MEPS 542:63-77 (2016)  -  DOI: https://doi.org/10.3354/meps11560

Molecular gut content analysis demonstrates that Calanus grazing on Phaeocystis pouchetii and Skeletonema marinoi is sensitive to bloom phase but not prey density

Jessica L. Ray1,*, Katrine S. Skaar1, Paolo Simonelli2, Aud Larsen1, Andrey Sazhin3, Hans H. Jakobsen4, Jens C. Nejstgaard5, Christofer Troedsson1

1Uni Research Environment, Uni Research AS, Postboks 7810, 5020 Bergen, Norway
2Department of Biology, University of Bergen, 5020 Bergen, Norway
3P. P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Laboratory of Ecology of Plankton Organisms, Nakhimovsky Prospect 36, Moscow, Russia
4Aarhus University, Bioscience, Frederiksborgvej 399, 4000 Roskilde, Denmark
5Leibniz Institute of Freshwater Ecology and Inland Fisheries, Dep. 3, Experimental Limnology, Alte Fischerhütte 2, 16775 Stechlin, Germany
*Corresponding author:

ABSTRACT: Mesozooplankton grazing selection in complex marine microbial communities is a poorly understood yet critical structuring component of marine microbial food webs. We wished to quantitatively assess how relative grazing by the calanoid copepod Calanus spp. changed as a function of prey abundance dynamics in a controlled experimental setting. Our study focused on haptophyte- (Phaeocystis pouchetii) and diatom- (Skeletonema marinoi) dominated plankton communities in a 22 d seawater mesocosm experiment during the spring bloom in southwestern Norway. Using quantitative PCR, we analyzed the ratios of P. pouchetii or S. marinoi abundances in copepod gut content to their abundance in mesocosm seawater as proxies for understanding relative grazing across phytoplankton bloom development. We observed low relative grazing by Calanus on P. pouchetii and S. marinoi in mesocosms during peaks in phytoplankton abundance, suggesting that Calanus grazing on these phytoplankton was both low and uncoupled from phytoplankton density. We did observe a small but signficant increase in relative grazing on S. marinoi after the demise of the diatom bloom, suggesting that senescent S. marinoi may be more bioavailable prey for Calanus. In conclusion, the use of qPCR ratios as proxy for relative prey consumption indicates the potential importance of phytoplankton bloom phase, but not relative prey density, for Calanus prey selection.


KEY WORDS: Calanus · Raunefjorden · qPCR · Copepod grazing · Mesocosm


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Cite this article as: Ray JL, Skaar KS, Simonelli P, Larsen A and others (2016) Molecular gut content analysis demonstrates that Calanus grazing on Phaeocystis pouchetii and Skeletonema marinoi is sensitive to bloom phase but not prey density. Mar Ecol Prog Ser 542:63-77. https://doi.org/10.3354/meps11560

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