1. |
- Gollnisch, Raphael, et al.
(författare)
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Calcium and pH interaction limits bloom formation and expansion of a nuisance microalga
- 2021
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590.
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Tidskriftsartikel (refereegranskat)abstract
- Microalgal range expansions are increasing in frequency and magnitude but generally remain unnoticed until mass development occurs. Gonyostomum semen is a freshwater raphidophyte that causes nuisance blooms in lakes and has recently expanded its distribution across Europe. G. semen was considered to mainly occur in humic lakes in the boreal region but is now found in high density also in other freshwater habitats on a larger geographic scale with growing incidence. In this study, we focused on which environmental factors limit its expansion. Our hypothesis was that G. semen occurs in many different lake types, except for high alkalinity lakes, in which high pH in combination with high calcium concentration would inhibit its growth. Results from our field study illustrate the environmental heterogeneity of G. semen bloom sites across Europe and the United States. Nevertheless, none of these sites combined high pH and high calcium concentration. In a mesocosm study, as well as a laboratory experiment, we further demonstrated that growth of G. semen is inhibited in conditions combining both high pH and high calcium concentration. We also discuss the function of Sphagnum peat mosses in rendering an alkaline habitat suitable to G. semen growth. Our study highlights that high alkalinity environments act as a major colonization barrier to G. semen. While this finding explains which environmental filters limit G. semen distribution it also helps in understanding its current expansion. With globally decreasing calcium concentrations in freshwater ecosystems, new habitats have and will become conducive to G. semen growth.
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2. |
- Lebret, Karen, et al.
(författare)
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Grazing resistance allows bloom formation and may explain invasion success of Gonyostomum semen
- 2012
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 57:3, s. 727-734
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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3. |
- Rengefors, Karin, et al.
(författare)
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Toxicity in Peridinium aciculiferum—an adaptive strategy to outcompete other winter phytoplankton?
- 2001
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 46:8, s. 1990-1997
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Tidskriftsartikel (refereegranskat)abstract
- Freshwater dinoflagellates may form dense blooms during winter in ice-covered lakes. Unlike their marine counterparts, freshwater dinoflagellates are rarely considered to be potential toxin producers. Here we tested whether the winter species Peridinium aciculiferum produces a toxin(s) and investigated the potential adaptive function of that toxin, i.e., predator defense or inhibition of competitors (allelopathy). Using traditional toxicity bioassays (Artemia toxicity test and hemolytic activity assay). we detected the production of a toxic substance by P. aciculiferum cells from both the field and from laboratory cultures. Cultures deprived of phosphorus and in stationary phase showed highest toxicity. Potential predators, such as Daphnia galeata (Cladocera) and Eudiaptomus graciloides (Copepoda), were apparently not harmed by P. aciculiferum toxicity. However, the naturally coaccurring competitor Rhodomonas lacustris (Cryptophyceae) was killed by P. aciculiferum. An allelopathic substance(s) caused the cells of R. lacustris to form blisters and subsequently lyse. We concluded that our results support the hypothesis that P. aciculiferum is allelopathic, but not that toxins serve as predator defense. We therefore suggest that allelopathy may be an adaptive strategy of winter dinoflagellates, which could allow them to outcompete other phytoplankton species and thereby dominate the algal biomass.
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4. |
- Anderson, D M, et al.
(författare)
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Community assembly and seasonal succession of marine dinoflagellates in a temperate estuary: The importance of life cycle events
- 2006
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 51:2, s. 860-873
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Tidskriftsartikel (refereegranskat)abstract
- Dinoflagellate successional strategies and community structure were investigated in Perch Pond, a temperate estuary on the North American east coast by field surveys as well as laboratory investigations on growth rates, cyst maturation period, and cyst germination temperature thresholds. The dominant species were those predicted by the Smayda and Reynolds Rules of Assembly life form model. Three successional strategies were characterized: (1) holoplanktonic, (2) meroplanktonic (i.e., germinated from cysts), and (3) introduced by advection. The seasonal succession of the meroplanktonic dinoflagellates that were studied reflects the differential lengths of their mandatory dormancy periods as well as differences in their temperature thresholds or "windows" for germination. The holoplanktonic species present at low densities year-round in Perch Pond had a wide temperature tolerance for growth and thus did not need a cyst stage to survive seasonal extremes. Another non-cyst-forming species relied solely on advection to inoculate the salt pond; thus, blooms in successive years would be expected to be more stochastic in nature than for the other two strategies. The timing of cyst formation and population decline for meroplanktonic species corresponded on several occasions to an increase in grazers, suggesting that grazing might have contributed to bloom decline from cyst formation. This timing also suggests the possibility of encystment as a predator avoidance strategy. We suggest that seasonal succession of cyst-forming dinoflagellates is not stochastic. Instead, the appearance of these species in the plankton is predictable on the basis of measurable physiological responses to both endogenous and exogenous factors that they experience during dormancy and quiescence.
