient status, although the expression of the response varied between nutrients.Significant colony suppression (in terms of percent of cells allocated to colonies) occurred in both NP-sufficientand P-deficient experiments, with the response being dependent on the density of grazers for NP-sufficient cells.The percent of cells in colonial form in N-deficient P. globosa decreased in response to low grazer density filtratesbut increased in response to high grazer density filtrates. These opposite results for the N-deficient experiment arerelated to a high mortality of Acartia in the high grazer density filtrate treatment, which may affect theinfochemicals released from such grazers

  • 15.
    Martínez-García, Sandra
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. University of Hawaii, USA.
    Microbial respiration in the mesopelagic zone at Station ALOHA2017In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, no 1, p. 320-333Article in journal (Refereed)
    Abstract [en]

    Measurements of the temporal and depth variability of microbial community respiration (MCR) in the mesopelagic zone (200-1,000 m) at Station ALOHA were made approximately monthly from November 2011 to October 2012 using the in vivo INT method. MCR in the summed and in each of the 0.2-0.8 mu m and >0.8 mu m size-fractions in the upper mesopelagic zone (200-350 m) (mean [+/- SE], 107.1 [+/- 16.3], 57.5 [+/- 8.4], and 49.6 [+/- 9.0] mu mol O-2 m(-3)day(-1), respectively) were higher than in the lower mesopelagic zone (350-1000 m) (56.1 [+/- 4.5], 30.8 [+/- 2.9], and 25.3 [+/- 3.1] mu mol O-2 m(-3)day(-1), respectively). The average > 0.8 mu m/0.2-0.8 m MCR in the mesopelagic zone was 0.97 [+/- 0.16]) and was indistinguishable in the upper and lower portions of the mesopelagic zone. A recurrent local peak in MCR was found at 600-650 m for both non-winter and winter measurements. Total depth-integrated MCR (200-1,000 m) was higher during the non-winter than during winter months (55.7 [+/- 3.4] and 44.8 [+/- 2.4] mmol O-2 m(-2) day(-1)). Variability of total MCR rates was controlled by changes in the >0.8 mu m size fraction, and was possibly related to higher primary production and export from the euphotic zone during the non-winter period. These findings suggest seasonal variability in respiration rates in the mesopelagic zone at Station ALOHA and support the current steady-state model where export flux controls respiration in the mesopelagic zone

  • 16.
    Martínez-García, Sandra
    et al.
    Univ Hawaii, USA.
    Karl, David M.
    Univ Hawaii, USA.
    Microbial respiration in the euphotic zone at Station ALOHA2015In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 60, no 3, p. 1039-1050Article in journal (Refereed)
    Abstract [en]

    Measurements of the temporal and vertical variability of microbial community respiration (MCR) in the euphotic zone (0-200m) at Station ALOHA were made using the in vivo INT method to constrain oxygen and carbon cycling at this oceanic site. Mean (+/- 1 SE) MCR was higher in the upper (0-100m) (0.89 +/- 0.05mmol O-2 m(-3) d(-1)) than in the lower (100-200 m) portion of the euphotic zone (0.52 +/- 0.05mmol O-2 m(-3) d(-1)). Respiration in the 0.8 mu m size-fraction relative to respiration in the 0.2-0.8 mu m size-fraction was on average 1.4 +/- 0.1. Variability in MCR was observed on both daily and monthly time scales, suggesting that respiration is a dynamic process throughout the year at Station ALOHA. MCR in the 0.2-0.8 mu m size fraction was more variable than >0.8 mu m MCR. Despite significant vertical and temporal variability in MCR, the euphotic zone depth-integrated (0-200m) MCR was relatively constant (134.8 +/- 11.8 mmol O-2 m(-2) d(-1)) throughout the period of observation. Oxygen consumption via MCR always exceeded O-2 production extrapolated from C-14-primary production estimation, assuming a photosynthetic quotient of 1.13mol O-2 produced : mol CO2 fixed. MCR plus particulate carbon export from the euphotic zone for the period November 2011-October 2012 at Station ALOHA can be used to set a lower limit of similar to 45mol C m(-2) yr(-1) for gross primary production.

  • 17. Sarmento, Hugo
    et al.
    Romera-Castillo, Cristina
    Lindh, Markus V.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Pinhassi, Jarone
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Sala, M. Montserrat
    Gasol, Josep M.
    Marrase, Celia
    Taylor, Gordon T.
    Phytoplankton species-specific release of dissolved free amino acids and their selective consumption by bacteria2013In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 58, no 3, p. 1123-1135Article in journal (Refereed)
    Abstract [en]

    Despite representing only a small fraction of the ocean's dissolved organic matter pool, dissolved free amino acids (DFAA) have high turnover rates and are major nitrogen and carbon sources for bacterioplankton. Both phytoplankton and bacterioplankton assimilate and release DFAA, but their consumption and production are difficult to quantify in nature due to their short residence times (min) as dissolved monomers. We segregated DFAA production by phytoplankton and bacterial consumption by measuring individual DFAA concentrations in four axenic phytoplankton cultures during the exponential growth phase, and also after 4 d incubations in the presence of a natural bacterioplankton community. The amounts and composition of the DFAA pool varied widely among phytoplankton species. The proportion of dissolved organic carbon attributed to DFAA varied among cultures. The picoeukaryotic prasinophyte, Micromonas pusilla, released higher amounts of DFAA than the other species tested (diatoms and dinoflagellate), especially alanine, which has been reported as the dominant individual DFAA in some oligotrophic environments. Community structure of heterotrophic prokaryotes responded to differences in the quality of organic matter released among microalgal species, with Roseobacter-related bacteria responding strongly to exudate composition. Our results demonstrate the specificity of DFAA extracellular release among several algal species and their preferential uptake by members of bacterial communities.

