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Aquatic Microbial Ecology

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AME 59:239-255 (2010)  -  DOI:

Ecology of Gymnodinium aureolum. I. Feeding in western Korean waters

Hae Jin Jeong1,*, Yeong Du Yoo1, Nam Seon Kang1, Jung Rae Rho2, Kyeong Ah Seong3, Jong Woo Park2, Gui Sook Nam4, Wonho Yih2

1School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea
2Department of Oceanography, Kunsan National University, Kunsan 573-701, Korea
3Saemankeum Environmental Research Center, Kunsan National University, Kunsan 573-701, Korea
4Rural Research Institute, Korea Rural Community Cooperation, Ansan 426-908, Korea

ABSTRACT: A bloom-forming dinoflagellate was isolated from coastal waters in western Korea during a red tide event in March 2008 and clonal cultures were established. The dinoflagellate was identified as Gymnodinium aureolum based on morphological and genetic analyses (GenBank accession no. FN392226). We report here for the first time that the red-tide dinoflagellate G. aureolum, which has previously been thought to be exclusively autotrophic, is a mixotrophic species. G. aureolum fed on algal prey using a peduncle. Among the algal prey provided, G. aureolum ingested heterotrophic bacteria, the cyanobacterium Synechococcus sp., and small algal species that had equivalent spherical diameters (ESDs) of ≤11.5 µm. However, it did not feed on larger algal species (ESD ≥12 µm) or the small diatom Skeletonema costatum. The specific growth rates for G. aureolum on the cryptophyte Teleaulax sp. increased continuously with increasing mean prey concentration before saturating at prey concentrations of ca. 190 ng C ml–1 (11050 cells ml–1). The maximum specific growth rate (mixotrophic growth) of G. aureolum on Teleaulax sp. was 0.169 d–1, at 20°C under a 14:10 h light:dark cycle of 20 µE m–2 s–1, while its growth rate (phototrophic growth) under the same light conditions without added prey was 0.120 d–1. The maximum ingestion and clearance rates of G. aureolum on Teleaulax sp. were 0.058 ng C grazer–1 d–1 (3.4 cells grazer–1 d–1) and 0.003 µl grazer–1 h–1, respectively. The calculated in situ grazing coefficient for G. aureolum on co-occurring cryptophytes ranged up to 0.498 d–1. Bioassay results indicated that this strain of G. aureolum is not toxic. Results of the present study suggest that G. aureolum has a potentially considerable grazing impact on algal populations.

KEY WORDS: Growth · Harmful algal bloom · HAB · Ingestion · Mixotrophy · Peduncle · Protist

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Cite this article as: Jeong HJ, Yoo YD, Kang NS, Rho JR and others (2010) Ecology of Gymnodinium aureolum. I. Feeding in western Korean waters. Aquat Microb Ecol 59:239-255.

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