Eucampia antarctica var. recta (Mangin) stat. nov. (Biddulphiaceae, Bacillariophyceae): life stages at the Weddell Sea ice edge

Abstract

Eucampia antarctica var. recta (Mangin) stat. nov. is proposed as a truly Antarctic, ice-edge organism. Morphological differences, including symmetry, are noted between this and the nominate variety, which has a subpolar distribution. Observations from four cruises during different seasons in the Weddell Sea area allowed a more complete documentation of the life history. Vegetative cells are lightly silicified. Austral autumn conditions trigger heavily silicified doublet cells, and the vegetative frustule is thrown off. The heavily silicified hypovalves are overlapped by functional, but delicate, girdle bands. Living doublet cells are not packed with storage products. For the first time, winter observations near the ice edge in the water column revealed germination of the doublets into short chains of 4–16 similar, heavily silicified cells. Although these doublets have been called resting spores, they have characteristics of a winter growth stage. Only the specialized terminal valves of the original doublet cells have pointed elevations. As heavily silicified cells often reach the sediment, it is proposed that the proportion of the flattened intercalary to terminal valves can provide an ecological and paleoecological index to the amount of growth from the onset of winter conditions and ice cover until the vegetative stage is triggered in the spring.