| 1. |
- Alonso-Saez, Laura, et al.
(författare)
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Changes in marine prokaryotic community induced by varying types of dissolved organic matter and subsequent grazing pressure
- 2009
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 31:11, s. 1373-1383
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Tidskriftsartikel (refereegranskat)abstract
- We analysed changes in the abundance, biomass, activity and composition of coastal marine prokaryotic communities after the addition of organic substrates, such as glucose, leucine and yeast extract, and the effect of grazing pressure exerted by nanoflagellates. The addition of a carbon source (i.e. glucose) promoted the growth of Gammaproteobacteria, while a combined source of C and N (i.e. leucine) favoured the development of Alphaproteobacteria. The addition of yeast extract, a complex substrate rich in N and growth factors, promoted the proliferation of Alphaproteobacteria and Gammaproteobacteria. Grazing pressure exerted by nanoflagellates produced marked differences on the size structure of the prokaryotic biomass. A pronounced tendency to filamentation and aggregation was observed in the glucose treatment, while in the case of yeast extract, small and mainly freely dispersed prokaryotes were maintained throughout the incubations. Thus, the final community in the yeast extract treatment showed a high percentage of edible biomass, while an important fraction of potentially grazing-resistant prokaryotes (more than 50% of total prokaryotic biomass) was detected in the microcosms enriched with glucose. These results suggest a marked effect of DOM sources on the development of grazing-resistant prokaryotes.
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| 2. |
- Berggren, Martin, et al.
(författare)
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Toward an ecologically meaningful view of resource stoichiometry in DOM-dominated aquatic systems
- 2015
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 37:3, s. 489-499
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Tidskriftsartikel (refereegranskat)abstract
- Research on nutrient controls of planktonic productivity tends to focus on a few standard fractions of inorganic or total nitrogen (N) and phosphorus (P). However, there is a wide range in the degree to which land-derived dissolved organic nutrients can be assimilated by biota. Thus, in systems where such fractions form a majority of the macronutrient resource pool, including many boreal inland waters and estuaries, our understanding of bacterio-and phytoplankton production dynamics remains limited. To adequately predict aquatic productivity in a changing environment, improved standard methods are needed for determining the sizes of active (bioavailable) pools of N, P and organic carbon (C). A synthesis of current knowledge suggests that variation in the C:N:P stoichiometry of bioavailable resources is associated with diverse processes that differentially influence the individual elements across space and time. Due to a generally increasing organic nutrient bioavailability from C to N to P, we hypothesize that the C:N and N:P of bulk resources often vastly overestimates the corresponding ratios of bioavailable resources. It is further proposed that basal planktonic production is regulated by variation in the source, magnitude and timing of terrestrial runoff, through processes that have so far been poorly described.
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| 3. |
- Berglund, Johnny, et al.
(författare)
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Relative strength of resource and predation limitation of heterotrophic nanoflagellates in a low-productive sea area
- 2005
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Ingår i: Journal of Plankton Research. - London : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 27:9, s. 923-935
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Tidskriftsartikel (refereegranskat)abstract
- The magnitude of resource and predation limitation of heterotrophic nanoflagellales (HMF) was studied in two short-term enclosure experiments performed in a low-productive sea area in the northern Baltic Sea in 2001. A cross-factorial design was used to simultaneously assess the relative importance of the two factors. Resource limitation was removed by adding bacteria, and predation limitation was eliminated by selective filtration. The first experiment was performed in June just after the spring bloom decline and the second in September at the end of the productive season. Resource limitation prevailed during both experiments, contributing to 60% of the net growth increase in June and 74% in September. Removal of predators had a significant effect only in June. Evidence for simultaneous resource and predation limitation was thus found only during the post-bloom situation. The results were applied to a model on resource and predation control of HNF abundances. To evaluate seasonal differences, field data on HNF and bacteria from a whole year study were applied to the model. Except for a few occasions during spring, the model indicated prevailing resource control of HNF at two locations with slightly different productivity. © The Author 2005. Published by Oxford University Press. All rights reserved.
