Size scaling of photophysiology and growth in four freshly isolated diatom species from Ryder Bay, western Antarctic peninsula

Diatomsare one of the dominant groups in phytoplankton communities of the western Antarctic Peninsula (WAP). Although generally well-studied, little is known about size dependent photophysiological responses in diatombloom formation and succession. To increase this understanding, four Antarctic diatomspecies covering two orders of magnitude in cell size were isolated in northern Marguerite Bay (WAP). Fragilariopsis sp., Pseudo-nitzschiacf. subcurvata, Thalassiosira cf. antarctica, and Proboscia cf. alata were acclimated to three different irradiances after which photophysiology, electron transport, carbon fixationand growth were assessed. The small species Fragilariopsis sp., Pseudo-nitzschiacf. subcurvata, and large species Proboscia cf. alata showed similar photoacclimation to higher irradiances with a decrease in cellular chlorophyll a and an increase in chlorophyll a specific absorption and xanthophyllcycle pigments and activity. In contrast, pigment concentrations and absorption remained unaffected by higher irradiances in the large species Thalassiosira cf. antarctica. Overall, the small species showed significantly higher growth rates compared to the large species, which was related to relatively high light harvesting capacity and electron transport rates in the smaller species. However, photophysiological responses related to photoinhibitionand photoprotectionand carbon fixationshowed no relationship to cell size. The present study supports the dominance of small diatomsat low irradiances during winter and early spring, but does not provide photophysiological evidence for the dominance of large diatomsduring the phytoplankton bloom in the WAP. This suggests that other factors such as grazing and nutrient availability are likely to play a major role in diatombloom formation. This article is protected by copyright. All rights reserved.