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Ecophysiology of the brine dinoflagellate, Polarella glacialis, and Antarctic fast ice brine communities

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Thomson, PG (2000) Ecophysiology of the brine dinoflagellate, Polarella glacialis, and Antarctic fast ice brine communities. PhD thesis, University of Tasmania.

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Abstract

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 °C. 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.

Item Type: Thesis (PhD)
Keywords: Dinoflagellates, Ice
Copyright Holders: The Author
Copyright Information:

Copyright 2000 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2000. Includes bibliographical references

Date Deposited: 04 Feb 2015 23:27
Last Modified: 11 Mar 2016 05:54
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