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| 4. |
- Bertilsson, S, et al.
(författare)
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Size-selective predation on pelagic microorganisms in Arctic freshwaters
- 2003
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 25:6, s. 621-631
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Tidskriftsartikel (refereegranskat)abstract
- Herbivorous zooplankton may have a pronounced influence on pelagic microorganisms in Arctic freshwaters. We quantified experimentally the size-selective feeding of several zooplankton groups on pelagic microorganisms in high Arctic tundra systems. Our experiments and field study focused on dominant herbivores in Arctic freshwaters, including the cladoceran Dophnia, the copepod Diaptomus and the anostracan Branchinecta, and their effects on prey ranging in size from bacteria to large phytoplankton. Grazing experiments showed that Dophnia were effective predators on all types of prey, whereas Diaptomus grazed preferentially on larger phytoplankton with low clearance rates for bacterial cells. Further analysis by flow cytometry indicated that Diaptomus grazed selectively on the largest bacteria. In contrast to the results obtained in the controlled experiments, Arctic lakes and ponds with a zooplankton community dominated by Dophnia had a higher bacterial production and abundance than systems not dominated by this grazer. This may indicate that the stimulatory effect of grazers on bacterial growth is more pronounced in natural systems, or that factors other than zooplankton grazing are more important in regulating bacterial abundance and production in natural systems. Although Arctic waters differ considerably from temperate systems with respect to temperature and light regime, herbivore-prey dynamics as well as the bacterial response to temperature appear to be similar between the climatic regions.
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| 5. |
- Bjærke, Oda, et al.
(författare)
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Is chain length in phytoplankton regulated to evade predation?
- 2015
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 37:6, s. 1110-1119
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Tidskriftsartikel (refereegranskat)abstract
- Formation of cell chains in phytoplankton is ecologically important, but no single factor driving the evolution of chain formation has been identified. Chain length in the diatom Skeletonema marinoi declines in response to grazer cues, which reduces grazing losses in simple laboratory incubations. Here we explore a more ecologically relevant scenario with fluctuating populations of different sized grazers, and test whether chain-length plasticity provides a selective advantage by lower grazing mortality. We used a model with empirical grazer densities, the effect of grazer cues on chain length, and size selective grazing rates. Finally we compared the model outcome with Skeletonema chain length and copepod biomass in the field. Low copepod densities induced chain-length reduction in Skeletonema, showing that the signaling system is sensitive enough to operate in nature. The model shows that reducing chain length in response to copepod cues reduces annual grazing losses by 31 and 36% compared with fixed traits with either single cells or long chains, respectively. The field measurements agree well with chain length being regulated by grazer abundances. We conclude that chain-length plasticity is a selective trait, and suggest that grazer regime could be an evolutionary driver of chain formation in phytoplankton.
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| 6. |
- Bolton, T. F., et al.
(författare)
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Physiological acclimation to decreased water temperature and the relative importance of water viscosity in determining the feeding performance of larvae of a serpulid polychaete
- 2005
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 27:9, s. 875-879
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Tidskriftsartikel (refereegranskat)abstract
- Ambient temperature exerts both physiological and mechanical effects on the rates of functional processes of small aquatic ectotherms. Physiological effects of temperature result from its influence on the rates of chemical reactions. Mechanical effects of temperature result from the inverse relationship between the temperature of water and its dynamic viscosity. We measured the relative importance of these components of temperature on the feeding performance of polychaete larvae. Cohorts of larvae were reared for 24 h at 20 degrees C and 10 degrees C in treatments where the physiological and mechanical effects of these temperatures were separated. The feeding performance of these larvae was subsequently measured in treatments where these components of temperature were similarly partitioned. Cold-reared larvae displayed complete acclimation of feeding performance to the physiological effects of decreased temperature: thus, increased viscosity was responsible for 100% of the difference in feeding performance between 20 degrees C and 10 degrees C. The physiological ability of small aquatic ectotherms to acclimate functional processes to temperature variation may be greater than previously thought, and these results have implications for understanding the responses of aquatic ectotherms' to global temperature change.
