Daniel B. Mills et al., The Rise of Algae promoted eukaryote predation in the Neoproterozoic benthos. Sci. Adv. 11, eadt2147(2025). DOI:10.1126/sciadv.adt2147
The ancient ocean is still full of secrets.
As the cradle of early life and a driving force behind life today, understanding its past helps us make sense of how the modern ocean came to be.
Take algae, for instance—they didn’t just appear out of nowhere. Between 820 and 635 million years ago, the fossil record shows a clear rise in red and then green algae. To trace this shift, paleoceanographers drill sediment cores—layered like a cake—to read Earth’s marine geological and biological history.
This moment in time, when early photosynthetic eukaryotes (aka archaeplastids) began to bloom, is often called the “Rise of the Algae.” Unlike modern cyanobacteria (the so-called “false algae”), these early algae were true eukaryotes—with nuclei and membrane-bound organelles—and their rise was a turning point in shaping early food webs.
Who’s for lunch?
Around the same time, scientists see signs of eukaryovory—eukaryotes eating other eukaryotes. Rather than relying solely on sunlight or chemicals in the surrounding environment, some cells started feeding on others. This likely kickstarted the evolution of predator-prey dynamics, especially in early protists, and helped energize early marine ecosystems.
Fast forward to today’s microbial loop: a key concept in oceanography where protists eat smaller organisms like bacteria and take in dissolved organic matter, passing carbon and energy up the food chain. But this loop, as we teach it, usually centers on oxygen-rich surface waters. So where did it begin?
Clues suggest it may have started in anoxic sediments, where early anaerobic protists roamed. Even without oxygen, these organisms could maintain high growth rates by growing larger and taking in more nutrients via phagocytosis (i.e., cell-eating). That extra energy could then be passed up to promote and support more complex life. So with more algae raining down following the Rise of the Algae, more energy and nutrients could be resuspended and passed up to higher trophic levels.
Bless the rains down in Africa
To test this, researchers looked at the Benguela Upwelling System off southern Africa—a highly productive area with low-oxygen seafloor sediments. They added algal particulate matter (APM) to sediment samples, sealed them in gas-tight flasks, and observed the microbial response.
What they found was striking: gene expression among microbial eukaryotes surged in response to APM. The dominant genes pointed to phagotrophy—cell-eating—ramping up even in low-oxygen conditions.
So who was doing the eating? Mainly amoebas, cercozoans, and foraminiferans—all lineages present during the Rise of the Algae. This modern experiment gives us insight into ancient dynamics: as algae proliferated, more APM sank to the seafloor, fueling microbial predation and reinforcing the foundation of marine food webs, allowing for further complexity to arise.
Setting the foundation, even when tiny
In short, the Rise of the Algae wasn’t just about photosynthesis and increased oxygen in the ancient world. It set the stage for active microbial predation—even in oxygen-poor environments—and helped build the ecological scaffolding for complex life.
So next time you’re floating in today’s oxygen-rich waters, give a silent thanks to the bottom-dwellers of Earth’s distant past—they helped get it all started.
Cover photo from ChatGPT Image Generator.
I’m a former oceanographer with an MSc in Biological Oceanography from UConn where I studied mixotrophy in marine ciliates. After a year in Poland (studying freshwater critters) I moved to California. I currently work as a lab technician at Stanford. Outside of science, I enjoy a good book, a long run, and frozen fruit.