2023 Volume 39 Pages 12-20
Information on the flora of ice algae is essential for understanding the biological processes related to sea ice melting (e.g., seeding phytoplankton blooms) in polar oceans. Here, we report on the biomass and species composition of ice algae collected off Cape Darnley (Southern Ocean) in February 2019. Sea-ice chlorophyll a concentration ranged from 3.4 to 127.9 µg l-1. The diatom Fragilariopsis curta (Van Heurck) Hustedt was predominant in samples with ice-algal blooms (>110 µg chlorophyll a l-1), accounting for 79.7–87.7% of total cells and 73.2–84.7% of total algal carbon. Fragilariopsis cylindrus (Grunow ex Cleve) Helmcke & Krieger was predominant in the remaining samples with low chlorophyll a concentration (<4.0 µg l-1). The ice-algal bloom samples showed a low particulate organic carbon: nitrogen ratio (6.9–7.5) and a high total algal carbon relative to particulate organic carbon (0.67–1.46). In contrast to the high F. curta cell abundance in sea ice, phytoplankton in surface seawater was dominated by F. cylidrus (45.7% of total cells). The long periods after substantial sea ice melting likely helped F. cylindrus, which is better adopted to the open-water environment, to become more predominant over F. curta in seawater. Our results suggest that F. curta may be an important species for ice-algal production and as the assemblages released into seawater as well as F. cylindrus in this region.
