Photophysiological responses of marine phytoplankton and ice algae to temperature, iron and light availability in subpolar and polar regions

• Main Author: Yoshida, K
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: Aquatic photosynthesis; Active chlorophyll a fluorescence; Gene expression; Psychrophilic microalgae; Iron availability; Sea ice; Subarctic; Antarctic; Oyashio; Antarc*; ice algae
• Online Access: https://eprints.utas.edu.au/34654/; https://eprints.utas.edu.au/34654/1/Yoshida_whole_thesis.pdf

Global warming increases sea temperatures and intensifies stratification of the water column, which directly and indirectly affects marine ecosystems and biogeochemistry, for example, less nutrient supply due to stratification. It has been suggested that the effects of climate change may emerge earlier in the highly productive and ecologically important subpolar and polar regions. In these regions, an increase in temperature may benefit some algal primary producers but a reduction in the extent of sea ice will limit the habitat of ice-associated biota. Light is also a crucial factor for all photosynthetic organisms and its availability can change dramatically when sea ice melts. Iron (Fe) as a micro-nutrient plays a key role in algal metabolic processes, including photosynthesis. This study thus aimed at clarifying the effects of temperature, light and Fe availability on the photophysiology of phytoplankton and ice algae in the changing subpolar and polar oceans.The effects of temperature on a spring diatom bloom in the coastal Oyashio (COY) were investigated as a representative subpolar coastal spring bloom. The spring diatom blooms in COY waters are highly productive in spite of the low sea surface temperature (SST) (−1−2 ºC in early spring). This study thus focused on the photophysiology and community composition of phytoplankton in COY waters during the pre-bloom and bloom periods from March to April 2015. Next-generation sequencing, targeting the 18S rRNA gene, revealed that the diatom genus Thalassiosira generally dominated the phytoplankton community. Additionally, the relative contribution of Thalassiosira to the total diatom assemblages showed a positive correlation with maximum photosynthetic rates (P\(^B\)\(_{max}\)) throughout this study, suggesting that the genus was the largest contributor to the bloom. A short-term on-deck incubation experiment was also conducted to clarify the role of temperature in determining the photosynthetic functioning of phytoplankton. Here, rising temperature led to an ...