To survive the impact of asteroids, algae learned to hunt

Tiny, seemingly harmless ocean plants survived the darkness of the asteroid attack that killed the dinosaurs by learning macabre behavior – eating other living creatures.

Large amounts of debris, soot and aerosols were blown into the atmosphere when an asteroid crashed into Earth 66 million years ago, plunging the planet into darkness, cooling the climate and acidifying the earth. oceans. With dinosaurs on land and giant reptiles in the ocean, the dominant species of marine algae were instantly wiped out – except for one rare type.

A team of scientists, including researchers from UC Riverside, wanted to understand how these algae managed to grow as mass extinction spread throughout the rest of the global food chain.

“This event was the closest to wiping out all multicellular life on this planet, at least in the ocean,” said UCR geologist and study co-author Andrew Ridgwell. “If you remove the algae, which forms the basis of the food chain, everything else should die. We wanted to know how Earth’s oceans avoided this fate and how our modern marine ecosystem reassessed after such a disaster.

To answer their questions, the team examined well-preserved fossils of the surviving algae and created detailed computer models to simulate the likely changes in algae eating habits over time. Their results are now published in the journal Science Advances.

According to Ridgwell, the scientists were somewhat lucky to find the nanoscale fossils in the first place. They were located in rapidly accumulating sediments with a high clay content, which aided in their preservation in the same way that the La Brea tar pits provide a special environment to help preserve the mammoths.

Most of the fossils had calcium carbonate shields, as well as holes in their shields. The holes indicate the presence of flagella – thin, tail-like structures that allow tiny organisms to swim.

“The only reason you have to move is to catch your prey,” Ridgwell explained.

The modern parents of ancient algae also have chloroplasts, which allow them to use sunlight to make food from carbon dioxide and water. This ability to survive both by feeding on other organisms and through photosynthesis is called mixotrophy. Some of the few land plants with this ability include Venus fly traps and sundews.

Researchers found that once the post-asteroid darkness dissipated, these mixotrophic algae spread from coastal shelf areas to the open ocean where they became a dominant life form for the next million years, helping quickly rebuild the food chain. It also helped that the larger creatures that normally feed on these algae were initially absent from post-extinction oceans.

“The results illustrate both the extreme adaptability of oceanic plankton and its ability to evolve rapidly, but also, for plants with a single-day generation, that you are still only a year of darkness away from it. ‘extinction,’ Ridgwell said.

It wasn’t until much later that algae evolved, losing the ability to eat other creatures and recovering to become one of the dominant algae species in today’s ocean.

“Mixotrophy was both the initial means of survival and then an advantage after
the post-asteroid darkness has lifted due to the abundant pretty little cells, probably surviving cyanobacteria, ”Ridgwell said. “This is the ultimate Halloween story – when the lights go out, everyone starts to eat each other.”