Many diatoms form long chains and the relative abundance of these compared to single-celled species depend on several environmental factors, among them grazing risk. Larger grazers, such as copepods, efficiently handle and ingest even very long chains, whereas some smaller grazers are unable to feed on chains exceeding a few cells in length. Thus, theory predicts that cues from small grazers should induce increased chain lengths, but this remains to be tested. How these smaller grazers influence colony formation has frequently been studied in prymnesiophytes and freshwater green algae, but there has been little focus on diatoms, despite their importance in marine food webs. We exposed three species of chain-forming diatoms to the indirect presence of micrograzers and recorded their response. We find that the effect of grazer presence on chain length varies depending on both the type of grazer and diatom. For example, Skeletonema marinoi increased its chain length when exposed to cues from the heterotrophic dinoflagellate Gyrodinium dominans and the ciliate Euplotes spp. by up to 40%, thus bringing the diatoms outside the prey size spectrum of the grazers. In contrast, Thalassiosira rotula did not respond to cues from G. dominans, but rather employed other defenses. Our results suggest that chain-forming diatoms are able to sense and appropriately respond to fast growing micrograzers, thus contributing to the success of diatoms in marine environments.

Primary Presenter: Fredrik Ryderheim, Technical University of Denmark (fred.ryderheim@gmail.com)

Authors:

Yuan Huang, Nanjing Normal University  ()

Erik Selander, University of Gothenburg  ()

Thomas Kiørboe, Technical University of Denmark  ()