The physiological behavior of bottom ice algal assemblages has been studied intensively at several locations, particularly over the last decade. Ice algal populations can be studied for 1-3 months because they are stationary and their environmental conditions can also be manipulated in situ. Therefore, they present a model system for studies of the physiological ecology of natural microalgal populations. Physiological responses to major environmental variables, including temperature, salinity, irradiance and nutrients, have been characterized. Ice algae are physiologically similar to polar phytoplankton, but there are important differences which appear to reflect their respective environmental conditions.Photosynthesis vs. irradiance responses, photosynthate allocation and biochemical composition have been determined for vernal blooms. Ice algae and phytoplankton have similar gross biochemical compositions (e.g., C:N, C:Si, C:Chl), but lipid contents can be markedly higher in ice algae. Ice algae normally exhibit relatively low maximal assimilation numbers (except at subpolar latitudes) but markedly higher photosynthetic efficiencies than planktonic diatoms; large low frequency fluctuations in photosynthetic performance are common during the later phases of blooms. Ice algae have relatively low photoadaptive indices Ik and optimal irradiances Im, reflecting their average growth irradiance. Compared to phytoplankton, photosynthate allocation by ice algae is lower for protein, similar for lipid but higher for polysaccharide and metabolites at the same irradiance. In several respects the physiological behavior of ice algae appears to be fundamentally different than that of phytoplankton. |
