Tuesday November 8, 2022, 4pm CET

Francine M.G. McCARTHY^1,2*
Donya C. STINIS-DANESH^3,4*

Why do the cysts of freshwater dinoflagellates remain underutilised in paleolimnological studies?

¹ Department of Earth Sciences, Brock University, St. Catharines, Canada
² Natural History, Plants and Climate Change, Royal Ontario Museum, Toronto, Canada
^* fmccarthy@brocku.ca
³ Paleoecological Environmental Assessment and Research Laboratory (PEARL), Department of Biology, Queen’s University, Kingston, Canada
⁴ Department of Ecosystems and Landscape Dynamics, Institute of Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands

Although they are known from non-marine sediments at least as old as Cretaceous, the cysts of freshwater dinoflagellates are rarely employed as paleolimnological proxies, especially compared to other algal microfossil groups. There are two main reasons for this: 1) taxonomic- most palynologists fail to recognize cysts other than those with clear peridinialean morphologies as having dinoflagellate affinities, and theca-cyst relationships have been conclusively documented for a relatively small proportion of freshwater dinoflagellate taxa; and 2) taphonomic – the few attempts to relate cyst assemblages with phycological assemblages have identified a complex relationship, and the effects of taphonomy, on cyst assemblages remain relatively poorly understood. Water column-to-lakebed studies (including sediment trap analysis) and laboratory exposure of cyst assemblages to oxidation undertaken from lakes in the Dorset Lakes region of south-central Ontario has shed light on these issues, in particular illustrating the effects of differential susceptibility to oxidation on cyst assemblages. While taxonomic and taphonomic issues exist in marine environments, substantial effort has been expended to relate the distribution of dinoflagellate cysts in modern marine sediments with environmental parameters, allowing development of transfer functions. In contrast, the first calibration set was recently created, identifying lake depth, trophic state and pH as the most important environmental variables controlling the distribution of 38 cyst morphotypes in 32 lakes in the Experimental Lakes Area of northwestern Ontario, Canada. Applying lessons learned from these investigations to a core from which several other paleoenvironmental proxies have been studied illustrates the current value of dinoflagellate cysts in paleolimnological investigations and suggests where additional effort should be focused to maximize their potential.