  • 18. Thingstad, T.F.
    et al.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Rassoulzadegan, F.
    Export of degradable DOC from oligotrophic surface waters: Is it caused by a malfunctioning microbial loop?1997In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 42, p. 398-404Article in journal (Refereed)
  • 19.
    Weissbach, Astrid
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Rudström, Maria
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Olofsson, Martin
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Bechemin, Christian
    IFREMER, France.
    Icely, John D
    Sagremarisco, Portugal.
    Newton, Alice
    Norwegian Institute for Air Research NIVA.
    Tillmann, Urban
    Alfred Wegener Institute for Polar and Marine Research, Germany.
    Legrand, Catherine
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Phytoplankton allelochemical interactions change microbial food web dynamics2011In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 56, p. 899-909Article in journal (Refereed)
    Abstract [en]

    This study investigates the effect of filtrates from an allelopathic dinoflagellate, Alexandrium tamarense, onfour microbial food webs that have been manipulated experimentally from natural seawater by modifying theavailability of resources in the form of dissolved organic carbon with additions of peptone, and by altering thegrazing pressure with size fractionation. Bacterial production was generally not affected by allelochemicals, butbacteria showed higher net growth in all food webs when allelochemicals were added, whereas heterotrophicnanoflagellates . 7 mm and ciliates were constrained in all food webs. Allelochemicals had the largest negativeeffects on microbial communities with low grazing pressure. In food webs with high grazing pressure andadditional resources, phytoplankton and small nanoflagellates were positively affected by the addition ofallelochemicals, suggesting that those were interfering with trophic interactions in the microbial communities. Bythe lysis of organisms sensitive towards allelochemicals, resources are made available and grazing pressure oncertain microorganisms is reduced. However, the intensity of these interactions is modulated by both theavailability of resources and the biomass of grazers in the initial food web.

  • 20. Wikner, J.
    et al.
    Hagström, Åke
    Department of Microbiology, University of Umeå .
    Annual Study of Bacterioplankton Community Dynamics.1991In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 36, no 7, p. 1313-1324Article in journal (Refereed)
    Abstract [en]

    Bacterial growth, abundance, and grazing were measured simultaneously during a full seasonal cycle in a temperate brackish water estuary, covering diel and seasonal variability. Growth of bacteria was balanced by bacterivory on an annual basis, and observed net change in bacterial numbers matched the net change calculated by a simple Lotka-Volterra equation lacking immigration or emigration terms. Bacterial growth was dependent on water temperature below 6-degrees-C, but other factors dominated at higher temperatures. The community clearance rate of the bacterivores was stringently regulated at 0.6 d-1, showing a linear functional response within the range of natural bacterial abundances recorded. Furthermore, bacterivores showed a threshold at 7 x 10(5) bacteria ml-1 when grazing ceased, suggesting that pelagic bacteria have a numerical refuge promoting coexistence with bacterivores in aquatic environments. The observed lack of timing between bacterial growth and grazing in spring allowed accumulation of bacterial cells, but grazing exceeded growth in winter. We inferred that the specific growth rate of the bacterial community and the community clearance rate of bacterivores together determined change in and abundance of bacterioplankton in the waters examined. 

  • 21. Wikner, J.
    et al.
    Rassoulzadegan, F.
    Hagström, Åke
    Department of Microbiology, University of Umeå .
    Periodic bacterivore activity counterbalances bacterial growth in the marine enviroment.1990In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 35, p. 313-324Article in journal (Refereed)
  • 22.
    Williams, Richard A. J.
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Univ Kansas, USA.;Univ Complutense Madrid, Spain.
    Owens, Hannah L.
    Univ Kansas, USA;Univ Florida, USA.
    Clamp, John
    North Carolina Cent Univ, USA.
    Peterson, A. Townsend
    Univ Kansas, USA.
    Warren, Alan
    Nat Hist Museum, UK.
    Martin-Cereceda, Mercedes
    Univ Complutense Madrid, Spain.
    Endemicity and climatic niche differentiation in three marine ciliated protists2018In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 63, no 6, p. 2727-2736Article in journal (Refereed)
    Abstract [en]

    The biogeographic pattern of single-celled eukaryotes (protists), including ciliates, is poorly understood. Most marine species are believed to have a relatively high dispersal potential, such that both globally distributed and geographically isolated taxa exist. Primary occurrence data for three large, easily identified ciliate species, Parafavella gigantea, Schmidingerella serrata, and Zoothamnium pelagicum, and environmental data drawn from the National Oceanic and Atmospheric Administration's World Ocean Atlas were used to estimate each species' spatial and environmental distributions using Maxent v3.3.3k. The predictive power of the models was tested with a series of spatial stratification studies, which were evaluated using partial receiver operating characteristic (ROC) statistics. Differences between niches occupied by each taxon were evaluated using background similarity tests. All predictions showed significant ability to anticipate test points. The null hypotheses of niche similarity were rejected in all background similarity tests comparing the niches among the three species. This article provides the first quantitative assessment of environmental conditions associated with three species of ciliates and a first estimate of their spatial distributions in the North Atlantic, which can serve as a benchmark against which to document distributional shifts. These species follow consistent, predictable patterns related to climate and environmental biochemistry; the importance of climatic conditions as regards protist distributions is noteworthy considering the effects of global climate change.

  • 23.
    Zweifel, Ulla Li
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Wikner, J.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Lundberg, E.
    Norrman, B.
    Dynamics of Dissolved Organic Carbon in a Coastal Ecosystem.1995In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 40, p. 299-305Article in journal (Refereed)
1 - 23 of 23
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