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Aquatic Microbial Ecology

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AME 55:17-30 (2009)  -  DOI:

Grazing by Karenia brevis on Synechococcus enhances its growth rate and may help to sustain blooms

Patricia M. Glibert1,*, JoAnn M. Burkholder2, Todd M. Kana1, Jeffrey Alexander1, Hayley Skelton2, Carol Shilling3

1University of Maryland Center for Environmental Science, Horn Point Laboratory, PO Box 775, Cambridge, Maryland 21613, USA
2Center for Applied Aquatic Ecology, North Carolina State University, Raleigh, North Carolina 27695, USA
3Watkins Mill High School, 10301 Apple Ridge Road, Gaithersburg, Maryland 20879, USA

ABSTRACT: Grazing rates of Karenia brevis Clones CCMP2228 and CCMP2229 were determined in laboratory experiments using Synechococcus sp. Clone CCMP1768 as food. Growth (days to weeks) and uptake rates (hours to days) were assessed. In the growth experiments, K. brevis, previously depleted in nitrogen (N), was grown at 2 light intensities in the presence of varying concentrations of Synechococcus. Under high irradiance (300 µmol photons m–2 s–1; 14 h light:10 h dark cycle), exponential growth rates approximated those of phototrophic growth without Synechococcus (0.26 to 0.35 d–1). At this irradiance, K. brevis cells in all treatments grew for about 10 d. Under lower irradiance (43 µmol photons m–2 s–1), exponential growth rates of K. brevis cells varied with the enrichment level of Synechococcus, with rates under the highest Synechococcus enrichment level being nearly twice (0.58 d–1) those observed for the high irradiance treatments. Short-term uptake experiments (3 experiments, 2 clones) were done to examine the N-specific rates of grazing of 15N-labeled Synechococcus. N-specific rates of grazing ranged from 9.28 × 10–4 h–1 to 1.22 × 10–2 h–1 and varied with the relative proportion of Synechococcus:K. brevis. These rates represent a range of 0.026 to 2.15 pmol-N K. brevis–1 d–1, or 0.96 to 83.8 Synechococcus K. brevis–1 h–1. Evidence of Synechococcus inside K. brevis was provided by confocal microscopy. Grazing by K. brevis thus enhances the range of nutritional substrates available to meet its growth requirements, and may play a substantial role in sustaining natural populations in inorganic N-poor waters.

KEY WORDS: Karenia brevis · Synechococcus · Mixotrophy · Grazing rate · Irradiance · Nitrogen source · Harmful algal bloom · Red tide

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Cite this article as: Glibert PM, Burkholder JM, Kana TM, Alexander J, Skelton H, Shilling C (2009) Grazing by Karenia brevis on Synechococcus enhances its growth rate and may help to sustain blooms. Aquat Microb Ecol 55:17-30.

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