October 22, 2020

Scientists Find an Earthquake’s Toll in an Organism’s DNA

Waving fronds of seaweed form a peaceful underwater scene, with dappled sunlight pouring down. Hidden in the organisms’ genes, however, may be evidence of the planet’s past geological violence.

In a paper published last week in the journal Proceedings of the Royal Society B, researchers say that the genes of bull kelp along the shore of the South Island of New Zealand bear marks of an earthquake that occurred 800 years ago, when part of the ocean floor rose upward and wiped out its inhabitants. That made way for newcomers of a different genetic background, the ancestors of today’s kelp. The finding suggests that moments of cataclysmic change in an environment can be revealed by comparing genes across populations of some organisms.

New Zealand lies atop a nest of fault lines. After a quake four years ago, the edge of a fault near the town of Kaikoura shot more than six feet out of the water, and Jon Waters, a professor of zoology at University of Otago, and his colleagues began to wonder what happened to kelps after such destruction. Those stranded above the high tide line die swiftly, but as the ecosystem below the water shifts into a new normal, there’s suddenly a lot of free real estate, where new individuals can sweep in and take over. And because of the way that a population of kelp carpets an area for the long term and makes little room for new arrivals, Dr. Waters said, the algae provided an ideal test bed for seeing whether a disaster’s effects on the gene pool persist over time.

About 800 years ago, according to the geological record, there was a similar quake in New Zealand along the coastline near Dunedin. The scientists took samples of kelp along a 60-mile stretch of that shore. Each individual kelp looked much the same as the others of its species. However, when the scientists examined the genetics, there were large differences linked to where the kelps had been collected. Bull kelp that lived along a 15-mile stretch that had been forced into the air during that long-ago earthquake were distinct from their neighbors of the same species on either side, whose homes had long lain undisturbed.

“We were just gobsmacked when we looked,” Dr. Waters said. “We could see where the uplift zone was just by looking at the genetics.”

When wandering bull kelps from farther down the coast arrived at the wasteland left by the earthquake, they most likely proliferated swiftly, dominating the entire footprint of the uplifted area within a few decades, before any others could get in. Their descendants are still living there. Their presence is a sign of an ancient disruption, but also of renewal.

“One of the things we learned from this is how quickly nature recovers,” Dr. Waters said. “It’s reassuring that nature has that power.”

The work corroborates the idea that after ecosystems recover from catastrophes, the genetic makeup of the organisms there can bear signatures of the change for hundreds of years or longer. The fact that the new kelp has barely mixed with its neighbors 800 years after the earthquake is particularly interesting — it suggests that a “winner takes all” effect is going on, where the first individuals on the scene can maintain their dominance for centuries, the researchers wrote. The group is now watching the recolonization of the Kaikoura earthquake’s uplifted zone, collecting samples as new kelps arrive. Kelps are travelers, it turns out. Individuals can float thousands of miles and still be viable when they wash up on a distant shore.

And when the kelp proliferates, Dr. Waters said, many small creatures that live within it can return, too. The tangled strands that attach kelp to rocks form tiny, protected worlds in the surf where small crustaceans and other animals take up residence.

“You’ve got a sheltered little environment for things to go about their daily lives,” he said.