Multi-year assessment of coastal sea-ice algae and phytoplankton in an Arctic port ecosystem, Nunavut, Canada

This study provides a rare multi-year assessment of sea-ice algal and phytoplankton species diversity in the coastal Canadian Arctic, across sea-ice and open-water habitats, that reflect seasonal gradients critical to ecosystem function. Samples were collected near Iqaluit, Nunavut, in 2018–2022. A total of 562 taxa were identified with Nitzschia frigida Grunow, 1880, unidentified flagellates, Thalassiosira spp . (Cleve, 1873) (20–50 µm), and Chaetoceros spp. (Ehrenberg, 1844) (5–10 µm) numerically dominating sea-ice, under-ice, ice-crack, and open-water surface habitat, respectively. Simpson diversity of these habitats was highest in ice-crack surface waters (0.94, July 2019), suggesting a physical concentration of cells. Variability in community composition followed Arctic phenology. Sea-ice, open-water bloom, and under-ice/transitional assemblages were differentiated by pennate diatoms (e.g., Navicula pelagica Cleve, 1896 and centric diatoms (e.g., Chaetoceros spp.), as well as Prymnesiophyceae, including Chrysochromulina spp. Lackey, 1939. Six potential toxin producing species were present at low frequency of occurrence (<1%–12% of sampling events). Community composition was homogenous among stations and inlets, but variability in phytoplankton bloom seasonality altered the relative abundance of the under-ice/transitional assemblage. This project provides updated records of sea-ice algae and phytoplankton diversity for the only deep-water port in the eastern Canadian Arctic, documenting seasonal and interannual community variability required to identify potential effects of climate-driven or anthropogenic events.