Relative strength of resource and predation limitation of heterotrophic nanoflagellates in a low-productive sea area

Berglund, Johnny; Samuelsson, Kersti; Kull, Tomas; Müren, Umut; Andersson, Agneta

doi:10.1093/plankt/fbi067

Cited by 17 publications

(7 citation statements)

References 54 publications

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“…Furthermore, previous results from field studies in the northern Baltic Sea indicate that the food web structure is rather robust to changes in productivity. Berglund et al (2005) did not find any difference in the food web structure or trophic level control in a gradient with fourfold increase in productivity. We therefore conclude that a reduced basal productivity in the CNP treatment to one-third of its actual level would not change the food web structure.…”

Section: Discussionmentioning

confidence: 56%

Efficiency of a phytoplankton‐based and a bacterial‐based food web in a pelagic marine system

Berglund

Müren

Båmstedt

et al. 2007

Limnology & Oceanography

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151

138

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The food web efficiency in two contrasting food webs, one phytoplankton based and one bacteria based, was studied in a mesocosm experiment using seawater from the northern Baltic Sea. Organisms included in the experiment were bacteria, phytoplankton, protozoa, and mesozooplankton (copepods). A phytoplankton-based food web was generated by incubating at a high light level with the addition of nitrogen and phosphorus (NP). A bacteria-based food web was created by adding carbon, nitrogen, and phosphorus (CNP) and incubating at a lower light level. In the CNP treatment bacteria dominated the productivity (91%), while in the NP treatment phytoplankton were dominant producers (74%). The phytoplankton community in the NP treatment was dominated by autotrophic nanoflagellates. The food web efficiency, defined as mesozooplankton productivity per basal productivity (phytoplankton + bacteria), was 22% in the phytoplankton-based food web and 2% in the bacteria-based food web. This discrepancy could be explained by 1-2 extra trophic levels in the bacteria-based food web where carbon passed through flagellates and ciliates before reaching mesozooplankton, while in the phytoplankton-based food web there was a direct pathway from phytoplankton to mesozooplankton. The results were supported by stable isotope analysis of mesozooplankton. We propose that climate change, with increased precipitation and river runoff in the Baltic Sea, might favor a bacteria-based food web and thereby reduce pelagic productivity at higher trophic levels.

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Section: Discussionmentioning

confidence: 56%

Efficiency of a phytoplankton‐based and a bacterial‐based food web in a pelagic marine system

Berglund

Müren

Båmstedt

et al. 2007

Limnology & Oceanography

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151

138

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“…This is in agreement with a previous study, where a positive correlation between BP and PP was observed in freshwater and marine ecosystems (Cole et al 1988). In a lowproductivity aquatic system, flagellates have been shown to be mainly resource-limited or -controlled (Berglund et al 2005). This indicates that the biomass resulting from an increase in bacterial productivity is consumed by the flagellates, and the bacterial biomass thus remains unchanged.…”

Section: Discussionmentioning

confidence: 99%

Predation pressure on bacteria increases along aquatic productivity gradients

Thelaus¹,

Haecky²,

Forsman³

et al. 2008

Aquat. Microb. Ecol.

