Climate change induced shifts in polar microalgae nutritional content : species, community and trophic implications
- Publication Type:
- Thesis
- Issue Date:
- 2024
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The Arctic and Southern oceans are some of the most rapidly changing environments on the planet. At the base of the productive polar marine food webs are pelagic phytoplankton and sea-ice algae. Together, the pulsed production of spring bottom-ice blooms and summer open-water blooms are responsible for structuring ocean biogeochemical dynamics and supplying energy to marine biota. The nutritional value of microalgae depends on the community composition, and individual cellular biomolecular content (i.e. storage of proteins, lipids, fatty acids, carbohydrates). However, climate change driven environmental perturbations, including decreasing sea-ice extent and ocean acidification, are expected to alter microalgal carbon allocation and community structure, with cascading effects on the entire marine ecosystem.
Detecting the ecological consequences of environmental change on species’ nutritional quality requires disentangling community responses from taxon-specific effects. Such high-resolution insight can best be achieved by investigating marine microalgae metabolisms, one cell at a time. Using synchrotron-based Fourier transform microspectroscopy (s-FTIR) on natural microalgal communities from Arctic sea ice and Southern Ocean waters, this thesis explores the metabolic plasticity of polar microalgae at a single-cell level, elucidating how key taxa are likely to alter their biomolecular content under environmental perturbations.
Our findings show that the nutritional content of sea-ice diatoms are taxon-specific and closely linked to environmental changes. Key findings from this work revealed that light transmittance to bottom-ice determined microalgal community composition, and increased irradiance resulted in greater lipid content, until a threshold (~15% incoming irradiance). In tracing one taxon over time, it was revealed that environmental triggers indicating the end of primary productivity in the ice and onset of ice melt, including nitrogen limitation and increased water temperature, drove an increase in lipid and fatty acid content, with a concomitant decline in protein and carbohydrate stores. We may anticipate future assemblages with higher lipid, fatty acid and carbohydrate content, as light transmitted to the bottom-ice and ocean temperatures increase, but only until certain thresholds. Finally, projected ocean acidification for 2100 was shown to drive a community shift toward smaller taxa whilst increasing lipid and protein stores in key pelagic Southern Ocean diatoms, revealing that end of century conditions may alter food quality and availability for secondary production.
This thesis delivers unprecedented insight into individual species’ phenotypic plasticity, exposing the adaptation potential of polar microalgae, and enabling projections of how energy supply to the polar marine ecosystem may be affected under expected climate change driven scenarios.
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