Spatial distribution of planktonic ciliates in waters around the northeastern Antarctic Peninsula and the South Orkney Plateau

The Antarctic Peninsula and adjacent region is one of the planet’s fastest warming areas and has experienced remarkable environmental change. Planktonic ciliates are sensitive to environmental change because of their short lifespans and limited mobility. However, not much research has been done on the distribution of planktonic ciliates and their relation to environmental factors in waters around the Antarctic Peninsula and the South Orkney Plateau. Here, we investigated planktonic ciliate distribution in different areas of the Antarctic Peninsula and the South Orkney Plateau region during 26 December 2015 and 11 January 2016. Tintinnids made up less than 10% and 15% of total planktonic ciliate abundance and biomass, respectively. Aloricate ciliates and tintinnids showed different vertical profiles, indicating their different responses to environmental change. In the Bransfield Strait, tintinnids mainly occurred in the south side of the strait. In the South Orkney Plateau with well-stratified water column, Laackmanniella naviculaefera occurred in the surface 0–25-m Summer Surface Water (SSW), while Cymatocylis cf . cristallina occurred in the 50–150-m Winter Water. Along a transect between the Central Basin and Eastern Basin, warmer Antarctic Circumpolar Current waters intruded southward and overlay the SSW of the Weddell Sea confluence. Consequently, L. naviculaefera was suppressed into deeper water than in the South Orkney Plateau. This study showed that the characteristic hydrography of the Antarctic Peninsula and the South Orkney Plateau shaped the distribution patterns of planktonic ciliates. Our results are helpful for understanding the future dynamics of pelagic ecosystems in this rapidly changing area.