Collaborative Research: Iron and Light Effects on Phaeocystis antarctica Isolates from the Ross Sea

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The colonial prymnesiophyte Phaeocystis antarctica is a major bloom-forming alga in Antarctic shelf waters; where, alongside diatoms, it is considered a keystone species in its impact on regional biogeochemical cycling and ecosystem structure. Iron levels in these waters fall to values as low as ~0.1 nM during the mid to late summer, concentrations that are likely to limit the growth of phytoplankton, including P. antarctica. However, in contrast to diatoms, very little work has been conducted to examined the effects of iron, or the combined effects of iron and irradiance, on the growth, physiology and biochemical composition of P. antarctica. In this project, P. antarctica will be collected from the southern Ross Sea and grown in semi-continuous batch cultures for use in experiments at the University of Charleston to investigate the effects of iron availability and irradiance on the growth rate, cellular iron quota, buoyancy, biogenic sulfur production, pigment content, redox-protein expression, and photosynthetic efficiency of P. antarctica. Phaeocystis antarctica is known to have a significant impact on the regional biogeochemical cycles of carbon, nutrient elements and sulfur in the Ross Sea, over timescales ranging from seasonal to interannual. This species may have also played a central role in the inferred basin- scale changes in biogeochemical cycles linked to glacial-interglacial climatic change. Thus it is important to develop a mechanistic understanding of the factors that control the growth, physiology and biochemical composition of P. antarctica, in order to better understand the biogeochemical ecology of the Ross Sea and the wider Southern Ocean, and the possible linkages with regional and global climate. Together with the results of recent and ongoing field and modeling studies, the information provided by these laboratory experiments will substantially improve our ability to predict how the Antarctic region will be affected by and modulate future climate change.