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Marine Ecology Progress Series

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MEPS 383:27-36 (2009)  -  DOI:

Role of heterotrophic dinoflagellates in the fate of diatoms released from fast ice in coastal water of Lützow-Holm Bay, East Antarctica

Mutsuo Ichinomiya1,*, Miwa Nakamachi1, Masaki Honda2, Mitsuo Fukuchi3, Akira Taniguchi4

1Tohoku National Fisheries Research Institute, Shinhamacho 3–27–5, Shiogama, Miyagi 985–0001, Japan
2Central Research Institute of Electric Power Industry, Abiko, Chiba 270–1194, Japan
3National Institute of Polar Research, Kaga, Tokyo 173–8515, Japan
4Tokyo University of Agriculture, Abashiri, Hokkaido 099–2493, Japan

ABSTRACT: To understand the fate of ice algal diatoms released from fast ice, we investigated the abundance and sinking loss of diatoms and the grazing impact on diatoms by heterotrophic dinoflagellates (HD) under the ice near Syowa Station, Antarctica, during the austral summer of 2005–2006. After a rapid increase, diatoms showed a clear declining phase. Among the diatom assemblage, Porosira pseudodenticulata and Pseudo-nitzschia cf. turgiduloides were abundant in the water column but low in the sinking flux as they are able to maintain their position in the surface layer after release from the fast ice. Potential grazing impact by HD was calculated to reach 233 mg C m–2 d–1, equivalent to 48.7% d–1 of the diatom biomass being removed daily. Only 14.9 to 71.3 mg C m–2 d–1 (2.5 to 3.2% d–1) was attributable to diatom sinking loss. This suggests that a significant fraction of the diatoms was consumed in the surface layer and the sinking loss was comparatively small. HD often had ingested diatoms in their cells, although ciliates rarely did, and the abundance of HD fecal pellets peaked after the diatom peak. In bottle incubations at in situ temperature, the growth rates of HD ranged from 0 to 0.19 d–1, indicating almost positive growth of HD in the water column. This demonstrates that HD are major consumers of the diatoms released from the fast ice, forming a dominant trophic link between diatoms and HD in the Antarctic under-ice ecosystem.

KEY WORDS: Heterotrophic dinoflagellates · Diatoms · Ciliates · Fast ice · Antarctica

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Cite this article as: Ichinomiya M, Nakamachi M, Honda M, Fukuchi M, Taniguchi A (2009) Role of heterotrophic dinoflagellates in the fate of diatoms released from fast ice in coastal water of Lützow-Holm Bay, East Antarctica. Mar Ecol Prog Ser 383:27-36.

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