1. Microalgae - definitions ICE ALGAE Microalgae that live within the sea ice attached to ice crystals, or associated with the undersurface of the ice as floating mats, lumps, or strands that extend downward into the water column. PHYTOPLANKTON Microalgae that float aimlessly or swim too feebly to maintain a constant position against a water current. Not only do morphological characteristics vary, but also physiological characteristics may vary within a species. A better understanding of the species composition may therefore improve the knowledge also about ecology and physiology of species as well as interactions and processes in the ecosystem. Some species may indicate the condition of the ecosystem (indicator species). C. H. von Quillfeldt, Norwegian Polar Institute In addition, there are microalgae that live within the sediment or associated with the surface of the ocean floor, as well as on marine vegetation and animals.

2. Distribution: Predominant influencing factors: Size of the cells (0.2-2000  m), passive transport, living in the euphothic zone and rapid vegetative growth (0.2-2 divisions/24 hours). Ice drift and ocean currents cause comparable species composition over huge areas in the Arctic. Diversity reflects Habitat: Types of habitats: - Sea ice –Important factors: Age Construction Degree of motion Snow on top - Water column - Ocean floor - Other organisms Season Environmental conditions - Dependent on locality –Deep ocean – coast - Different requirements among species - Variations between years Geography - Classification according to affinity to the coast or to water masses : - Oceanic, neritic or littoral species - Circumpolar, bipolar and/or disjunct species - Cosmopolitian, cold/warm or temperate species Annual cycle and north south gradient As the season advance the algae will disappear from the underside of the ice C. H. von Quillfeldt, Norwegian Polar Institute Modified from Syvertsen (1991)

3. Example: Different ice algal communities Sub-ice communities Melt pond community Band community C. H. von Quillfeldt, Norwegian Polar Institute Modified from Syvertsen (1991) Central Arctic Ocean: Water column suffer from light limitation by multi-year ice, making ice algae the most important contributor of the annual primary production.

4. Factors influencing on diversity results Snapshot –Sampling in an area: Not continuously sampling throughout the year Visited different time from year to year It is likely to be interannual differences Patchy distribution (horizontal and vertical) Sampling methods –Ice cores Sub-ice community lost –Divers necessary –Phytoplankton net Mesh size Actual depth sometimes difficult to know –Water bottles –Sediment cores Separating sections – some species may be lost –Preservation Different needs for different algal groups Identification –Misidentifications in the literature –Identified as similar species from other areas –Only referred to by their genus name –Have changed name –Some are impossible to separate unless resting spores are present –Described as a number of different species: polymorphic stages of a single species –Some are not yet described Fossula arctica Often dominant in ice algal communities and early phytoplankton blooms in the Arctic. Described: 1996 Before that misidentified!!! Example – identification C. H. von Quillfeldt, Norwegian Polar Institute