Thursday October 7, 2021, 1pm GMT+2

Michaela E. LARSSON^1,2*, Anna R. BRAMUCCI¹, Sinead COLLINS³, Gustaaf HALLEGRAEFF⁴, Tim KAHLKE¹, Jean-Baptiste RAINA¹, Justin R. SEYMOUR¹, Martina A. DOBLIN¹

Mucospheres produced by the mixotrophic dinoflagellate Prorocentrum cf. balticum impact ocean carbon cycling

¹ Climate Change Cluster (C3), University of Technology Sydney, New South Wales, Australia
² Phytoplankton Ecology Unit, Department of Water and Environmental Regulation, Joondalup, Western Australia, Australia
³ Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
⁴ Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, 7001, Australia
^* Michaela.Larsson@uts.edu.au

Marine microbes govern ocean productivity and biogeochemistry, which ultimately regulates global climate (Falkowski et al., 1998). Mixotrophic protists (single celled eukaryotic organisms) that engage both phototrophy (photosynthesise) and phago-heterotrophy (engulfment of particles) (Flynn et al. 2019) – contribute substantially to energy fluxes and biogeochemical cycles because of their nutritional flexibility (Mitra et al. 2016), ability to occupy wide environmental niches (Edwards 2019; Ward et al. 2011), and influence on trophic dynamics (Caron 2016; Ward and Follows 2016). However, the degree to which this important functional group and their behaviours shape these global scale processes remains largely unquantified (Worden et al. 2015). In this seminar, we will reveal the feeding mechanism of the mixotrophic dinoflagellate, Prorocentrum cf. balticum, and describe the sophisticated foraging strategy it uses to attract, capture, and immobilise microbial prey. We will also discuss how this previously undescribed behaviour involving the production of carbon-rich mucoid structures we have termed ‘mucospheres’, represents an overlooked, yet potentially significant mechanism for oceanic carbon export.

References

• Falkowski, P.G., Barber, R.T., Smetacek, V., 1998. Biogeochemical controls and feedbacks on ocean primary production. Science 281, 200–206.
• Flynn, K.J. et al., 2019. Mixotrophic protists and a new paradigm for marine ecology: where does plankton research go now? Journal of Plankton Research 41, 375–391.
• Mitra, A. et al., 2016. Defining planktonic protist functional groups on mechanisms for energy and nutrient acquisition: incorporation of diverse mixotrophic strategies. Protist 167, 106–120.
• Edwards, K.F., 2019. Mixotrophy in nanoflagellates across environmental gradients in the ocean. Proceedings of the National Academy of Sciences 116, 6211–6220.
• Ward, B.A., Dutkiewicz, S., Barton, A.D., Follows, M.J., 2011. Biophysical aspects of resource acquisition and competition in algal mixotrophs. The American Naturalist 178, 98–112.
• Caron, D.A., 2016. Mixotrophy stirs up our understanding of marine food webs. Proceedings of the National Academy of Sciences 113, 2806–2808.
• Ward, B.A., Follows, M.J., 2016. Marine mixotrophy increases trophic transfer efficiency, mean organism size, and vertical carbon flux. Proceedings of the National Academy of Sciences 113, 2958–2963.
• Worden, A.Z. et al., 2015. Rethinking the marine carbon cycle: factoring in the multifarious lifestyles of microbes. Science 347.