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| 7. |
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| 8. |
- Båmstedt, Ulf, et al.
(författare)
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Fecundity and early life of the deep-water jellyfish Periphylla periphylla
- 2020
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Ingår i: Journal of Plankton Research. - : OXFORD UNIV PRESS. - 0142-7873 .- 1464-3774. ; 42:1, s. 87-101
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Tidskriftsartikel (refereegranskat)abstract
- Comparisons over 6 years of three Norwegian fjord populations of the deep-water scyphomedusa Periphylla periphylla are presented. A minor part of the population in Lurefjord is migrating to the surface during night, which benefits mating encounters by increasing abundance per unit volume and decreasing the distance between individuals. Simulations using a typical water-column density profile and Stoke's law show that fertilized eggs released in the surface quickly reach a depth where light is insufficient for visual predators. Consequently, the distribution of the smallest juveniles was strongly skewed towards higher depths in all three fjords studied. Mature females in Sognefjord were 4-5 times less abundant than in Lurefjord and Halsafjord, but due to a larger size and strong exponential relationship between size and number of mature oocytes, the potential recruitment rate as recruits m(-2) year(-1) was not much different from the other two fjords. Nevertheless, the observed number of small (<1 cm) juveniles was 18-31 times higher in Sognefjord than in the other two fjords, and it is assumed that the deeper habitat (up to 1300 m) compared to the other fjords (up to 440 and 530 m) is a superior habitat for the early development of P. periphylla.
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| 9. |
- Carey, Cayelan C., et al.
(författare)
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The cyanobacterium Gloeotrichia echinulata stimulates the growth of other phytoplankton
- 2010
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 32:9, s. 1349-1354
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Tidskriftsartikel (refereegranskat)abstract
- We tested the effect of the cyanobacterium Gloeotrichia echinulata on a diverse array of phytoplankton. We found that Gloeotrichia increased the growth rates of five of seven phytoplankton species up to 620% in comparison with a medium-only control after 96 h.
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| 10. |
- Chauton, M, et al.
(författare)
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Changes in pigmentation, bio-optical characteristics and photophysiology, during phytoflagellate succession in mesocosms
- 2004
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Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 26:3, s. 315-324
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Tidskriftsartikel (refereegranskat)abstract
- Pigmentation, bio-optical characteristics and photophysiology, were studied in mesocosms with different N:P ratios. No significant difference in biomass or species composition was seen under different nitrogen to phosphorus ratios (N:P), but a temporal succession of different flagellate groups was observed in all mesocosms. An initial bloom of prymnesiophytes containing chlorophyll (Chl) c and 19' hexanoyloxyfucoxanthin (19' HOF) was followed by prasinophytes containing Chl b. Electron microscope analysis confirmed the presence of genera such as Chrysochromulina (Prymnesiophyceae), Tetraselmis and Pyramimonas (Prasinophyceae). Traces of prasinoxanthin in the pigment samples showed that smaller prasinophytes were also present. Chl b influenced the photophysiology of the prasinophytes resulting in higher Chl a-specific absorption, but a greater difference between absorption and scaled fluorescence excitation spectra indicated that light absorbed by Chl b is associated with photosystem I (PSI). Since a larger fraction of the light was absorbed by chlorophyll in PSI and/or photoprotective carotenoids, the light-saturated Chl a-specific rate of photosynthesis (P-m(B)) and maximum light utilization coefficient (alpha(B)) decreased when [Chl b] increased. The highest P-m(B) values were seen when the ratios of fucoxanthins to Chl a were high, indicating that prymnesiophytes might be more efficient in light harvesting and electron transport through photosystem II (PSII) by fucoxanthins and Chl c. Our results therefore indicate different light acclimation strategies in prasinophytes versus prymnesiophytes, which may be reflected in the successional appearance of these communities in the natural environment. We also suggest that grazing by ciliates and rotifers caused periodic decreases in phytoplankton biomass, which in turn gave rise to the phytoflagellate succession observed in the mesocosms.
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