Spatial and temporal occurrence of two Gyrodinium species in the seasonal ice zone off Wilkes Land, Southern Ocean

Abstract

Sea ice is crucial for regulating primary production and carbon export. Among sea ice-dwelling organisms, the genus Gyrodinium (Dinophyceae) are particularly significant, with their release into the water column influencing carbon flow in the lower food web. Specifically, G. rubrum and G. heterogrammum feed on phytoplankton and may contribute to carbon export, as their cells resemble fecal pellets. However, due to the challenges in quantifying Gyrodinium cells microscopically, the species-specific dynamics of these organisms remained unclear in the seasonal ice zone of the Southern Ocean. This study investigates the abundance of G. rubrum and G. heterogrammum in sea ice, seawater, and sinking particles using quantitative PCR analysis. Our results indicate that G. rubrum is widely distributed from coastal polynyas to continental slopes, whereas G. heterogrammum is confined to coastal areas. Sediment trap data showed G. rubrum flux at 60 m depth increased with sea ice melting. In contrast, G. heterogrammum fluxes at depths of 150 and 500 m were observed more frequently than those of G. rubrum, with no apparent correlation to sea ice melting. These findings suggest that G. rubrum distribution is closely linked to sea ice melt, whereas G. heterogrammum appears to be unaffected by such changes.