| 1. |
- Brüsin, Martin, et al.
(author)
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Individual changes in zooplankton pigmentation in relation to ultraviolet radiation and predator cues
- 2016
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 61:4, s. 1337-1344
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Journal article (peer-reviewed)abstract
- 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.
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| 2. |
- Ekvall, Mikael, et al.
(author)
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Diel vertical migration, size distribution and photoprotection in zooplankton as response to UV-A radiation
- 2015
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 60:6, s. 2048-2058
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Journal article (peer-reviewed)abstract
- 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.
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| 3. |
- Fridolfsson, Emil, et al.
(author)
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Thiamin (vitamin B1) content in phytoplankton and zooplankton in the presence of filamentous cyanobacteria
- 2018
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In: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 63:6, s. 2423-2435
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Hylander, Samuel, et al.
(author)
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Concentrations of sunscreens and antioxidant pigments in Arctic Calanus spp. in relation to ice cover, ultraviolet radiation, and the phytoplankton spring bloom
- 2015
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 60, s. 2197-2206
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Journal article (peer-reviewed)abstract
- 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.
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| 5. |
- Koehler, Birgit, et al.
(author)
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Apparent quantum yield of photochemical dissolvedorganic carbon mineralization in lakes
- 2016
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 61:6, s. 2207-2221
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Martínez-García, Sandra, et al.
(author)
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Microbial respiration in the euphotic zone at Station ALOHA
- 2015
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 60:3, s. 1039-1050
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Journal article (peer-reviewed)abstract
- 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.
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| 7. |
- Martínez-García, Sandra
(author)
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Microbial respiration in the mesopelagic zone at Station ALOHA
- 2017
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In: Limnology and Oceanography. - : Wiley-Blackwell. - 0024-3590 .- 1939-5590. ; 62:1, s. 320-333
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Journal article (peer-reviewed)abstract
- 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
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| 8. |
- Williams, Richard A. J., et al.
(author)
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Endemicity and climatic niche differentiation in three marine ciliated protists
- 2018
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In: Limnology and Oceanography. - : Wiley-Blackwell. - 0024-3590 .- 1939-5590. ; 63:6, s. 2727-2736
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Journal article (peer-reviewed)abstract
- 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.
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