Ecophysiology of the brine dinoflagellate, Polarella glacialis, and Antarctic fast ice brine communities
Creators: name: Thomson, PG
Publisher: name: University Of Tasmania
Year: 2023

description: Extremes in salinity and temperature and high levels of incident ultraviolet radiation (UVR) characterise the brine pockets and channels of upper Antarctic fast ice. Data on the composition and distribution of the microbial community inhabiting this environment is limited. Furthermore, how this community tolerates the immoderate physical and chemical parameters of the upper ice brine is poorly understood. The microbial community in the Davis upper fast ice consists of cryo- and halotolerant autotrophic flagellates, a few diatoms, one ciliate species and several heterotrophic species. Small autotrophic dinoflagellates and chrysophytes dominate a community containing greater flagellate diversity than previously reported. A cryptomonad and two species of Pyramimonas are reported for the first time. The abundant dinoflagellate of Davis fast ice, identified using molecular taxonomy, is Polarella glacialis Montresor et al. Observations of P. glacialis in this study from fast and pack ice brine samples along the East Antarctic coastline, with others from the literature, indicate that this species has a circumpolar distribution. The perfect match between the large subunit ribosomal RNA sequences of the Davis and McMurdo Sound P. glacialis strains suggests a single Antarctica population of this species. The Davis fast ice brine community shows a remarkable resemblance to that of McMurdo Sound. The dominant taxa of the Davis ice, P. glacialis and the chrysophytes, are abundant in McMurdo Sound. These similarities point to at least a disparate distribution of this community throughout Antarctic fast ice. _However, the probable circumpolar occurrence of P. glacialis and similar taxa from other coastal regions indicate a more continuous fast ice distribution. For the first time, P. glacialis is described in terms of its pigments and lipids. The extremely high polyunsaturated fatty acid composition of this species (up to 76%) most likely enhances its tolerance of the cold brine environment. The sterol profile of P. glacialis is atypical of dinoflagellates and is dominated by the 4-desmethylsterol, 27-nor-24-methylcholest-5,22E-3B-ol. This sterol is rare in other dinoflagellates and unknown in other algal classes, suggesting its potential as a biomarker for P. glacialis in the environment. Sediment records of this biomarker may prove useful in determining past Antarctic climate change and fast ice extent. The upper fast ice of Davis Station is characterised by extreme and transitory salinities and temperatures over the spring-summer transition. Salinities decrease from 96 to 2.5 psu whilst temperatures increase from -4.5 to -0.3 ¬¨‚àûC. These parameters and the relatively high UVR environment of the upper ice are identified as major ecophysiological stresses in the brine channels. The osmoregulatory and cryoprotectant role of dimethylsulphoniopropionate (DMSP) in P. glacialis and the Davis fast ice community are investigated in the field and the laboratory. DMSP concentrations in the brine (450 to 230 nM) decrease in linear proportion to salinity and temperature, implicating DMSP as a possible osmolyte and cryoprotectant. In laboratory studies,. P. glacialis cultures produce up to 47 fM DMSP cell-1. However, under salinity upshock, no clear relationship between DMSP production and salinity is evident. Under the nitrogen replete culture conditions used here, DMSP is not considered a primary osmolyte in P. glacialis. The effects of UV radiation (280 - 400 nm) on the brine community are assessed in situ using spectral perturbation methods. Under the conditions of this experiment, UV-B radiation (280 - 320 nm) inhibited chl a production within the upper ice whilst UV-A (320 - 400nm) appeared to have little effect. All UV radiation retarded the growth of P. glacialis asexual cells, however it is not possible to differentiate between the effects of UV-A and UV-B. DMSP concentrations within the brine are reduced under the influence of UV-A alone. UV absorbing compounds, with absorption. spectra between 310 and 335 nm, are evident in the brine. As light perturbation did not show trends in the accumulation of these compounds, it is concluded that the UV absorbing compounds present are not photoinducible.