A glimpse into the future: How the timing of sea ice formation influences associated microalgal communities.

This study investigates the impact of unseasonable storm events in McMurdo Sound, Antarctica, in 2022 on eukaryotic microalgal communities (EMCs). We assessed EMCs from the fast-ice and sub-ice platelet layer (SIPL) associated with fast-ice formed during March (historical timing) and September (five months later). We compared three ice conditions: March-ice (fast ice with SIPL, frozen in March), September-ice (fast ice with SIPL, frozen in September), and September-no-SIPL (fast-ice without SIPL, frozen in September). Using metabarcoding and light microscopy, results showed higher diversity in March-ice EMCs compared to September-no-SIPL. Community structure was significantly influenced by ice condition and ice type. March-ice had the most unique ASVs, of all ice conditions. Biomass peaked in March-ice SIPLs at 25-50 cm, while September-ice SIPLs peaked at 0-25 cm. These findings demonstrate delayed ice formation alters EMC structure, diversity, and biomass, potentially impacting primary productivity, nutrient cycling, and Antarctic sea ice ecosystems.