| 1. |
- Bresolin de Souza, Karine, et al.
(författare)
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Species-specific dinoflagellate vertical distribution in temperature-stratified waters
- 2014
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Ingår i: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 161:8, s. 1725-1734
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Tidskriftsartikel (refereegranskat)abstract
- Thermal stratification is increasing in strength as a result of higher surface water temperature. This could influence the vertical distribution of vertically migrating dinoflagellates. We studied the diel vertical distribution of the dinoflagellates Heterocapsa triquetra and Prorocentrum minimum using stratified laboratory columns with two thermoclines of different strength (Delta TA degrees A = 10 or 17 A degrees C), with below cline temperature of 8 A degrees C. Above the thermocline, nutrient depletion simulated the natural summer conditions in the Baltic Sea. Our study shows that H. triquetra and P. minimum can behave differently in terms of their vertical occurrence, both in space and in time when subjected to thermoclines of different strength. Also, both dinoflagellate species showed species-specific distribution patterns. In the Delta TA degrees A = 10 A degrees C treatment, H. triquetra cells performed a diel vertical migration (DVM) behavior just above the thermocline, but not in the Delta TA degrees A = 17 A degrees C. In the Delta TA degrees A = 17 A degrees C, the cells did not migrate and cell densities in the water column decreased over time. Opposing results were observed for P. minimum, where a DVM pattern was found exclusively below the thermocline of Delta TA degrees A = 17 A degrees C, while in the Delta TA degrees A = 10 A degrees C treatment, no clear DVM pattern was observed, and the highest number of cells were found in the cold bottom water. These results indicate that an increase in thermal stratification can influence species-specific dinoflagellate distribution, behavior, and survival.
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| 2. |
- Fagerberg, Tony, et al.
(författare)
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Molecular size of riverine dissolved organic matter influences coastal phytoplankton communities
- 2010
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Ingår i: Marine Ecology - Progress Series. - : Inter-Research Science Center. - 1616-1599 .- 0171-8630. ; 409, s. 17-25
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Tidskriftsartikel (refereegranskat)abstract
- Dissolved organic matter (DOM) concentrations in many northern European freshwater systems have been increasing during the past decades. DOM affects the marine plankton community where rivers discharge into the sea. Large DOM molecules have been suggested to be more available to aquatic plankton than smaller ones due to their more recent origin in the degradation process. In this study, we investigated the effect of riverine DOM molecular size on coastal plankton with the hypothesis that nitrogen associated with large molecules stimulates the plankton more than nitrogen in smaller molecules. Three size fractions of riverine DOM were isolated with tangential ultrafiltration and introduced at similar nitrogen concentrations to mesocosms with a natural coastal marine plankton community under nitrogen limiting conditions. The results show that growth of bacteria and dinoflagellates, but not diatoms, was stimulated by addition of large DOM molecules. Even though organic nitrogen concentrations tended to decrease more in large DOM treatments compared to smaller DOM treatments, no significant differences were detected. However, proteolytic enzyme activities were elevated in treatments with the largest DOM molecules, suggesting that more organic nitrogen was utilized in this treatment. We suggest that input of larger river DOM molecules to nitrogen limited coastal systems may influence the composition of the coastal phytoplankton community in favour of dinoflagellates.
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| 3. |
- Hylander, Samuel, et al.
(författare)
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Climate-induced input of turbid glacial meltwater affects vertical distribution and community composition of phyto- and zooplankton
- 2011
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 33:8, s. 1239-1248
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Tidskriftsartikel (refereegranskat)abstract
- Receding glaciers are among the most obvious changes caused by global warming, and glacial meltwater entering lakes generally forms plumes of particles. By taking vertical samples along a horizontal gradient from such a particle source, we found that photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) attenuated 20-25% faster close to the inflow of suspended particles compared with the more transparent part of the gradient. All sampled stations had a deep chlorophyll a (Chl a) maximum at 15-20 m which was more distinct in the transparent part of the horizontal gradient. Picocyanobacteria increased in abundance in more transparent water and their numbers were tightly correlated with the intensity of the deep Chl a maxima. Motile species of phytoplankton had a deeper depth distribution in transparent versus less transparent water. Yet other species, like Chrysochromulina parva, that can withstand high PAR intensities and low nutrient concentrations, increased in abundance as the water became more transparent. Also copepods increased in abundance, indicating that they are more successful in transparent water. We conclude that sediment input into lakes creates horizontal gradients in PAR and UVR attenuation which strongly affect both distribution and behavior of phyto-and zooplankton. The input of glacial flour creates a sub-habitat that can function as a refuge for species that are sensitive to high PAR and UVR exposure. When the glacier has vanished, this habitat may disappear. During the melting period, with heavy sediment input, we predict that competitive species in transparent waters, like Chrysocromulina, picocyanobacteria and copepods, will become less common. The deep Chl a maxima is also likely to become less developed. Hence, glacier melting will probably have profound effects on both species composition and behavior of several planktonic taxa with potential effects on the food web.
