Abstract: The proliferation of marine algae in the Neoproterozoic Era is thought to have stimulated the ecology of predatory microbial eukaryotes (protists) and the evolution of more modern marine food webs. Paleontologists and geochemists have predicted that these algae-eating microbial predators would have been restricted to well-oxygenated marine waters, and would have been near-absent in anoxic settings. This prediction, however, clashes with the observation that eukaryote-eating protists like foraminifera and ciliates are abundant and diverse in anoxic systems today. Thus, more constraints from modern marine ecosystems and extant protists are needed to more accurately reconstruct Neoproterozoic ecosystems. In this spirit, I will summarize the results of a series of sediment incubation experiments where algal particulate matter (APM) was added to marine sediments collected from a modern marine oxygen minimum zone where bottom-water oxygen concentrations approximate those of the late Neoproterozoic water column. My colleagues and I found that under anoxia, APM significantly stimulated microbial eukaryote gene expression, particularly genes involved in anaerobic energy metabolism and phagocytosis, and increased the relative abundance of 18S rRNA from known predatory clades. We additionally confirmed that APM promoted the reproduction of benthic foraminifera under anoxia with higher-than-expected net growth efficiencies. Overall, our findings suggest that algal biomass exported to the Neoproterozoic benthos stimulated the ecology of benthic predatory protists under anoxia, thereby creating more modern food webs by enhancing the transfer of fixed carbon and energy to eukaryotes occupying higher trophic levels, including the earliest benthic metazoans.

Bio: Dan Mills is a postdoctoral researcher and geobiologist at the Institute for Molecular Evolution at the University of Düsseldorf in Germany. He primarily studies the co-evolution of eukaryotic life and the Proterozoic biosphere through the lens of eukaryote physiology and ecology. He has a BSc in Geobiology from Penn State, and a PhD in Biology from the University of Southern Denmark. He was an Agouron Institute Geobiology Postdoctoral Fellow at Stanford from 2019 to 2021, and will begin as a Lecturer in Biosphere-Geosphere Interactions at the University of Leeds in the fall of 2026.