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Phytoplankton allelochemical interactions change microbial food web dynamics
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Marine Ecology)
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Marine Ecology)
Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. (Marine Ecology)
IFREMER, France.
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2011 (English)In: Limnology and Oceanography, ISSN 0024-3590, Vol. 56, 899-909 p.Article in journal (Refereed) Published
Abstract [en]

This study investigates the effect of filtrates from an allelopathic dinoflagellate, Alexandrium tamarense, onfour microbial food webs that have been manipulated experimentally from natural seawater by modifying theavailability of resources in the form of dissolved organic carbon with additions of peptone, and by altering thegrazing pressure with size fractionation. Bacterial production was generally not affected by allelochemicals, butbacteria showed higher net growth in all food webs when allelochemicals were added, whereas heterotrophicnanoflagellates . 7 mm and ciliates were constrained in all food webs. Allelochemicals had the largest negativeeffects on microbial communities with low grazing pressure. In food webs with high grazing pressure andadditional resources, phytoplankton and small nanoflagellates were positively affected by the addition ofallelochemicals, suggesting that those were interfering with trophic interactions in the microbial communities. Bythe lysis of organisms sensitive towards allelochemicals, resources are made available and grazing pressure oncertain microorganisms is reduced. However, the intensity of these interactions is modulated by both theavailability of resources and the biomass of grazers in the initial food web.

Place, publisher, year, edition, pages
2011. Vol. 56, 899-909 p.
Keyword [en]
allelopathy, microbial foodweb, bacteria, Alexandrium, phytoplankton, upwelling
National Category
Ecology
Research subject
Natural Science, Microbiology; Natural Science, Aquatic Ecology
Identifiers
URN: urn:nbn:se:lnu:diva-7334DOI: 10.4319/lo.2011.56.3.0899OAI: oai:DiVA.org:lnu-7334DiVA: diva2:343800
Projects
ALGBACTAllelopathy among phytoplankton - a structuring force among phytoplankton
Available from: 2010-08-16 Created: 2010-08-16 Last updated: 2015-09-04Bibliographically approved
In thesis
1. The role of allelopathy in microbial food webs
Open this publication in new window or tab >>The role of allelopathy in microbial food webs
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Phytoplankton produce allelochemicals; excreted chemical substances that are affecting other microorganisms in their direct environment.

In my thesis, I investigated strain specific variability in the expression of allelochemicals of the harmful flagellate Prymnesium parvum, that is euryhaline but mainly bloom forming in brackish water. I found a large variation among strains, but further showed that all strains of P. parvum were more allelopathic in brackish water compared to marine water.

In a marine microbial community, allelochemicals can affect prey, competitors and grazers both, directly and indirectly. For instance, in a food web where grazing controls prey abundance, the negative direct effect of allelochemicals on grazers will positive affect their prey. During my thesis, I investigated how marine microbial communities respond to the addition of allelochemicals. I performed field experiments with microbial communities from seawater collected from different places over Europe, and tested how this communities respond to the addition of allelochemicals from the dinoflagellate Alexandrium tamarense. Before I incubated the microbial communities for several days with A. tamarense algal filtrate, I evaluated the allelopathic efficiency of the algal filtrates with an algal monoculture of Rhodomonas spp. This allowed me to compare the effect of A. tamarense filtrate between the different microbial communities.

In general, bacteria reached higher abundances when allelochemicals were present. As allelochemicals also inhibited nanoflagellates and ciliates, we concluded, that allelochemicals indirectly benefit bacteria by reducing grazing pressure. In microbial food webs with many heterotrophic grazers, allelochemicals further benefitted other phytoplankton by inhibiting grazers.

It was also shown that bioavailable DOM is released from a microbial community when allelochemicals are present. As most DOM was released from the seawater fraction > 60 μm, we concluded, that larger microorganisms are more affected by allelochemicals than smaller microorganisms. The results can be explained by the surface to volume ratio of microorganisms: Larger organisms provide more contact surface for allelochemicals, and therefore, are probably more vulnerable towards allelochemicals.

In conclusion, the effect of allelochemicals on a microbial community depends among others on the structure of the microbial food web, the amount of available DOM, the particle density in the seawater and the composition of the phytoplankton community.

Place, publisher, year, edition, pages
Växjö, Kalmar: Linnaeus University Press, 2011
Series
Linnaeus University Dissertations, 33/2011
Keyword
Microbial food web, Allelopathy, Alexandrium tamarense, Prymnesium parvum, Infochemicals, marine plankton community
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-11375 (URN)978-91-86491-62-8 (ISBN)
Public defence
2011-03-04, Fullrigarren, Barlastgatan 11, Kalmar, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2011-04-13 Created: 2011-04-12 Last updated: 2014-05-12Bibliographically approved

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