Planktonic centric diatom Minidiscus chilensis dominated sediment trap material in eastern Bransfield Strait, Antarctica

The planktonic centric diatom Minidiscus chilensis Rivera was collected over 1 yr in a sediment trap at 1000 m depth in one of the deep basins in the eastern Bransfield Strait, Antarctica. The valves of this diatom are 3 to 8 mu m in diameter and quadrangular in girdle view. The center of each valve is prominently hyaline with 3 strutted processes and a labiate process. M. chilensis was observed in all of the sediment trap samples collected between December 25, 1998 and December 24, 1999. The flux of M. chilensis into the trap varied considerably according to season, with the highest flux of 2.4 x 10 super(9) valves/m super(2)/d (87% of total diatom valve flux) occurring in mid January when the mooring area was free of sea-ice. The dominance of M. chilensis among planktonic diatoms in Antarctic open waters has not been previously recorded. Our study suggests that M. chilensis should be included in future quantitative analyses and should be considered an important species for understanding the ecological structure of Antarctic waters.