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To elucidate how predation pressure on bacteria is affected by increasing productivity in aquatic systems, we ran model simulations of a microbial food web. In addition, we conducted a meta-analysis of data from studies in seas and lakes. The model was run as a flow-through system simulating conditions ranging from oligotrophic to hypertrophic. The organisms included in the model were heterotrophic bacteria, phytoplankton, 3 size classes of protozoa and metazooplankton. Predation pressure was defined as flagellate and ciliate grazing per bacterial biomass. The food-web model simulations showed increasing predation pressure on bacteria with increasing productivity (estimated chlorophyll a concentration 0.2 to 112 µg l -1). This was explained by an increase in bacterial production and the ratio of protozoan to bacterial biomass with increasing productivity. The results of the model simulation were supported by the meta-analysis, which showed increasing protozoan predation pressure on bacteria with increasing productivity in aquatic systems (chlorophyll a concentration 0.1 to 250 µg l -1). The ratio of protozoan to bacterial biomass also increased with productivity in the meta-analysis of field data. Our results suggest that protozoa control the bacterial community by predation in high-productivity environments.KEY WORDS: Bacteria · Protozoa · Predation · Microbial food web · Productivity · Regulation · Model · Omnivory Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 52: [45][46][47][48][49][50][51][52][53][54][55] 2008 sources in the food web, i.e. phytoplankton and heterotrophic bacteria (Cole et al. 1988). Increases in basal productivity cascade up through the food web via the predator-prey chain, possibly resulting in increased predation on bacteria and phytoplankton. If the food web is linear and prey organisms do not develop predation defense mechanisms, the top predator would exhibit an increase in biomass with increasing productivity, while lower trophic levels might exhibit alternating responses in biomass levels (according to the exploitation ecosystem hypothesis) (Oksanen et al. 1981, Thingstad & Sakshaug 1990. Thus, mechanisms controlling the structure of the microbial food web would shift between predation and resource control at different trophic levels. However, several mechanisms are known to modify this simple pattern: omnivory is common in aquatic food webs, increasing the complexity of trophic interactions (Diehl 2003). Introducing heterogeneity of trophic levels alters the response to increasing productivity compared to the predictions made by the exploitation ecosystem hypothesis (Leibold 1989, Abrams 1993. Furthermore, predation defense mechanisms are common in phytoplankton and bacterial communities in nutrient-rich waters, possibly as a response to increased predation pressure (Jürgens & Güde 1994, Rousseau et al. 2000. In a microcosm study, Hall et al. (2006) showed that an inedible producer influenced the degree of top-down vers...

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“…CFUs were recorded after 4 days of incubation. For the analysis of small flagellates, 5–10‐mL water samples were filtered onto black 0.6‐μm polycarbonate filters (Poretics), stained with 4′,6‐diamino‐2‐phenylindole (Porter & Feig, 1980) and analysed using a Nikon TE2000‐U fluorescence microscope (Berglund et al , 2005). Larger flagellates and ciliates were fixed using Lugol's solution to a final concentration of 2% and counted in sedimentation chambers.…”

Section: Methodsmentioning

confidence: 99%

Influence of nutrient status and grazing pressure on the fate of Francisella tularensis in lake water

Thelaus

Andersson²,

Mathisen

et al. 2009

FEMS Microbiology Ecology

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The natural reservoir of Francisella tularensis, the causative agent of tularaemia, is yet to be identified. We investigated the possibility that Francisella persists in natural aquatic ecosystems between outbreaks. It was hypothesized that nutrientrich environments, with strong protozoan predation, favour the occurrence of the tularaemia bacterium. To investigate the differences in adaptation to aquatic environments of the species and subspecies of Francisella, we screened 23 strains for their ability to survive grazing by the ciliate Tetrahymena pyriformis. All the Francisella strains tested were consumed at a low rate, although significant differences between subspecies were found. The survival and virulence of gfp-labelled F. tularensis ssp. holarctica were then studied in a microcosm experiment using natural lake water, with varying food web complexities and nutrient availabilities. High nutrient conditions in combination with high abundances of nanoflagellates were found to favour F. tularensis ssp. holarctica. The bacterium was observed both free-living and within the cells of a nanoflagellate. Francisella tularensis entered a viable but nonculturable state during the microcosm experiment. When studied over a longer period of time, F. tularensis ssp. holarctica survived in the lake water, but loss of virulence was not prevented by either high nutrient availability or the presence of predators.

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Relative strength of resource and predation limitation of heterotrophic nanoflagellates in a low-productive sea area

Cited by 17 publications

References 54 publications

Efficiency of a phytoplankton‐based and a bacterial‐based food web in a pelagic marine system

Efficiency of a phytoplankton‐based and a bacterial‐based food web in a pelagic marine system

Predation pressure on bacteria increases along aquatic productivity gradients

Influence of nutrient status and grazing pressure on the fate of Francisella tularensis in lake water

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