The comparative UVB photobiology of Phaeocystis antarctica and selected species of Antarctic marine diatoms

• Main Author: Davidson, Andrew T
• Format: Thesis
• Language: English
• Published: 1996
• Subjects: Antarctic; Davis Station; Davis-Station; Southern Ocean; Antarc*; Antarctica; Sea ice
• Online Access: https://eprints.utas.edu.au/19657/; https://eprints.utas.edu.au/19657/1/whole_DavidsonAndrewT1997_thesis.pdf

Stratospheric ozone protects the earth's surface from short wavelength UVB radiation. Over Antarctica, ozone concentrations presently fall to less than 30% of pre-ozone hole values during spring and ozone depletion persists into January and February. UVB reduces phytoplankton growth, primary production and survival in the upper 10-20 meters of the water column. Shallow phytoplankton blooms in the sea ice and marginal ice zone, which are responsible for much of the primary production in the Southern Ocean, appear vulnerable to damage by increased UV-B radiation. This thesis examines the effect of UVB radiation on Phaeocystis antarctica and selected species of Antarctic marine diatoms. The colonial stage in the life cycle of P. antarctica was found to possess high concentrations of UV-absorbing compounds but diatoms lacked significant concentrations of these compounds. Results from the laboratory using artificial sources of UVB, and obtained under natural solar radiation at Davis Station, Antarctica, showed marked interspecific differences in the tolerance of Antarctic phytoplankton to UVB. Survival, primary production and growth of colonial P. antarctica when exposed to UVB was compared with that of the flagellate stage in the life cycle of this alga and selected diatom species. Unexpectedly, laboratory experiments showed that the diatoms, which lacked UV absorbing compounds, survived UVB irradiances three to five times higher than those that caused mortality in colonial stage P. antarctica. Exposure of diatoms to PAR and UVA reduced their survival. However, low UVB irradiances increased their survival to levels similar to PAR exposed control treatments. Thus, UVB may be involved in photorepair mechanism for UVA induced damage. Competition experiments, using cultures of motile and colonial P. antarctica together with diatoms, were exposed to natural Antarctic irradiance at Davis Station. These showed direct evidence of UVB induced changes in phytoplankton species composition. Growth of the colonial stage of P. antarctica was enhanced at the expense of diatoms. Thus, laboratory experiments which showed that the colonial life stage of P. antarctica was the most susceptible species to UVB induced mortality were not indicative of its relative success at natural Antarctic sublethal fluxes. P. antarctica is important in Antarctic waters for several reason. Its blooms are, pivotal in determining trophic function, poorly grazed by metazooplankton, contribute little to the flux of carbon to deep water and are known to release high concentrations of dimethylsulfide to the atmosphere which act as cloud condensation nuclei. Results reported here indicate the potential for altered trophodynamics, vertical carbon flux and global albedo as a result of Antarctic ozone depletion.