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| 4. |
- Hylander, Samuel, et al.
(författare)
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UV protective compounds transferred from a marine dinoflagellate to its copepod predator
- 2010
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981 .- 1879-1697. ; 389:1-2, s. 38-44
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Tidskriftsartikel (refereegranskat)abstract
- Planktonic organisms living in surface waters can be exposed to harmful levels of ultraviolet radiation (UVR), but few studies have examined accumulation of UV protective compounds in marine zooplankton. Zooplankters are suggested to lack the ability to synthesize these substances and hence must accumulate them from their algal food. Here, we show that both phytoplankton (dinoflagellates) and their zooplankton grazers (copepods) respond strongly to UVR exposure by, respectively, synthesizing and accumulating the natural sunscreens mycosporine-like amino acids (MAAs). In our experiment, the MAAs content increased approximately four times in dinoflagellates exposed to UVR and PAR, as compared to non-UVR controls only receiving PAR (PAR = photosynthetically active radiation). The elevated MAAs level in the dinoflagellates was mirrored in the copepods, which accumulated more MAAs when exposed to UVR as compared to a non-UVR treatment. Overall, copepods accumulated approximately 2-5% of the total MAAs pool. Other UV protective compounds, like carotenoids, were however not accumulated by the copepods. The ability of some species to produce or accumulate photoprotective compounds may lead to increased fitness, and thus these taxa may become more dominant in plankton communities. (C) 2010 Elsevier B.V. All rights reserved.
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| 5. |
- Jephson, Therese, et al.
(författare)
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Dependency of dinoflagellate vertical migration on salinity stratification
- 2011
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Ingår i: Aquatic Microbial Ecology. - : Inter-Research Science Center. - 0948-3055 .- 1616-1564. ; 63:3, s. 255-264
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Tidskriftsartikel (refereegranskat)abstract
- Increasing precipitation and surface water temperature due to global change may strengthen the salinity gradient in coastal regions, which could influence the behaviour of dinoflagellate migration. We studied diel vertical migration (DVM) behaviour in the dinoflagellates Prorocentrum minimum and Heterocapsa triquetra using vertically stratified laboratory columns with 3 different salinity gradients (difference of 6, 11 and 16 psu). With nutrient-depleted conditions at the surface, and with nutrients added below the halocline, P. minimum remained mainly concentrated in the bottom water, while H. triquetra performed DVM under all 3 salinity treatments. H. triquetra migrated through a salinity difference of 6 and 11 psu, concentrated at the surface at noon, then migrated to the nutrient-rich bottom water during the night. A salinity gradient of 16, however, stopped H. triquetra cells from moving through the gradient and resulted in a concentration of cells in the cline during the night. At midday, cells were again found at the surface. P. minimum and H. triquetra grown in 4 different salinities (10, 15, 20, 26 psu) and at 3 different temperatures (10, 15, 20 degrees C) showed higher specific growth rates with increasing temperature only in the 2 highest salinity treatments. At 10 degrees C, specific growth rates were not affected by different salinities.
