Ph.d.-forsvar Sara Hadarsdottir – Københavns Universitet

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Ph.d.-forsvar Sara Hadarsdottir

Sara Harðardóttir is defending her PhD thesis on September 22, 2017, at 1pm in the geological museum auditorium, Øster Voldgade 5-7.

The Thesis is entitled “Marine Battlefields: Toxic diatoms and their copepod grazers

Diatoms are tremendously important primary producers found in most aquatic habitats. Copepods prey on diatoms and mediate the energy to higher trophic levels. For both diatoms and copepods, predation is a major cause of mortality and strategies for protection or avoidance are crucial for survival. Diatoms of the genera Pseudo-nitzschia are known to produce a neuro-toxin, domoic acid, a potent toxin that causes harm to multiple organisms, including humans. Despite the toxin production, Pseudo-nitzschia cells are nevertheless consumed by copepods that have previously been considered resistant to the toxin. We discovered that the trait of induced toxin production is diatom specific, as not all tested diatoms reacted to the copepods, and grazer specific, as diatoms do not respond to grazers that does not pose threat. The toxin production does not seem to have an effect prior to ingestion and the diatom cells are eaten nonetheless. By investigating gene-expression in the copepod, it became evident that several genes are repressed after toxin exposure. Further we found that copepods can suffer reduced escape responses and mortality, suggesting that the copepods become an easier prey after consuming toxic diatoms. The biosynthetic pathway for domoic acid is not fully revealed and by studying gene-expression in Pseudo-nitzschia it became evident that the C10 isoprenoid metabolite is used for domoic acid biosynthesis arises from the methylerythriol phosphate metabolic pathway.

Assessment Committee

  • Chair: Professor Per Juel Hansen, Biological Institute, University of Copenhagen
  • Senior Researcher Maria I. Ferrante, Stazione Zoologica Anton Dohrn Napoli, Italy
  • Professor Hans Dam Guerrero, University of Connecticut, US


  • Associate Professor Nina Lundholm, Natural History Museum, University of Copenhagen
  • Senior Researcher Uwe John, Alfred Wegener Institute, Germany
  • Professor Torkel Gissel Hansen, DTU Aqua, Technical University of Denmark