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5. |
- Kremp, Anke, et al.
(författare)
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Species-specific encystment patterns in three Baltic cold-water dinoflagellates: The role of multiple cues in resting cyst formation
- 2009
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 54:4, s. 1125-1138
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Tidskriftsartikel (refereegranskat)abstract
- The relationships among cellular nutrient status, environmental conditions (temperature and nutrient availability), and cyst production were studied in batch cultures of three cold-water dinoflagellates (Scrippsiella hangoei, Gymnodinium corollarium, and Woloszynskia halophila) isolated from the Baltic Sea. We tested the effect of increasing temperature while providing nutrient-replete conditions as well as the effect of ambient nutrient (N, P) deficiency. The results revealed different encystment cues and patterns in the three species. While depletion of ambient nitrogen and subsequent internal N stress were the primary factors behind cyst production of G. corollarium, higher temperature led to substantial encystment of S. hangoei and W. halophila without a direct link to cellular nutrient physiology. In W. halophila, N limitation induced a transition of the population to small cells presumably representing gametes, but this process was not followed by cyst formation. Phosphorus stress was not directly linked to cyst formation in any of the species. Our data indicate that both reliable token cues (such as temperature) and ultimate causes (for example, nutrient depletion) for encystment are likely involved in the cystformation process. Such duality might provide an explanation for multiple triggers inducing encystment in laboratory settings and the lack of evidence for a direct relationship between nutrient depletion and cyst formation in the field.
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6. |
- Rengefors, Karin, et al.
(författare)
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Experimental investigation of taxon-specific response of alkaline phosphatase activity in natural freshwater phytoplankton
- 2003
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Ingår i: Limnology and Oceanography. - 1939-5590. ; 48:3, s. 1167-1175
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Tidskriftsartikel (refereegranskat)abstract
- It is widely accepted that alkaline phosphatase activity (APA) is an efficient indicator of phosphate limitation in freshwater phytoplankton communities. In this study, we investigated whether the response in APA to phosphate limitation differs among the taxa in a mixed phytoplankton assemblage. We used the new enzyme-labeled fluorescence (ELF) technique, which allows microscopic detection of phosphate limitation in individual cells of multiple species. The most prominent findings of this study were that alkaline phosphatase (AP) was induced in many, but not all taxa and that different taxa, as well as different cells within a single taxon, experienced different degrees of phosphate stress under the same environmental conditions. Our approach was to manipulate the limiting nutrient in a natural freshwater phytoplankton community by incubating lake water in the laboratory. We induced nitrogen (N) or phosphate limitation through additions of inorganic nutrients. Both the ELF assay and bulk APA indicated that the lake phytoplankton were not phosphate limited at the start of the experiment. During the experiment, several chlorophyte taxa (e.g., Eudorina and an unidentified solitary spiny coccoid) were driven to phosphate limitation when inorganic N was added, as evidenced by a higher percentage of ELF-labeled cells relative to controls, whereas other chlorophyte taxa such as Actinastrum and Dicryosphaerium were not phosphate stressed under these conditions. In the phosphate-limited treatments, little or no ELF labeling was observed in any cyanobacterial taxa. Furthermore, all taxa observed after the ELF labeling procedure (>10-mum fraction) were labeled with ELF at least on one occasion, demonstrating the wide applicability of the ELF method. By using ELF labeling in tandem with bulk APA, the resolution and analysis of phosphate limitation was increased, allowing the identification of specific phosphate-stressed taxa.
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