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| 6. |
- Jephson, Therese
(författare)
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Diel vertical migration in marine dinoflagellates
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing precipitation and surface water temperature due to global change may strengthen stratification in coastal regions, which could influence the behavior of dinoflagellate diel vertical migration (DVM). DVM is a behavioral mechanism by which dinoflagellates can access photosynthetically active radiation near the surface, and nutrients at depth. During this process, cells may need to cross both salinity and temperature gradients (haloclines and thermoclines, respectively). My results show that different dinoflagellate species display unique DVM behaviors in stratified waters and increasing halo- and thermocline strength may act as barriers between the surface- and bottom water. There is, however, large variation in how dinoflagellates cope with stratification and even closely related species have different strategies. Different DVM strategies may lead to a niche separation among species, which was also observed in my research. Moreover, during powerful mixing of the water column i.e. during strong winds in situ, the continuous DVM behavior was disrupted. In addition, as indicated by my experiments, dinoflagellates were influenced by the combination of salinity and temperature. An increase in temperature had no significant effect on growth rate if cells were grown in low salinity environments. The results indicate higher growth rates for two bloom-forming species when growing in salinities corresponding to bottom water conditions on the west coast of Sweden. Thus, there is a trade-off for dinoflagellates between low-salinity light-rich surface conditions and high-nutrient, low-light and high salinity bottom water conditions. If different species have different optimal growth conditions, a geographical separation among species is to be expected. Furthermore, the results indicate that the primary trigger for vertical migration is light in combination with an internal clock controlling the behavior. I show that there is a positive phototactic response to both white, blue and red light and demonstrate that the non-photosynthetic photoreceptor rhodopsin gene exists and is expressed in the cells. Harmful algal blooms (HABs) affect nearly every coastal region of the world and dinoflagellate blooms is a major problem for the shellfish industry. Efforts are made into designing accurate models that predict harmful algae blooms and these models need to be derived from reliable experimental and observational data. High resolution sampling and repeated measurements in time is needed to be able to detect DVM behavior in the field and species-specific data may need to be coordinated and integrated in the models. To predict harmful algal blooms of vertically migrating species, the migration patterns and the growth rates in the natural environment should be further clarified for each species. If increasing precipitation and temperature strengthen the gradient in coastal regions, the nutrient-rich bottom water will be inaccessible to cells unable to migrate through the gradient. Thus, stronger stratification will benefit migrating species able to cross the gradient during DVM and generate more variability in were we can expect to find specific species in situ.
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| 7. |
- Jephson, Therese, et al.
(författare)
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Dominant impact of water exchange and disruption of stratification on dinoflagellate vertical distribution
- 2012
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Ingår i: Estuarine, Coastal and Shelf Science. - : Elsevier BV. - 1096-0015 .- 0272-7714. ; 112, s. 198-206
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Tidskriftsartikel (refereegranskat)abstract
- The vertical positions of four dinoflagellate species in three 48 h periods in late summer in a Swedish fjord (the Gullmar Fjord) reflect changes to the depth of the halocline. During stable, stratified conditions, the chlorophyll a maximum exhibited a diurnal migration pattern, which was disrupted when the halocline was forced closer to the surface by the inflow of more saline water. While conditions were stable, all studied dinoflagellate species were most abundant below the halocline at 06:00 in contrast to the other times of the day when the highest cell concentrations were above the halocline, indicating diurnal vertical migration. However, when wind-induced inflow of more saline water forced the halocline closer to the surface, these patterns were disrupted and there was no sign of diurnal vertical migration. Despite this, there was a vertical heterogeneity in the distribution of dinoflagellates with Dinophysis spp. found mainly above the halocline, while Ceratium spp. also occurred in high cell numbers below the halocline. We acknowledge the importance of representative resolution when sampling in the field, both in time and concerning vertical resolution. (C) 2012 Elsevier Ltd. All rights reserved.
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| 8. |
- Jönsson, Mikael, et al.
(författare)
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Glacial clay affects foraging performance in a Patagonian fish and cladoceran
- 2011
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 663:1, s. 101-108
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is altering temperatures and precipitation patterns all over the world. In Patagonia, Argentina, predicted increase in precipitation together with rapidly melting glaciers increase the surface runoff, and thereby the transport of suspended solids to recipient lakes. Suspended solids affect the visual conditions in the water which in turn restricts visual foraging. The native fish Aplochiton zebra Jenyns, and its filter-feeding cladoceran prey, Daphnia commutata Ekman, were subjected to foraging experiments at three turbidity levels. A. zebra foraging rate was substantially reduced at naturally occurring turbidity levels and the filtering rate of D. commutata was reduced at the highest turbidity level. This indicates that Daphnia may be partly released from predation from A. zebra at the same time as it can maintain relatively high feeding rates as turbidity increases. Lower foraging rates at the same time as the metabolic demand increases, through increased temperatures, may result in larger effects on A. zebra than could be expected from increases in turbidity or temperature alone. Turbidity may, as an indirect effect of climate change, decrease planktivore foraging rates and thereby alter the interaction strength between trophic levels.
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