How a prehistoric catastrophe forced ocean plants to become predators
In short: The world fell into shadow 66 million years ago following an asteroid impact. While the dinosaurs perished, a rare type of algae survived by adopting a ghoulish new behavior: they stopped relying solely on sunlight and started eating other living creatures.
The asteroid strike 66 million years ago sent vast amounts of debris, soot, and aerosols into the atmosphere. This caused a global cooling of the climate and acidified the oceans, creating a mass extinction event that nearly wiped out all multicellular life. While dominant marine algae species were instantly wiped out, a specific type survived by evolving mixotrophy—the ability to use sunlight for photosynthesis while also consuming other organisms for food. This event was significant because it nearly eliminated every multicellular organism in the sea. Without these resilient algae, the entire global food chain would have collapsed.
Researchers at UC Riverside used well-preserved, nano-sized fossils found in high-clay-content sediments to study this transition. These fossils often featured calcium carbonate shields with holes, indicating the presence of flagella. These thin, tail-like structures allowed the organisms to swim, a vital trait for seeking out prey in the dark, post-impact oceans. These ancient fossils were preserved in a manner similar to mammoths in the La Brea tar pits. Scientists discovered these tiny specimens within fast-accumulating sediments.
This evolutionary pivot is a profound example of survival through dietary flexibility. By becoming predators, these algae ensured they could thrive even when sunlight was obscured. This mechanism allowed the base of the marine food chain to persist, eventually enabling the modern marine ecosystem to re-evolve after the catastrophe. This dietary shift allowed the organisms to survive despite the lack of light. Such flexibility proved essential for the survival of the ocean's foundational species.
Today, we see remnants of such complex behaviors in the ocean. For example, the fish-killing species Heterosigma has been observed fleeing from predators by moving into low-salinity water layers. This ability to actively move and seek refuge highlights how even microscopic plants can exhibit sophisticated survival strategies. This specific behavior helps the species avoid being consumed by single-celled predators. Such movements allow the algae to double their population numbers every two days.
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Sources
- Summary by Intellect · source: When Algae Learned to Hunt
- Also: To survive asteroid impact, algae learned to hunt | UCR News | UC Riverside
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