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<p>The genus <i>Gyrodinium</i> comprises heterotrophic dinoflagellates that serve as primary consumers and detritus feeders in the ocean. The fecal pellet (FP)-like <i>Gyrodinium</i> species (<i>G. rubrum</i> and <i>G. heterogrammum</i>) have been observed in the seasonal ice zone of the Southern Ocean. The feeding activity of these two <i>Gyrodinium</i> species plays a crucial role in their cell size change process, making prey identification important for understanding their occurrence and sinking processes. However, prey organisms of these two FP-like <i>Gyrodinium</i> species remain unexplored. This study aimed to identify prey organisms in the food vacuoles of both FP-like <i>Gyrodinium</i> species using microscopic and DNA analysis to reveal the dietary components contributing to their transformation into FP-like morphology. The FP-like <i>Gyrodinium</i> cells contained diatom valves and fragments, with diatoms of the genus <i>Fragilariopsis</i> being the most frequently observed in both species. Cell volume measurements and the presence of intracellular diatom valves suggest that the two FP-like <i>Gyrodinium</i> species grow in size by feeding on particulate matter, such as FPs and phyto-aggregates rather than on individual phytoplankton cells. The <i>Gyrodinium</i> cells transform into an FP-like morphology by feeding on particulate matter and subsequently sink below the mixed layer. These findings enhance our understanding of the physiological ecology of <i>Gyrodinium</i> species in the Southern Ocean.</p>

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Prey items of two fecal pellet-like Gyrodinium species revealed through microscopic and molecular analyses

  • 期刊论文

  • 发表日期：

    2025年7月12日

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  • Ryo Matsuda,
  • Keigo D. Takahashi,
  • Masayoshi Sano,
  • Ryosuke Makabe,
  • Norio Kurosawa

摘要

The genus Gyrodinium comprises heterotrophic dinoflagellates that serve as primary consumers and detritus feeders in the ocean. The fecal pellet (FP)-like Gyrodinium species (G. rubrum and G. heterogrammum) have been observed in the seasonal ice zone of the Southern Ocean. The feeding activity of these two Gyrodinium species plays a crucial role in their cell size change process, making prey identification important for understanding their occurrence and sinking processes. However, prey organisms of these two FP-like Gyrodinium species remain unexplored. This study aimed to identify prey organisms in the food vacuoles of both FP-like Gyrodinium species using microscopic and DNA analysis to reveal the dietary components contributing to their transformation into FP-like morphology. The FP-like Gyrodinium cells contained diatom valves and fragments, with diatoms of the genus Fragilariopsis being the most frequently observed in both species. Cell volume measurements and the presence of intracellular diatom valves suggest that the two FP-like Gyrodinium species grow in size by feeding on particulate matter, such as FPs and phyto-aggregates rather than on individual phytoplankton cells. The Gyrodinium cells transform into an FP-like morphology by feeding on particulate matter and subsequently sink below the mixed layer. These findings enhance our understanding of the physiological ecology of Gyrodinium species in the Southern Ocean.