Temporal changes in size distributions of the Southern Ocean diatom Fragilariopsis kerguelensis through high-throughput microscopy of sediment trap samples

Abstract

Some aspects of the life cycle of the Southern Ocean diatom Fragilariopsis kerguelensis have been investigated previously, but many of its details have not been surveyed in nature. We investigated material from a two-year sediment trap time series by high-throughput imaging and image analysis, looking for morphometric signals of life cycle stages. Valve length distributions appeared close to unimodal but positively (right-) skewed. Size cohorts resulting from synchronized sexual reproduction events were not clearly distinguishable. Nevertheless, based on changes in valve length distributions, we found three general seasonal phases. These corresponded to periods of proliferation (with higher proportions of smaller cells during late spring/early summer), cessation of growth (relative loss of smaller cells during late summer/early autumn), and overwintering (little change in size distributions, with an increased proportion of large cells). We discuss possible causes of these signals, and their relevance to growth, sexual activity and adaption to environmental conditions, such as grazing pressures and the need for an overwintering strategy.

Keywords:

• morphometry
• phytoplankton
• SHERPA
• slide scanner
• valve size distribution

Acknowledgements

We would like to express our gratitude to Fenina Buttler for scanning most slides from sampling year 2002/2003.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental data

Supplemental data for this article can be accessed at https://doi.org/10.1080/0269249X.2019.1626770.

ORCID

Michael Kloster http://orcid.org/0000-0001-9244-4925

Andrés S. Rigual-hernández http://orcid.org/0000-0003-1521-3896

Leanne K. Armand http://orcid.org/0000-0003-3995-308X

Thomas W. Trull http://orcid.org/0000-0001-9717-3802

Bánk Beszteri http://orcid.org/0000-0002-6852-1588

Additional information

Funding

This work was supported by the Deutsche Forschungsgemeinschaft (DFG) in the framework of the priority programme 1158 ‘Antarctic Research with comparative investigations in Arctic ice areas’ under grant nr. BE4316/4-1, KA1655/3-1; and by an outgoing scholarship, as well as travel expenses, granted by the Helmholtz Graduate School for Polar and Marine Research (POLMAR). Part of this work was supported by the Australian Government’s Australian Antarctic Science Grant Program under project number 4078, and Macquarie University (A. Rigual-Hernández and L. Armand). The sediment trap samples were collected by the ACE CRC with logistic support from the Australian Antarctic Division under grants AAS1156 and AAS2256 to T.W. Trull.