Phytoplankton and sea ice algal biomass and physiology during the transition between winter and spring (McMurdo Sound, Antarctica)

The phytoplankton and sea ice algal communities at the end of winter in McMurdo Sound were dominated by Fragilariopsis sublineata, with Thalassiosira antarctica, Melosira adele, Pinnularia quadreata, Entomoneis kjellmannii and heterotrophic dinoflagellates also present. Sea ice algal biomass at the end of winter was very low, only 0.050 ± 0.019 mg chla m⁻² in 2007 and 0.234 ± 0.036 mg chla m⁻² in 2008, but this increased to 0.377 ± 0.078 mg chla m⁻² by early October in 2007 and to 1.07 ± 0.192 by late September in 2008. Under ice phytoplankton biomass remained consistently below 0.1 μg chla l⁻¹ throughout the measuring period in both years. The photosynthetic parameters Fv/Fm, rETRmax and α document microalgal communities that are mostly healthy and well adapted to their low light under ice environment. Our results also suggest that species such as Fragilariopsis sublineata are well adapted to deal with low winter light levels but are unlikely to survive an increase in irradiance, whereas other taxa, such as Thalassiosira antarctica, will do better in a higher light environment.