| Summary: | Polar marine regions are dominated by sea ice, where large gradients in temperature, salinity, nutrients and light occur. Despite this, a rich community exists within the sea ice, consisting of prokaryotic organisms, several algal groups and small zooplankton. Prokaryotes are present in the largest abundance in the sea ice; however, diatoms dominate in biomass. Diatoms are the main primary producers within the ice and they form a vital food source for many organisms. However, factors determining species composition, abundance, spatial and temporal variability and nutrient requirement are relatively poorly understood. In order to increase understanding of these processes, an integrated approach was used in this thesis to provide an insight into the potential changes to the ecology of the Southern Ocean in relation to predicted climate change. In this thesis, I studied ice algal community structure, diversity and nutrient requirements at several locations in the sea ice of the Ross Sea, Antarctica. Though many previous studies have focussed on these organisms, this is the first study to I) integrate recent and historical data collected over 30 years and to compare spatial and temporal differences in sea ice communities, II) use the near real time nutrient induced fluorescence transient (NIFT) method to study nutrient limitation in sea ice and further develop this method for use with the imaging pulse amplitude modulator (I-PAM), III) show that Antarctic diatoms may be more susceptible to silica limitation than previously thought, despite the fact that the silica concentration in the Southern Ocean are relatively high. Results from these studies provide important new information on community structure and how it is influenced by and responds to the environment .
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