Effects of microzooplankton and mixotrophy in an experimental planktonic food web.

Ptacnik, Robert, Sommer, Ulrich, Hansen, Thomas and Martens, Volker (2004) Effects of microzooplankton and mixotrophy in an experimental planktonic food web. Limnology and Oceanography, 49 . pp. 1435-1445. DOI 10.4319/lo.2004.49.4_part_2.1435.

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Abstract

Microzooplankton have received increased attention as an important trophic link between the microbial loop and calanoid copepods. On the basis of food size spectra overlap in some microzooplankton groups and calanoid copepods, however, such microzooplankton could function as competitors rather than as food for calanoid copepods (intraguild prey). Mixotrophic flagellates presumably represent a link between the microbial loop and the micro and mesozooplankton. We investigated the effects of microzooplankton and mixotrophy by altering the presence of a heterotrophic dinoflagellate and of a mixotrophic nanoflagellate in artificial food webs with calanoid copepods as terminal consumers. Overall system productivity was manipulated by two levels of nutrient enrichment. The heterotrophic dinoflagellate drastically reduced the nanophytoplankton and enhanced the reproduction of the copepods, suggesting that its role as a competitor is negligible compared to its function as a trophic link. In spite of the presence of heterotrophic nanoflagellates, the mixotroph had a strong negative effect on the picophytoplankton and (presumably) on bacterial biomass. At the same time, the mixotroph enhanced the atomic C:N ratio of the seston biomass, indicating a higher efficiency in overall primary production. Copepod reproduction was enhanced in the presence of the mixotrophic nanoflagellate. Results did not support predictions of the intraguild predation theory: The ratios of the intraguild predators and their preys were not affected by overall system productivity

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
OceanRep > Leibniz-Institut für Meereswissenschaften
OceanRep > Institute for Marine Science Kiel
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.4319/lo.2004.49.4_part_2.1435
ISSN: 0024-3590
Date Deposited: 10 Feb 2010 15:29
Last Modified: 14 Aug 2018 09:43
URI: http://oceanrep.geomar.de/id/eprint/5193

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