Plankton began hunting their own food to survive a mass extinction event

Plankton began hunting their own food to survive a mass extinction event. Researchers at the University of Southampton have discovered that microscopic algae turned to hunting to survive a mass extinction event. Before an asteroid impact 66 million years ago, nannoplankton relied exclusively on energy from the sun. But then, after three-quarters of life on Earth was wiped out, the remaining nannoplankton were capable of capturing food and eating it.

The research suggests that when sunlight was unavailable, some species were killed while others evolved and adapted. 

In collaboration with experts at UCL and in Paris, California, Bristol, and Edinburgh, the researchers analyzed an exceptional record of plankton fossils. They used eco-evolutionary modeling techniques to examine how organisms behaved before and after the asteroid impact and to understand why some survived and some did not.

The international team had a breakthrough when they noticed that the anatomy of many of the nannoplankton skeletons had changed after the extinction event. These skeletons contained a large hole which represented the position of flagella, tiny tail-like structures used for movement and feeding. This discovery indicated that nannoplankton which survived the asteroid strike were capable of hunting and ingesting food.

“Those species that were lost at the mass extinction show no evidence of a mixotrophic lifestyle and were likely to be completely reliant on sunlight and photosynthesis,” said study co-author Dr. Samantha Gibbs. 

“Fossils following the Cretaceous-Paleogene (K-Pg) extinction show that mixotrophy dominated and our model indicates this is because of the exceptional abundance of small prey cells – most likely surviving bacteria – and reduced numbers of larger ‘grazers’ in the post-extinction oceans.”

As a result of environmental changes, nannoplankton gradually shifted back to relying on photosynthesis. Today, most open ocean nannoplankton use only photosynthesis.

The asteroid impact, which formed the Chicxulub crater in Mexico, is most famous for killing off the dinosaurs. The K-Pg extinction event occurred after sunlight was blocked out.

“This huge impact flung vast amounts of debris, aerosols and soot into the atmosphere, causing darkness, cooling and acidification over days and years,” said study co-author Professor Paul Bown. “The significant bias found in the nannoplankton extinctions – removal of open-ocean photoautotrophs but survival of mixotrophs that could hunt and feed – can only be fully explained by the darkness caused by the asteroid impact acting as a kill mechanism.”

“This ‘blackout’ or shutdown of primary productivity would have been felt across all of Earth’s ecosystems and reveals that the K/Pg event is distinct from all other mass extinctions that have shaped the history of life, both in its rapidity, related to an instantaneous impact event, and its darkness kill mechanism, which shook the foundations of the food chains,” explained Dr. Gibbs. “The K/Pg boundary event likely represents the only truly geologically instantaneous mass extinction event.”

The study is published in the journal Science Advances.

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By Chrissy Sexton, Earth.com Staff Writer