Latitudinal biodiversity of surface eukaryotic plankton across oceanic fronts in the Indian sector of the Southern Ocean

The marine latitudinal diversity gradient represents a fundamental pattern of large-scale biodiversity variation extending from the poles to the tropics. However, our understanding of the biodiversity in the seasonal ice zone of the Southern Ocean remains limited. In this study, we investigated the surface eukaryotic community structure from the subtropical zone to the summer ice-edge zone along the 110°E transect in the Indian sector of the Southern Ocean. Notably, the microeukaryotic diversity in the ice-edge zone was as high as that observed in the Subantarctic Zone. The unique microeukaryotic amplicon sequence variants (ASVs) in the ice-edge zone were lower than those in the subtropical zone; however, the shared ASVs, primarily consisting of Dinophyta and phyla corresponding to stramenopiles, of the ice-edge zone between microeukaryotes and pico/nanoeukaryotes were higher. Compared with the latitudinal diversity gradient hypothesis, biodiversity seasonally increased at the summer ice edge. This pattern might have been driven by changes in the physical environment associated with sea ice meltwater and the release of sea-ice-associated organisms into the water column. These findings suggest the potential impact of sea ice melt on microeukaryotic plankton diversity in the seasonal ice zone.